Mineralocorticoid Receptor Mediates Cortisol Regulation of Ionocyte Development in Tilapia (Oreochromis mossambicus)

Cortisol is the predominant corticosteroid in ray-finned fish since it does not possess aldosterone synthase necessary to produce specific mineralocorticoids. traditionally believed function as a mineralocorticoid. However, effects of cortisol are mediated through receptors other vertebrates, and there an ongoing debate about whether acts glucocorticoid receptor (GR) or mineralocorticoid (MR) teleosts. To investigate this issue, we conducted study using euryhaline Mozambique tilapia (Oreochromis mossambicus) experimental species. The experiment was designed effect on ionocyte development at both cellular gene expression levels tilapia. We administered exogenous antagonists, used immunohistochemistry quantify numbers, performed real-time PCR assess differentiation factor tumor protein 63 (P63) mRNA, epidermal stem cell marker. observed that increased number Na+-K+-ATPase (NKA)-immunoactive ionocytes (increased by 1.6-fold) promoted P63 mRNA 1.4-fold). Furthermore, found addition antagonist Spironolactone inhibited increase (decreased level control group) suppressed (similarly decreased group). also provided evidence for gr, mr, p63 localization cells. At transcript level, mr ubiquitously expressed gill sections present cells (cells labeled with p63), supporting antagonism functional assay results larvae. Our confirmed stimulates MR, rather than GR. Therefore, provide new direction investigating dual action osmotic regulation skin/gill epithelial tilapia, which could help resolve previously inconsistent conflicting findings.