Parvin is essential for indirect flight muscle (IFM) performance and Zasp52 localisation to the Z-disc in Drosophila...

The integrin-associated proteins (IAPs) function in a tightly regulated and coordinated manner to maintain the complex cytoarchitecture at the myotendinous junctions (MTJs) of Drosophila indirect flight muscles (IFMs). Parvin, a conserved but less explored IAP, forms a ternary complex with ILK and PINCH (the IPP complex). Although the IPP complex is functionally conserved, playing a central role in integrin-mediated adhesion, its individual components may also exert independent roles. The present study investigates parvin as a critical regulator of IFM function and sarcomeric integrity. Downregulation of parvin in IFM leads to altered sarcomere organisation and lowered accumulation of essential thin filament genes, including Act88F, wupA, up, TpnC4, and TM2 transcripts. Furthermore, Z-disc-associated proteins such as Zasp52 and its binding partner α-actinin, which are vital for myofibril stability, showed markedly reduced expression in parvin-deficient muscles. Notably, Zasp52 failed to localise to the Z-discs in IFMs, despite being detectable in leg muscles, suggesting tissue-specific mislocalisation. The expression of sallimus, a titin orthologue contributing to muscle elasticity, remained unchanged. Our findings underscore parvin's essential role in preserving IFM ultrastructure and function. We also emphasise the importance of maintaining the stoichiometric balance within the IPP complex-including its extended member Ras suppressor 1 (RSU1)-for proper muscle performance. Additionally, perturbation of parvin expression in a tissue-specific manner revealed its broader role in fly viability and muscle-driven behaviours, including larval locomotion and leg muscle function. Collectively, this study positions parvin as a pivotal component in maintaining muscle integrity across multiple muscle types in Drosophila.