RESUMEN
Cajal-Retzius neurons (CRs) are among the first-born neurons in the developing cortex of reptiles, birds and mammals, including humans. The peculiarity of CRs lies in the fact they are initially embedded into the immature neuronal network before being almost completely eliminated by cell death at the end of cortical development. CRs are best known for controlling the migration of glutamatergic neurons and the formation of cortical layers through the secretion of the glycoprotein reelin. However, they have been shown to play numerous additional key roles at many steps of cortical development, spanning from patterning and sizing functional areas to synaptogenesis. The use of genetic lineage tracing has allowed the discovery of their multiple ontogenetic origins, migratory routes, expression of molecular markers and death dynamics. Nowadays, single-cell technologies enable us to appreciate the molecular heterogeneity of CRs with an unprecedented resolution. In this Review, we discuss the morphological, electrophysiological, molecular and genetic criteria allowing the identification of CRs. We further expose the various sources, migration trajectories, developmental functions and death dynamics of CRs. Finally, we demonstrate how the analysis of public transcriptomic datasets allows extraction of the molecular signature of CRs throughout their transient life and consider their heterogeneity within and across species.
Asunto(s)
Proteínas del Tejido Nervioso/metabolismo , Neuronas/metabolismo , Animales , Moléculas de Adhesión Celular Neuronal , Muerte Celular , Corteza Cerebral/crecimiento & desarrollo , Proteínas de la Matriz Extracelular , Hipocampo/crecimiento & desarrollo , Humanos , Proteínas del Tejido Nervioso/genética , Neurogénesis/fisiología , Neuronas/citología , Proteína Reelina , Serina Endopeptidasas , TranscriptomaRESUMEN
In the developing cerebral cortex, how progenitors that seemingly display limited diversity end up producing a vast array of neurons remains a puzzling question. The prevailing model suggests that temporal maturation of progenitors is a key driver in the diversification of the neuronal output. However, temporal constraints are unlikely to account for all diversity, especially in the ventral and lateral pallium where neuronal types significantly differ from their dorsal neocortical counterparts born at the same time. In this study, we implemented single-cell RNAseq to sample the diversity of progenitors and neurons along the dorso-ventral axis of the early developing pallium. We first identified neuronal types, mapped them on the tissue and determined their origin through genetic tracing. We characterised progenitor diversity and disentangled the gene modules underlying temporal versus spatial regulations of neuronal specification. Finally, we reconstructed the developmental trajectories followed by ventral and dorsal pallial neurons to identify lineage-specific gene waves. Our data suggest a model by which discrete neuronal fate acquisition from a continuous gradient of progenitors results from the superimposition of spatial information and temporal maturation.
Asunto(s)
Corteza Cerebral/metabolismo , Neuronas/metabolismo , Transcriptoma , Animales , Diferenciación Celular/fisiología , Corteza Cerebral/patología , Embrión de Mamíferos , Femenino , Factores de Transcripción Forkhead , Regulación del Desarrollo de la Expresión Génica , Proteínas de Homeodominio/metabolismo , Ratones , Ratones Endogámicos C57BL , Proteínas del Tejido Nervioso , Neurogénesis/fisiología , Proteínas Proto-Oncogénicas/metabolismoRESUMEN
The chromosome translocations generating PAX3-FOXO1 and PAX7-FOXO1 chimeric proteins are the primary hallmarks of the paediatric fusion-positive alveolar subtype of Rhabdomyosarcoma (FP-RMS). Despite the ability of these transcription factors to remodel chromatin landscapes and promote the expression of tumour driver genes, they only inefficiently promote malignant transformation in vivo. The reason for this is unclear. To address this, we developed an in ovo model to follow the response of spinal cord progenitors to PAX-FOXO1s. Our data demonstrate that PAX-FOXO1s, but not wild-type PAX3 or PAX7, trigger the trans-differentiation of neural cells into FP-RMS-like cells with myogenic characteristics. In parallel, PAX-FOXO1s remodel the neural pseudo-stratified epithelium into a cohesive mesenchyme capable of tissue invasion. Surprisingly, expression of PAX-FOXO1s, similar to wild-type PAX3/7, reduce the levels of CDK-CYCLIN activity and increase the fraction of cells in G1. Introduction of CYCLIN D1 or MYCN overcomes this PAX-FOXO1-mediated cell cycle inhibition and promotes tumour growth. Together, our findings reveal a mechanism that can explain the apparent limited oncogenicity of PAX-FOXO1 fusion transcription factors. They are also consistent with certain clinical reports indicative of a neural origin of FP-RMS.
