To model human neural-cell-fate specification and to provide cells for regenerative therapies, we have developed a method to generate human neural progenitors and neurons from human embryonic stem cells, which recapitulates human fetal brain development. Through the addition of a small molecule that activates canonical WNT signaling, we induced rapid and efficient dose-dependent specification of regionally defined neural progenitors ranging from telencephalic forebrain to posterior hindbrain fates. Ten days after initiation of differentiation, the progenitors could be transplanted to the adult rat striatum, where they formed neuron-rich and tumor-free grafts with maintained regional specification. Cells patterned toward a ventral midbrain (VM) identity generated a high proportion of authentic dopaminergic neurons after transplantation. The dopamine neurons showed morphology, projection pattern, and protein expression identical to that of human fetal VM cells grafted in parallel. VM-patterned but not forebrain-patterned neurons released dopamine and reversed motor deficits in an animal model of Parkinson's disease.

Recent reports demonstrate that somatic mouse cells can be directly converted to other mature cell types by using combined expression of defined factors. Here we show that the same strategy can be applied to human embryonic and postnatal fibroblasts. By overexpression of the transcription factors Ascl1, Brn2, and Myt1l, human fibroblasts were efficiently converted to functional neurons. We also demonstrate that the converted neurons can be directed toward distinct functional neurotransmitter phenotypes when the appropriate transcriptional cues are provided together with the three conversion factors. By combining expression of the three conversion factors with expression of two genes involved in dopamine neuron generation, Lmx1a and FoxA2, we could direct the phenotype of the converted cells toward dopaminergic neurons. Such subtypespecific induced neurons derived from human somatic cells could be valuable for disease modeling and cell replacement therapy. C ellular reprogramming, the process by which somatic cells can be converted into induced pluripotent stem (iPS) cells and subsequently differentiated to mature cells, including specific types of neurons, has opened up new possibilities for disease modeling and cellular repair (1-5). Recently, it was shown that somatic cells can also be directly converted to other mature cell types by expression of a specific combinations of genes (6-9). Expression of Ascl1, Brn2, and Myt1l efficiently converted mouse embryonic fibroblasts (MEFs) and postnatal fibroblasts into functional neurons (induced neurons, or iN cells) (10). Cells generated via direct conversion do not pass through a pluripotent state, are probably not tumorigenic, and may serve as an interesting alternative to iPS cells for generating patient-and/or disease-specific neurons.Here, we show the direct conversion of human fibroblasts into functional neurons using the same combination of neural conversion factors used for iN conversion of mouse fibroblasts (10). We also demonstrate that the expression of additional transcription factors leads to the generation of cells with properties of dopaminergic neurons, which is the cell type lost in Parkinson's disease. Our findings provide proof of principle that specific subtypes of iN cells can be produced from human somatic cells by transcription factor-mediated fate instruction combined with the three neural conversion factors. ResultsTo investigate whether direct conversion into neurons from human somatic cells is possible, we established fibroblast cultures from human embryos aged 5.5-7 wk postconception (for details see Table S1). The head, the dorsal part of the embryo containing the spinal cord, and all red organs were removed, and the remaining tissue was dissociated and plated under standard fibroblast conditions (Fig. 1A). After one passage followed by a freeze-thaw cycle, the fibroblast identity and the absence of the neural crest marker SOX10 in the resulting cell lines were confirmed (Fig. 1B, Figs. S1 and S2, and Tables S2 and S3). The cells were then...

SummaryConsiderable progress has been made in generating fully functional and transplantable dopamine neurons from human embryonic stem cells (hESCs). Before these cells can be used for cell replacement therapy in Parkinson’s disease (PD), it is important to verify their functional properties and efficacy in animal models. Here we provide a comprehensive preclinical assessment of hESC-derived midbrain dopamine neurons in a rat model of PD. We show long-term survival and functionality using clinically relevant MRI and PET imaging techniques and demonstrate efficacy in restoration of motor function with a potency comparable to that seen with human fetal dopamine neurons. Furthermore, we show that hESC-derived dopamine neurons can project sufficiently long distances for use in humans, fully regenerate midbrain-to-forebrain projections, and innervate correct target structures. This provides strong preclinical support for clinical translation of hESC-derived dopamine neurons using approaches similar to those established with fetal cells for the treatment of Parkinson’s disease.

