Figure 3

Myosin heavy chain IIb isoform (MyHC-IIb) promoter responsiveness and messenger RNA (mRNA) expression in human muscle cells. (A) The mouse and human 1.0 kb MyHC-IIb promoter regions were equally responsive to myogenic regulatory factor (MyoD, myogenin and calcineurin (CN)) over-expression in both mouse and human cells. (B) MyHC-IIb mRNA expression was significantly greater in primary fetal human myotubes (MT) compared to confluent myoblasts (MB). (C) In differentiated (day 5) human myotubes, the level of MyHC-IIb mRNA expression was comparable to that seen for MyHC-β, -IIa and IId/x. Overall, MyHC-Embryonic demonstrated the highest relative expression and MyHC-Perinatal the lowest. (D) MyHC-IIb mRNA expression was significantly increased in Duchene muscular dystrophy (DMD) biopsy samples (n = 7) compared to healthy control samples (n = 7), limb-girdle muscular dystrophy (LGMD) samples (n = 4) or spinal muscular atrophy (SMA) samples (n = 2). Values represent mean ± standard error of mean and are the result of at least three duplicate experiments. *P < 0.05 versus control or green fluorescent protein (GFP); **P < 0.01 versus confluent myoblasts or control, ***P < 0.05 versus MyHC-IIb.