Maintenance of neural stem cell positional identity by mixed-lineage leukemia 1

KAT6B is required for histone 3 lysine 9 acetylation and SOX gene expression in the developing brain

Heterozygous mutations in the histone lysine acetyltransferase gene KAT6B (MYST4/MORF/QKF) underlie neurodevelopmental disorders, but the mechanistic roles of KAT6B remain poorly understood. Here, we show that loss of KAT6B in embryonic neural stem and progenitor cells (NSPCs) impaired cell proliferation, neuronal differentiation, and neurite outgrowth. Mechanistically, loss of KAT6B resulted in reduced acetylation at histone H3 lysine 9 and reduced expression of key nervous system development genes in NSPCs and the developing cortex, including the SOX gene family, in particular Sox2, which is a key driver of neural progenitor proliferation, multipotency and brain development. In the fetal cortex, KAT6B occupied the Sox2 locus. Loss of KAT6B caused a reduction in Sox2 promoter activity in NSPCs. Sox2 overexpression partially rescued the proliferative defect of Kat6b -/- NSPCs. Collectively, these results elucidate molecular requirements for KAT6B in brain development and identify key KAT6B targets in neural precursor cells and the developing brain.

The Organism as the Niche: Physiological States Crack the Code of Adult Neural Stem Cell Heterogeneity

Neural stem cells (NSCs) persist in the adult mammalian brain and are able to give rise to new neurons and glia throughout life. The largest stem cell niche in the adult mouse brain is the ventricular-subventricular zone (V-SVZ) lining the lateral ventricles. Adult NSCs in the V-SVZ coexist in quiescent and actively proliferating states, and they exhibit a regionalized molecular identity. The importance of such spatial diversity is just emerging, as depending on their position within the niche, adult NSCs give rise to distinct subtypes of olfactory bulb interneurons and different types of glia. However, the functional relevance of stem cell heterogeneity in the V-SVZ is still poorly understood. Here, we put into perspective findings highlighting the importance of adult NSC diversity for brain plasticity, and how the body signals to brain stem cells in different physiological states to regulate their behavior.

A scalable, high-throughput neural development platform identifies shared impact of ASD genes on cell fate and differentiation

Background

Deleterious mutations in hundreds of genes confer high risk for neurodevelopmental disorders (NDDs), posing significant challenges for therapeutic development. Identifying convergent pathways shared across NDD genes could reveal high-impact therapeutic targets.

Methods

To identity convergent pathways in NDD genes, we optimized Perturb-seq, a method combining CRISPR perturbation with single-cell RNA sequencing (scRNA-seq), and applied structural topic modeling (STM) to simultaneously assess impact on cell fate and developmental stage. We then studied a subset of autism spectrum disorder (ASD) genes implicated in regulation of gene expression using these improved molecular and analytical approaches.

Results

Results from targeting 60 high-confidence ASD risk genes revealed significant effects on neural development. As expected, ASD risk genes impacted both progenitor fate and/or neuronal differentiation. Using STM, we could identify latent topics jointly capturing cell types, cell fate, and differentiation stages. Repression of ASD risk genes led to changes in topic proportions and effects of four genes (DEAF1, KMT2A, MED13L, and MYT1L) were validated in an independent dataset.

Conclusions

Our optimized Perturb-seq method, combined with a novel analytical approach, provides a powerful, cost-effective framework for uncovering convergent mechanisms among genes involved in complex neurodevelopmental processes. Application of these methods advanced understanding of the impact of ASD mutations on multiple dimensions of neural development, and provides a framework for a broader examination of the function of NDD risk genes.

Epigenetic maintenance of adult neural stem cell quiescence in the mouse hippocampus via Setd1a

Quiescence, a hallmark of adult neural stem cells (NSCs), is required for maintaining the NSC pool to support life-long continuous neurogenesis in the adult dentate gyrus (DG). Whether long-lasting epigenetic modifications maintain NSC quiescence over the long term in the adult DG is not well-understood. Here we show that mice with haploinsufficiency of Setd1a, a schizophrenia risk gene encoding a histone H3K4 methyltransferase, develop an enlarged DG with more dentate granule cells after young adulthood. Deletion of Setd1a specifically in quiescent NSCs in the adult DG promotes their activation and neurogenesis, which is countered by inhibition of the histone demethylase LSD1. Mechanistically, RNA-sequencing and CUT & RUN analyses of cultured quiescent adult NSCs reveal Setd1a deletion-induced transcriptional changes and many Setd1a targets, among which down-regulation of Bhlhe40 promotes quiescent NSC activation in the adult DG in vivo. Together, our study reveals a Setd1a-dependent epigenetic mechanism that sustains NSC quiescence in the adult DG.

