Fig. 1.

Reprogramming of gene expression in heterokaryons formed between differentiating murine myoblasts and human primary keratinocytes. (A) Keratinocyte populations uniformly expressing keratin-5 (K-5) were fused with myotubes using PEG, and resulting cultures were grown in low-serum medium supplemented with ara-c and ouabain (K-5, green; Hoechst, blue). Skeletal muscle NCAM is expressed by keratinocyte nuclei only after fusion with muscle cells (NCAM, red). (B) Individual cells are determined to be heterokaryons by the presence of nuclei derived from both human (uniform staining pattern) and mouse (punctate staining pattern) nuclei. (C Lower Left) Frequency of reprogramming is scored as the percentage of individual heterokaryons that express human NCAM. Error bars indicate the standard error of the proportion calculated from the binomial equation. (C Upper) Reprogramming of gene expression over time after fusion is shown. RT-PCR using human-specific primers for MyoD, keratin-14 (K-14), β-globin, and GAPDH. PCR was performed on control samples to test primer specificity and absence of amplification in mouse muscle cells. C2, C2C12 myoblasts; Rh, Rh30 human rhabdomyosarcoma cell line; K, keratinocytes; E, TF-1 human erythroleukemia cell line. (C Lower Right) Time course of gene expression by keratinocyte nuclei before and at daily time points after fusion (MyoD, 35 cycles; K-14, 26 cycles; β-globin, 35 cycles; GAPDH, 29 cycles).