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Abstract: Recent studies have shown that histone code dictates the type and structure of chromatin. Bearing in mind the importance of A-type lamins for chromatin arrangement, we studied the effect of trichostatin A (TSA)-induced histone hyperacetylation in lamin A/C-deficient (LMNA−/−) fibroblasts. Lamin A/C deficiency caused condensation of chromosome territories and the nuclear reorganization of centromeric heterochromatin, which was accompanied by the appearance of a chain-like morphology of HP1β foci. Conversely, histone deacetylase (HDAC) inhibition induced de-condensation of chromosome territories, which compensated the effect of lamin A/C deficiency on chromosome regions. The amount of heterochromatin in the area associated with the nuclear membrane was significantly reduced in LMNA−/− cells when compared with lamin A/C-positive (LMNA+/+) fibroblasts. TSA also decreased the amount of peripheral heterochromatin, similarly as lamin A/C deficiency. In both LMNA+/+ and LMNA−/− cells, physically larger chromosomes were positioned more peripherally as compared with the smaller ones, even after TSA treatment. Our observations indicate that lamin A/C deficiency causes not only reorganization of chromatin and some chromatin-associated domains, but also has an impact on the extent of chromosome condensation. As HDAC inhibition can compensate the lamin A/C-dependent chromatin changes, the interaction between lamins and specifically modified histones may play an important role in higher-order chromatin organization, which influences transcriptional activity. [Copyright &y& Elsevier]