The LINC complex inhibits excessive chromatin repression

We show here that the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex is needed to minimize chromatin repression. The genomic binding profile of Polycomb, Heterochromatin Protein1 (HP1a) repressors, and of RNA-Pol II were studied in Drosophila larval muscles lacking functional LINC complex. A significant increase in the binding of Polycomb, and parallel reduction of RNA-Pol-II binding to a set of muscle genes was observed. Consistently, enhanced tri-methylated H3K9 and H3K27 repressive modifications, and reduced chromatin activation by H3K9 acetylation were found. Furthermore, larger tri-methylated H3K27me3 repressive clusters, and chromatin redistribution from the nuclear periphery towards nuclear center, were detected in live LINC mutant larval muscles. Computer simulation indicated that the observed dissociation of the chromatin from the nuclear envelope promotes growth of tri-methylated H3K27 repressive clusters. Thus, we suggest that by promoting chromatin-nuclear envelope binding, the LINC complex restricts the size of repressive H3K27 tri-methylated clusters, thereby limiting the binding of Polycomb transcription repressor, directing robust transcription in muscle fibers.