Effects of 2-mercapto-1-(beta-4-pyridethyl)-benzimidazole (MPB) on Ehrlich cell nucleoli: stereological analysis.

The effects of MPB, a strong inhibitor of RNA synthesis, have been analysed at the ultrastructural level by means of stereological methods. After treatment, an increase in the nucleolar volume is observed. This enlargement is due to vacuolization of the nucleoli. However, the relative volumes of the nucleolar components are modified in various directions: the volume of the granular component decreases whereas the fibrillar centres increase in size. These results are discussed in terms of relations between morphology and function of the nucleolus.