Sarcomere in striate muscle is the basic unit of contractile apparatuses. Assembly and maintenance of organized sarcomeric structure are essential for producing contractile forces. Actin is one of the major components of sarcomeric thin filaments, and length and orientation of the filaments are precisely regulated in striated muscle. However, the mechanism of assembly and maintenance of sarcomeric actin filaments is complex and poorly understood. What is more puzzling is that actin subunits within thin filaments are dynamically exchanged without compromising overall structure and contractile functions. A number of regulators of actin dynamics have been identified in skeletal muscle, and some of them are linked to genetic muscle disorders. In particular, nemaline myopathy involves formation of abnormal actin-rich aggregates or rods in skeletal muscle and is caused by mutations in actin or regulators of actin dynamics including nebulin, tropomyosin, and cofilin. Therefore, the regulation of actin dynamics is fundamentally important for building functional contractile apparatuses in skeletal muscle, and malfunction in this system leads to muscle disorders. To investigate the regulatory mechanism of actin dynamics in striated muscle, we have been using the nematode Caenorhabditis elegans as a model system. Body wall muscle of C. elegans is striated muscle, and most of sarcomeric proteins are conserved between C. elegans and humans. Powerful genetic studies on these muscle proteins advanced our knowledge on the mechanism of myofibril assembly and function. Using this system, we have identified that ADF/cofilin and AIP1 enhance turnover of actin filaments and essential for organized assembly of sarcomeric actin filaments, and that tropomyosin and calponin-like protein antagonize ADF/cofilin and stabilize sarcomeric actin filaments. These findings led us to hypothesize that a balance between enhancers and suppressors of actin dynamics is crucial for sarcomere assembly and maintenance. Recently, we obtained evidence that additional regulators of actin dynamics are involved in sarcomeric actin regulation. Therefore, we propose to further investigate their roles in myofibril assembly in three specific aims:
(Aim 1) We identified a cyclase-associated protein isoform that is enriched in body wall muscle and will determine how cyclase-associated protein cooperate with ADF/cofilin and AIP1 to regulate actin turnover, (Aim 2) We identified a gelsolin-like protein with strong actin-severing activity that is enriched in body wall muscle and will investigate its role in actin organization, and (Aim 3) We demonstrated distinct localization patterns of actin-regulatory proteins near the pointed ends of sarcomeric thin filaments and will investigate how actin dynamics are regulated in this specialized region. We expect that results of this research will provide new insight into the regulation of actin dynamics in striated muscle.

Public Health Relevance

In skeletal muscle, organized assembly of specific proteins into contractile apparatuses is required for efficient muscle contraction. Misregulation of protein assembly leads to muscle disorders. This project will investigate the mechanism of assembly and maintenance of contractile proteins in muscle of a model organism.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
2R01AR048615-11A1
Application #
8372541
Study Section
Skeletal Muscle and Exercise Physiology Study Section (SMEP)
Program Officer
Boyce, Amanda T
Project Start
2002-05-01
Project End
2017-07-31
Budget Start
2012-08-01
Budget End
2013-07-31
Support Year
11
Fiscal Year
2012
Total Cost
$350,813
Indirect Cost
$125,813
Name
Emory University
Department
Pathology
Type
Schools of Medicine
DUNS #
066469933
City
Atlanta
State
GA
Country
United States
Zip Code
30322
Hwang, Hyundoo; Barnes, Dawn E; Matsunaga, Yohei et al. (2016) Muscle contraction phenotypic analysis enabled by optogenetics reveals functional relationships of sarcomere components in Caenorhabditis elegans. Sci Rep 6:19900
Barnes, Dawn E; Hwang, Hyundoo; Ono, Kanako et al. (2016) Molecular evolution of troponin I and a role of its N-terminal extension in nematode locomotion. Cytoskeleton (Hoboken) 73:117-30
Lee, Cho-Yin; Lou, Jizhong; Wen, Kuo-Kuang et al. (2016) Regulation of actin catch-slip bonds with a RhoA-formin module. Sci Rep 6:35058
Nomura, Kazumi; Hayakawa, Kimihide; Tatsumi, Hitoshi et al. (2016) Actin-interacting Protein 1 Promotes Disassembly of Actin-depolymerizing Factor/Cofilin-bound Actin Filaments in a pH-dependent Manner. J Biol Chem 291:5146-56
Ono, Kanako; Ono, Shoichiro (2016) Two distinct myosin II populations coordinate ovulatory contraction of the myoepithelial sheath in the Caenorhabditis elegans somatic gonad. Mol Biol Cell 27:1131-42
Shukla, Vaibhav Kumar; Kabra, Ashish; Maheshwari, Diva et al. (2015) Solution structures and dynamics of ADF/cofilins UNC-60A and UNC-60B from Caenorhabditis elegans. Biochem J 465:63-78
Shukla, Vaibhav Kumar; Kabra, Ashish; Yadav, Rahul et al. (2015) NMR assignments of actin depolymerizing factor (ADF) like UNC-60A and cofilin like UNC-60B proteins of Caenorhabditis elegans. Biomol NMR Assign 9:261-5
Ono, Kanako; Obinata, Takashi; Yamashiro, Sawako et al. (2015) UNC-87 isoforms, Caenorhabditis elegans calponin-related proteins, interact with both actin and myosin and regulate actomyosin contractility. Mol Biol Cell 26:1687-98
Ono, Shoichiro (2014) Regulation of structure and function of sarcomeric actin filaments in striated muscle of the nematode Caenorhabditis elegans. Anat Rec (Hoboken) 297:1548-59
Cox-Paulson, Elisabeth; Cannataro, Vincent; Gallagher, Thomas et al. (2014) The minus-end actin capping protein, UNC-94/tropomodulin, regulates development of the Caenorhabditis elegans intestine. Dev Dyn 243:753-64

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