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Papers by Barbara Carter

Research paper thumbnail of T 2 changes following shunt-treatment of neonatal hydrocephalic H-Tx rats

Research paper thumbnail of Complex Genetic and Maternal Effects in Fetal-Onset Rat Hydrocephalus

Research paper thumbnail of Generation of Congenic Lines for H-Tx Hydrocephalus by Introgression to Fisher F344 rats

Research paper thumbnail of Genetic loci for ventricular dilatation in the LEW/Jms rat with fetal-onset hydrocephalus are influenced by gender and genetic background

Cerebrospinal fluid research, Jan 12, 2005

The LEW/Jms rat strain has inherited hydrocephalus, with more males affected than females and an ... more The LEW/Jms rat strain has inherited hydrocephalus, with more males affected than females and an overall expression rate of 28%. This study aimed to determine chromosomal positions for genetic loci causing the hydrocephalus. An F1 backcross was made to the parental LEW/Jms strain from a cross with non-hydrocephalic Fischer 344 rats. BC1 rats were generated for two specific crosses: the first with a male LEW/Jms rat as parent and grandparent, [(F x L) x L], designated B group, and the second with a female LEW/Jms rat as the parent and grandparent [L x (L x F)], designated C group. All hydrocephalic and a similar number of non-hydrocephalic rats from these two groups were genotyped with microsatellite markers and the data was analyzed separately for each sex by MAPMAKER. The frequency of hydrocephalus was not significantly different between the two groups (18.2 and 19.9 %), but there was a significant excess of males in the B group. The mean severity of hydrocephalus, measured as the ...

Research paper thumbnail of Characteristics of hydrocephalus expression in the LEW/Jms rat strain with inherited disease

Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery, 2003

The expression and severity of hydrocephalus was characterized in LEW/Jms rats with inherited hyd... more The expression and severity of hydrocephalus was characterized in LEW/Jms rats with inherited hydrocephalus. The frequency of overt disease (lethal) was 27.7%, but varied depending on breeding line. It increased to 31.5% when rats with mild disease were included. Most breeding pairs (48/51) produced hydrocephalic offspring with significantly more males than females affected. Some adult rats were also found to have mild (nonlethal) ventricular dilatation. When bred to Fisher F344 rats, 3% of the F(1) progeny had overt hydrocephalus, indicating that the trait is not recessive. Overt hydrocephalus was 9-20% in N(2) rats (F(1) rats x LEW/Jms). The frequency of hydrocephalus and the presence of an excess of hydrocephalic males, varied depending on the direction of the cross. Mild hydrocephalus in N(2) rats was 3.1%. It is concluded that the inheritance of hydrocephalus in LEW/Jms strain is probably not mendelian recessive but may be semidominant or involve more than one gene and has a ma...

Research paper thumbnail of Chromosomal linkage associated with disease severity in the hydrocephalic H-Tx rat

Behavior genetics, 2001

Infantile hydrocephalus results in neurological deficits despite surgical treatment. Fetal-onset ... more Infantile hydrocephalus results in neurological deficits despite surgical treatment. Fetal-onset hydrocephalus in humans can be caused by developmental abnormalities that are genetic in origin. The H-Tx rat has hydrocephalus with 40% penetrance and a polygenic inheritance. A backcross with Fisher F344 inbred strain produced a total of 1500 progeny with 17.5% hydrocephalus. Of these, only 12.3% had overt disease and the remaining 5.2% had mild disease seen only after fixation of the brain. Disease severity was measured for all affected rats using the ratio of ventricle to brain width. The severity measure confirmed that there are two populations, mild hydrocephalus (M; ratio, <0.4) and severe hydrocephalus (S; ratio, >0.4), with a small overlap. For genotyping, the two populations were each subdivided based on the ratio measure to give a total of four groups of increasing severity. After an initial genome scan with microsatellite markers, all hydrocephalic rats and a subset of ...

Research paper thumbnail of Single and multiple congenic strains for hydrocephalus in the H-Tx rat

Mammalian Genome, 2005

The H-Tx rat has fetal-onset hydrocephalus with a complex mode of inheritance. Previously, quanti... more The H-Tx rat has fetal-onset hydrocephalus with a complex mode of inheritance. Previously, quantitative trait locus mapping using a backcross with Fischer F344 rats demonstrated genetic loci significantly linked to hydrocephalus on Chromosomes 10, 11, and 17. Hydrocephalus was preferentially associated with heterozygous alleles on Chrs 10 and 11 and with homozygous alleles on Chr 17. This study aimed to determine the phenotypic contribution of each locus by constructing single and multiple congenic strains. Single congenic rats were constructed using Fischer F344 as the recipient strain and a marker-assisted protocol. The homozygous strains were maintained for eight generations and the brains examined for dilated ventricles indicative for hydrocephalus. No congenic rats had severe (overt) hydrocephalus. A few pups and a significant number of adults had mild disease. The incidence was significantly higher in the C10 and C17 congenic strains than in the nonhydrocephalic F344 strain. Breeding to F344 to make F.H-Tx C10 or C11 rats heterozygous for the hydrocephalus locus failed to produce progeny with severe disease. Both bicongenic and tricongenic rats of different genotype combinations were constructed by crossing congenic rats. None had severe disease but the frequency of mild hydrocephalus in adults was similar to congenic rats and significantly higher than in the F344 strain. Rats with severe hydrocephalus were recovered in low numbers when single congenic or bicongenic rats were crossed with the parental H-Tx strain. It is concluded that the genetic and epigenetic factors contributing to severe hydrocephalus in the H-Tx strain are more complex than originally anticipated.

Research paper thumbnail of Genome-wide linkage analysis of inherited hydrocephalus in the H-Tx rat

Mammalian Genome, 2001

Inherited hydrocephalus in humans has received very little attention, most probably because known... more Inherited hydrocephalus in humans has received very little attention, most probably because known occurrences are sporadic and systematic investigation is difficult. The H-Tx rat, one of a number of rodent strains with inherited hydrocephalus, has a complex inheritance with more than one postulated susceptibility gene and 40% penetrance. The aim of this study was to perform a genome-wide scan on backcross progeny derived from H-Tx and Fisher F344 rats, to identify genomic regions associated with hydrocephalus. Penetrance of hydrocephalus in (H-Tx x F344) F1 x H-Tx was 12.3%. All severely hydrocephalic progeny (n = 185) and a subset of normal progeny (n = 128) were screened with 110 simple sequence length polymorphisms (SSLPs) with 83% coverage of the genome. A significant susceptibility locus was found on chromosome (Chr) 11 (LOD = 3.1). Three loci with suggestive linkage were found on Chr 17 (LOD = 2.4), on Chr 9 (LOD = 1.94), and on Chr 19 (LOD = 1.91). For the loci on Chr 11 and 19, hydrocephalus was associated with the heterozygous genotype, while the other two were recessive. Although none of the four loci was essential for the hydrocephalic phenotype, the additive effects of two, three, or four loci increased the penetrance in a linear fashion. Altogether these four loci accounted for 13.5% of the total variance. It is concluded that hydrocephalus in the H-Tx rat is associated with two, possibly four genetic loci, but that there may be additional undefined genetic and environmental influences.

