Explore the vast range of titles available.

The human cortex comprises diverse cell types that emerge from an initially uniform neuroepithelium that gives rise to radial glia, the neural stem cells of the cortex. To characterize the earliest stages of human brain development, we performed single-cell RNA-sequencing across regions of the developing human brain, including the telencephalon, diencephalon, midbrain, hindbrain and cerebellum. We identify nine progenitor populations physically proximal to the telencephalon, suggesting more heterogeneity than previously described, including a highly prevalent mesenchymal-like population that disappears once neurogenesis begins. Comparison of human and mouse progenitor populations at corresponding stages identifies two progenitor clusters that are enriched in the early stages of human cortical development. We also find that organoid systems display low fidelity to neuroepithelial and early radial glia cell types, but improve as neurogenesis progresses. Overall, we provide a comprehensive molecular and spatial atlas of early stages of human brain and cortical development. Eze et al. use single-cell sequencing and immunohistochemical validation to create an atlas of early human brain development. In the telencephalon, they discover a diversity of progenitor subtypes, including two that are enriched in humans.

Satiety and other core physiological functions are modulated by sensory signals arising from the surface of the gut. Luminal nutrients and bacteria stimulate epithelial biosensors called enteroendocrine cells. Despite being electrically excitable, enteroendocrine cells are generally thought to communicate indirectly with nerves through hormone secretion and not through direct cell-nerve contact. However, we recently uncovered in intestinal enteroendocrine cells a cytoplasmic process that we named neuropod. Here, we determined that neuropods provide a direct connection between enteroendocrine cells and neurons innervating the small intestine and colon. Using cell-specific transgenic mice to study neural circuits, we found that enteroendocrine cells have the necessary elements for neurotransmission, including expression of genes that encode pre-, post-, and transsynaptic proteins. This neuroepithelial circuit was reconstituted in vitro by coculturing single enteroendocrine cells with sensory neurons. We used a monosynaptic rabies virus to define the circuit's functional connectivity in vivo and determined that delivery of this neurotropic virus into the colon lumen resulted in the infection of mucosal nerves through enteroendocrine cells. This neuroepithelial circuit can serve as both a sensory conduit for food and gut microbes to interact with the nervous system and a portal for viruses to enter the enteric and central nervous systems.

Human embryonic stem cells (hESC) and induced pluripotent stem cells (iPSC) provide new prospects for studying human neurodevelopment and modeling neurological disease. In particular, iPSC-derived neural cells permit a direct comparison of disease-relevant molecular pathways in neurons and glia derived from patients and healthy individuals. A prerequisite for such comparative studies are robust protocols that efficiently yield standardized populations of neural cell types. Here we show that long-term self-renewing neuroepithelial-like stem cells (lt-NES cells) derived from 3 hESC and 6 iPSC lines in two independent laboratories exhibit consistent characteristics including i) continuous expandability in the presence of FGF2 and EGF; ii) stable neuronal and glial differentiation competence; iii) characteristic transcription factor profile; iv) hindbrain specification amenable to regional patterning; v) capacity to generate functionally mature human neurons. We further show that lt-NES cells are developmentally distinct from fetal tissue-derived radial glia-like stem cells. We propose that lt-NES cells provide an interesting tool for studying human neurodevelopment and may serve as a standard system to facilitate comparative analyses of hESC and hiPSC-derived neural cells from control and diseased genetic backgrounds.

Krencik et al . present a chemically defined system for differentiating human pluripotent stem cells to large numbers of immature astrocytes, which mature further after transplantation to the neonatal mouse brain. By applying regional patterning factors at the neuroepithelial stage, the authors also succeed in generating different astrocytes subtypes. Human pluripotent stem cells (hPSCs) have been differentiated efficiently to neuronal cell types. However, directed differentiation of hPSCs to astrocytes and astroglial subtypes remains elusive. In this study, hPSCs were directed to nearly uniform populations of immature astrocytes (>90% S100β + and GFAP + ) in large quantities. The immature human astrocytes exhibit similar gene expression patterns as primary astrocytes, display functional properties such as glutamate uptake and promotion of synaptogenesis, and become mature astrocytes by forming connections with blood vessels after transplantation into the mouse brain. Furthermore, hPSC-derived neuroepithelia, patterned to rostral-caudal and dorsal-ventral identities with the same morphogens used for neuronal subtype specification, generate immature astrocytes that express distinct homeodomain transcription factors and display phenotypic differences of different astroglial subtypes. These human astroglial progenitors and immature astrocytes will be useful for studying astrocytes in brain development and function, understanding the roles of astrocytes in disease processes and developing novel treatments for neurological disorders.

Forebrain γ-aminobutyric acid (GABA) interneurons have crucial roles in high-order brain function via modulating network activities and plasticity, and they are implicated in many psychiatric disorders. Availability of enriched functional human forebrain GABA interneurons, especially those from people affected by GABA interneuron deficit disease, will be instrumental to the investigation of disease pathogenesis and development of therapeutics. We describe a protocol for directed differentiation of forebrain GABA interneurons from human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) in a chemically defined system. In this protocol, human PSCs are first induced to primitive neuroepithelial cells over 10 d, and then patterned to NKX2.1-expressing medial ganglionic eminence progenitors by simple treatment with sonic hedgehog or its agonist purmorphamine over the next 2 weeks. These progenitors generate a nearly pure population of forebrain GABA interneurons by the sixth week. This simple and efficient protocol does not require transgenic modification or cell sorting, and it has been replicated with multiple human ESC and iPSC lines.

