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Trevor Williams - One of the best experts on this subject based on the ideXlab platform.
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Anomalous incisor morphology indicates tissue-specific roles for TFAP2A and Tfap2b in tooth development.
Developmental biology, 2021Co-Authors: Emily D. Woodruff, Eric Van Otterloo, Galaxy C. Gutierrez, Trevor Williams, Martin J. CohnAbstract:Mice possess two types of teeth that differ in their cusp patterns; incisors have one cusp and molars have multiple cusps. The patterning of these two types of teeth relies on fine-tuning of the reciprocal molecular signaling between dental epithelial and mesenchymal tissues during embryonic development. The AP-2 transcription factors, particularly TFAP2A and Tfap2b, are essential components of such epithelial-mesenchymal signaling interactions that coordinate craniofacial development in mice and other vertebrates, but little is known about their roles in the regulation of tooth development and shape. Here we demonstrate that incisors and molars differ in their temporal and spatial expression of TFAP2A and Tfap2b. At the bud stage, TFAP2A is expressed in both the epithelium and mesenchyme of the incisors and molars, but Tfap2b expression is restricted to the molar mesenchyme, only later appearing in the incisor epithelium. Tissue-specific deletions show that loss of the epithelial domain of TFAP2A and Tfap2b affects the number and spatial arrangement of the incisors, notably resulting in duplicated lower incisors. In contrast, deletion of these two genes in the mesenchymal domain has little effect on tooth development. Collectively these results implicate epithelial expression of TFAP2A and Tfap2b in regulating the extent of the dental lamina associated with patterning the incisors and suggest that these genes contribute to morphological differences between anterior (incisor) and posterior (molar) teeth within the mammalian dentition.
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Anomalous incisor morphology indicates tissue-specific roles for TFAP2A and Tfap2b in tooth development
2020Co-Authors: Emily D. Woodruff, Eric Van Otterloo, Galaxy C. Gutierrez, Trevor Williams, Martin J. CohnAbstract:Mice possess two types of teeth that differ in their cusp patterns; incisors have one cusp and molars have multiple cusps. The patterning of these two types of teeth relies on fine-tuning of the reciprocal molecular signaling between dental epithelial and mesenchymal tissues during embryonic development. Here we show that the incisors are populated only at early time points by the neural crest, whereas the molars continue to receive contributions at later stages, revealing a temporal difference that could alter epithelial-mesenchymal signaling dynamics between these two types of teeth. The AP-2 transcription factors, particularly TFAP2A and Tfap2b, are essential components of such epithelial-mesenchymal signaling interactions that coordinate craniofacial development in mice and other mammals, but little is known about their roles in the regulation of tooth development and shape. We demonstrate that incisors and molars differ in their temporal and spatial expression of TFAP2A and Tfap2b; in particular, at the bud stage, TFAP2A is expressed in both the epithelium and mesenchyme of the incisors and molars but expression of Tfap2b is restricted to the mesenchyme of the molars. Tissue-specific deletions show that loss of the epithelial domain of TFAP2A and Tfap2b affects the number and spatial arrangement of the incisors, notably resulting in duplicated lower incisors. In contrast, deletion of these two genes in the mesenchymal domain has little effect on tooth development. Collectively these results implicate epithelial expression of TFAP2A and Tfap2b in dorsal-ventral patterning of the incisors and suggest that these genes contribute to morphological differences between anterior (incisor) and posterior (molar) teeth within the mammalian dentition. HighlightsO_LILate-migrating cranial neural crest cells contribute extensively to the developing molar tooth germs but minimally to the incisors. C_LIO_LIDuring tooth development, transcription factors TFAP2A and Tfap2b are expressed in spatially and temporally dynamic patterns and differ between incisor and molar tooth germs. C_LIO_LIEpithelial expression of TFAP2A and Tfap2b is necessary for incisor development, but mesenchymal expression of these genes is not required. C_LI
