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The fusion of digits or toes, syndactyly, can be part of complex syndromes, including van der Woude syndrome. A subset of van der Woude cases is caused by dominant-negative mutations in the epithelial transcription factor Grainyhead like-3 (GRHL3), and Grhl3-/-mice have soft-tissue syndactyly. Although impaired interdigital cell death of mesenchymal cells causes syndactyly in multiple genetic mutants, Grhl3-/- embryos had normal interdigital cell death, suggesting alternative mechanisms for syndactyly. We found that in digit separation, the overlying epidermis forms a migrating interdigital epithelial tongue (IET) when the epithelium invaginates to separate the digits. Normally, the non-adhesive surface periderm allows the IET to bifurcate as the digits separate. In contrast, in Grhl3-/- embryos, the IET moves normally between the digits but fails to bifurcate because of abnormal adhesion of the periderm. Our study identifies epidermal developmental processes required for digit separation.

The fusion of digits or toes, syndactyly, can be part of complex syndromes, including van der Woude syndrome. A subset of van der Woude cases is caused by dominant-negative mutations in the epithelial transcription factor Grainyhead like-3 (GRHL3), and Grhl3-/-mice have soft-tissue syndactyly. Although impaired interdigital cell death of mesenchymal cells causes syndactyly in multiple genetic mutants, Grhl3-/- embryos had normal interdigital cell death, suggesting alternative mechanisms for syndactyly. We found that in digit separation, the overlying epidermis forms a migrating interdigital epithelial tongue (IET) when the epithelium invaginates to separate the digits. Normally, the non-adhesive surface periderm allows the IET to bifurcate as the digits separate. In contrast, in Grhl3-/- embryos, the IET moves normally between the digits but fails to bifurcate because of abnormal adhesion of the periderm. Our study identifies epidermal developmental processes required for digit separation.

The fusion of digits or toes, syndactyly, can be part of complex syndromes, including van der Woude syndrome. A subset of van der Woude cases is caused by dominant-negative mutations in the epithelial transcription factor Grainyhead like-3 (GRHL3), and Grhl3-/-mice have soft-tissue syndactyly. Although impaired interdigital cell death of mesenchymal cells causes syndactyly in multiple genetic mutants, Grhl3-/- embryos had normal interdigital cell death, suggesting alternative mechanisms for syndactyly. We found that in digit separation, the overlying epidermis forms a migrating interdigital epithelial tongue (IET) when the epithelium invaginates to separate the digits. Normally, the non-adhesive surface periderm allows the IET to bifurcate as the digits separate. In contrast, in Grhl3-/- embryos, the IET moves normally between the digits but fails to bifurcate because of abnormal adhesion of the periderm. Our study identifies epidermal developmental processes required for digit separation.

Rare mutations in IRF6 and GRHL3 cause Van der Woude syndrome, an autosomal dominant orofacial clefting disorder. Common variants in IRF6 and GRHL3 also contribute risk for isolated orofacial clefting. Similarly, variants within genes that encode receptor tyrosine kinase (RTK) signaling components, including members of the FGF pathway, EPHA3 and SPRY2, also contribute risk for isolated orofacial clefting. In the mouse, loss of Irf6 or perturbation of Fgf signaling leads to abnormal oral epithelial adhesions and cleft palate. Oral adhesions can result from a disruption of periderm formation. Here, we find that IRF6 and SPRY4 signaling interact in periderm function. We crossed Irf6 heterozygous ( Irf6+/-) mice with transgenic mice that express Spry4 in the basal epithelial layer ( TgKRT14::Spry4). While embryos with either of these mutations can have abnormal oral adhesions, using a new quantitative assay, we observed a nonadditive effect of abnormal oral epithelial adhesions in the most severely affected double mutant embryos ( Irf6+/-;TgKRT14::Spry4). At the molecular level, the sites of abnormal oral adhesions maintained periderm-like cells that express keratin 6, but we observed abnormal expression of GRHL3. Together, these data suggest that Irf6 and RTK signaling interact in regulating periderm differentiation and function, as well as provide a rationale to screen for epistatic interactions between variants in IRF6 and RTK signaling pathway genes in human orofacial clefting populations.

