Cardiac myofibril formation is not affected by modification of both N- and C-termini of sarcomeric tropomyosin

Although the role of tropomyosin is well-defined in striated muscle, the precise mechanism of how tropomyosin functions is still unclear. It has been shown that extension of either N- or C-terminal ends of sarcomeric tropomyosin do not affect cardiac myofibrillogenesis, but it is not known whether simultaneous extension of both ends affects the process. For studying structural/functional relationships of sarcomeric tropomyosin, we have chosen the Ambystoma mexicanum because cardiac mutant hearts are deficient in sarcomeric tropomyosin. In this study, we have made an expression construct, pEGFP. TPM4α.E-L-FLAG, that, on transfection into normal and mutant axolotl hearts in organ culture, expresses GFP. TPM4α.E-L-FLAG fusion protein in which both the N- and C-termini of TPM4α are being extended. TPM4α is one of the three tropomyosins expressed in normal axolotl hearts. Both confocal and electron microscopic analyses show that this modified sarcomeric tropomyosin can form organized myofibrils in axolotl hearts.