Cinemicrographic studies on granulopoiesis.

Abstract

Time-lapse photomicrographic studies were made on the growth of the proliferation compartment of the granulocytes of the mouse. Granulocytes obtained from bone marrow, spleen, and blood were grown In a liquid medium. Granulocytic colonies appeared to multiply and differentiate on top of large, macrophage-like cells that acted as natural feeder cells for the colonies. A total of 6 sequential cell divisions was observed for a promyelocyte to differentiate into 64 mature granulocytes. The time required for the last 5 sequential divisions was 95.1 hours. The average generation time for each cell division was 19 hours (ranging from 12.8 to 23.5 hr). If one assumes that the generation time for the promyelocyte was also 19 hours, the total time required for complete differentiation of a promyelocyte would be about 5 days. After the last cell division, granulocytes began to show small projections, which evolved into large projections, followed by persistent shaking of the cells before their leaving the colony. This was designated the “weaning phenomenon,” because the cells were struggling to leave their mother (the feeder cell). The weaning phenomenon lasted for an average of 2 days. The detached granulocytes were then referred to as “weaning cells.” The number of granulocytic colonies decreased progressively in the cultures. The longest maintenance of a colony was 24 days. Death of colony cells was observed between 6 and 19 days of cultivation. The feeder cells resembled the large macrophages present in the cultures. Division of the feeder cells was observed during the growth of cell colonies.