UNC-87, a calponin-related protein in C. elegans , antagonizes ADF/cofilin-mediated actin filament dynamics

Yamashiro

2008

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The somatic gonad of the nematode Caenorhabditis elegans contains a myoepithelial sheath, which surrounds oocytes and provides contractile forces during ovulation. Contractile apparatuses of the myoepithelial-sheath cells are non-striated and similar to those of smooth muscle. We report the identification of a specific isoform of actin depolymerizing factor (ADF)/cofilin as an essential factor for assembly of contractile actin networks in the gonadal myoepithelial sheath. Two ADF/cofilin isoforms, UNC-60A and UNC-60B, are expressed from the unc-60 gene by alternative splicing. RNA interference of UNC-60A caused disorganization of the actin networks in the myoepithelial sheath. UNC-60B, which is known to function in the body-wall muscle, was not necessary or sufficient for actin organization in the myoepithelial sheath. However, mutant forms of UNC-60B with reduced actin-filament-severing activity rescued the UNC-60A-depletion phenotype. UNC-60A has a much weaker filament-severing activity than UNC-60B, suggesting that an ADF/cofilin with weak severing activity is optimal for assembly of actin networks in the myoepithelial sheath. By contrast, strong actin-filament-severing activity of UNC-60B was required for assembly of striated myofibrils in the body-wall muscle. Our results suggest that an optimal level of actin-filament-severing activity of ADF/cofilin is required for assembly of actin networks in the somatic gonad.

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Section: Discussionsupporting

confidence: 64%

Essential role of ADF/cofilin for assembly of contractile actin networks in the C. elegans somatic gonad

Yamashiro

2008

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“…Studies in C. elegans striated muscle show that tropomyosin (LEV-11) (Ono and Ono, 2002;Yu and Ono, 2006) and UNC-87, a calponin-like protein (Yamashiro et al, 2007), protect actin filaments from severing by ADF/cofilin, while actin-interacting protein 1 (AIP1) enhances disassembly of ADF/cofilin-bound actin filaments (Mohri et al, 2006;Mohri and Ono, 2003;Ono, 2001;Ono et al, 2011). Tropomodulin (UNC-94/TMD-1) caps the pointed ends of actin filaments and protects them from ADF/cofilin-mediated depolymerization .…”

Section: Introductionmentioning

confidence: 99%

CAS-1, a C. elegans cyclase-associated protein, is required for sarcomeric actin assembly in striated muscle

Nomura

2012

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SummaryAssembly of contractile apparatuses in striated muscle requires precisely regulated reorganization of the actin cytoskeletal proteins into sarcomeric organization. Regulation of actin filament dynamics is one of the essential processes of myofibril assembly, but the mechanism of actin regulation in striated muscle is not clearly understood. Actin depolymerizing factor (ADF)/cofilin is a key enhancer of actin filament dynamics in striated muscle in both vertebrates and nematodes. Here, we report that CAS-1, a cyclase-associated protein in Caenorhabditis elegans, promotes ADF/cofilin-dependent actin filament turnover in vitro and is required for sarcomeric actin organization in striated muscle. CAS-1 is predominantly expressed in striated muscle from embryos to adults. In vitro, CAS-1 binds to actin monomers and enhances exchange of actin-bound ATP/ADP even in the presence of UNC-60B, a muscle-specific ADF/cofilin that inhibits the nucleotide exchange. As a result, CAS-1 and UNC-60B cooperatively enhance actin filament turnover. The two proteins also cooperate to shorten actin filaments. A cas-1 mutation is homozygous lethal with defects in sarcomeric actin organization. cas-1-mutant embryos and worms have aggregates of actin in muscle cells, and UNC-60B is mislocalized to the aggregates. These results provide genetic and biochemical evidence that cyclase-associated protein is a critical regulator of sarcomeric actin organization in striated muscle.

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“…ADF/cofilin (UNC-60B) (Ono et al, 2003; Ono et al, 1999) and AIP1 (UNC-78) (Ono, 2001) enhance actin filament dynamics and are required for assembly of sarcomeric actin filaments. Tropomyosin (Ono and Ono, 2002), kettin (Ono et al, 2006), and UNC-87 (a calponin-like protein) (Yamashiro et al, 2007) bind to the side of actin filaments and stabilize them. PFN-3 is a muscle-specific profilin isoform, but its function is still unclear because a pfn-3 null mutant shows only minor muscle defects (Polet et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

Sarcomeric actin organization is synergistically promoted by tropomodulin, ADF/cofilin, AIP1 and profilin in C. elegans

Yamashiro

Cox

Baillie

et al. 2008

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