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analysis of TFAP2A mutations in branchio oculo facial syndrome indicates functional complexity within the ap 2α dna binding domain
Human Molecular Genetics, 2013Co-Authors: Ryan M Sheridan, Trevor WilliamsAbstract:Multiple lines of evidence indicate that the AP-2 transcription factor family has an important regulatory function in human craniofacial development. Notably, mutations in TFAP2A, the gene encoding AP-2α, have been identified in patients with Branchio-Oculo-Facial Syndrome (BOFS). BOFS is an autosomal-dominant trait that commonly presents with facial clefting, eye defects and branchial skin anomalies. Examination of multiple cases has suggested either simple haploinsufficiency or more complex genetic causes for BOFS, especially as the clinical manifestations are variable, with no clear genotype-phenotype correlation. Mutations occur throughout TFAP2A, but mostly within conserved sequences within the DNA contact domain of AP-2α. However, the consequences of the various mutations for AP-2α protein function have not been evaluated. Therefore, it remains unclear if all BOFS mutations result in similar changes to the AP-2α protein or if they each produce specific alterations that underlie the spectrum of phenotypes. Here, we have investigated the molecular consequences of the mutations that localize to the DNA-binding region. We show that although individual mutations have different effects on DNA binding, they all demonstrate significantly reduced transcriptional activities. Moreover, all mutant derivatives have an altered nuclear:cytoplasmic distribution compared with the predominantly nuclear localization of wild-type AP-2α and several can exert a dominant-negative activity on the wild-type AP-2α protein. Overall, our data suggest that the individual TFAP2A BOFS mutations can generate null, hypomorphic or antimorphic alleles and that these differences in activity, combined with a role for AP-2α in epigenetic events, may influence the resultant pathology and the phenotypic variability.
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identification and analysis of a conserved tcfap2a intronic enhancer element required for expression in facial and limb bud mesenchyme
Molecular and Cellular Biology, 2008Co-Authors: Weiguo Feng, Jian Huang, Jian Zhang, Trevor WilliamsAbstract: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 role for this enhancer resides within the limb bud, and it serves to maintain a level of Tcfap2a expression that limits the size of the hand plate and the associated number of digit primordia. The potential role of this cis-acting sequence in modeling the size and shape of the face and limbs during evolution is discussed.
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wnt1 cre mediated deletion of ap 2alpha causes multiple neural crest related defects
Developmental Biology, 2004Co-Authors: Stephanie Brewer, Trevor Williams, Weiguo Feng, Jian Huang, Shelley SullivanAbstract: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.
Thomas F Schilling - One of the best experts on this subject based on the ideXlab platform.
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ap2 dependent signals from the ectoderm regulate craniofacial development in the zebrafish embryo
Development, 2005Co-Authors: Rob Knight, Yashar Javidan, Tailin Zhang, S J Nelson, Thomas F SchillingAbstract:AP2 transcription factors regulate many aspects of embryonic development. Studies of AP2a (TFAP2A) function in mice and zebrafish have demonstrated a role in patterning mesenchymal cells of neural crest origin that form the craniofacial skeleton, while the mammalian Tfap2b is required in both the facial skeleton and kidney. Here, we show essential functions for zebrafish TFAP2A and tfap2b in development of the facial ectoderm, and for signals from this epithelium that induce skeletogenesis in neural crest cells (NCCs). Zebrafish embryos deficient for both TFAP2A and tfap2b show defects in epidermal cell survival and lack NCC-derived cartilages. We show that cartilage defects arise after NCC migration during skeletal differentiation, and that they can be rescued by transplantation of wild-type ectoderm. We propose a model in which AP2 proteins play two distinct roles in cranial NCCs: an early cell-autonomous function in cell specification and survival, and a later non-autonomous function regulating ectodermal signals that induce skeletogenesis.
