Structure and tissue distribution of prolactin receptor mRNA in Japanese flounder (Paralichtys olivaceus): Conserved and preferential expression in osmoregulatory organs

In diadromous and euryhaline teleosts, it has been established that prolact in (PRL) is a major hormone regulating the maintenance of water and electro lyte homeostasis by acting on its receptor (PRLR) expressed in the osmoregu latory organs. To investigate the major physiological role of PRL in a mari ne teleost, cDNA for the Japanese flounder (Paralichtys olivaceus) prolacti n receptor (fPRLR) has been cloned and characterized. The predicted fPRLR i s composed of 636 amino acids conserving common structural features, such a s the WSXWS motif and box 1, that are observed in the members of the cytoki ne receptor superfamily. By Northern blot analysis, 3.5-kb transcripts for fPRLR were clearly detected in the gill, kidney, and intestine. By RNase pr otection assay, similarly high levels of mRNA expression were detected in t hese osmoregulatory organs and lower expression levels were seen in the bra in for both males and females. Interestingly, a distinct expression level o f fPRLR mRNA was observed in the testis, but not in the ovary. The present results suggest that PRL may play an important role in the control of water and electrolyte balance through PRLR expressed in the osmoregulatory organ s in the marine teleost the Japanese flounder as well as in other teleosts. Furthermore, PRL may differentially regulate gonadal functions in males an d females of Japanese flounder. (C) 2001 Academic Press.