Trevor Williams - Academia.edu (original) (raw)

Papers by Trevor Williams

Investigative ophthalmology & visual science, 2018

The combined action of the activating protein-2 (AP-2) transcription factors, AP-2α and AP-2β, is... more The combined action of the activating protein-2 (AP-2) transcription factors, AP-2α and AP-2β, is important in early retinal development, specifically in the formation of horizontal cells. However, in previous studies, it was not possible to analyze postnatal development and function of additional retinal subtypes. We used a double conditional deletion of AP-2α and AP-2β from the retina to further examine the combinatory role of these genes in retinal cell patterning and function in postnatal adult mice as measured by Voronoi domain area and nearest-neighbor distance spatial analyses and ERGs, respectively. Conditional deletion of both AP-2α and AP-2β from the retina resulted in a variety of abnormalities, including the absence of horizontal cells, defects in the photoreceptor ribbons in which synapses failed to form, along with evidence of aberrant amacrine cell arrangement. Although no significant changes in amacrine cell population numbers were observed in the double mutants, sig...

Nature communications, Dec 6, 2017

Robustness to perturbation is a fundamental feature of complex organisms. Mutations are the raw m... more Robustness to perturbation is a fundamental feature of complex organisms. Mutations are the raw material for evolution, yet robustness to their effects is required for species survival. The mechanisms that produce robustness are poorly understood. Nonlinearities are a ubiquitous feature of development that may link variation in development to phenotypic robustness. Here, we manipulate the gene dosage of a signaling molecule, Fgf8, a critical regulator of vertebrate development. We demonstrate that variation in Fgf8 expression has a nonlinear relationship to phenotypic variation, predicting levels of robustness among genotypes. Differences in robustness are not due to gene expression variance or dysregulation, but emerge from the nonlinearity of the genotype-phenotype curve. In this instance, embedded features of development explain robustness differences. How such features vary in natural populations and relate to genetic variation are key questions for unraveling the origin and evo...

PloS one, 2017

Primary cilia are nearly ubiquitous, cellular projections that function to transduce molecular si... more Primary cilia are nearly ubiquitous, cellular projections that function to transduce molecular signals during development. Loss of functional primary cilia has a particularly profound effect on the developing craniofacial complex, causing several anomalies including craniosynostosis, micrognathia, midfacial dysplasia, cleft lip/palate and oral/dental defects. Development of the craniofacial complex is an intricate process that requires interactions between several different tissues including neural crest cells, neuroectoderm and surface ectoderm. To understand the tissue-specific requirements for primary cilia during craniofacial development we conditionally deleted three separate intraflagellar transport genes, Kif3a, Ift88 and Ttc21b with three distinct drivers, Wnt1-Cre, Crect and AP2-Cre which drive recombination in neural crest, surface ectoderm alone, and neural crest, surface ectoderm and neuroectoderm, respectively. We found that tissue-specific conditional loss of ciliary g...

Molecular and cellular biology, 2008

Tcfap2a, the gene encoding the mouse AP-2alpha transcription factor, is required for normal devel... more Tcfap2a, the gene encoding the mouse AP-2alpha transcription factor, is required for normal development of multiple structures during embryogenesis, including the face and limbs. Using comparative sequence analysis and transgenic-mouse experiments we have identified an intronic enhancer within this gene that directs expression to the face and limb mesenchyme. There are two conserved sequence blocks within this intron, and the larger of these directs tissue-specific activity and is found in all vertebrate Tcfap2a genes analyzed. To assess the role of the enhancer in regulating endogenous mouse Tcfap2a expression, we have deleted this cis-regulatory sequence from the genome. Loss of this element severely impairs Tcfap2a expression in the limb bud mesenchyme but generates only a modest reduction in the facial mesenchyme. The reduction in Tcfap2a transcription is accompanied by altered patterning of the forelimb, resulting in postaxial polydactyly. These results indicate that the major ...

PLoS Computational Biology, 2009

Developmental Dynamics, 2008

In this study, we have created a conditional deletion of AP‐2α in the developing mouse lens (Le‐A... more In this study, we have created a conditional deletion of AP‐2α in the developing mouse lens (Le‐AP‐2α mutants) to determine the cell‐autonomous requirement(s) for AP‐2α in lens development. Embryonic and adult Le‐AP‐2α mutants exhibited defects confined to lens placode derivatives, including a persistent adhesion of the lens to the overlying corneal epithelium (or lens stalk). Expression of known regulators of lens vesicle separation, including Pax6, Pitx3, and Foxe3 was observed in the Le‐AP‐2α mutant lens demonstrating that these genes do not lie directly downstream of AP‐2α. Unlike germ‐line mutants, Le‐AP‐2α mutants did not exhibit defects in the optic cup, further defining the tissue specific role(s) for AP‐2α in eye development. Finally, comparative microarray analysis of lenses from the Le‐AP‐2α mutants vs. wild‐type littermates revealed differential expression of 415 mRNAs, including reduced expression of genes important for maintaining the lens epithelial cell phenotype, su...

