p27Kip1 alters the response of cells to mitogen and is part of a cell-intrinsic timer that arrests the cell cycle and initiates differentiation

Zic-r.b controls cell numbers in Ciona embryos by activating CDKN1B

The control of cell numbers and the establishment of cell types are two processes that are essential in early embryonic development. We have a reasonable understanding of how these processes occur individually, but we have considerably less sophisticated understanding of how these processes are linked. Tunicates have fixed cell lineages with predictable cell cycles, making them well suited to investigate these processes. In the ascidian Ciona, we show that the transcription factor Zic-r.b, known to be involved in establishing several cell types in early development also activates the expression of the cell cycle inhibitor CDKN1B. Zic-r.b is a major missing component of the cell division clock establishing specific cell numbers. We also show that a larvacean homolog of Zic-r.b is expressed one cell cycle earlier than its Ciona counterpart. The early expression in larvaceans may explain why they have half as many notochord cells as ascidians and may illustrate a general mechanism to evolve changes in morphology.

The rates of adult neurogenesis and oligodendrogenesis are linked to cell cycle regulation through p27-dependent gene repression of SOX2

Cell differentiation involves profound changes in global gene expression that often has to occur in coordination with cell cycle exit. Because cyclin-dependent kinase inhibitor p27 reportedly regulates proliferation of neural progenitor cells in the subependymal neurogenic niche of the adult mouse brain, but can also have effects on gene expression, we decided to molecularly analyze its role in adult neurogenesis and oligodendrogenesis. At the cell level, we show that p27 restricts residual cyclin-dependent kinase activity after mitogen withdrawal to antagonize cycling, but it is not essential for cell cycle exit. By integrating genome-wide gene expression and chromatin accessibility data, we find that p27 is coincidentally necessary to repress many genes involved in the transit from multipotentiality to differentiation, including those coding for neural progenitor transcription factors SOX2, OLIG2 and ASCL1. Our data reveal both a direct association of p27 with regulatory sequences in the three genes and an additional hierarchical relationship where p27 repression of Sox2 leads to reduced levels of its downstream targets Olig2 and Ascl1. In vivo, p27 is also required for the regulation of the proper level of SOX2 necessary for neuroblasts and oligodendroglial progenitor cells to timely exit cell cycle in a lineage-dependent manner.

CHIQUITA1 maintains the temporal transition between proliferation and differentiation in Arabidopsis thaliana

Body size varies widely among species, populations and individuals, depending on the environment. Transitioning between proliferation and differentiation is a crucial determinant of final organ size, but how the timing of this transition is established and maintained remains unknown. Using cell proliferation markers and genetic analysis, we show that CHIQUITA1 (CHIQ1) is required to maintain the timing of the transition from proliferation to differentiation in Arabidopsis thaliana. Combining kinematic and cell lineage-tracking studies, we found that the number of actively dividing cells in chiquita1-1 plants decreases prematurely compared with wild-type plants, suggesting CHIQ1 maintains the proliferative capacity in dividing cells and ensures that cells divide a specific number of times. CHIQ1 belongs to a plant-specific gene family of unknown molecular function and genetically interacts with three close members of its family to control the timing of proliferation exit. Our work reveals the interdependency between cellular and organ-level processes underlying final organ size determination.

Selective translation of epigenetic modifiers affects the temporal pattern and differentiation of neural stem cells

The cerebral cortex is formed by diverse neurons generated sequentially from neural stem cells (NSCs). A clock mechanism has been suggested to underlie the temporal progression of NSCs, which is mainly defined by the transcriptome and the epigenetic state. However, what drives such a developmental clock remains elusive. We show that translational control of histone H3 trimethylation in Lys27 (H3K27me3) modifiers is part of this clock. We find that depletion of Fbl, an rRNA methyltransferase, reduces translation of both Ezh2 methyltransferase and Kdm6b demethylase of H3K27me3 and delays the progression of the NSC state. These defects are partially phenocopied by simultaneous inhibition of H3K27me3 methyltransferase and demethylase, indicating the role of Fbl in the genome-wide H3K27me3 pattern. Therefore, we propose that Fbl drives the intrinsic clock through the translational enhancement of the H3K27me3 modifiers that predominantly define the NSC state.

The temporal development of tissues and organs may be defined by the genome-wide epigenetic and transcriptional state functioning as the clock. Here the authors found that Fbl, a ribosomal RNA methyltransferase, potentially behaves as a clock during neural stem cell (NSC) development by controlling translational efficiencies of epigenetic modifiers in the cerebral cortex primordium.

The Quaking RNA-binding proteins as regulators of cell differentiation

The RNA-binding protein Quaking (QKI) has emerged as a potent regulator of cellular differentiation in developmental and pathological processes. The QKI gene is itself alternatively spliced to produce three major isoforms, QKI-5, QKI-6, and QKI-7, that possess very distinct functions. Here, we highlight roles of the different QKI isoforms in neuronal, vascular, muscle, and monocyte cell differentiation, and during epithelial-mesenchymal transition in cancer progression. QKI isoforms control cell differentiation through regulating alternative splicing, mRNA stability and translation, with activities in gene transcription now also becoming evident. These diverse functions of the QKI isoforms contribute to their broad influences on RNA metabolism and cellular differentiation. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA Processing > Splicing Regulation/Alternative Splicing RNA in Disease and Development > RNA in Development.

Retinoic acid influences the timing and scaling of avian wing development

A fundamental question in biology is how embryonic development is timed between different species. To address this problem, we compared wing development in the quail and the larger chick. We reveal that pattern formation is faster in the quail as determined by the earlier activation of 5′Hox genes, termination of developmental organizers (Shh and Fgf8), and the laying down of the skeleton (Sox9). Using interspecies tissue grafts, we show that developmental timing can be reset during a critical window of retinoic acid signaling. Accordingly, extending the duration of retinoic acid signaling switches developmental timing between the quail and the chick and the chick and the larger turkey. However, the incremental growth rate is comparable between all three species, suggesting that the pace of development primarily governs differences in the expansion of the skeletal pattern. The widespread distribution of retinoic acid could coordinate developmental timing throughout the embryo.