Research paper thumbnail of Altered gene expression in the brain and liver of female fathead minnows Pimephales promelas Rafinesque exposed to fadrozole

Journal of Fish Biology, 2008

The fathead minnow Pimephales promelas is a small fish species widely used for ecotoxicology rese... more The fathead minnow Pimephales promelas is a small fish species widely used for ecotoxicology research and regulatory testing in North America. This study used a 2000 gene oligonucleotide microarray to evaluate the effects of the aromatase inhibitor, fadrozole, on gene expression in the liver and brain tissue of exposed females. Reproductive measures, plasma vitellogenin and gene expression data for the brain isoform of aromatase (cytP19B), vitellogenin precursors and transferrin provided evidence supporting the efficacy of the fadrozole exposure. Unsupervised analysis of the microarray results identified 20 genes in brain and 41 in liver as significantly up-regulated and seven genes in brain and around 45 in liver as significantly down-regulated. Differentially expressed genes were associated with a broad spectrum of biological functions, many with no obvious relationship to aromatase inhibition. However, in brain, fadrozole exposure elicited significant up-regulation of several genes involved in the cholesterol synthesis, suggesting it as a potentially affected pathway. Gene ontologybased analysis of expression changes in liver suggested overall down-regulation of protein biosynthesis. While real-time polymerase chain reaction analyses supported some of the microarray responses, others could not be verified. Overall, results of this study provide a foundation for developing novel hypotheses regarding the system-wide effects of fadrozole, and other chemical stressors with similar modes of action, on fish biology.

Research paper thumbnail of Transcriptional response of hepatic largemouth bass (Micropterus salmoides) mRNA upon exposure to environmental contaminants

Journal of Applied Toxicology, 2010

Microarrays enable gene transcript expression changes in near-whole genomes to be assessed in res... more Microarrays enable gene transcript expression changes in near-whole genomes to be assessed in response to environmental stimuli. We utilized oligonucleotide microarrays and subsequent gene set enrichment analysis (GSEA) to assess patterns of gene expression changes in male largemouth bass (Micropterus salmoides) hepatic tissues after a 96 h exposure to common environmental contaminants. Fish were exposed to atrazine, cadmium chloride, PCB 126, phenanthrene and toxaphene via intraperitoneal injection with target body burdens of 3.0, 0.00067, 2.5, 50 and 100 mg g-1 , respectively. This was conducted in an effort to identify potential biomarkers of exposure. The expressions of 4, 126, 118, 137 and 58 mRNA transcripts were significantly (P Յ 0.001, fold change Ն2¥) affected by exposure to atrazine, cadmium chloride, PCB 126, phenanthrene and toxaphene exposures, respectively. GSEA revealed that none, four, five, five and three biological function gene ontology categories were significantly influenced by exposure to these chemicals, respectively. We observed that cadmium chloride elicited ethanol metabolism responses, and along with PCB 126 and phenanthrene affected transcripts associated with protein biosynthesis. PCB 126, phenanthrene and toxaphene also influenced one-carbon compound metabolism while PCB 126 and phenanthrene affected mRNA transcription and mRNA export from the nucleus and may have induced an antiestrogenic response. Atrazine was found to alter the expression of few hepatic transcripts. This work has highlighted several biological processes of interest that may be helpful in the development of gene transcript biomarkers of chemical exposure in fish.

Research paper thumbnail of Genetic analysis of inherited hydrocephalus in a rat model

Experimental Neurology, 2004

Congenital hydrocephalus is a serious neurological disorder with a diverse etiology. Although the... more Congenital hydrocephalus is a serious neurological disorder with a diverse etiology. Although there is strong evidence for genetic causes, few genes have been identified in humans. The rodent model, the H-Tx rat, has hydrocephalus with an onset in late gestation and a complex mode of inheritance. Ventricular dilatation is associated with abnormalities in the cerebral aqueduct and subcommissural organ. Quantitative trait locus (QTL) mapping was performed on DNA from the progeny of a backcross with the non-hydrocephalic Fischer F344 strain, using DNA microsatellite markers. The hydrocephalus trait was quantified by measuring the severity of the ventricular dilatation. Four chromosomes, each with a locus for hydrocephalus (Chrs 9, 10, 11, and 17), were mapped using additional markers and DNA from four subsets of backcross progeny with allelic recombination at or near each locus. The genetic positions for the markers and the loci were located using the Ensemble Rat Genome Browser. For each chromosome studied, the interval containing the locus was examined for known rat genes and for human genes identified from human-rat homology. Genes expressed in brain and with a function associated with known causes of hydrocephalus were identified as possible candidate genes. Future studies to characterize the causative genes in this animal model will improve the understanding of genetic causes in humans.

Research paper thumbnail of The Frequency of Inherited Hydrocephalus Is Influenced by Intrauterine Factors in H-Tx Rats

Experimental Neurology, 2002

H-Tx rats have fetal-onset inherited hydrocephalus. Linkage analysis has determined the genetics ... more H-Tx rats have fetal-onset inherited hydrocephalus. Linkage analysis has determined the genetics is complex, with at least three loci associated with hydrocephalus. In addition, maternal and/or intrauterine factors influence the frequency of expression. The aim of this study was to characterize nongenetic (epigenetic) factors that affect hydrocephalus in this strain. Groups of primiparous and multiparous females were used to breed fetuses for examination in utero. Multiparous females were manipulated to have either gestation with lactation or, by removal of pups at birth, gestation without lactation. In addition, hydrocephalus expression in postnatal rats from the breeding colony was analyzed for primiparous and multiparous females. The latter were subdivided according to the interval between the litter examined and the previous litter. There was no particular uterine position or horn that favored hydrocephalus and hydrocephalic fetuses were the same weight as normal littermates. The frequency of hydrocephalus was 16-20% in primiparous females and twofold higher in multiparous females that were lactating during pregnancy. Removal of the suckling pups prevented this increase. The severity of hydrocephalus was measured on 1-mmthick fixed brain slices. Fetuses from lactating females had hydrocephalus that was significantly more severe than the nonlactating groups. However, all fetus groups had hydrocephalus that was very much less severe than the postnatal pups, suggesting that severity increases after birth. It is concluded that there is an epigenetic factor that increases the frequency of inherited hydrocephalus in fetuses if suckling pups are present during gestation. Future experiments will examine possible mechanisms for this genotype-environment interaction.

