Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
Development. 2010 Dec;137(23):4083-90. doi: 10.1242/dev.053678.
The pigmentation of insects has served as an excellent model for the study of morphological trait evolution and developmental biology. The melanism (mln) mutant of the silkworm Bombyx mori is notable for its strong black coloration, phenotypic differences between larval and adult stages, and its widespread use in strain selection. Here, we report the genetic and molecular bases for the formation of the mln morphological trait. Fine mapping revealed that an arylalkylamine N-acetyltransferase (AANAT) gene co-segregates with the black coloration patterns. Coding sequence variations and expression profiles of AANAT are also associated with the melanic phenotypes. A 126 bp deletion in the mln genome causes two alternatively spliced transcripts with premature terminations. An enzymatic assay demonstrated the absolute loss of AANAT activity in the mutant proteins. We also performed RNA interference of AANAT in wild-type pupae and observed a significant proportion of adults with ectopic black coloration. These findings indicate that functional deletion of this AANAT gene accounts for the mln mutation in silkworm. AANAT is also involved in a parallel melanin synthesis pathway in which ebony plays a role, whereas no pigmentation defect has been reported in the Drosophila model or in other insects to date. To the best of our knowledge, the mln mutation is the first characterized mutant phenotype of insects with AANAT, and this result contributes to our understanding of dopamine metabolism and melanin pattern polymorphisms.
昆虫的色素沉着一直是研究形态特征进化和发育生物学的极好模型。家蚕的黑化（mln）突变体以其强烈的黑色着色、幼虫和成虫阶段之间的表型差异以及在品系选择中的广泛应用而引人注目。在这里，我们报告了 mln 形态特征形成的遗传和分子基础。精细定位表明，芳烷基胺 N-乙酰转移酶（AANAT）基因与黑色着色模式共分离。AANAT 的编码序列变异和表达谱也与黑色素表型相关。mln 基因组中的 126 bp 缺失导致两个具有过早终止的选择性剪接转录本。酶促测定表明突变蛋白的 AANAT 活性完全丧失。我们还在家蚕蛹中进行了 AANAT 的 RNA 干扰，并观察到相当一部分成虫出现异位黑色着色。这些发现表明，该 AANAT 基因的功能缺失导致了家蚕的 mln 突变。AANAT 还参与了黑檀木发挥作用的平行黑色素合成途径，而迄今为止，在果蝇模型或其他昆虫中尚未报道过色素沉着缺陷。据我们所知，mln 突变是第一个具有 AANAT 的昆虫表型突变，这一结果有助于我们理解多巴胺代谢和黑色素模式多态性。
