Drosophila Transglutaminase preserves the integrity of muscle attachments with and without mechanical strain

The strict control, yet dynamic nature of adhesive structures that form in the extracellular environment are crucial for the development and homoeostasis of multicellular organisms. A gradual increase in the strength of the myotendinous junction (MTJ) occurs as ligands accumulate in the extracellular matrix (ECM) and bind to opposing integrin complexes at muscle junction interfaces. Although proteomic studies of the muscle-tendon junction in mice and humans have revealed the complexity of protein classes in this extracellular environment, the functions of many ECM proteins remain elusive. To fill this gap in knowledge, we performed a sensitized genetic screen to expose MTJ-relevant genes in Drosophila melanogaster whose functions might be redundant or sensitive to mechanical strain. Aside from the expected ECM proteins that comprise the basement membrane, we uncovered functional roles for other classes of ECM-affiliated proteins. Here, we follow up on the sole ortholog of Transglutaminase (Tg) encoded in the Drosophila genome. Either Tg RNAi knockdown or expression of catalytically inactive Tg causes detachment of direct muscle-cuticle attachments at different stages in development. In adults, MTJ stability is further weakened in response to increased mechanical tension. These studies together describe a previously unappreciated role for Tg crosslinking in preserving muscle attachments in response to tension.