Dynamic organization of neuronal extracellular matrix revealed by HaloTag-HAPLN1.

ABSTRACT

The brain's extracellular matrix (ECM) regulates neuronal plasticity and animal behavior. ECM staining shows a net-like structure around a subset of neurons, a ring-like structure at the Nodes of Ranvier, and diffuse staining in the interstitial matrix. However, understanding the structural features of ECM deposition across various neuronal types and subcellular compartments remains limited. To visualize the organization pattern and assembly process of the hyaluronan-scaffolded ECM in the brain, we fused a HaloTag to HAPLN1, which links hyaluronan and proteoglycans. Expression or application of the probe in primary rat neuronal cultures enables us to identify spatial and temporal regulation of ECM deposition and heterogeneity in ECM aggregation among neuronal populations. Dual-color birthdating shows the ECM assembly process in culture and in vivo. Sparse expression in mouse brains of either sex reveals detailed ECM architectures around excitatory neurons and developmentally regulated dendritic ECM. Our study uncovers extensive structural features of the brain's ECM, suggesting diverse roles in regulating neuronal plasticity.Significance Statement Our tool, H-Link, provides a technical advance to reveal the extensive structural features and assembly process of the brain's extracellular matrix (ECM). H-Link reveals hyaluronic acid (HA)-based ECM clustered on both excitatory and inhibitory neurons. ECM clusters on hippocampal granule cells are developmentally regulated and extend to the dendrites. We can also longitudinally follow the assembly of the ECM in vivo and in culture. Our study provides a significant technical advance that will be of broad interest to the neuroscience community, particularly those interested in niche-dependent regulation of plasticity.