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Fig. 5 | BMC Developmental Biology

Fig. 5

From: Relating proton pumps with gap junctions: colocalization of ductin, the channel-forming subunit c of V-ATPase, with subunit a and with innexins 2 and 3 during Drosophila oogenesis

Fig. 5

Summary of colocalization or local enrichment of ductin, V-ATPase subunit a, Inx2 and Inx3, respectively, during previtellogenic stages (up to stage 7) and vitellogenic stages (up to stage 13). a, a’: Ductin (subunit c) and V-ATPase subunit a; b, b’: Ductin and Inx2; c, c’: Ductin and Inx3. Ductin and subunit a (a, a’) are stage-specifically either colocalized in plasma membranes or in the cytoplasm (yellow), which is supposed to represent the distribution of V-ATPases, or separately enriched in different cellular regions of germ-line and soma cells. Frequently, ductin (red) is more prominent in plasma membranes, while subunit a (green) is more prominent in cytoplasmic and nuclear particles or vesicles. Punctate membrane labeling (red, example shown in the box) is presumed to originate from ductin as part of membrane channels or gap-junctional structures. a: In previtellogenic stages (e.g. stage 7 is shown), ductin (red) is enriched in posterior polar cells (pPC) and in stalk cells (SC), while subunit a (green) is enriched in cytoplasmic particles or vesicles in follicle cells (FC), nurse cells (NC) and the oocyte (Ooc). a’: In vitellogenic stages (e.g. stage 10b is shown), the dorsoventral gradient of V-ATPase distribution in the FC epithelium (yellow) is in accordance with the gradual distribution of epithelial membrane potentials [19]. While ductin (red) is enriched in NC, pPC and SC, subunit a (green) is enriched in border cells (BC) and nuclear particles or vesicles in FC (FCN; N, oocyte nucleus; NCN, nurse-cell nuclei). Since PC, BC and ventral FC are also characterized through a high activity of L-type Ca2+-channels, alterations of membrane potentials through V-ATPase activity are supposed to result in cellular responses due to voltage-dependent Ca2+-currents [19]. Ductin and Inx2 (b, b’) as well as ductin and Inx3 (c, c’) are stage-specifically either colocalized (yellow) or separately enriched (red vs. green) in different cellular regions of germ-line and soma cells. Frequently, ductin (red) shows a rather continuous membrane distribution, presumably representing V-ATPases, while the distribution of both innexins (green) is more punctate, presumably representing gap-junctional structures. In lateral FC membranes (FCM), both ductin and Inx2 as well as ductin and Inx3 are often found concentrated in different plaques (red vs. green) that are presumed to represent different gap-junctional structures (example shown in the box in b’). b: In previtellogenic stages, ductin (red) is enriched in NC membranes (NCM) and in the oolemma (Ool) as well as in PC and SC, whereas Inx2 (green) is enriched in cytoplasmic particles or vesicles in germ-line cells. b’: In vitellogenic stages, ductin (red) is enriched in pPC, while Inx2 (green) is enriched in the Ool. Antibodies directed against presumed cytoplasmic regions of both ductin or Inx2 microinjected into the oocyte specifically blocked intercellular communication through ductin- or Inx2-containing gap junctions [11, 15, 18]. c: In previtellogenic stages, ductin (red) is more prominent in NCM and in the Ool as well as in PC, in SC and in the cytoplasm of germ-line cells, while Inx3 (green) is more prominent around NCN and in lateral plasma membranes of the prospective centripetally migrating FC (cFC, bars). c’: In vitellogenic stages, ductin (red) is enriched in apical FCM and in the Ool as well as in pPC, BC and SC, while Inx3 (green) forms prominent plaques in lateral membranes of cFC (bars). Inx3-containing gap junctions are supposed to specifically regulate the distribution of membrane potentials, intracellular pH and ions within cFC and to establish a communication border to neighboring FC [12, 13, 16, 19, 60]

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