Differential expression of two distinct aromatase genes (cyp19a1a and cyp19a1b) during vitellogenesis and gestation in the viviparous black rockfish Sebastes schlegelii

Abstract

Oviparous fishes are known to possess two types of aromatase, which are ovary type (cyp19a1a) and brain type (cyp19a1b). These aromatases play important roles in the reproduction of oviparous fish. However, little information is available on the role of aromatases in the reproduction of viviparous fish. This study has been carried out to examine the changes of aromatase gene expression prior to and during vitellogenesis and during gestation in a marine viviparous fish, black rockfish, Sebastes schlegelii. The coding sequence of cyp19a1b gene cloned from rockfish brain was 1497 nucleotides (nt). Rockfish cyp19a1b was more similar to cyp19a1b from other fish species than to rockfish cyp19a1a in amino acid sequence. In addition, phylogenetic analysis showed that aromatases of this viviparous rockfish were more similar to those of oviparous fishes than those of viviparous mammals. Cyp19a1a mRNA was expressed most strongly in the ovary and weakly in the testis, brain, and spleen. Cyp19a1b mRNA was detected only in the brain at cortical alveolus stage (CA) but, additionally, detected in the ovary during vitellogenesis and gestation. The expression of both aromatase mRNAs was the highest at the vitellogenic stage (V) and the expression of cyp19a1a mRNA far exceeded that of cyp19a1b mRNA in the ovary of all reproductive stages studied here. Results from this study suggests that viviparous rockfish also has two distinct aromatase genes as oviparous fish do, and that the expression of cyp19a1a, rather than cyp19a1b, in the ovary is closely related to the vitellogenic activity in this species.