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

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 synthesis. At this stage, about half of the egg cell nuclei had two nucleoli.This paper is dedicated with respect and admiration to Professor D.F. Poulson, who has made many significant contributions on the genetics, embryology and cytology of Drosophila as well as other Insecta, in commemoration of his retirement