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

Citations Over TimeTop 10% of 2010 papers

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.

Related Papers

• → Cytochrome P450 CYP307A1/Spook: A regulator for ecdysone synthesis in insects(2005)191 cited
• → The ecdysteroidogenic P450 Cyp302a1/disembodied from the silkworm, Bombyx mori , is transcriptionally regulated by prothoracicotropic hormone(2005)118 cited
• → Short-loop negative and positive feedback on ecdysone secretion by prothoracic gland in the tobacco hornworm, Manduca sexta(1989)71 cited
• → Accumulation of 2-deoxy-ecdysteroids in ovaries of the silkworm, Bombyx mori(1981)47 cited
• → Sterols that modify moulting in insects(1996)14 cited