p-oily (op) is a novel mutant of Bombyx mori exhibiting translucent larval integument and male infertility. Elucidation of the causative gene of the op mutant will help understand the genetic mechanism underlying larval integument coloration and male fertility. Using polymorphisms between B. mori and B. mandarina, the op locus was narrowed down to a 375-kb region. Using RNA-seq analysis, we found that op mutants have a frameshift mutation in the KWMTBOMO13770 gene located in the 375-kb region. A database search indicated that this gene is the human cytosolic 5ʹ-nucleotidase II gene (cN-II) homolog in Bombyx, which mediates the conversion of inosine monophosphate (IMP) to inosine, a precursor of uric acid. CRISPR/Cas9-mediated knockout mutants of the Bm-cN-II gene showed translucent integuments, and there appeared translucent larvae in the crosses between knockout moths and +/op moths. Moreover, the translucent phenotype of, and decreased uric acid content in the larval integument caused by the mutations in the Bm-cN-II gene were rescued by oral administration of inosine. These results indicated that the Bm-cN-II gene is responsible for the op phenotype and that the molecular function of the Bm-cN-II gene is the conversion of IMP to inosine. We also discuss the genetic relationship between the Bm-cN-II gene and male fertility.

p-oily（op）是家蚕的新型突变体，具有半透明的幼虫外皮和雄性不育。阐明op突变体的致病基因将有助于理解幼虫外皮颜色和雄性育性的遗传机制。使用之间多态性家蚕和B.桑蚕，所述运算基因座缩小到375-kb的区域。使用RNA序列分析，我们发现op突变体位于375 KB区域的KWMTBOMO13770基因中具有移码突变。数据库搜索表明该基因是人类胞质5'-核苷酸酶II基因（cN-II）的同源基因Bombyx，介导肌苷一磷酸（IMP）转化为肌苷（尿酸的前体）。CRISPR / Cas9介导的Bm-cN-II基因敲除突变体显示出半透明的珠被，在敲除蛾和+ / op蛾之间的杂交中出现了半透明的幼虫。此外，通过肌苷口服可以挽救由Bm-cN-II基因突变引起的半透明表型和幼虫被膜中尿酸含量的降低。这些结果表明Bm-cN-II基因负责op表型和Bm-cN-II的分子功能基因是IMP转化为肌苷。我们还讨论了Bm-cN-II基因与男性生育力之间的遗传关系。