May regulate the number of excitatory synapses that are formed on hippocampus neurons. Has no effect on inhibitory synapses (By similarity). Forms homotrimers which can further assemble to form higher-order oligomeric complexes. Interacts with ADGRB3. May interact with ERFE. Forms heterooligomers with C1QL3 and C1QL4, when proteins are coexpressed; this interaction does not occur after secretion.