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 a mutated version of Talin (Talin-T150/T152A) is reduced at muscle attachment sites and can only partially rescue muscle attachment compared with 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.

Muscle type-specific expression of Zasp52 isoforms in Drosophila.

Zasp52 is a member of the PDZ-LIM domain protein family in Drosophila, which comprises Enigma, ENH, ZASP, Alp, CLP36, RIL, and Mystique in vertebrates. Drosophila Zasp52 colocalizes with integrins at myotendinous junctions and with α-actinin at Z-disks, and is required for muscle attachment as well as Z-disk assembly and maintenance. Here we document 13 Zasp52 splice variants giving rise to six different LIM domains. We demonstrate stage- and tissue-specific expression in different muscle types for Zasp52 isoforms encoding different LIM domains. In particular, LIM1b is expressed only in heart muscle and certain somatic muscles, implying muscle-specific functions in Z-disk assembly or maintenance.