RESUMO
The extracellular protein Reelin, expressed by Cajal-Retzius (CR) cells at early stages of cortical development and at late stages by GABAergic interneurons, regulates radial migration and the "inside-out" pattern of positioning. Current models of Reelin functions in corticogenesis focus on early CR cell-derived Reelin in layer I. However, developmental disorders linked to Reelin deficits, such as schizophrenia and autism, are related to GABAergic interneuron-derived Reelin, although its role in migration has not been established. Here we selectively inactivated the Reln gene in CR cells or GABAergic interneurons. We show that CR cells have a major role in the inside-out order of migration, while CR and GABAergic cells sequentially cooperate to prevent invasion of cortical neurons into layer I. Furthermore, GABAergic cell-derived Reelin compensates some features of the reeler phenotype and is needed for the fine tuning of the layer-specific distribution of cortical neurons. In the hippocampus, the inactivation of Reelin in CR cells causes dramatic alterations in the dentate gyrus and mild defects in the hippocampus proper. These findings lead to a model in which both CR and GABAergic cell-derived Reelin cooperate to build the inside-out order of corticogenesis, which might provide a better understanding of the mechanisms involved in the pathogenesis of neuropsychiatric disorders linked to abnormal migration and Reelin deficits.
Assuntos
Córtex Cerebral , Proteínas do Tecido Nervoso , Neurônios , Proteína Reelina , Animais , Movimento Celular , Córtex Cerebral/citologia , Córtex Cerebral/embriologia , Neurônios GABAérgicos/enzimologia , Hipocampo/embriologia , Hipocampo/enzimologia , Interneurônios/enzimologia , Camundongos , Proteínas do Tecido Nervoso/genética , Proteínas do Tecido Nervoso/metabolismo , Neurônios/citologia , Neurônios/enzimologia , Proteína Reelina/genética , Proteína Reelina/metabolismoRESUMO
Axonal growth and guidance rely on correct growth cone responses to guidance cues. Unlike the signaling cascades that link axonal growth to cytoskeletal dynamics, little is known about the crosstalk mechanisms between guidance and membrane dynamics and turnover. Recent studies indicate that whereas axonal attraction requires exocytosis, chemorepulsion relies on endocytosis. Indeed, our own studies have shown that Netrin-1/Deleted in Colorectal Cancer (DCC) signaling triggers exocytosis through the SNARE Syntaxin-1 (STX1). However, limited in vivo evidence is available about the role of SNARE proteins in axonal guidance. To address this issue, here we systematically deleted SNARE genes in three species. We show that loss-of-function of STX1 results in pre- and post-commissural axonal guidance defects in the midline of fly, chick, and mouse embryos. Inactivation of VAMP2, Ti-VAMP, and SNAP25 led to additional abnormalities in axonal guidance. We also confirmed that STX1 loss-of-function results in reduced sensitivity of commissural axons to Slit-2 and Netrin-1. Finally, genetic interaction studies in Drosophila show that STX1 interacts with both the Netrin-1/DCC and Robo/Slit pathways. Our data provide evidence of an evolutionarily conserved role of STX1 and SNARE proteins in midline axonal guidance in vivo, by regulating both pre- and post-commissural guidance mechanisms.
Assuntos
Neurogênese/genética , Sintaxina 1/genética , Sintaxina 1/fisiologia , Animais , Axônios/metabolismo , Quimiotaxia/genética , Embrião de Galinha , Drosophila/genética , Proteínas de Drosophila/genética , Exocitose/genética , Regulação da Expressão Gênica no Desenvolvimento/genética , Glicoproteínas/genética , Glicoproteínas/metabolismo , Camundongos , Camundongos Knockout , Fatores de Crescimento Neural/genética , Proteínas do Tecido Nervoso/genética , Proteínas do Tecido Nervoso/metabolismo , Sistema Nervoso/embriologia , Netrina-1/genética , Netrina-1/metabolismo , Neurogênese/fisiologia , Proteínas Qa-SNARE/genética , Proteínas Qa-SNARE/fisiologia , Proteínas SNARE/genética , Proteínas SNARE/metabolismo , Transdução de Sinais/genética , Medula Espinal/embriologia , Medula Espinal/metabolismoRESUMO
Aging is the major risk factor for most human diseases and represents a major socio-economical challenge for modern societies. Despite its importance, the process of aging remains poorly understood. Epigenetic dysregulation has been proposed as a key driver of the aging process. Modifications in transcriptional networks and chromatin structure might be central to age-related functional decline. A prevalent feature described during aging is the overall reduction in heterochromatin, specifically marked by the loss of repressive histone modification, Histone 3 lysine 9 trimethylation (H3K9me3). However, the role of H3K9me3 in aging, especially in mammals, remains unclear. Here we show using a novel mouse strain, (TKOc), carrying a triple knockout of three methyltransferases responsible for H3K9me3 deposition, that the inducible loss of H3K9me3 in adulthood results in premature aging. TKOc mice exhibit reduced lifespan, lower body weight, increased frailty index, multi-organ degeneration, transcriptional changes with significant upregulation of transposable elements, and accelerated epigenetic age. Our data strongly supports the concept that the loss of epigenetic information directly drives the aging process. These findings reveal the importance of epigenetic regulation in aging and suggest that interventions targeting epigenetic modifications could potentially slow down or reverse age-related decline. Understanding the molecular mechanisms underlying the process of aging will be crucial for developing novel therapeutic strategies that can delay the onset of age-associated diseases and preserve human health at old age specially in rapidly aging societies.