Asunto(s)
Transdiferenciación Celular/genética , Transformación Celular Neoplásica/genética , Proteínas de Fusión Oncogénica/metabolismo , Factores de Transcripción Paired Box/metabolismo , Rabdomiosarcoma Alveolar/genética , Animales , Biopsia , Embrión de Pollo , Niño , Ciclina D1/genética , Conjuntos de Datos como Asunto , Modelos Animales de Enfermedad , Perfilación de la Expresión Génica , Regulación Neoplásica de la Expresión Génica , Humanos , Proteína Proto-Oncogénica N-Myc/genética , Invasividad Neoplásica/genética , Células-Madre Neurales/patología , Tubo Neural/citología , Proteínas de Fusión Oncogénica/genética , Factor de Transcripción PAX3/genética , Factor de Transcripción PAX3/metabolismo , Factor de Transcripción PAX7/genética , Factor de Transcripción PAX7/metabolismo , Factores de Transcripción Paired Box/genética , Rabdomiosarcoma Alveolar/patología , Fase S/genéticaRESUMEN
BACKGROUND: Despite undisputable benefits, midtrimester prenatal surgery is not a cure for myelomeningocele (MMC): residual intracranial and motor deficits leading to lifelong handicap question the timing of prenatal surgery. Indeed, the timing and intensity of intrauterine spinal cord injury remains ill defined. OBJECTIVE: We aimed to describe the natural history of neuronal loss in MMC in utero based on postmortem pathology. STUDY DESIGN: Pathology findings were analyzed in 186 cases of myelomeningocele with lesion level between S1 and T1. Using a case-control, cross-sectional design, we investigated the timewise progression and topographic extension of neuronal loss between 13 and 39 weeks. Motor neurons were counted on histology at several spinal levels in 54 isolated MMC meeting quality criteria for cell counting. These were expressed as observed-to-expected ratios, after matching for gestational age and spinal level with 41 controls. RESULTS: Chiari II malformation increased from 30.7% to 91.6% after 16 weeks. The exposed spinal cord displayed early, severe, and progressive neuronal loss: the observed-to-expected count dropped from 17% to ≤2% after 16 weeks. Neuronal loss extended beyond the lesion to the upper levels: in cases <16 weeks, the observed-to-expected motor neuron count was 60% in the adjacent spinal cord, decreasing at a rate of 16% per week. Progressive loss was also found in the upper thoracic cord, but in much smaller proportions. The observed-over-expected ratio of motor neurons was not correlated with the level of myelomeningocele. CONCLUSIONS: Significant neuronal loss is present ≤16 weeks in the exposed cord and progressively extends cranially. Earlier prenatal repair (<16 weeks) could prevent Chiari II malformation in 69.3% of cases, rescue the 17% remaining motor neurons in the exposed cord, and prevent the extension to the upper spinal cord.
