title: A novel type of P450c17 lacking the lyase activity is responsible for C21-steroid biosynthesis in the fish ovary and head kidney.
abstract: Cytochrome P450c17 is the single enzyme that mediates the 17 alpha-hydroxylase and 17, 20 lyase activities during the biosynthesis of steroid hormones in the gonads and adrenal gland. However, the mechanism underlying its dual action continues to be a controversy in the field of steroidogenesis in fish. In an attempt to resolve this issue, we identified a novel type of P450c17 (P450c17-II) by an in silico analysis from the genomes of six fish species. We cloned P450c17-II from tilapia and medaka, and comparison with the conventional P450c17-I revealed that they differ in gene structure and enzymatic activity. Enzymatic assays by thin-layer chromatography revealed that P450c17-II possesses only the 17 alpha-hydroxylase activity without any 17, 20 lyase activity, unlike P450c17-I, which has both these activities. In testis, both P450c17-I and -II express in the interstitial cells. Remarkable differences, revealed by in situ hybridization, in the expression patterns of the P450c17-I and -II in the ovary and head kidney of tilapia during various stages of development strongly suggest that P450c17-I is responsible for the synthesis of estradiol-17beta in the ovary, whereas P450c17-II is required for the production of C21 steroids such as cortisol in the head kidney. More interestingly, a temporally controlled switching is observable in the expression of these two genes during the steroidogenic shift from estradiol-17beta to the C21 steroid, 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (maturation-inducing hormone of fish oocytes) in the fish ovary, revealing a role for P450c17-II in the production of hormones that induce oocyte maturation in fish.
authors.affiliation: Laboratory of Reproductive Biology, National Institute for Basic Biology, Graduate University for Advanced Studies, Okazaki 444-8585, Japan.
authors.forename: Lin-Yan
authors.initials: LY
authors.lastname: Zhou
authors.forename: De-Shou
authors.initials: DS
authors.lastname: Wang
authors.forename: Tohru
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Akihiro
authors.initials: A
authors.lastname: Yano
authors.forename: Bindhu
authors.initials: B
authors.lastname: Paul-Prasanth
authors.forename: Aya
authors.initials: A
authors.lastname: Suzuki
authors.forename: Fumie
authors.initials: F
authors.lastname: Sakai
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Nagahama
mesh_terms: D000818:Animals; D002645:Chickens; D005260:Female; D029941:Fish Proteins / Q000235:genetics*; D005399:Fishes; D005618:Fresh Water; D016678:Genome; D007668:Kidney / Q000201:enzymology*; D008969:Molecular Sequence Data; D010053:Ovary / Q000201:enzymology*; D013254:Steroid 17-alpha-Hydroxylase / Q000235:genetics* / Q000378:metabolism; D013256:Steroids / Q000096:biosynthesis*; D015027:Zebrafish
chemical_list: D029941:Fish Proteins; D013256:Steroids; D013254:Steroid 17-alpha-Hydroxylase