Factors regulating the onset of epithelial like polygonal architecture in the syncytial drosophila embryo

Abstract

Epithelial cell shapes in metazoans have a conserved hexagon dominatedpolygon distribution However the geometric constraints and mechanisms that resultin the spherical to polygonal transition remain to be elucidated Here we usesyncytial Drosophila embryos to characterize the temporal onset of polygonal plasmamembrane organization We find that circular to polygonal plasma membrane shapetransition occurs when the length of the lateral membrane increases beyond athreshold from interphase to metaphase in each nuclear division cycle DE cadherinlevels increase while Myosin II levels decrease during the threshold ingression DEcadherin depletion leads to decrease in furrow length and increase in circularity Increased Myosin II activity results in complete loss of lateral membrane extension thereby giving rise to spherical plasma membrane architecture Decreased myosinactivity on the other hand leads to the transition to polygonal shape at a lengthbelow the threshold length Our study thus elucidates the role of a balance betweenDE cadherin and Myosin II across the lateral domain length in stable formation ofpolygonal architecture in syncytial Drosophila embryos It further highlights theimportance of fine tuning Myosin II based contractility for achieving this thresholdlength We also look at the onset of epithelial like polarity in the syncytial Drosophilaembryos and find that the onset of epithelial like polarity occurs at nuclear divisioncycle 12 This is coincident with the onset of hexagon dominance Knockdown ofpolarity proteins like Bazooka and Peanut results in delayed onset of this hexagondominance while DE cadherin depletion results in loss of hexagon dominance Taken together we show that the syncytial Drosophila embryo showsepithelial like characteristics in terms of shape distributions and polarity despitelacking a basal domain newline newline