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Quail wings develop faster than chick and turkey wings

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Retinoic acid can set the species timing of wing development

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Developmental timing is independent of growth and scales the skeletal pattern

Targeting Orphan G Protein-Coupled Receptor 17 with T0 Ligand Impairs Glioblastoma Growth

Simple Summary

Glioblastoma multiforme (GBM), or glioblastoma chemotherapy, has one of the poorest improvements across all types of cancers. Despite the different rationales explored in targeted therapy for taming the GBM aggressiveness, its phenotypic plasticity, drug toxicity, and adaptive resistance mechanisms pose many challenges in finding an effective cure. Our manuscript reports the expression and prognostic role of orphan receptor GPR17 in glioma, the molecular mechanism of action of the novel ligand of GPR17, and provides evidence how the T0 agonist promotes glioblastoma cell death through modulation of the MAPK/ERK, PI3K–Akt, STAT, and NF-κB pathways. The highlights are as follows: GPR17 expression is associated with greater survival for both low-grade glioma (LGG) and GBM; GA-T0, a potent GPR17 receptor agonist, causes significant GBM cell death and apoptosis; GPR17 signaling promotes cell cycle arrest at the G1 phase in GBM cells; key genes are modulated in the signaling pathways that inhibit GBM cell proliferation; and GA-T0 crosses the blood–brain barrier and reduces tumor volume.

Abstract

Glioblastoma, an invasive high-grade brain cancer, exhibits numerous treatment challenges. Amongst the current therapies, targeting functional receptors and active signaling pathways were found to be a potential approach for treating GBM. We exploited the role of endogenous expression of GPR17, a G protein-coupled receptor (GPCR), with agonist GA-T0 in the survival and treatment of GBM. RNA sequencing was performed to understand the association of GPR17 expression with LGG and GBM. RT-PCR and immunoblotting were performed to confirm the endogenous expression of GPR17 mRNA and its encoded protein. Biological functions of GPR17 in the GBM cells was assessed by in vitro analysis. HPLC and histopathology in wild mice and an acute-toxicity analysis in a patient-derived xenograft model were performed to understand the clinical implication of GA-T0 targeting GPR17. We observed the upregulation of GPR17 in association with improved survival of LGG and GBM, confirming it as a predictive biomarker. GA-T0-stimulated GPR17 leads to the inhibition of cyclic AMP and calcium flux. GPR17 signaling activation enhances cytotoxicity against GBM cells and, in patient tissue-derived mesenchymal subtype GBM cells, induces apoptosis and prevents proliferation by stoppage of the cell cycle at the G1 phase. Modulation of the key genes involved in DNA damage, cell cycle arrest, and in several signaling pathways, including MAPK/ERK, PI3K–Akt, STAT, and NF-κB, prevents tumor regression. In vivo activation of GPR17 by GA-T0 reduces the tumor volume, uncovering the potential of GA-T0–GPR17 as a targeted therapy for GBM treatment. Conclusion: Our analysis suggests that GA-T0 targeting the GPR17 receptor presents a novel therapy for treating glioblastoma.

Ablation of neuronal ADAM17 impairs oligodendrocyte differentiation and myelination

Myelin, one of the most important adaptations of vertebrates, is essential to ensure efficient propagation of the electric impulse in the nervous system and to maintain neuronal integrity. In the central nervous system (CNS), the development of oligodendrocytes and the process of myelination are regulated by the coordinated action of several positive and negative cell-extrinsic factors. We and others previously showed that secretases regulate the activity of proteins essential for myelination. We now report that the neuronal α-secretase ADAM17 controls oligodendrocyte differentiation and myelin formation in the CNS. Ablation of Adam17 in neurons impairs in vivo and in vitro oligodendrocyte differentiation, delays myelin formation throughout development and results in hypomyelination. Furthermore, we show that this developmental defect is, in part, the result of altered Notch/Jagged 1 signaling. Surprisingly, in vivo conditional loss of Adam17 in immature oligodendrocytes has no effect on myelin formation. Collectively, our data indicate that the neuronal α-secretase ADAM17 is required for proper CNS myelination. Further, our studies confirm that secretases are important post-translational regulators of myelination although the mechanisms controlling CNS and peripheral nervous system (PNS) myelination are distinct.

Paired Related Homeobox Protein 1 Regulates Quiescence in Human Oligodendrocyte Progenitors

Human oligodendrocyte progenitor cells (hOPCs) persist into adulthood as an abundant precursor population capable of division and differentiation. The transcriptional mechanisms that regulate hOPC homeostasis remain poorly defined. Herein, we identify paired related homeobox protein 1 (PRRX1) in primary PDGFαR⁺ hOPCs. We show that enforced PRRX1 expression results in reversible G_1/0 arrest. While both PRRX1 splice variants reduce hOPC proliferation, only PRRX1a abrogates migration. hOPC engraftment into hypomyelinated shiverer/rag2 mouse brain is severely impaired by PRRX1a, characterized by reduced cell proliferation and migration. PRRX1 induces a gene expression signature characteristic of stem cell quiescence. Both IFN-γ and BMP signaling upregulate PRRX1 and induce quiescence. PRRX1 knockdown modulates IFN-γ-induced quiescence. In mouse brain, PRRX1 mRNA was detected in non-dividing OPCs and is upregulated in OPCs following demyelination. Together, these data identify PRRX1 as a regulator of quiescence in hOPCs and as a potential regulator of pathological quiescence.

An autoregulatory cell cycle timer integrates growth and specification in chick wing digit development

A fundamental question is how proliferation and growth are timed during embryogenesis. Although it has been suggested that the cell cycle could be a timer, the underlying mechanisms remain elusive. Here we describe a cell cycle timer that operates in Sonic hedgehog (Shh)-expressing polarising region cells of the chick wing bud. Our data are consistent with Shh signalling stimulating polarising region cell proliferation via Cyclin D2, and then inhibiting proliferation via a Bmp2-p27^kip1 pathway. When Shh signalling is blocked, polarising region cells over-proliferate and form an additional digit, which can be prevented by applying Bmp2 or by inhibiting D cyclin activity. In addition, Bmp2 also restores posterior digit identity in the absence of Shh signalling, thus indicating that it specifies antero-posterior (thumb to little finger) positional values. Our results reveal how an autoregulatory cell cycle timer integrates growth and specification and are widely applicable to many tissues.

Misactivation of Hedgehog signaling causes inherited and sporadic cancers

The Hedgehog pathway is critical for the development of diverse organs. Misactivation of the Hedgehog pathway can cause developmental abnormalities and cancers, including medulloblastoma, the most common pediatric brain tumor, and basal cell carcinoma, the most common cancer in the United States. Here, we review how basic, translational, and clinical studies of the Hedgehog pathway have helped reveal how cells communicate, how intercellular communication controls development, how signaling goes awry to cause cancer, and how to use targeted molecular agents to treat both inherited and sporadic cancers.

