Expression and activity profiling of the steroidogenic enzymes of glucocorticoid biosynthesis and the fdx1 co-factors in zebrafish

The spatial and temporal expression of steroidogenic genes in zebrafish has not been fully characterized. Since zebrafish are increasingly employed in endocrine and stress research, a better characterization of steroidogenic pathways is required to target specific steps in the biosynthetic pathways in the future. Here, we have systematically defined the temporal and spatial expression of steroidogenic enzymes involved in glucocorticoid biosynthesis (cyp21a2, cyp11c1, cyp11a1, cyp11a2, cyp17a1, cyp17a2, hsd3b1, hsd3b2), as well as the mitochondrial electron-providing co-factors ferredoxin (fdx1, fdx1b) during zebrafish development. Our studies showed an early expression of all these genes during embryogenesis. In larvae, expression of cyp11a2, cyp11c1, cyp17a2, cyp21a2, hsd3b1 and fdx1b can be detected in the interrenal gland, the zebrafish counterpart of the mammalian adrenal gland, whereas the fdx1 transcript is mainly found in the digestive system. Gene expression studies using quantitative RT-PCR and whole-mount in situ hybridization in the adult zebrafish brain revealed a wide expression of these genes throughout the encephalon, including neurogenic regions. Using ultra-high-performance liquid chromatography tandem mass spectrometry, we were able to demonstrate the presence of the glucocorticoid cortisol in the adult zebrafish brain. Moreover, we demonstrate de novo biosynthesis of cortisol and the neurosteroid THDOC in the adult zebrafish brain from radiolabeled pregnenolone. Taken together, our study is a comprehensive characterization of the steroidogenic genes and the fdx co-factors facilitating glucocorticoid biosynthesis in zebrafish. Furthermore, we provide additional evidence of de novo neurosteroid biosynthesizing in the brain of adult zebrafish facilitated by enzymes involved on glucocorticoid biosynthesis. Our work provides a valuable source for establishing the zebrafish as a translational model to understand the roles of the genes of glucocorticoid biosynthesis and fdx co-factors during embryonic development, stress and in brain homeostasis and function.