Distinct progenitor behavior underlying neocortical gliogenesis related to tumorigenesis.

Radial glial progenitors (RGPs) give rise to the vast majority of neurons and glia in the neocortex. Although RGP behavior and progressive generation of neocortical neurons have been delineated, the exact process of neocortical gliogenesis remains elusive. Here, we report the precise progenitor behavior and gliogenesis program at single-cell resolution in the mouse neocortex. Fractions of dorsal RGPs transition from neurogenesis to gliogenesis progressively, producing astrocytes, oligodendrocytes, or both in well-defined propensities of ∼60%, 15%, and 25%, respectively, by fate-restricted "intermediate" precursor cells (IPCs). Although the total number of IPCs generated by individual RGPs appears stochastic, the output of individual IPCs exhibit clear patterns in number and subtype and form discrete local subclusters. Clonal loss of tumor suppressor Neurofibromatosis type 1 leads to excessive production of glia selectively, especially oligodendrocyte precursor cells. These results quantitatively delineate the cellular program of neocortical gliogenesis and suggest the cellular and lineage origin of primary brain tumor.

The Mode of Stem Cell Division Is Dependent on the Differential Interaction of ß-Catenin with the Kat3 Coactivators CBP or p300.

Normal long-term repopulating somatic stem cells (SSCs) preferentially divide asymmetrically, with one daughter cell remaining in the niche and the other going on to be a transient amplifying cell required for generating new tissue in homeostatic maintenance and repair processes, whereas cancer stem cells (CSCs) favor symmetric divisions. We have previously proposed that differential ß-catenin modulation of transcriptional activity via selective interaction with either the Kat3 coactivator CBP or its closely related paralog p300, regulates symmetric versus asymmetric division in SSCs and CSCs. We have previously demonstrated that SSCs that divide asymmetrically per force retain one of the dividing daughter cells in the stem cell niche, even when treated with specific CBP/ß-catenin antagonists, whereas CSCs can be removed from their niche via forced stochastic symmetric differentiative divisions. We now demonstrate that loss of p73 in early corticogenesis biases ß-catenin Kat3 coactivator usage and enhances ß-catenin/CBP transcription at the expense of ß-catenin/p300 transcription. Biased ß-catenin coactivator usage has dramatic consequences on the mode of division of neural stem cells (NSCs), but not neurogenic progenitors. The observed increase in symmetric divisions due to enhanced ß-catenin/CBP interaction and transcription leads to an immediate increase in NSC symmetric differentiative divisions. Moreover, we demonstrate for the first time that the complex phenotype caused by the loss of p73 can be rescued in utero by treatment with the small-molecule-specific CBP/ß-catenin antagonist ICG-001. Taken together, our results demonstrate the causal relationship between the choice of ß-catenin Kat3 coactivator and the mode of stem cell division.

The centrosome protein AKNA regulates neurogenesis via microtubule organization.

The expansion of brain size is accompanied by a relative enlargement of the subventricular zone during development. Epithelial-like neural stem cells divide in the ventricular zone at the ventricles of the embryonic brain, self-renew and generate basal progenitors1 that delaminate and settle in the subventricular zone in enlarged brain regions2. The length of time that cells stay in the subventricular zone is essential for controlling further amplification and fate determination. Here we show that the interphase centrosome protein AKNA has a key role in this process. AKNA localizes at the subdistal appendages of the mother centriole in specific subtypes of neural stem cells, and in almost all basal progenitors. This protein is necessary and sufficient to organize centrosomal microtubules, and promote their nucleation and growth. These features of AKNA are important for mediating the delamination process in the formation of the subventricular zone. Moreover, AKNA regulates the exit from the subventricular zone, which reveals the pivotal role of centrosomal microtubule organization in enabling cells to both enter and remain in the subventricular zone. The epithelial-to-mesenchymal transition is also regulated by AKNA in other epithelial cells, demonstrating its general importance for the control of cell delamination.

