[The ultrastructural characteristics of the metaphase chromosomal regions (telomere, centromere, nucleolar organizer) in the pig]

Abstract

The ultrastructural organization of some chromosome regions (telomere, centromere, nucleolus organizer region), which can be identified undoubtedly under electron microscope after in situ fixation, was studied using serial ultrathin sections of pig embryo kidney cells. The ultrastructure of these regions was compared with patterns of their differential staining revealed by C-method and by fluorochromes, chromomycin A3 and DAPI, specific for GC- and AT-rich base pair regions. It is shown that telomere regions of chromosome are organized primarily by 20 nm fibrils of DNP, which form a clear chromonema--a thread of chromatin with thickness nearly 100 nm. In the centromere regions of metacentric chromosomes, fibrils 20 nm in diameter predominate, while in several acrocentric chromosomes--fibrils 10 nm thick are prevailing. It was suggested that the observed differences may depend on the DNA composition in these regions. The nucleolus organizer regions contain the fibrillar material 5-11 nm in diameter.