Myosin heavy chain isoform (MyHC) expression patternin human extraocular muscles

Human extraocular muscles (EO) express a complex pattern of MyHC isoforms as the specific EO, skeletal ones (type 1, 2A, 2X), developmental isoforms (Embryonic and Perinatal, all life long), the alpha cardiac, also expressed in masseter and laryngeal, and the recently found 2B. Moreover, in EO muscles another isoform was identified, the slow tonic, but is not well characterized at genomic and protein level. Recently, Schiaffino and collaborators (Rossi et al., J Physiol 588.2, 2010) studied two new genes concluding that MYH14/7b correspond to slow tonic and MYH15 gene to ventricular isoform of chicken. Another author found, on the contrary, that the slow tonic is codified by MYH15 gene (Rahnert et al., Cell Tissues Organs 191, 2010). Our results, assessed by Realtime PCR and protein electrophoresis, comparing skeletal, laryngeal, EO, masseter and atrium human muscles, confirmed, at RNA and protein level, that MYH14/7b correspond to the slow tonic isoform. For the first time, we clarify the electrophoretic position of slow tonic MyHC between EO and cardiac bands.