Dynamic assembly of cuticular proteins into the elytral procuticle of Tribolium castaneum

This study is focused on the functional characterization of several Tribolium castaneum genes that encode Cuticular Proteins Analogous to Peritrophins (CPAP) and their assembly into the developing cuticle. These proteins contain one or three copies of the chitin-binding domain, ChtBD2, with its six characteristically spaced cysteine residues. CPAP genes are expressed exclusively in cuticle-forming tissues and have been classified into two families, CPAP1 and CPAP3. The CPAP1 family has 10 members, each with one ChtBD2 domain, while the CPAP3 family has eight members, each with three ChtBD2 domains. Individual members of the CPAP1 and CPAP3 gene families have distinct developmental patterns of expression. Many of these genes are essential for development, molting, cuticle integrity or proper locomotion and fecundity. RNA interference (RNAi) targeting TcCPAP1-C, TcCPAP1-H, TcCPAP1-J or TcCPAP3-C transcripts results in death at the pharate adult stage of development. RNAi for other CPAP3 genes results in different developmental defects, including abnormal elytra or hindwings, abnormal gait, and/or adult/embryonic mortality. Immunohistochemistry and confocal microscopic analysis of multiple developmental stages of wild type insects shows that TcCPAP3-C protein is confined to  the assembly zone near the cell surface. These results provide experimental support for specialization in the functions of several CPAP proteins in T. castaneum and provide a biological rationale for the conservation of orthologs within these CPAP families of proteins in insects of different orders. Many of these proteins serve essential and non-redundant functions in maintaining the structural integrity of the cuticle.

Supported by grants from the National Science Foundation (IOS-1022227) and Kansas Idea Network for Biomedical Research Excellence (P20RR016475, P20GM103418)