Rewitz Kim F, O'Connor Michael B, Gilbert Lawrence I
Department of Science, Systems and Models, Roskilde University, P.O. Box 260, 4000 Roskilde, Denmark.
Insect Biochem Mol Biol. 2007 Aug;37(8):741-53. doi: 10.1016/j.ibmb.2007.02.012. Epub 2007 Mar 5.
The insect molting hormone, 20-hydroxyecdysone (20E), is a major modulator of the developmental processes resulting in molting and metamorphosis. During evolution selective forces have preserved the Halloween genes encoding cytochrome P450 (P450) enzymes that mediate the biosynthesis of 20E. In the present study, we examine the phylogenetic relationships of these P450 genes in holometabolous insects belonging to the orders Hymenoptera, Coleoptera, Lepidoptera and Diptera. The analyzed insect genomes each contains single orthologs of Phantom (CYP306A1), Disembodied (CYP302A1), Shadow (CYP315A1) and Shade (CYP314A1), the terminal hydroxylases. In Drosophila melanogaster, the Halloween gene spook (Cyp307a1) is required for the biosynthesis of 20E, although a function has not yet been identified. Unlike the other Halloween genes, the ancestor of this gene evolved into three paralogs, all in the CYP307 family, through gene duplication. The genomic stability of these paralogs varies among species. Intron-exon structures indicate that D. melanogaster Cyp307a1 is a mRNA-derived paralog of spookier (Cyp307a2), which is the ancestral gene and the closest ortholog of the coleopteran, lepidopteran and mosquito CYP307A subfamily genes. Evolutionary links between the insect Halloween genes and vertebrate steroidogenic P450s suggest that they originated from common ancestors, perhaps destined for steroidogenesis, before the deuterostome-arthropod split. Conservation of putative substrate recognition sites of orthologous Halloween genes indicates selective constraint on these residues to prevent functional divergence. The results suggest that duplications of ancestral P450 genes that acquired novel functions may have been an important mechanism for evolving the ecdysteroidogenic pathway.
昆虫蜕皮激素20-羟基蜕皮酮（20E）是导致蜕皮和变态发育过程的主要调节因子。在进化过程中，选择力保留了编码介导20E生物合成的细胞色素P450（P450）酶的“万圣节”基因。在本研究中，我们研究了膜翅目、鞘翅目、鳞翅目和双翅目全变态昆虫中这些P450基因的系统发育关系。所分析的昆虫基因组各自包含末端羟化酶Phantom（CYP306A1）、Disembodied（CYP302A1）、Shadow（CYP315A1）和Shade（CYP314A1）的单个直系同源基因。在黑腹果蝇中，尽管尚未确定其功能，但“万圣节”基因spook（Cyp307a1）是20E生物合成所必需的。与其他“万圣节”基因不同，该基因的祖先通过基因复制进化为三个旁系同源基因，均属于CYP307家族。这些旁系同源基因的基因组稳定性在不同物种间有所不同。内含子-外显子结构表明，黑腹果蝇Cyp307a1是spookier（Cyp307a2）的mRNA衍生旁系同源基因，spookier是祖先基因，也是鞘翅目、鳞翅目和蚊类CYP307A亚家族基因最接近的直系同源基因。昆虫“万圣节”基因与脊椎动物类固醇生成P—450之间的进化联系表明，它们起源于共同祖先，可能在原口动物—节肢动物分化之前就注定用于类固醇生成。直系同源“万圣节”基因假定底物识别位点的保守性表明对这些残基存在选择性限制，以防止功能分化。结果表明，获得新功能的祖先P450基因的复制可能是蜕皮甾体生成途径进化的重要机制。
