C1qlike

C1qlike refers to a family of secreted proteins that contain a C1q-like globular domain and belong to the C1q/TNF-related protein (C1QTNF) superfamily. In humans, the best known members are C1QL1, C1QL2, C1QL3, and C1QL4; homologs exist in other vertebrates and some invertebrates. The proteins are typically encoded by four genes (C1QL1-4) and are named for their similarity to the complement component C1q.

Biology and distribution: These proteins are secreted glycoproteins with an N-terminal signal peptide followed by a C1q-like domain; they are predicted to form trimeric assemblies and are often found in brain regions such as the hippocampus and cerebellum, with expression patterns suggesting roles in synapse organization and neural development.

Function: C1qlike proteins act as ligands for adhesion G protein-coupled receptors, notably the BAI family members (such as ADGRB3/BAI3). They are thought to serve as synaptic organizers that promote or specify synapse formation and maintenance in particular neural circuits. Disruption of C1QL signaling in animal models can alter synaptic connectivity, supporting a role in neural circuit assembly.

Clinical relevance and research: Variants or misexpression of C1QL genes have been explored in the context of neurodevelopmental and psychiatric conditions, though direct causal relationships remain to be established. Current research uses molecular biology, imaging, and genetic models to elucidate receptor interactions, signaling pathways, and circuit-level functions.