Synchronized and Differentiated Modes of Cellular Dynamics

Intercellular communication serves a variety of purposes in metazoan systems, including, (i) the recruitment of individual cells into multicellular aggregates, as in the transition from vegetative growth to the slug stage in the slime mold Dictyostelium discoideum (Dd hereafter), (ii) the initiation and/or synchronization of collective activities such as the repetitive contraction in the myocardium, (iii) the initiation and coordination of spatial differentiation in developing systems, and (iv) the guidance of cell movement during morphogenesis. It is conveient to classify the different modes of intercellular communication that have evolved for these purposes as either long-range or short-range, according as the distances involved are greater or less than about 0.25 mm, this being the distance for which the relaxation time for diffusion is of the order of one minute. Long-range signal transmission can occur via convective transport, as in hormonal interactions via a circulatory system, or it may involve diffusion coupled with a spatially-distributed mechanism for regenerating and relaying the signal, such as occurs in nerve impulse conduction and in the aggregation phase of Dd.