Developmental Dynamics, 2012

Background-We have previously shown that the transcription factor AP-2α (Tcfap2a) is expressed in... more Background-We have previously shown that the transcription factor AP-2α (Tcfap2a) is expressed in postmitotic developing amacrine cells in the mouse retina. Although retina-specific deletion of Tcfap2a did not affect retinogenesis, two other family members, AP-2β and AP-2γ, showed expression patterns similar to AP-2α. Results-Here we show that, in addition to their highly overlapping expression patterns in amacrine cells, AP-2α and AP-2β are also co-expressed in developing horizontal cells. AP-2γ expression is restricted to amacrine cells, in a subset that is partially distinct from the AP-2α/βimmunopositive population. To address possible redundant roles for AP-2α and AP-2β during retinogenesis, Tcfap2a/b-deficient retinas were examined. These double mutants showed a striking loss of horizontal cells and an altered staining pattern in amacrine cells that were not detected upon deletion of either family member alone. Conclusions-These studies have uncovered critical roles for AP-2 activity in retinogenesis, delineating the overlapping expression patterns of Tcfap2a, Tcfap2b, and Tcfap2c in the neural retina, and revealing a redundant requirement for Tcfap2a and Tcfap2b in horizontal and amacrine cell development.

Developmental Cell, 2011

Morphogenesis of mammalian facial processes requires coordination of cellular proliferation, migr... more Morphogenesis of mammalian facial processes requires coordination of cellular proliferation, migration, and apoptosis to develop intricate features. Cleft lip and/or palate (CL/P), the most frequent human craniofacial birth defect, can be caused by perturbation of any of these programs. Mutations of WNT, P63, and IRF6 yield CL/P in humans and mice; however, how these genes are regulated remains elusive. We generated mouse lines lacking Pbx genes in cephalic ectoderm and demonstrated that they exhibit fully penetrant CL/P and perturbed Wnt signaling. We also characterized a midfacial regulatory element that Pbx proteins bind to control the expression of Wnt9b-Wnt3, which in turn regulates p63. Altogether, we establish a Pbx-dependent Wnt-p63-Irf6 regulatory module in midfacial ectoderm that is conserved within mammals. Dysregulation of this network leads to localized suppression of midfacial apoptosis and CL/P. Ectopic Wnt ectodermal expression in Pbx mutants rescues the clefting, opening avenues for tissue repair.

Developmental Biology, 2012

Morphogenesis of the vertebrate head relies on proper dorsal-ventral (D-V) patterning of neural c... more Morphogenesis of the vertebrate head relies on proper dorsal-ventral (D-V) patterning of neural crest cells (NCC) within the pharyngeal arches. Endothelin-1 (Edn1)-induced signaling through the endothelin-A receptor (Ednra) is crucial for cranial NCC patterning within the mandibular portion of the first pharyngeal arch, from which the lower jaw arises. Deletion of Edn1, Ednra or endothelin-converting enzyme in mice causes perinatal lethality due to severe craniofacial birth defects. These include homeotic transformation of mandibular arch-derived structures into more maxillary-like structures, indicating a loss of NCC identity. All cranial NCCs express Ednra whereas Edn1 expression is limited to the overlying ectoderm, core paraxial mesoderm and pharyngeal pouch endoderm of the mandibular arch as well as more caudal arches. To define the developmental significance of Edn1 from each of these layers, we used Cre/loxP technology to inactivate Edn1 in a tissue-specific manner. We show that deletion of Edn1 in either the mesoderm or endoderm alone does not result in cellular or molecular changes in craniofacial development. However, ectodermal deletion of Edn1 results in craniofacial defects with concomitant changes in the expression of early mandibular arch patterning genes. Importantly, our results also both define for the first time in mice an intermediate mandibular arch domain similar to the one defined in zebrafish and show that this region is most sensitive to loss of Edn1. Together, our results illustrate an integral role for ectoderm-derived Edn1 in early arch morphogenesis, particularly in the intermediate domain.

