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Quantitative ultrastructural study of nucleolus‐organizing regions at some stages of the cell cycle (G0 period, G2 period, mitosis)
Author(s) -
Zatsepina O.,
Hozak P.,
Babadjanyan D.,
Chentsov Y.
Publication year - 1988
Publication title -
biology of the cell
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.543
H-Index - 85
eISSN - 1768-322X
pISSN - 0248-4900
DOI - 10.1111/j.1768-322x.1988.tb00723.x
Subject(s) - nucleolus , biology , metaphase , mitosis , interphase , period (music) , nucleolus organizer region , cell cycle , microbiology and biotechnology , chromosome , cell , gene , genetics , nucleus , physics , acoustics
The quantitative characteristics of chromosomal nucleolus‐organizing regions (NORs) and some other nucleolar components were studied on ultra‐thin sections of pig embryo kidney cells (PK cells). It was shown that: 1) nucleoli‐per‐cell volumes were 3 times smaller in the G0 period than in the G2 period; 2) the number of fibrillar centers (FCs) per cell in the G0 period, the G2 period, and at metaphase was equal to 7, 33.7, and 8, respectively; 3) mean volumes of individual FCs in the G0 period (0.033±0.005 μm 3 ), G2 period (0.014±0.001 μm 3 ), and at metaphase (0.04±0.05 μ 3 ) were significantly different; 4) the total volumes of FCs calculated per haploid set of chromosomes were practically the same in the G0 (0.105 μm 3 ) and G2 (0.107 μm 3 ) periods, but were twice as large as those at metaphase (0.04–0.05 μm 3 ). These data show that partial activation and inactivation of ribosomal genes in interphase PK cells are not accompanied by a considerable change in the total volume of FCs and may be due to the fragmentation and fusion of individual FCs. Complete inactivation of ribosomal genes in mitosis results in a decrease of total volumes of FCs per cell; 5) in G0 and G2 periods the total volume of the dense fibrillar component per nucleolus is practically proportional to the nucleolus volume (r = 0.99);6) in the G2 period, the nucleolus volume is also proportional to the number of FCs (r = 0.99;7) the volume of the dense fibrillar component within individual fibrillar complexes is not a constant one. This is indirect evidence for a different level of NOR functional activity in different NO‐chromosomes at interphase.