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

Abstract

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.

Facioscapulohumeral muscular dystrophy region gene-1 (FRG-1) is an actin-bundling protein associated with muscle-attachment sites

“…These data also place FRG-1 distal to PAT-3 and the basal lamina, where ALP1a and ATN-1 accumulate; actin thin filaments attach to these densebody projections (Fig. 4M) (Han and Beckerle, 2009), further supporting FRG-1 as a component of the actin-associated machinery of the dense body.…”

“…4G-I). ALP-1a is a conserved dense-body protein that interacts with a-actinin (ATN-1), a conserved actin-bundling protein similarly localized to the dense bodies and distal to the sarcolemma (Barstead et al, 1991;Han and Beckerle, 2009;Xia et al, 1997). P myo-3 ::frg-1::yfp adult animals showed a cytoplasmic dense-body-like pattern (Fig.…”

“…Finally, we evaluated FRG-1 localization in the atn-1(ok84) mutant (Fig. 4J-L), which contains a 1.1 kb deletion within atn-1 and is predicted to be a null mutant (Han and Beckerle, 2009). In atn-1(ok84) mutants, the dense bodies are less well defined, but retain a periodic punctate appearance following PAT-3 staining (Fig.…”

Deletion of Drosophila muscle LIM protein decreases flight muscle stiffness and power generation

“…Proteins that cross-link actin at the Z-disk are a major contributor to Z-disk stiffness (28). While the major actin cross-linking protein in the Z-disk is ␣-actinin, genetic and biochemical studies indicate that other Z-disk-associated proteins also have important roles in maintaining Z-disk structure and function (17,50,55).Muscle LIM protein (MLP) is a LIM domain protein found at the Z-disk that associates with several other Z-disk proteins including ␣-actinin (27) and Titin via Tcap/telethonin (22). Mice lacking MLP develop dilated cardiomyopathy (3), and mutations in human MLP are linked to familial hypertrophic cardiomyopathy (2,5,13,22,35,38,49), indicating its importance for maintaining normal cardiac function.…”

“…Proteins that cross-link actin at the Z-disk are a major contributor to Z-disk stiffness (28). While the major actin cross-linking protein in the Z-disk is ␣-actinin, genetic and biochemical studies indicate that other Z-disk-associated proteins also have important roles in maintaining Z-disk structure and function (17,50,55).…”