Revealing the Landscape of Synaptic Diversity by Cell type- and Synapse-specific Proteomics and Transcriptomics

Introduction

Synapses differ in their shape, size, and function and exhibit ongoing plasticity during the development and modification of neural circuits. The structural diversity of synapses is largely known, whereas the molecular diversity of synapses is much less well understood. While most synaptic molecules have been identified by immunolabeling and bulk proteomic approaches, the complement of proteins present at individual synapse types, as well as their stoichiometric relationships with other molecules, remains unknown.

Current Classification

Indeed, our current classification mostly relies on neurotransmitter/receptor phenotypes, leading to broad descriptors like “excitatory” or “inhibitory” synapses. Because the function of the synapse, as well as its ability to change, is largely determined by the quality and quantity of molecules that inhabit it, it is essential to understand synaptic molecular diversity.

Aims of the Proposal

The aims of this proposal are to:

1. Determine the proteomes and transcriptomes of genetically identifiable synaptic populations in different brain areas.
2. Determine the molecular diversity in these same synapse populations using transcriptomic analysis of individual synapses.
3. Assess how these synaptic proteomes, transcriptomes, and the transcriptomic diversity respond to plasticity.

Methodology

To study synaptic proteomes and transcriptomes, we will use Fluorescence-Activated Synaptosome Sorting to purify different synaptic populations (excitatory, inhibitory, dopaminergic) from different brain areas.

We will:

• Use state-of-the-art methods optimized for quantitative transcriptomic and proteomic profiling of very small amounts of sorted synapses.
• Develop a method, SynDrops, for the transcriptomic analysis of individual synapses.
• Examine how synaptic proteomes and transcriptomes change during plasticity.

Expected Outcomes

These studies will reveal the landscape of synaptic diversity within synapse types and across brain areas, allowing the field to probe “diseased” synapses in the future.