Molecular characterization of inception of polarity in plasma membrane during early Drosophila embryogenesis

Abstract

Epithelial cells have a characteristic Plasma (PM) organization in all organisms, with different polarity protein complexes marking apical, lateral and basal membrane. The syncytial embryo of Drosophila is a stage prior to the de novo formation of epithelial cells. Despite the absence of complete PM boundaries around each nucleus, the syncytium has been shown to exhibit polarized distribution of some molecules found in epithelial cells. The syncytium is a good model to study the temporal onset of polarized protein distribution and the mechanisms which govern this. Rapid remodeling of the PM during the syncytial division cycles makes it especially suited for observing the onset of polarized distribution of PM de novo. I have used time lapse confocal laser scanning microscopy of fluorescently tagged transgenes present in epithelial cells for their temporal distribution on the PM in the syncytial division cycle. This work shows that at least three PM domains, one apical and two lateral, are formed during last four syncytial nuclear division cycles before the embryo forms complete epithelial cells. The plasma membrane is completely marked on the apical and lateral domain by phospholipid binding proteins. Transmembrane proteins capable of interlinking across adjacent PM like DE-Cadherin and Toll mark the entire lateral membrane, whereas PM associating proteins like septins, Bazooka and PatJ are localized to the lower regions of the lateral membrane. Finally, preliminary results using Anillin mutants and laser ablation of centrosomes shows that they are important for lateral membrane organization in the syncytium.