Research paper thumbnail of Development and Validation of a 2,000-GENE Microarray for the Fathead Minnow (Pimephales Promelas)

Environmental Toxicology and Chemistry, 2007

Gene microarrays provide the field of ecotoxicology new tools to identify mechanisms of action of... more Gene microarrays provide the field of ecotoxicology new tools to identify mechanisms of action of chemicals and chemical mixtures. Herein we describe the development and application of a 2,000-gene oligonucleotide microarray for the fathead minnow Pimephales promelas, a species commonly used in ecological risk assessments in North America. The microarrays were developed from various cDNA and subtraction libraries that we constructed. Consistency and reproducibility of the microarrays were documented by examining multiple technical replicates. To test application of the fathead minnow microarrays, gene expression profiles of fish exposed to 17␤-estradiol, a well-characterized estrogen receptor (ER) agonist, were examined. For these experiments, adult male fathead minnows were exposed for 24 h to waterborne 17␤-estradiol (40 or 100 ng/L) in a flow-through system, and gene expression in liver samples was characterized. Seventy-one genes were identified as differentially regulated by estradiol exposure. Examination of the gene ontology designations of these genes revealed patterns consistent with estradiol's expected mechanisms of action and also provided novel insights as to molecular effects of the estrogen. Our studies indicate the feasibility and utility of microarrays as a basis for understanding biological responses to chemical exposure in a model ecotoxicology test species.

Research paper thumbnail of A Graphical Systems Model to Facilitate Hypothesis-Driven Ecotoxicogenomics Research on the Teleost Brain−Pituitary−Gonadal Axis

Environmental Science & Technology, 2007

Research paper thumbnail of Taking Microarrays to the Field: Differential Hepatic Gene Expression of Caged Fathead Minnows from Nebraska Watersheds

Environmental Science & Technology, 2012

This study aimed to evaluate the utility of microarrays as a biomonitoring tool in field studies.... more This study aimed to evaluate the utility of microarrays as a biomonitoring tool in field studies. A 15,000-oligonucleotide microarray was used to measure the hepatic gene expression of fathead minnows (Pimephales promelas) caged in four Nebraska, USA watersheds - the Niobrara and Dismal Rivers (low-impact agricultural sites) and the Platte and Elkhorn Rivers (high-impact agricultural sites). Gene expression profiles were site specific and fish from the low- and high-impact sites aggregated into distinct groups. Over 1500 genes were differentially regulated between fish from the low- and high-impact sites. Many gene expression differences (1218) were also noted when the Platte and Elkhorn minnows were compared to one another and Platte fish experienced a higher degree of transcript alterations than Elkhorn fish. These findings indicate that there are differences between the low-impact and high-impact sites, as well as between the two high-impact sites. Historical water quality data support these results as only trace levels of agrichemicals have been detected at the low-impact sites, while substantial levels of agrichemicals have been reported at the high-impact sites with agrichemical loads at the Platte generally exceeding those at the Elkhorn. Overall, this study demonstrates that microarrays can be utilized to discriminate sites with different contaminant loads from one another.

Research paper thumbnail of The expression of inherited hydrocephalus in H-Tx rats

Child's Nervous System, 2000

Objectives: H-Tx rats develop severe hydrocephalus in late gestation. The breeding colony maintai... more Objectives: H-Tx rats develop severe hydrocephalus in late gestation. The breeding colony maintained at the University of Florida stems from one pair obtained in 1992. The aims of this study were to characterize the expression of hydrocephalus in the H-Tx rat colony, to perform within-strain and betweenstrain DNA analysis and to examine hydrocephalus expression in specific breeding experiments. Methods and observations: Matings between normal rats produce hydrocephalic offspring almost without exception, and the overall frequency is stable between generations at 40%. However, frequency varies with parity, being only 27% in the first litters, and it also varies with sex, there being an excess of male hydrocephalics. Mating between shunt-treated hydrocephalic rats did not increase the frequency. DNA typing with microsatellite markers showed that there was some residual heterogeneity in the colony despite inbreeding for 22 generations, although it did not segregate with hydrocephalus. Test mating with two other inbred strains, F344 and LEW produced some affected pups in the LEW cross only. A backcross experiment between H-Tx and F344 produced 12.3% severely-affected pups and 5.4% pups with a mild form, indicating the presence of several susceptibility genes. Conclusions: All animals in our H-Tx colony are homozygous for the hydrocephalus loci, but there is incomplete penetrance.

Research paper thumbnail of Gene set enrichment analysis of microarray data from Pimephales promelas (Rafinesque), a non-mammalian model organism

BMC Genomics, 2011

Background: Methods for gene-class testing, such as Gene Set Enrichment Analysis (GSEA), incorpor... more Background: Methods for gene-class testing, such as Gene Set Enrichment Analysis (GSEA), incorporate biological knowledge into the analysis and interpretation of microarray data by comparing gene expression patterns to pathways, systems and emergent phenotypes. However, to use GSEA to its full capability with non-mammalian model organisms, a microarray platform must be annotated with human gene symbols. Doing so enables the ability to relate a model organism's gene expression, in response to a given treatment, to potential human health consequences of that treatment. We enhanced the annotation of a microarray platform from a non-mammalian model organism, and then used the GSEA approach in a reanalysis of a study examining the biological significance of acute and chronic methylmercury exposure on liver tissue of fathead minnow (Pimephales promelas). Using GSEA, we tested the hypothesis that fathead livers, in response to methylmercury exposure, would exhibit gene expression patterns similar to diseased human livers. Results: We describe an enhanced annotation of the fathead minnow microarray platform with human gene symbols. This resource is now compatible with the GSEA approach for gene-class testing. We confirmed that GSEA, using this enhanced microarray platform, is able to recover results consistent with a previous analysis of fathead minnow exposure to methylmercury using standard analytical approaches. Using GSEA to compare fathead gene expression profiles to human phenotypes, we also found that fathead methylmercury-treated livers exhibited expression profiles that are homologous to human systems & pathways and results in damage that is similar to those of human liver damage associated with hepatocellular carcinoma and hepatitis B. Conclusions: This study describes a powerful resource for enabling the use of non-mammalian model organisms in the study of human health significance. Results of microarray gene expression studies involving fathead minnow, typically used for aquatic ecological toxicology studies, can now be used to generate hypotheses regarding consequences of contaminants and other stressors on humans. The same approach can be used with other model organisms with microarray platforms annotated in a similar manner.

