Flotillin-1 mediates neurite branching induced by synaptic adhesion-like molecule 4 in hippocampal neurons

Proper development of neurons in the hippocampus is essential for learning and memory. Our laboratory previously discovered a family of synaptic adhesion-like molecules (SALMs) which induce neurite outgrowth in this brain region (Wang et al., 2006). Here we establish flotillin-1 (flot-1) as a molecular mediator of neurite branching for SALM4. Knockdown of flot-1 alone in cultured hippocampal neurons using siRNA from 3–7 days in vitro (DIV) impaired neurite branching, whereas overexpression of flot-1 during the same time period increased the number of processes and branching. We show that induction of neurite outgrowth by flot-1 depends on amino acids 134–151 as well as lipid raft microdomains, SoHo proteins to regulate the actin cytoskeleton, and the exocyst complex to deliver new membrane proteins to growing neurites. When each of SALMs 1–5 was overexpressed, siRNA knockdown of flot-1 prevented neurite branching by SALM4. Overall, our data reveal a flot-1 signaling pathway for hippocampal neurite branching that is regulated by SALM4.