Menglong Zeng: Characterizing the molecular architecture of excitatory synapses onto GABAergic interneurons

Abstract:

Normal brain function requires a delicate balance between excitation and inhibition. While representing a small portion of neurons in the cortex, GABAergic interneurons are essential to maintaining excitation-inhibition balance and supporting higher-order brain function. 

GABAergic interneuron dysfunction is tightly associated with autism pathophysiology. Intriguingly, a major category of autism risk genes encodes excitatory synaptic proteins. However, a mechanistic understanding of the excitatory synapses onto GABAergic interneurons has not been well established to improve our understanding and treatment of autism.  

How can we investigate the structure and function of minority cell type-specific synapses within an intact brain circuit? We used a combination of in vivo proximity labeling, expansion microscopy, gene editing, electrophysiology and behavior to comprehensively investigate excitatory synapses onto GABAergic interneurons. Our study discovered that interneurons use different molecular strategies to diversify their synaptic structure and function, which provide new insights into autism pathophysiology and novel targets for therapy. 

Yixi Liu: Expansion microscopy at subzero temperatures for ultrastructural preservation

Expansion microscopy (ExM) is a powerful technique that enables nanoscale imaging on a conventional light microscope by physically expanding biological specimens permeated by a hydrogel (Science, 347(6221), 543-548). We here introduce subzero expansion microscopy (subExM), a new technique enhancing the nanoscale imaging capabilities of expansion microscopy (ExM) by conducting key processes at subzero temperatures (-20°C or lower). It employs a new chemical for simultaneous specimen fixation and biomolecule anchoring to the hydrogel matrix, ensuring minimal protein-protein crosslinking and epitope masking. This enables better signal intensity and target specificity in post-expansion staining. Gelation at subzero temperatures can further enhance the ultrastructure integrity by minimizing perturbation. The effectiveness of subExM is demonstrated through better preservation and imaging of biological structures such as microtubules, mitochondria, and Golgi apparatus, with improved ultrastructural continuity and antigen preservation. This method holds the potential to enhance the detailed and faithful study of the architecture of biological systems using ExM.