SDCCAG8 regulates pericentriolar material recruitment and neuronal migration in the developing cortex.

Mutations of SDCCAG8 are associated with nephronophthisis and Bardet-Biedl syndrome, as well as schizophrenia; however, the function of SDCCAG8 remains largely unknown. Here, we show that SDCCAG8 regulates centrosomal accumulation of pericentriolar material and neuronal polarization and migration in the developing mouse cortex. Sdccag8 expression is selectively elevated in newborn neurons prior to their commencement of radial locomotion, and suppression of this expression by short-hairpin RNAs or a loss-of-function allele impairs centrosomal recruitment of γ-tubulin and pericentrin, interferes with microtubule organization, decouples the centrosome and the nucleus, and disrupts neuronal migration. Moreover, SDCCAG8 interacts and cotraffics with pericentriolar material 1 (PCM1), a centriolar satellite protein crucial for targeting proteins to the centrosome. Expression of SDCCAG8 carrying a human mutation causes neuronal migration defects. These results reveal a critical role for SDCCAG8 in controlling centrosomal properties and function, and provide insights into the basis of neurological defects linked to SDCCAG8 mutations.

Clonal origins of neocortical interneurons.

Once referred to as 'short-axon' neurons by Cajal, GABA (gamma-amino butyric acid)-ergic interneurons are essential components of the neocortex. They are distributed throughout the cortical laminae and are responsible for shaping circuit output through a rich array of inhibitory mechanisms. Numerous fate-mapping and transplantation studies have examined the embryonic origins of the diversity of interneurons that are defined along various parameters such as morphology, neurochemical marker expression and physiological properties, and have been extensively reviewed elsewhere. Here, we focus on discussing two recent studies that have, for the first time, examined the production and organization of neocortical interneurons originated from individual progenitors, that is, with clonal resolution, and provided important new insights into the cellular processes underlying the development of inhibitory interneurons in the neocortex.

Specification of functional cranial placode derivatives from human pluripotent stem cells.

Cranial placodes are embryonic structures essential for sensory and endocrine organ development. Human placode development has remained largely inaccessible despite the serious medical conditions caused by the dysfunction of placode-derived tissues. Here, we demonstrate the efficient derivation of cranial placodes from human pluripotent stem cells. Timed removal of the BMP inhibitor Noggin, a component of the dual-SMAD inhibition strategy of neural induction, triggers placode induction at the expense of CNS fates. Concomitant inhibition of fibroblast growth factor signaling disrupts placode derivation and induces surface ectoderm. Further fate specification at the preplacode stage enables the selective generation of placode-derived trigeminal ganglia capable of in vivo engraftment, mature lens fibers, and anterior pituitary hormone-producing cells that upon transplantation produce human growth hormone and adrenocorticotropic hormone in vivo. Our results establish a powerful experimental platform to study human cranial placode development and set the stage for the development of human cell-based therapies in sensory and endocrine disease.

Par proteins and neuronal polarity.

A hallmark of neurons is their ability to polarize with dendrite and axon specification to allow the proper flow of information through the nervous system. Over the past decade, extensive research has been performed in an attempt to understand the molecular and cellular machinery mediating this neuronal polarization process. It has become evident that many of the critical regulators involved in establishing neuronal polarity are evolutionarily conserved proteins that had previously been implicated in controlling the polarization of other cell types. At the forefront of this research are the partition defective (Par) proteins. In this review,we will provide a commentary on the progress of work regarding the central importance of Parproteins in the establishment of neuronal polarity.

Prospective isolation of cortical interneuron precursors from mouse embryonic stem cells.