RESUMO
In addition to neuronal migration, brain development, and adult plasticity, the extracellular matrix protein Reelin has been extensively implicated in human psychiatric disorders such as schizophrenia, bipolar disorder, and autism spectrum disorder. Moreover, heterozygous reeler mice exhibit features reminiscent of these disorders, while overexpression of Reelin protects against its manifestation. However, how Reelin influences the structure and circuits of the striatal complex, a key region for the above-mentioned disorders, is far from being understood, especially when altered Reelin expression levels are found at adult stages. In the present study, we took advantage of complementary conditional gain- and loss-of-function mouse models to investigate how Reelin levels may modify adult brain striatal structure and neuronal composition. Using immunohistochemical techniques, we determined that Reelin does not seem to influence the striatal patch and matrix organization (studied by µ-opioid receptor immunohistochemistry) nor the density of medium spiny neurons (MSNs, studied with DARPP-32). We show that overexpression of Reelin leads to increased numbers of striatal parvalbumin- and cholinergic-interneurons, and to a slight increase in tyrosine hydroxylase-positive projections. We conclude that increased Reelin levels might modulate the numbers of striatal interneurons and the density of the nigrostriatal dopaminergic projections, suggesting that these changes may be involved in the protection of Reelin against neuropsychiatric disorders.
RESUMO
The induction of cellular reprogramming via expression of the transcription factors Oct4, Sox2, Klf4 and c-Myc (OSKM) can drive dedifferentiation of somatic cells and ameliorate age-associated phenotypes in multiple tissues and organs. However, the benefits of long-term in vivo reprogramming are limited by detrimental side-effects. Here, using complementary genetic approaches, we demonstrated that continuous induction of the reprogramming factors in vivo leads to hepatic and intestinal dysfunction resulting in decreased body weight and contributing to premature death (within 1 week). By generating a transgenic reprogrammable mouse strain, avoiding OSKM expression in both liver and intestine, we reduced the early lethality and adverse effects associated with in vivo reprogramming and induced a decrease in organismal biological age. This reprogramming mouse strain, which allows longer-term continuous induction of OSKM with attenuated toxicity, can help better understand rejuvenation, regeneration and toxicity during in vivo reprogramming.
Assuntos
Insuficiência Intestinal , Camundongos , Animais , Mortalidade Prematura , Reprogramação Celular/genética , Fatores de Transcrição/genética , Camundongos Transgênicos , Fígado/metabolismoRESUMO
INTRODUCTION: The prion protein (PrP) binds to various molecular partners, but little is known about their potential impact on the pathogenesis of prion diseases RESULTS: Here, we show that PrP can interact in vitro with acetylcholinesterase (AChE), a key protein of the cholinergic system in neural and non-neural tissues. This heterologous association induced aggregation of monomeric PrP and modified the structural properties of PrP amyloid fibrils. Following its recruitment into PrP fibrils, AChE loses its enzymatic activity and enhances PrP-mediated cytotoxicity. Using several truncated PrP variants and specific tight-binding AChE inhibitors (AChEis), we then demonstrate that the PrP-AChE interaction requires two mutually exclusive sub-sites in PrP N-terminal domain and an aromatic-rich region at the entrance of AChE active center gorge. We show that AChEis that target this site impair PrP-AChE complex formation and also limit the accumulation of pathological prion protein (PrPSc) in prion-infected cell cultures. Furthermore, reduction of AChE levels in prion-infected heterozygous AChE knock-out mice leads to slightly but significantly prolonged incubation time. Finally, we found that AChE levels were altered in prion-infected cells and tissues, suggesting that AChE might be directly associated with abnormal PrP. CONCLUSION: Our results indicate that AChE deserves consideration as a new actor in expanding pathologically relevant PrP morphotypes and as a therapeutic target.