Figure 5.
D4Z4 chromatin is quite resistant and the adjacent p13E-11 chromatin is very sensitive to DNaseI in all studied FSHD and control cell populations. Nuclei (FSHD myoblasts, control fetal myoblasts, one control fibroblast cell strain) or permeabilized cells (LCLs) were treated with four or five different concentrations of DNaseI. The results are given for only one concentration of DNaseI (20, 50 or 100 U/ml) but these are representative of the results at each concentration (e.g. Figure 4) and all differences in sensitivity between different types of DNA sequences were highly significant (P < 10−4, see text). The analyzed DNA sequences for each cell type are as follows, from left to right in each bar graph: two untranscribed gene standards (Untr, CST5 and GHRHR), p13E-11 (11; bar denoted by a vertical arrow), D4Z4 (D4, 4q-type and 10q-type arrays), constitutively transcribed gene standards (Tr, B2M and HMBS), and the constitutive heterochromatin standard (Sat2). After size normalization, the percentage of DNA remaining in the parent band for each sequence was divided by that for the average of the untranscribed standards. In parentheses is the number of copies of the D4Z4 repeat unit for the allelic 4q-type arrays (no BlnI site and a single StyI site per 3.3 kb) and the allelic 10q-type arrays (one BlnI site and two StyI sites per 3.3 kb) (51). The control myoblasts and the fibroblasts had one of the 4q D4Z4 arrays replaced by a canonical 10q-type array, as is seen in some individuals, but this has no effect on phenotype (51).