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skeletal and pigment cell defects in the lockjaw mutant reveal multiple roles for zebrafish TFAP2A in neural crest development
Developmental Dynamics, 2004Co-Authors: Rob Knight, Yashar Javidan, Tailin Zhang, Sarah Nelson, Thomas F SchillingAbstract:Members of the AP-2 transcription factor family have critical roles in many aspects of embryonic development. The zebrafish TFAP2A mutant lockjaw (low) displays defects in skeletal and pigment cell derivatives of the neural crest. Here we show essential roles for TFAP2A in subsets of embryonic cartilages and pigment cells. Defects in cartilage of the hyoid arch in low correlate with a loss of Hox group 2 gene expression and are suggestive of a transformation to a mandibular fate. In contrast, loss of joints in the mandibular arch and defects in certain types of pigment cells suggest a requirement for TFAP2A independent of Hox regulation. Early melanophores do not develop in low mutants, and we propose that this results in part from a loss of kit function, leading to defects in migration, as well as kit-independent defects in melanophore specification. Iridophores are also reduced in low, in contrast to xanthophores, revealing a role for TFAP2A in the development of pigment subpopulations. We propose a model of TFAP2A function in the neural crest in which there are independent functions for TFAP2A in specification of subpopulations of pigment cells and segmental patterning of the pharyngeal skeleton through the regulation of Hox genes. Developmental Dynamics 229:87–98, 2004. © 2003 Wiley-Liss, Inc.
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lockjaw encodes a zebrafish TFAP2A required for early neural crest development
Development, 2003Co-Authors: Rob Knight, Yashar Javidan, Sarah Nelson, Sreelaja Nair, Ali Afshar, Robert Geisler, Gerd Joerg Rauch, Thomas F SchillingAbstract:The neural crest is a uniquely vertebrate cell type that gives rise to much of the craniofacial skeleton, pigment cells and peripheral nervous system, yet its specification and diversification during embryogenesis are poorly understood. Zebrafish homozygous for the lockjaw (low) mutation show defects in all of these derivatives and we show that low (allelic with montblanc) encodes a zebrafish TFAP2A, one of a small family of transcription factors implicated in epidermal and neural crest development. A point mutation in low truncates the DNA binding and dimerization domains of TFAP2A, causing a loss of function. Consistent with this, injection of antisense morpholino oligonucleotides directed against splice sites in TFAP2A into wild-type embryos produces a phenotype identical to low. Analysis of early ectodermal markers revealed that neural crest specification and migration are disrupted in low mutant embryos. TUNEL labeling of dying cells in mutants revealed a transient period of apoptosis in crest cells prior to and during their migration. In the cranial neural crest, gene expression in the mandibular arch is unaffected in low mutants, in contrast to the hyoid arch, which shows severe reductions in dlx2 and hoxa2 expression. Mosaic analysis, using cell transplantation, demonstrated that neural crest defects in low are cell autonomous and secondarily cause disruptions in surrounding mesoderm. These studies demonstrate that low is required for early steps in neural crest development and suggest that TFAP2A is essential for the survival of a subset of neural crest derivatives.
Rob Knight - One of the best experts on this subject based on the ideXlab platform.
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ap2 dependent signals from the ectoderm regulate craniofacial development in the zebrafish embryo
Development, 2005Co-Authors: Rob Knight, Yashar Javidan, Tailin Zhang, S J Nelson, Thomas F SchillingAbstract:AP2 transcription factors regulate many aspects of embryonic development. Studies of AP2a (TFAP2A) function in mice and zebrafish have demonstrated a role in patterning mesenchymal cells of neural crest origin that form the craniofacial skeleton, while the mammalian Tfap2b is required in both the facial skeleton and kidney. Here, we show essential functions for zebrafish TFAP2A and tfap2b in development of the facial ectoderm, and for signals from this epithelium that induce skeletogenesis in neural crest cells (NCCs). Zebrafish embryos deficient for both TFAP2A and tfap2b show defects in epidermal cell survival and lack NCC-derived cartilages. We show that cartilage defects arise after NCC migration during skeletal differentiation, and that they can be rescued by transplantation of wild-type ectoderm. We propose a model in which AP2 proteins play two distinct roles in cranial NCCs: an early cell-autonomous function in cell specification and survival, and a later non-autonomous function regulating ectodermal signals that induce skeletogenesis.
