D. Sakhrani | University of British Columbia (original) (raw)

Papers by D. Sakhrani

Proceedings of the Royal Society B: Biological Sciences

Carotenoid pigmentation in salmon: variation in expression at BCO2-l locus controls a key fitness... more Carotenoid pigmentation in salmon: variation in expression at BCO2-l locus controls a key fitness trait affecting red coloration.

Transactions of the American Fisheries Society

Marine Biotechnology, 2015

Growth hormone (GH) transgenic salmon possesses markedly increased metabolic rate, appetite, and ... more Growth hormone (GH) transgenic salmon possesses markedly increased metabolic rate, appetite, and feed conversion efficiency, as well as an increased ability to compete for food resources. Thus, the ability of GH-transgenic fish to withstand periods of food deprivation as occurs in nature is potentially different than that of nontransgenic fish. However, the physiological and genetic effects of transgenic GH production over long periods of food deprivation remain largely unknown. Here, GH-transgenic coho salmon (Oncorhynchus kisutch) and nontransgenic, wild-type coho salmon were subjected to a 3month food deprivation trial, during which time performance characteristics related to growth were measured along with proximate compositions. To examine potential genetic effects of GH-transgenesis on long-term food deprivation, a group of genes related to muscle development and liver metabolism was selected for quantitative PCR analysis. Results showed that GH-transgenic fish lose weight at an increased rate compared to wild-type even though proximate compositions remained relatively similar between the groups. A total of nine genes related to muscle physiology (cathepsin, cee, insulin-like growth factor, myostatin, murf-1, myosin, myogenin, proteasome delta, tumor necrosis factor) and five genes related to liver metabolism (carnitine palmitoyltransferase, fatty acid synthase, glucose-6-phosphatase, glucose-6-phosphate dehydrogenase, glucokinase) were shown to be differentially regulated between GH-transgenic and wild-type coho salmon over time. These genetic and physiological responses assist in identifying differences between GH-transgenic and wild-type salmon in relation to fitness effects arising from elevated growth hormone during periods of long-term food shortage.

… of Fisheries and …, 2005

Two Y-chromosome DNA markers (a repetitive sequence, OtY1, and a single-copy marker, GH-Y) tightl... more Two Y-chromosome DNA markers (a repetitive sequence, OtY1, and a single-copy marker, GH-Y) tightly linked to the sex-determination locus have been examined for their association with sexual development among 55 populations of Chinook salmon (Oncorhynchus tshawytscha) from the Yukon, British Columbia, Washington, Oregon, and Idaho. Normal linkage has been observed in 96.7% of 2478 individuals examined. Only five males (0.44%) were found lacking both markers (none from Canadian systems), and 14 females (1.04%) from US populations and two females (0.15%) from Canadian populations were found to possess both markers. Variants identified included weakly amplifying alleles for GH-Y and OtY1 and structural variants identified by Southern-blot analysis. The frequency of variants in males was more than 2-fold that in females, and males deficient in GH-Y were more common (3.6%) than males deficient in the repetitive OtY1 sequence (0.7%). Some individuals (of both sexes) possessed fewer copies of the OtY1 repeat than normal males, revealing molecular dynamics that alter Y-chromosome structure within and among populations. A population (Hanford Reach) previously reported as having a high incidence of females possessing the OtY1 marker, and suspected of being sex-reversed, was found to have normal sex-marker genotypes in the present study.

Proceedings of the National Academy of Sciences, 2009

Domestication has been extensively used in agricultural animals to modify phenotypes such as grow... more Domestication has been extensively used in agricultural animals to modify phenotypes such as growth rate. More recently, transgenesis of growth factor genes [primarily growth hormone (GH)] has also been explored as a rapid approach to accelerating performance of agricultural species. Growth rates of many fishes respond dramatically to GH gene transgenesis, whereas genetic engineering of domestic mammalian livestock has resulted in relatively modest gains. The most dramatic effects of GH transgenesis in fish have been seen in relatively wild strains that have undergone little or no selection for enhanced growth, whereas genetic modification of livestock necessarily has been performed in highly domesticated strains that already possess very rapid growth. Such fast-growing domesticates may be refractory to further stimulation if the same regulatory pathways are being exploited by both genetic approaches. By directly comparing gene expression in wild-type, domestic, and GH transgenic strains of coho salmon, we have found that domestication and GH transgenesis are modifying similar genetic pathways. Genes in many different physiological pathways show modified expression in domestic and GH transgenic strains relative to wild-type, but effects are strongly correlated. Genes specifically involved in growth regulation (IGF1, GHR, IGF-II, THR) are also concordantly regulated in domestic and transgenic fish, and both strains show elevated levels of circulating IGF1. Muscle expression of GH in nontransgenic strains was found to be elevated in domesticated fish relative to wild type, providing a possible mechanism for growth enhancement. These data have implications for genetic improvement of existing domesticated species and risk assessment and regulation of emerging transgenic strains.

