[Differential activity of chromosomal nucleolus-organizer regions during postimplantation embryogenesis in mink]

Using cytological preparations, we have conducted analysis of the activity of chromosomal nucleolus organizers during postimplantation embryogenesis in mink. The analysis was conducted by visual evaluation of their staining pattern with silver nitrate and incidence rate in satellite associations. The data obtained provide evidence that each nucleolus organizer during embryonic mink development shows a characteristic pattern of activity depending on cell type, tissue type, and the stage of development and also depending on changing location in the interphase nucleus. We discuss biological significance of the existence of "indispensable long-satellite" chromosome in the genome.