Fig. 3

Temporal and spatial expression of TPM3 isoforms in skeletal muscle. A Cytoskeletal (i.e., low molecular weight isoforms, LMW) and striated isoforms (i.e., Tpm3.12) show opposite expression patterns during myogenic differentiation (in vitro) and skeletal muscle development (in vivo). Additionally, striated tropomyosin isoforms show fiber-type specific expression in postnatal muscles. Striated Tpm3.12 isoform is exclusively expressed in postnatal slow muscle fibers. In contrast, striated Tpm1.1 isoform (encoded by the TPM1 gene is exclusively expressed in fast muscle fibers. The striated Tpm2.2 isoform (encoded by the TPM2 gene) is expressed in both slow and fast muscle fibers. The low molecular weight isoforms (LMW) are expressed at a low level in both slow and fast muscle fibers. B Cytoskeletal and striated isoforms also show different sub-localizations in muscle fibers. The striated Tpm3.12 isoform incorporates into actin thin filaments at the sarcomere in slow muscle fibers. In contrast, the cytoskeletal Tpm3.1 isoform incorporates into γ-actin in both subsarcolemmal area and region adjacent to the Z-line, and co-localized with glucose transporter GLUT4 and T-Tubule constituent DHPR. Abbreviations: SR: sarcoplasmic reticulum