Molecular Characterization of Plasma Membrane Organization during Early Drosophila Embryogenesis

Abstract

Metazoan embryo development starts with division of a simple cell to epithelial cells containing a predominant hexagonal organization. Epithelial cells have distinct morphology and protein complexes demarcating the apical, lateral and basal domains. Drosophila embryogenesis is used as a model system to study the onset of this polarity and epithelial sheet organization. The plasma membrane (PM) of the syncytial embryo shows a microvillus contained apical domain and junctional protein contained lateral domain even before the formation of complete cells. Using time-lapse confocal microscopy of fluorescently tagged transgenes, we have found an increased hexagonal organization in the PM similar to epithelial cells in the syncytial cycle 13. Junctional proteins, Cadherin and Bazooka are present in the lateral domain of the syncytial PM. Bazooka is distributed more on the edges of polygonal PM, while cytoskeletal remodeling proteins of the Septin family are predominantly present in the vertices. Photo bleaching experiments with Cadherin-GFP show that its movement is restricted within one edge and does not cross over to the neighboring edge of a polygon. Although a similar phenomenon is observed in the syncytium with the labeled trans-membrane protein, Toll-Venus, but in cellularization it moves freely across edges. To elucidate on the mechanism by which the lateral membrane, polygonal polarity and packing arises, embryos mutant for Cadherin, Bazooka and Peanut are being studied. Preliminary analysis with Cadherin mutant embryos shows loose PM organization along with compromised lateral membrane length. Packing analysis shows more pentagons instead of hexagons in syncytial cycle 13 implying a role for the protein in PM organization during Drosophila embryogenesis.