Two cytochrome P450 aromatase genes in the hermaphrodite ricefield eel Monopterus albus: mRNA expression during ovarian development and sex change

Abstract

Previously, the ricefield eel (Monopterus albus) was speculated to have only one cytochrome p450 aromatase gene. In this study, however, the cDNAs encoding two distinct cytochrome p450 aromatases, cyp19a1a and cyp19a1b, were isolated. The genomic organizations of both cyp19 genes were conserved when compared with other teleosts. Northern blot detected an abundant expression of cyp19a1a in the ovary, and cyp19a1b in the hypothalamus. RT-PCR coupled with Southern blot showed that cyp19a1a was expressed predominantly in the gonads of both sexes, with higher levels in the ovary than testis, while cyp19a1b was expressed in all the tissues examined in the male, but only in the brain and pituitary in the female. The levels of cyp19a1a mRNA in the ovary were increased significantly during vitellogenesis, but decreased significantly at mature stage. The levels of cyp19a1b mRNA in the brain and pituitary did not vary significantly during vitellogenesis. As ovarian development shifted from vitellogenesis to maturation, the levels of cyp19a1b mRNA was decreased significantly in the brain, but increased significantly in the pituitary. During natural sex change from female to male, the levels of cyp19a1a mRNA in the gonad were significantly decreased. The levels of cyp19a1b mRNA in the hypothalamus were significantly increased at the early intersexual phase, whereas the expression levels in the pituitary were significantly decreased at the intersexual phases. Taken together, these results showed a novel sexual dimorphism of cyp19a1b mRNA tissue distribution, and both CYP19 genes were associated with the ovarian development and natural sex change of the ricefield eel.

Bending Genders: The Biology of Natural Sex Change in Fish

“…Wnt4a and sf1 expression drop off concurrently but are not halted completely. Arrested cyp19a1a expression during early female-to-male sex change is widely reported in single-gene studies of other protogynous species [e.g., Li et al, 2006;Zhang et al, 2008;Liu et al, 2009] and is consistent with arrested E2 production at this stage ( fig. 3 A).…”

Aromatase in the brain of teleost fish: Expression, regulation and putative functions

“…They generate two structurally and functionally different isoforms that, in this review, will be referred to as aromatase A and aromatase B, mostly expressed in the ovary and brain, respectively. Two such genes were identified in an increasing number of species including the rainbow trout [40; 42], the zebrafish [43; 44], the Nile tilapia [45], the European sea bass [46], the protogynous wrasse, Halichoeres tenuispinis [47], the killifish Fundulus heteroclitus [48], the orange-spotted grouper Epinephelus coioides [49] and the ricefield eel Monopterus albus [50]. However, importantly, so far only one gene has been retrieved from either the European or the Japanese eel.…”

Molecular basis and genetic improvement of economically important traits in aquaculture animals

“…In hermaphrodite red-spotted grouper and rice field eel [83,84], the gonad-specific aromatase (cyp19a1a) had been also demonstrated to be expressed by follicular cells of follicular layer around oocytes. The promoter activity analysis showed a number of potential binding sites for some transcriptional factors, such as SOX5, GATA gene family, CREB, AP1, FOXL1, C/EBP, ARE and SF-1, and most of the motifs are conserved among the studied fish species.…”