Structural Architecture and Evolutionary Conservation of Cerebellin-Mediated Trans-Synaptic Signaling

The cerebellin (CBLN) family includes CBLN1, CBLN2, CBLN3, and CBLN4, which are important secreted glycoproteins that play roles in synaptogenesis and the maintenance and plasticity of synapses across various regions of the central nervous system (CNS). Generally known for their implications in cerebellar parallel fiber-Purkinje cell synapses, CBLNs also play a comprehensive role in synaptic regulation in the CNS. By forming trans-synaptic complexes with postsynaptic glutamate delta receptors (GluDs) and presynaptic neurexins (NRXNs), CBLNs significantly impact the synaptic specificity and potency. Each CBLN protein has its own expression signature and function. Current research points to a key role for CBLN1 in forming excitatory synapses, especially in the cerebellum, while CBLN2 is reported to regulate inhibitory synaptic transmission and serotonergic circuits. In addition, CBLN3 regulates synaptic stability and is associated with many neurodevelopmental problems. Apart from its role in the regulation of inhibitory synapse formation, CBLN4 is also linked to many neurodegenerative disorders. Dysfunction of pathways associated with CBLN signaling has been linked to several neuropsychiatric and neurological disorders, such as ataxia and schizophrenia. This review article compares existing data on the structure, expression, and functional properties of CBLN proteins, their roles in synapse organization, and their potential as therapeutic targets for neurological disease.