Slik phosphorylation of talin T152 is crucial for proper talin recruitment and maintenance of muscle attachment in Drosophila

Talin is the major scaffold protein linking integrin receptors with the actin cytoskeleton. In Drosophila, extended talin generates a stable link between the sarcomeric cytoskeleton and the tendon matrix at muscle attachment sites. Here we identify phosphorylation sites on Drosophila talin by mass spectrometry. Talin is phosphorylated in late embryogenesis when muscles differentiate, especially on T152 in the exposed loop of the F1 domain of the talin head. Localization of talin-T150/T152A is reduced at muscle attachment sites and can only partially rescue muscle attachment compared to wild type talin. We also identify Slik as the kinase phosphorylating talin at T152. Slik localizes to muscle attachment sites, and the absence of Slik reduces the localization of talin at muscle attachment sites causing phenotypes similar to talin-T150/T152A. Thus, our results demonstrate that talin phosphorylation by Slik plays an important role in fine-tuning talin recruitment to integrin adhesion sites and maintaining muscle attachment.