Abstract
We show that interfering with insect chitin deacetylation by down-regulation of specific chitin deacetylase (CDA) isoforms, belonging to subfamily group I, causes breakage of the chitinous internal tendon cuticle at the femur–tibia joint, muscle detachment from both internal and external tendon cells, and defective locomotion. Our studies reveal a previously unrecognized role of CDA-like proteins in cooperation with zona pellucida domain-containing proteins in musculoskeletal connectivity, maintenance of tendon cell microtubule integrity, muscle force transmission, limb movement, and locomotion. We propose an essential function for group I CDAs, which are highly conserved among insect and other arthropod species, in invertebrate musculoskeletal connectivity involving partially deacetylated chitin in the extracellular matrix overlying the tendon cells.
Muscle attachment sites (MASs, apodemes) in insects and other arthropods involve specialized epithelial cells, called tendon cells or tenocytes, that adhere to apical extracellular matrices containing chitin. Here, we have uncovered a function for chitin deacetylases (CDAs) in arthropod locomotion and muscle attachment using a double-stranded RNA-mediated gene-silencing approach targeted toward specific CDA isoforms in the red flour beetle, Tribolium castaneum (Tc). Depletion of TcCDA1 or the alternatively spliced TcCDA2 isoform, TcCDA2a, resulted in internal tendon cuticle breakage at the femur–tibia joint, muscle detachment from both internal and external tendon cells, and defective locomotion. TcCDA deficiency did not affect early muscle development and myofiber growth toward the cuticular MASs but instead resulted in aborted microtubule development, loss of hemiadherens junctions, and abnormal morphology of tendon cells, all features consistent with a loss of tension within and between cells. Moreover, simultaneous depletion of TcCDA1 or TcCDA2a and the zona pellucida domain protein, TcDumpy, prevented the internal tendon cuticle break, further supporting a role for force-dependent interactions between muscle and tendon cells. We propose that in T. castaneum, the absence of N-acetylglucosamine deacetylation within chitin leads to a loss of microtubule organization and reduced membrane contacts at MASs in the femur, which adversely affect musculoskeletal connectivity, force transmission, and physical mobility.
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