Expression of zebrafish cyp11a1 as a maternal transcript and in yolk syncytial layer.

Cyp11a1 (P450scc, cholesterol side-chain cleavage enzyme) is the first enzyme for the synthesis of all steroid hormones. The regulation of steroid synthesis has been extensively investigated, except during embryogenesis. To study steroidogenesis in embryos, we have isolated the zebrafish cyp11a1 gene, which consists of 11 exons. Reverse transcription-polymerase chain reaction analysis indicates that zebrafish cyp11a1 is expressed temporally in two waves during embryonic stages and when sexual differentiation begins. It is expressed in adult brain, testicular Leydig cells, and the granulosa/theca layer of the ovary. In addition, zebrafish cyp11a1 is expressed in oocytes, and is inherited as a maternal transcript in early embryos. Throughout zebrafish epiboly and segmentation stages, cyp11a1 is expressed in the yolk syncytial layer. At 36 h post fertilization, cyp11a1 transcript is located ventral to the third somite, where the primordial interrenal gland is located. In summary, zebrafish cyp11a1 is expressed in the cytoplasm of oocytes, as a maternal transcript, and in yolk syncytial layer during early embryogenesis.