Journal of Molecular Endocrinology, 2006

The objectives of this study are to examine hepatic gene expression changes caused by GH transgen... more The objectives of this study are to examine hepatic gene expression changes caused by GH transgenesis and enhanced growth. This is the first use of cDNA microarrays to study the influence of GH transgenesis on liver gene expression in a nonmammalian vertebrate, and the first such study using sexually immature animals. Three groups of coho salmon were examined: GH transgenic on full ration (T), GH transgenic on restricted ration (R), and control non-transgenic (C). Specific growth rates for weight in T were approximately eightfold higher than in C, and fourfold higher than in R. Differential gene expression in T, R, and C samples was determined using w3500 and 16 000 gene microarrays, and R and C samples were compared on a different w4000 gene microarray. The use of multiple microarray platforms increased the overall proportion of the hepatic transcriptome considered in these studies. Cross-platform comparisons identified genes behaving similarly between studies. For example, genes encoding a precerebellin-like protein and complement component C3 were downregulated in R relative to C (R!C) in two microarray studies, and hemoglobins a and b were ROC in all three studies. Comparisons of informative gene lists within and between studies inferred causes of altered gene expression. For example, ten genes, including 78 kDa glucose-regulated protein, glycerol-3-phosphate dehydrogenase, hemoglobins a and b, and a C-type lectin, were likely induced by GH transgenesis due to their presence in both TOC and ROC gene lists. Eleven genes, including hepcidin, nuclear protein p8, precerebellin-like, transketolase, and fatty acid-binding protein, were present in both T!C and R!C gene lists and were, therefore, likely suppressed by GH transgenesis. A large number of salmonid genes identified in these studies are involved in iron homeostasis, mitochondrial function, carbohydrate metabolism, cellular proliferation, and innate immunity. Pentose phosphate pathway genes phosphogluconate dehydrogenase, transaldolase, and transketolase, were dysregulated in GH transgenic samples relative to control samples. Changes in the expression of genes involved in maintaining hemoglobin levels (heme oxygenase, hemoglobins a and b, Kruppel-like globin gene activator, hepcidin) in R and T fish indicate a need for additional hemoglobin in the transgenic fish, perhaps due to higher metabolic rate required for enhanced growth.

Journal of Animal Science, 2013

Growth rate can be genetically modified in many vertebrates by domestication and selection and mo... more Growth rate can be genetically modified in many vertebrates by domestication and selection and more recently by transgenesis overexpressing growth factor genes [e.g., growth hormone (GH)]. Although the phenotypic end consequence is similar, it is currently not clear whether the same modifications to physiological pathways are occurring in both genetic processes or to what extent they may interact when combined. To investigate these questions, microarray analysis has been used to assess levels of mRNA in liver of wild-type and growth-modified strains of rainbow trout (Oncorhynchus mykiss). This species has been used as a model because nondomesticated wild strains are available as comparators to assess genetic and physiological changes that have arisen both from domestication and from GH transgenesis. The analysis examined pure wild-type and pure domesticated strains as well as 2 different GH transgenes (with markedly different growth effects) both in pure wild and in wild × domesticated hybrid backgrounds. Liver mRNA showed highly concordant changes (Pearson correlations; r>0.828; P<0.001) in levels in domesticated and GH transgenic fish, relative to wild-type, for both up- and downregulated genes. Furthermore, among domesticated, transgenic, and their hybrid genotypes, a strong correlation (P<0.001) was found between growth rate and the number of genes affected (r=0.761 for downregulated mRNA and r=0.942 for upregulated mRNA) or between growth rate and mRNA levels relative to wild-type (r=0.931 for downregulated mRNA and r=0.928 for upregulated mRNA). One GH transgenic strain was found to affect growth and mRNA levels similar to domestication whereas effects of the other GH transgenic strain were much stronger. For both GH transgenes, a hybrid domesticated×wild background influenced growth rate and mRNA levels to only a small extent relative to the transgenes in a pure wild-type genetic background. Functional analysis found that genes involved in immune function, carbohydrate metabolism, detoxification, transcription regulation, growth regulation, and lipid metabolism were affected in common by domestication and GH transgenesis. The common responses of mRNAs in domesticated and GH transgenic strains is consistent with the GH pathway or its downstream effects being upregulated in domesticated animals during their modification from wild-type growth rates.

