Novel steroidogenic factor-1 homolog (ff1d) is coexpressed with anti-Mullerian hormone (AMH) in zebrafish

ff1d is a novel zebrafish FTZ-F1 gene with sequence characteristics indicating similar basic regulatory mechanisms as the previously characterized ff1 based on the presence of an FTZ-F1 box in the DNA binding domain and an interactive domain (I-Box) and an AF-2 in the ligand binding domain. The highest sequence similarity was found between ff1d and ff1b (NR5A4), a gene previously shown to be a functional homolog to the steroidogenic factor 1 (SF-1). The expression pattern of ff1d was comparable to ff1b both in brain and gonads in adults and in the pituitary and interrenal cells in embryos. SF-1 is crucial in mammalian steroidogenesis and in sex determination by regulating the anti-Mullerian hormone (AMH). In fish, AMH has not been described previously. In this study, we cloned a partial zebrafish AMH. AMH was detected in growing oocytes, the ovarian follicular layer and testicular Sertoli cells, similar to the mammalian pattern, suggesting a conserved role between zebrafish and mammalian AMH. Teleosts lack a gene homolog to SRY, which constitute the universal testis-determining factor in mammalian sex determination. Comparison of sequences and expression patterns indicate that ff1d is a new candidate for sex determination and differentiation in a way similar to SF-1, possibly involving AMH.