Braun MH, Steele SL, Ekker M, Perry SF. Nitrogen excretion in developing zebrafish (Danio rerio): a role for Rh proteins and urea transporters.

SUMMARYAfter demonstrating phylogenetic relatedness to orthologous mammalian genes, tools were developed to investigate the roles of three members (A3, A4 and A6c) of the SLC26 anion exchange gene family in Cl -uptake and HCO 3 excretion in embryos and larvae of zebrafish (Danio rerio). Whole-mount in situ hybridization revealed the presence of SLC26 mRNA in gill primordia, mesonephros and heart (slc26a3 and a4 only) at 5-9 days postfertilization (d.p.f.). SLC26A3 protein was highly expressed in lateral line neuromasts and within the gill, was localized to a sub-population of epithelial cells, which often (but not always) coexpressed Na

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SUMMARYRhag expression appeared to be limited to the pillar cells lining the blood spaces of the lamellae while Rhbg was localized to the outer layer of both the lamellae and the filament, upon the pavement cells. Exposure to high external ammonia (HEA) or phloretin increased tissue levels of ammonia and urea, respectively, in adult and juvenile zebrafish; however, the responses to these stressors were age dependent. HEA increased mRNA levels for a number of Rh proteins in embryos and larvae but did not elicit similar effects in adult gills, which appear to compensate for the unfavourable ammonia excretory gradient by increasing expression of V-type H + -ATPase. Phloretin exposure increased UT mRNA levels in embryos and larvae but was without effect in adult gill tissue. Surprisingly, in both adults and juveniles, HEA increased the mRNA expression of UT and phloretin increased the mRNA expression of Rh proteins. These results imply that, in zebrafish, there may be a tighter link between ammonia and urea excretion than is thought to occur in most teleosts.