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First published online July 6, 2005
Journal of Experimental Biology 208, 2783-2798 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01680

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V-ATPase expression during development of Artemia franciscana embryos: potential role for proton gradients in anoxia signaling

Joseph A. Covi^* and Steven C. Hand

Division of Cellular, Developmental and Integrative Biology, Department of Biological Science, Louisiana State University, Baton Rouge, LA 70803, USA

^* Author for correspondence (e-mail: jcovi1{at}lsu.edu)

Accepted 11 May 2005

Under anoxia, Artemia franciscana embryos downregulate metabolic processes and approach an ametabolic state. Entrance into this quiescent state is accompanied by a profound acidification of the intracellular space, and more than two decades of research now clearly demonstrates that this acidification is critical to metabolic downregulation in anoxic embryos. However, the proximal mechanisms responsible for the pH shift remain largely unidentified. Here, we report evidence demonstrating expression of the V-ATPase in encysted embryos and present an argument for its involvement in the intracellular acidification induced by anoxia. We identified a single B-subunit cDNA sharing the greatest degree of sequence similarity with `generalist-type' homologues from mammals (brain-type) and invertebrates. Quantitative analysis of B-subunit mRNA demonstrates differential expression throughout early development, and western blot analyses confirm the expression of at least six V-ATPase subunits in both heavy membranes and microsomal vesicles. The critical need for proton pumping during the anoxia-tolerant stage of development is demonstrated by incubation with the V-ATPase inhibitor bafilomycin A₁, which halts embryonic development. Importantly, net proton flux from V-ATPase-acidified compartments to the surrounding cytoplasm is likely under anoxia and may significantly contribute to the enigmatic acidification critical to quiescence.

Key words: V-type ATPase, mRNA expression, protein expression, quiescence, diapause, brine shrimp, B-subunit cDNA, acidification, bafilomycin, oligomycin, hatching success

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