Differing intrinsic biological properties between forebrain and spinal oligodendroglial lineage cells

Differentiation of oligodendroglial progenitor cells (OPCs) into myelinating oligodendrocytes is known to be regulated by the microenvironment where they differentiate. However, current research has not verified whether or not oligodendroglial lineage cells (OLCs) derived from different anatomical regions of the central nervous system (CNS) respond to microenvironmental cues in the same manner. Here, we isolated pure OPCs from rat neonatal forebrain (FB) and spinal cord (SC) and compared their phenotypes in the same in vitro conditions. We found that although FB and SC OLCs responded differently to the same external factors; they were distinct in proliferation response to mitogens, oligodendrocyte phenotype after differentiation, and cytotoxic responses to α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate-type glutamate receptor-mediated excitotoxicity at immature stages of differentiation in a cell-intrinsic manner. Moreover, transcriptome analysis identified genes differentially expressed between these OPC populations, including those encoding transcription factors (TFs), cell surface molecules, and signaling molecules. Particularly, FB and SC OPCs retained the expression of FB- or SC-specific TFs, such as Foxg1 and Hoxc8, respectively, even after serial passaging in vitro. Given the essential role of these TFs in the regional identities of CNS cells along the rostrocaudal axis, our results suggest that CNS region-specific gene regulation by these TFs may cause cell-intrinsic differences in cellular responses between FB and SC OLCs to extracellular molecules. Further understanding of the regional differences among OPC populations will help to improve treatments for demyelination in different CNS regions and to facilitate the development of stem cell-derived OPCs for cell transplantation therapies for demyelination. Cover Image for this issue: doi. 10.1111/jnc.13809.

Quiescence of adult oligodendrocyte precursor cells requires thyroid hormone and hypoxia to activate Runx1

The adult mammalian central nervous system (CNS) contains a population of slowly dividing oligodendrocyte precursor cells (OPCs), i.e., adult OPCs, which supply new oligodendrocytes throughout the life of animal. While adult OPCs develop from rapidly dividing perinatal OPCs, the mechanisms underlying their quiescence remain unknown. Here, we show that perinatal rodent OPCs cultured with thyroid hormone (TH) under hypoxia become quiescent and acquire adult OPCs-like characteristics. The cyclin-dependent kinase inhibitor p15/INK4b plays crucial roles in the TH-dependent cell cycle deceleration in OPCs under hypoxia. Klf9 is a direct target of TH-dependent signaling. Under hypoxic conditions, hypoxia-inducible factors mediates runt-related transcription factor 1 activity to induce G1 arrest in OPCs through enhancing TH-dependent p15/INK4b expression. As adult OPCs display phenotypes of adult somatic stem cells in the CNS, the current results shed light on environmental requirements for the quiescence of adult somatic stem cells during their development from actively proliferating stem/progenitor cells.

Resveratrol Increases Osteoblast Differentiation In Vitro Independently of Inflammation

Low-grade inflammation negatively affects bone. Resveratrol is a natural compound proven to possess both anti-inflammatory and bone protective properties. However, it is uncertain if the bone effects are mediated though anti-inflammatory effects. Firstly, we investigated if resveratrol affects proliferation and differentiation of human bone marrow-derived mesenchymal stem cells. Secondly, we investigated if inflammation negatively affects proliferation and differentiation, and if resveratrol counteracts this through anti-inflammatory effects. Mesenchymal stem cells were obtained from bone marrow aspiration in 13 healthy individuals and cultured towards the osteoblast cell lineage. The cells were stimulated with resveratrol, lipopolysaccharide (LPS), LPS + resveratrol, or vehicle (control) for 21 days. Compared to control, resveratrol decreased cell number by 35 % (p < 0.05) and induced differentiation (a 3-fold increase in alkaline phosphatase (p < 0.002), while P1NP and OPG showed similar trends). LPS induced inflammation with a 44-fold increase in interleukin-6 (p < 0.05) and an extremely prominent increase in interleukin-8 production (p < 0.05) relative to control. In addition, LPS increased cell count (p < 0.05) and decreased differentiation (a reduction in P1NP production (p < 0.02)). Co-stimulation with LPS + resveratrol did not reduce interleukin-6 or interleukin-8, but nonetheless, cell count was reduced (p < 0.05) and alkaline phosphatase, P1NP, and OPG increased (p < 0.05 for all). Thus, resveratrol stimulates osteoblast differentiation independently of inflammation.

Remyelinating Oligodendrocyte Precursor Cell miRNAs from the Sfmbt2 Cluster Promote Cell Cycle Arrest and Differentiation

Oligodendrocyte (OL) loss contributes to the functional deficits underlying diseases with a demyelinating component. Remyelination by oligodendrocyte progenitor cells (OPCs) can restore these deficits. To understand the role that microRNAs (miRNAs) play in remyelination, 2',3'-cyclic-nucleotide 3'-phosphodiesterase-EGFP(+) mice were treated with cuprizone, and OPCs were sorted from the corpus callosum. Microarray analysis revealed that Sfmbt2 family miRNAs decreased during cuprizone treatment. One particular Sfmbt2 miRNA, miR-297c-5p, increased during mouse OPC differentiation in vitro and during callosal development in vivo. When overexpressed in both mouse embryonic fibroblasts and rat OPCs (rOPCs), cell cycle analysis revealed that miR-297c-5p promoted G1/G0 arrest. Additionally, miR-297c-5p transduction increased the number of O1(+) rOPCs during differentiation. Luciferase reporter assays confirmed that miR-297c-5p targets cyclin T2 (CCNT2), the regulatory subunit of positive transcription elongation factor b, a complex that inhibits OL maturation. Furthermore, CCNT2-specific knockdown promoted rOPC differentiation while not affecting cell cycle status. Together, these data support a dual role for miR-297c-5p as both a negative regulator of OPC proliferation and a positive regulator of OL maturation via its interaction with CCNT2.

SIGNIFICANCE STATEMENT

This work describes the role of oligodendrocyte progenitor cell (OPC) microRNAs (miRNAs) during remyelination and development in vivo and differentiation in vitro. This work highlights the importance of miRNAs to OPC biology and describes miR-297c-5p, a novel regulator of OPC function. In addition, we identified CCNT2 as a functional target, thus providing a mechanism by which miR-297c-5p imparts its effects on differentiation. These data are important, given our lack of understanding of OPC miRNA regulatory networks and their potential clinical value. Therefore, efforts to understand the role of miR-297c-5p in pathological conditions and its potential for facilitating repair may provide future therapeutic strategies to treat demyelination.

