Macroglobulin complement-related, coracle and Neuroglian are required for Drosophila egg morphogenesis

Abstract

Morphogenesis, along with cell growth and differentiation are crucial processes that define the body plan of an organism. Morphogenetic movements such as neural tube formation, gastrulation and organogenesis are accomplished by precisely timed and coordinated changes in cell shape and rearrangement. Throughout morphogenesis, epithelial cells maintain their physical connection with each other through intercellular junctions that reside along the lateral membrane of the adjoining cells. Our lab previously demonstrated that core components of septate junctions (SJs), which are analogous to vertebrate tight junctions in that they provide an important occluding function to the epithelium, are essential for embryonic morphogenesis of Drosophila melanogaster. To extend these studies we are investigating the role of three core SJ genes Macroglobulin complement-related (Mcr), coracle (cor) and Neuroglian (Nrg) during morphogenetic events that occur in the Drosophila oogenesis. The Drosophila egg has been an excellent biological system to investigate aspects of cell and developmental biology because of its simple tissue structure and the number of morphogenetic changes occurring during oogenesis that similar to those occurring during embryos development. Based on the immunohistochemistry analysis, we find that Mcr, cor and Nrg are expressed throughout oogenesis. Mcr shows different expression pattern in the germarium region when compared to Cor and Nrg. High expression of Mcr is detected in the germline stem cells including germ line cells, whereas Cor and Nrg are expressed in the somatic follicle cells within the germarium. We then show that SJ proteins are essential for border cell migration as mutant border cell clusters for Mcr, cor or Nrg display different border cell migration defects including migration delay and border cell cluster disassembly. These phenotypes demonstrate a role for SJ proteins in border cell cluster guidance and cohesion. Knocking down Mcr and Nrg in all the follicle cells early in oogenesis results in middle stages egg chambers that fail to pass mid-oogenesis checkpoint. Moreover, the later stages egg chambers mutant for Mcr, Cor or Nrg were significantly rounded when compared to the elongated wild type eggs. We also demonstrated that Mcr is not required for the correct localization of alpha-spectrin, aPKC, and Cor localization proteins in the Drosophila egg. Together, these observations indicate a role for SJ proteins in regulating morphogenesis that is independent of the occluding function.