Topographical cuescontrol the morphology and dynamics of migrating cortical interneurons

Abstract

In mammalian embryos, cortical interneurons travel long distances among complex threedimensional tissues before integrating into cortical circuits. Several molecular guiding cues involved in this migration process have been identified, but the influence of physical parameters remains poorly understood. In the present study, we have investigated in vitro the influence of the topography of the microenvironment on the migration of primary cortical interneurons released from mouse embryonic explants.We found that arrays of 10 µm-sized PDMS micro-pillars, either round or square, influenced both the morphology and the migratory behavior of interneurons. Strikingly, most interneurons exhibited a single and long leading process oriented along the diagonals of the square pillared array, whereas leading processes of interneurons migrating in-between round pillars were shorter, often branched and oriented in all available directions. Accordingly, dynamic studies revealed that growth cone divisions were twice more frequent in round than in square pillars. Both soma and leading process tips presented forward directed movements within square pillars, contrasting with the erratic trajectories and more dynamic movements observed among round pillars. In support of these observations, long interneurons migrating in square pillars displayed tight bundles of stable microtubules aligned in the direction of migration.Overall, our results show that micron-sized topography provides global spatial constraints promoting the establishment of two different morphological and migratory states.Remarkably, both states belong to the natural range of migratory behaviors of cortical interneurons, highlighting the potential importance of topographical cues in the guidance of these embryonic neurons, and more generally in brain development.In this study, we investigated this question using microstructured substrates and demonstrated the high sensitivity of cortical interneurons to the architecture of their environment. Our results revealed that topographical constraints efficiently modulate the migratory behavior of interneurons by controlling cell morphology, branching dynamics and cytoskeletal organization. In particular, by using two shapes of micron-sized pillars, we have been able to select and stabilize in vitro two main migratory behaviors observed in vivo, associated with specific morphologies: non-branched cells with long leading processes showed a directional movement among square pillars, and branched cells with short leading processes displayed a fast, exploratory migration among round pillars. This study therefore provides new insights into the guidance and the biology of these cells. The in vitro model described in this study thus emerges as a new promising tool to control and study interneuron migratory behaviors in physiological or pathological conditions.