Asunto(s)
Malformación de Arnold-Chiari/patología , Edad Gestacional , Meningomielocele/patología , Neuronas Motoras/patología , Médula Espinal/patología , Aborto Inducido , Malformación de Arnold-Chiari/embriología , Autopsia , Progresión de la Enfermedad , Femenino , Terapias Fetales , Humanos , Vértebras Lumbares , Meningomielocele/embriología , Meningomielocele/cirugía , Procedimientos Neuroquirúrgicos , Embarazo , Primer Trimestre del Embarazo , Segundo Trimestre del Embarazo , Estudios Retrospectivos , Sacro , Vértebras TorácicasRESUMEN
Transcription factors are key orchestrators of the emergence of neuronal diversity within the developing spinal cord. As such, the two paralogous proteins Pax3 and Pax7 regulate the specification of progenitor cells within the intermediate neural tube, by defining a neat segregation between those fated to form motor circuits and those involved in the integration of sensory inputs. To attain insights into the molecular means by which they control this process, we have performed detailed phenotypic analyses of the intermediate spinal interneurons (IN), namely the dI6, V0D, V0VCG and V1 populations in compound null mutants for Pax3 and Pax7. This has revealed that the levels of Pax3/7 proteins determine both the dorso-ventral extent and the number of cells produced in each subpopulation; with increasing levels leading to the dorsalisation of their fate. Furthermore, thanks to the examination of mutants in which Pax3 transcriptional activity is skewed either towards repression or activation, we demonstrate that this cell diversification process is mainly dictated by Pax3/7 ability to repress gene expression. Consistently, we show that Pax3 and Pax7 inhibit the expression of Dbx1 and of its repressor Prdm12, fate determinants of the V0 and V1 interneurons, respectively. Notably, we provide evidence for the activity of several cis-regulatory modules of Dbx1 to be sensitive to Pax3 and Pax7 transcriptional activity levels. Altogether, our study provides insights into how the redundancy within a TF family, together with discrete dynamics of expression profiles of each member, are exploited to generate cellular diversity. Furthermore, our data supports the model whereby cell fate choices in the neural tube do not rely on binary decisions but rather on inhibition of multiple alternative fates.
Asunto(s)
Proteínas de Homeodominio/fisiología , Interneuronas/fisiología , Proteínas del Tejido Nervioso/fisiología , Factor de Transcripción PAX3/fisiología , Factor de Transcripción PAX7/fisiología , Médula Espinal/citología , Animales , Diferenciación Celular/fisiología , Embrión de Pollo , Regulación del Desarrollo de la Expresión Génica , Interneuronas/citología , Ratones , Tubo Neural/fisiología , Médula Espinal/embriología , Células Madre/citología , Células Madre/fisiologíaRESUMEN
Reelin (RELN) is a secreted glycoprotein essential for cerebral cortex development. In humans, recessive RELN variants cause cortical and cerebellar malformations, while heterozygous variants were associated with epilepsy, autism, and mild cortical abnormalities. However, the functional effects of RELN variants remain unknown. We identified inherited and de novo RELN missense variants in heterozygous patients with neuronal migration disorders (NMDs) as diverse as pachygyria and polymicrogyria. We investigated in culture and in the developing mouse cerebral cortex how different variants impacted RELN function. Polymicrogyria-associated variants behaved as gain-of-function, showing an enhanced ability to induce neuronal aggregation, while those linked to pachygyria behaved as loss-of-function, leading to defective neuronal aggregation/migration. The pachygyria-associated de novo heterozygous RELN variants acted as dominant-negative by preventing WT RELN secretion in culture, animal models, and patients, thereby causing dominant NMDs. We demonstrated how mutant RELN proteins in vitro and in vivo predict cortical malformation phenotypes, providing valuable insights into the pathogenesis of such disorders.
