Evidence That Aquaporin 11 (AQP11) in the Spiny Dogfish (Squalus acanthias) May Represent a Pseudogene

Various attempts to amplify an AQP11 cDNA from tissues of the spiny dogfish (Squalus acanthias) were made. Two pairs of deoxy-inosine-containing degenerate primers were designed based on conserved amino acid sequences from an AQP11 alignment. These primers yielded some faint bands from gill cDNA that were sequenced. Blast searches with the sequences showed they were not AQP11. An elasmobranch AQP11 nucleotide sequence alignment was produced to identify conserved regions to make further degenerate primers. One primer pair produced a short 148 bp fragment showing particularly strong amplification in gill and intestine. It was sequenced and represented a piece of the AQP11 gene. However, as the fragment may have resulted from contaminating genomic DNA (in total RNA used to make cDNA), 5′ and 3′ RACE were performed to amplify the two ends of the putative cDNA. Furthermore, 5′ and 3′ RACE amplifications depend on the presence of a 5′ cap nucleotide and a poly A tail, respectively on the putative AQP11 mRNA. Hence, successful amplification was only possible from cDNA and not genomic DNA. Nested RACE amplifications were performed using gill and intestinal RACE cDNA, but none of the DNA fragments sequenced were AQP11. Consequently, the spiny dogfish AQP11 gene may represent a pseudogene.