Growth of the developing cerebral cortex is controlled by microRNA-7 through the p53 pathway

Micromanaging the neuroendocrine system - A review on miR-7 and the other physiologically relevant miRNAs in the hypothalamic-pituitary axis

The hypothalamic-pituitary axis is central to the functioning of the neuroendocrine system and essential for regulating physiological and behavioral homeostasis and coordinating fundamental body functions. The expanding line of evidence shows the indispensable role of the microRNA pathway in regulating the gene expression profile in the developing and adult hypothalamus and pituitary gland. Experiments provoking a depletion of miRNA maturation in the context of the hypothalamic-pituitary axis brought into focus a prominent involvement of miRNAs in neuroendocrine functions. There are also a few individual miRNAs and miRNA families that have been studied in depth revealing their crucial role in mediating the regulation of fundamental processes such as temporal precision of puberty timing, hormone production, fertility and reproduction capacity, and energy balance. Among these miRNAs, miR-7 was shown to be hypothalamus-enriched and the top one highly expressed in the pituitary gland, where it has a profound impact on gene expression regulation. Here, we review miRNA profiles, knockout phenotypes, and miRNA interaction (targets) in the hypothalamic-pituitary axis that advance our understanding of the roles of miRNAs in mammalian neurosecretion and related physiology.

Chronic Lead Exposure in Adult Mice: Associations with miR-671/CDR1as Regulation, NF-κB Signaling, and Alzheimer's Disease-like Pathology

Long-term exposure to lead (Pb) can result in chronic damage to the body through accumulation in the central nervous system (CNS) leading to neurodegenerative diseases, such as Alzheimer's disease (AD). This study delves into the intricate role of miR-671/CDR1as regulation in the etiology of AD-like lesions triggered by chronic Pb exposure in adult mice. To emulate the chronic effects of Pb, we established a rodent model spanning 10 months of controlled Pb administration, dividing 52 C57BL/6J mice into groups receiving varying concentrations of Pb (1, 2, or 4 g/L) alongside an unexposed control. Blood Pb levels were monitored using serum samples to ensure accurate dosing and to correlate with observed toxicological outcomes. Utilizing the Morris water maze, a robust behavioral assay for assessing cognitive functions, we documented a dose-dependent decline in learning and memory capabilities among the Pb-exposed mice. Histopathological examination of the hippocampal tissue revealed tell-tale signs of AD-like neurodegeneration, characterized by the accumulation of amyloid plaques and neurofibrillary tangles. At the molecular level, a significant upregulation of AD-associated genes, namely amyloid precursor protein (APP), β-secretase 1 (BACE1), and tau, was observed in the hippocampal tissue of Pb-exposed mice. This was accompanied by a corresponding surge in the protein levels of APP, BACE1, amyloid-β (Aβ), and phosphorylated tau (p-tau), further implicating Pb in the dysregulation of these key AD markers. The expression of CDR1as, a long non-coding RNA implicated in AD pathogenesis, was found to be suppressed in Pb-exposed mice. This observation suggests a potential mechanistic link between Pb-induced neurotoxicity and the dysregulation of the CDR1as/miR-671 axis, which warrants further investigation. Moreover, our study identified a dose-dependent alteration in the intracellular and extracellular levels of the transcription factor nuclear factor-kappa B (NF-κB). This finding implicates Pb in the modulation of NF-κB signaling, a pathway that plays a pivotal role in neuroinflammation and neurodegeneration. In conclusion, our findings underscored the deleterious effects of Pb exposure on the CNS, leading to the development of AD-like pathology. The observed modulation of NF-κB signaling and miR-671/CDR1as regulation provides a plausible mechanistic framework for understanding the neurotoxic effects of Pb and its potential contribution to AD pathogenesis.

miR-7 controls glutamatergic transmission and neuronal connectivity in a Cdr1as-dependent manner

