Regulation of Neural Crest Development by Chemically Targetable Pathways

Abstract

The neural crest provides an excellent model for the study of cellular behavior during development. Arising at the border of neural and non-neural ectoderm, this dynamic cell population migrates throughout the embryo and differentiates into a variety of tissue types, including pigment cells like melanocytes. Previous work indicates that melanocytes re-acquire a neural crest cell fate during the process of malignant transformation. To better understand pathways that regulate neural crest development and identify potential therapeutic avenues for melanoma treatment, I conducted a screen in primary zebrafish embryo cultures for chemicals that decrease neural crest formation, as read out by crestin:EGFP expression. This led to the identification of chemicals that disrupt neural crest development and reduce melanoma viability. First, I found that the natural product caffeic acid phenethyl ester (CAPE) disrupts neural crest gene expression, migration, and melanocytic differentiation in zebrafish embryos by inhibiting Akt and reducing Sox10 activity. CAPE inhibits PI3K/Akt signaling specifically in FGF-stimulated cells, and neural crest defects in CAPE-treated embryos are suppressed by constitutively active Akt1. Inhibition of Akt activity by constitutively active PTEN similarly decreases crestin expression and Sox10 activity in zebrafish embryos. This work addresses a knowledge gap in the mechanisms of neural crest development and suggests that Akt may play a cell type-specific role in melanoma initiation in additional to its canonical role in cell survival and proliferation. Second, I discovered that the calcium channel inhibitor mibefradil selectively kills melanoma cells and reduces tumor burden in a zebrafish transplant model of melanoma. This work indicates that melanoma cells share chemical sensitivities with the embryonic neural crest and may lead to the development of novel therapeutics. In summary, my work has generated insight into both neural crest and melanoma biology and lays a foundation for future studies of melanoma initiation and treatment.