Knockdown of BmorCPR67 gene disrupts prepupal–pupal transition of silkworm Bombyx mori by thinning the endocuticle

The cuticle of insects serves as a crucial organ for preserving body
composition, protecting against pathogen invasion, and retaining moisture
in their bodies. Cuticular proteins (CPs) are the main constituents of
insect cuticles and interact with chitin to form cuticle structural
framework and mechanical properties. In this study, we investigated the
role of a cuticular protein with R&R consensus (CPR), BmorCPR67, a
member of the RR-2 subfamily, during the prepupal-to-pupal transition in
Bombyx mori. The BmorCPR67 gene exhibited high expression levels during
the prepupal stage, with the highest expression detected in the epidermis
of the day-1 pupa in B. mori. And the expression of BmorCPR67 gene was
induced by 20-hydroxyecdysone (20E). Chitin-binding assays indicated that
the BmorCPR67 protein selectively binds to crystalline chitin and chitosan
but not to amorphous chitin. Silencing BmorCPR67 gene disrupted the
molting process from prepupa to pupa, resulting in silkworms mortality.
Furthermore, knockdown of BmorCPR67 altered the expression profiles of key
genes involved in chitin metabolism. Notably, significant thinning of the
endocuticle was observed 48 to 96 h after siRNA injection in
BmorCPR67-silenced silkworms. These findings highlight the critical role
of BmorCPR67 in cuticle development during the prepupal-to-pupal
transition in B. mori, contributing to our understanding of the functions
of CPs in insect metamorphosis.