Isoforms vatB1 and vatB2 of the vacuolar type ATPase subunit B are differentially expressed in embryos of the zebrafish (Danio rerio).

The v-type ATPase is a membrane anchored, multi-subunit proton pump, which in freshwater fish appears to play a major role in ionoregulative processes in the apical membrane of specialized gill cells. Very little is known about free-living fish embryos and larvae that are exposed to hypo-osmotic conditions with spawning but do not have their gills fully developed. By using reverse transcriptase-polymerase chain reaction and immunological methods, we could demonstrate the presence of two isoforms of the subunit B of this v-type ATPase in the early development of the zebrafish. Immunohistochemical analysis revealed the presence of one isoform (vatB1) in the apical membrane of embryonic skin cells, while vatB2 has been found ubiquitously. This differential localization of the two isoforms supports the hypothesis that vatB1 is preferentially involved in ionoregulative functions, while vatB2 may be preferentially responsible for acidification of intracellular vesicles.

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