During mammalian development, neuroepithelial cells function as mitotic progenitors, which self-renew and generate neurons. Although spindle orientation is important for such polarized cells to undergo symmetric or asymmetric divisions 1 , 2 , its role in mammalian neurogenesis remains unclear. Here we show that control of spindle orientation is essential in maintaining the population of neuroepithelial cells, but dispensable for the decision to either proliferate or differentiate. Knocking out LGN , (the G protein regulator) 3 , 4 , randomized the orientation of normally planar neuroepithelial divisions. The resultant loss of the apical membrane from daughter cells frequently converted them into abnormally localized progenitors without affecting neuronal production rate. Furthermore, overexpression of Inscuteable 5 to induce vertical neuroepithelial divisions shifted the fate of daughter cells. Our results suggest that planar mitosis ensures the self-renewal of neuroepithelial progenitors by one daughter inheriting both apical and basal compartments during neurogenesis.

Regionally and functionally diverse types of astrocytes exist throughout the central nervous system and participate in nearly every aspect of normal and abnormal neural function. Therefore, human astrocyte subtypes are useful tools for understanding brain function, modulating disease processes and promoting neural regeneration. Here we describe a protocol for directed differentiation and maintenance of functional astroglia from human pluripotent stem cells in a chemically defined system. Human stem cells are first differentiated into neuroepithelial cells with or without exogenous patterning molecules (days 0–21). Regular dissociation of the neuroepithelial clusters in suspension, and in the presence of mitogens, permits generation of astroglial subtypes over a long-term expansion (days 21–90). Finally, the astroglial progenitors are either amplified for an extended time or differentiated into functional astrocytes on removal of mitogens and the addition of ciliary neurotrophic factor (days >90). This method generates robust populations of functionally diversified astrocytes with high efficiency.

In Drosophila coordinated proliferation of two neural stem cells, neuroblasts (NB) and neuroepithelial (NE) cells, is pivotal for proper larval brain growth that ultimately determines the final size and performance of an adult brain. The larval brain growth displays two phases based on behaviors of NB and NEs: the first one in early larval stages, influenced by nutritional status and the second one in the last larval stage, promoted by ecdysone signaling after critical weight checkpoint. Mutations of the baboon ( babo ) gene that produces three isoforms (BaboA-C), all acting as type-I receptors of Activin-type transforming growth factor β (TGF-β) signaling, cause a small brain phenotype due to severely reduced proliferation of the neural stem cells. In this study we show that loss of babo function severely affects proliferation of NBs and NEs as well as conversion of NEs from both phases. By analyzing babo -null and newly generated isoform-specific mutants by CRISPR mutagenesis as well as isoform-specific RNAi knockdowns in a cell- and stage-specific manner, our data support differential contributions of the isoforms for these cellular events with BaboA playing the major role. Stage-specific expression of EcR-B1 in the brain is also regulated primarily by BaboA along with function of the other isoforms. Blocking EcR function in both neural stem cells results in a small brain phenotype that is more severe than baboA -knockdown alone. In summary, our study proposes that the Babo-mediated signaling promotes proper behaviors of the neural stem cells in both phases and achieves this by acting upstream of EcR-B1 expression in the second phase.

We have developed a four-part protocol to differentiate human embryonic stem cells (hESCs) to oligodendrocyte progenitor cells (OPCs) according to developmental principles. In the first 2 weeks, hESCs are induced to differentiate into neuroepithelial cells, which form neural tube–like rosettes. In the following 10 d, these neuroepithelial cells are specified to OLIG2-expressing progenitors in the presence of retinoic acid (RA) and sonic hedgehog (SHH). Upon treatment with fibroblast growth factor 2 (FGF2) for another 10 d, these progenitors convert to OLIG2 and NKX2.2-expressing pre-OPCs. Finally, the pre-OPCs take 8–9 weeks to differentiate into OPCs, which express additional markers of oligodendrocytes, such as SOX10, platelet-derived growth factor receptor alpha (PDGFRα) and NG2. The unique aspects of the protocol are the use of FGF2 to promote the differentiation of gliogenic pre-OPCs in the third part and the removal of FGF2 during the transition of pre-OPCs to OPCs. This 3-month differentiation protocol consistently yields OPCs of high purity capable of producing myelin sheaths in vivo .

The earliest step in creating the cerebral cortex is the specification of neuroepithelium to a cortical fate. Using mouse genetic mosaics and timed inactivations, we demonstrated that Lhx2 acts as a classic selector gene and essential intrinsic determinant of cortical identity. Lhx2 selector activity is restricted to an early critical period when stem cells comprise the cortical neuroepithelium, where it acts cell-autonomously to specify cortical identity and suppress alternative fates in a spatially dependent manner. Laterally, Lhx2 null cells adopt antihem identity, whereas medially they become cortical hem cells, which can induce and organize ectopic hippocampal fields. In addition to providing functional evidence for Lhx2 selector activity, these findings show that the cortical hem is a hippocampal organizer.