Suppression of brain aromatase decreases the expression of dopaminergic neuron in early development of zebrafish

Cytochrome P450 aromatase, the product of the CYP19A1 gene, is a key enzyme in estrogen biosynthesis. Most teleost fish have two distinct isoforms of aromatase, ovarian aromatase (AroA) and brain aromatase (AroB) encoded by cyp19a1a and cyp19a1b, respectively. Although aromatase is expressed in the brain across vertebrates, it is present at uniquely high levels in teleost fish, where its role in brain development is not fully understood. Therefore, in this study, the effects of exposure to fadrozole (Fad), an aromatase inhibitor, and knockdown of the AroB gene by using a morpholino antisense oligonucleotide (MO) on the expression of dopaminergic (DAergic) neurons were investigated in zebrafish embryos and larvae. Fad exposure decreased the expression of tyrosine hydroxylase (TH) as detected by immunostaining at 48 h post fertilization (hpf) and impaired locomotor activities including tactile response at 72 hpf and swimming distance at 6 days post fertilization (dpf), which was reversed by the addition of 17β-estradiol (E2). Additionally, in real-time PCR analysis, Fad exposure significantly reduced the gene expression of TH (th1 and th2), AroB, and estrogen receptors (esr2a and esr2b), whereas the expression of another estrogen receptor gene, esr1, and the AroA gene remained unchanged. Similarly, AroB-MO injection decreased immunostained TH expression, which was rescued by co-injection with AroB mRNA or the addition of E2. AroB-MO injection reduced locomotor activity, which was partially restored by the addition of E2 or L-dopa. In conclusion, the results indicate that brain-formed estrogen plays a significant role in the maintenance of DAergic neurons in the early development of zebrafish.