Partial Deletion in the Cuticular Protein Gene BmorCPR2 Results in a Body Shape Mutant in Silkworm, Bombyx Mori L. (lepidoptera: Bombycidae)

The Bombyx mori L. (Lepidoptera: Bombycidae) is a significant economic insect used for silk production. A novel body shape mutant, stony^sunken (st^sk), that exhibits a sunken intersegmental membrane was isolated from the wild type of st^sk (WT-n08). Investigation indicated that the mutation had no significant effect on its growth and development. To elucidate the molecular mechanism underlying this body shape mutant, genetic analysis, positional cloning, and the CRISPR/Cas9 gene editing system were performed. Genetic analysis demonstrated that the mutant trait in st^sk is controlled by an autosomal recessive gene and follows Mendelian inheritance. Positional cloning showed that a putative cuticular protein gene, BmorCPR2 on chromosome 8, was the candidate gene. Sequencing analysis revealed partial deletion of BmorCPR2 exon 2 and intron 2 sequences occurred and subsequently resulted in the premature termination of gene expression. Knock-out of BmorCPR2 using the CRISPR/Cas9 gene editing system led to the sunken intersegmental membrane phenotype. These findings highlight the essential role of BmorCPR2 in silkworm cuticular formation, providing a foundation for further research on cuticular protein function.