Epigenetics in NG2 glia cells

The interplay of transcription and epigenetic marks is essential for oligodendrocyte progenitor cell (OPC) proliferation and differentiation during development. Here, we review the recent advances in this field and highlight mechanisms of transcriptional repression and activation involved in OPC proliferation, differentiation and plasticity. We also describe how dysregulation of these epigenetic events may affect demyelinating disorders, and consider potential ways to manipulate NG2 cell behavior through modulation of the epigenome. This article is part of a Special Issue entitled SI:NG2-glia(Invited only).

Sonic hedgehog patterning during cerebellar development

The morphogenic factor sonic hedgehog (Shh) actively orchestrates many aspects of cerebellar development and maturation. During embryogenesis, Shh signaling is active in the ventricular germinal zone (VZ) and represents an essential signal for proliferation of VZ-derived progenitors. Later, Shh secreted by Purkinje cells sustains the amplification of postnatal neurogenic niches: the external granular layer and the prospective white matter, where excitatory granule cells and inhibitory interneurons are produced, respectively. Moreover, Shh signaling affects Bergmann glial differentiation and promotes cerebellar foliation during development. Here we review the most relevant functions of Shh during cerebellar ontogenesis, underlying its role in physiological and pathological conditions.

Oligodendrocyte Development and Plasticity

Oligodendrocyte precursor cells (OPCs) originate in the ventricular zones (VZs) of the brain and spinal cord and migrate throughout the developing central nervous system (CNS) before differentiating into myelinating oligodendrocytes (OLs). It is not known whether OPCs or OLs from different parts of the VZ are functionally distinct. OPCs persist in the postnatal CNS, where they continue to divide and generate myelinating OLs at a decreasing rate throughout adult life in rodents. Adult OPCs respond to injury or disease by accelerating their cell cycle and increasing production of OLs to replace lost myelin. They also form synapses with unmyelinated axons and respond to electrical activity in those axons by generating more OLs and myelin locally. This experience-dependent "adaptive" myelination is important in some forms of plasticity and learning, for example, motor learning. We review the control of OL lineage development, including OL population dynamics and adaptive myelination in the adult CNS.

Intracellular Protein Shuttling: A Mechanism Relevant for Myelin Repair in Multiple Sclerosis?

A prominent feature of demyelinating diseases such as multiple sclerosis (MS) is the degeneration and loss of previously established functional myelin sheaths, which results in impaired signal propagation and axonal damage. However, at least in early disease stages, partial replacement of lost oligodendrocytes and thus remyelination occur as a result of resident oligodendroglial precursor cell (OPC) activation. These cells represent a widespread cell population within the adult central nervous system (CNS) that can differentiate into functional myelinating glial cells to restore axonal functions. Nevertheless, the spontaneous remyelination capacity in the adult CNS is inefficient because OPCs often fail to generate new oligodendrocytes due to the lack of stimulatory cues and the presence of inhibitory factors. Recent studies have provided evidence that regulated intracellular protein shuttling is functionally involved in oligodendroglial differentiation and remyelination activities. In this review we shed light on the role of the subcellular localization of differentiation-associated factors within oligodendroglial cells and show that regulation of intracellular localization of regulatory factors represents a crucial process to modulate oligodendroglial maturation and myelin repair in the CNS.

Overexpression of cyclin dependent kinase inhibitor P27/Kip1 increases oligodendrocyte differentiation from induced pluripotent stem cells

Cell transplantation therapy with oligodendrocyte precursor cells (OPCs) is a promising and effective treatment for diseases involving demyelination in the central nervous system (CNS). In previous studies, we succeeded in producing O4(+) oligodendrocytes (OLs) from mouse- and human-induced pluripotent stem cells (iPSCs) in vitro; however, the efficiency of differentiation into OLs was lower for iPSCs than that for embryonic stem cells (ESCs). To clarify the cause of this difference, we compared the expression of proteins that contribute to OL differentiation in mouse iPSC-derived cells and in mouse ESC-derived cells. The results showed that the expression levels of cyclin dependent kinase inhibitor P27/Kip1, mitogen-activated protein kinase (MAPK) JNK3, and transcription factor Mash1 were lower in iPSC-derived cells. In contrast, the expression levels of MAPK P38α, P38γ, and thyroid hormone receptor β1 were higher in iPSC-derived cells. We attempted to compensate for the expression changes in P27/Kip1 protein and Mash1 protein in iPSC-derived cells through retrovirus vector-mediated gene expression. Although the overexpression of Mash1 had no effect, the overexpression of P27/Kip1 increased the differentiation efficiency of iPSC-derived cells into O4(+) OLs.

The cyclin-like protein Spy1 regulates growth and division characteristics of the CD133+ population in human glioma

The heterogeneity of brain cancers, as most solid tumors, complicates diagnosis and treatment. Identifying and targeting populations of cells driving tumorigenesis is a top priority for the cancer biology field. This is not a trivial task; considerable variance exists in the driving mutations, identifying markers, and evolutionary pressures influencing initiating cells in different individual tumors. Despite this, the ability to self-renew and differentiate must be conserved to reseed a heterogeneous tumor mass. Focusing on one example of a tumor-initiating cell population, we demonstrate that the atypical cyclin-like protein Spy1 plays a role in balancing the division properties of glioma cells with stemness properties. This mechanistic insight may provide new opportunities for therapeutic intervention of brain cancer.

Mcl1 regulates the terminal mitosis of neural precursor cells in the mammalian brain through p27Kip1

Cortical development requires the precise timing of neural precursor cell (NPC) terminal mitosis. Although cell cycle proteins regulate terminal mitosis, the factors that influence the cell cycle machinery are incompletely understood. Here we show in mice that myeloid cell leukemia 1 (Mcl1), an anti-apoptotic Bcl-2 protein required for the survival of NPCs, also regulates their terminal differentiation through the cell cycle regulator p27(Kip1). A BrdU-Ki67 cell profiling assay revealed that in utero electroporation of Mcl1 into NPCs in the embryonic neocortex increased NPC cell cycle exit (the leaving fraction). This was further supported by a decrease in proliferating NPCs (Pax6(+) radial glial cells and Tbr2(+) neural progenitors) and an increase in differentiating cells (Dcx(+) neuroblasts and Tbr1(+) neurons). Similarly, BrdU birth dating demonstrated that Mcl1 promotes premature NPC terminal mitosis giving rise to neurons of the deeper cortical layers, confirming their earlier birthdate. Changes in Mcl1 expression within NPCs caused concomitant changes in the levels of p27(Kip1) protein, a key regulator of NPC differentiation. Furthermore, in the absence of p27(Kip1), Mcl1 failed to induce NPC cell cycle exit, demonstrating that p27(Kip1) is required for Mcl1-mediated NPC terminal mitosis. In summary, we have identified a novel physiological role for anti-apoptotic Mcl1 in regulating NPC terminal differentiation.

