MicroRNA miR-196a controls neural crest patterning by repressing immature neural ectoderm programs in Xenopus embryos.
Neural crest (NC) cells form a multipotent stem cell population specified during neurulation, which undergoes an epithelial-to-mesenchymal transition (EMT) and migrate extensively in the developing embryo, to generate numerous tissues and cell types including the craniofacial skeleton, the peripheral nervous system and pigment cells. The genetic and molecular details of neural crest specification are governed by a complex, yet still partially understood gene regulatory network (NC-GRN). In particular, the precise function of microRNAs in this network remains poorly known. MicroRNAs are short non-coding 20-22 nucleotides long RNAs which control gene expression through post-transcriptional repression. Since miRNA-196a is expressed in the developing neural and neural crest cells of Xenopus laevis embryos we here investigated miR-196a function in the NC-GRN, by knocking-down its expression using antisense morpholinos. Depletion of miR-196a revealed major neural crest and craniofacial phenotypes. These defects were preceded by the perturbed expression of key neural, neural border and neural crest markers such as sox2/3, zic1/3, pax3, sox10 and snail2. Using RNA sequencing of individual neural border and neural crest explants, we have identified a signature of genes up- and down-regulated by miR-196a and validate these with rescue experiments using a miR mimic. We show that Sox10, a predicted target of miR-196a, is lost following morpholino knockdown and rescued upon miR 196a mimic expression. Our study identifies miR-196a as a key actor of early patterning in the dorsal ectoderm, balancing the extent of immature neural plate progenitors with neural crest and placode specification, while also promoting neuron differentiation within the neural plate. Overall design: RNA-seq profiling of morpholino knockdown of miR-196a in Xenopus laevis neural crest tissue with accompanying control and mismatch morpholino injections. These were conducted on wild-type embryos that were injected at 4-cell stage into right dorsal blastomere and grown to NF stage 14 and 17 before total RNA extraction and RNA-sequencing.