The circular RNA (circRNA) Cdr1as is conserved across mammals and highly expressed in neurons, where it directly interacts with microRNA miR-7. However, the biological function of this interaction is unknown. Here, using primary cortical murine neurons, we demonstrate that stimulating neurons by sustained depolarization rapidly induces two-fold transcriptional upregulation of Cdr1as and strong post-transcriptional stabilization of miR-7. Cdr1as loss causes doubling of glutamate release from stimulated synapses and increased frequency and duration of local neuronal bursts. Moreover, the periodicity of neuronal networks increases, and synchronicity is impaired. Strikingly, these effects are reverted by sustained expression of miR-7, which also clears Cdr1as molecules from neuronal projections. Consistently, without Cdr1as, transcriptomic changes caused by miR-7 overexpression are stronger (including miR-7-targets downregulation) and enriched in secretion/synaptic plasticity pathways. Altogether, our results suggest that in cortical neurons Cdr1as buffers miR-7 activity to control glutamatergic excitatory transmission and neuronal connectivity important for long-lasting synaptic adaptations.

Evaluation of histological and ultrastructural changes provoked by prenatal tramadol on postnatal cortical cerebellar neuronal development in rats: possible implication of Ki67, GFAP and MicroRNA-7/P53 signalling trajectories

Tramadol is a novel centrally acting analgesic. Despite, its implementation during pregnancy may impair neuronal survival and synaptic development in neonatal cerebella. The current investigation assessed the histological and ultrastructural alterations in postnatal cortical cerebellar neuronal development induced by prenatal tramadol. 30 offsprings were divided to control group I: fifteen pups born to mothers given saline from D10 till D21 of gestation. Tramadol-treated group II: fifteen pups born to mothers received tramadol HCL (50 mg/kg/day) from D10 till D21 of gestation. Pups were categorized into three subgroups (a, b, and c) and offered for sacrifice on the seventh, fourteenth and twenty-first post-natal days. Light microscopic examination revealed the overcrowding and signs of red degeneration affecting purkinje cell layer. Neurodegenerative signs of both purkinje and granule cell neurons were also confirmed by TEM in form of chromatin condensation, dilated Golgi channels, disrupted endoplasmic reticulum, marked infolding of the nuclear envelope and decrease in granule cell precursors. In addition, the astrocytic processes and terminal nerve axons appeared with different degrees of demyelination and decreased number of oligodendrocytes and degenerated mitochondria. Furthermore, group II exhibited an increase in P53 immune expression. The area percentage of apoptotic cells detected by TUNEL assay was significantly increased. Besides to the significant decrease of Ki67 immunoreactivity in the stem neuronal cell progenitors. Quantitative PCR results showed a significant decline in micro RNA7 gene expression in tramadol treated groups resulting in affection of multiple target genes in P53 signaling pathways, improper cortical size and defect in neuronal development.

Genetic variants for head size share genes and pathways with cancer

The size of the human head is highly heritable, but genetic drivers of its variation within the general population remain unmapped. We perform a genome-wide association study on head size (N = 80,890) and identify 67 genetic loci, of which 50 are novel. Neuroimaging studies show that 17 variants affect specific brain areas, but most have widespread effects. Gene set enrichment is observed for various cancers and the p53, Wnt, and ErbB signaling pathways. Genes harboring lead variants are enriched for macrocephaly syndrome genes (37-fold) and high-fidelity cancer genes (9-fold), which is not seen for human height variants. Head size variants are also near genes preferentially expressed in intermediate progenitor cells, neural cells linked to evolutionary brain expansion. Our results indicate that genes regulating early brain and cranial growth incline to neoplasia later in life, irrespective of height. This warrants investigation of clinical implications of the link between head size and cancer.

Use of microRNAs as Diagnostic, Prognostic, and Therapeutic Tools for Glioblastoma