Developmental Biology, 2004

The AP-2a transcription factor is required for multiple aspects of vertebrate development and mic... more The AP-2a transcription factor is required for multiple aspects of vertebrate development and mice lacking the AP-2a gene (tcfap2a) die at birth from severe defects affecting the head and trunk. Several of the defects associated with the tcfap2a-null mutation affect neural crest cell (NCC) derivatives including the craniofacial skeleton, cranial ganglia, and heart outflow tract. Consequently, there is considerable interest in the role of AP-2a in neural crest cell function in development and evolution. In addition, the expression of the AP-2a gene is utilized as a marker for premigratory and migratory neural crest cells in many vertebrate species. Here, we have specifically addressed how the presence of AP-2a in neural crest cells affects development by creating a conditional (floxed) version of tcfap2a which has subsequently been intercrossed with mice expressing Cre recombinase under the control of Wnt1 cis-regulatory sequences. Neural crest-specific disruption of tcfap2a results in frequent perinatal lethality associated with neural tube closure defects and cleft secondary palate. A small but significant fraction of mutant mice can survive into adulthood, but have retarded craniofacial growth, abnormal middle ear development, and defects in pigmentation. The phenotypes obtained confirm that AP-2a directs important aspects of neural crest cell function. At the same time, we did not observe several neurocristopathies affecting the head and heart that might be expected based on the phenotype of the AP-2a-null mouse. These results have important implications for the evolution and function of the AP-2 gene family in both the neural crest and the vertebrate embryo.

Developmental Biology, 2006

Epidermal morphogenesis begins with the commitment of the single-layered surface ectoderm to init... more Epidermal morphogenesis begins with the commitment of the single-layered surface ectoderm to initiate a stratification program, a process that requires the expression of the transcription factor TAp63a. To determine the molecular mechanism by which TAp63a induces genes associated with the commitment to stratification, such as K14, we have used a combination of in vitro and in vivo approaches. Our initial gene expression profiling studies suggested that TAp63a could regulate one or more AP-2 genes, which have been implicated in development and maintenance of the epidermis. We now demonstrate that TAp63a directly induces AP-2g expression in embryonic epidermis, when commitment to stratification occurs. Furthermore, we show that, in the absence of AP-2g, TAp63a fails to induce K14 expression in vitro. Our data identify AP-2g as the first in vivo target gene of TAp63a, and provide novel insights into the molecular mechanisms associated with early events in epidermal morphogenesis.

Developmental Biology, 2007

mutation maps to proximal mouse chromosome 18, and "Heartburn" has been mapped to a 20 MB interva... more mutation maps to proximal mouse chromosome 18, and "Heartburn" has been mapped to a 20 MB interval on chromosome 13. The characterization of these new models and the identification of genes associated with these phenotypes will provide us with important insights into the mechanisms of diaphragm development.

Developmental Biology, 2011

Developmental Biology, 1997

Embryonic facial development in chick embryos involves a sequential activation of genes that cont... more Embryonic facial development in chick embryos involves a sequential activation of genes that control differential growth and patterning of the beak. In the present study we isolate one such gene, the transcription factor, AP-2, that is known to be expressed in the face of mouse embryos. The protein sequence of chick AP-2a is 94% homologous to human and mouse AP-2. Wholemount in situ hybridization with a probe for chick AP-2 identifies expression from primitive streak stages up to stage 28. The most striking expression patterns in the head are during neural crest cell migration when AP-2 transcripts follow closely the tracts previously mapped for neural crest cells. Later, expression in the facial mesenchyme is strongest in the frontonasal mass and lateral nasal prominences and is downregulated in the maxillary and mandibular prominences. Once limb buds are visible, high expression is seen in the distal mesenchyme but not in the apical ectodermal ridge. The expression patterns of AP-2 in stage 20 embryos suggested that the gene may be important in ''budding out'' of facial prominences and limb buds. We implanted beads soaked in retinoic acid in the right nasal pit of stage 20 embryos resulting in a specific inhibition of outgrowth of the frontonasal mass and lateral nasal prominences. AP-2 expression was completely down-regulated in the lateral nasal within 8 hr of bead application. In addition, the normal up-regulation of AP-2 in the frontonasal mass did not occur following retinoic-acid treatment. There was an increase in programmed cell death around the right nasal pit that accompanied the down-regulation of AP-2. Prominences whose morphogenesis were not affected by retinoic acid did not have altered expression patterns. We removed the apical ectodermal ridge in stage 20 limb buds and found that AP-2 expression was partially downregulated 4 hr following ridge removal and completely downregulated 8 hr following stripping. Application of an FGF-4 soaked bead to the apex of the limb bud maintained AP-2 expression. Thus AP-2 is involved in outgrowth and could be regulated by factors such as FGFs that are present in the ectoderm of both the face and limb.

