Integrative sequence and tissue expression profiling of chicken and mammalian aquaporins

Abstract

BackgroundProteins that selectively transport water across the membranes of cells are recognized as important in the normal functioning of the body systems of vertebrates. There are 13 known mammalian aquaporins (AQP0 to AQP12), some of which have been shown to have unexpected cellular roles beyond transmembrane water transport. The availability of non-mammalian vertebrate animal models has the potential to provide insight into the emergence of diverse function in the aquaporins. The domesticated chicken (Gallus gallus) is the premier avian model for biological research; however, only a limited number of studies have compared chicken and mammalian aquaporins. The identification of aquaporins that share functional motifs or are expressed in the same tissues in human and chicken could allow the further functional analyses of homologous aquaporins in both species. We hypothesize that integrative analyses of protein sequences and body site expression of human, mouse, rat and chicken aquaporins has the potential to yield novel biological hypotheses about the unexpected cellular roles of aquaporins beyond transmembrane water transport.ResultsA total of 76 aquaporin transcript models derived from 47 aquaporin genes were obtained for human, mouse, rat and chicken. Eleven body sites (brain, connective tissue, head, heart, liver, muscle, ovary, pancreas, small intestine, spleen and testis) were identified in which there is suggested expression of at least one mammalian and one chicken aquaporin. This study demonstrates that modern on-line analysis tools, a novel matrix integration technique, and the availability of the chicken genome for comparative genomics and expression analysis enables hypothesis generation in several important areas including: (i) alternative transcription and speciation effects on the conservation of functional motifs in vertebrate aquaporins; (ii) the emergence of basolateral targeting in mammalian species; (iii) the potential of the cysteine-rich AQP11 as a possible target in the pathophysiology of neurodegenerative disorders such as autism that involve Purkinje cells; and (iv) possible impairment of function of pancreas-expressed AQP12 during pancreatotropic necrosis in avian influenza virus infection.ConclusionThe investigation of aquaporin function in chicken and mammalian species has the potential to accelerate the discovery of novel knowledge of aquaporins in both avian and mammalian species.

Comparative Digestive Physiology

“…Under similar recirculating duodenal perfusion conditions, anesthetized rats, and pigeons absorbed D-glucose at a comparable rate but pigeons had significantly greater (>2× higher) absorption of inert carbohydrate probes (280). The difference in paracellular solute absorption between mammals and birds cannot be linked to differences in solvent drag because it is so difficult (155) to distinguish between water absorbed by the paracellular route versus aquaporins, which occur in intestine of both mammals and birds (229). …”

The evolutionary aspects of aquaporin family

“…Although the zebrafish underwent another round of whole genome duplication, its AQP number is not twice as many as that of humans (112). Interestingly, the orthologs of AQP2, AQP6, and AQP10 are missing in the chicken (48). Further analyses of tissue distribution and hormonal regulation of each AQP ortholog in vertebrates will be useful to obtain an insight into the functions and roles of mammalian AQPs (44).…”

Aquaporins in avian kidneys: function and perspectives

“…1), and an AQP4 homologue has been reported in cyclostomes (78). Elucidation of the role of AQP4 in birds and other nonmammalian animals may shed light on functions of AQP4 other than a water channel (48).…”