Research paper thumbnail of The genomic transcriptional response of female fathead minnows (Pimephales promelas) to an acute exposure to the androgen, 17β-trenbolone

Aquatic Toxicology, 2009

We investigated the genomic transcriptional response of female fathead minnows (Pimephales promel... more We investigated the genomic transcriptional response of female fathead minnows (Pimephales promelas) to an acute (4 day) exposure to 0.1 or 1.0 μg/L of 17β-trenbolone (TB), the active metabolite of an anabolic androgenic steroid used as a growth promoter in cattle and a contaminant of concern in aquatic systems. Our objectives were to investigate the gene expression profile induced by TB, define biomarkers of exposure to TB, and increase our understanding of the mechanisms of adverse effects of TB on fish reproduction. In female gonad tissue, microarray analysis using a 22K oligonucleotide microarray (EcoArray Inc., Gainesville, FL) showed 99 significantly upregulated genes and 741 significantly downregulated genes in response to 1 μg TB/L. In particular, hydroxysteroid (17β) dehydrogenase 12a (hsd17b12a), zona pellucida glycoprotein 2.2 (zp2.2), and protein inhibitor of activated STAT, 2 (pias2) were all downregulated in gonad. Q-PCR measurements in a larger sample set were consistent with the microarray results in the direction and magnitude of these changes in gene expression. However, several novel potential biomarkers were verified by Q-PCR in the same samples, but could not be validated in independent samples. In liver, Q-PCR measurements showed a significant decrease in vitellogenin 1 (vtg1) mRNA expression. In brain, cytochrome P450, family 19, subfamily A, polypeptide 1b (cyp19a1b, previously known as aromatase B) transcript levels were significantly reduced following TB exposure. Our study provides a candidate gene involved in mediating the action of TB, hsd17b12a, and two potential biomarkers sensitive to acute TB exposure, hepatic vtg1 and brain cyp19a1b.

Research paper thumbnail of Effects of brevetoxin exposure on the immune system of loggerhead sea turtles

Aquatic Toxicology, 2010

Blooms of the toxic dinoflagellate, Karenia brevis, occur almost annually off the Florida coast. ... more Blooms of the toxic dinoflagellate, Karenia brevis, occur almost annually off the Florida coast. These blooms, commonly called "red tides", produce a group of neurotoxins collectively termed brevetoxins. Many species of sealife, including sea turtles, are severely impacted by brevetoxin exposure. Effects of brevetoxins on immune cells were investigated in rescued loggerhead sea turtles, Caretta caretta, as well as through in vitro experiments using peripheral blood leukocytes (PBL) collected from captive sea turtles. In rescued animals, plasma brevetoxin concentrations were measured using a competitive ELISA. Plasma lysozyme activity was measured using a turbidity assay. Lysozyme activity correlated positively with plasma brevetoxin concentrations. Differential expression of genes affected by brevetoxin exposure was determined using two separate suppression subtractive hybridization experiments. In one experiment, genes from PBL collected from sea turtles rescued from red tide toxin exposure were compared to genes from PBL collected from healthy captive loggerhead sea turtles. In the second experiment, PBL from healthy captive loggerhead sea turtles were exposed to brevetoxin (500 ng PbTx-2/ml) in vitro for 18 h and compared to unexposed PBL. Results from the subtraction hybridization experiment conducted with red tide rescued sea turtle PBL indicated that genes involved in oxidative stress or xenobiotic metabolism were up-regulated. Using quantitative real-time PCR, a greater than 2-fold increase in superoxide dismutase and thioredoxin and greater than 10-fold increase in expression of thiopurine S-methyltransferase were observed. Results from the in vitro subtraction hybridization experiment indicated that genes coding for cytochrome c oxidases were the major up-regulated genes. Using quantitative real-time PCR, a greater than 8-fold increase in expression of ␤-tubulin and greater than 3-fold increase in expression of ubiquinol were observed. Brevetoxin exposure may have significant implications for immune function in loggerhead sea turtles.

Research paper thumbnail of Gene expression changes in bottlenose dolphin, Tursiops truncatus, skin cells following exposure to methylmercury (MeHg) or perfluorooctane sulfonate (PFOS)

Aquatic Toxicology, 2009

Methylmercury (MeHg) and perfluorooctane sulfonate (PFOS) bioaccumulate and biomagnify in the env... more Methylmercury (MeHg) and perfluorooctane sulfonate (PFOS) bioaccumulate and biomagnify in the environment and increasing concentrations of these pollutants have been found in wildlife and humans. Both chemicals are worldwide contaminants with wide ranging biological effects and have been identified in relatively high concentrations in apex level marine mammals such as bottlenose dolphins. The primary objective of this study was to determine if exposure to MeHg or PFOS would alter the gene expression in primary bottlenose dolphin epidermal cell cultures. Primary skin cells were isolated and cultured from skin samples collected from wild bottlenose dolphins. The cells were subsequently exposed to 13 ppm PFOS or 1 ppm MeHg and changes in gene expression were analyzed by suppressive subtractive hybridization (SSH) and quantitative real-time PCR (QPCR). 116 genes were positively identified in the dolphin skin cells by SSH. Of these, 16 total genes were analyzed by QPCR (9 and 11 genes following PFOS or MeHg exposure, respectively, with four overlapping genes). Results indicate MeHg significantly alters gene expression patterns following 24 h exposure, but has no measurable effect after only 1 h. PFOS exposure, however, caused significant alterations following both 1 and 25 h. Overall, the changes in gene expression observed indicate these concentrations of MeHg and PFOS significantly alter normal gene expression patterns. The changes in gene expression following exposure to these contaminants not only indicate a cellular stress response, but also decreased cell cycle progression and cellular proliferation and reduced protein translation. Alterations in normal cellular biology, like those observed, may lead to changes in health in marine mammals exposed to contaminants; however, this warrants further investigation.

