Ikaros-1 couples cell cycle arrest of late striatal precursors with neurogenesis of enkephalinergic neurons.

During central nervous system development, several transcription factors regulate the differentiation of progenitor cells to postmitotic neurons. Here we describe a novel role for Ikaros-1 in the generation of late-born striatal neurons. Our results show that Ikaros-1 is expressed in the boundary of the striatal germinal zone (GZ)/mantle zone (MZ), where it induces cell cycle arrest of neural progenitors by up-regulation of the cyclin-dependent kinase inhibitor (CDKi) p21(Cip1/Waf1). This effect is coupled with the neuronal differentiation of late precursors, which in turn is critical for the second wave of striatal neurogenesis that gives rise to matrix neurons. Consistently, Ikaros(-/-) mice had fewer striatal projecting neurons and, in particular, enkephalin (ENK)-positive neurons. In addition, overexpression of Ikaros-1 in primary striatal cultures increases the number of calbindin- and ENK-positive neurons. Our results also show that Ikaros-1 acts downstream of the Dlx family of transcription factors, insofar as its expression is lost in Dlx1/2 double knockout mice. However, we demonstrate that Ikaros-1 and Ebf-1 independently regulate the final determination of the two populations of striatal projection neurons of the matrix compartment, ENK- and substance P-positive neurons. In conclusion, our findings identify Ikaros-1 as a modulator of cell cycle exit of neural progenitors that gives rise to the neurogenesis of ENK-positive striatal neurons.We thank M.T. Mun ̃oz, A. Lo ́pez, T. Gil, and M. Bonete for technical support and Dr. Maria Calvo and Anna Bosch from the confocal microscopy unit at the Serveis Cientı ́fico-Te`cnics (Universitat de Barcelona) for their sup-port and advice on confocal techniques. We also thank Dr.K. Campbell for providing Dlx5/6Cre-IRES-EGFP trans-genic mice, Dr. Rudolf Grosschedl for Ebf1–/– mice, and Dr.Susan Winandy for Ikaros constructs. We are also very grateful to Robin Rycroft for the English language revisionS

Nolz1 promotes striatal neurogenesis through the regulation of retinoic acid signaling

Background: Nolz1 is a zinc finger transcription factor whose expression is enriched in the lateral ganglionic eminence (LGE), although its function is still unknown. Results: Here we analyze the role of Nolz1 during LGE development. We show that Nolz1 expression is high in proliferating neural progenitor cells (NPCs) of the LGE subventricular zone. In addition, low levels of Nolz1 are detected in the mantle zone, as well as in the adult striatum. Similarly, Nolz1 is highly expressed in proliferating LGE-derived NPC cultures, but its levels rapidly decrease upon cell differentiation, pointing to a role of Nolz1 in the control of NPC proliferation and/or differentiation. In agreement with this hypothesis, we find that Nolz1 over-expression promotes cell cycle exit of NPCs in neurosphere cultures and negatively regulates proliferation in telencephalic organotypic cultures. Within LGE primary cultures, Nolz1 over-expression promotes the acquisition of a neuronal phenotype, since it increases the number of β-III tubulin (Tuj1)- and microtubule-associated protein (MAP)2-positive neurons, and inhibits astrocyte generation and/or differentiation. Retinoic acid (RA) is one of the most important morphogens involved in striatal neurogenesis, and regulates Nolz1 expression in different systems. Here we show that Nolz1 also responds to this morphogen in E12.5 LGE-derived cell cultures. However, Nolz1 expression is not regulated by RA in E14.5 LGE-derived cell cultures, nor is it affected during LGE development in mouse models that present decreased RA levels. Interestingly, we find that Gsx2, which is necessary for normal RA signaling during LGE development, is also required for Nolz1 expression, which is lost in Gsx2 knockout mice. These findings suggest that Nolz1 might act downstream of Gsx2 to regulate RA-induced neurogenesis. Keeping with this hypothesis, we show that Nolz1 induces the selective expression of the RA receptor (RAR)β without altering RARα or RARγ. In addition, Nozl1 over-expression increases RA signaling since it stimulates the RA response element. This RA signaling is essential for Nolz1-induced neurogenesis, which is impaired in a RA-free environment or in the presence of a RAR inverse agonist. It has been proposed that Drosophila Gsx2 and Nolz1 homologues could cooperate with the transcriptional co-repressors Groucho-TLE to regulate cell proliferation. In agreement with this view, we show that Nolz1 could act in collaboration with TLE-4, as they are expressed at the same time in NPC cultures and during mouse development. Conclusions: Nolz1 promotes RA signaling in the LGE, contributing to the striatal neurogenesis during development

Id4 promotes the elimination of the pro-activation factor ascl1 to maintain quiescence of adult hippocampal stem cells