Asunto(s)
Moléculas de Adhesión Celular Neuronal , Movimiento Celular , Proteínas de la Matriz Extracelular , Mutación Missense , Proteínas del Tejido Nervioso , Proteína Reelina , Serina Endopeptidasas , Humanos , Animales , Proteínas de la Matriz Extracelular/genética , Proteínas de la Matriz Extracelular/metabolismo , Serina Endopeptidasas/genética , Serina Endopeptidasas/metabolismo , Moléculas de Adhesión Celular Neuronal/genética , Moléculas de Adhesión Celular Neuronal/metabolismo , Proteínas del Tejido Nervioso/genética , Proteínas del Tejido Nervioso/metabolismo , Ratones , Femenino , Masculino , Movimiento Celular/genética , Neuronas/metabolismo , Neuronas/patología , Polimicrogiria/genética , Polimicrogiria/patología , Corteza Cerebral/metabolismo , Corteza Cerebral/patología , Heterocigoto , Lisencefalia/genética , Lisencefalia/patología , AlelosRESUMEN
Patterning of the cortical neuroepithelium occurs at early stages of embryonic development in response to secreted molecules from signaling centers. These signals have been shown to establish the graded expression of transcription factors in progenitors within the ventricular zone and to control the size and positioning of cortical areas. Cajal-Retzius (CR) cells are among the earliest generated cortical neurons and migrate from the borders of the developing pallium to cover the cortical primordium by E11.5. We show that molecularly distinct CR subtypes distribute in specific combinations in pallial territories at the time of cortical regionalization. By means of genetic ablation experiments in mice, we report that loss of septum Dbx1-derived CR cells in the rostromedial pallium between E10.5 and E11.5 results in the redistribution of CR subtypes. This leads to changes in the expression of transcription factors within the neuroepithelium and in the proliferation properties of medial and dorsal cortical progenitors. Early regionalization defects correlate with shifts in the positioning of cortical areas at postnatal stages in the absence of alterations of gene expression at signaling centers. We show that septum-derived CR neurons express a highly specific repertoire of signaling factors. Our results strongly suggest that these cells, migrating over long distances and positioned in the postmitotic compartment, signal to ventricular zone progenitors and, thus, function as modulators of early cortical patterning.
Asunto(s)
Tipificación del Cuerpo , Corteza Cerebral/citología , Corteza Cerebral/embriología , Proteínas de Homeodominio/metabolismo , Células Neuroepiteliales/citología , Células Neuroepiteliales/metabolismo , Animales , Tipificación del Cuerpo/genética , Proliferación Celular , Corteza Cerebral/metabolismo , Citometría de Flujo , Perfilación de la Expresión Génica , Regulación del Desarrollo de la Expresión Génica , Proteínas de Homeodominio/genética , Ratones , Neurogénesis , ARN Mensajero/genética , ARN Mensajero/metabolismo , Tabique del Cerebro/citología , Tabique del Cerebro/embriología , Tabique del Cerebro/metabolismo , Proteínas Wnt/metabolismoRESUMEN
Hindbrain rhombomere 1 (r1) is located caudal to the isthmus, a critical organizer region, and rostral to rhombomere 2 in the developing mouse brain. Dorsal r1 gives rise to the cerebellum, locus coeruleus, and several brainstem nuclei, whereas cells from ventral r1 contribute to the trochlear and trigeminal nuclei as well as serotonergic and GABAergic neurons of the dorsal raphe. Recent studies have identified several molecular events controlling dorsal r1 development. In contrast, very little is known about ventral r1 gene expression and the genetic mechanisms regulating its formation. Neurons with distinct neurotransmitter phenotypes have been identified in ventral r1 including GABAergic, serotonergic, and cholinergic neurons. Here we show that PITX2 marks a distinct population of GABAergic neurons in mouse embryonic ventral r1. This population appears to retain its GABAergic identity even in the absence of PITX2. We provide a comprehensive map of markers that places these PITX2-positive GABAergic neurons in a region of r1 that intersects and is potentially in communication with the dorsal raphe.
