Chromatin marks define heterochromatin and euchromatin. (A) Diagram of the heterochromatic and euchromatic regions in the D. melanogaster genome. For each chromosome, euchromatin is represented in black, heterochromatin in light blue or light gray, and “C” is the centromere. The targets of this analysis, the assembled heterochromatic sequences in Release 5 of the D. melanogaster genome (h and Het regions), are indicated in light blue. (B) Euchromatin and heterochromatin occupy distinct genomic compartments. Polytene chromosomes from third instar larvae of Oregon R (wild type) (top) or interphase nuclei of S2 cells (bottom) were stained with antibodies specific for H3K4me2, which is enriched in euchromatic regions of the genome, and for H3K9me2, which is enriched in heterochromatin. (Left to right) Phase image (polytene) or DAPI staining (S2 cells); H3K4me2 staining (red); H3K9me2 (green); merged image of the signals for H3K4me2 (red) and H3K9me2 (green).
