PgmNr D1451: Macroglobulin complement-related is required for border cell migration and proper egg shape during Drosophila melanogaster oogenesis.

Authors:
H. Alhadyian; R. Ward


Institutes
The University of Kansas, Lawrence, KS.


Keyword: other ( Septate Junction, Oogenesis )

Abstract:

Macroglobulin complement-related (Mcr) encodes an ~200 kDa protein with α-2-Macroglobulin and LDL receptor class A domains. We initially identified Mcr in a genetic screen of mutations that dominantly enhanced a malformed leg phenotype in broad mutant animals, suggesting a role for Mcr in imaginal disc morphogenesis. We subsequently determined that Mcr is a core component of epithelial septate junctions (SJs), which are analogous to the vertebrate tight junction in providing an essential occluding function to the epithelium. Interestingly, homozygous mutations in Mcr are embryonic lethal with defects in developmental process including head involution and dorsal closure that occur prior to the establishment of the SJ, suggesting a role in morphogenesis that is independent of its role in the occluding junction. To extend these studies we are investigating the role of Mcr during morphogenetic events that occur during oogenesis. First, we investigated the expression of Mcr in oogenesis, and determined that it is expressed in the germarium, where it is enriched in the germline stem cells. It is also expressed in follicle cells, with the strongest expression in the polar cells. We next used cell-type and stage specific Gal4 drivers and mosaic analysis to examine the function of Mcr during oogenesis. We find that reducing Mcr in border cells using slbo-GAL4 to drive Mcr-RNAi results in 45% of the border cell clusters splitting apart. Knocking down Mcr in all the follicle cells including the follicle stem cells (GR1-GAL4>Mcr-RNAi) resulted in degeneration of middle stages egg chambers, whereas knocking down Mcr in all the follicle cells from stage 8 onwards (c204-GAL4>Mcr-RNAi) perturbs eggs elongation, resulting in stage 14 egg chambers that are significantly rounder than wild type egg chambers. Mosaic analysis using the strong loss of function allele Mcr1 revealed that germline clones formed germ cell cysts that fail to separate from the germarium. In addition, Mcr clones in the anterior and posterior follicle cells, including stalk cells, results in rupture of the epithelium. Together, these observations suggest that Mcr plays an important role in multiple aspects of egg chamber morphogenesis during oogenesis.