Glioblastoma (GB) is the most aggressive and common type of cancer within the central nervous system (CNS). Despite the vast knowledge of its physiopathology and histology, its etiology at the molecular level has not been completely understood. Thus, attaining a cure has not been possible yet and it remains one of the deadliest types of cancer. Usually, GB is diagnosed when some symptoms have already been presented by the patient. This diagnosis is commonly based on a physical exam and imaging studies, such as computed tomography (CT) and magnetic resonance imaging (MRI), together with or followed by a surgical biopsy. As these diagnostic procedures are very invasive and often result only in the confirmation of GB presence, it is necessary to develop less invasive diagnostic and prognostic tools that lead to earlier treatment to increase GB patients' quality of life. Therefore, blood-based biomarkers (BBBs) represent excellent candidates in this context. microRNAs (miRNAs) are small, non-coding RNAs that have been demonstrated to be very stable in almost all body fluids, including saliva, serum, plasma, urine, cerebrospinal fluid (CFS), semen, and breast milk. In addition, serum-circulating and exosome-contained miRNAs have been successfully used to better classify subtypes of cancer at the molecular level and make better choices regarding the best treatment for specific cases. Moreover, as miRNAs regulate multiple target genes and can also act as tumor suppressors and oncogenes, they are involved in the appearance, progression, and even chemoresistance of most tumors. Thus, in this review, we discuss how dysregulated miRNAs in GB can be used as early diagnosis and prognosis biomarkers as well as molecular markers to subclassify GB cases and provide more personalized treatments, which may have a better response against GB. In addition, we discuss the therapeutic potential of miRNAs, the current challenges to their clinical application, and future directions in the field.

MicroRNA‑124: an emerging therapeutic target in central nervous system disorders

The central nervous system (CNS) consists of neuron and non-neuron cells including neural stem/precursor cells (NSPCs), neuroblasts, glia cells (mainly astrocyte, oligodendroglia and microglia), which thereby form a precise and complicated network and exert diverse functions through interactions of numerous bioactive ingredients. MicroRNAs (miRNAs), with small size approximately  ~ 21nt and as well-documented post-transcriptional key regulators of gene expression, are a cluster of evolutionarily conserved endogenous non-coding RNAs. More than 2000 different miRNAs has been discovered till now. MicroRNA-124(miR-124), the most brain-rich microRNA, has been validated to possess important functions in the central nervous system, including neural stem cell proliferation and differentiation, cell fate determination, neuron migration, synapse plasticity and cognition, cell apoptosis etc. According to recent studies, herein, we provide a review of this conversant miR-124 to further understand the potential functions and therapeutic and clinical value in brain diseases.

Translational control in cortical development

Differentiation of specific neuronal types in the nervous system is worked out through a complex series of gene regulation events. Within the mammalian neocortex, the appropriate expression of key transcription factors allocates neurons to different cortical layers according to an inside-out model and endows them with specific properties. Precise timing is required to ensure the proper sequential appearance of key transcription factors that dictate the identity of neurons within the different cortical layers. Recent evidence suggests that aspects of this time-controlled regulation of gene products rely on post-transcriptional control, and point at micro-RNAs (miRs) and RNA-binding proteins as important players in cortical development. Being able to simultaneously target many different mRNAs, these players may be involved in controlling the global expression of gene products in progenitors and post-mitotic cells, in a gene expression framework where parallel to transcriptional gene regulation, a further level of control is provided to refine and coordinate the appearance of the final protein products. miRs and RNA-binding proteins (RBPs), by delaying protein appearance, may play heterochronic effects that have recently been shown to be relevant for the full differentiation of cortical neurons and for their projection abilities. Such heterochronies may be the base for evolutionary novelties that have enriched the spectrum of cortical cell types within the mammalian clade.

MicroRNA-7 regulates melanocortin circuits involved in mammalian energy homeostasis

MicroRNAs (miRNAs) modulate physiological responses by repressing the expression of gene networks. We found that global deletion of microRNA-7 (miR-7), the most enriched miRNA in the hypothalamus, causes obesity in mice. Targeted deletion of miR-7 in Single-minded homolog 1 (Sim1) neurons, a critical component of the hypothalamic melanocortin pathway, causes hyperphagia, obesity and increased linear growth, mirroring Sim1 and Melanocortin-4 receptor (MC4R) haplo-insufficiency in mice and humans. We identified Snca (α-Synuclein) and Igsf8 (Immunoglobulin Superfamily Member 8) as miR-7 target genes that act in Sim1 neurons to regulate body weight and endocrine axes. In humans, MIR-7-1 is located in the last intron of HNRNPK, whose promoter drives the expression of both genes. Genetic variants at the HNRNPK locus that reduce its expression are associated with increased height and truncal fat mass. These findings demonstrate that miR-7 suppresses gene networks involved in the hypothalamic melanocortin pathway to regulate mammalian energy homeostasis.

