Figure 1.Telomere shortening and heterochromatin defects in Lmna^Δ9/Δ9 MEFs. (A) Telomere restriction fragment (TRF) analysis shows faster migration of telomeres and thus telomere shortening in Lmna^Δ9/Δ9 MEFs. (B) Three independent Q-FISH analyses of telomere length in wild-type and Lmna^Δ9/Δ9 MEFs. Telomere length of at least 20 metaphases was measured per experiment. Note the decreased average telomere length in Lmna^Δ9/Δ9 fibroblasts. (C) ChIP analysis performed on wild-type and Lmna^Δ9/Δ9 MEFs with antibodies recognizing H3K9me3 and H4K20me3. Immunoprecipitated DNA was dot blotted and hybridized to a telomere probe, stripped and rehybridized to a centromere probe (major satellite). (D) Quantitation of immunoprecipitated telomeric DNA after normalization to input signals with H3K9me3 (3 experiments) or H4K20me3 (4 experiments). Bars represent standard deviation. (E) Western blots to monitor global levels of H3K9me3 and H4K20me3 in wild-type, Lmna^{Δ8–11/Δ8–11} and Lmna^Δ9/Δ9 MEFs. β-Tubulin was used as loading control. (F) Immunofluorescence performed in wild-type and Lmna^Δ9/Δ9 MEFs with antibodies recognizing H3K9me3 and H4K20me3 (green). DAPI is shown in blue. Note the diffuse and irregular distribution of heterochromatin domains in the mutant cells. *P, represents value of statistical significance; P ≤ 0.05 is considered significant.