The Semaphorins constitute a large family of secreted and membrane-tethered cell signaling molecules. They have functions in neural development, immunology, cardiac growth, vascular development, lung morphogenesis and axial bone patterning. Semaphorins are defined by the presence of a conserved Sema domain at the N-terminus. These proteins can be classified into eight classes depending on their structure and species origin. Classes 3 through 7 are found in vertebrates; class 3 are secreted, class 7 are GPI-anchored and class 4 through 6 are transmembrane proteins. Two distinct transmembrane receptor families have been identified as Semaphorin receptors. Neuropilins provide binding specificity for the class 3 Semaphorins, whereas Plexins, which also contain a Sema domain serve as signaling partners for class 3 Semaphorins and as functional receptors for transmembrane Semaphorins. Semaphorin 3c inhibits axonal extension by providing local signals to specify territories inaccessible for growing axons. It is expressed maximally between days E10-12 with moderate levels from day E13 until birth.

Secreted