Two Zebrafish hsd3b Genes Are Distinct in Function, Expression, and Evolution

Abstract

HSD3B catalyzes the synthesis of δ4 steroids such as progesterone in the adrenals and gonads. Individuals lacking HSD3B2 activity experience congenital adrenal hyperplasia with imbalanced steroid synthesis. To develop a zebrafish model of HSD3B deficiency, we characterized 2 zebrafish hsd3b genes. Our phylogenetic and conserved synteny analyses showed that the tandemly duplicated human HSD3B1 and HSD3B2 genes are coorthologs of zebrafish hsd3b1 on chromosome 9 (Dre9), whereas the gene called hsd3b2 resides on Dre20 in an ancestral chromosome segment, from which its ortholog was lost in the tetrapod lineage. Zebrafish hsd3b1(Dre 9) was expressed in adult gonads and headkidney, which contains interrenal glands, the zebrafish counterpart of the tetrapod adrenal. Knockdown of hsd3b1(Dre 9) caused the interrenal and anterior pituitary to expand and pigmentation to increase, resembling human HSD3B2 deficiency. The zebrafish hsd3b2(Dre 20) gene was expressed in zebrafish early embryos as maternal transcripts that disappeared 1 day after fertilization. Morpholino inactivation of hsd3b2(Dre 20) led to embryo elongation, which was rescued by the injection of hsd3b2 mRNA. Thus, zebrafish hsd3b2(Dre 20) evolved independently of hsd3b1(Dre 9) with a morphogenetic function during early embryogenesis. Zebrafish hsd3b1(Dre 9), on the contrary, functions like mammalian HSD3B2, whose deficiency leads to congenital adrenal hyperplasia.

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

“…hsd3b2 transcript levels decrease at the 4 somites stage and remain very low (Figure J). The hsd3b2 transcript patterns are consistent with the described role of hsd3b2 in early embryogenesis . cyp21a2 transcript is almost undetectable until primordium‐5 (24 hpf) (Figure K).…”

“…Thus, it is tempting to speculate that only the later highly expressed genes, which are also expressed in the larval interrenal gland, have functions similar to those in mammals with respect to glucocorticoid biosynthesis during larval stages. Indeed, recent studies have demonstrated that cyp11a2 , fdx1b and hsd3b1 , but not their corresponding paralogues, are involved in cortisol synthesis in zebrafish . In addition, we have recently shown a key role for cyp21a2 in glucocorticoid biosynthesis in zebrafish …”

“…In the case of the HSD3B genes, the situation is more complex because there is one orthologue in zebrafish, hsd3b1 (Figure C), for the duplicated human HSD3B1 and HSD3B2 genes. The hsd3b2 gene appears to be a zebrafish‐specific gene duplication . In addition, two orthologues, fdx1 and fdx1b , for the human FDX1 are present in the zebrafish (Figure D).…”

“…More recently, novel insights into the expression and/or role of these steroidogenic enzymes, as well as their corresponding paralogues, were obtained in zebrafish. [28][29][30][31] This clearly emphasises the importance of a precise characterisation of the zebrafish paralogues and their role in steroidogenesis. Thus, further in-depth analysis for those genes and particularly their paralogues in the adult zebrafish brain is required to facilitate the correct targeting of steps in the biosynthetic pathways in the future.…”

“…Previous studies have analysed the expression of key enzymes of steroidogenesis (Cyp11, Hsd3b, Cyp17) in the adult zebrafish brain; however, it is not clear from these studies which of the corresponding paralogues were analysed. More recently, novel insights into the expression and/or role of these steroidogenic enzymes, as well as their corresponding paralogues, were obtained in zebrafish . This clearly emphasises the importance of a precise characterisation of the zebrafish paralogues and their role in steroidogenesis.…”