Gap junctions in the ovary of Drosophila melanogaster: localization of innexins 1, 2, 3 and 4 and evidence for intercellular communication via innexin-2 containing channels.
BACKGROUND
In the Drosophila ovary, germ-line and soma cells are interconnected via gap junctions. The main gap-junction proteins in invertebrates are members of the innexin family. In order to reveal the role that innexins play in cell-cell communication during oogenesis, we investigated the localization of innexins 1, 2, 3 and 4 using immunohistochemistry, and analyzed follicle development following channel blockade.


RESULTS
We found innexin 1 predominantly localized to the baso-lateral domain of follicle cells, whereas innexin 2 is positioned apico-laterally as well as apically between follicle cells and germ-line cells. Innexin 3 was observed laterally in follicle cells and also in nurse cells, and innexin 4 was detected in the oolemma up to stage 8 and in nurse-cell membranes up to stage 12. In order to test whether innexins form channels suitable for intercellular communication, we microinjected innexin antibodies in combination with a fluorescent tracer into the oocyte of stage-10 follicles. We found that dye-coupling between oocyte and follicle cells was largely reduced by innexin-2 antibodies directed against the intracellular C-terminus as well as against the intracellular loop. Analyzing in vitro, between stages 10 and 14, the developmental capacities of follicles following microinjections of innexin-2 antibodies revealed defects in follicle-cell differentiation, nurse-cell regression, oocyte growth and choriogenesis.


CONCLUSIONS
Our results suggest that all analyzed innexins are involved in the formation of gap junctions in the ovary. While innexins 2 and 3 are colocalized between soma cells, innexins 2 and 4 are colocalized between soma and germ-line cells. Innexin 2 is participating in cell-cell communication via hemichannels residing in the oolemma. It is obvious that gap-junctional communication between germ-line and soma cells is essential for several processes during oogenesis.
Bohrmann
Johannes
J
RWTH Aachen University, Institut für Biologie II, Abt. Zoologie und Humanbiologie, Kopernikusstrasse 16, 52056 Aachen, Germany. bohrmann@bio2.rwth-aachen.de
Zimmermann
Jennifer
J
D000818:Animals; D002450:Cell Communication / Q000502:physiology*; D017630:Connexins / Q000032:analysis* / Q000378:metabolism / Q000502:physiology*; D029721:Drosophila Proteins / Q000032:analysis* / Q000378:metabolism / Q000502:physiology*; D004331:Drosophila melanogaster / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000378:metabolism; D005260:Female; D017629:Gap Junctions / Q000378:metabolism*; D007150:Immunohistochemistry; D008565:Membrane Proteins / Q000032:analysis / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000378:metabolism; D009866:Oogenesis / Q000502:physiology; D010053:Ovary / Q000378:metabolism
D017630:Connexins; D029721:Drosophila Proteins; C438564:INX3 protein, Drosophila; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C459601:Zpg protein, Drosophila; C120024:inx2 protein, Drosophila; C079326:ogre protein, Drosophila