Studies on nucleoli of maturing frog erythroblasts

Summary Frog erythroblasts were studied in summer animals with a very active as well as reduced erythropoiesis due to experimental hibernation, the latter being administered in order to get more information on the frequency of various nucleolar types in maturing cells. The results suggest that nucleoli with nucleolonemata are a transitional nucleolar type between compact and ringshaped nucleoli. Since micronucleoli represent final nucleolar maturation changes and compact nucleoli are present in most immature cells, the sequence of nucleolar changes based on the frequency of investigated nucleolar types is as follows: compact nucleolinucleoli with nucleolonemataringshaped nucleolimicronucleoli. The experimental hibernation produces a shift of nucleoli to less active and maturer nucleolar types in all stages of the erythroblastic maturation. In addition, the experimental hibernation produces the formation of ringshaped nucleoli in the first stages of the erythroblastic maturation which in summer animals usually contain compact nucleoli and/or nucleoli with distinct nucleolonemata.