Abstract:
Distinct apico-basal domain identity is achieved in epithelial cells via the presence of
apical microvilli and basolateral surface with adherence junctions. Syncytial cells
in Drosophila embryogenesis display similar onset and maintenance of asymmetric
identities, which makes it an excellent and tractable system to study the role of plasma
membrane (PM)-actin interactions. Previous studies in the lab have shown an onset of
epithelial-like organization at cycle 11. My studies show that the apical cap expands
followed by stabilization and adhesion to form the lateral furrow in each syncytial cycle.
Phospholipids and their interaction with actin are known to regulate polarity and PM
remodeling processes in other organisms. We found that genetically increasing the
dosage of phosphatidylinositol(3,4,5)-trisphosphate (PIP3) binding tGPH (tubulin
promoter-GFP-PH domain of GRP1) tag resulted in defective polygonal epithelial-like
architecture and short lateral furrows. Down regulation of PI3-Kinase, which presumably
lowers PIP3 levels or supposedly increasing PIP3 via its antagonist PTEN phosphatase
resulted in global defects in cortical actin and desynchronized division cycles. An
imbalance in either of these two phospholipids resulted in the loss of cap stabilization
and short lateral furrows. Actin remodeling protein Arpc1 is enriched at the actin cap
edges during expansion and formin Dia is enriched during cap adhesion and furrow
extension. Cap expansion is disrupted in arp3 RNAi whereas expanded caps are visible
in dia RNAi. Recruitment of adhesion and actin remodeling proteins such as DE-
Cadherin, Rac1 and Dia but not Arp2/3 are lowered in PI3K and PTEN mutant embryos.
These studies together show that phospholipid balance is crucial for the recruitment of
Dia during cap stabilization and formation of furrow during the syncytial division cycle.
