Acts as a synaptic organizer in specific subsets of neurons in the brain (PubMed:29691328). Essential for the formation and maintenance of inhibitory GABAergic synapses (PubMed:25534236). Promotes the development of dendrite-targeting inhibitory GABAergic synapses made by somatostatin-positive interneurons (PubMed:30679375). May contribute to the function of ventral medial habenula region of the brain implicated in the regulation of anxiety-related behaviors (PubMed:30287486). May play a role in CBLN3 export from the endoplasmic reticulum and secretion (PubMed:17030622). Homohexamer; disulfide-linked homotrimers. The trimers are assembled via the globular C1q domains. The trimers associate via N-terminal cysteine residues to form disulfide-linked hexamers (By similarity). May form oligomers with CBLN1, CBLN2 and CBLN3 prior to secretion (PubMed:17030622, PubMed:29782851). Once secreted, does not interact with other CBLN family members (PubMed:17030622). Strongly interacts with DCC in a NTN1-displaceable fashion (PubMed:22220752, PubMed:29782851). Weakly binds to NRXN1 and NRXN2 long and short isoforms produced by alternative promoter usage (PubMed:22220752, PubMed:29782851). Interaction with NRXN3 short isoform is hardly detectable; no interaction at all with NRXN3 long isoform (PubMed:22220752, PubMed:29782851). Does not interact with NEO1, GRID1 and GRID2 (PubMed:22220752, PubMed:29782851). Detected at GABAergic synapses. Expressed in brain with high levels in particular thalamic nuclei. In the thalamus, predominantly expressed in neurons within the parafascicular nucleus. Found in the hippocampus, mostly in the dendrites and somata of pyramidal neurons (at protein level). Very low or no expression in most other brain regions. Highly expressed in the ventral medial habenula. In the developing brain, expressed as early as 10-13 dpc. Expression level peaks at 18 dpc and gradually decreases afterwards. Expressed in developing somatostatin-positive basket cells. Sialoglycoprotein. Mutant animals are fertile, have normal life spans and have no overt anatomical abnormalities (PubMed:22220752). They have a normal corpus callosum, hippocampal commisure and pontine nucleus and no other gross neuroanatomical abnormalities (PubMed:22220752). Mice exhibit increased anxiety-related behavior (PubMed:30287486). Triple CBLN1, CBLN2 and CBLN4 knockout mice exhibit impairments in sensory processing and sensorimotor gating, in addition to severe motor deficits, seizures and reduced synapse density in the hippocampus of aging mice (PubMed:29691328).