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skeletal and pigment cell defects in the lockjaw mutant reveal multiple roles for zebrafish TFAP2A in neural crest development
Developmental Dynamics, 2004Co-Authors: Rob Knight, Yashar Javidan, Tailin Zhang, Sarah Nelson, Thomas F SchillingAbstract:Members of the AP-2 transcription factor family have critical roles in many aspects of embryonic development. The zebrafish TFAP2A mutant lockjaw (low) displays defects in skeletal and pigment cell derivatives of the neural crest. Here we show essential roles for TFAP2A in subsets of embryonic cartilages and pigment cells. Defects in cartilage of the hyoid arch in low correlate with a loss of Hox group 2 gene expression and are suggestive of a transformation to a mandibular fate. In contrast, loss of joints in the mandibular arch and defects in certain types of pigment cells suggest a requirement for TFAP2A independent of Hox regulation. Early melanophores do not develop in low mutants, and we propose that this results in part from a loss of kit function, leading to defects in migration, as well as kit-independent defects in melanophore specification. Iridophores are also reduced in low, in contrast to xanthophores, revealing a role for TFAP2A in the development of pigment subpopulations. We propose a model of TFAP2A function in the neural crest in which there are independent functions for TFAP2A in specification of subpopulations of pigment cells and segmental patterning of the pharyngeal skeleton through the regulation of Hox genes. Developmental Dynamics 229:87–98, 2004. © 2003 Wiley-Liss, Inc.
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lockjaw encodes a zebrafish TFAP2A required for early neural crest development
Development, 2003Co-Authors: Rob Knight, Yashar Javidan, Sarah Nelson, Sreelaja Nair, Ali Afshar, Robert Geisler, Gerd Joerg Rauch, Thomas F SchillingAbstract:The neural crest is a uniquely vertebrate cell type that gives rise to much of the craniofacial skeleton, pigment cells and peripheral nervous system, yet its specification and diversification during embryogenesis are poorly understood. Zebrafish homozygous for the lockjaw (low) mutation show defects in all of these derivatives and we show that low (allelic with montblanc) encodes a zebrafish TFAP2A, one of a small family of transcription factors implicated in epidermal and neural crest development. A point mutation in low truncates the DNA binding and dimerization domains of TFAP2A, causing a loss of function. Consistent with this, injection of antisense morpholino oligonucleotides directed against splice sites in TFAP2A into wild-type embryos produces a phenotype identical to low. Analysis of early ectodermal markers revealed that neural crest specification and migration are disrupted in low mutant embryos. TUNEL labeling of dying cells in mutants revealed a transient period of apoptosis in crest cells prior to and during their migration. In the cranial neural crest, gene expression in the mandibular arch is unaffected in low mutants, in contrast to the hyoid arch, which shows severe reductions in dlx2 and hoxa2 expression. Mosaic analysis, using cell transplantation, demonstrated that neural crest defects in low are cell autonomous and secondarily cause disruptions in surrounding mesoderm. These studies demonstrate that low is required for early steps in neural crest development and suggest that TFAP2A is essential for the survival of a subset of neural crest derivatives.
Helen C Hurst - One of the best experts on this subject based on the ideXlab platform.
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alternative TFAP2A isoforms have distinct activities in breast cancer
Breast Cancer Research, 2011Co-Authors: Chiara Berlato, Angelo G Scibetta, Kayi V Chan, Monica Canosa, Anna M Price, Helen C HurstAbstract:AP-2α is a transcription factor implicated in the regulation of differentiation and proliferation in certain tissues, including the mammary gland. In breast tumours, continued expression of AP-2α has been correlated with a better prognosis, but this is hard to reconcile with a reported role in the upregulation of the ERBB2 oncogene. The existence of TFAP2A isoforms, deriving from alternative first exons and differing in their N-terminal sequence, has been described in some mammals, but their relative abundance and activity has not been investigated in the human breast. Expression levels of four TFAP2A isoforms were assayed at the level of RNA and protein (via the generation of isoform-specific antibodies) in a panel of breast tumour cell lines and in tissue from normal breast and primary tumour samples. Expression constructs for each isoform were used in reporter assays with synthetic and natural promoters (cyclin D3 and ERBB2) to compare the activation and repression activity of the isoforms. We demonstrate that the two isoforms AP-2α 1b and AP-2α 1c, in addition to the originally cloned, AP-2α 1a, are conserved throughout evolution in vertebrates. Moreover, we show that isoform 1c in particular is expressed at levels at least on a par with the 1a isoform in breast epithelial lines and tissues and may be more highly expressed in tamoxifen resistant tumours. The isoforms share a similar transactivation mechanism involving the recruitment of the adaptors CITED2 or 4 and the transactivators p300 or CBP. However, isoform 1b and 1c are stronger transactivators of the ERBB2 promoter than isoform 1a. In contrast, AP-2α 1a is the only isoform able to act as a repressor, an activity that requires an intact sumoylation motif present within the N-terminus of the protein, and which the other two isoforms lack. Our findings suggest that TFAP2A isoforms may be differentially regulated during breast tumourigenesis and this, coupled with differences in their transcriptional activity, may impact on tumour responses to tamoxifen therapy. These data also have implications for the interpretation of tumour studies that seek to correlate outcomes with TFAP2A expression level.
