On the presence of micronucleoli in mature avian erythrocytes.

Chick, hen, duck and pigeon mature erythrocytes were investigated by means of a simple cytochemical procedure for the selective demonstration of the RNA-containing structures to provide more information on the presence or absence of nucleoli in these cells. The results clearly demonstrated that almost all mature erythrocytes of ducks, chickens and hens possessed micronucleoli. In "not-flying" pigeons micronucleoli were present in about two thirds of mature erythrocytes and in contrast, about two thirds of these cells in "flying" pigeons did not contain any nucleoli. Since the formation of micronucleoli reflects the cessation of the nucleolar and presumably ribosomal RNA synthesis, the mature erythrocytes of the investigated birds containing such nucleoli do not synthetize this nucleic acid. Similarly, mature pigeon erythrocytes without nucleoli also do not synthetize the ribosomal RNA since nucleoli are responsible for this process in the nucleus. Both these observations and conclusions are in perfect accordance with previous biochemical studies which demonstrated the cessation of the ribosomal RNA synthesis in these cells. The differences in the presence of micronucleoli between pigeon mature erythrocytes and these cells in other birds investigated in the present study, just as the difference in the presence of micronucleoli in mature erythrocytes between "not-flying" and "flying" pigeons, indicate that a certain maturation specificity may exist in the erythropoiesis of various species of birds and even in birds of the same species, depending on their living conditions.