Quiescence is essential for the long-term maintenance of adult stem cells but how stem cells maintain quiescence is poorly understood. Here we show that neural stem cells in the adult mouse hippocampus actively transcribe the pro-activation factor Ascl1 regardless of their activated or quiescent states. We found that the inhibitor of DNA binding protein Id4 is enriched in quiescent neural stem cells and that elimination of Id4 results in abnormal accumulation of Ascl1 protein and premature stem cell activation. Accordingly, Id4 and other Id proteins promote elimination of Ascl1 protein in neural stem cell cultures. Id4 sequesters Ascl1 heterodimerisation partner E47, promoting Ascl1 protein degradation and stem cell quiescence. Our results highlight the importance of non-transcriptional mechanisms for the maintenance of neural stem cell quiescence and reveal a role for Id4 as a quiescence-inducing factor, in contrast with its role of promoting the proliferation of embryonic neural progenitors

Caracterización de factores de transcripción estriatales para su uso en la diferenciación de células madre

[spa] El objetivo de este trabajo ha sido el estudio de dos factores genéticos implicados en la diferenciación de las neuronas GABAérgicas de proyección estriatales: Nolz1 e Ikaros. Además se ha estudiado el potencial de estos factores de transcripción en la diferenciación de células madre neurales in vitro hacia un fenotipo estriatal para entender mejor los mecanismos que regulan la aparición de este tipo de neuronas. Hemos demostrado que Nolz1 es un gen que interviene en la especificación de los precursores neurales de la SVZ de la eminencia ganglionar lateral (LGE), los llamados progenitores basales. Las células Nolz1 positivas provienen de precursores positivos para Gsh2, y su expresión contribuye a la aparición de la señalización de ácido retinoico en el núcleo estriado durante el desarrollo. Nolz1, además, regula la vía de Notch en precursores neurales i promueve la aparición de precursores oligodendrogliales mediante un mecanismo no autónomo en la LGE. Por otra parte, demostramos que la isoforma de Ikaros Ik1 es esencial para la correcta generación de las neuronas encefalinérgicas estriatales a partir de la diferenciación de precursores neurales Dlx2 positivos de la LGE. Mostramos que Ik1 es necessario para sacar de ciclo los precursores que formarán el núcleo estriado mediante el incremento de los niveles del inhibidor de ciclinas p21. En consonancia con esta observación, la falta de Ikaros durante el desarrollo, afecta la neurogénesis tardía en el estriado. Esto se traduce en que el animal deficiente de Ikaros presenta un núcleo estriado más pequeño debido a una disminución en el número de neuronas de proyección encefalinérgicas de la matriz. Así, Nolz1 e Ikaros intervienen en diferentes momentos del desarrollo estriatal, siendo el papel de Nolz1 anterior y centrado en el control de precursores neurales, y el de Ikaros algo posterior, centrado en la diferenciación de neuronas estriatales de proyección encefalinégicas[eng] The main goal of this work has been the study of two genetic factors implied in the differentiation of the striatal GABAergic projection neurons: Nolz1 and Ikaros. Moreover, we have studied the potential of these transcription factors to direct the differentiation of neural stem cells in vitro towards a striatal phenotype, in order to understand some aspects of the generation of this kind of neurons. We have demonstrated that the action of Nolz1 is involved in the specification of the neural precursors which reside in the SVZ ol the lateral ganglionic eminencie (LGE), the so-called basal progenitors. The cells positive for Nolz1 come from Gsh2 positive neural precursors, and its expression contributes to the inititation of a source of retinoic acid signalling within the striatum during development. Nolz1, in addition, regulates the Notch pathway in neural precursors an promotes the appearance of oligodendrocyte precursors in the LGE by a non-autonomous mechanism. On the other hand, we demostrate that the Ikaros isoform Ik1 is essential for the correct generation of the striatal enkephalinergic neurons from the differentiation of Dlx2 positive neural precursors of the LGE. We show that Ik1 is necessary for the cell-cycle exit of the neural precursors which will populate the striatum by the increase of the cyclin inhibitor p21. According with this observation, Ikaros absence during development specifically affects late striatal neurogenesis. This is translated in the adult Ikaros deficient animal in a reduced striatum due to a reduced number of matrix enkephalinergic projection neurons. Thus, Nolz1 and Ikaros exhert its actions during different times in striatal development, being Nolz1 role earlier and focused in the control of neural precursors, and Ikaros role occurs later, focused in the differentiation of the enkephalinergic projection neurons

A Nuclear Role for miR-9 and Argonaute Proteins in Balancing Quiescent and Activated Neural Stem Cell States

