DECIPHERING THE ROLE OF CYCLASE-ASSOCIATED PROTEIN 2 (CAP2) IN STRIATED MUSCLE

Marcela Suarez-Berumen , Chinedu Nworu, Carol Gregorio

DECIPHERING THE ROLE OF CYCLASE-ASSOCIATED PROTEIN 2 (CAP2) IN STRIATED MUSCLE

Proper muscle contraction is due to the interactions between myosin and actin within the sarcomere (single contractile unit of striated muscle). Actin filaments are regulated to maintain a uniform length within each myofibril. Actin filaments fail to regulate uniform lengths on their own, requiring other proteins within the sarcomere to take on this role. The goal of this project is to determine what role Cyclase-Associated Protein 2 (CAP2) has in actin-thin filament regulation.

Our studies included the over-expression of CAP2 in both chick heart and skeletal muscle cells, and the knockdown of CAP2 in Xenopus laevis (frog). Through the use of immunofluorescence microscopy we visualized CAP2 at the M-line and occasionally at the Z-disc of the sarcomere. CAP2 was observed in Xenopus throughout different stages of development. In early Xenopus stages (stages 20 and 24-36), CAP2 was seen diffusely organized within the cytoplasm. In late stages of development (stage 32-39), CAP2 was seen in a striated pattern at the M-line of the sarcomere, indicating that CAP2’s role may be dependent on the maturity of the myofibril. Actin thin-filament measurements on images of myofibrils using ImageJ revealed shorter actin-thin filament lengths in cardiac myocytes that overexpressed CAP2. Measurements of actin-thin filament lengths in Xenopus somites which were treated with CAP2-specific morpholinos (i.e., knockdown of CAP2) revealed longer actin-thin filaments. These data suggest that the presence of CAP2 is required for the regulation of uniform actin lengths. Immediate studies include observing CAP2’s localization and impact on filament lengths through days in culture (days 2, 4, 6, 8 and 10) in both chick heart and skeletal muscle cells, along with studying CAP2 during de novo assembly in skeletal tissue in vivo, to better decipher CAP2’s function(s) in striated muscle.

 

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