GPR56 S4 variant is required for microglia-mediated synaptic pruning.

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• ADGRG1 (GPR56) is vital for brain development, including cortical lamination, CNS myelination, and synaptic refinement.
• The precise mechanisms underlying GPR56's diverse functions are not fully elucidated.
• Alternative splicing of GPR56 may contribute to its varied roles.

Purpose of the Study:

• To investigate the specific function of the GPR56 splice variant 4 (S4).
• To test the hypothesis that GPR56 splice variants mediate distinct functions.
• To determine the role of the GPR56 S4 variant in brain development and synaptic regulation.

Main Methods:

• Generation of a novel transgenic mouse line (Gpr56^∆S4) using CRISPR/Cas9 to specifically delete the GPR56 S4 isoform.
• Comprehensive phenotypic analysis of Gpr56^∆S4 mice, including assessments of cortical architecture, CNS myelination, synapse density, and microglial activity.
• Evaluation of visual system development, specifically eye-segregation, in the mutant mice.

Main Results:

• Gpr56^∆S4 mice showed no defects in cortical architecture or CNS myelination compared to wild-type controls.
• These mice exhibited significantly increased synapse densities.
• A notable decrease in synapse engulfment by microglia and impaired eye-segregation were observed in Gpr56^∆S4 mice.

Conclusions:

• The GPR56 S4 splice variant is dispensable for cortical development and CNS myelination.
• The GPR56 S4 variant is essential for proper microglia-mediated synaptic pruning.
• These findings highlight the specific role of alternative splicing in diversifying GPR56 functions during neural development.