Epigenetic regulation in adult neural stem cells

Neural stem cells (NSCs) exhibit self-renewing and multipotential properties. Adult NSCs are located in two neurogenic regions of adult brain: the ventricular-subventricular zone (V-SVZ) of the lateral ventricle and the subgranular zone of the dentate gyrus in the hippocampus. Maintenance and differentiation of adult NSCs are regulated by both intrinsic and extrinsic signals that may be integrated through expression of some key factors in the adult NSCs. A number of transcription factors have been shown to play essential roles in transcriptional regulation of NSC cell fate transitions in the adult brain. Epigenetic regulators have also emerged as key players in regulation of NSCs, neural progenitor cells and their differentiated progeny via epigenetic modifications including DNA methylation, histone modifications, chromatin remodeling and RNA-mediated transcriptional regulation. This minireview is primarily focused on epigenetic regulations of adult NSCs during adult neurogenesis, in conjunction with transcriptional regulation in these processes.

NFIB-MLL1 complex is required for the stemness and Dlx5-dependent osteogenic differentiation of C3H10T1/2 mesenchymal stem cells

Despite significant progress in our understanding of the molecular mechanism of mesenchymal stem cell (MSC) differentiation, less is known about the factors maintaining the stemness and plasticity of MSCs. Here, we show that the NFIB-MLL1 complex plays key roles in osteogenic differentiation and stemness of C3H10T1/2 MSCs. We find that depletion of either NFIB or MLL1 results in a severely hampered osteogenic potential and failed activation of key osteogenic transcription factors, such as Dlx5, Runx2, and Osx, following osteogenic stimuli. In addition, the NFIB-MLL1 complex binds directly to the promoter of Dlx5, and exogenous expression of Myc-Dlx5, but not the activation of either the BMP- or the Wnt-signaling pathway, is sufficient to restore the osteogenic potential of cells depleted of NFIB or MLL1. Moreover, chromatin immunoprecipitation (ChIP) and ChIP-sequencing analysis showed that the NFIB-MLL1 complex mediates the deposition of trimethylated histone H3K4 at both Dlx5 and Cebpa, key regulator genes that function at the early stages of osteogenic and adipogenic differentiation, respectively, in uncommitted C3H10T1/2 MSCs. Surprisingly, the depletion of either NFIB or MLL1 leads to decreased trimethylated histone H3K4 and results in elevated trimethylated histone H3K9 at those developmental genes. Furthermore, gene expression profiling and ChIP-sequencing analysis revealed lineage-specific changes in chromatin landscape and gene expression in response to osteogenic stimuli. Taken together, these data provide evidence for the hitherto unknown role of the NFIB-MLL1 complex in the maintenance and lineage-specific differentiation of C3H10T1/2 MSCs and support the epigenetic regulatory mechanism underlying the stemness and plasticity of MSCs.

Endogenous neural stem cells characterization using omics approaches: Current knowledge in health and disease

Neural stem cells (NSCs), an invaluable source of neuronal and glial progeny, have been widely interrogated in the last twenty years, mainly to understand their therapeutic potential. Most of the studies were performed with cells derived from pluripotent stem cells of either rodents or humans, and have mainly focused on their potential in regenerative medicine. High-throughput omics technologies, such as transcriptomics, epigenetics, proteomics, and metabolomics, which exploded in the past decade, represent a powerful tool to investigate the molecular mechanisms characterizing the heterogeneity of endogenous NSCs. The transition from bulk studies to single cell approaches brought significant insights by revealing complex system phenotypes, from the molecular to the organism level. Here, we will discuss the current literature that has been greatly enriched in the “omics era”, successfully exploring the nature and function of endogenous NSCs and the process of neurogenesis. Overall, the information obtained from omics studies of endogenous NSCs provides a sharper picture of NSCs function during neurodevelopment in healthy and in perturbed environments.

