A genetically specified connectomics approach applied to long-range feeding regulatory circuits

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Neural circuits' information processing relies on synaptic connectivity and molecular composition.
• Nanometer resolution is crucial for structural analysis of neural circuits, typically achieved via serial-section electron microscopy.
• Reconstructing molecularly defined synapses using electron microscopy presents significant challenges.

Purpose of the Study:

• To develop and validate a novel method for visualizing molecularly defined synapses with electron microscopy.
• To enable the study of long-range neural connectivity in genetically defined cell populations.
• To characterize the circuit organization of specific hypothalamic neurons involved in feeding behavior.

Main Methods:

• Development of a genetically encoded synaptic marker for electron microscopy (GESEM).
• Intra-vesicular generation of electron-dense labeling in axonal boutons for synapse identification.
• Application of GESEM in mouse and fly models, combined with functional and viral circuit mapping.

Main Results:

• GESEM successfully identified synapses from specific neuronal populations (Cre or GAL4 expressing) in mouse and fly.
• Excellent ultrastructural preservation was achieved, facilitating detailed analysis.
• Long-range connectivity of AGRP and POMC neurons in the mouse hypothalamus was visualized.
• Basic circuit organization features of these hypothalamic cell types were characterized.

Conclusions:

• GESEM is a powerful tool for high-resolution connectomics of molecularly defined cell types.
• This method overcomes previous limitations in reconstructing molecularly defined synapses.
• The findings provide insights into the neural circuitry underlying feeding behavior.