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Contact-dependent signaling requires the establishment of a direct contact between cells for communication.

In some tissues, cell junctions, such as gap junctions act as contact points between neighboring cells and facilitate contact-dependent signaling.

Gap junctions are specialized protein channels that connect the cytoplasms of  adjacent cells.

These junctions allow selective small ions and water-soluble molecules to pass through but exclude macromolecules like large peptides.

Gap junctions are composed of transmembrane connexin  proteins. Six connexin proteins assemble to form a connexon.

When one connexon on a cell membrane encounters another connexon on the adjacent cell, they create a complete continuous channel that can open and close.

Similarly, in plants, the rigid walls of adjacent cells are connected via membrane-lined channels called plasmodesmata.

Each plasmodesma allows the transport of molecules between cells through the connected cytoplasm as well as through a desmotubule, the tubular continuation of the smooth endoplasmic reticulum.