The role of cell fusion in erythropoiesis--Part 2

In a prior study, cell fusion was found to play an important part in erythropoiesis in both the chicken and frog. Erythropoiesis in both organisms could be traced back to groups of embryonic cells which first fused to form an aggregate structure consisting of multiple nuclei enclosed by a common cytoplasm. The cytoplasm of the fused aggregate underwent dissolution to give rise to a set of denuded nuclei which, by manufacturing a haemoglobinized cytoplasm, were transformed into erythroblasts. Following these findings, the question of cell fusion in erythropoiesis in the human was investigated, and the results are reported here. Leishman stained smears of marrow aspirate were used, and care taken to prevent the immature cells coming into contact with plasma. The reason for this was that plasma was found to alter the normal structure of the immature haemopoietic cells, particularly the megakaryocyte series. Free from plasma contact, the nucleus of the megakaryocyte was found to be not multilobulated, but composed of a compact set of small nuclei. The mode of development of the megakaryocyte and its fate could be deciphered in the smears. The megakaryocytes arose as a result of fusion of small basophilic embryonic-like cells. After the megakaryocyte had attained a certain size, fusion ceased and the cytoplasm of the megakaryocyte underwent dissolution and was shed in the form of platelets, thus denuding the nuclei. The latter, bared of cytoplasm, were transformed directly into erythroblasts. The fate of the denuded nuclei in this manner goes against the accepted view that the denuded nucleus is phagocytosed.(ABSTRACT TRUNCATED AT 250 WORDS)