Jm. Trant et al., Developmental expression of cytochrome P450 aromatase genes (CYP19a and CYP19b) in zebrafish fry (Danio rerio), J EXP ZOOL, 290(5), 2001, pp. 475-483
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.