title: A novel RIPK4-IRF6 connection is required to prevent epithelial fusions characteristic for popliteal pterygium syndromes.
abstract: Receptor-interacting protein kinase 4 (RIPK4)-deficient mice have epidermal defects and fusion of all external orifices. These are similar to Bartsocas-Papas syndrome and popliteal pterygium syndrome (PPS) in humans, for which causative mutations have been documented in the RIPK4 and IRF6 (interferon regulatory factor 6) gene, respectively. Although genetically distinct, these syndromes share the anomalies of marked pterygia, syndactyly, clefting and hypoplastic genitalia. Despite the strong resemblance of these two syndromes, no molecular connection between the transcription factor IRF6 and the kinase RIPK4 was known and the mechanism underlying the phenotype was unclear. Here we describe that RIPK4 deficiency in mice causes epithelial fusions associated with abnormal periderm development and aberrant ectopic localization of E-cadherin on the apical membrane of the outer peridermal cell layers. In Xenopus, RIPK4 depletion causes the absence of ectodermal epiboly and concomitant gastrulation defects that phenocopy ectopic expression of dominant-negative IRF6. We found that IRF6 controls RIPK4 expression and that wild-type, but not kinase-dead, RIPK4 can complement the gastrulation defect in Xenopus caused by IRF6 malfunctioning. In contrast to the mouse, we observed only minor effects on cadherin membrane expression in Xenopus RIPK4 morphants. However, gastrulation defects were associated with a virtual absence of cortical actin in the ectodermal cells that face the blastocoel cavity and this was phenocopied in embryos expressing dominant-negative IRF6. A role for RIPK4 in actin cytoskeleton organization was also revealed in mouse epidermis and in human epithelial HaCaT cells. In conclusion, we showed that in mice RIPK4 is implicated in cortical actin organization and in E-cadherin localization or function, which can explain the characteristic epithelial fusions observed in PPSs. In addition, we provide a novel molecular link between IRF6 and RIPK4 that unifies the different PPSs to a common molecular pathway.
authors.affiliation: 1] Inflammation Research Center, Ghent 9052, Belgium [2] Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: P
authors.initials: P
authors.lastname: De Groote
authors.affiliation: Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: H T
authors.initials: HT
authors.lastname: Tran
authors.affiliation: Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: M
authors.initials: M
authors.lastname: Fransen
authors.affiliation: 1] Inflammation Research Center, Ghent 9052, Belgium [2] Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: G
authors.initials: G
authors.lastname: Tanghe
authors.affiliation: Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: C
authors.initials: C
authors.lastname: Urwyler
authors.affiliation: 1] Inflammation Research Center, Ghent 9052, Belgium [2] Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: B
authors.initials: B
authors.lastname: De Craene
authors.affiliation: 1] Inflammation Research Center, Ghent 9052, Belgium [2] Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: K
authors.initials: K
authors.lastname: Leurs
authors.affiliation: 1] Inflammation Research Center, Ghent 9052, Belgium [2] Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: B
authors.initials: B
authors.lastname: Gilbert
authors.affiliation: Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: G
authors.initials: G
authors.lastname: Van Imschoot
authors.affiliation: 1] Inflammation Research Center, Ghent 9052, Belgium [2] Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: R
authors.initials: R
authors.lastname: De Rycke
authors.affiliation: 1] Inflammation Research Center, Ghent 9052, Belgium [2] Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: C J
authors.initials: CJ
authors.lastname: Guérin
authors.affiliation: Amgen, Seattle, WA 1201, USA.
authors.forename: P
authors.initials: P
authors.lastname: Holland
authors.affiliation: 1] Inflammation Research Center, Ghent 9052, Belgium [2] Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: G
authors.initials: G
authors.lastname: Berx
authors.affiliation: 1] Inflammation Research Center, Ghent 9052, Belgium [2] Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: P
authors.initials: P
authors.lastname: Vandenabeele
authors.affiliation: 1] Inflammation Research Center, Ghent 9052, Belgium [2] Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: S
authors.initials: S
authors.lastname: Lippens
authors.affiliation: Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: K
authors.initials: K
authors.lastname: Vleminckx
authors.affiliation: 1] Inflammation Research Center, Ghent 9052, Belgium [2] Department of Biomedical Molecular Biology, Ghent University, Ghent 9052, Belgium.
authors.forename: W
authors.initials: W
authors.lastname: Declercq
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D002460:Cell Line; D002971:Cleft Lip / Q000235:genetics / Q000378:metabolism*; D002972:Cleft Palate / Q000235:genetics / Q000378:metabolism*; D005124:Eye Abnormalities / Q000235:genetics / Q000378:metabolism*; D005385:Fingers / Q000002:abnormalities*; D006801:Humans; D007150:Immunohistochemistry; D050835:Interferon Regulatory Factors / Q000235:genetics / Q000378:metabolism*; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism; D007719:Knee Joint / Q000002:abnormalities* / Q000378:metabolism; D016086:Lentivirus; D038061:Lower Extremity Deformities, Congenital / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D046529:Microscopy, Electron, Transmission; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D013576:Syndactyly / Q000235:genetics / Q000378:metabolism*; D014564:Urogenital Abnormalities / Q000235:genetics / Q000378:metabolism*
chemical_list: C528250:IRF6 protein, mouse; D050835:Interferon Regulatory Factors; D017346:Protein Serine-Threonine Kinases; C430884:Ripk4 protein, mouse