Asunto(s)
Neuronas GABAérgicas/metabolismo , Proteínas de Homeodominio/metabolismo , Neuronas/metabolismo , Rombencéfalo/citología , Rombencéfalo/metabolismo , Factores de Transcripción/metabolismo , Animales , Diferenciación Celular/fisiología , Cerebelo/embriología , Cerebelo/metabolismo , Neuronas GABAérgicas/clasificación , Neuronas GABAérgicas/citología , Regulación del Desarrollo de la Expresión Génica , Ratones , Ratones Endogámicos C57BL , Ratones Mutantes , Neuronas/citología , Rombencéfalo/embriología , Proteína del Homeodomínio PITX2RESUMEN
Cajal-Retzius cells (CRs) are a transient neuronal type of the developing cerebral cortex. Over the years, they have been shown or proposed to play important functions in neocortical and hippocampal morphogenesis, circuit formation, brain evolution and human pathology. Because of their short lifespan, CRs have been pictured as a purely developmental cell type, whose production and active elimination are both required for correct brain development. In this review, we present some of the findings that allow us to better appreciate the identity and diversity of this very special cell type, and propose a unified definition of what should be considered a Cajal-Retzius cell, especially when working with non-mammalian species or organoids. In addition, we highlight a flurry of recent studies pointing to the importance of CRs in the assembly of functional and dysfunctional cortical networks.
Asunto(s)
Corteza Cerebral , Neuronas , Humanos , Neuronas/fisiología , Hipocampo/fisiologíaRESUMEN
In vertebrates, the embryonic olfactory epithelium contains progenitors that will give rise to distinct classes of neurons, including olfactory sensory neurons (OSNs; involved in odor detection), vomeronasal sensory neurons (VSNs; responsible for pheromone sensing), and gonadotropin-releasing hormone (GnRH) neurons that control the hypothalamic-pituitary-gonadal axis. Currently, these three neuronal lineages are usually believed to emerge from uniform pools of progenitors. Here, we found that the homeodomain transcription factor Dbx1 is expressed by neurogenic progenitors in the developing and adult mouse olfactory epithelium. We demonstrate that Dbx1 itself is dispensable for neuronal fate specification and global organization of the olfactory sensory system. Using lineage tracing, we characterize the contribution of Dbx1 lineages to OSN, VSN, and GnRH neuron populations and reveal an unexpected degree of diversity. Furthermore, we demonstrate that Dbx1-expressing progenitors remain neurogenic in the absence of the proneural gene Ascl1. Our work therefore points to the existence of distinct neurogenic programs in Dbx1-derived and other olfactory lineages.
Asunto(s)
Mucosa Olfatoria , Neuronas Receptoras Olfatorias , Ratones , Animales , Neuronas Receptoras Olfatorias/metabolismo , Factores de Transcripción/genética , Regulación de la Expresión Génica , Hormona Liberadora de Gonadotropina/metabolismo , Proteínas de Homeodominio/genéticaRESUMEN
Cajal-Retzius cells (CRs) are key players in cerebral cortex development, and they display a unique transcriptomic identity. Here, we use scRNA-seq to reconstruct the differentiation trajectory of mouse hem-derived CRs, and we unravel the transient expression of a complete gene module previously known to control multiciliogenesis. However, CRs do not undergo centriole amplification or multiciliation. Upon deletion of Gmnc, the master regulator of multiciliogenesis, CRs are initially produced but fail to reach their normal identity resulting in their massive apoptosis. We further dissect the contribution of multiciliation effector genes and identify Trp73 as a key determinant. Finally, we use in utero electroporation to demonstrate that the intrinsic competence of hem progenitors as well as the heterochronic expression of Gmnc prevent centriole amplification in the CR lineage. Our work exemplifies how the co-option of a complete gene module, repurposed to control a distinct process, may contribute to the emergence of novel cell identities.