Research paper thumbnail of T 2 changes following shunt-treatment of neonatal hydrocephalic H-Tx rats

Research paper thumbnail of Complex Genetic and Maternal Effects in Fetal-Onset Rat Hydrocephalus

Research paper thumbnail of Generation of Congenic Lines for H-Tx Hydrocephalus by Introgression to Fisher F344 rats

Research paper thumbnail of Genetic loci for ventricular dilatation in the LEW/Jms rat with fetal-onset hydrocephalus are influenced by gender and genetic background

Cerebrospinal fluid research, Jan 12, 2005

The LEW/Jms rat strain has inherited hydrocephalus, with more males affected than females and an ... more The LEW/Jms rat strain has inherited hydrocephalus, with more males affected than females and an overall expression rate of 28%. This study aimed to determine chromosomal positions for genetic loci causing the hydrocephalus. An F1 backcross was made to the parental LEW/Jms strain from a cross with non-hydrocephalic Fischer 344 rats. BC1 rats were generated for two specific crosses: the first with a male LEW/Jms rat as parent and grandparent, [(F x L) x L], designated B group, and the second with a female LEW/Jms rat as the parent and grandparent [L x (L x F)], designated C group. All hydrocephalic and a similar number of non-hydrocephalic rats from these two groups were genotyped with microsatellite markers and the data was analyzed separately for each sex by MAPMAKER. The frequency of hydrocephalus was not significantly different between the two groups (18.2 and 19.9 %), but there was a significant excess of males in the B group. The mean severity of hydrocephalus, measured as the ...

Research paper thumbnail of Characteristics of hydrocephalus expression in the LEW/Jms rat strain with inherited disease

Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery, 2003

The expression and severity of hydrocephalus was characterized in LEW/Jms rats with inherited hyd... more The expression and severity of hydrocephalus was characterized in LEW/Jms rats with inherited hydrocephalus. The frequency of overt disease (lethal) was 27.7%, but varied depending on breeding line. It increased to 31.5% when rats with mild disease were included. Most breeding pairs (48/51) produced hydrocephalic offspring with significantly more males than females affected. Some adult rats were also found to have mild (nonlethal) ventricular dilatation. When bred to Fisher F344 rats, 3% of the F(1) progeny had overt hydrocephalus, indicating that the trait is not recessive. Overt hydrocephalus was 9-20% in N(2) rats (F(1) rats x LEW/Jms). The frequency of hydrocephalus and the presence of an excess of hydrocephalic males, varied depending on the direction of the cross. Mild hydrocephalus in N(2) rats was 3.1%. It is concluded that the inheritance of hydrocephalus in LEW/Jms strain is probably not mendelian recessive but may be semidominant or involve more than one gene and has a ma...

Research paper thumbnail of Chromosomal linkage associated with disease severity in the hydrocephalic H-Tx rat

Behavior genetics, 2001

Infantile hydrocephalus results in neurological deficits despite surgical treatment. Fetal-onset ... more Infantile hydrocephalus results in neurological deficits despite surgical treatment. Fetal-onset hydrocephalus in humans can be caused by developmental abnormalities that are genetic in origin. The H-Tx rat has hydrocephalus with 40% penetrance and a polygenic inheritance. A backcross with Fisher F344 inbred strain produced a total of 1500 progeny with 17.5% hydrocephalus. Of these, only 12.3% had overt disease and the remaining 5.2% had mild disease seen only after fixation of the brain. Disease severity was measured for all affected rats using the ratio of ventricle to brain width. The severity measure confirmed that there are two populations, mild hydrocephalus (M; ratio, <0.4) and severe hydrocephalus (S; ratio, >0.4), with a small overlap. For genotyping, the two populations were each subdivided based on the ratio measure to give a total of four groups of increasing severity. After an initial genome scan with microsatellite markers, all hydrocephalic rats and a subset of ...

Research paper thumbnail of Single and multiple congenic strains for hydrocephalus in the H-Tx rat

Mammalian Genome, 2005

The H-Tx rat has fetal-onset hydrocephalus with a complex mode of inheritance. Previously, quanti... more The H-Tx rat has fetal-onset hydrocephalus with a complex mode of inheritance. Previously, quantitative trait locus mapping using a backcross with Fischer F344 rats demonstrated genetic loci significantly linked to hydrocephalus on Chromosomes 10, 11, and 17. Hydrocephalus was preferentially associated with heterozygous alleles on Chrs 10 and 11 and with homozygous alleles on Chr 17. This study aimed to determine the phenotypic contribution of each locus by constructing single and multiple congenic strains. Single congenic rats were constructed using Fischer F344 as the recipient strain and a marker-assisted protocol. The homozygous strains were maintained for eight generations and the brains examined for dilated ventricles indicative for hydrocephalus. No congenic rats had severe (overt) hydrocephalus. A few pups and a significant number of adults had mild disease. The incidence was significantly higher in the C10 and C17 congenic strains than in the nonhydrocephalic F344 strain. Breeding to F344 to make F.H-Tx C10 or C11 rats heterozygous for the hydrocephalus locus failed to produce progeny with severe disease. Both bicongenic and tricongenic rats of different genotype combinations were constructed by crossing congenic rats. None had severe disease but the frequency of mild hydrocephalus in adults was similar to congenic rats and significantly higher than in the F344 strain. Rats with severe hydrocephalus were recovered in low numbers when single congenic or bicongenic rats were crossed with the parental H-Tx strain. It is concluded that the genetic and epigenetic factors contributing to severe hydrocephalus in the H-Tx strain are more complex than originally anticipated.

Research paper thumbnail of Genome-wide linkage analysis of inherited hydrocephalus in the H-Tx rat

Mammalian Genome, 2001

Inherited hydrocephalus in humans has received very little attention, most probably because known... more Inherited hydrocephalus in humans has received very little attention, most probably because known occurrences are sporadic and systematic investigation is difficult. The H-Tx rat, one of a number of rodent strains with inherited hydrocephalus, has a complex inheritance with more than one postulated susceptibility gene and 40% penetrance. The aim of this study was to perform a genome-wide scan on backcross progeny derived from H-Tx and Fisher F344 rats, to identify genomic regions associated with hydrocephalus. Penetrance of hydrocephalus in (H-Tx x F344) F1 x H-Tx was 12.3%. All severely hydrocephalic progeny (n = 185) and a subset of normal progeny (n = 128) were screened with 110 simple sequence length polymorphisms (SSLPs) with 83% coverage of the genome. A significant susceptibility locus was found on chromosome (Chr) 11 (LOD = 3.1). Three loci with suggestive linkage were found on Chr 17 (LOD = 2.4), on Chr 9 (LOD = 1.94), and on Chr 19 (LOD = 1.91). For the loci on Chr 11 and 19, hydrocephalus was associated with the heterozygous genotype, while the other two were recessive. Although none of the four loci was essential for the hydrocephalic phenotype, the additive effects of two, three, or four loci increased the penetrance in a linear fashion. Altogether these four loci accounted for 13.5% of the total variance. It is concluded that hydrocephalus in the H-Tx rat is associated with two, possibly four genetic loci, but that there may be additional undefined genetic and environmental influences.

