Non-molting glossy/shroud encodes a short-chain dehydrogenase/reductase that functions in the 'Black Box' of the ecdysteroid biosynthesis pathway

Ryusuke Niwa, Toshiki Namiki, Katsuhiko Ito, Yuko Shimada-Niwa, Makoto Kiuchi, Shinpei Kawaoka, Takumi Kayukawa, Yutaka Banno, Yoshinori Fujimoto, Shuji Shigenobu, Satoru Kobayashi, Toru Shimada, Susumu Katsuma, Tetsuro Shinoda

Research output: Contribution to journalArticlepeer-review

112 Citations (Scopus)

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 5β-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 5β-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.

Original languageEnglish
Pages (from-to)1991-1999
Number of pages9
JournalDevelopment
Volume137
Issue number12
DOIs
Publication statusPublished - Jun 15 2010

All Science Journal Classification (ASJC) codes

  • Molecular Biology
  • Developmental Biology

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