並列摘要
It is becoming increasingly clear that communication between cells is carried out not only by the signaling molecules themselves, but also by many contextual and positional cues that arise from the way the signal is distributed and presented to the receptor. Many cells express transmembrane growth factors that use their extracellular domain for signaling to cells connected by adhesion. Some of these growth factors can also be receptors for a reverse signal from the adhesion partner. Secreted growth factors or their receptors can engage in contact-dependent signaling by associating with extracellular matrix (ECM) components and integrins. Signaling molecules can also reach cells at a distance via cytonemes that contact and activate the target cell through synapse-like structures.