The semaphorins are a family of proteins that are involved in signaling. All the family members have a secretion signal, a 500-amino acid sema domain, and 16 conserved cysteine residues(Kolodkin et al., 1993 [PubMed 8269517]). 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; MIM 603961), 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 (Luo et al., 1993 [PubMed 8402908]) through an interaction with a collapsin response mediator protein of relative molecular mass 62K (CRMP62) (Goshima et al., 1995 [PubMed7637782]), a putative homolog of an axonal guidance associated UNC33 gene product (MIM 601168). SEMA3F is a secreted member of the semaphorin III family.