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dual association by TFAP2A during activation of the p21cip cdkn1a promoter
Cell Cycle, 2010Co-Authors: Angelo G Scibetta, Pingpui Wong, Kayi V Chan, Monica Canosa, Helen C HurstAbstract:The cyclin-dependent kinase inhibitor p21cip/CDKN1A is induced to promote growth arrest in response to a variety of stimuli in normal cells and loss of correct regulation of this gene is frequently observed in cancer. In particular, the upregulation of CDKN1A by p53 is considered to be a central mechanism of tumor suppression. Other transcription factors with tumor suppressor activity can also regulate CDKN1A, including the developmentally regulated factor, TFAP2A. Here we identify a novel AP-2 binding site within the proximal promoter of the CDKN1A gene and show this is required for optimal, p53-independent expression of p21cip/CDKN1A. We further describe a non-tumorgenic breast epithelial cell line model to study the role of endogenous TFAP2A and p53 in the control of drug-induced p21cip expression using ChIP. Maximal expression of CDKN1A requires TFAP2A which binds to two regions of the promoter: the proximal region where the AP-2 site lies and upstream near the major p53 binding site. The pattern of binding alters with time post-induction, with the proximal, p53-independent site becoming more important at later stages of p21cip induction. This pattern of promoter interaction by TFAP2A is distinct from that seen for the TFAP2C family member which represses CDKN1A expression.
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human creb binding protein p300 interacting transactivator with ed rich tail cited 4 a new member of the cited family functions as a co activator for transcription factor ap 2
Journal of Biological Chemistry, 2002Co-Authors: Jose Braganca, Tracey Swingler, Fatima I R Marques, Tania A Jones, Jyrki J Eloranta, Helen C Hurst, Toshihiro Shioda, Shoumo BhattacharyaAbstract:Abstract Members of the CREB-binding protein/p300-interacting transactivator with ED-rich tail (CITED) family bind CREB-binding protein and p300 with high affinity and regulate gene transcription. Gene knockout studies indicate that CITED2 is required for neural crest and neural tube development and that it functions as a co-activator for transcription factor AP-2 (TFAP2). Here we describe human CITED4, a new member of this family, which is encoded by a single exon mapping to chromosome 1p34–1p35. CITED4 and p300/CREB-binding protein are present in endogenous naturally occurring complexes, indicating that they interact physiologically. The interaction occurs between the cysteine-histidine-rich domain 1 of p300 and the carboxyl terminus of CITED4. In keeping with this, CITED4 functions as a transactivator when artificially targeted to a promoter element. CITED4 physically interacts with all TFAP2 isoforms in vitro and strongly co-activates all TFAP2 isoforms in Hep3B cells. Co-activation of TFAP2 requires amino-terminal and carboxyl-terminal residues of CITED4. In HepG2 cells, CITED4 is significantly weaker than CITED2 for TFAP2C co-activation. These results suggest that CITED4 may function as a co-activator for TFAP2. They also suggest the existence of cell type- and TFAP2 isoform-specific co-activation by CITED2 and CITED4, which may result in differential modulation of TFAP2 function.
