Neural crest are a population of multipotent stem cells that originate in the dorsal part of the forming neural tube. Around the time of neural tube closure, they lose their epithelial characteristics and delaminate, by process known as epithelial-to-mesenchymal transition (EMT), acquiring migratory ability. Once neural crest cells reach their destination, they differentiate into numerous derivatives including neurons and glia of sensory ganglia. In a manner that is essentially the reverse of EMT, the formation of sensory ganglia requires the coalescence of neural crest cells via a process of mesenchymal-to-epithelial transition (MET). Both embryonic EMT and MET bear similarities to the molecular pathways and cellular changes undertaken by cancer cells during metastasis and establishment of secondary tumors. In recent years, there has been demonstrated that epigenetic-miRNA circuitries regulate EMT in various type of cancerous cells. However, the in vivo study of MET in cancer cells is very complex and unpredictable. In contrast, neural crest development is highly regulated and predictable, since the migratory pathways and process of condensation into sensory ganglia are well characterized. Based on this, we hypothesize that reversible epigenetic-microRNA regulatory networks may occur during transitional states of neural crest cells delamination (EMT) and sensory ganglia coalescence (MET). In this context, the goal of Aim 1 is to identify a core miRNA signature necessary for neural crest delamination and sensory ganglion condensation. Here we propose to perform using Ago2-HITS-CLIP assays, the first transcriptome-wide map of miRNA targeting events associated with epithelial plasticity during neural crest delamination and sensory ganglia condensation. Then, we will perform gain and loss-of-function experiments in chick embryos to validate the role of selected miRNAs in vivo. Next, we propose to determine the epigenetic regulation of core miRNAs expression (Aim 2). To this end, we will determine the DNA methylation status of selected miRNAs loci during transitional states of neural crest delamination and coalescence. Finally, Aim 3 will evaluate the epigenetic writers and erasers that control the core miRNA expression. Based on the proposed reversibility of the EMT and MET processes, we will examine the role of DNA methyltransferases (DNMT) and ten-eleven translocation (TET) as key regulators of DNA methylation/demethylation status of the core miRNAs necessary for neural crest delamination and sensory ganglion coalescence. Taken together, this study proposes to identify a core miRNA signature, their epigenetic regulation and regulators necessary for the EMT and MET during sensory ganglion formation. These studies hopes to lay the foundation for therapeutic intervention for certain types of neurocristopathies, neuropathies, and neural crest- derived cancers like neuroblastoma.
Cranial sensory ganglia mediate critical functions, including somatosensation, taste, and the visceral sensation of internal organs such as the heart, lungs and gastrointestinal tract. Their formation requires, in part, the initial delamination and the posterior coalescence of migratory neural crest cells. Several types of neurocristopathies, neuropathies, and neural crest-derived cancers involve defects on the transitional states (EMT and MET) required during delamination and coalescence. Although the epigenetic-miRNA contribution during EMT mechanism have been extensively studied in cancer metastasis, very little is known about the reversibility of this regulation during MET. Here we propose to understand the epigenetic-miRNA circuitry regulating neural crest delamination and sensory ganglion coalescence. The outcome of these studies will provide significant new insights into the epigenetic-miRNA regulation and may lay the foundation for the basis of therapeutics for certain types of neurocristopathies, neuropathies, and neural crest-derived cancers like neuroblastoma.