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First insight into non-mammalian SLCs: functional characterization of zebrafish (Danio rerio) uptake transporters (Solute Carrier families SLC21 and SLC22)

Membrane transporters of families SLC21 (Organic anion polypeptides ; Oatp) and SLC22 (Organic cation/anion/zwitterions transporters) are involved in uptake of various endogenous and foreign compounds. However, their role has not yet been comprehensively investigated in non-mammalian organisms. The goal of our study was molecular characterization of toxicologically relevant uptake transporters in zebrafish (Danio rerio). Using phylogenetic analysis, we annotated 29 zebrafish genes within SLC21 and SLC22 families and conducted tissue expression profiling using qPCR. Using the transiently transfected HEK293 cells and radioactively labeled model substrates, estrone-3-sulfate and p-aminohippurate, we conducted functional characterization of Oatp1d1 (SLC21) and seven members of organic anion transporters (SLC22). Within vertebrate and invertebrate lineages, we found that Oatp1d subfamily is present only in teleosts fish and consist of two members: Oatp1d1 and Oatp1d2. According to our results, physiological role of zebrafish Oatp1d1 could be transport of specific hormones and bile salts, while it also interacts with a wide range of pharmaceuticals and environmental contaminants. Oatp1d1 significantly differs from four mammalian Oatp1 subfamily genes in terms of its substrate specificity. Within the SLC22 family, two co-orthologs of mammalian OAT1 and OAT3, zebrafish Oat1/3 and Oatlike1, show overlapping substrate range but different affinities. Human OAT2 has 5 co-orthologs in zebrafish, Oat2a-Oat2d, that show differential substrate specificities among each other and in comparison with its mammalian ortholog. In conclusion, our study presents the first functional characterization of non-mammalian SLC genes. We showed that gene orthology relationship within human and zebrafish SLC21 and SLC22 genes are complex with differential substrate range and affinities among organisms.

uptake transporters; zebrafish; function

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