Chick cranial neural crest cell migration
This thesis presents work toward understanding how chick neural crest cells polarize their protrusions to achieve directed motility. There are multiple strategies that cells can use to generate directed migration. They can read gradients of guidance cues spatially across their surface or compare the concentration of agonist in time. Cells can bias the generation of protrusions or their lifetime. Determining the logical framework that cells use for migration is often challenging as it is not readily deduced from knockout phenotypes.
Here we use 3D two-photon imaging of chick branchial arch 2 directed neural crest cells to probe how these mechanisms contribute to directed movement (Chapter two). We find that cells throughout the stream are morphologically polarized along the direction of overall stream movement and that there is a progressive sharpening of the morphological polarity program. Neural crest cells have weak spatial biases in filopodia generation and lifetime. Local bursts of filopodial generation precede the generation of larger protrusions. These larger protrusions are more spatially biased than the filopodia, and the subset of protrusions that power motility are the most polarized of all. Orientation rather than position is the best correlate of the protrusions that are selected for cell movement. This progressive polarity refinement strategy may enable neural crest cells to efficiently explore their environment and migrate accurately in the face of noisy guidance cues.
Neural crest cell migration occurs in a 3D environment. However, published protocols for culturing migratory neural crest cells and performing chemotaxis assays have all made use of 2D culture. We sought to determine whether neural crest cell morphology in 2D culture systems resembled that in vivo and if not to explore whether 3D culture techniques could improve neural crest cell behavior (Chapter 3).