Integrins pattern the Drosophila embryonic neuroepithelium by influencing progenitor morphodynamics, division and position

Gene regulatory networks that confer cell fate and intracellular force generation mechanisms that drive cellular morphodynamics guide the patterning of tissues, but the nature of their interplay is poorly understood. We explore this during Drosophila embryonic neurogenesis whose first step, the delamination of a neuroblast from the surface epithelium, resembles an epithelial to mesenchymal transition (EMT). Using real-time, 3D confocal microscopy combined with quantitative morphometry, we identify robust morphometric state transitions that culminate in the basal delamination of the neuroblast (NB) from an equipotent epidermal proneural cluster, and find that mitotic rounding occurs concomitantly with delamination. We uncover marked heterogeneity and reduced collectivity in the morphodynamics of the NB and its nearest neighbours, and suggest their origins in the morphogenetic activity in the extending germband. We show that the appearance and distribution of the NB and GMC fate determinants Deadpan/dpn and Prospero/pros respectively correlate temporally with distinct morphometric states. We identify changes in cell-cell and cell-substrate adhesion that accompany neuroblast delamination and division and show that the adhesive microenvironment provided by integrin-ECM interactions patterns the neuroepithelium by influencing the spatiotemporal control of cell shape, division and position.