Conserved and Distinct Functions of the Autism-Related Chromatin Remodeler CHD8 in Embryonic and Adult Forebrain Neurogenesis

The chromatin remodeler CHD8 represents a high-confidence risk factor in autism, a multistage progressive neurologic disorder, however the underlying stage-specific functions remain elusive. In this study, by analyzing Chd8 conditional knock-out mice (male and female), we find that CHD8 controls cortical neural stem/progenitor cell (NSC) proliferation and survival in a stage-dependent manner. Strikingly, inducible genetic deletion reveals that CHD8 is required for the production and fitness of transit-amplifying intermediate progenitors (IPCs) essential for upper-layer neuron expansion in the embryonic cortex. p53 loss of function partially rescues apoptosis and neurogenesis defects in the Chd8-deficient brain. Further, transcriptomic and epigenomic profiling indicates that CHD8 regulates the chromatin accessibility landscape to activate neurogenesis-promoting factors including TBR2, a key regulator of IPC neurogenesis, while repressing DNA damage- and p53-induced apoptotic programs. In the adult brain, CHD8 depletion impairs forebrain neurogenesis by impeding IPC differentiation from NSCs in both subventricular and subgranular zones; however, unlike in embryos, it does not affect NSC proliferation and survival. Treatment with an antidepressant approved by the Federal Drug Administration (FDA), fluoxetine, partially restores adult hippocampal neurogenesis in Chd8-ablated mice. Together, our multistage functional studies identify temporally specific roles for CHD8 in developmental and adult neurogenesis, pointing to a potential strategy to enhance neurogenesis in the CHD8-deficient brain.SIGNIFICANCE STATEMENT The role of the high-confidence autism gene CHD8 in neurogenesis remains incompletely understood. Here, we identify a stage-specific function of CHD8 in development of NSCs in developing and adult brains by conserved, yet spatiotemporally distinct, mechanisms. In embryonic cortex, CHD8 is critical for the proliferation, survival, and differentiation of both NSC and IPCs during cortical neurogenesis. In adult brain, CHD8 is required for IPC generation but not the proliferation and survival of adult NSCs. Treatment with FDA-approved antidepressant fluoxetine partially rescues the adult neurogenesis defects in CHD8 mutants. Thus, our findings help resolve CHD8 functions throughout life during embryonic and adult neurogenesis and point to a potential avenue to promote neurogenesis in CHD8 deficiency.

Soma-to-germline transformation in chromatin-linked neurodevelopmental disorders?

Mutations in numerous chromatin regulators cause neurodevelopmental disorders (NDDs) with unknown mechanisms. Understandably, most research has focused on how chromatin regulators control gene expression that is directly relevant to brain development and function, such as synaptic genes. However, some NDD models surprisingly show ectopic expression of germline genes in the brain. These germline genes are usually expressed only in the primordial germ cells, testis, and ovaries for germ cell development and sexual reproduction. Such ectopic germline gene expression has been reported in several NDDs, including immunodeficiency, centromeric instability, facial anomalies syndrome 1; Kleefstra syndrome 1; MeCP2 duplication syndrome; and mental retardation, X-linked syndromic, Claes-Jensen type. The responsible genes, DNMT3B, G9A/GLP, MECP2, and KDM5C, all encode chromatin regulators for gene silencing. These mutations may therefore lead to germline gene derepression and, in turn, a severe identity crisis of brain cells-potentially interfering with normal brain development. Thus, the ectopic expression of germline genes is a unique hallmark defining this NDD subset and further implicates the importance of germline gene silencing during brain development. The functional impact of germline gene expression on brain development, however, remains undetermined. This perspective article explores how this apparent soma-to-germline transformation arises and how it may interfere with neurodevelopment through genomic instability and impaired sensory cilium formation. Furthermore, we also discuss how to test these hypotheses experimentally to ultimately determine the contribution of ectopic germline transcripts to chromatin-linked NDDs.

Puerarin action on stem cell proliferation, differentiation and apoptosis: Therapeutic implications for geriatric diseases

BACKGROUND

Aging is associated with a decline in cognitive and physical functions and various geriatric diseases, such as cardiovascular and neurodegenerative diseases. Puerarin (Pue), one of the main active flavonoids of Radix Puerariae (R. pueraria), is reportedly effective in treating geriatric diseases, including cardiovascular disease and hypertension.

PURPOSE

This review aims to summarize and discuss the profound physiological impact of Pue on various stem cell populations and provide new insights into the use of Pue for the prevention and treatment of geriatric diseases.

METHODS

The literature was retrieved from the core collection of electronic databases, such as Web of Science, Google Scholar, PubMed, and Science Direct, using the following keywords and terms: Puerarin, Stem Cell, Proliferation, Differentiation, Apoptosis, and Geriatric diseases. These keywords were used in multiple overlapping combinations.

