Targeted disruption of the mouse gene encoding the V-ATPase accessory subunit Ac45

Acidification of organelles of the eukaryotic vacuolar system is important for multiple intracellular processes including receptormediated endocytosis, proteolytic activity in lysosomes, and prohormone sorting and processing in secretory granules. Responsible for the generation of a proton gradient across a membrane is vacuolar H + -ATPase (V-ATPase).How the activity of this multisubunit enzyme is regulated remains tobe established. Accessory subunits of the V-ATPase may be involved in the organelle-specific regulation, one candidate being the chromaffin granular V-ATPase-associated protein Ac45. To assess the function ofAc45, wedisrupted its gene by gene targeting in male mouse embryonic stem cells. We have successfully generated Ac45 null mutant (- /Y) embryonic stem cells and injected them into C57BL/6 recipient blastocysts. The blastocysts were replaced into pseudopregnant foster mothers, giving rise to 16 littermates. One of these appeared to be a low-chimeric female mouse that died 6 weeks after birth. No signs of late abortion were detected in the foster mothers. The results suggest that the injected Ac45 null mutant embryonic stem cells affectthe normal development of the blastocyst and are in line with knockout studies on other V-ATPase subunits that point to an essential role for the V-ATPase in early embryonic development.