昆虫是世界上种类最多的高等生物类群，已经鉴定的种类达到100多万种以上。它们多样性的分化机制被认为是高度适应环境和长期进化的结果，但产生的原因和内在遗传机制并不清楚。为了研究这种机制，研究人员尝试研究多种突变基因及其对应的表型。

昆虫的黑化现象被认为是理想的模型之一。在鳞翅目昆虫的代表种类家蚕长期的饲养和保存过程中，研究人员已收集了多种类型的突变体。其中，家蚕黑化突变体，melanism(mln)具有良好的表型特征。成虫期，全体显著黑化，在幼虫期只有头部、前足和尾斑局部黑化。

中科院上海生科院植生生态所黄勇平研究组利用他们已经构建的家蚕基因定位克隆体系，完成了家蚕体色突变体mln的定位克隆，并通过表达谱和表型之间的关联分析、靶标基因的系统进化分析、突变体酶活检测和靶标基因干涉，验证了结论的可靠性，并结合相关文献报道对昆虫的体色决定机制进行了讨论。研究结果发现家蚕的一种乙酰转移酶基因的突变导致了体色突变体mln的形成——突变体中该基因位点在编码区的缺失产生移码突变，失去活性的突变体乙酰转移酶无法在黑色素代谢途径中发挥正常作用，导致黑色素的过量沉积。家蚕mln突变体是发现的第一个关于乙酰转移酶参与昆虫体色决定的表型证据，而在此之前，乙酰转移酶是整个黑色素代谢途径中唯一一个还没有报道对应表型的酶。

此项研究成果得到了科技部、国家自然科学基金的资助。

英文摘要：

Development. 2010 Dec;137(23):4083-90.

Disruption of an N-acetyltransferase gene in the silkworm reveals a novel role in pigmentation.
Zhan S, Guo Q, Li M, Li M, Li J, Miao X, Huang Y.

Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, 200032, China.

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.