Analysis of regulation of epithelial-like architecture formation by mitochondrial dynamics in Drosophila embryogenesis

Abstract

Mitochondrial morphology and dynamics play a crucial role in epithelial cell formation and maintenance, however the mechanisms by which they affect these processes remains to be completely investigated. Here we have attempted to study the role of mitochondrial fission in the onset of polarity during epithelial cell formation in Drosophila embryogenesis. Our previous studies show that the depletion of the mitochondrial fission protein Drp1 leads to fused mitochondria which accumulate basally of the cells during cellularization. We further elucidated the changes in epithelial polarity proteins in embryos depleted of Drp1. We find that though the apical cell area remains the same as controls and there is depletion of apical and basal adherens’ junction protein DE-cadherin in Drp1 depleted embryos. Reactive oxygen species have been previously found to be decreased in Drp1 depleted embryos. We find that restoration of ROS in the mitochondrial SOD2 RNAi expressing embryos leads to a reversal of the defect in DE-cadherin distribution in Drp1 depleted embryos. Subsequently, we also observed reduction in levels of Bazooka protein which helps recruit DE-Cadherin apically. The basal activation of actomyosin ring constriction is decreased in Drp1 depleted embryos and myosin II is enriched in the cytoplasm. The polarity protein PatJ which is present at the apical membrane and at the ring is seen to be increased in the cytoplasm in Drp1 depleted embryos. Dlg, a lateral membrane protein appears to be increased basally in Drp1 depleted embryos. We further tested the role of trafficking pathways in mediating these polarity protein defects by staining for amphiphysin, Rab5, Rab11 and Rab7 in Drp1 depleted embryos. We found that amphiphysin, a marker for endocytosis is accumulated at the ring. Amphiphysin labelled endocytic tubes at the furrow are increased indicating that there is a delay in endocytosis. Further there is a depletion and mislocalization of endocytic pathway components Rab5, Rab11 and Rab7. Together these data indicate that epithelial polarity proteins are likely to affected at the plasma membrane during their formation in cellularization in Drp1 depleted embryos due to a defect in trafficking. It is likely that decrease in mitochondrial ROS may play a role in regulating these defects.