Fig. 2. Nuclear reorganisation is an early event in lymphocyte reprogramming. (A) Single optical section showing lamin A/C immunofluorescence-labelling of human B lymphocyte nuclei (hB) before day 0 (d0) and three days (d3) after fusion with C2C12 myotubes. (B) Volume of hB nuclei before (d0), and 2 and 4 days after heterokaryon formation (d2 and d4, respectively) compared with C2C12 myotubes 2 and 4 days after serum withdrawal and differentiation (d2 and d4, respectively). Nuclear volume was estimated as described in Materials and Methods (mean ± s.d., n=3 with 50 nuclei per experiment). (C) CREST antisera (green) reveal the centromere distribution in hB nuclei (d0) and two days after heterokaryon formation (d2), where individual chromocentres are indicated (arrowed). Confocal images are maximal projection of multiple optical z-sections. (D) Distribution of constitutive heterochromatin in hB nuclei before (d0, open bars) and 2 days after fusion in hNCAM expressing (d2, black bars) and hNCAM-negative (not yet reprogrammed) heterokaryons (grey bars) was compared by assessing the number of discrete CREST signals and number of chromocentres per nucleus (n=100). (E) Myogenin protein (green) in a human nucleus (arrowheads) 1 day after fusion. Images show single optical sections. Bars, 10 µm.