miR-409-3p represses Cited2 to refine neocortical layer V projection neuron identity

The evolutionary emergence of the corticospinal tract and corpus callosum are thought to underpin the expansion of complex motor and cognitive abilities in mammals. Molecular mechanisms regulating development of the neurons whose axons comprise these tracts, the corticospinal and callosal projection neurons, remain incompletely understood. Our previous work identified a genomic cluster of microRNAs (miRNAs), Mirg/12qF1, that is unique to placental mammals and specifically expressed by corticospinal neurons, and excluded from callosal projection neurons, during development. We found that one of these, miR-409-3p, can convert layer V callosal into corticospinal projection neurons, acting in part through repression of the transcriptional regulator Lmo4. Here we show that miR-409-3p also directly represses the transcriptional co-regulator Cited2, which is highly expressed by callosal projection neurons from the earliest stages of neurogenesis. Cited2 is highly expressed by intermediate progenitor cells (IPCs) in the embryonic neocortex while Mirg, which encodes miR-409-3p, is excluded from these progenitors. miR-409-3p gain-of-function (GOF) in IPCs results in a phenocopy of established Cited2 loss-of-function (LOF). At later developmental stages, both miR-409-3p GOF and Cited2 LOF promote the expression of corticospinal at the expense of callosal projection neuron markers in layer V. Taken together, this work identifies previously undescribed roles for miR-409-3p in controlling IPC numbers and for Cited2 in controlling callosal fate. Thus, miR-409-3p, possibly in cooperation with other Mirg/12qF1 miRNAs, represses Cited2 as part of the multifaceted regulation of the refinement of neuronal cell fate within layer V, combining molecular regulation at multiple levels in both progenitors and post-mitotic neurons.

Evolution of genetic mechanisms regulating cortical neurogenesis

The size of the cerebral cortex increases dramatically across amniotes, from reptiles to great apes. This is primarily due to different numbers of neurons and glial cells produced during embryonic development. The evolutionary expansion of cortical neurogenesis was linked to changes in neural stem and progenitor cells, which acquired increased capacity of self‐amplification and neuron production. Evolution works via changes in the genome, and recent studies have identified a small number of new genes that emerged in the recent human and primate lineages, promoting cortical progenitor proliferation and increased neurogenesis. However, most of the mammalian genome corresponds to noncoding DNA that contains gene‐regulatory elements, and recent evidence precisely points at changes in expression levels of conserved genes as key in the evolution of cortical neurogenesis. Here, we provide an overview of basic cellular mechanisms involved in cortical neurogenesis across amniotes, and discuss recent progress on genetic mechanisms that may have changed during evolution, including gene expression regulation, leading to the expansion of the cerebral cortex.

Evolving features of human cortical development and the emerging roles of non-coding RNAs in neural progenitor cell diversity and function

The human cerebral cortex is a uniquely complex structure encompassing an unparalleled diversity of neuronal types and subtypes. These arise during development through a series of evolutionary conserved processes, such as progenitor cell proliferation, migration and differentiation, incorporating human-associated adaptations including a protracted neurogenesis and the emergence of novel highly heterogeneous progenitor populations. Disentangling the unique features of human cortical development involves elucidation of the intricate developmental cell transitions orchestrated by progressive molecular events. Crucially, developmental timing controls the fine balance between cell cycle progression/exit and the neurogenic competence of precursor cells, which undergo morphological transitions coupled to transcriptome-defined temporal states. Recent advances in bulk and single-cell transcriptomic technologies suggest that alongside protein-coding genes, non-coding RNAs exert important regulatory roles in these processes. Interestingly, a considerable number of novel long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) have appeared in human and non-human primates suggesting an evolutionary role in shaping cortical development. Here, we present an overview of human cortical development and highlight the marked diversification and complexity of human neuronal progenitors. We further discuss how lncRNAs and miRNAs constitute critical components of the extended epigenetic regulatory network defining intermediate states of progenitors and controlling cell cycle dynamics and fate choices with spatiotemporal precision, during human neurodevelopment.