Developmental Biology, 1999

AP-2 transcription factors are a family of retinoic acid-responsive genes, which are involved in ... more AP-2 transcription factors are a family of retinoic acid-responsive genes, which are involved in complex morphogenetic processes. In the current study, we determine the requirement for AP-2␣ in early morphogenesis of the eye by examining the nature of the ocular defects in AP-2␣ null and chimeric mice. AP-2␣ null embryos exhibited ocular phenotypes ranging from a complete lack of eyes (anophthalmia) to defects in the developing lens involving a persistent adhesion of the lens to the overlying surface ectoderm. Two genes involved in lens development and differentiation, Pax6 and MIP26 were also misexpressed. AP-2␣ mutants also exhibited defects in the optic cup consisting of transdifferentiation of the dorsal retinal pigmented epithelium into neural retina and the absence of a defined ganglion cell layer. Newly generated chimeric embryos consisting of a population of AP-2␣ ؊/؊ and AP-2␣ ؉/؉ cells exhibit ocular defects similar to those seen in the knockout embryos. Immunolocalization of AP-2 proteins (␣, ␤, and ␥) to the normal developing eye revealed both unique and overlapping expression patterns, with AP-2␣ expressed in a number of the ocular tissues that exhibited defects in the mutants, including the developing lens where AP-2␣ is uniquely expressed. Together these findings demonstrate a requirement for AP-2␣ in early morphogenesis of the eye.

BMC Bioinformatics, 2009

Background In response to the frequently overwhelming output of high-throughput microarray experi... more Background In response to the frequently overwhelming output of high-throughput microarray experiments, we propose a methodology to facilitate interpretation of biological data in the context of existing knowledge. Through the probabilistic integration of explicit and implicit data sources a functional interaction network can be constructed. Each edge connecting two proteins is weighted by a confidence value capturing the strength and reliability of support for that interaction given the combined data sources. The resulting network is examined in conjunction with expression data to identify groups of genes with significant temporal or tissue specific patterns. In contrast to unstructured gene lists, these networks often represent coherent functional groupings. Results By linking from shared functional categorizations to primary biological resources we apply this method to craniofacial microarray data, generating biologically testable hypotheses and identifying candidate genes for cr...

Molecular and Cellular Biology, 2003

Pax6 is a paired box containing transcription factor that resides at the top of a genetic hierarc... more Pax6 is a paired box containing transcription factor that resides at the top of a genetic hierarchy controlling eye development. It continues to be expressed in tissues of the adult eye, but its role in this capacity is unclear. Pax6 is present in the adult corneal epithelium, and we showed that the amount of Pax6 is increased at the migrating front as the epithelium resurfaces the cornea after injury (J. M. Sivak, R. Mohan, W. B. Rinehart, P. X. Xu, R. L. Maas, and M. E. Fini, Dev. Biol. 222:41-54, 2000). We also showed that Pax6 controls activity of the transcriptional promoter for the matrix metalloproteinase, gelatinase B (gelB; MMP-9) in cell culture transfection studies. gelB expression is turned on at the migrating epithelial front in the cornea, and it coordinates and effects aspects of epithelial regeneration (R. Mohan, S. K. Chintala, J. C. Jung, W. V. Villar, F. McCabe, L. A. Russo, Y. Lee, B. E. McCarthy, K. R. Wollenberg, J. V. Jester, M. Wang, H. G. Welgus, J. M. Shipl...

Development (Cambridge, England), Jul 10, 2016

The FaceBase Consortium, funded by the National Institute of Dental and Craniofacial Research, Na... more The FaceBase Consortium, funded by the National Institute of Dental and Craniofacial Research, National Institutes of Health, is designed to accelerate understanding of craniofacial developmental biology by generating comprehensive data resources to empower the research community, exploring high-throughput technology, fostering new scientific collaborations among researchers and human/computer interactions, facilitating hypothesis-driven research, and translating science into improved health care to benefit patients. The resources generated by the FaceBase projects include a number of dynamic imaging modalities, genome-wide association studies, software tools for analyzing human facial abnormalities, detailed phenotyping, anatomical and molecular atlases, global and specific gene expression patterns, and transcriptional profiling over the course of embryonic and postnatal development in animal models and humans. The integrated data visualization tools, faceted search infrastructure,...

Developmental biology, Jul 30, 2015

The cranial base is a component of the neurocranium and has a central role in the structural inte... more The cranial base is a component of the neurocranium and has a central role in the structural integration of the face, brain and vertebral column. Consequently, alteration in the shape of the human cranial base has been intimately linked with primate evolution and defective development is associated with numerous human facial abnormalities. Here we describe a novel recessive mutant mouse strain that presented with a domed head and fully penetrant cleft secondary palate coupled with defects in the formation of the underlying cranial base. Mapping and non-complementation studies revealed a specific mutation in Memo1-a gene originally associated with cell migration. Expression analysis of Memo1 identified robust expression in the perichondrium and periosteum of the developing cranial base, but only modest expression in the palatal shelves. Fittingly, although the palatal shelves failed to elevate in Memo1 mutants, expression changes were modest within the shelves themselves. In contrast...