Differential requirement of cyclin-dependent kinase 2 for oligodendrocyte progenitor cell proliferation and differentiation

Cyclin-dependent kinases (Cdks) and their cyclin regulatory subunits control cell growth and division. Cdk2-cyclin E complexes, phosphorylating the retinoblastoma protein, drive cells through the G1/S transition into the S phase of the cell cycle. Despite its fundamental role, Cdk2 was found to be indispensable only in specific cell types due to molecular redundancies in its function. Converging studies highlight involvement of Cdk2 and associated cell cycle regulatory proteins in oligodendrocyte progenitor cell proliferation and differentiation. Giving the contribution of this immature cell type to brain plasticity and repair in the adult, this review will explore the requirement of Cdk2 for oligodendrogenesis, oligodendrocyte progenitor cells proliferation and differentiation during physiological and pathological conditions.

Loss of protein-tyrosine phosphatase α (PTPα) increases proliferation and delays maturation of oligodendrocyte progenitor cells

Tightly controlled termination of proliferation determines when oligodendrocyte progenitor cells (OPCs) can initiate differentiation and mature into myelin-forming cells. Protein-tyrosine phosphatase α (PTPα) promotes OPC differentiation, but its role in proliferation is unknown. Here we report that loss of PTPα enhanced in vitro proliferation and survival and decreased cell cycle exit and growth factor dependence of OPCs but not neural stem/progenitor cells. PTPα(-/-) mice have more oligodendrocyte lineage cells in embryonic forebrain and delayed OPC maturation. On the molecular level, PTPα-deficient mouse OPCs and rat CG4 cells have decreased Fyn and increased Ras, Cdc42, Rac1, and Rho activities, and reduced expression of the Cdk inhibitor p27Kip1. Moreover, Fyn was required to suppress Ras and Rho and for p27Kip1 accumulation, and Rho inhibition in PTPα-deficient cells restored expression of p27Kip1. We propose that PTPα-Fyn signaling negatively regulates OPC proliferation by down-regulating Ras and Rho, leading to p27Kip1 accumulation and cell cycle exit. Thus, PTPα acts in OPCs to limit self-renewal and facilitate differentiation.

The APC/C Ubiquitin Ligase: From Cell Biology to Tumorigenesis

The ubiquitin proteasome system (UPS) is required for normal cell proliferation, vertebrate development, and cancer cell transformation. The UPS consists of multiple proteins that work in concert to target a protein for degradation via the 26S proteasome. Chains of an 8.5-kDa protein called ubiquitin are attached to substrates, thus allowing recognition by the 26S proteasome. Enzymes called ubiquitin ligases or E3s mediate specific attachment to substrates. Although there are over 600 different ubiquitin ligases, the Skp1-Cullin-F-box (SCF) complexes and the anaphase promoting complex/cyclosome (APC/C) are the most studied. SCF involvement in cancer has been known for some time while APC/C's cancer role has recently emerged. In this review we will discuss the importance of APC/C to normal cell proliferation and development, underscoring its possible contribution to transformation. We will also examine the hypothesis that modulating a specific interaction of the APC/C may be therapeutically attractive in specific cancer subtypes. Finally, given that the APC/C pathway is relatively new as a cancer target, therapeutic interventions affecting APC/C activity may be beneficial in cancers that are resistant to classical chemotherapy.

Development and maturation of the spinal cord: implications of molecular and genetic defects

The human central nervous system (CNS) may be the most complex structure in the universe. Its development and appropriate specification into phenotypically and spatially distinct neural subpopulations involves a precisely orchestrated response, with thousands of transcriptional regulators combining with epigenetic controls and specific temporal cues in perfect synchrony. Understandably, our insight into the sophisticated molecular mechanisms which underlie spinal cord development are as yet limited. Even less is known about abnormalities of this process - putative genetic and molecular causes of well-described defects have only begun to emerge in recent years. Nonetheless, modern scientific techniques are beginning to demonstrate common patterns and principles amid the tremendous complexity of spinal cord development and maldevelopment. These advances are important, given that developmental anomalies of the spinal cord are an important cause of mortality and morbidity (Sadler, 2000); it is hoped that research advances will lead to better methods to detect, treat, and prevent these lesions.

Mechanisms limiting body growth in mammals

Recent studies have begun to provide insight into a long-standing mystery in biology-why body growth in animals is rapid in early life but then progressively slows, thus imposing a limit on adult body size. This growth deceleration in mammals is caused by potent suppression of cell proliferation in multiple tissues and is driven primarily by local, rather than systemic, mechanisms. Recent evidence suggests that this progressive decline in proliferation results from a genetic program that occurs in multiple organs and involves the down-regulation of a large set of growth-promoting genes. This program does not appear to be driven simply by time, but rather depends on growth itself, suggesting that the limit on adult body size is imposed by a negative feedback loop. Different organs appear to use different types of information to precisely target their adult size. For example, skeletal and cardiac muscle growth are negatively regulated by myostatin, the concentration of which depends on muscle mass itself. Liver growth appears to be modulated by bile acid flux, a parameter that reflects organ function. In pancreas, organ size appears to be limited by the initial number of progenitor cells, suggesting a mechanism based on cell-cycle counting. Further elucidation of the fundamental mechanisms suppressing juvenile growth is likely to yield important insights into the pathophysiology of childhood growth disorders and of the unrestrained growth of cancer. In addition, improved understanding of these growth-suppressing mechanisms may someday allow their therapeutic suspension in adult tissues to facilitate tissue regeneration.

Looking back

In this Perspective, I review my scientific career, which began after I trained in medicine in Montreal and in neurology in Boston. I started in immunology in London with Avrion Mitchison, using antibodies against cell-surface antigens to study the development and functions of mouse T and B cells. The finding that antibody binding causes immunoglobulin on B cells to redistribute rapidly on the cell surface and be endocytosed transformed me from an immunologist into a cell biologist. I moved with Mitchison to University College London, where my colleagues and I used the antibody approach to study cells of the rodent nervous system, focusing on the intrinsic and extrinsic molecular mechanisms that control the development and behavior of myelinating glial cells-Schwann cells and oligodendrocytes. I retired from active research in 2002 and now spend much of my time on scientific advisory boards and thinking about autism.

