Nucleolar size in parallel with ribosomal RNA synthesis at diapause termination in the eggs of Bombyx mori

Abstract

The eggs of Bombyx mori, both in diapause and nondiapause, were subjected to cytological examination of nucleoli and measurement of RNA precursor incorporation (2 hours) into ribosomal RNA. In diapause eggs, the nucleoli were very small and the rate of ribosomal RNA synthesis was the lowest of the samples tested. Most cells in diapause possessed nuclei with one nucleolus. In contrast, the eggs activated from diapause by long chilling attained the largest size of nucleoli and the highest rate of ribosomal RNA synthesis. A significant proportion of the cell nuclei still had only one nucleolus at this stage. Three days after activation, the eggs exhibited intermediate levels in both the size of nucleoli and the rate of ribosomal RNA sythesis. At this stage, about half of the egg cell nuclei had two nucleoli.

Changes in polysome content during development after diapause of Bombyx mori embryos

“…For the labeling of developing eggs we applied a culture system instead of the microinjection method [4,7,10], considering an egg is composed of a complex population of cells that are compartmented. Moreover, the post-diapause embryos cultured in a medium under the presence of yolky substances are known to grow at a rate similar to that in vivo at least until stage 20, the period before katatrepsis [11,15].…”

“…RNA was extracted from eggs by the phenol method and electrophoresed in gels as in [7]. The areas of peaks were measured planimetrically to calculate the ratios of rRNA (28 S + 18 S) and 'sRNA' (4 S + 5 S) to total RNA.…”

RNA polymerase III transcription and cancer

“…Indeed, enlarged nucleoli are used by pathologists as a strong diagnostic indicator of cell transformation (Busch and Smetana, 1970;Derenzini and Ploton, 1994;King, 1996). This indicates that transformation in situ is tightly linked to the deregulation of pols I and III, because the size of the nucleolus reflects the level of rRNA synthesis (Kurata et al, 1978;Altmann and Leblond, 1982;Moss and Stefanovsky, 1995). A wide variety of transformed cell types have been shown to overexpress the products of pols I and III, including lines transformed by DNA tumour viruses (e.g.…”

A quantitative morphology of nucleoli of erythroblasts in the mouse spleen: An electron microscopic study.

“…It is well known that the nucleolus is the site of RNA concentration (see reviews by BUscH and SMETANA, 1970;MILLER, 1981), and that its morphologic feature reflects the activity of ribosomal RNA synthesis (GoEssENs, 1978;KURATA et al, 1978). As is generally accepted, the cells that have a euchromatic nucleus with large prominent nucleoli show very intense protein-synthetic activity.…”