The morphology of hematopoietic layers in long-term cultures of mouse bone marrow.

Mouse bone marrow cells in long-term culture were examined with scanning electron microscopy during the first 10 days of growth and with phase contrast microscopy during the first 4 weeks. The development of stroma and hematopoiesis was studied, and phase microscopic observation was used in order to achieve positive cell identifications with scanning EM. We analyzed those cell populations that could not be washed away from the adherent culture layer. These adherent cells in 24-hour cultures contain the full potential of hematopoietic long-term production. Stromal cells started to spread almost immediately and by 5 days had established several layers. Although in early cultures hematopoietic cells were found resting on the surfaces of stromal cells, they were later packed between stromal layers. The blast cells, especially, were usually buried under and between thin sheets of reticulum cells. The study confirms the three-dimensional nature of bone marrow in culture and points to close correspondence with bone marrow structure as studied by others in vivo.