Organic anion transporting polypeptides (OATP) in zebrafish (Danio rerio): phylogenetic analysis and tissue distribution

The aim of our study was initial characterization of Organic anion transporting polypeptides (Oatp ; SLC21 gene superfamily) in zebrafish (Danio rerio), as an important model species in biomedical and ecotoxicological research, using phylogenetic analysis, membrane topology prediction and tissue expression profiling. Phylogenetic tree of Oatp superfamily in vertebrates was constructed in Mega Software version 3.1., membrane topology was predicted using HMMTOP algorithm, while qRT-PCR was used to determine tissue specific gene expression levels. Phylogenetic analysis revealed that Oatp superfamily in zebrafish consists of five families that include 14 SLCO genes. Eight out of 14 transporters do have orthologs or co-orthologs in other vertebrates, while 6 members are found only in fish lineage. Topology analysis showed that all zebrafish Oatps consist of 12 transmembrane domains with the large fifth extracellular loop (LP5). Tissue distribution analysis revealed that the expression patterns of Oatp2a1, Oatp2b1 and Oatp3a1 follows tissue distribution patterns of their mammalian (co)orthologs. Expression pattern of a newly identified Oatp1d1 is similar to mouse Oatp1a4, while other new zebrafish Oatps (Oatp1e1, 1f2 and 1f4) do not resemble any of the mammalian Oatps. In summary, the described comprehensive analysis of Oatp superfamily in fish represents the first research step needed for understanding of ecotoxicological relevance of uptake transporters in aquatic organisms.