Research paper thumbnail of Altered gene expression in the brain and liver of female fathead minnows Pimephales promelas Rafinesque exposed to fadrozole

Journal of Fish Biology, 2008

The fathead minnow Pimephales promelas is a small fish species widely used for ecotoxicology rese... more The fathead minnow Pimephales promelas is a small fish species widely used for ecotoxicology research and regulatory testing in North America. This study used a 2000 gene oligonucleotide microarray to evaluate the effects of the aromatase inhibitor, fadrozole, on gene expression in the liver and brain tissue of exposed females. Reproductive measures, plasma vitellogenin and gene expression data for the brain isoform of aromatase (cytP19B), vitellogenin precursors and transferrin provided evidence supporting the efficacy of the fadrozole exposure. Unsupervised analysis of the microarray results identified 20 genes in brain and 41 in liver as significantly up-regulated and seven genes in brain and around 45 in liver as significantly down-regulated. Differentially expressed genes were associated with a broad spectrum of biological functions, many with no obvious relationship to aromatase inhibition. However, in brain, fadrozole exposure elicited significant up-regulation of several genes involved in the cholesterol synthesis, suggesting it as a potentially affected pathway. Gene ontologybased analysis of expression changes in liver suggested overall down-regulation of protein biosynthesis. While real-time polymerase chain reaction analyses supported some of the microarray responses, others could not be verified. Overall, results of this study provide a foundation for developing novel hypotheses regarding the system-wide effects of fadrozole, and other chemical stressors with similar modes of action, on fish biology.

Research paper thumbnail of Transcriptional response of hepatic largemouth bass (Micropterus salmoides) mRNA upon exposure to environmental contaminants

Journal of Applied Toxicology, 2010

Microarrays enable gene transcript expression changes in near-whole genomes to be assessed in res... more Microarrays enable gene transcript expression changes in near-whole genomes to be assessed in response to environmental stimuli. We utilized oligonucleotide microarrays and subsequent gene set enrichment analysis (GSEA) to assess patterns of gene expression changes in male largemouth bass (Micropterus salmoides) hepatic tissues after a 96 h exposure to common environmental contaminants. Fish were exposed to atrazine, cadmium chloride, PCB 126, phenanthrene and toxaphene via intraperitoneal injection with target body burdens of 3.0, 0.00067, 2.5, 50 and 100 mg g-1 , respectively. This was conducted in an effort to identify potential biomarkers of exposure. The expressions of 4, 126, 118, 137 and 58 mRNA transcripts were significantly (P Յ 0.001, fold change Ն2¥) affected by exposure to atrazine, cadmium chloride, PCB 126, phenanthrene and toxaphene exposures, respectively. GSEA revealed that none, four, five, five and three biological function gene ontology categories were significantly influenced by exposure to these chemicals, respectively. We observed that cadmium chloride elicited ethanol metabolism responses, and along with PCB 126 and phenanthrene affected transcripts associated with protein biosynthesis. PCB 126, phenanthrene and toxaphene also influenced one-carbon compound metabolism while PCB 126 and phenanthrene affected mRNA transcription and mRNA export from the nucleus and may have induced an antiestrogenic response. Atrazine was found to alter the expression of few hepatic transcripts. This work has highlighted several biological processes of interest that may be helpful in the development of gene transcript biomarkers of chemical exposure in fish.

Research paper thumbnail of Genetic analysis of inherited hydrocephalus in a rat model

Experimental Neurology, 2004

Congenital hydrocephalus is a serious neurological disorder with a diverse etiology. Although the... more Congenital hydrocephalus is a serious neurological disorder with a diverse etiology. Although there is strong evidence for genetic causes, few genes have been identified in humans. The rodent model, the H-Tx rat, has hydrocephalus with an onset in late gestation and a complex mode of inheritance. Ventricular dilatation is associated with abnormalities in the cerebral aqueduct and subcommissural organ. Quantitative trait locus (QTL) mapping was performed on DNA from the progeny of a backcross with the non-hydrocephalic Fischer F344 strain, using DNA microsatellite markers. The hydrocephalus trait was quantified by measuring the severity of the ventricular dilatation. Four chromosomes, each with a locus for hydrocephalus (Chrs 9, 10, 11, and 17), were mapped using additional markers and DNA from four subsets of backcross progeny with allelic recombination at or near each locus. The genetic positions for the markers and the loci were located using the Ensemble Rat Genome Browser. For each chromosome studied, the interval containing the locus was examined for known rat genes and for human genes identified from human-rat homology. Genes expressed in brain and with a function associated with known causes of hydrocephalus were identified as possible candidate genes. Future studies to characterize the causative genes in this animal model will improve the understanding of genetic causes in humans.

Research paper thumbnail of The Frequency of Inherited Hydrocephalus Is Influenced by Intrauterine Factors in H-Tx Rats

Experimental Neurology, 2002

H-Tx rats have fetal-onset inherited hydrocephalus. Linkage analysis has determined the genetics ... more H-Tx rats have fetal-onset inherited hydrocephalus. Linkage analysis has determined the genetics is complex, with at least three loci associated with hydrocephalus. In addition, maternal and/or intrauterine factors influence the frequency of expression. The aim of this study was to characterize nongenetic (epigenetic) factors that affect hydrocephalus in this strain. Groups of primiparous and multiparous females were used to breed fetuses for examination in utero. Multiparous females were manipulated to have either gestation with lactation or, by removal of pups at birth, gestation without lactation. In addition, hydrocephalus expression in postnatal rats from the breeding colony was analyzed for primiparous and multiparous females. The latter were subdivided according to the interval between the litter examined and the previous litter. There was no particular uterine position or horn that favored hydrocephalus and hydrocephalic fetuses were the same weight as normal littermates. The frequency of hydrocephalus was 16-20% in primiparous females and twofold higher in multiparous females that were lactating during pregnancy. Removal of the suckling pups prevented this increase. The severity of hydrocephalus was measured on 1-mmthick fixed brain slices. Fetuses from lactating females had hydrocephalus that was significantly more severe than the nonlactating groups. However, all fetus groups had hydrocephalus that was very much less severe than the postnatal pups, suggesting that severity increases after birth. It is concluded that there is an epigenetic factor that increases the frequency of inherited hydrocephalus in fetuses if suckling pups are present during gestation. Future experiments will examine possible mechanisms for this genotype-environment interaction.

