Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo, 113-8657, Japan.
Insect Biochem Mol Biol. 2023 Aug;159:103982. doi: 10.1016/j.ibmb.2023.103982. Epub 2023 Jun 23.
The dilute black (bd) of the silkworm Bombyx mori is a recessive mutant that produces a grayish-black color in the larval integument, instead of the characteristic white color found in wild-type larvae. In addition, eggs produced by bd females are sterile due to a deficiency in the micropylar apparatus. We identified candidate genes responsible for the bd phenotype using publicly available RNA-seq data. One of these candidate genes was homologous to the maternal gene required for meiosis (mamo) of Drosophila melanogaster, which encodes a broad-complex, tramtrack, and bric-à-brac-zinc finger (BTB-ZF) transcription factor essential for female fertility. In three independent bd strains, the expression of the B. mori mamo (Bmmamo) was downregulated in the larval integument. Using a CRISPR/Cas9-mediated knockout strategy, we found that Bmmamo knockout mutants exhibit a grayish-black color in the larval integument and female infertility. Moreover, larvae obtained from the complementation cross between bd/+ mutants and heterozygous knockouts for the Bmmamo also exhibited a grayish-black color, indicating that Bmmamo is responsible for the bd phenotype. Gene expression analysis using Bmmamo knockout mutants suggested that the BmMamo protein suppresses the expression of melanin synthesis genes. Previous comparative genome analysis revealed that the Bmmamo was selected during silkworm domestication, and we found that Bmmamo expression in the larval integument is higher in B. mori than in the wild silkworm B. mandarina, suggesting that the Bmmamo is involved in domestication-associated pigmentation changes of the silkworm.
家蚕的稀释黑（bd）是一种隐性突变体，其幼虫表皮呈现出灰黑色，而不是野生型幼虫的典型白色。此外，bd 雌蚕所产的卵由于微管器官缺陷而不育。我们使用公开的 RNA-seq 数据鉴定了导致 bd 表型的候选基因。其中一个候选基因为 Drosophila melanogaster 减数分裂所需的母性基因（mamo）的同源物，该基因编码一种广泛复合物、tramtrack 和 bric-à-brac-zinc finger（BTB-ZF）转录因子，对雌性育性至关重要。在三个独立的 bd 品系中，B. mori mamo（Bmmamo）在幼虫表皮中的表达下调。使用 CRISPR/Cas9 介导的敲除策略，我们发现 Bmmamo 敲除突变体在幼虫表皮呈现灰黑色，并且雌性不育。此外，bd/+ 突变体与 Bmmamo 杂合敲除体之间的互补交叉获得的幼虫也呈现灰黑色，表明 Bmmamo 是 bd 表型的原因。使用 Bmmamo 敲除突变体的基因表达分析表明，BmMamo 蛋白抑制黑色素合成基因的表达。先前的比较基因组分析表明，Bmmamo 在蚕的驯化过程中被选择，我们发现 Bmmamo 在幼虫表皮中的表达在家蚕中比在野蚕 B. mandarina 中更高，表明 Bmmamo 参与了蚕的驯化相关的色素变化。
