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Chitinase 7 (TcCHT7) is required for cuticle lamina organization and chitin deposition in Tribolium castaneum
Insect chitinases (CHTs), an extracellular enzyme, belong to family 18 glycosyl hydrolases that hydrolyze chitin by an endo-type manner. In insect genomes, there are a large number of genes encoding CHT-like proteins, and they have been classified into eleven groups based on phylogenetic analysis. In this study, we have investigated functions of a group III chitinase (TcCHT7) in Tribolium castaneum. Although, unlike most insect CHTs, TcCHT7 contains a predicted transmembrane segment in N-terminal, immunohistochemical analysis reveals that it is localized in the newly forming procuticle, suggesting that TcCHT7 is released from the plasma membrane of underlying epidermal cells. RNAi for TcCHT7 does not affect on any types of molting. However the resulting pupae and adults fail to undergo wing-expansion and abdominal contraction. In addition, TcCHT7-deficient insects exhibit ultrastructural defects in both rigid (e.g. elytron) and soft (e.g. hindwing) cuticles. These results demonstrate that functional importance of TcCHT7 in the formation of the rigid and soft cuticles of the beetle.