Role of circRNA-miRNA-mRNA interaction network in diabetes and its associated complications

The majority of the non-protein-coding RNAs are being identified with diversified functions that participate in cellular homeostasis. The circular RNAs (circRNAs) are emerging as noncoding transcripts with a key role in the initiation and development of many physiological and pathological conditions. The advancements in high-throughput RNA sequencing and bioinformatics tools help us to identify several circRNA regulatory pathways, one of which is microRNA (miRNA)-mediated regulation. Besides the direct influence over mRNA transcription, the circRNA can also control the target's expression via sponging miRNAs or the RNA-binding proteins. Studies have demonstrated the dysregulation of the circRNA-miRNA-mRNA interaction network in the pathogenesis of many diseases, including diabetes. This intricate mechanism is associated with the pathogenesis of diabetes and its complications. This review will focus on the circRNA-miRNA-mRNA interaction network that influences the gene expression in the progression of diabetes and its associated complications.

Evaluation of circulating miRNAs and mRNAs expression patterns in autism spectrum disorder

Background

Autism spectrum disorder is a condition related to brain development that affects a person’s perception and socialization, resulting in problems in social interaction and communication. It has no single known cause, yet several different genes appear to be involved in autism. As a genetically complex disease, dysregulation of miRNA expression and miRNA–mRNA interactions might be a feature of autism spectrum disorder. The aim of the current study was to investigate the expression profile of circulating miRNA-128, miRNA-7 and SHANK gene family in ASD patients and to assess the possible influence of miRNA-128 and miRNA-7 on SHANK genes, which might provide an insight into the pathogenic mechanisms of ASD and introduce noninvasive molecular biomarkers for the disease diagnosis and prognosis. Quantitative real-time PCR technique was employed to determine expression levels of miRNA-128, miRNA-7 and SHANK gene family in blood samples of 40 autistic cases along with 30 age- and sex-matched normal volunteer subjects.

Results

Our study revealed a statistical significant upregulation of miRNA-128 expression levels in ASD cases compared to controls (p value < 0.001). A statistical significant difference in SHANK-3 expression was encountered on comparing cases to controls (p value < 0.001). However, miRNA-7 expression showed no significant difference between the studied groups.

Conclusions

MiRNA-128 and SHANK-3 gene are emerging players in the field of ASD. They are promising candidates as noninvasive biomarkers in autism. Future studies are needed to emphasize their pivotal role.

MicroRNA-7 overexpression positively regulates the CD8+ SP cell development via targeting PIK3R1

microRNA-7 (miR-7), a distinct miRNA family member, has been reported to be involved in the biological functions of immune cells. However, the potential role of miR-7 in the CD8⁺ T cell development remains to be elucidated. In this study, we estimated the potential effects of miR-7 overexpression in the thymic CD8⁺ SP cell development using miR-7 overexpression mice. Our results showed that compared with those in control wild type (WT) mice, the volume, weight and total cell numbers of thymus in miR-7 overexpression (OE) mice increased significantly. The absolute cell number of CD8⁺ SP cells in miR-7 OE mice increased and its ability of activation and proliferation enhanced. Futhermore, we clarified that miR-7 overexpression had an intrinsic promote role in CD8⁺ SP cell development by adoptive cell transfer assay. Mechanistically, the expression level of PIK3R1, a target of miR-7, decreased significantly in CD8⁺ SP cells of miR-7 OE mice. Moreover, the expression level of phosphorylated (p)-AKT and p-ERK changed inversely and indicating that miR-7 overexpression impaired the balance of AKE and ERK pathways. In summary, our work reveals an essential role of miR-7 in promoting CD8⁺ SP cell development through the regulation of PIK3R1 and balance of AKT and ERK pathways.

