Nucleolar changes during the differentiation of erythroblasts in the mouse spleen were examined quantitatively by electron microscopy. On the basis of a three-dimensional nuclear analysis, as reported previously, the erythroblasts could be classified into four types: small (S), medium (M), large (L) and extra-large (EL). Extra-large and large erythroblasts have large prominent nucleoli which are usually attached to the nuclear membrane. Medium and small erythroblasts have small nucleoli which are generally separated from the nuclear margin. The volumetric ratio of nucleoli to nucleus obtained by a point-counting method is 0.157 +/- 0.016 in EL; 0.135 +/- 0.011 in L; 0.035 +/- 0.004 in M and 0.015 +/- 0.004 in S, and the volume of nucleoli is 37.8 microns3 in EL; 17.3 microns3 in L; 2.3 microns3 in M; 0.5 microns3 in S, respectively. The number of nucleoli per nucleus is largest (3.9) in EL and smallest (0.6) in S. The nucleolar changes are discussed in relation to the developmental sequence of the erythroid series.
Aging Animals