Accelerated turnover of taste bud cells in mice deficient for the cyclin-dependent kinase inhibitor p27Kip1

Background

Mammalian taste buds contain several specialized cell types that coordinately respond to tastants and communicate with sensory nerves. While it has long been appreciated that these cells undergo continual turnover, little is known concerning how adequate numbers of cells are generated and maintained. The cyclin-dependent kinase inhibitor p27^Kip1 has been shown to influence cell number in several developing tissues, by coordinating cell cycle exit during cell differentiation. Here, we investigated its involvement in the control of taste cell replacement by examining adult mice with targeted ablation of the p27^Kip1 gene.

Results

Histological and morphometric analyses of fungiform and circumvallate taste buds reveal no structural differences between wild-type and p27^Kip1-null mice. However, when examined in functional assays, mutants show substantial proliferative changes. In BrdU incorporation experiments, more S-phase-labeled precursors appear within circumvallate taste buds at 1 day post-injection, the earliest time point examined. After 1 week, twice as many labeled intragemmal cells are present, but numbers return to wild-type levels by 2 weeks. Mutant taste buds also contain more TUNEL-labeled cells and 50% more apoptotic bodies than wild-type controls. In normal mice, p27 ^Kip1 is evident in a subset of receptor and presynaptic taste cells beginning about 3 days post-injection, correlating with the onset of taste cell maturation. Loss of gene function, however, does not alter the proportions of distinct immunohistochemically-identified cell types.

Conclusions

p27^Kip1 participates in taste cell replacement by regulating the number of precursor cells available for entry into taste buds. This is consistent with a role for the protein in timing cell cycle withdrawal in progenitor cells. The equivalence of mutant and wild-type taste buds with regard to cell number, cell types and general structure contrasts with the hyperplasia and tissue disruption seen in certain developing p27^Kip1-null sensory organs, and may reflect a compensatory capability inherent in the regenerative taste system.

Mathematical and experimental approaches to identify and predict the effects of chemotherapy on neuroglial precursors

The adverse effects of chemotherapy on normal cells of the body create substantial clinical problems for many cancer patients. However, relatively little is known about the effects, other than promotion of cell death, of such agents on the function of normal precursor cells critical in tissue homeostasis and repair. We have combined mathematical and experimental analyses to identify the effects of sublethal doses of chemotherapy on glial precursor cells of the central nervous system. We modeled the temporal development of a population of precursor and terminally differentiated cells exposed to sublethal doses of carmustine (BCNU), a classic alkylating chemotherapeutic agent used in treatment of gliomas and non-Hodgkin's lymphomas, as a multitype age-dependent branching process. We fitted our model to data from in vitro clonal experiments using the method of pseudo-likelihood. This approach identifies several novel drug effects, including modification of the cell cycle length, the time between division and differentiation, and alteration in the probability of undergoing self-renewal division in precursor cells. These changes of precursor cell function in the chemotherapy-exposed brain may have profound clinic implications.

MAJOR FINDINGS

We applied our computational approach to analyze the effects of BCNU on clonal cultures of oligodendrocyte progenitor cells-one of the best-characterized neural progenitor cells in the mammalian brain. Our analysis reveals that transient exposures to BCNU increased the cell cycle length of progenitor cells and decreased their time to differentiation, while also decreasing the likelihood that they will undergo self-renewing divisions. By investigating the behavior of our mathematical model, we demonstrate that precursor cell populations should recover spontaneously from transient modifications of the timing of division and of differentiation, but such recovery will not happen after alteration of cell fate. These studies identify means by which precursor cell function can be critically compromised by transient exposure to chemotherapy with long-term consequences on the progenitor cell pool even in the absence of drug-induced apoptosis. These analyses also provide novel tools that apply broadly to identify effects of chemotherapeutic agents and other physiological stressors.

Regulation of memory CD8 T-cell differentiation by cyclin-dependent kinase inhibitor p27Kip1

Induction of potent T-cell memory is the goal of vaccinations, but the molecular mechanisms that regulate the formation of memory CD8 T cells are not well understood. Despite the recognition that controls of cellular proliferation and apoptosis govern the number of memory T cells, the cell cycle regulatory mechanisms that control these key cellular processes in CD8 T cells during an immune response are poorly defined. Here, we have identified the cyclin-dependent kinase inhibitor p27(Kip1) as a critical regulator of the CD8 T-cell homeostasis at all phases of the T-cell response to an acute viral infection in mice. By acting as a timer for cell cycle exit, p27(Kip1) curtailed the programmed expansion of interleukin-2-producing memory precursors and markedly limited the magnitude and quality of CD8 T-cell memory. In the absence of p27(Kip1), CD8 T cells showed superior recall responses shortly after vaccination with recombinant Listeria monocytogenes. Additionally, we show that p27(Kip1) constrains proliferative renewal of memory CD8 T cells, especially of the effector memory subset. These findings provide critical insights into the cell cycle regulation of CD8 T-cell homeostasis and suggest that modulation of p27(Kip1) could bolster vaccine-induced T-cell memory and protective immunity.

Tapping into the glial reservoir: cells committed to remaining uncommitted

The development and maturation of the oligodendrocyte requires a series of highly orchestrated events that coordinate the proliferation and differentiation of the oligodendrocyte precursor cell (OPC) as well as the spatiotemporal regulation of myelination. In recent years, widespread interest has been devoted to the therapeutic potential of adult OPCs scattered throughout the central nervous system (CNS). In this review, we highlight molecular mechanisms controlling OPC differentiation during development and the implication of these mechanisms on adult OPCs for remyelination. Cell-autonomous regulators of differentiation and the heterogeneous microenvironment of the developing and the adult CNS may provide coordinated inhibitory cues that ultimately maintain a reservoir of uncommitted glia.

The human papillomavirus type 16 E5 oncoprotein synergizes with EGF-receptor signaling to enhance cell cycle progression and the down-regulation of p27(Kip1)

E5 oncoprotein activity from high risk human papillomaviruses (HPVs) is associated with growth factor receptor signaling, but the function of this protein is not well understood. In this study, we investigated the role of HPV-16 E5 on the cell cycle progression during EGF-stimulation. Wild-type and NIH 3T3 cells over-expressing human EGF-receptor were transfected with HPV-16 E5 gene and the cell cycle progression was characterized. This analysis showed that the E5-expressing cells increased DNA synthesis (S-phase) by around 40%. Cell cycle protein analysis of E5-expressing cells showed a reduction in the half-life of p27(Kip1) protein as compared to control cells (18.4 vs. 12.7 h), an effect that was enhanced in EGF-stimulated cells (12.8 vs. 3.6 h). Blockage of EGF-receptor activity abrogated E5 signals as well as p27(Kip1) down-regulation. These results suggest that E5 and the EGF-receptor cooperate to enhance cell cycle entry and progression through regulating p27(Kip1) expression at protein level.

