Septate junction proteins are required for egg elongation and border cell migration during oogenesis in Drosophila

Abstract

Protein components of the invertebrate occluding junction - known as the septate junction (SJ) - are required for morphogenetic developmental events during embryogenesis in Drosophila melanogaster. In order to determine whether SJ proteins are similarly required for morphogenesis during other developmental stages, we investigated the localization and requirement of four representative SJ proteins during oogenesis: Contactin, Macroglobulin complement-related, Neurexin IV, and Coracle. A number of morphogenetic processes occur during oogenesis, including egg elongation, formation of dorsal appendages, and border cell migration. We found that all four SJ proteins are expressed in egg chambers throughout oogenesis, with the highest and most sustained levels in the follicular epithelium (FE). In the FE, SJ proteins localize along the lateral membrane during early and mid-oogenesis, but become enriched in an apical-lateral domain (the presumptive SJ) by stage 10b. SJ protein relocalization requires the expression of other SJ proteins, as well as rab5 and rab11 in a manner similar to SJ biogenesis in the embryo. Knocking down the expression of these SJ proteins in follicle cells throughout oogenesis results in egg elongation defects and abnormal dorsal appendages. Similarly, reducing the expression of SJ genes in the border cell cluster results in border cell migration defects. Together, these results demonstrate an essential requirement for SJ genes in morphogenesis during oogenesis, and suggests that SJ proteins may have conserved functions in epithelial morphogenesis across developmental stages. Article SummarySeptate junction (SJ) proteins are essential for forming an occluding junction in epithelial tissues of Drosophila melanogaster, and also for morphogenetic events that occur prior to the formation of the junction during embryogenesis. Here we show that SJ proteins are expressed in the follicular epithelium of egg chambers during oogenesis and are required for morphogenetic events including egg elongation, dorsal appendages formation, and border cell migration. Additionally, the formation of SJs during oogenesis is similar to that in embryonic epithelia.