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The overall structure, function, and composition of the basic functional unit of muscle is highly conserved between nematodes and vertebrates, making the nematode Caenorhabditis elegans (C. elegans) an effective model organism for the study of muscle development, organization, and function (Gieseler et al., 2017). In C. elegans, the M-line is found at the center of the sarcomere, the smallest contractile unit of muscle tissue. The myosin filaments that drive muscle contraction are anchored at the M-line, which contains many structural and signaling proteins whose functions have not been fully defined. We have developed an in vivo system to dissect the protein-protein interactions that attach myosin filaments to this complex structure. Worms with a myo-3 mutation, lacking wild type myosin A, but rescued with a myosin A transgene expressing a mutated myosin A protein produce ectopic accumulations of myosin A filaments outside the contractile apparatus. These accumulations recruit UNC-89/obscurin and the zinc-finger (ZnF) protein UNC-98 is required for this interaction (Sarah Almuhanna, unpublished). Others have shown that the M-line protein UNC-97/PINCH, binds to UNC-98/ZnF (Mercer et al., 2003), and together these proteins recruit myosin A to the M-line (Miller et al., 2006). Since UNC-98/ZnF associates with myosin A through both UNC-89/obscurin and UNC-97/PINCH, we hypothesized that UNC-97/PINCH is also recruited to the ectopic myosin A accumulations. This hypothesis was tested using animals expressing an unc-97 transgene tagged with the fluorescent marker GFP and a transgene producing myosin A accumulations. Animals were double stained with a mouse antibody specific for myosin A and a rabbit antibody specific for GFP and were visualized using fluorescence microscopy. UNC-97::GFP was not detected in the ectopic myosin A accumulations, suggesting that the attachment of myosin A to UNC-89/obscurin through UNC-98/ZnF is an independent and novel mechanism that anchor myosin A to the M-line.
Oishi, Humayra, "The role of the M-line protein UNC-97/PINCH in myosin A attachment to the M-line using ectopic myosin A accumulations in striated muscle of Caenorhabditis elegans" (2021). Honors Theses. 3446.
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