Gap junctions in blood forming tissues.

More than ten research groups have now reported the presence of gap junctions in blood-forming tissue or cultured cells. It is time to accept that these cell-coupling structures are present in this tissue. To find out what they are doing here we need to develop appropriate experimental techniques. This review covers the particular problems of investigating direct cell-cell communication by gap or other junctions in undisturbed haemopoietic tissue. It then describes and assesses the published reports of haemopoietic gap junctions. Recently, in the author's laboratory, three means of increasing the number of gap junctions 50- to 100-fold in mouse marrow have been described, as well as techniques for doing so in culture. There is a complete report of this work here. At present it is quite unclear what function gap junctions serve in blood-formation, perhaps it is some consolation that 30 years after their ultramicroscopic discovery it is also true for all other unexcitable tissues. Possibly the ability to up-regulate their expression in haemopoietic tissue will help us find out what their role is in blood formation.