Despite their therapeutic potential, progress in generating fully differentiated forebrain neurons from embryonic stem cells (ESCs) has lagged behind that from more caudal regions of the neuraxis. GABAergic interneuron precursors have the remarkable ability to migrate extensively and survive after transplantation into postnatal cortex, making them an attractive candidate for use in cell-based therapy for seizures or other neuropsychiatric disorders. We have modified a mouse ESC line with an Lhx6-GFP reporter construct that allows for the isolation of newly generated cortical interneuron precursors. When transplanted into postnatal cortex, these cells can migrate into the cortical parenchyma, survive for months, and display morphological, neurochemical, and electrophysiological properties characteristic of mature interneurons. This work demonstrates that forebrain neuronal subtypes with complex traits can be generated from embryonic stem cells, and provides a novel approach to the study of cortical interneuron development and to the establishment of cell-based therapies for neurological disease.

Common molecular pathways mediate long-term potentiation of synaptic excitation and slow synaptic inhibition.

Synaptic plasticity, the cellular correlate for learning and memory, involves signaling cascades in the dendritic spine. Extensive studies have shown that long-term potentiation (LTP) of the excitatory postsynaptic current (EPSC) through glutamate receptors is induced by activation of N-methyl-D-asparate receptor (NMDA-R)--the coincidence detector--and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). Here we report that the same signaling pathway in the postsynaptic CA1 pyramidal neuron also causes LTP of the slow inhibitory postsynaptic current (sIPSC) mediated by metabotropic GABA(B) receptors (GABA(B)-Rs) and G protein-activated inwardly rectifying K(+) (GIRK) channels, both residing in dendritic spines as well as shafts. Indicative of intriguing differences in the regulatory mechanisms for excitatory and inhibitory synaptic plasticity, LTP of sIPSC but not EPSC was abolished in mice lacking Nova-2, a neuronal-specific RNA binding protein that is an autoimmune target in paraneoplastic opsoclonus myoclonus ataxia (POMA) patients with latent cancer, reduced inhibitory control of movements, and dementia.

APC and GSK-3beta are involved in mPar3 targeting to the nascent axon and establishment of neuronal polarity.

In developing hippocampal neurons in culture, the evolutionarily conserved polarity complex mPar3/mPar6/aPKC selectively accumulates at the tip of one, and only one, of the immature neurites of a neuron and thus specifies the axon and generates neuronal polarity. How mPar3/mPar6 is enriched at the tip of the nascent axon, but not the dendrites, is not fully understood. Here, we report that mPar3 forms a complex with adenomatous polyposis coli (APC) and kinesin superfamily (KIF) 3A, proteins that move along microtubules. In polarizing hippocampal neurons, APC selectively accumulates at the nascent axon tip and colocalizes with mPar3. Expression of dominant-negative C terminus deletion mutants of APC or ectopic expression of APC leads to dislocalization of mPar3 and defects in axon specification and neuronal polarity. In addition to spatial polarization of APC, the selective inactivation of the GSK-3beta activity at the nascent axon tip is required for mPar3 targeting and polarization and establishing neuronal polarity. These results suggest that mPar3 is polarized in developing neurons through APC- and kinesin-mediated transport to the plus ends of rapidly growing microtubules at the nascent axon tip, a process that involves a spatially regulated GSK-3beta activity.

PKA phosphorylation of AMPA receptor subunits controls synaptic trafficking underlying plasticity.

The regulated incorporation of AMPA receptors into synapses is important for synaptic plasticity. Here we examine the role of protein kinase A (PKA) in this process. We found that PKA phosphorylation of the AMPA receptor subunits GluR4 and GluR1 directly controlled the synaptic incorporation of AMPA receptors in organotypic slices from rat hippocampus. Activity-driven PKA phosphorylation of GluR4 was necessary and sufficient to relieve a retention interaction and drive receptors into synapses. In contrast, PKA phosphorylation of GluR1 and the activity of calcium/calmodulin-dependent kinase II (CaMKII) were both necessary for receptor incorporation. Thus, PKA phosphorylation of AMPA receptor subunits contributes to diverse mechanisms underlying synaptic plasticity.