The semaphorins are a family of proteins that are involved in signaling. Sequence comparisons have grouped the secreted semaphorins into 3 general classes, all of which also have an immunoglobulin domain. The semaphorin III family, consisting of human semaphorin III (SEMA3A), chicken collapsin, and mouse semaphorins A, D, and E, all have a basic domain at the C terminus. Chicken collapsin contributes to path finding by axons during development by inhibiting extension of growth cones through an interaction with a collapsin response mediator protein of relative molecular mass 62K (CRMP62), a putative homolog of an axonal guidance associated UNC33 gene product. SEMA3F is a secreted member of the semaphorin III family.