Aquaporin and aquaglyceroporin in silkworms, differently expressed in the hindgut and midgut of <i>Bombyx mori</i>

Abstract

Two cDNAs similar to aquaporins (AQPs) from other insect species were identified and characterized from the silkworm larva, Bombyx mori. The first cDNA (AQP-Bom1) cloned from the anterior silk gland encodes a 25 900 Da protein similar to insect AQPs isolated from several liquid-feeding insects. The second cDNA (AQP-Bom2) cloned from the posterior midgut encodes a 27 694 Da protein. Northern blot analysis has revealed that the AQP-Bom1 mRNA (2.3 kb) is expressed predominantly in the hindgut (colon and rectum), and moderately or minimally in the silk gland, midgut and Malpighian tubules, while the AQP-Bom2 mRNA (1.3 kb) is mainly expressed in the posterior midgut and Malpighian tubules. Functional analysis in Xenopus oocytes microinjected with the cRNA of these AQPs revealed that the AQP-Bom1 mRNA encodes a water-specific aquaporin, likely involved in the water retrieval function of the hindgut, while the AQP-Bom2 mRNA encodes an aquaglyceroporin, increasing glycerol and urea uptake.