The human cognition-enhancing CORD7 mutation increases active zone number and synaptic release

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• The CORD7 mutation in RIMS1/RIM1 is linked to enhanced verbal IQ and working memory.
• RIM protein is crucial for presynaptic active zones and neurotransmitter release.
• The precise impact of the CORD7 mutation on synaptic function was previously unknown.

Purpose of the Study:

• To investigate the effects of the CORD7 mutation on RIM function and synaptic vesicle release using a Drosophila melanogaster disease model.
• To elucidate the molecular mechanisms underlying the CORD7-associated cognitive enhancements.

Main Methods:

• X-ray crystallography to determine the structure of the Drosophila RIM C2A domain.
• CRISPR/Cas9 gene editing to create Drosophila models with CORD7-like mutations.
• Electrophysiology (two-electrode voltage clamp, focal recordings) to analyze synaptic transmission.
• Super-resolution microscopy to examine presynaptic active zone organization.

Main Results:

• The CORD7 mutation in Drosophila RIM causes semi-dominant effects on synaptic transmission.
• Observed faster, more efficient synaptic release, an increased readily releasable pool, and more release sites.
• The mutation did not alter the nanoscopic organization of presynaptic active zones.

Conclusions:

• The CORD7 mutation enhances synaptic efficiency through tighter release coupling and an expanded readily releasable pool.
• These synaptic improvements likely contribute to the enhanced cognitive functions observed in CORD7 patients.
• Drosophila serves as a valuable model for studying CORD7 and related synaptic disorders.