Defective DNA double-strand break repair underlies enhanced tumorigenesis and chromosomal instability in p27-deficient mice with growth factor-induced oligodendrogliomas

The tumor suppressive activities of the Kip-family of cdk inhibitors often go beyond their role in regulating the cell cycle. Here, we demonstrate that p27 enhances Rad51 accumulation during repair of double-strand DNA breaks. Progression of PDGF-induced oligodendrogliomas was accelerated in mice lacking the cyclin-cdk binding activities of p27^kip1. Cell lines were developed from RCAS-PDGF infection of nestin-tv-a brain progenitor cells in culture. p27 deficiency did not affect cell proliferation in early passage cell lines; however, the absence of p27 affected chromosomal stability. In p27 deficient cells, the activation of Atm and Chk2, and the accumulation of γH2AX was unaffected compared to wild type cells, and the number of phospho-histone H3 staining mitotic cells was decreased, consistent with a robust G2/M checkpoint activation. However, the percentage of Rad51 foci positive cells was decreased, and the kinase activity that targets the C-terminus of BRCA2, regulating BRCA2/Rad51 interactions, was increased in lysates derived from p27 deficient cells. Increased numbers of chromatid breaks in p27 deficient cells that adapted to the checkpoint were also observed. These findings suggest that Rad51-dependent repair of double stranded breaks was hindered in p27 deficient cells, leading to chromosomal instability, a hallmark of cancers with poor prognosis.

Long-term multilayer adherent network (MAN) expansion, maintenance, and characterization, chemical and genetic manipulation, and transplantation of human fetal forebrain neural stem cells

Human neural stem/precursor cells (hNSC/hNPC) have been targeted for application in a variety of research models and as prospective candidates for cell-based therapeutic modalities in central nervous system (CNS) disorders. To this end, the successful derivation, expansion, and sustained maintenance of undifferentiated hNSC/hNPC in vitro, as artificial expandable neurogenic micro-niches, promises a diversity of applications as well as future potential for a variety of experimental paradigms modeling early human neurogenesis, neuronal migration, and neurogenetic disorders, and could also serve as a platform for small-molecule drug screening in the CNS. Furthermore, hNPC transplants provide an alternative substrate for cellular regeneration and restoration of damaged tissue in neurodegenerative disorders such as Parkinson's disease and Alzheimer's disease. Human somatic neural stem/progenitor cells (NSC/NPC) have been derived from a variety of cadaveric sources and proven engraftable in a cytoarchitecturally appropriate manner into the developing and adult rodent and monkey brain while maintaining both functional and migratory capabilities in pathological models of disease. In the following unit, we describe a new procedure that we have successfully employed to maintain operationally defined human somatic NSC/NPC from developing fetal, pre-term post-natal, and adult cadaveric forebrain. Specifically, we outline the detailed methodology for in vitro expansion, long-term maintenance, manipulation, and transplantation of these multipotent precursors.

p57kip2 is dynamically regulated in experimental autoimmune encephalomyelitis and interferes with oligodendroglial maturation

The mechanisms preventing efficient remyelination in the adult mammalian central nervous system after demyelinating inflammatory diseases, such as multiple sclerosis, are largely unknown. Partial remyelination occurs in early disease stages, but repair capacity diminishes over time and with disease progression. We describe a potent candidate for the negative regulation of oligodendroglial differentiation that may underlie failure to remyelinate. The p57kip2 gene is dynamically regulated in the spinal cord during MOG-induced experimental autoimmune encephalomyelitis. Transient down-regulation indicated that it is a negative regulator of post-mitotic oligodendroglial differentiation. We then applied short hairpin RNA-mediated gene suppression to cultured oligodendroglial precursor cells and demonstrated that down-regulation of p57kip2 accelerates morphological maturation and promotes myelin expression. We also provide evidence that p57kip2 interacts with LIMK-1, implying that p57kip2 affects cytoskeletal dynamics during oligodendroglial maturation. These data suggest that sustained down-regulation of p57kip2 is important for oligodendroglial maturation and open perspectives for future therapeutic approaches to overcome the endogenous remyelination blockade in multiple sclerosis.

p27(KIP1) regulates neurogenesis in the rostral migratory stream and olfactory bulb of the postnatal mouse

Neuronal progenitor cells of the anterior subventricular zone (SVZa) migrate along the rostral migratory stream (RMS) to the olfactory bulb, where they exit the cell cycle and differentiate. The molecular mechanisms that regulate SVZa progenitor proliferation and cell-cycle exit are largely undefined. We investigated the role of p27(KIP1) in regulating cell proliferation and survival in the RMS and olfactory bulb between postnatal day 1 (P1) and P14, the peak period of olfactory bulb neuron generation. A large proportion of cells in the RMS and the olfactory bulb express cytoplasmic p27(KIP1), but a small percentage display high nuclear p27(KIP1) immunostaining, which exhibit a caudal(low)-rostral(high) gradient: lowest in the SVZa and highest in the glomerular layer of the olfactory bulb. p27(KIP1) is also present in the nucleus and/or the cytoplasm of neuron-specific type III beta-tubulin(+) cells. Cells with strong nuclear p27(KIP1) expression are BrdU(-) and Ki67(-). The percentage of BrdU(+) cells in the SVZa, RMS, and olfactory bulb is higher in p27(KIP1) null than wild-type (WT) mice at all ages analyzed. Consistent with these findings, p27(KIP1) overexpression in cultured p27(KIP1) null and WT SVZ cells reduced cell proliferation and self-renewal. Finally, in p27(KIP1) null mice, the diameter of the horizontal limb of the RMS is larger than in WT mice, and development of the olfactory bulb granule cell layer is delayed, together with increased apoptotic cell density. Our results indicate that in the postnatal brain, p27(KIP1) regulates the proliferation and survival of neuronal cells in the RMS and olfactory bulb.

