The cell lineage of the ascidian embryos, from the fertilized egg to the larval stage, has been completely elucidated. It has been shown which regions of the embryos make up the larval brain. The cell lineage of Ciona's brain is well known, and it is possible to answer the biological big question, "How is the brain made during embryogenesis?"  We are trying to elucidate this question at a truly single-cell resolution. The single-cell transcriptomics of the ascidian embryos from the 110-cells stage (gastrula) to the larval stage has been reported (Cao et al., Nature 2019). Based on this single-cell transcriptomics data, we have determined the gene expression profile of individual neurons from the neural progenitor cell to the terminally differentiated neurons. We are now able to perform a comprehensive analysis of larval CNS development. We will research to elucidate the development, and differentiation mechanisms of all neurons present in the CNS of the ascidian larva from the progenitor cell to the terminally differentiated neurons at the single-cell resolutions. Also, we will elucidate the gene regulatory mechanism in each neuron. We have already identified a large number of genes expressed in individual neurons. Based on these data, we will perform a comprehensive analysis of gene expression mechanisms in each neuron to elucidate the molecular mechanisms that allow each neuron to acquire specific functions.