Intercellular communication in three-dimensional culture

Abstract

The coordination of cell growth and differentiation as well as of tissue homeostasis and synchronization of tissue functions requires the transfer of information between cells. This may be achieved by an unidirectional signal flow, as is the case with secreted molecules (hormones. neurotransmitters) and or with membrane-bound receptors (sperm-egg binding, immune system). It can also follow a nonrectifying mode. as is observed for direct intercellular communication via gap junctions that are founed in regions of close cell-to-cell contact. These membrane channels are not only bidirectionally permeable and facilitate the free exchange of charged and neutral molecules, but also connect adjacent cells mechanically. They must be clearly discriminated from desmosomes, which anchor cells together to form structural or functional units, as well as from tight junctions that seal membranes of epithelial cells to each other so that the paracellular path becomes impermeable to molecules, and a polarity of apical and basolateral surface is maintained.