Junctional Structures in Haemopoiesis: a Study of Bone Marrow using Freeze‐Fracture and Lanthanum Impregnation Techniques

Summary. Intercellular regions of contact in the haemopoietic compartment of normal rat bone marrow were studied using freeze‐fracture and lanthanum tracer techniques. Small adhering junctions (like desmosomes and their variants) were found between haemopoietic and stromal cells but tight, gap or septate junctions could not be identified. These findings are in agreement with the concept that extensive junctional structures may be inconsistent with orderly development of this transient cell system, preventing the delivery of mature cells into the circulation and resulting in ineffective haemopoiesis. Occasionally ‘pinching off’of a portion of the cytoplasm of erythroid cells by stromal cells was seen, providing a means for intercellular communication. Structures similar to intercellular bridges responsible for direct intercellular communication were also seen.