MicroRNA miR-219 is required for neural border and neural crest development in Xenopus neurulas

Neural crest (NC) multipotent stem cells give rise to many tissues including most of the peripheral nervous system, pigment cells and the craniofacial mesenchyme and skeleton. During gastrulation and early neurulation, cranial NC cells are specified in the ectoderm territory located between the anterior neural plate ectoderm and the future pre-placodal and lateral non-neural ectoderm. At the end of neurulation, NC cells undergo an epithelial-to-mesenchymal transition and migrate to various locations in the developing embryo where they differentiate. While the fine-tuning of NC specification is increasingly being elucidated, many questions remain, including how microRNAs may govern expression of gene programs during these processes. MicroRNAs are short non-coding 20-22 nucleotides-long RNAs which regulate gene expression through post-transcriptional repression. We have identified miR-219 as a candidate regulator of Xenopus NC development. Here, miR-219-dependent molecular pathways were investigated by morpholino knock-down and reveal NC phenotypes. The development of the NC and adjacent ectoderm was evaluated using whole mount in situ hybridization of key markers (pax3, zic1, xhe2, sox10, snai2, sox2), alcian blue cartilage staining, phenotype analysis, RNA sequencing of microdissected dorsal ectoderm and microRNA rescue experiments. While neural induction is mainly unaffected, miR-219 depletion alters gene expression programs associated with neural border development, resulting in loss of NC specification.