RESULTS

Pue is effective in the treatment and management of age-related diseases, such as cardiovascular disease, diabetes, hypertension, and cerebrovascular disease. Pue exerts significant physiological effects on various stem cell populations, including their self-renewal/proliferation, differentiation and apoptosis. Most importantly, it could improve the efficiency and accuracy of stem cell therapy for treating various geriatric diseases. Further studies are essential to improve our understanding of the underlying mechanisms and elucidate their significance for future clinical applications.

CONCLUSION

The effects of Pue on various stem cell populations and their regulatory mechanisms are discussed in detail to provide new insights into the use of Pue in the prevention and treatment of geriatric diseases.

GLI3 Is Required for OLIG2+ Progeny Production in Adult Dorsal Neural Stem Cells

The ventricular-subventricular zone (V-SVZ) is a postnatal germinal niche. It holds a large population of neural stem cells (NSCs) that generate neurons and oligodendrocytes for the olfactory bulb and (primarily) the corpus callosum, respectively. These NSCs are heterogeneous and generate different types of neurons depending on their location. Positional identity among NSCs is thought to be controlled in part by intrinsic pathways. However, extrinsic cell signaling through the secreted ligand Sonic hedgehog (Shh) is essential for neurogenesis in both the dorsal and ventral V-SVZ. Here we used a genetic approach to investigate the role of the transcription factors GLI2 and GLI3 in the proliferation and cell fate of dorsal and ventral V-SVZ NSCs. We find that while GLI3 is expressed in stem cell cultures from both dorsal and ventral V-SVZ, the repressor form of GLI3 is more abundant in dorsal V-SVZ. Despite this high dorsal expression and the requirement for other Shh pathway members, GLI3 loss affects the generation of ventrally-, but not dorsally-derived olfactory interneurons in vivo and does not affect trilineage differentiation in vitro. However, loss of GLI3 in the adult dorsal V-SVZ in vivo results in decreased numbers of OLIG2-expressing progeny, indicating a role in gliogenesis.

MLL1 is required for maintenance of intestinal stem cells

Epigenetic mechanisms are gatekeepers for the gene expression patterns that establish and maintain cellular identity in mammalian development, stem cells and adult homeostasis. Amongst many epigenetic marks, methylation of histone 3 lysine 4 (H3K4) is one of the most widely conserved and occupies a central position in gene expression. Mixed lineage leukemia 1 (MLL1/KMT2A) is the founding mammalian H3K4 methyltransferase. It was discovered as the causative mutation in early onset leukemia and subsequently found to be required for the establishment of definitive hematopoiesis and the maintenance of adult hematopoietic stem cells. Despite wide expression, the roles of MLL1 in non-hematopoietic tissues remain largely unexplored. To bypass hematopoietic lethality, we used bone marrow transplantation and conditional mutagenesis to discover that the most overt phenotype in adult Mll1-mutant mice is intestinal failure. MLL1 is expressed in intestinal stem cells (ISCs) and transit amplifying (TA) cells but not in the villus. Loss of MLL1 is accompanied by loss of ISCs and a differentiation bias towards the secretory lineage with increased numbers and enlargement of goblet cells. Expression profiling of sorted ISCs revealed that MLL1 is required to promote expression of several definitive intestinal transcription factors including Pitx1, Pitx2, Foxa1, Gata4, Zfp503 and Onecut2, as well as the H3K27me3 binder, Bahcc1. These results were recapitulated using conditional mutagenesis in intestinal organoids. The stem cell niche in the crypt includes ISCs in close association with Paneth cells. Loss of MLL1 from ISCs promoted transcriptional changes in Paneth cells involving metabolic and stress responses. Here we add ISCs to the MLL1 repertoire and observe that all known functions of MLL1 relate to the properties of somatic stem cells, thereby highlighting the suggestion that MLL1 is a master somatic stem cell regulator.

Histological Studies of the Ventricular-Subventricular Zone as Neural Stem Cell and Glioma Stem Cell Niche

The neural stem cell niche of the ventricular-subventricular zone supports the persistence of stem and progenitor cells in the mature brain. This niche has many notable cytoarchitectural features that affect the activity of stem cells and may also support the survival and growth of invading tumor cells. Histochemical studies of the niche have revealed many proteins that, in combination, can help to reveal stem-like cells in the normal or cancer context, although many caveats persist in the quest to consistently identify these cells in the human brain. Here, we explore the complex relationship between the persistent proliferative capacity of the neural stem cell niche and the malignant proliferation of brain tumors, with a special focus on histochemical identification of stem cells and stem-like tumor cells and an eye toward the potential application of high-dimensional imaging approaches to the field.

