Distinct cytochrome P450 aromatase isoforms in zebrafish (Danio rerio) brain and ovary are differentially programmed and estrogen regulated during early development

As a first step toward understanding estrogen's role in neurodevelopment, a PCR cloning strategy was used to isolate complementary DNAs encoding two d istinct cytochrome P450 aromatase isoforms in adult zebrafish (Danio rerio) brain and ovary (termed P450aromB and P450aromA, respectively). Sequence a nd phylogenetic analysis showed that the zebrafish P450arom forms are ortho logs of previously identified cyp19b and cyp19a. genes in goldfish. On Nort hern blots, a single 4.4-kb transcript of the P450aromB subtype was identif ied in brain, and a 2.1-kb transcript of the P450aromA subtype in ovary, bu t RT-PCR showed a degree of overlapping expression. Both messenger RNA (mRN A) forms were detected in unfertilized eggs and 1.5 hpf (cleavage stage) em bryos but declined by 12 hpf, indicating maternal transfer. A secondary ris e in mRNAs between 12-24 hpf indicated the onset of embryonic cyp19b and -a lpha transcription. Both mRNA species accumulated progressively to 120 hpf (early larval stage), but the relative magnitude and pattern of change was isoform specific. Estradiol (E-2,1 muM) advanced and amplified the developm entally programmed accumulation of P450aromB mRNA, and ICI164.384 decreased expressed levels, implying blockade of an endogenous estrogen mediated reg ulatory component. Conversely, E-2 had no effect or decreased P450aromA mRN A. The early embryonic expression of P450aromB and P450aromA isoforms, and differences in developmental programming and estrogen regulation, imply ind ependent regulatory mechanisms and unique functions during major morphogene tic and differentiative events.