The 5-HT receptor interacts with adhesion molecule L1 to modulate morphogenic signaling in neurons.

Morphological remodeling of dendritic spines is critically involved in memory formation and depends on adhesion molecules. Serotonin receptors are also implicated in this remodeling, though the underlying mechanisms remain enigmatic. Here, we uncovered a signaling pathway involving the adhesion molecule L1CAM (L1) and serotonin receptor 5-HT (5-HTR, encoded by ). Using Förster resonance energy transfer (FRET) imaging, we demonstrated a physical interaction between 5-HTR and L1, and found that 5-HTR-L1 heterodimerization facilitates mitogen-activated protein kinase activation in a G-dependent manner. We also found that 5-HTR-L1-mediated signaling is involved in G-dependent modulation of cofilin-1 activity. In hippocampal neurons , the 5-HTR-L1 pathway triggers maturation of dendritic spines. Thus, the 5-HTR-L1 signaling module represents a previously unknown molecular pathway regulating synaptic remodeling.