Prenatal stress leads to deficits in brain development, mood related behaviors and gut microbiota in offspring

Early exposure to stressful and adverse life events at fetal and neonatal stages is one of crucial risk factors for mood disorders such as anxiety and depressive disorder in adulthood. Intergenerational effects of prenatal stress on offspring are still not fully understood. We here uncover a significant negative impact of prenatal stress on brain development in embryos and newborns, and on mood-related behaviors and gut microbiota in adult offspring. Prenatal stress leads to reduced numbers in neural progenitors and newborn neurons, and altered gene expression profiles in the mouse embryonic cerebral cortex. Adult mouse offspring exposed to prenatal stress displays altered gene expression in the cortex and elevated responses in anxiety- and depression-like behaviors. Interestingly, prenatal stress has an enduring effect on gut microbiota, as specific microbial community structure is altered in adult F1 offspring treated with prenatal stress, compared to that of the control. Our results highlight the essential impact of prenatal stress on cortical neurogenesis, gene expression patterns, mood-related behaviors, and even gut microbiota in the next generation.

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Prenatal stress causes reduced neurogenesis.

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Altered gene expression/ behavior/ microbial communities in F1.

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High association of altered metabolisms between gut microbiota and brain.

miR-7b-3p Exerts a Dual Role After Spinal Cord Injury, by Supporting Plasticity and Neuroprotection at Cortical Level

Spinal cord injury (SCI) affects 6 million people worldwide with no available treatment. Despite research advances, the inherent poor regeneration potential of the central nervous system remains a major hurdle. Small RNAs (sRNAs) 19-33 nucleotides in length are a set of non-coding RNA molecules that regulate gene expression and have emerged as key players in regulating cellular events occurring after SCI. Here we profiled a class of sRNA known as microRNAs (miRNAs) following SCI in the cortex where the cell bodies of corticospinal motor neurons are located. We identified miR-7b-3p as a candidate target given its significant upregulation after SCI in vivo and we screened by miRWalk PTM the genes predicted to be targets of miR-7b-3p (among which we identified Wipf2, a gene regulating neurite extension). Moreover, 16 genes, involved in neural regeneration and potential miR-7b-3p targets, were found to be downregulated in the cortex following SCI. We also analysed miR-7b-3p function during cortical neuron development in vitro: we observed that the overexpression of miR-7b-3p was important (1) to maintain neurons in a more immature and, likely, plastic neuronal developmental phase and (2) to contrast the apoptotic pathway; however, in normal conditions it did not affect the Wipf2 expression. On the contrary, the overexpression of miR-7b-3p upon in vitro oxidative stress condition (mimicking the SCI environment) significantly reduced the expression level of Wipf2, as observed in vivo, confirming it as a direct miR-7b-3p target. Overall, these data suggest a dual role of miR-7b-3p: (i) the induction of a more plastic neuronal condition/phase, possibly at the expense of the axon growth, (ii) the neuroprotective role exerted through the inhibition of the apoptotic cascade. Increasing the miR-7b-3p levels in case of SCI could reactivate in adult neurons silenced developmental programmes, supporting at the same time the survival of the axotomised neurons.

MiR-7 in Cancer Development

MicroRNAs (miRNAs) are short non-coding RNA involved in the regulation of specific mRNA translation. They participate in cellular signaling circuits and can act as oncogenes in tumor development, so-called oncomirs, as well as tumor suppressors. miR-7 is an ancient miRNA involved in the fine-tuning of several signaling pathways, acting mainly as tumor suppressor. Through downregulation of PI3K and MAPK pathways, its dominant role is the suppression of proliferation and survival, stimulation of apoptosis and inhibition of migration. Besides these functions, it has numerous additional roles in the differentiation process of different cell types, protection from stress and chromatin remodulation. One of the most investigated tissues is the brain, where its downregulation is linked with glioblastoma cell proliferation. Its deregulation is found also in other tumor types, such as in liver, lung and pancreas. In some types of lung and oral carcinoma, it can act as oncomir. miR-7 roles in cell fate determination and maintenance of cell homeostasis are still to be discovered, as well as the possibilities of its use as a specific biotherapeutic.

