Roles of cell-to-cell communication in development.

Possible roles of cell-to-cell communication mediated by intercellular bridges and gap junctions in development of the female gamete and embryo are discussed. Synchronization of cell cycle events is presumably a role for intercellular bridges between germ cells. The follicle of the Cecropia moth reveals that an electrical polarity exists between nurse cells and oocytes which are connected by intercellular bridges and this polarity may generate differences that result in differentiation of the oogonia to become either the oocyte or nurse cells. Gap junction-mediated transfer of cyclic AMP, made in response to gonadotropin stimulation, between granulosa cells is discussed as a mechanism that allows cells within a tissue to respond to an external stimulus even though all cells in that tissue may not be exposed to the stimulus. A nutritional role for heterologous cell communication between follicle cells and the oocyte in oocyte growth is presented as an example of how gap junction-mediated communication can allow one cell type to influence the behavior of another cell type. During development, a restriction in communication between differentiating cells is frequently observed. Examples of this phenomenon in a mammal and an insect are presented.