Cloning and characterization of estrogen hydroxylase (cyp1a1 and cyp1b1) genes in the stinging catfish Heteropneustes fossilis and induction of mRNA expression during final oocyte maturation

Estrogen hydroxylases (EHs) are cytochrome P450 Family 1 (Cyp1, Clan 2) proteins involved in estrogen hydroxylations at 2-, 4- or 16- carbon positions to form catecholestrogens. EHs are encoded by CYP1A1, CYP1A2 and CYP1B1 in mammals. In the catfish Heteropneustes fossilis, cyp1a1 and cyp1b1 cDNAs were cloned and characterized from liver and ovary. The cyp1a1 cDNA is 2071 bp long and codes for a 518 amino acids (aa) long protein. The cloned cyp1b1 cDNA is 1927 bp long and codes for a 509 residue protein. The deduced proteins clustered distinctly into teleost Cyp1a1 and Cyp1b1 clades, distinct from the tetrapod clusters and featured common function domains and homology with other teleost proteins. In the qPCR assay, the transcripts were the most abundant in the liver, followed by brain and ovary, and moderate in gill, kidney and muscle. Evidence was presented to show the involvement of the genes in reproduction. Expression of brain and ovarian transcripts showed significant seasonal variations with the highest abundance in the spawning phase. In situ hybridization showed the transcripts in the follicular layer (theca and granulosa) of the ovarian follicles. Periovulatory changes in the expression cyp1a1 and cyp1b1 were obtained during final oocyte maturation (FOM) and ovulation induced by human chorionic gonadotropin (hCG), both in vivo and in vitro, and by 2-hydroxyestradiol-17β (catecholestrogen) in vitro. In the brain, the transcript levels increased with time but in the ovary, the increase was maximal at 16 h and decreased at 24 h. The periovulatory activation of the cyp1 genes was reported in this study and discussed on the basis of complex regulation of FOM and ovulation.