Meeting Abstract
The genetic and developmental mechanisms underlying the tremendous morphological diversity of the vertebrate jaw apparatus remain poorly understood. Skeletal progenitors may coordinate their morphogenetic behaviors via planar cell polarity (PCP) signaling – a system best known for its role in propagating consistent hair/bristle orientation across mammalian skin/insect cuticle. Two main pathways regulate PCP independently in Drosophila: the Frizzled (Fz) pathway and the Fat/Dachsous (Dchs) pathway. Here we use the accessibility and miniature organization of the zebrafish jaw skeleton to show that cartilage morphogenesis depends upon both pathways. Using in vivo time-lapse imaging, we show that cartilage elongation results from oriented cell-cell intercalations and that this collective behavior involves both Fz- and Fat/Dchs signaling. Cell transplantation analyses show that Fat3 and Dchs2 are required non-cell autonomously and over several cell-diameters for cartilage intercalation, consistent with activation of a secondary signal that regulates polarized cell-cell intercalation. Interestingly, additional chimaeric experiments show that a member of the Fz pathway – the diffusible signal Wnt5b – is also required at long-range, suggesting that it may be activated downstream from Fat3/Dchs2 signaling to control intercalation of skeletal progenitors. Ultimately, modulation of cell-cell intercalation by the Fat3/Dchs2- and/or the Fz pathway constitutes an attractive evolutionary mechanism regulating the diversification of jaw shape and size.