General and Comparative Endocrinology, 2008

Non-transgenic (wild-type) coho salmon (Oncorhynchus kisutch), growth hormone (GH) transgenic sal... more Non-transgenic (wild-type) coho salmon (Oncorhynchus kisutch), growth hormone (GH) transgenic salmon (with highly elevated growth rates), and GH transgenic salmon pair fed a non-transgenic ration level (and thus growing at the non-transgenic rate) were examined for plasma hormone concentrations, and liver, muscle, hypothalamus, telencephalon, and pituitary mRNA levels. GH transgenic salmon exhibited increased plasma GH levels, and enhanced liver, muscle and hypothalamic GH mRNA levels. Insulin-like growth factor-I (IGF-I) in plasma, and growth hormone receptor (GHR) and IGF-I mRNA levels in liver and muscle, were higher in fully fed transgenic than non-transgenic fish. GHR mRNA levels in transgenic fish were unaffected by ration-restriction, whereas plasma GH was increased and plasma IGF-I and liver IGF-I mRNA were decreased to wild-type levels. These data reveal that strong nutritional modulation of IGF-I production remains even in the presence of constitutive ectopic GH expression in these transgenic fish. Liver GHR membrane protein levels were not different from controls, whereas, in muscle, GHR levels were elevated approximately 5-fold in transgenic fish. Paracrine stimulation of IGF-I by ectopic GH production in non-pituitary tissues is suggested by increased basal cartilage sulphation observed in the transgenic salmon. Levels of mRNA for growth hormone-releasing hormone (GHRH) and cholecystokinin (CCK) did not differ between groups. Despite its role in appetite stimulation, neuropeptide Y (NPY) mRNA was not found to be elevated in transgenic groups.

Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 2009

Growth hormone (GH) transgenesis results in increased growth, feed intake and consequent metaboli... more Growth hormone (GH) transgenesis results in increased growth, feed intake and consequent metabolic rates in fish, and alters the utilization of dietary and stored carbohydrates, lipid and protein. However, the manner in which GH transgenesis differentially alters these energy sources in fish has not been well explored. We examined the effects of GH transgenesis and dietary carbohydrate, lipid and protein levels on metabolic enzyme activity in coho salmon (Oncorhynchus kisutch). In white muscle, increased activities of glycolytic enzymes and decreased activities of lipolytic enzymes in transgenic fish indicate a sparing of lipids through the preferential use of carbohydrates for energy production. In liver, transgenic fish showed increased activity of lipid synthesis enzymes and a shift in amino acid metabolism from catabolic to synthetic roles, suggesting a larger emphasis on anabolic pathways in transgenic fish to support accelerated growth. Unlike nontransgenic fish, transgenic fish fed a diet high in carbohydrates maintained growth rates, had increased capacity for lipid synthesis, and increased potential for biosynthetic roles of amino acids. GH transgenesis influences metabolic reactions in coho salmon by emphasizing carbohydrate degradation for energy production and lipid synthesis, and increasing utilization of lipids and proteins for synthetic roles necessary to maintain accelerated growth.

General and Comparative Endocrinology, 2012

To examine the relative growth, endocrine, and gene expression effects of growth hormone (GH) tra... more To examine the relative growth, endocrine, and gene expression effects of growth hormone (GH) transgenesis vs. GH protein treatment, wild-type non-transgenic and GH transgenic coho salmon were treated with a sustained-release formulation of recombinant bovine GH (bGH; Posilac™). Fish size, specific growth rate (SGR), and condition factor (CF) were monitored for 14 weeks, after which endocrine parameters were measured. Transgenic fish had much higher growth, SGR and CF than non-transgenic fish, and bGH injection significantly increased weight and SGR in non-transgenic but not transgenic fish. Plasma salmon GH concentrations decreased with bGH treatment in non-transgenic but not in transgenic fish where levels were similar to controls. Higher GH mRNA levels were detected in transgenic muscle and liver but no differences were observed in GH receptor (GHR) mRNA levels. In non-transgenic pituitary, GH and GHR mRNA levels per mg pituitary decreased with bGH dose to levels seen in transgenic salmon. Plasma IGF-I was elevated with bGH dose only in non-transgenic fish, while transgenic fish maintained an elevated level of IGF-I with or without bGH treatment. A similar trend was seen for liver IGF-I mRNA levels. Thus, bGH treatment increased fish growth and influenced feedback on endocrine parameters in nontransgenic but not in transgenic fish. A lack of further growth stimulation of GH transgenic fish suggests that these fish are experiencing maximal growth stimulation via GH pathways.