Wang Niannian, Zhang Yinxia, Li Wei, Peng Zhangchuan, Pan Huan, Li Shan, Cheng Tingcai, Liu Chun
State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, 400716, China.
State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, 400716, China; Key Laboratory of Sericultural Biology and Genetic Breeding, Ministry of Agriculture, Southwest University, Chongqing, 400715, China; Cancer Center, Reproductive Medicine Center, Medical Research Institute, Southwest University, 400716, Chongqing, China.
Insect Biochem Mol Biol. 2022 Oct;149:103832. doi: 10.1016/j.ibmb.2022.103832. Epub 2022 Sep 5.
The pigment and structural color of insects play crucial roles in body protection, ecological adaptation, and signal communication. Epidermal melanization is a common and main coloring pattern, which results in broad phenotypic diversity. Melanin is one of the compounds contributing to dark brown-black pigmentation, which is synthesized from dopamine and tyrosine by the melanin metabolism pathway. The Ursa mutant of the silkworm Bombyx mori is a body-color mutant characterized by excessive melanin pigmentation in the larval epidermis. However, the exact gene responsible for this phenotype remains unclear. Here, we performed positional cloning of the gene responsible for Ursa, which was mapped to an 83-kb region on chromosome 14. The genomic region contains a protein-coding gene encoding a transcription factor, which was designated BmSoxD. The mutation site was determined by analysis of nucleotide sequences of the genomic region corresponding to BmSoxD, which identified a 449-bp transposable sequence similar to that of the B. mori transposon Helitron inserted into the sixth intron. BmSoxD was dramatically overexpressed in the epidermis of Ursa at the end of the molting stage compared with that of wild-type B. mori. Overexpression of BmSoxD led to upregulation of genes involved in the melanin metabolism pathway, whereas knocking down BmSoxD via small interfering RNAs blocked melanin pigment production in the larval epidermis. These data indicate that the mutation in BmSoxD is responsible for the Ursa mutant phenotype. We propose that the transposable sequence insertion causes abnormal overexpression of BmSoxD at the molting stage in the Ursa mutant, resulting in excessive melanin synthesis and its accumulation in epidermal cells.
昆虫的色素和结构色在身体保护、生态适应及信号交流中发挥着关键作用。表皮黑化是一种常见且主要的着色模式，可导致广泛的表型多样性。黑色素是导致深棕黑色色素沉着的化合物之一，它通过黑色素代谢途径由多巴胺和酪氨酸合成。家蚕的Ursa突变体是一种体色突变体，其特征是幼虫表皮黑色素过度沉着。然而，导致这种表型的确切基因仍不清楚。在此，我们对负责Ursa的基因进行了定位克隆，该基因被定位到14号染色体上一个83 kb的区域。该基因组区域包含一个编码转录因子的蛋白质编码基因，命名为BmSoxD。通过分析与BmSoxD对应的基因组区域的核苷酸序列确定了突变位点，该分析鉴定出一个449 bp的转座序列，类似于插入到第六内含子中的家蚕转座子Helitron。与野生型家蚕相比，在蜕皮阶段末期，BmSoxD在Ursa的表皮中显著过表达。BmSoxD的过表达导致黑色素代谢途径中相关基因的上调，而通过小干扰RNA敲低BmSoxD则阻断了幼虫表皮中黑色素的产生。这些数据表明BmSoxD中的突变是Ursa突变体表型的原因。我们推测，转座序列插入导致Ursa突变体在蜕皮阶段BmSoxD异常过表达，从而导致黑色素过度合成并在表皮细胞中积累。
