Morphogenesis of the first branchial arch - by Sevan Hopyan
Sevan Hopyan Developmental & Stem Cell Biology Program, The Hospital for Sick Children; Departments of Molecular Genetics & Surgery, The University of Toronto
Host: Cristina Marchetti | Contact: Tyler Engstrom, firstname.lastname@example.org
The nuanced shapes of emerging organ primordia are intimately related to pattern formation and postnatal function, although the mechanisms that shape a volume of tissue in the embryo are not well understood. The mandibular portion of the first branchial arch is composed of a volume of mesenchyme surrounded by a single cell layer epithelium. Here we ask how this structure acquires a proximally narrow and distally bulbous shape during outgrowth. Using the mouse embryo as a model system, we measured cell cycle times, as well as Young’s modulus and viscosity using atomic force microscopy. Incorporating these data into a finite element model, we show that the spatial variation of cell division and physical properties is insufficient to explain mandibular arch shape. By combining time lapse light sheet microscopy of intact mouse embryos with custom cell tracking, we observed that volumetric convergent extension due to the intercalation of mesenchymal cells in 3D likely underlies the narrow and elongate shape of the mandiublar arch mid-portion. By knocking-in a transgenic FRET-based vinculin tension sensor into the mouse genome, we show that relatively high amplitude cortical force oscillations correlate with mesenchymal cell intercalations, and are oriented by polarised actomyosin. Evidence from loss and gain of function studies suggest that Wnt5a acts as a directional cue to regulate both the orientation and oscillation amplitude of cell cortices.