Developmental expression of cytochrome P450 aromatase genes (CYP19a and CYP19b) in zebrafish fry (Danio rerio)

Cytochrome P450 aromatase (CYP19) is the terminal enzyme in the steroidogen ic pathway that converts androgens (e.g., testosterone) into estrogens (e.g ., estradiol). Regulation of this gene dictates the ratio of androgens to e strogens; therefore, appropriate expression of this enzyme is critical for reproduction as well as being pivotal in sex differentiation for most verte brates. It is assumed that most vertebrates have a single C-YP19 gene that is regulated by multiple tissue-specific promoter regions. However, the zeb rafish (Danio rerio) has two genes (CYP19a and CYP19b), each encoding a sig nificantly different protein and possessing its own regulatory mechanism. T he primary purpose of this study was to determine the pattern of expression of each of the CYP19 genes in the developing zebrafish. A fluorescent-base d method of real-time, quantitative RT-PCR provided the sensitivity and spe cificity to determine transcript abundance in single embryos/juveniles harv ested at days 0 through 41 days post-fertilization (dpf), which encompasses the developmental events of sex determination and gonadal differentiation. CYP19 transcripts could be detected as early as 3 or 4 dpf, (CYP19a and CY P19b, respectively) and peak abundance was detected on day five. In general , the CYP19 genes differed significantly in the ontogeny of their expressio n. In most cases, the gonadal form of CYP19 (CYP19a) was more abundant than the brain form (CYP19b); however, unlike CYP19a, the pattern of CYP19b exp ression could be clearly segregated into two populations, suggesting an ass ociation with sex differentiation. Pharmacological steroids (ethinylestradi ol and 17 alpha -methyltestosterone) enhanced the expression of the CYP19b gene at all three days examined (4, 6, and 10 dpf). These data suggest that the timely and appropriate expression of CYP19 is important in development and that the expression of CYP19b (the "extra-gonadal" form) may be associ ated with sexual differentiation if not sexual determination. J. Exp. Zool. 290:475-483, 2001. (C) 2001 Wiley-Liss, Inc.