Required for synapse integrity and synaptic plasticity. During cerebellar synapse formation, essential for the matching and maintenance of pre- and post-synaptic elements at parallel fiber-Purkinje cell synapses, the establishment of the proper pattern of climbing fiber-Purkinje cell innervation, and induction of long-term depression at parallel fiber-Purkinje cell synapses (PubMed:16234806). Plays a role as a synaptic organizer that acts bidirectionally on both pre- and post-synaptic components (PubMed:20395510). On the one hand induces accumulation of synaptic vesicles in the pre-synaptic part by binding with NRXN1 and in other hand induces clustering of GRID2 and its associated proteins at the post-synaptic site through association of GRID2 (PubMed:21410790). NRXN1-CBLN1-GRID2 complex directly induces parallel fiber protrusions that encapsulate spines of Purkinje cells leading to accumulation of GRID2 and synaptic vesicles (PubMed:23141067). Required for CBLN3 export from the endoplasmic reticulum and secretion (PubMed:17030622, PubMed:17331201). NRXN1-CBLN1-GRID2 complex mediates the D-Serine-dependent long term depression signals and AMPA receptor endocytosis (By similarity). Essential for long-term maintenance but not establishment of excitatory synapses (PubMed:29691328). Inhibits the formation and function of inhibitory GABAergic synapses in cerebellar Purkinje cells (PubMed:24467251). The cerebellin peptide exerts neuromodulatory functions. Directly stimulates norepinephrine release via the adenylate cyclase/PKA-dependent signaling pathway; and indirectly enhances adrenocortical secretion in vivo, through a paracrine mechanism involving medullary catecholamine release (By similarity). 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 (PubMed:16135095). May form oligomers with CBLN2, CBLN3 AND CBLN4 prior to secretion (PubMed:29782851). Once secreted, does not interact with other CBLN family members (PubMed:17030622, PubMed:17331201, PubMed:10964938). Interacts with GRID1 (PubMed:22220752). Interacts with NRXN1 and NRXN2 long (alpha) and short (beta) isoforms produced by alternative promoter usage (PubMed:21410790, PubMed:22220752, PubMed:29782851). Competes with NLGN1 for NRXN1-binding. Weakly interacts with NRXN3 short isoform and not at all with NRXN3 long isoform (PubMed:21410790, PubMed:22220752, PubMed:29782851). Interacts (via C1q domain) with GRID2; GRID2-binding is calcium-independent; CBLN1 hexamers anchor GRID2 N-terminal domain dimers to monomeric NRXN1 isoform beta; promotes synaptogenesis and mediates the D-Serine-dependent long term depression signals and AMPA receptor endocytosis (PubMed:20395510, PubMed:21410790, PubMed:22220752, PubMed:29782851). Interacts with OTOL1 (PubMed:20856818). Interaction with CBLN3 may cause partial retention in the endoplasmic reticulum. Expressed and secreted by presynaptic neurons, such as cerebellar granule cells. Following secretion, the protein binds to GRID2 on the postsynaptic Purkinje cell membranes. Expressed at the highest level in the cerebellar cortex. High levels are also seen in the olfactory bulb, posterior part of the cerebral cortex, certain thalamic nuclei, and deep cerebellar nuclei. Low to moderate levels are detected in some hypothalamic and brainstem nuclei. In the thalamus, expressed in parafascicular nucleus neurons and other regions (at protein level). In the developing brain, expressed as early as embryonic day 10-13, and transiently up-regulated during the late embryonic and neonatal periods. Cerebellin and [des-Ser1]-cerebellin are expressed as easly as postnatal day 3-4. The levels of both peptides rise rapidly to a maximum at approximately day 25-30 after birth, whereafter they fall to stable adult values. The proteolytic processing to yield cerebellin seems to occur either prior to the secretion by presynaptic neurons and subsequent oligomerization or in some other location after release of the mature protein. In the cerebellum, cerebellin is much more abundant than [des-Ser1]-cerebellin. Sialoglycoprotein. Mice (reeler, weaver and staggerer) show defects in granule cell migration and parallel fiber formation, synaptogenesis, Purkinje cell dendritic maturation and establishment of adult cytoarchitecture show a correlation between the formation and number of parallel fiber-Purkinje cell synapses and cerebellin levels (PubMed:3199194). CBLN1 single knockout mice show a major impairment in motor behaviors (PubMed:3420533). Double CBLN1 and CBLN2 knockout mice exhibit gait abnormalities, impairments in balance and coordination and develop seizures (PubMed:3420533). Synapse density in the hippocampus is normal in 1-2 months old mice, but severely decreased in 6 month old mice (PubMed:3420533). 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:3420533). Wrong choice of frame.