Distinct requirements for wnt9a and irf6 in extension and integration mechanisms during zebrafish palate morphogenesis

Abstract

SUMMARYDevelopment of the palate in vertebrates involves cranial neural crest migration, convergence of facial prominences and extension of the cartilaginous framework. Dysregulation of palatogenesis results in orofacial clefts, which represent the most common structural birth defects. Detailed analysis of zebrafish palatogenesis revealed distinct mechanisms of palatal morphogenesis: extension, proliferation and integration. We show that wnt9a is required for palatal extension, wherein the chondrocytes form a proliferative front, undergo morphological change and intercalate to form the ethmoid plate. Meanwhile, irf6 is required specifically for integration of facial prominences along a V-shaped seam. This work presents a mechanistic analysis of palate morphogenesis in a clinically relevant context.

Cichlid fishes as a model to understand normal and clinical craniofacial variation

“…For example, mammalian and fish palates have distinct morphologies and are comprised of non-homologous elements (Dougherty, et al 2013; Murray and Schutte 2004; Swartz, et al 2011). Despite this, their development requires the action of homologous cell- and tissue-level processes including migration of cranial neural crest cells, as well as the coordinated outgrowth and fusion of multiple processes and structures (Dougherty, et al 2013; Murray and Schutte 2004). Further, homologous genes regulate these cellular mechanisms.…”

“…Further, homologous genes regulate these cellular mechanisms. For instance, loss of irf6 or the microRNA Mirn140 and Pdgf signaling network results in conspicuous orofacial clefting in both humans and zebrafish (Dougherty, et al 2013; Eberhart, et al 2008; Kondo, et al 2002; Li, et al 2010; Rattanasopha, et al 2012). These insights confirm the deep homology of the vertebrate skull.…”

Zebrafish Craniofacial Development

“…Comparable phenotypes have been observed in zebrafish “midline” mutants, ranging from a complete absence of the anterior neurocranium to the formation of two unfused, parallel rods or a single rod instead of a plate (Eberhart et al, 2008; Eberhart, Swartz, Crump, & Kimmel, 2006; Kimmel, Miller, & Moens, 2001; Swartz, Sheehan-Rooney, Dixon, & Eberhart, 2011; Wada et al, 2005). Importantly, zebrafish mutant for Pdgf, Shh, or Bmp pathway components, or deficient in irf6 , all show cleft or midline phenotypes resembling those of their mammalian counterparts (Table 1; Dougherty et al, 2013; Eberhart et al, 2008, 2006; Swartz et al, 2011; Wada et al, 2005). These findings indicate that a conserved genetic network regulates the formation of this part of the face across vertebrates and support the use of the zebrafish anterior neurocranium as a model for the mammalian hard palate.…”

“…Within the first stream of neural crest, the initial, premigratory rostral–caudal position alongside the brain determines whether NCCs will migrate over or behind the eye (Dougherty et al, 2012; Wada et al, 2005), as well as whether their progeny will contribute to the anterior neurocranium or the upper or lower jaw (Dougherty et al, 2013, 2012; Eberhart et al, 2006; Wada et al, 2005). Additional analyses demonstrated that NCCs at certain anterior–posterior and mediolateral coordinates within each arch reproducibly contribute not only to particular skeletal elements but also to specific domains of said elements (Fig.…”

Using frogs faces to dissect the mechanisms underlying human orofacial defects

“…4C–D) were observed. Further, we noted that the ethmoid cartilage, thought to be analogous to the mammalian palate in non-amniotes [69], was significantly reduced or absent. These defects were accompanied by a reduced midface area that was at least in part due to a decrease in cell proliferation in the dorsal facial prominences.…”