Brain-Wide Mapping and Synaptic Localization of C1QL3 Using a Novel Epitope-Tagged Knock-In Mouse

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Synaptic proteins regulate neuronal signaling, plasticity, and specificity, with many linked to neuropsychiatric disorders.
• Members of the C1q/TNF superfamily, like C1QL3, act as synaptic organizers.
• Previous studies on C1QL3 were limited by the lack of specific antibodies for detection and localization.

Purpose of the Study:

• To develop a novel tool for studying the endogenous C1QL3 protein.
• To enable specific detection, purification, and subcellular localization of C1QL3.
• To investigate the neuroanatomical distribution and synaptic positioning of C1QL3.

Main Methods:

• Generation of a novel epitope-tagged knock-in mouse line (C1ql3^2HA) inserting hemagglutinin (HA) epitopes.
• Validation of the mouse model for normal mRNA expression, biochemical properties, and behavior.
• Utilized native PAGE, light-sheet microscopy, immunohistochemistry, and STED microscopy for analysis.

Main Results:

• The C1ql3^2HA mouse model accurately reflects endogenous C1QL3 properties without overexpression.
• An expanded neuroanatomical map of C1QL3 expression was identified, including novel brain regions and the retina.
• C1QL3 was localized to hippocampal mossy fiber synapses, supporting its role in trans-synaptic complexes.

Conclusions:

• The C1ql3^2HA knock-in mouse line provides a specific and reliable method for studying C1QL3.
• This tool facilitates research into C1QL3's role in synaptic organization, function, and potential links to neurological disorders.
• Enables comprehensive investigation of C1QL3 in various cellular and tissue contexts.