Gene expression profiling of proximal and distal renal tubules in Atlantic salmon (Salmo salar) acclimated to fresh water and seawater.

Euryhaline teleost kidneys undergo a major functional switch from being filtratory in fresh water (FW) to being predominantly secretory in seawater (SW) conditions. The transition involves both vascular and tubular effects. There is consensus that glomerular filtration rate is greatly reduced upon exposure to hyperosmotic conditions. Yet, regulation at the tubular level has only been examined sporadically in a few different species. This study aimed to obtain a broader understanding of transcriptional regulation in proximal vs. distal tubular segments during osmotic transitions. Proximal and distal tubule cells were dissected separately by laser capture micro-dissection, RNA was extracted, and relative mRNA expression level of >30 targets involved in solute and water transport were quantified by qPCR in relation to segment type in fish acclimated to FW or SW. The gene categories were aquaporins, solute transporters, fxyd proteins and tight junction proteins. aqp8bb1, aqp10b1, nhe3, sglt1, slc41a1, cnnm3, fxyd12a, cldn3b, cldn10b, cldn15a and cldn12 were expressed at higher level in proximal compared to distal tubules. aqp1aa, aqp1ab, nka-a1a, nka-a1b, nkcc1a, nkcc2, ncc, clc-k, slc26a6C, sglt2, fxyd2, cldn3a and occln were expressed at higher level in distal compared to proximal tubules. Expression of aqp1aa, aqp3a1, aqp10b1, ncc, nhe3, cftr, sglt1, slc41a1, fxyd12a, cldn3a, cldn3b, cldn3c, cldn10b, cldn10e, cldn28a and cldn30c were higher in SW- than in FW-acclimated salmon, whereas the opposite was the case for aqp1ab, slc26a6C and fxyd2. The data shows distinct segmental distribution of transport genes and a significant regulation of tubular transcripts when kidney function is modulated during salinity transitions.