SummaryStem cell treatments for neurodegenerative diseases are expected to reach clinical trials soon. Most of the approaches currently under development involve transplantation of immature progenitors that subsequently undergo phenotypic and functional maturation in vivo, and predicting the long-term graft outcome already at the progenitor stage remains a challenge. Here, we took an unbiased approach to identify predictive markers expressed in dopamine neuron progenitors that correlate with graft outcome in an animal model of Parkinson’s disease through gene expression analysis of >30 batches of grafted human embryonic stem cell (hESC)-derived progenitors. We found that many of the commonly used markers did not accurately predict in vivo subtype-specific maturation. Instead, we identified a specific set of markers associated with the caudal midbrain that correlate with high dopaminergic yield after transplantation in vivo. Using these markers, we developed a good manufacturing practice (GMP) differentiation protocol for highly efficient and reproducible production of transplantable dopamine progenitors from hESCs.

Generation of precisely patterned neural cells from human pluripotent stem cells (hPSCs) is instrumental in developing disease models and stem cell therapies. Here, we provide a detailed 16-d protocol for obtaining high-purity ventral midbrain (VM) dopamine (DA) progenitors for intracerebral transplantation into animal models and for in vitro maturation into neurons. We have successfully transplanted such cells into the rat; however, in principle, the cells can be used for transplantation into any animal model, and the protocol is designed to also be compatible with clinical transplantation into humans. We show how to precisely set the balance of patterning factors to obtain specifically the caudal VM progenitors that give rise to DA-rich grafts. By specifying how to perform quality control (QC), troubleshooting and adaptation of the procedure, this protocol will facilitate implementation in different laboratories and with a variety of hPSC lines. To facilitate reproducibility of experiments and enable shipping of cells between centers, we present a method for cryopreservation of the progenitors for subsequent direct transplantation or terminal differentiation into DA neurons. This protocol is free of xeno-derived products and can be performed under good manufacturing practice (GMP) conditions.

Stem cell engineering and grafting of mesencephalic dopamine (mesDA) neurons is a promising strategy for brain repair in Parkinson's disease (PD). Refinement of differentiation protocols to optimize this approach will require deeper understanding of mesDA neuron development. Here, we studied this process using transcriptome-wide single-cell RNA sequencing of mouse neural progenitors expressing the mesDA neuron determinant Lmx1a. This approach resolved the differentiation of mesDA and neighboring neuronal lineages and revealed a remarkably close relationship between developing mesDA and subthalamic nucleus (STN) neurons, while also highlighting a distinct transcription factor set that can distinguish between them. While previous hESC mesDA differentiation protocols have relied on markers that are shared between the two lineages, we found that application of these highlighted markers can help to refine current stem cell engineering protocols, increasing the proportion of appropriately patterned mesDA progenitors. Our results, therefore, have important implications for cell replacement therapy in PD.

Trait-associated loci often map to genomic regions encoding long noncoding RNAs (lncRNAs), but the role of these lncRNAs in disease etiology is largely unexplored. We show that a pair of sense/antisense lncRNA (6p22lncRNAs) encoded by CASC15 and NBAT1 located at the neuroblastoma (NB) risk-associated 6p22.3 locus are tumor suppressors and show reduced expression in high-risk NBs. Loss of functional synergy between 6p22lncRNAs results in an undifferentiated state that is maintained by a gene-regulatory network, including SOX9 located on 17q, a region frequently gained in NB. 6p22lncRNAs regulate SOX9 expression by controlling CHD7 stability via modulating the cellular localization of USP36, encoded by another 17q gene. This regulatory nexus between 6p22.3 and 17q regions may lead to potential NB treatment strategies.

No abstract