Chromatin structure in somatic nucleus of ciliate Didinium nasutum

The structural organization of macronuclear chromatin of the ciliate Didinium nasutum was studied. The macronuclear genome of D. nasutum is represented by DNA molecules of subchromosomal size. At interphase, macronuclear chromatin is organized into chromatin of 100–200-nm clumps. Some of these clumps form short, thick fibers that consist of several chromatin clumps. Using the differential staining of nucleic acids on ultrathin sections, we revealed perichromatin fibers and granules on the surface of many chromatin clumps. A 3D model of the spatial distribution of chromatin clumps in the macronucleus was built based on serial ultrathin sections and peculiar features of chromatin spatial organization were studied.