Asunto(s)
Corteza Cerebral , Redes Reguladoras de Genes , Ratones , Animales , Corteza Cerebral/metabolismo , Neuronas/metabolismo , Diferenciación Celular/fisiología , Neurogénesis/genéticaRESUMEN
Multiciliated ependymal cells and adult neural stem cells are components of the adult neurogenic niche, essential for brain homeostasis. These cells share a common glial cell lineage regulated by the Geminin family members Geminin and GemC1/Mcidas. Ependymal precursors require GemC1/Mcidas expression to massively amplify centrioles and become multiciliated cells. Here, we show that GemC1-dependent differentiation is initiated in actively cycling radial glial cells, in which a DNA damage response, including DNA replication-associated damage and dysfunctional telomeres, is induced, without affecting cell survival. Genotoxic stress is not sufficient by itself to induce ependymal cell differentiation, although the absence of p53 or p21 in progenitors hinders differentiation by maintaining cell division. Activation of the p53-p21 pathway downstream of GemC1 leads to cell-cycle slowdown/arrest, which permits timely onset of ependymal cell differentiation in progenitor cells.
Asunto(s)
Células-Madre Neurales , Proteína p53 Supresora de Tumor , Geminina/genética , Geminina/metabolismo , Proteína p53 Supresora de Tumor/metabolismo , Epéndimo/metabolismo , Células Ependimogliales/metabolismo , Células-Madre Neurales/metabolismo , Diferenciación CelularRESUMEN
The normal formation and function of the mammalian cerebral cortex depend on the positioning of its neurones, which occurs in a highly organized, layer-specific manner. The correct morphology and movement of neurones rely on synchronized regulation of their actin filaments and microtubules. The p21-activated kinase (Pak1), a key cytoskeletal regulator, controls neuronal polarization, elaboration of axons and dendrites, and the formation of dendritic spines. However, its in vivo role in the developing nervous system is unclear. We have utilized in utero electroporation into mouse embryo cortices to reveal that both loss and gain of Pak1 function affect radial migration of projection neurones. Overexpression of hyperactivated Pak1 predominantly caused neurones to arrest in the intermediate zone (IZ) with apparently misoriented and disorganized leading projections. Loss of Pak1 disrupted the morphology of migrating neurones, which accumulated in the IZ and deep cortical layers. Unexpectedly, a significant number of neurones with reduced Pak1 expression aberrantly entered into the normally cell-sparse marginal zone, suggesting their inability to cease migrating that may be due to their impaired dissociation from radial glia. Our findings reveal the in vivo importance of temporal and spatial regulation of the Pak1 kinase during key stages of cortical development.
Asunto(s)
Movimiento Celular/fisiología , Corteza Cerebral/enzimología , Neuronas/enzimología , Quinasas p21 Activadas/fisiología , Animales , Células COS , Diferenciación Celular/fisiología , Corteza Cerebral/citología , Corteza Cerebral/embriología , Chlorocebus aethiops , Proteínas de la Membrana/antagonistas & inhibidores , Proteínas de la Membrana/biosíntesis , Proteínas de la Membrana/fisiología , Ratones , Neurogénesis/fisiología , Neuronas/citología , Neuronas/metabolismo , Ratas , Quinasas p21 Activadas/antagonistas & inhibidores , Quinasas p21 Activadas/biosíntesisRESUMEN
Netrin-1 was previously shown to be required for the tangential migration and survival of neurons that will form the inferior olivary nucleus (ION). Surprisingly, the compared analysis of mutant mice lacking either Netrin-1 or its major receptor DCC reveals striking phenotypic differences besides common features. Although ectopic stops of ION cell bodies occur in the same positions along the migratory stream in both mutants, the ION neurons' number is not affected by the lack of DCC whereas it is reduced in Netrin-1 mutant mice. Thus, cell death results from the absence of Netrin-1 and not from neuron mis-routing, arguing for a role of Netrin-1 as a survival factor in vivo. The secretion of Netrin-1 by the floor plate (FP) is strictly required - whereas DCC is not - to avoid ION axons' repulsion by the FP and allows them to cross it. Leading processes of neurons of other caudal precerebellar nuclei (PCN) cannot cross the FP in either mutant mouse, suggesting differential sensitivity or mechanism of action of Netrin-1 for leading processes of ION and other PCN neurons.
