Aquaporins in chicken: localization of ck-AQP5 along the small and large intestine.

Aquaporins (AQPS) are transmembrane water channels poorly investigated in birds. Using degenerated primers and RT-PCR, we identified in kidney and gastrointestinal tract of Hubbard chickens (Gallus gallus) three fragments, corresponding to ck-AQP2, ck-AQP4, and ck-AQP5 mRNAs. Comparison of nucleotide ck-AQPs sequences to their rat and human orthologues revealed an overall identity of 75-90%. Expression in the renal and gastrointestinal systems of the three ck-AQPs mRNA was analysed by Northern assays. Transcript of ck-AQP2 was only identified in kidney. ck-AQP4 mRNA was highly expressed in brain, and to a lesser extent in kidney and stomach. ck-AQP5 mRNA was found in jejunum and ileum, and to a lesser extent in colon and lung. In situ hybridisation showed ck-AQP5 mRNA in the crypt cells of jejunum, ileum and colon, whereas it was absent from the cells lining the villi. Levels of ck-AQP5 mRNA (analyzed by Northern and in situ hybridisation assays) and protein (analysed by immunohistochemistry) decreased from the jejunum to the colon. This work confirmed the presence of AQPs in chicken, and showed that chicken and mammalian AQPs share a high degree of similarity in nucleotide sequence and tissue distribution.