Screening method for agonists or antagonists of semaphorin 6C by determining the effect of a test compound on the interaction between semaphorin 6C and plexin-A1

A screening method for agonists or antagonists of Semaphorin 6C, comprising the steps of

• 1) contacting Plexin-A1 consisting of SEQ ID NO:5 or SEQ D NO:6 with a target substance in an in vitro assay system, and
• 2) measuring Semaphorin 6C activity in said assay system by detecting the presence or absence of a signal arising from an interaction between a protein having an extracellular domain of Semaphorin 6C comprising the 1st to 599th amino acid residue in the sequence of Semaphorin 6C consisting of SEQ ID NO:7, SEQ ID NO:8, SEQ ID NO:9 or SEQ ID NO:10 and Plexin-A1, wherein the signal is
• i) a growth cone collapse activity, or
• ii) a contractile activity of a Plexin-A1 expressing cell,
• wherein a decrease in said Semaphorin 6C activity indicates that said target substance is an antagonist and an increase in said Semaphorin 6C activity indicates that said target substance is an agonist.