Fig. 3. Ordered expression of human myogenic genes by lymphocyte-derived nuclei. (A) Expression of human muscle-specific (hMYF5, hMYOG, hMRF4) and human lymphocyte-specific (hCD45, hPAX5) genes detected by RT-PCR. Prior to fusion, human B cells expressed hGAPDH, hCD45 and hPAX5, but not muscle-specific genes. Following heterokaryon formation, human MYF5, MYOG and MRF4 expression was initiated and the expression of human lymphocyte-specific genes CD45 and PAX5 declined. Mouse C2C12 samples (C2) were used as negative controls to confirm the specificity of primers to human transcripts and hGAPDH was used to standardise input. (B) Expression kinetics of human NCAM in hBxC2 heterokaryons in the presence (solid line) or absence (broken line) of TSA (20 nM). For each time point, 100 heterokaryons were analysed in two separate experiments and values shown are the mean ± s.d. (C) hMYOG, hMRF4, hMYF5 and hGAPDH gene expression in human B lymphocytes (hB) and in day 4 (d4) and day 7 (d7) hBxC2 heterokaryons cultured in the presence (+) or absence (–) of 20 nM TSA. As positive controls for PCR analysis (hC+) RNA was isolated from differentiating human muscle. Mouse C2C12 cells (C2) were used as negative control. hGAPDH was used to standardise input.