Single-cell analysis of the ventricular-subventricular zone reveals signatures of dorsal & ventral adult neurogenesis

The ventricular-subventricular zone (V-SVZ), on the walls of the lateral ventricles, harbors the largest neurogenic niche in the adult mouse brain. Previous work has shown that neural stem/progenitor cells (NSPCs) in different locations within the V-SVZ produce different subtypes of new neurons for the olfactory bulb. The molecular signatures that underlie this regional heterogeneity remain largely unknown. Here, we present a single-cell RNA-sequencing dataset of the adult mouse V-SVZ revealing two populations of NSPCs that reside in largely non-overlapping domains in either the dorsal or ventral V-SVZ. These regional differences in gene expression were further validated using a single-nucleus RNA-sequencing reference dataset of regionally microdissected domains of the V-SVZ and by immunocytochemistry and RNAscope localization. We also identify two subpopulations of young neurons that have gene expression profiles consistent with a dorsal or ventral origin. Interestingly, a subset of genes are dynamically expressed, but maintained, in the ventral or dorsal lineages. The study provides novel markers and territories to understand the region-specific regulation of adult neurogenesis.

Nerve cells, or neurons, are the central building blocks of brain circuits. Their damage, death or loss of function leads to cognitive decline. Neural stem/progenitor cells (NSPCs) first appear during embryo development, generating most of the neurons found in the nervous system. However, the adult brain retains a small subpopulation of NSPCs, which in some species are an important source of new neurons throughout life.

In the adult mouse brain the largest population of NSPCs, known as B cells, is found in an area called the ventricular-subventricular zone (V-SVZ). These V-SVZ B cells have properties of specialized support cells known as astrocytes, but they can also divide and generate intermediate ‘progenitor cells’ called C cells. These, in turn, divide to generate large numbers of young ‘A cells’ neurons that undertake a long and complex migration from V-SVZ to the olfactory bulb, the first relay in the central nervous system for the processing of smells.

Depending on their location in the V-SVZ, B cells can generate different kinds of neurons, leading to at least ten subtypes of neurons. Why this is the case is still poorly understood.

To examine this question, Cebrián-Silla, Nascimento, Redmond, Mansky et al. determined which genes were expressed in B, C and A cells from different parts of the V-SVZ. While cells within each of these populations had different expression patterns, those that originated in the same V-SVZ locations shared a set of genes, many of which associated with regional specification in the developing brain. Some, however, were intriguingly linked to hormonal regulation.

Salient differences between B cells depended on whether the cells originated closer to the top (‘dorsal’ position) or to the bottom of the brain (‘ventral’ position). This information was used to stain slices of mouse brains for the RNA and proteins produced by these genes in different regions. These experiments revealed dorsal and ventral territories containing B cells with distinct ‘gene expression’.

This study highlights the heterogeneity of NSPCs, revealing key molecular differences among B cells in dorsal and ventral areas of the V-SVZ and reinforcing the concept that the location of NSPCs determines the types of neuron they generate. Furthermore, the birth of specific types of neurons from B cells that are so strictly localized highlights the importance of neuronal migration to ensure that young neurons with specific properties reach their appropriate destination in the olfactory bulb.

The work by Cebrián-Silla, Nascimento, Redmond, Mansky et al. has identified sets of genes that are differentially expressed in dorsal and ventral regions which may contribute to regional regulation. Furthering the understanding of how adult NSPCs differ according to their location will help determine how various neuron types emerge in the adult brain.

Abnormal neocortex arealization and Sotos-like syndrome-associated behavior in Setd2 mutant mice

Proper formation of area identities of the cerebral cortex is crucial for cognitive functions and social behaviors of the brain. It remains largely unknown whether epigenetic mechanisms, including histone methylation, regulate cortical arealization. Here, we removed SETD2, the methyltransferase for histone 3 lysine-36 trimethylation (H3K36me3), in the developing dorsal forebrain in mice and showed that Setd2 is required for proper cortical arealization and the formation of cortico-thalamo-cortical circuits. Moreover, Setd2 conditional knockout mice exhibit defects in social interaction, motor learning, and spatial memory, reminiscent of patients with the Sotos-like syndrome bearing SETD2 mutations. SETD2 maintains the expression of clustered protocadherin (cPcdh) genes in an H3K36me3 methyltransferase-dependent manner. Aberrant cortical arealization was recapitulated in cPcdh heterozygous mice. Together, our study emphasizes epigenetic mechanisms underlying cortical arealization and pathogenesis of the Sotos-like syndrome.