The anaphase promoting complex induces substrate degradation during neuronal differentiation

The anaphase promoting complex (APC) is an E3 ubiquitin ligase required for the metaphase-to-anaphase transition and mitotic exit. However, APC also plays roles in G(1), where it is regulated by Cdh1, and APC activity has also been detected in differentiated and non-proliferating cells, suggesting that it may play roles outside the cell cycle. Here, we report that disrupting APC(Cdh1) activity inhibits neurite outgrowth of both PC12 pheochromocytoma cells and primary cerebellar granule cells. APC(Cdh1) activity dramatically increases as PC12 cells differentiate in response to nerve growth factor. Furthermore, a key target degraded by APC(Cdh1) following nerve growth factor treatment is the F-box protein Skp2, and APC(Cdh1)-mediated destruction of Skp2 is essential for proper terminal differentiation of neuronal precursors.

Essential function, sophisticated regulation and pathological impact of the selective RNA-binding protein QKI in CNS myelin development

The selective RNA-binding protein QKI play a key role in advancing oligodendrocyte-dependent myelination, which is essential for the function and development of the CNS. The emerging evidence that QKI abnormalities are associated with schizophrenia and may underlie myelin impairment in this devastating disease has greatly increased interest in understanding the function of QKI. Despite the discovery of the biochemical basis for QKI-RNA interaction, a comprehensive model is currently missing regarding how QKI regulates its mRNA ligands to promote normal myelinogenesis and how deficiency of the QKI pathway is involved in the pathogenesis of human diseases that affect CNS myelin. In this review, we will focus on the role of QKI in regulating distinct mRNA targets at critical developmental steps to promote oligodendrocyte differentiation and myelin formation. In addition, we will discuss molecular mechanisms that control QKI expression and activity during normal myelinogenesis as well as the pathological impact of QKI deficiency in dysmyelination mutant animals and in human myelin disorders.

Molecular titration and ultrasensitivity in regulatory networks

Protein sequestration occurs when an active protein is sequestered by a repressor into an inactive complex. Using mathematical and computational modeling, we show how this regulatory mechanism (called "molecular titration") can generate ultrasensitive or "all-or-none" responses that are equivalent to highly cooperative processes. The ultrasensitive nature of the input-output response is mainly determined by two parameters: the dimer dissociation constant and the repressor concentration. Because in vivo concentrations are tunable through a variety of mechanisms, molecular titration represents a flexible mechanism for generating ultrasensitivity. Using physiological parameters, we report how details of in vivo protein degradation affect the strength of the ultrasensitivity at steady state. Given that developmental systems often transduce signals into cell-fate decisions on timescales incompatible with steady state, we further examine whether molecular titration can produce ultrasensitive responses within physiologically relevant time intervals. Using Drosophila somatic sex determination as a developmental paradigm, we demonstrate that molecular titration can generate ultrasensitivity on timescales compatible with most cell-fate decisions. Gene duplication followed by loss-of-function mutations can create dominant negatives that titrate and compete with the original protein. Dominant negatives are abundant in gene regulatory circuits, and our results suggest that molecular titration might be generating an ultrasensitive response in these networks.

Post-translational modifications of nucleosomal histones in oligodendrocyte lineage cells in development and disease

The role of epigenetics in modulating gene expression in the development of organs and tissues and in disease states is becoming increasingly evident. Epigenetics refers to the several mechanisms modulating inheritable changes in gene expression that are independent of modifications of the primary DNA sequence and include post-translational modifications of nucleosomal histones, changes in DNA methylation, and the role of microRNA. This review focuses on the epigenetic regulation of gene expression in oligodendroglial lineage cells. The biological effects that post-translational modifications of critical residues in the N-terminal tails of nucleosomal histones have on oligodendroglial cells are reviewed, and the implications for disease and repair are critically discussed.

The balance between oligodendrocyte and astrocyte production in major white matter tracts is linearly related to serum total thyroxine

Thyroid hormone (TH) may control the ratio of oligodendrocytes to astrocytes in white matter by acting on a common precursor of these two cell types. If so, then TH should produce an equal but opposite effect on the density of these two cells types across all TH levels. To test this, we induced graded TH insufficiency by treating pregnant rats with increasing doses of propylthiouracil. Propylthiouracil induced a dose-dependent decrease in serum T(4) in postnatal d 15 pups, a dose-dependent decrease in the density of MAG-positive oligodendrocytes, and an equal increase in the density of glial fibrillary acidic protein-positive astrocytes in both the corpus callosum and anterior commissure. Linear regression analyses demonstrated a strong correlation between glial densities and serum T(4); this correlation was positive for astrocytes and negative for oligodendrocytes. Surprisingly, oligodendrocyte density in the corpus callosum was more sensitive to changes in TH than in the anterior commissure, as indicated by the slope of the regressions. Furthermore, we measured an overall reduction in the cellular density that was independent of changes in myelin-associated glycoprotein and glial fibrillary acidic protein-positive cells. These data strongly support the interpretation that TH controls the balance of production of oligodendrocytes and astrocytes in major white matter tracts of the developing brain by acting on a common precursor of these cell types. Moreover, these findings indicate that major white matter tracts may differ in their sensitivity to TH insufficiency.

Cux2 (Cutl2) integrates neural progenitor development with cell-cycle progression during spinal cord neurogenesis

Neurogenesis requires the coordination of neural progenitor proliferation and differentiation with cell-cycle regulation. However, the mechanisms coordinating these distinct cellular activities are poorly understood. Here we demonstrate for the first time that a Cut-like homeodomain transcription factor family member, Cux2 (Cutl2), regulates cell-cycle progression and development of neural progenitors. Cux2 loss-of-function mouse mutants exhibit smaller spinal cords with deficits in neural progenitor development as well as in neuroblast and interneuron differentiation. These defects correlate with reduced cell-cycle progression of neural progenitors coupled with diminished Neurod and p27(Kip1) activity. Conversely, in Cux2 gain-of-function transgenic mice, the spinal cord is enlarged in association with enhanced neuroblast formation and neuronal differentiation, particularly with respect to interneurons. Furthermore, Cux2 overexpression induces high levels of Neurod and p27(Kip1). Mechanistically, we discovered through chromatin immunoprecipitation assays that Cux2 binds both the Neurod and p27(Kip1) promoters in vivo, indicating that these interactions are direct. Our results therefore show that Cux2 functions at multiple levels during spinal cord neurogenesis. Cux2 initially influences cell-cycle progression in neural progenitors but subsequently makes additional inputs through Neurod and p27(Kip1) to regulate neuroblast formation, cell-cycle exit and cell-fate determination. Thus our work defines novel roles for Cux2 as a transcription factor that integrates cell-cycle progression with neural progenitor development during spinal cord neurogenesis.