Asunto(s)
Movimiento Celular/fisiología , Factores de Crecimiento Nervioso/metabolismo , Neuronas/fisiología , Núcleo Olivar/citología , Núcleo Olivar/embriología , Receptores de Superficie Celular/metabolismo , Proteínas Supresoras de Tumor/metabolismo , Animales , Axones/fisiología , Receptor DCC , Embrión de Mamíferos , Regulación del Desarrollo de la Expresión Génica/genética , Ratones , Ratones Transgénicos , Mutación/fisiología , Factores de Crecimiento Nervioso/genética , Proteínas del Tejido Nervioso/metabolismo , Netrina-1 , Vías Nerviosas/embriología , Vías Nerviosas/fisiología , Neurogénesis/genética , Neuronas/citología , Técnicas de Cultivo de Órganos , Receptores de Superficie Celular/genética , Proteínas Supresoras de Tumor/genéticaRESUMEN
The correct morphology and migration of neurons, which is essential for the normal development of the nervous system, is enabled by the regulation of their cytoskeletal elements. We reveal that Neurabin-I, a neuronal-specific F-actin-binding protein, has an essential function in the developing forebrain. We show that gain and loss of Neurabin-I expression affect neuronal morphology, neurite outgrowth, and radial migration of differentiating cortical and hippocampal neurons, suggesting that tight regulation of Neurabin-I function is required for normal forebrain development. Importantly, loss of Neurabin-I prevents pyramidal neurons from migrating into the cerebral cortex, indicating its essential role during early stages of corticogenesis. We demonstrate that in neurons Rac1 activation is affected by the expression levels of Neurabin-I. Furthermore, the Cdk5 kinase, a key regulator of neuronal migration and morphology, directly phosphorylates Neurabin-I and controls its association with F-actin. Mutation of the Cdk5 phosphorylation site reduces the phenotypic consequences of Neurabin-I overexpression both in vitro and in vivo, suggesting that Neurabin-I function depends, at least in part, on its phosphorylation status. Together our findings provide new insight into the signaling pathways responsible for controlled changes of the F-actin cytoskeleton that are required for normal development of the forebrain.
Asunto(s)
Movimiento Celular , Chlorocebus aethiops/metabolismo , Quinasa 5 Dependiente de la Ciclina/metabolismo , Proteínas de Microfilamentos/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Neuronas/citología , Neuronas/metabolismo , Actinas/metabolismo , Animales , Encéfalo/embriología , Encéfalo/metabolismo , Forma de la Célula , Células Cultivadas , Regulación hacia Abajo , Regulación del Desarrollo de la Expresión Génica , Proteínas de Microfilamentos/genética , Proteínas del Tejido Nervioso/genética , Fosforilación , Unión Proteica , Ratas , Ratas Sprague-Dawley , Transducción de Señal , Proteína de Unión al GTP rac1/metabolismoAsunto(s)
Redes Reguladoras de Genes , Neuronas , Humanos , Neuronas/fisiología , Hipocampo/fisiología , Corteza CerebralRESUMEN
In multicellular organisms, cell death pathways allow the removal of abnormal or unwanted cells. Their dysregulation can lead either to excessive elimination or to inappropriate cell survival. Evolutionary constraints ensure that such pathways are strictly regulated in order to restrain their activation to the appropriate context. We have previously shown that the transmembrane receptor Kremen1 behaves as a dependence receptor, triggering cell death unless bound to its ligand Dickkopf1. In this study, we reveal that Kremen1 apoptotic signaling requires homodimerization of the receptor. Dickkopf1 binding inhibits Kremen1 multimerization and alleviates cell death, whereas forced dimerization increases apoptotic signaling. Furthermore, we show that Kremen2, a paralog of Kremen1, which bears no intrinsic apoptotic activity, binds and competes with Kremen1. Consequently, Kremen2 is a very potent inhibitor of Kremen1-induced cell death. Kremen1 was proposed to act as a tumor suppressor, preventing cancer cell survival in a ligand-poor environment. We found that KREMEN2 expression is increased in a large majority of cancers, suggesting it may confer increased survival capacity. Consistently, low KREMEN2 expression is a good prognostic for patient survival in a variety of cancers.
