Larval anopheline mosquito recta exhibit a dramatic change in localization patterns of ion transport proteins in response to shifting salinity: a comparison between anopheline and culicine larvae.

Mosquito larvae live in dynamic aqueous environments, which can fluctuate drastically in salinity due to environmental events such as rainfall and evaporation. Larval survival depends upon the ability to regulate hemolymph osmolarity by absorbing and excreting ions. A major organ involved in ion regulation is the rectum, the last region for modification of the primary urine before excretion. The ultrastructure and function of culicine larval recta have been studied extensively; however, very little published data exist on the recta of anopheline larvae. To gain insight into the structure and functions of this organ in anopheline species, we used immunohistochemistry to compare the localization of three proteins [carbonic anhydrase (CA9), Na+/K+ P-ATPase and H+ V-ATPase] in the recta of anopheline larvae reared in freshwater and saline water with the localization of the same proteins in culicine larvae reared under similar conditions. Based on the following key points, we concluded that anophelines differ from culicines in larval rectal structure and in regulation of protein expression: (1) despite the fact that obligate freshwater and saline-tolerant culicines have structurally distinct recta, all anophelines examined (regardless of saline-tolerance) have a structurally similar rectum consisting of distinct DAR (dorsal anterior rectal) cells and non-DAR cells; (2) anopheline larvae undergo a dramatic shift in rectal Na+/K+-ATPase localization when reared in freshwater vs saline water. This shift is not seen in any culicine larvae examined. Additionally, we use these immunohistochemical analyses to suggest possible functions for the DAR and non-DAR cells of anopheline larvae in freshwater and saline conditions.

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

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 CO(2) produced by the metabolically active alimentary canal cells. Here, we report the cloning and characterization of a novel cytoplasmic-type alpha-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 alpha-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.