The brain contains billions of neurons and the interactions between neurons enable people to think, move, and feel emotions. These interactions happen at specialized junctions, called synapses. At synaptic sites, electric impulses trigger the release of neurotransmitter from the presynaptic terminal that activates the neurotransmitter receptors on the postsynaptic membrane and passes the information to the postsynaptic neuron. This process is called synaptic transmission. Importantly, synapses are not static but can be strengthened or weakened in response to life experiences. This dynamic change, namely synaptic plasticity, is the basis of learning and memory.

Our overarching research objective is to understand the basic mechanisms underlying synaptic transmission and plasticity and the perturbations occurring in these mechanisms that give rise to neurological disorders.

Synaptic transmission is maintained by a delicate subsynaptic architecture, and key to this architecture is how the distribution of transmitter release sites at presynaptic terminals corresponds to the position of receptor densities on the postsynaptic neurons. We have recently discovered a new organizing principle of synapses, namely transsynaptic nanocolumn. The nanocolumn aligns the high-density protein nanoclusters across the cleft, including presynaptic active zone proteins critical for vesicle fusion, postsynaptic scaffolds, and receptors, so that presynaptic neurotransmitter is released preferentially at the postsynaptic receptor densities, which would enhance the efficiency of synaptic transmission [see details]. This demonstrates that besides the well-recognized presynaptic release probability and postsynaptic receptor number or density, the nanoscale organization of these two elements and the spatial relationship between them could also be key to the maintenance and plasticity of synaptic transmission. More importantly, it reveals a sensitive point by which disease-associated pathways may disrupt synapse function.

Therefore, our current work are focusing on molecular mechanisms underlying the nanoculomn structure and how these proteins are reorganized to mediate the synaptic changes in response to plasticity induction or pathological challenges. Besides, we are also interested in other processes that regulate synaptic function in a spatially or temporally confined manner, including protein synthesis and activities of organelles such as lysosome. 

Understanding these complex molecular interactions and physiological processes requires examining these protein organizations and synaptic functions with sufficiently high spatiotemporal resolution. To achieve this, we use cutting-edge live-cell confocal and super-resolution imaging techniques on cultured neurons and brain tissue sections. In particular, we exploit single-molecule localization microscopy, including MINFLUX, PALM, STORM and PAINT, that allow us to investigate protein organization within individual synapses at nanometer resolution. By combining these with electrophysiology and genetic approaches, we are able to examine the structure-function relationship at individual synapses.

Spatial transcriptomics

The spatial pattern of RNAs in tissue determines the key life processes from cell differentiation and development to aging and disease. However, it is a huge technical challenge to obtain the full transcriptome of single cells and the information of their spatial distribution at the same time. The development of spatial transcriptomics technology overcomes this technical barrier. Therefore, it was selected as the technology of the year 2020 by Nature Methods and one of the seven key technologies to watch in 2022 by Nature. At present, the spatial transcriptomics is achieved with either sequencing-based or imaging-based methods . There have been several pretty mature commercialized products for the former, but they are largely limited by resolution. The latter is still in rapid development and can easily achieve single-cell or subcellular accuracy, but they are suffering from limited gene species, imaging efficiency and high cost.

Cooperating with Professor Qu Kun's lab in USTC, we have developed a new spatial transcriptomics method - "fluorescence in situ hybridization technology of encoded amplified characteristic sequence" or BASSFISH. By optimizing the hardware and developing a full set of algorithms, we are able to image and analyze hundreds of RNA species in various of tissue samples. We believe that the BASSFISH technology has achieved a better balance between gene throughput, imaging efficiency and cost, which enables us to conduct high-throughput and cost-efficient analysis on large samples.