Summary: Throughout life, adult neural stem cells (NSCs) produce new neurons and glia that contribute to crucial brain functions. Quiescence is an essential protective feature of adult NSCs; however, the establishment and maintenance of this state remain poorly understood. We demonstrate that in the adult zebrafish pallium, the brain-enriched miR-9 is expressed exclusively in a subset of quiescent NSCs, highlighting a heterogeneity within these cells, and is necessary to maintain NSC quiescence. Strikingly, miR-9, along with Argonaute proteins (Agos), is localized to the nucleus of quiescent NSCs, and manipulating their nuclear/cytoplasmic ratio impacts quiescence. Mechanistically, miR-9 permits efficient Notch signaling to promote quiescence, and we identify the RISC protein TNRC6 as a mediator of miR-9/Agos nuclear localization in vivo. We propose a conserved non-canonical role for nuclear miR-9/Agos in controlling the balance between NSC quiescence and activation, a key step in maintaining adult germinal pools. : An essential protective feature of adult neural stem cells is their relative quiescence. Katz et al. identify microRNA-9 as crucial factor that maintains adult NSCs quiescence and sets a heterogeneity within these cells, through a non-canonical nuclear mode of action. Keywords: neural stem cell, radial glia, quiescence, adult neurogenesis, telencephalon, miR-9, Argonaute, Notch, zebrafis

Nipbl Interacts with Zfp609 and the Integrator Complex to Regulate Cortical Neuron Migration

textabstractMutations in NIPBL are the most frequent cause of Cornelia de Lange syndrome (CdLS), a developmental disorder encompassing several neurological defects, including intellectual disability and seizures. How NIPBL mutations affect brain development is not understood. Here we identify Nipbl as a functional interaction partner of the neural transcription factor Zfp609 in brain development. Depletion of Zfp609 or Nipbl from cortical neural progenitors in vivo is detrimental to neuronal migration. Zfp609 and Nipbl overlap at genomic binding sites independently of cohesin and regulate genes that control cortical neuron migration. We find that Zfp609 and Nipbl interact with the Integrator complex, which functions in RNA polymerase 2 pause release. Indeed, Zfp609 and Nipbl co-localize at gene promoters containing paused RNA polymerase 2, and Integrator similarly regulates neuronal migration. Our data provide a rationale and mechanistic insights for the role of Nipbl in the neurological defects associated with CdLS. NIPBL mutations cause Cornelia de Lange syndrome, but Nipbl function in brain development is not well understood. Van den Berg et al. show that Nipbl interacts with Zfp609 and the Integrator complex to transcriptionally regulate cortical neuron migration

Helios transcription factor expression depends on Gsx2 and Dlx1&2 function in developing striatal matrix neurons

Development of the nervous system is finely regulated by consecutive expression of cell-specific transcription factors. Here we show that Helios, a member of the Ikaros transcription factor family, is expressed in ectodermal and neuroectodermal-derived tissues. During embryonic development, Helios is expressed by several brain structures including the lateral ganglionic eminence (LGE, the striatal anlage); the cingulated, insular and retrosplenial cortex; the hippocampus; and the accessory olfactory bulb. Moreover, Helios is also expressed by Purkinje neurons during postnatal cerebellar development. Within the LGE, Helios expression follows a dynamic spatio-temporal pattern starting at embryonic stages (E14.5), peaking at E18.5, and completely disappearing during postnatal development. Helios is expressed by a small population of nestin-positive neural progenitor cells located in the subventricular zone as well as by a larger population of immature neurons distributed throughout the mantle zone. In the later, Helios is preferentially expressed in the matrix compartment, where it colocalizes with Bcl11b and Foxp1, well-known markers of striatal projection neurons. In addition, we observed that Helios expression is not detected in Dlx1/2 and Gsx2 null mutants, while its expression is maintained in Ascl1 mutants. These findings allow us to introduce a new transcription factor in the cascade of events that take part of striatal development postulating the existence of at least 4 different neural progenitors in the LGE. An Ascl1-independent but Gsx2-& Dlx1/2-dependent precursor will express Helios defining a new lineage for a subset of matrix striatal neurons. © 2012, Mary Ann Liebert, Inc.Peer Reviewe

Return to Quiescence of mouse neural stem cells by degradation of a proactivation protein

Quiescence is essential for long-term maintenance of adult stem cells. Niche signals regulate the transit of stem cells from dormant to activated states. Here, we show that the E3-ubiquitin ligase Huwe1 (HECT, UBA, and WWE domain-containing 1) is required for proliferating stem cells of the adult mouse hippocampus to return to quiescence. Huwe1 destabilizes proactivation protein Ascl1 (achaete-scute family bHLH transcription factor 1) in proliferating hippocampal stem cells, which prevents accumulation of cyclin Ds and promotes the return to a resting state. When stem cells fail to return to quiescence, the proliferative stem cell pool becomes depleted. Thus, long-term maintenance of hippocampal neurogenesis depends on the return of stem cells to a transient quiescent state through the rapid degradation of a key proactivation factor