Neural crest migration is driven by a few trailblazer cells with a unique molecular signature narrowly confined to the invasive front

Abstract

Neural crest (NC) cell migration is crucial to the formation of peripheral tissues during vertebrate development. However, how NC cells respond to different microenvironments to maintain persistence of direction and cohesion in multicellular streams remains unclear. To address this, we profiled eight subregions of a typical cranial NC cell migratory stream. Hierarchical clustering showed significant differences in the expression profiles of the lead three subregions compared with newly emerged cells. Multiplexed imaging of mRNA expression using fluorescent hybridization chain reaction (HCR) quantitatively confirmed the expression profiles of lead cells. Computational modeling predicted that a small fraction of lead cells that detect directional information is optimal for successful stream migration. Single-cell profiling then revealed a unique molecular signature that is consistent and stable over time in a subset of lead cells within the most advanced portion of the migratory front, which we term trailblazers. Model simulations that forced a lead cell behavior in the trailing subpopulation predicted cell bunching near the migratory domain entrance. Misexpression of the trailblazer molecular signature by perturbation of two upstream transcription factors agreed with the in silico prediction and showed alterations to NC cell migration distance and stream shape. These data are the first to characterize the molecular diversity within an NC cell migratory stream and offer insights into how molecular patterns are transduced into cell behaviors.

An interdisciplinary approach to investigate collective cell migration in neural crest

“…With the present model described in this Commentary, there are still a number of tests that can be performed. For example, our mathematical model, based on McLennan et al's model, can make predictions on what would happen if other manipulations were carried out on the streaming cells. We illustrate this with two cases.…”

“…The initial studies assumed that the VEGF concentration was fixed at zero on the lateral boundaries creating an inward pointing VEGF gradient to ensure that the cells do not leave the domain . Later studies used zero flux boundary conditions for VEGF, and the key results of the model were independent of the choice of these two different sets of boundary conditions …”

“…Further, experimental photoablation methods to delete leader cells are difficult to interpret due to collateral damage of surrounding tissue within the cell migratory pathway . Therefore, the model is more appropriate for making qualitative predictions, and McLennan et al used their model to investigate how invasion depended on the proportion of cells that are leaders. The model predicted that it is possible for cells to invade ba2 for a wide range of leader cell numbers, but that beyond a certain (small) number of leaders, the total number of cells in a stream will decrease (Figure ).…”

“…To test these predictions, McLennan et al performed single‐cell gene expression profiling using real‐time qPCR. They discovered regional differences in gene expression and identified a unique stable molecular signature of the cells at the front of the migrating NC stream.…”

“…Collective NC cell migration can be facilitated by DAN expression through regulation of cell speed within range of the dorsal neural tube. (A) No reduction in speed: the model simulated is as in McLennan et al on a widened domain with cell speed 40 μm/h. Leader NC cells are in yellow, follower cells are in green, and the background blue color shows the VEGF chemoattractant concentration.…”