Innexin2 gap junctions in somatic support cells are required for cyst formation and for egg chamber formation in Drosophila

Abstract

Germ cells require intimate associations with surrounding somatic cells during gametogenesis. During oogenesis, gap junctions mediate communication between germ cells and somatic support cells. However, the molecular mechanisms by which gap junctions regulate the developmental processes during oogenesis are poorly understood. We have identified a female sterile allele of innexin2 (inx2), which encodes a gap junction protein in Drosophila. In females bearing this inx2 allele, cyst formation and egg chamber formation are impaired. In wild-type germaria, Inx2 is strongly expressed in escort cells and follicle cells, both of which make close contact with germline cells. We show that inx2 function in germarial somatic cells is required for the survival of early germ cells and promotes cyst formation, probably downstream of EGFR pathway, and that inx2 function in follicle cells promotes egg chamber formation through the regulation of DE-cadherin and Bazooka (Baz) at the boundary between germ cells and follicle cells. Furthermore, genetic experiments demonstrate that inx2 interacts with the zero population growth (zpg) gene, which encodes a germline-specific gap junction protein. These results indicate a multifunctional role for Inx2 gap junctions in somatic support cells in the regulation of early germ cell survival, cyst formation and egg chamber formation. Inx2 gap junctions may mediate the transfer of nutrients and signal molecules between germ cells and somatic support cells, as well as play a role in the regulation of cell adhesion.

The molecular and immunochemical expression of innexins in the yellow fever mosquito, Aedes aegypti: Insights into putative life stage- and tissue-specific functions of gap junctions

“…Notably, in the ovaries of D. melanogaster , Inx4 immunoreactivity colocalizes with that of Inx2 where it may form connections between soma and germ-cell lines (Bohrmann and Zimmermann, 2008). Moreover, in the ovaries of D. melanogaster, Inx4 and Inx2 are necessary for 1) germ cell differentiation and survival, and 2) cyst and egg chamber formation (Gilboa et al, 2003; Mukai et al, 2011). Interestingly, AeInx4 mRNA expression is also strong in the testes of males (Figure 3), but it must not be abundant enough for its detection in the whole animal (Figure 1).…”

Bi-directional gap junction-mediated Soma-Germline communication is essential for spermatogenesis

“…Furthermore, Inx2 was found to colocalize with Zpg at soma-germline boundaries (Bohrmann and Zimmermann, 2008). Phenotypic analysis of a hypomorphic inx2 mutation in the ovary suggested a role for Inx2 in the soma (Mukai et al, 2011). Therefore, expression of Inx2 was analysed in the testis (Fig.…”

Rescue of Notch signaling in cells incapable of GDP- l -fucose synthesis by gap junction transfer of GDP- l -fucose in Drosophila

“…These defects were completely rescued by the simultaneous overexpression of wild-type inx2 (n = 27) (Fig. 5 M-O) (41). Furthermore, a different inx2 RNAi line (v102194), which produced a hairpin dsRNA corresponding to a different part of the inx2 cDNA, showed the same result (n = 27 for inx2 RNAi and n = 32 for inx2 and Gmd RNAi) (Fig.…”

“…For knockdown of the other innexin family genes, we used the following RNAi lines from VDRC: v7136 for ogre, v39095 for inx3, and v33277 for inx4. UAS-inx2 was described previously (41). All flies were raised at 25°C, except for the experiments involving RNAi, which were carried out at 30°C.…”