Research paper thumbnail of Development and Validation of a 2,000-GENE Microarray for the Fathead Minnow (Pimephales Promelas)

Environmental Toxicology and Chemistry, 2007

Gene microarrays provide the field of ecotoxicology new tools to identify mechanisms of action of... more Gene microarrays provide the field of ecotoxicology new tools to identify mechanisms of action of chemicals and chemical mixtures. Herein we describe the development and application of a 2,000-gene oligonucleotide microarray for the fathead minnow Pimephales promelas, a species commonly used in ecological risk assessments in North America. The microarrays were developed from various cDNA and subtraction libraries that we constructed. Consistency and reproducibility of the microarrays were documented by examining multiple technical replicates. To test application of the fathead minnow microarrays, gene expression profiles of fish exposed to 17␤-estradiol, a well-characterized estrogen receptor (ER) agonist, were examined. For these experiments, adult male fathead minnows were exposed for 24 h to waterborne 17␤-estradiol (40 or 100 ng/L) in a flow-through system, and gene expression in liver samples was characterized. Seventy-one genes were identified as differentially regulated by estradiol exposure. Examination of the gene ontology designations of these genes revealed patterns consistent with estradiol's expected mechanisms of action and also provided novel insights as to molecular effects of the estrogen. Our studies indicate the feasibility and utility of microarrays as a basis for understanding biological responses to chemical exposure in a model ecotoxicology test species.

Research paper thumbnail of A Graphical Systems Model to Facilitate Hypothesis-Driven Ecotoxicogenomics Research on the Teleost Brain−Pituitary−Gonadal Axis

Environmental Science & Technology, 2007

Research paper thumbnail of Taking Microarrays to the Field: Differential Hepatic Gene Expression of Caged Fathead Minnows from Nebraska Watersheds

Environmental Science & Technology, 2012

This study aimed to evaluate the utility of microarrays as a biomonitoring tool in field studies.... more This study aimed to evaluate the utility of microarrays as a biomonitoring tool in field studies. A 15,000-oligonucleotide microarray was used to measure the hepatic gene expression of fathead minnows (Pimephales promelas) caged in four Nebraska, USA watersheds - the Niobrara and Dismal Rivers (low-impact agricultural sites) and the Platte and Elkhorn Rivers (high-impact agricultural sites). Gene expression profiles were site specific and fish from the low- and high-impact sites aggregated into distinct groups. Over 1500 genes were differentially regulated between fish from the low- and high-impact sites. Many gene expression differences (1218) were also noted when the Platte and Elkhorn minnows were compared to one another and Platte fish experienced a higher degree of transcript alterations than Elkhorn fish. These findings indicate that there are differences between the low-impact and high-impact sites, as well as between the two high-impact sites. Historical water quality data support these results as only trace levels of agrichemicals have been detected at the low-impact sites, while substantial levels of agrichemicals have been reported at the high-impact sites with agrichemical loads at the Platte generally exceeding those at the Elkhorn. Overall, this study demonstrates that microarrays can be utilized to discriminate sites with different contaminant loads from one another.

Research paper thumbnail of The expression of inherited hydrocephalus in H-Tx rats

Child's Nervous System, 2000

Objectives: H-Tx rats develop severe hydrocephalus in late gestation. The breeding colony maintai... more Objectives: H-Tx rats develop severe hydrocephalus in late gestation. The breeding colony maintained at the University of Florida stems from one pair obtained in 1992. The aims of this study were to characterize the expression of hydrocephalus in the H-Tx rat colony, to perform within-strain and betweenstrain DNA analysis and to examine hydrocephalus expression in specific breeding experiments. Methods and observations: Matings between normal rats produce hydrocephalic offspring almost without exception, and the overall frequency is stable between generations at 40%. However, frequency varies with parity, being only 27% in the first litters, and it also varies with sex, there being an excess of male hydrocephalics. Mating between shunt-treated hydrocephalic rats did not increase the frequency. DNA typing with microsatellite markers showed that there was some residual heterogeneity in the colony despite inbreeding for 22 generations, although it did not segregate with hydrocephalus. Test mating with two other inbred strains, F344 and LEW produced some affected pups in the LEW cross only. A backcross experiment between H-Tx and F344 produced 12.3% severely-affected pups and 5.4% pups with a mild form, indicating the presence of several susceptibility genes. Conclusions: All animals in our H-Tx colony are homozygous for the hydrocephalus loci, but there is incomplete penetrance.

Research paper thumbnail of Gene set enrichment analysis of microarray data from Pimephales promelas (Rafinesque), a non-mammalian model organism

BMC Genomics, 2011

Background: Methods for gene-class testing, such as Gene Set Enrichment Analysis (GSEA), incorpor... more Background: Methods for gene-class testing, such as Gene Set Enrichment Analysis (GSEA), incorporate biological knowledge into the analysis and interpretation of microarray data by comparing gene expression patterns to pathways, systems and emergent phenotypes. However, to use GSEA to its full capability with non-mammalian model organisms, a microarray platform must be annotated with human gene symbols. Doing so enables the ability to relate a model organism's gene expression, in response to a given treatment, to potential human health consequences of that treatment. We enhanced the annotation of a microarray platform from a non-mammalian model organism, and then used the GSEA approach in a reanalysis of a study examining the biological significance of acute and chronic methylmercury exposure on liver tissue of fathead minnow (Pimephales promelas). Using GSEA, we tested the hypothesis that fathead livers, in response to methylmercury exposure, would exhibit gene expression patterns similar to diseased human livers. Results: We describe an enhanced annotation of the fathead minnow microarray platform with human gene symbols. This resource is now compatible with the GSEA approach for gene-class testing. We confirmed that GSEA, using this enhanced microarray platform, is able to recover results consistent with a previous analysis of fathead minnow exposure to methylmercury using standard analytical approaches. Using GSEA to compare fathead gene expression profiles to human phenotypes, we also found that fathead methylmercury-treated livers exhibited expression profiles that are homologous to human systems & pathways and results in damage that is similar to those of human liver damage associated with hepatocellular carcinoma and hepatitis B. Conclusions: This study describes a powerful resource for enabling the use of non-mammalian model organisms in the study of human health significance. Results of microarray gene expression studies involving fathead minnow, typically used for aquatic ecological toxicology studies, can now be used to generate hypotheses regarding consequences of contaminants and other stressors on humans. The same approach can be used with other model organisms with microarray platforms annotated in a similar manner.