RESUMEN
In the developing forebrain, neuronal polarization is a stepwise and initially reversible process that underlies correct migration and axon specification. Many aspects of cytoskeletal changes that accompany polarization are currently molecularly undefined and thus poorly understood. Here we reveal that the p21-activated kinase (Pak1) is essential for the specification of an axon and dendrites. In hippocampal neurons, activation of Pak1 is spatially restricted to the immature axon despite its uniform presence in all neurites. Hyperactivation of Pak1 at the membrane of all neurites or loss of Pak1 expression disrupts both neuronal morphology and the distinction between an axon and dendrites. We reveal that Pak1 acts on polarity in a kinase-dependent manner, by affecting the F-actin and microtubule cytoskeleton at least in part through Rac1 and cofilin. Our data are the first to demonstrate the importance of localized Pak1 kinase activation for neuronal polarization and differentiation.
Asunto(s)
Polaridad Celular/fisiología , Neuronas/citología , Neuronas/enzimología , Proteínas Serina-Treonina Quinasas/metabolismo , Actinas/metabolismo , Animales , Encéfalo/citología , Encéfalo/embriología , Encéfalo/enzimología , Química Encefálica/fisiología , Células Cultivadas , Citoesqueleto/química , Citoesqueleto/genética , Citoesqueleto/metabolismo , Activación Enzimática/fisiología , Neuronas/química , Proteínas Serina-Treonina Quinasas/genética , Proteínas Serina-Treonina Quinasas/fisiología , Ratas , Quinasas p21 Activadas , Proteína de Unión al GTP rac1/metabolismo , Proteína de Unión al GTP rac1/fisiologíaRESUMEN
The mature cerebral cortex only contains a fraction of the cells that are generated during embryonic development. Indeed some neuronal populations are produced in excess and later subjected to partial elimination whereas others are almost completely removed during the first two postnatal weeks in mice. Although the identity of cells that disappear, the time course and mechanisms of their death are becoming reasonably well established, the meaning of producing supernumerary cells still remains elusive. In this review, we focus on recent data that shed a new light on the mechanisms involved in adjusting cell numbers and discuss the significance of refinement versus complete elimination of cell populations in the developing cortex.
Asunto(s)
Muerte Celular/fisiología , Corteza Cerebral/crecimiento & desarrollo , Desarrollo Embrionario/fisiología , Neuronas/fisiología , Animales , Corteza Cerebral/citología , Humanos , Neuronas/citologíaRESUMEN
BACKGROUND: Dbx1 is a homeodomain transcription factor involved in neuronal fate specification belonging to a widely conserved family among bilaterians. In mammals, Dbx1 was proposed to act as a transcriptional repressor by interacting with the Groucho corepressors to allow the specification of neurons involved in essential biological functions such as locomotion or breathing. RESULTS: Sequence alignments of Dbx1 proteins from different species allowed us to identify two conserved domains related to the Groucho-dependent Engrailed repressor domain (RD), as well as a newly described domain composed of clusterized acidic residues at the C-terminus (Cter) which is present in tetrapods but also several invertebrates. Using a heterologous luciferase assay, we showed that the two putative repressor domains behave as such in a Groucho-dependent manner, whereas the Cter does not bear any intrinsic transcriptional activity. Consistently with in vitro data, we found that both RDs are involved in cell fate specification using in vivo electroporation experiments in the chick spinal cord. Surprisingly, we show that the Cter domain is required for Dbx1 function in vivo, acting as a modulator of its repressive activity and/or imparting specificity. CONCLUSION: Our results strongly suggest that the presence of a Cter domain among tetrapods is essential for Dbx1 to regulate neuronal diversity and, in turn, nervous system complexity.