Transcriptional profiling of sequentially generated septal neuron fates

The septum is a ventral forebrain structure known to regulate innate behaviors. During embryonic development, septal neurons are produced in multiple proliferative areas from neural progenitors following transcriptional programs that are still largely unknown. Here, we use a combination of single-cell RNA sequencing, histology, and genetic models to address how septal neuron diversity is established during neurogenesis. We find that the transcriptional profiles of septal progenitors change along neurogenesis, coinciding with the generation of distinct neuron types. We characterize the septal eminence, an anatomically distinct and transient proliferative zone composed of progenitors with distinctive molecular profiles, proliferative capacity, and fate potential compared to the rostral septal progenitor zone. We show that Nkx2.1-expressing septal eminence progenitors give rise to neurons belonging to at least three morphological classes, born in temporal cohorts that are distributed across different septal nuclei in a sequential fountain-like pattern. Our study provides insight into the molecular programs that control the sequential production of different neuronal types in the septum, a structure with important roles in regulating mood and motivation.

Ontogeny of adult neural stem cells in the mammalian brain

Neural stem cells (NSCs) persist into adulthood in the subgranular zone (SGZ) of the dentate gyrus in the hippocampus and in the ventricular-subventricular zone (V-SVZ) of the lateral ventricles, where they generate new neurons and glia cells that contribute to neural plasticity. A better understanding of the developmental process that enables NSCs to persist beyond development will provide insight into factors that determine the size and properties of the adult NSC pool and thus the capacity for life-long neurogenesis in the adult mammalian brain. We review current knowledge regarding the developmental origins of adult NSCs and the developmental process by which embryonic NSCs transition into their adult form. We also discuss potential mechanisms that might regulate proper establishment of the adult NSC pool, and propose future directions of research that will be key to unraveling how NSCs transform to establish the adult NSC pool in the mammalian brain.

Small Molecule Regulation of Stem Cells that Generate Bone, Chondrocyte, and Cardiac Cells

Embryonic stem cells (ESCs) are stem cells (SCs) that can self-renew and differentiate into a myriad of cell types. The process of developing stemness is determined by signaling molecules that drive stem cells to a specific lineage. For example, ESCs can differentiate into mature cells (e.g., cardiomyocytes) and mature cardiomyocytes can be characterized for cell beating, action potential, and ion channel function. A goal of this Perspective is to show how small molecules can be used to differentiate ESCs into cardiomyocytes and how this can reveal novel aspects of SC biology. This approach can also lead to the discovery of new molecules of use in cardiovascular disease. Human induced pluripotent stem cells (hiPSCs) afford the ability to produce unlimited numbers of normal human cells. The creation of patient-specific hiPSCs provides an opportunity to study cell models of human disease. The second goal is to show that small molecules can stimulate hiPSC commitment to cardiomyocytes. How iPSCs can be used in an approach to discover new molecules of use in cardiovascular disease will also be shown in this study. Adult SCs, including mesenchymal stem cells (MSCs), can likewise participate in self-renewal and multilineage differentiation. MSCs are capable of differentiating into osteoblasts, adipocytes or chondrocytes. A third goal of this Perspective is to describe differentiation of MSCs into chondrogenic and osteogenic lineages. Small molecules can stimulate MSCs to specific cell fate both in vitro and in vivo. In this Perspective, some recent examples of applying small molecules for osteogenic and chondrogenic cell fate determination are summarized. Underlying molecular mechanisms and signaling pathways involved are described. Small molecule-based modulation of stem cells shows insight into cell regulation and potential approaches to therapeutic strategies for MSC-related diseases.

Neurogenesis From Embryo to Adult - Lessons From Flies and Mice

The human brain is composed of billions of cells, including neurons and glia, with an undetermined number of subtypes. During the embryonic and early postnatal stages, the vast majority of these cells are generated from neural progenitors and stem cells located in all regions of the neural tube. A smaller number of neurons will continue to be generated throughout our lives, in localized neurogenic zones, mainly confined at least in rodents to the subependymal zone of the lateral ventricles and the subgranular zone of the hippocampal dentate gyrus. During neurogenesis, a combination of extrinsic cues interacting with temporal and regional intrinsic programs are thought to be critical for increasing neuronal diversity, but their underlying mechanisms need further elucidation. In this review, we discuss the recent findings in Drosophila and mammals on the types of cell division and cell interactions used by neural progenitors and stem cells to sustain neurogenesis, and how they are influenced by glia.