HIGH-THROUGHPUT 3D CHEMOTACTIC ASSAYS REVEALS COMPLEX PATTERNS IN NEURONAL SENSATION TO MOLECULAR GRADIENT
City University of Hong Kong, Hong Kong
Cell migration and neurite projection are key cellular processes in the development of nervous system. Progenitor cells migrate to targeted coordinates from different origins and neurite outgrowth are guided to allow wiring of brain circuits. These processes are suggested to be regulated by graded distribution of diffusive or substrate-bounded guidance cues, or chemotaxis. In the past few decades, great efforts have been made to reveal various chemotactic molecules, such as neurotrophin factors, netrin-1, semapherin, slit family, and growth factors etc. Though many of these cues are suggested to play shared roles in the guidance of migrating neurons and axonal projection, little has been done to elucidate the integration of migration and neurite guidance programs within individual cells; and we know even less about how different gradient profiles affect these regulations. In this study, we developed a microfluidic platform that incorporates arrays of matrigel-cylinders to allow high-throughput generation of a large library of molecular gradients with distinct steepness. When primary neurons were seeded into the hydrogel, we can establish a massive array of three-dimensional (3D) neuron cultures, each of which exposes to a particular gradient profile. In this way, hundreds of 3D chemotactic assays could be performed in parallel and the regulation of both cellular migration and neurite projection could be simultaneously investigated. As a proof of concept, we tested three classical types of guidance molecule, NGF, Netrin-1, and Sema3A, by using the 3D chemotactic assays, and revealed dramatically diverse and complex neuronal chemosensation in relation to the gradient steepness of different molecules.