title: Non-molting glossy/shroud encodes a short-chain dehydrogenase/reductase that functions in the 'Black Box' of the ecdysteroid biosynthesis pathway.
abstract: In insects, the precise timing of molting and metamorphosis is strictly guided by a principal steroid hormone, ecdysone. Among the multiple conversion steps for synthesizing ecdysone from dietary cholesterol, the conversion of 7-dehydrocholesterol to 5beta-ketodiol, the so-called 'Black Box', is thought to be the important rate-limiting step. Although a number of genes essential for ecdysone synthesis have recently been revealed, much less is known about the genes that are crucial for functioning in the Black Box. Here we report on a novel ecdysteroidgenic gene, non-molting glossy (nm-g)/shroud (sro), which encodes a short-chain dehydrogenase/reductase. This gene was first isolated by positional cloning of the nm-g mutant of the silkworm Bombyx mori, which exhibits a low ecdysteroid titer and consequently causes a larval arrest phenotype. In the fruit fly, Drosophila melanogaster, the closest gene to nm-g is encoded by the sro locus, one of the Halloween mutant members that are characterized by embryonic ecdysone deficiency. The lethality of the sro mutant is rescued by the overexpression of either sro or nm-g genes, indicating that these two genes are orthologous. Both the nm-g and the sro genes are predominantly expressed in tissues producing ecdysone, such as the prothoracic glands and the ovaries. Furthermore, the phenotypes caused by the loss of function of these genes are restored by the application of ecdysteroids and their precursor 5beta-ketodiol, but not by cholesterol or 7-dehydrocholesterol. Altogether, we conclude that the Nm-g/Sro family protein is an essential enzyme for ecdysteroidogenesis working in the Black Box.
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Ibaraki 305-8572, Japan. ryusuke-niwa@umin.ac.jp
authors.forename: Ryusuke
authors.initials: R
authors.lastname: Niwa
authors.forename: Toshiki
authors.initials: T
authors.lastname: Namiki
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Ito
authors.forename: Yuko
authors.initials: Y
authors.lastname: Shimada-Niwa
authors.forename: Makoto
authors.initials: M
authors.lastname: Kiuchi
authors.forename: Shinpei
authors.initials: S
authors.lastname: Kawaoka
authors.forename: Takumi
authors.initials: T
authors.lastname: Kayukawa
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Banno
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Fujimoto
authors.forename: Shuji
authors.initials: S
authors.lastname: Shigenobu
authors.forename: Satoru
authors.initials: S
authors.lastname: Kobayashi
authors.forename: Toru
authors.initials: T
authors.lastname: Shimada
authors.forename: Susumu
authors.initials: S
authors.lastname: Katsuma
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Shinoda
mesh_terms: D000818:Animals; D012831:Bombyx / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D003684:Dehydrocholesterols / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D004440:Ecdysone / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D026461:Ecdysteroids / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D018978:Molting / Q000235:genetics*; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism
chemical_list: D003684:Dehydrocholesterols; D026461:Ecdysteroids; D004440:Ecdysone; C016705:7-dehydrocholesterol; D010088:Oxidoreductases