TheSemaphorinsconstitutealargefamilyofsecretedandmembrane-tetheredcellsignalingmolecules.Theyhavefunctionsinneuraldevelopment,immunology,cardiacgrowth,vasculardevelopment,lungmorphogenesisandaxialbonepatterning.SemaphorinsaredefinedbythepresenceofaconservedSemadomainattheN-terminus.Theseproteinscanbeclassifiedintoeightclassesdependingontheirstructureandspeciesorigin.Classes3through7arefoundinvertebrates;class3aresecreted,class7areGPI-anchoredandclass4through6aretransmembraneproteins.
TwodistincttransmembranereceptorfamilieshavebeenidentifiedasSemaphorinreceptors.Neuropilinsprovidebindingspecificityfortheclass3Semaphorins,whereasPlexins,whichalsocontainaSemadomainserveassignalingpartnersforclass3SemaphorinsandasfunctionalreceptorsfortransmembraneSemaphorins.
Semaphorin3cinhibitsaxonalextensionbyprovidinglocalsignalstospecifyterritoriesinaccessibleforgrowingaxons.ItisexpressedmaximallybetweendaysE10-12withmoderatelevelsfromdayE13untilbirth.