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One of a class of proteins that act as guidance molecules during the development of nerve cells, immune cells, blood vessels, bone, and other tissues. There are several classes, some occurring in invertebrates and others in vertebrates; some semaphorins are secreted by cells, whereas others remain bound to the plasma membrane. However, all semaphorin molecules have a characteristic region called a sema domain. Class 3 semaphorins act as short-range cues to guide the growth cone at the tip of elongating nerve fibres along appropriate pathways through tissue. They may either attract the growth cone or repel it, depending on the particular semaphorin and the type of nerve cell. The action of semaphorins is effected by binding to any of various cell surface receptors.

Subjects: Chemistry.

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