The ALP-Enigma Protein ALP-1 Functions in Actin Filament Organization to Promote Muscle Structural Integrity in Caenorhabditis elegans

Mutations that affect the Z-disk-associated ALP-Enigma proteins have been linked to human muscular and cardiac diseases. Despite their clear physiological significance for human health, the mechanism of action of ALP-Enigma proteins is largely unknown. In Caenorhabditis elegans, the ALP-Enigma protein family is encoded by a single gene, alp-1; thus C. elegans provides an excellent model to study ALP-Enigma function. Here we present a molecular and genetic analysis of ALP-Enigma function in C. elegans. We show that ALP-1 and alpha-actinin colocalize at dense bodies where actin filaments are anchored and that the proper localization of ALP-1 at dense bodies is dependent on alpha-actinin. Our analysis of alp-1 mutants demonstrates that ALP-1 functions to maintain actin filament organization and participates in muscle stabilization during contraction. Reducing alpha-actinin activity enhances the actin filament phenotype of the alp-1 mutants, suggesting that ALP-1 and alpha-actinin function in the same cellular process. Like alpha-actinin, alp-1 also interacts genetically with a connectin/titin family member, ketn-1, to provide mechanical stability for supporting body wall muscle contraction. Taken together, our data demonstrate that ALP-1 and alpha-actinin function together to stabilize actin filaments and promote muscle structural integrity.