Dynamic and non-uniform expression of key transcription factors provides insights into the emergence of neural crest cells at the neural plate border

The neural crest is a vertebrate stem cell population with broad developmental potential. While a gene regulatory network describing establishment of these cells has been generated, much remains to be learned about the dynamics of this process. Here, we use fluorescent in situ hybridization chain reaction to quantify the spatiotemporal dynamics of neural crest formation in Xenopus. We find that the initial onset of neural crest genes is broad and partially overlapping, with distinct anterior-posterior and medio-lateral biases. A shared neural crest domain emerges, but some genes retain relative expression differences that persist into migratory stages, producing stream-specific gene expression patterns. These differences correlate with dynamic expression of the neural plate border factors pax3 and zic1. Correlating relative intensities of pax3 and zic1 with the presence or absence of nascent neural crest transcripts predicts that these factors can differentially regulate snai2 and sox8, which we confirm experimentally. Strikingly, later stages display an inverse correlation between neural crest and neural plate border factors, suggesting that pax3 and zic1 initially promote neural crest gene activation but are downregulated as neural crest identity emerges.