Cell membrane family of growth regulatory factors.

: Both negative and positive regulators of cell growth and differentiation have been found in association with the surface of a variety of cell types, including fibroblasts, lymphocytes, undifferentiated components of the slug, neuronal cells, monocytes and mesenchymal cells (see Table 3). These molecules have been implicated in mediating contact inhibition, suppression of lymphopoiesis, inhibition of DNA synthesis in erythroid progenitors, induction of differentiation in Dictyostelium, stimulation of Schwann cell proliferation, and stimulation of the proliferation of a variety of hematopoietic cells, including myeloid (Price et al, 1975), erythroid and macrophage progenitor cells. In some cases, families of membrane bound growth factors have been described or are currently being appreciated. The importance of cell surface-associated regulators in mediating close cell-cell interactions in vitro and in vivo as well is under active investigation.