Studies on nucleoli of pigeon erythroid cells.

In order to provide more information on nucleolar changes occurring during cell differentiation and maturation, pigeon erythroid cells have been studied by means of a simple light microscopic cytochemical procedure for the demonstration of the RNA containing structures and with conventional transmission electron microscopy. Nucleoli with more or less distinct nucleolonemata present in early erythroblasts were replaced by ring-shaped nucleoli and, finally, by micronucleoli in more mature erythroid cells. In contrast to the previously studied chick embryos, chickens and hens which possess micronucleoli in almost all mature erythrocytes, mature pigeon erythrocytes are mostly without any nucleoli. The ultrastructural organization of nucleoli with more or less distinct nucleolonemata and ring-shaped nucleoli do not show differences, in comparison with such forms of nucleoli in other cells. Micronucleoli in pigeon erythroblasts are characterized by degranulation, suggesting the inhibition of the formation of the nucleolar granular components. Some nucleoli show a segregation of the nucleolar components, indicating the inactivation of the nucleolar RNA polymerase, and occasionally chromatin retraction from the nucleolar body, suggesting the loss of the template. In mature erythrocytes, micronucleoli consist mainly of fibrillar components, and the perinucleolar chromatin is partially retracted from the nucleolar body of such nucleoli.