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First published online November 2, 2007
Journal of Experimental Biology 210, 3919-3930 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.008342

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Cloning and characterization of AgCA9, a novel -carbonic anhydrase from Anopheles gambiae Giles sensu stricto (Diptera: Culicidae) larvae

Kristin E. Smith, Leslie A. VanEkeris and Paul J. Linser^*

The Whitney Laboratory for Marine Biology, University of Florida, 9505 Ocean Shore Boulevard, Saint Augustine, FL 32080, USA

^* Author for correspondence (e-mail: pjl{at}whitney.ufl.edu)

Accepted 16 August 2007

Mosquito larvae generate a luminal pH as high as 10.5 in the anterior region of their midgut. The mechanisms responsible for the generation and maintenance of this alkaline pH are largely unknown, but there is evidence suggesting a role for the enzyme carbonic anhydrase (CA). CA has been cloned from the alimentary canal epithelium of Anopheles gambiae larvae and can generate bicarbonate, which is implicated as a buffer for the larval lumen. The question remains as to how the bicarbonate is transported from the cells into the lumen. We hypothesize the presence of a CA within the lumen itself to generate bicarbonate from CO₂ produced by the metabolically active alimentary canal cells. Here, we report the cloning and characterization of a novel cytoplasmic-type -CA from the larval An. gambiae alimentary canal. Antibody immunolocalization reveals a unique protein distribution pattern that includes the ectoperitrophic fluid, `transitional region' of the alimentary canal, Malpighian tubules and a subset of cells in the dorsal anterior region of the rectum. Localization of this CA within the lumen of the alimentary canal may be a key to larval pH regulation, while detection within the rectum reveals a novel subset of cells in An. gambiae not described to date. Phylogenetic analysis of members of the -CA family from the Homo sapiens, Drosophila melanogaster, Aedes aegypti and An. gambiae genomes shows a clustering of the novel CA with Homo sapiens CAs but not with other insect CAs. Finally, a universal system for naming newly cloned An. gambiae CAs is suggested.

Key words: carbonic anhydrase, mosquito larvae, ectoperitrophic space, rectum, pH regulation, midgut alkalization

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