Meeting Abstract
Atlantic killifish is a hardy euryhaline teleost that thrives in both fresh water (FW) and seawater (SW). Compensatory salt transport in teleost fish is mainly branchial while volume regulation is renal in FW and intestinal in SW. Intestinal handling of imbibed SW must involve aquaporins, ion transporters and claudins. In this study of killifish, we analyzed salinity effects on the transcriptional, protein and morphological level to better identify the role of the intestine during the rapid salinity fluctuations experienced by an estuarine species. An organ distribution experiment was performed to analyze mRNA expression of known membrane proteins involved in water and ion transport. Aquaporin paralogs (aqp1, aqp8, aqp10a), two ion transporters (nka1a, nkcc2) and three claudin paralogs (cldn15a, cldn15b, cldn15like) were all expressed in both anterior and posterior intestine of all salinities but with segmental differences. Some genes showed elevated expression in SW compared to FW acclimated killifish (nkcc2, aqp1, aqp2), suggesting increased capacity for transcellular ion and water transport. Remarkably, cldn15b had 100-fold higher expression in posterior intestine only in FW acclimated fish. The minor or absent salinity regulation of many ion and water transport genes suggests partial maintenance of intestinal water handling capacity. However, some adjustment occurs and the dramatic elevated expression of cldn15b suggests a specific role of this paralog in the posterior intestinal segment but only in FW. Confocal microscopy revealed brush border localization of Aqp1 and significant morphological differences between anterior and posterior intestine supporting functional specialization.
