in ▁ 2 ▁( N pn 2 ) ▁interactions ▁medi ate ▁syn ap se ▁elim ination ▁and ▁ax onal ▁pr uning , ▁as ▁demonstrated ▁by ▁S ema 3 A / N pn 2 ▁loss - of - function ▁studies ▁in ▁m ice . ▁The ▁attract ive ▁c ues ▁medi ated ▁by ▁Sem ap hor ins ▁are ▁not ▁well ▁understood ▁at ▁the ▁moment ; ▁however , ▁protein ▁kin ase ▁foc al ▁ad hes ion ▁kin ase ▁( FA K ) ▁and ▁M AP ▁Kin ase ▁( MA PK ) ▁have ▁been ▁imp licated ▁in ▁medi ating ▁down stream ▁attract ive ▁signal ing ▁upon ▁Sem ap hor in ▁re ceptor ▁stim ulation . ▁ ▁Sem ap hor ins ▁also ▁play ▁a ▁critical ▁role ▁in ▁c ran ial ▁n erve ▁development ; ▁studies ▁using ▁m ice ▁def ic ient ▁in ▁S ema 3 A ▁and ▁S ema 3 F ▁have ▁resulted ▁in ▁ab normal ▁c ran ial ▁n erve ▁extension ▁and ▁def asc ic ulation , ▁while ▁S ema 3 F ▁has ▁been ▁suggested ▁to ▁be ▁required ▁in ▁order ▁to ▁establish ▁pro jections ▁of ▁c ran ial ▁n erves . ▁M ice ▁def ic ient ▁in ▁memb rane ▁bound ▁S ema 6 A ▁showed ▁mis pro jection ▁of ▁cort ic oth al am ic ▁fib ers ▁and ▁ax on ▁pro jections ▁from ▁the ▁hi pp oc amp us ▁to ▁ol factory ▁bul b . ▁Kno ck ing ▁out ▁certain ▁members ▁of ▁Sem ap hor ins , ▁such ▁as ▁S ema 5 A , ▁resulted ▁in ▁emb