Research paper thumbnail of The genomic transcriptional response of female fathead minnows (Pimephales promelas) to an acute exposure to the androgen, 17β-trenbolone

Aquatic Toxicology, 2009

We investigated the genomic transcriptional response of female fathead minnows (Pimephales promel... more We investigated the genomic transcriptional response of female fathead minnows (Pimephales promelas) to an acute (4 day) exposure to 0.1 or 1.0 μg/L of 17β-trenbolone (TB), the active metabolite of an anabolic androgenic steroid used as a growth promoter in cattle and a contaminant of concern in aquatic systems. Our objectives were to investigate the gene expression profile induced by TB, define biomarkers of exposure to TB, and increase our understanding of the mechanisms of adverse effects of TB on fish reproduction. In female gonad tissue, microarray analysis using a 22K oligonucleotide microarray (EcoArray Inc., Gainesville, FL) showed 99 significantly upregulated genes and 741 significantly downregulated genes in response to 1 μg TB/L. In particular, hydroxysteroid (17β) dehydrogenase 12a (hsd17b12a), zona pellucida glycoprotein 2.2 (zp2.2), and protein inhibitor of activated STAT, 2 (pias2) were all downregulated in gonad. Q-PCR measurements in a larger sample set were consistent with the microarray results in the direction and magnitude of these changes in gene expression. However, several novel potential biomarkers were verified by Q-PCR in the same samples, but could not be validated in independent samples. In liver, Q-PCR measurements showed a significant decrease in vitellogenin 1 (vtg1) mRNA expression. In brain, cytochrome P450, family 19, subfamily A, polypeptide 1b (cyp19a1b, previously known as aromatase B) transcript levels were significantly reduced following TB exposure. Our study provides a candidate gene involved in mediating the action of TB, hsd17b12a, and two potential biomarkers sensitive to acute TB exposure, hepatic vtg1 and brain cyp19a1b.

Research paper thumbnail of Effects of brevetoxin exposure on the immune system of loggerhead sea turtles

Aquatic Toxicology, 2010

Blooms of the toxic dinoflagellate, Karenia brevis, occur almost annually off the Florida coast. ... more Blooms of the toxic dinoflagellate, Karenia brevis, occur almost annually off the Florida coast. These blooms, commonly called "red tides", produce a group of neurotoxins collectively termed brevetoxins. Many species of sealife, including sea turtles, are severely impacted by brevetoxin exposure. Effects of brevetoxins on immune cells were investigated in rescued loggerhead sea turtles, Caretta caretta, as well as through in vitro experiments using peripheral blood leukocytes (PBL) collected from captive sea turtles. In rescued animals, plasma brevetoxin concentrations were measured using a competitive ELISA. Plasma lysozyme activity was measured using a turbidity assay. Lysozyme activity correlated positively with plasma brevetoxin concentrations. Differential expression of genes affected by brevetoxin exposure was determined using two separate suppression subtractive hybridization experiments. In one experiment, genes from PBL collected from sea turtles rescued from red tide toxin exposure were compared to genes from PBL collected from healthy captive loggerhead sea turtles. In the second experiment, PBL from healthy captive loggerhead sea turtles were exposed to brevetoxin (500 ng PbTx-2/ml) in vitro for 18 h and compared to unexposed PBL. Results from the subtraction hybridization experiment conducted with red tide rescued sea turtle PBL indicated that genes involved in oxidative stress or xenobiotic metabolism were up-regulated. Using quantitative real-time PCR, a greater than 2-fold increase in superoxide dismutase and thioredoxin and greater than 10-fold increase in expression of thiopurine S-methyltransferase were observed. Results from the in vitro subtraction hybridization experiment indicated that genes coding for cytochrome c oxidases were the major up-regulated genes. Using quantitative real-time PCR, a greater than 8-fold increase in expression of ␤-tubulin and greater than 3-fold increase in expression of ubiquinol were observed. Brevetoxin exposure may have significant implications for immune function in loggerhead sea turtles.

Research paper thumbnail of Gene expression changes in bottlenose dolphin, Tursiops truncatus, skin cells following exposure to methylmercury (MeHg) or perfluorooctane sulfonate (PFOS)

Aquatic Toxicology, 2009

Methylmercury (MeHg) and perfluorooctane sulfonate (PFOS) bioaccumulate and biomagnify in the env... more Methylmercury (MeHg) and perfluorooctane sulfonate (PFOS) bioaccumulate and biomagnify in the environment and increasing concentrations of these pollutants have been found in wildlife and humans. Both chemicals are worldwide contaminants with wide ranging biological effects and have been identified in relatively high concentrations in apex level marine mammals such as bottlenose dolphins. The primary objective of this study was to determine if exposure to MeHg or PFOS would alter the gene expression in primary bottlenose dolphin epidermal cell cultures. Primary skin cells were isolated and cultured from skin samples collected from wild bottlenose dolphins. The cells were subsequently exposed to 13 ppm PFOS or 1 ppm MeHg and changes in gene expression were analyzed by suppressive subtractive hybridization (SSH) and quantitative real-time PCR (QPCR). 116 genes were positively identified in the dolphin skin cells by SSH. Of these, 16 total genes were analyzed by QPCR (9 and 11 genes following PFOS or MeHg exposure, respectively, with four overlapping genes). Results indicate MeHg significantly alters gene expression patterns following 24 h exposure, but has no measurable effect after only 1 h. PFOS exposure, however, caused significant alterations following both 1 and 25 h. Overall, the changes in gene expression observed indicate these concentrations of MeHg and PFOS significantly alter normal gene expression patterns. The changes in gene expression following exposure to these contaminants not only indicate a cellular stress response, but also decreased cell cycle progression and cellular proliferation and reduced protein translation. Alterations in normal cellular biology, like those observed, may lead to changes in health in marine mammals exposed to contaminants; however, this warrants further investigation.