Figure 1. The cranial neural crest cell migratory pattern; cellular features and signaling pathways.

(A) A schematic representation showing recently discovered key guidance cues involved in CNCC migration. (B) The cranial NCCs migrate in 3 distinct streams as seen by membrane (Gap43-GFP) and nuclear (H2B-mCherry) labeling (introduced into premigratory NCCs by electroporation delivery) reduced to grayscale for clarity. (C) CNCCs that emerge from mid-r3 and more rostral migrate in a broad wave and display multiple filopodial protrusions. (D) CNCCs that emerge mid-r3 to mid-r5 are sculpted into a tight stream adjacent to r4 that spreads out at the front (E) Post-otic NCCs that emerge from mid-r5 and more caudal migrate as an initial wave, followed by NCCs that form chain-like arrays. The arrows point to cells that travel in a chain-like array. (F) A schematic representation of the molecules guiding the r4 NCC stream. The r4 NCCs express neuropilins, Plexin A1 and VEGFR2. The overlaying ectoderm expresses VEGF, which is a NCC chemoattractant. R3 and r5 secrete semaphorin3A, which is a NCC inhibitor. A guidance cue that prevents the r4 NCCs migrating ventromedially is as yet unknown (?). r, rhombomere; ba, branchial arch; OV, otic vesicle, NT, neural tube, N, notochord. The scale bars are 20um in (B) and 10um in (C–E).