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cardiac malformations adrenal agenesis neural crest defects and exencephaly in mice lacking cited2 a new tfap2 co activator
Nature Genetics, 2001Co-Authors: Simon D Bamforth, Jose Braganca, Fatima I R Marques, Jyrki J Eloranta, Helen C Hurst, Kamil R Kranc, Hend Farza, Deborah J Henderson, Jennifer N Murdoch, Shoumo BhattacharyaAbstract:The protein EP300 and its paralog CREBBP (CREB-binding protein) are ubiquitously expressed transcriptional co-activators and histone acetyl transferases. The gene EP300 is essential for normal cardiac and neural development, whereas CREBBP is essential for neurulation, hematopoietic differentiation, angiogenesis and skeletal and cardiac development. Mutations in CREBBP cause Rubinstein-Taybi syndrome, which is characterized by mental retardation, skeletal abnormalities and congenital cardiac defects. The CBP/p300-interacting transactivator with ED-rich tail 2 (CITED2) binds EP300 and CREBBP with high affinity and regulates gene transcription. Here we show that Cited2-/- embryos die with cardiac malformations, adrenal agenesis, abnormal cranial ganglia and exencephaly. The cardiac defects include atrial and ventricular septal defects, overriding aorta, double-outlet right ventricle, persistent truncus arteriosus and right-sided aortic arches. We find increased apoptosis in the midbrain region and a marked reduction in ErbB3-expressing neural crest cells in mid-embryogenesis. We show that CITED2 interacts with and co-activates all isoforms of transcription factor AP-2 (TFAP2). Transactivation by TFAP2 isoforms is defective in Cited2-/- embryonic fibroblasts and is rescued by ectopically expressed CITED2. As certain Tfap2 isoforms are essential in neural crest, neural tube and cardiac development, we propose that abnormal embryogenesis in mice lacking Cited2 results, at least in part, from its role as a Tfap2 co-activator.
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chromosomal mapping of the human and mouse homologues of two new members of the ap 2 family of transcription factors
Genomics, 1996Co-Authors: Jill Williamson, Trevor Williams, Julia M Bosher, Ann Skinner, Denise Sheer, Helen C HurstAbstract:The AP-2 transcription factor has been shown to play an important role in the development of tissues of ectodermal origin and has also been implicated in mammary oncogenesis. It has recently been found that AP-2 is encoded by a family of related genes, AP-2alpha, AP-2beta, and AP-2gamma. As a further step in understanding the role each of these genes has in development, we have used fluorescence in situ hybridization to map the chromosomal locations of the mouse and human homologues of the newly isolated AP-2beta and AP-2gamma genes. Tcfap2b and Tcfap2c map to mouse chromosomes 1A2-4 and 2H3-4, respectively, while TFAP2B and TFAP2C map to human chromosomes 6p12 and 20q13.2, the latter being a region that is frequently amplified in breast carcinoma.
Ela W Knapik - One of the best experts on this subject based on the ideXlab platform.
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TFAP2A and Foxd3 regulate early steps in the development of the neural crest progenitor population
Developmental biology, 2011Co-Authors: Wen-der Wang, David B. Melville, Mercedes Montero-balaguer, Antonis K. Hatzopoulos, Ela W KnapikAbstract:The neural crest is a stem cell-like population exclusive to vertebrates that gives rise to many different cell types including chondrocytes, neurons and melanocytes. Arising from the neural plate border at the intersection of Wnt and Bmp signaling pathways, the complexity of neural crest gene regulatory networks has made the earliest steps of induction difficult to elucidate. Here, we report that TFAP2A and foxd3 participate in neural crest induction and are necessary and sufficient for this process to proceed. Double mutant TFAP2A (mont blanc, mob) and foxd3 (mother superior, mos) mob;mos zebrafish embryos completely lack all neural crest-derived tissues. Moreover, TFAP2A and foxd3 are expressed during gastrulation prior to neural crest induction in distinct, complementary, domains; TFAP2A is expressed in the ventral non-neural ectoderm and foxd3 in the dorsal mesendoderm and ectoderm. We further show that Bmp signaling is expanded in mob;mos embryos while expression of dkk1, a Wnt signaling inhibitor, is increased and canonical Wnt targets are suppressed. These changes in Bmp and Wnt signaling result in specific perturbations of neural crest induction rather than general defects in neural plate border or dorso-ventral patterning. foxd3 overexpression, on the other hand, enhances the ability of TFAP2A to ectopically induce neural crest around the neural plate, overriding the normal neural plate border limit of the early neural crest territory. Although loss of either TFAP2A or Foxd3 alters Bmp and Wnt signaling patterns, only their combined inactivation sufficiently alters these signaling gradients to abort neural crest induction. Collectively, our results indicate that TFAP2A and foxd3, in addition to their respective roles in the differentiation of neural crest derivatives, also jointly maintain the balance of Bmp and Wnt signaling in order to delineate the neural crest induction domain.