Introduction: Cleft lip with or without cleft palate (CL/P) is one of the most common birth defects in the world. Prevalence varies between populations, with an average of 1/700. CL/P has a major clinical impact, requiring surgical, dental, orthodontic, speech, hearing and psychological management throughout childhood. The aetiology of CL/P is mostly unknown, and it is thought that both genetic and environmental factors play a role. Several causative genes for inherited syndromic forms of CL/P have been identified, and some recent studies have shown that these genes also contribute to the occurrence of isolated forms. Van der Woude syndrome (VWS) is one of the best models for non-syndromic CLP. It is an autosomal dominant disorder characterised by the presence of pits on the lower lip in addition to CL/P. Pits are the only feature distinguishing VWS from isolated clefts. Interestingly, in numerous VWS patients, the lip pits are very small and not readily diagnosed, thus mimicking isolated CL/P. Mutations in the IRF6 gene were shown to be the major genetic cause of VWS.1 Results: We performed direct sequence analysis of IRF6 on samples from a large European cohort and identified mutations in 27 (80%) families. This shows that IRF6 is the major causative gene of VWS in Europe also. Moreover, it is the gene to study when a seemingly isolated CL/P patient has minor signs, such as lip pits, since the identification of a mutation in IRF6 is associated with an increase in the risk of having a child with CL/P from 4-6%, the risk of transmission of an isolated cleft, to 50%, the risk of transmission of a dominant Mendelian disorder like VWS. Moreover, we studied the association of isolated CL/P with the IRF6 locus using two variants in a set of 195 patients from Belgium. As in an American study, a clear association was observed. This suggests that IRF6 also contributes to the occurrence of sporadic, isolated CL/P, even if no mutation in the gene can be identified in such pat, SCOPUS: cp.j, info:eu-repo/semantics/published

Introduction: Cleft lip with or without cleft palate (CL/P) is one of the most common birth defects in the world. Prevalence varies between populations, with an average of 1/700. CL/P has a major clinical impact, requiring surgical, dental, orthodontic, speech, hearing and psychological management throughout childhood. The aetiology of CL/P is mostly unknown, and it is thought that both genetic and environmental factors play a role. Several causative genes for inherited syndromic forms of CL/P have been identified, and some recent studies have shown that these genes also contribute to the occurrence of isolated forms. Van der Woude syndrome (VWS) is one of the best models for non-syndromic CLP. It is an autosomal dominant disorder characterised by the presence of pits on the lower lip in addition to CL/P. Pits are the only feature distinguishing VWS from isolated clefts. Interestingly, in numerous VWS patients, the lip pits are very small and not readily diagnosed, thus mimicking isolated CL/P. Mutations in the IRF6 gene were shown to be the major genetic cause of VWS.1 Results: We performed direct sequence analysis of IRF6 on samples from a large European cohort and identified mutations in 27 (80%) families. This shows that IRF6 is the major causative gene of VWS in Europe also. Moreover, it is the gene to study when a seemingly isolated CL/P patient has minor signs, such as lip pits, since the identification of a mutation in IRF6 is associated with an increase in the risk of having a child with CL/P from 4-6%, the risk of transmission of an isolated cleft, to 50%, the risk of transmission of a dominant Mendelian disorder like VWS. Moreover, we studied the association of isolated CL/P with the IRF6 locus using two variants in a set of 195 patients from Belgium. As in an American study, a clear association was observed. This suggests that IRF6 also contributes to the occurrence of sporadic, isolated CL/P, even if no mutation in the gene can be identified in such pat, SCOPUS: cp.j, info:eu-repo/semantics/published