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

Abstract

BackgroundIon-transport mechanisms and gap junctions are known to cooperate in creating bioelectric phenomena, like pH gradients, voltage gradients and ion fluxes within single cells, tissues, organs, and whole organisms. Such phenomena have been shown to play regulatory roles in a variety of developmental and regenerative processes. Using Drosophila oogenesis as a model system, we aim at characterizing in detail the mechanisms underlying bioelectric phenomena in order to reveal their regulatory functions. We, therefore, investigated the stage-specific distribution patterns of V-ATPase components in relation to gap-junction proteins.ResultsWe analysed the localization of the V-ATPase components ductin (subunit c) and subunit a, and the gap-junction components innexins 2 and 3, especially in polar cells, border cells, stalk cells and centripetally migrating cells. These types of follicle cells had previously been shown to exhibit characteristic patterns of membrane channels as well as membrane potential and intracellular pH. Stage-specifically, ductin and subunit a were found either colocalized or separately enriched in different regions of soma and germ-line cells. While ductin was often more prominent in plasma membranes, subunit a was more prominent in cytoplasmic and nuclear vesicles. Particularly, ductin was enriched in polar cells, stalk cells, and nurse-cell membranes, whereas subunit a was enriched in the cytoplasm of border cells, columnar follicle cells and germ-line cells. Comparably, ductin and both innexins 2 and 3 were either colocalized or separately enriched in different cellular regions. While ductin often showed a continuous membrane distribution, the distribution of both innexins was mostly punctate. Particularly, ductin was enriched in polar cells and stalk cells, whereas innexin 2 was enriched in the oolemma, and innexin 3 in centripetally migrating follicle cells. In lateral follicle-cell membranes, the three proteins were found colocalized as well as separately concentrated in presumed gap-junction plaques.ConclusionsOur results support the notion of a large variety of gap junctions existing in the Drosophila ovary. Moreover, since ductin is the channel-forming part of a proton pump and, like the innexins, is able to form junctional as well as non-junctional membrane channels, a plethora of cellular functions could be realized by using these proteins. The distribution and activity patterns of such membrane channels are expected to contribute to developmentally important bioelectric signals.

Bioelectrical and cytoskeletal patterns correlate with altered axial polarity in the follicular epithelium of the Drosophila mutant gurken

“…6), it is obvious that bioelectrical and cytoskeletal polarity are linked to axial polarity. The establishment of electrochemical gradients in the FE depends on asymmetrically distributed or activated ion-transport mechanisms and gap junctions [4,7,[40][41][42][43][44]. This asymmetry is presumed to depend on early Grk-Egfr signalling and continues to exert influence on cytoskeletal patterns later in development [7,8].…”

Autocrine insulin pathway signaling regulates actin dynamics in cell wound repair

“…3D-F', 3L-N; Video 2). Gp150 encodes a transmembrane glycoprotein that regulates Notch signaling during normal eye development in Drosophila [57], whereas Inx3 encodes a gap junction protein involved in morphogenesis and nervous system development [58,59]. Thor encodes a translation inhibitor functioning downstream of insulin signaling that is sensitive to reactive oxygen species [60].…”

Analysing bioelectrical phenomena in the Drosophila ovary with genetic tools: tissue-specific expression of sensors for membrane potential and intracellular pH, and RNAi-knockdown of mechanisms involved in ion exchange

“…Moreover, they are responsible for the acidification of cytoplasmic vesicles, e. g., in the follicular epithelium (FE) of Drosophila [3,16,27]. In Drosophila ovarian follicles, an involvement of V-ATPases in bioelectrical phenomena has been supposed [27,37]. In particular, the asymmetrical accumulation of V-ATPases on one side of the follicle points to a role in regulating spatial coordinates [3,37].…”

“…In Drosophila ovarian follicles, an involvement of V-ATPases in bioelectrical phenomena has been supposed [27,37]. In particular, the asymmetrical accumulation of V-ATPases on one side of the follicle points to a role in regulating spatial coordinates [3,37]. Several studies demonstrated that V-ATPases are also required for Notch and wingless signalling in Drosophila [29,38,39].…”