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neural crest survival and differentiation in zebrafish depends on mont blanc TFAP2A gene function
Development, 2004Co-Authors: Alejandro Barrallogimeno, Jochen Holzschuh, Wolfgang Driever, Ela W KnapikAbstract:Neural crest progenitor cells are the main contributors to craniofacial cartilage and connective tissue of the vertebrate head. These progenitor cells also give rise to the pigment, neuronal and glial cell lineages. To study the molecular basis of neural crest differentiation, we have cloned the gene disrupted in the mont blanc (mob(m610)) mutation, which affects all neural crest derivatives. Using a positional candidate cloning approach we identified an A to G transition within the 3' splice site of the sixth intron of the TFAP2A gene that abolishes the last exon encoding the crucial protein dimerization and DNA-binding domains. Neural crest induction and specification are not hindered in mob(m610) mutant embryos, as revealed by normal expression of early neural crest specific genes such as snail2, foxd3 and sox10. In addition, the initial stages of cranial neural crest migration appear undisturbed, while at a later phase the craniofacial primordia in pharyngeal arches two to seven fail to express their typical set of genes (sox9a, wnt5a, dlx2, hoxa2/b2). In mob(m610) mutant embryos, the cell number of neuronal and glial derivatives of neural crest is greatly reduced, suggesting that TFAP2A is required for their normal development. By tracing the fate of neural crest progenitors in live mont blanc (mob(m610)) embryos, we found that at 24 hpf neural crest cells migrate normally in the first pharyngeal arch while the preotic and postotic neural crest cells begin migration but fail to descend to the pharyngeal region of the head. TUNEL assay and Acridine Orange staining revealed that in the absence of TFAP2A a subset of neural crest cells are unable to undergo terminal differentiation and die by apoptosis. Furthermore, surviving neural crest cells in TFAP2A/mob(m610) mutant embryos proliferate normally and later differentiate to individual derivatives. Our results indicate that TFAP2A is essential to turn on the normal developmental program in arches 2-7 and in trunk neural crest. Thus, TFAP2A does not appear to be involved in early specification and cell proliferation of neural crest, but it is a key regulator of an early differentiation phase and is required for cell survival in neural crest derived cell lineages.
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noradrenergic neurons in the zebrafish hindbrain are induced by retinoic acid and require TFAP2A for expression of the neurotransmitter phenotype
Development, 2003Co-Authors: Jochen Holzschuh, Alejandro Barrallogimeno, Annekathrin Ettl, Katrin Durr, Ela W Knapik, Wolfgang DrieverAbstract:TFAP2A is a transcriptional activator expressed in many different cell types, including neurons, neural crest derivatives and epidermis. We show that mutations at the zebrafish locus previously called mont blanc (mob) or lockjaw (low) encode TFAP2A. The mutant phenotype reveals that TFAP2A is essential for the development of hindbrain noradrenergic (NA) neurons of the locus coeruleus, medulla and area postrema, as well as for sympathetic NA neurons, epibranchial placode derived visceral sensory ganglia, and craniofacial and trunk crest derivatives. We focus our analysis on the role of TFAP2A NA differentiation in the CNS. In the locus coeruleus, Phox2a and TFAP2A are co-expressed and are both required for NA development. By contrast, in the medulla Phox2a and TFAP2A are expressed in adjacent overlapping domains, but only TFAP2A activity is required for NA differentiation, as NA neurons develop normally in soulless/phox2a mutant medulla. phox2a and TFAP2A do not appear to affect each others expression. Our studies show that two distinct inductive mechanisms control NA development in the zebrafish hindbrain. For the posterior hindbrain, we identify retinoic acid as an important signal to induce NA differentiation in the medulla oblongata and area postrema, where it expands the TFAP2A expression domain and thus acts upstream of TFAP2A. By contrast, previous work revealed Fgf8 to be involved in specification of NA neurons in the locus coeruleus. Thus, although the inductive signals may be distinct, hindbrain NA neurons of the locus coeruleus and the posterior groups both require TFAP2A to establish their noradrenergic identity.