The role of cell fusion in erythropoiesis--Part 1

The present haemopoietic pathways have been deduced from fixed material, and can be criticised on the grounds that they are an interpretation of a highly complex cytological picture and open to error. Furthermore, the pathways have not helped in the search for the haemopoietic stem cell, the initiating and most essential element of the pathways. Hence a different approach to the study of haemopoiesis may be useful, and in this regard Sabin's work is valuable. Sabin is one of the few investigators who has carried out a study of erythropoiesis on the living organism. She studied hanging drop preparations of explanted blastoderms of the chicken, and found that special embryonic cells called angioblasts fused to form well demarcated aggregates which were transformed into erythroblastic islands. In this paper, cell fusion leading to erythropoiesis has been further explored. Leishman stained smears of the blastoderm of the chicken, the splanchnic mesenchyme of the tadpole, the bone marrow of the juvenile chicken and the bone marrow of the juvenile frog were studied. Aggregates consisting of a set of nuclei enclosed by a common cytoplasm were found in all four tissues, and the origin and fate of the aggregates could be deciphered. The aggregates arose by a fusion of embryonic cells, and after the aggregate had attained a certain size, the cytoplasm underwent dissolution, denuding the nuclei. The bare nuclei, by manufacturing a haemoglobinised cytoplasm, were transformed into erythroblasts. The findings not only confirmed Sabin's observations on erythropoiesis in the chicken blastoderm but also showed that cell fusion was an integral part of erythropoiesis on a wider scale.