Systematic Review and Bioinformatic Analysis of microRNA Expression in Autism Spectrum Disorder Identifies Pathways Associated With Cancer, Metabolism, Cell Signaling, and Cell Adhesion

Background: Previous studies have identified differentially expressed microRNAs in autism spectrum disorder (ASD), however, results are discrepant. We aimed to systematically review this topic and perform bioinformatic analysis to identify genes and pathways associated with ASD miRNAs. Methods: Following the Preferred Reporting Items for Systematic reviews and Meta-Analyses, we searched the Web of Science, PubMed, Embase, Scopus, and OVID databases to identify all studies comparing microRNA expressions between ASD persons and non-ASD controls on May 11, 2020. We obtained ASD miRNA targets validated by experimental assays from miRTarBase and performed pathway enrichment analysis using Metascape and DIANA-miRPath v3. 0. Results: Thirty-four studies were included in the systematic review. Among 285 altered miRNAs reported in these studies, 15 were consistently upregulated, 14 were consistently downregulated, and 39 were inconsistently dysregulated. The most frequently altered miRNAs including miR-23a-3p, miR-106b-5p, miR-146a-5p, miR-7-5p, miR-27a-3p, miR-181b-5p, miR-486-3p, and miR-451a. Subgroup analysis of tissues showed that miR-146a-5p, miR-155-5p, miR-1277-3p, miR-21-3p, miR-106b-5p, and miR-451a were consistently upregulated in brain tissues, while miR-4742-3p was consistently downregulated; miR-23b-3p, miR-483-5p, and miR-23a-3p were consistently upregulated in blood samples, while miR-15a-5p, miR-193a-5p, miR-20a-5p, miR-574-3p, miR-92a-3p, miR-3135a, and miR-103a-3p were consistently downregulated; miR-7-5p was consistently upregulated in saliva, miR-23a-3p and miR-32-5p were consistently downregulated. The altered ASD miRNAs identified in at least two independent studies were validated to target many autism risk genes. TNRC6B, PTEN, AGO1, SKI, and SMAD4 were the most frequent targets, and miR-92a-3p had the most target autism risk genes. Pathway enrichment analysis showed that ASD miRNAs are significantly involved in pathways associated with cancer, metabolism (notably Steroid biosynthesis, Fatty acid metabolism, Fatty acid biosynthesis, Lysine degradation, Biotin metabolism), cell cycle, cell signaling (especially Hippo, FoxO, TGF-beta, p53, Thyroid hormone, and Estrogen signaling pathway), adherens junction, extracellular matrix-receptor interaction, and Prion diseases. Conclusions: Altered miRNAs in ASD target autism risk genes and are involved in various ASD-related pathways, some of which are understudied and require further investigation.

MicroRNAs at the Crossroad of the Dichotomic Pathway Cell Death vs. Stemness in Neural Somatic and Cancer Stem Cells: Implications and Therapeutic Strategies

Stemness and apoptosis may highlight the dichotomy between regeneration and demise in the complex pathway proceeding from ontogenesis to the end of life. In the last few years, the concept has emerged that the same microRNAs (miRNAs) can be concurrently implicated in both apoptosis-related mechanisms and cell differentiation. Whether the differentiation process gives rise to the architecture of brain areas, any long-lasting perturbation of miRNA expression can be related to the occurrence of neurodevelopmental/neuropathological conditions. Moreover, as a consequence of neural stem cell (NSC) transformation to cancer stem cells (CSCs), the fine modulation of distinct miRNAs becomes necessary. This event implies controlling the expression of pro/anti-apoptotic target genes, which is crucial for the management of neural/neural crest-derived CSCs in brain tumors, neuroblastoma, and melanoma. From a translational point of view, the current progress on the emerging miRNA-based neuropathology therapeutic applications and antitumor strategies will be disclosed and their advantages and shortcomings discussed.

An evolutionarily acquired microRNA shapes development of mammalian cortical projections

The mammalian central nervous system contains unique projections from the cerebral cortex thought to underpin complex motor and cognitive skills, including the corticospinal tract and corpus callosum. The neurons giving rise to these projections—corticospinal and callosal projection neurons—develop from the same progenitors, but acquire strikingly different fates. The broad evolutionary conservation of known genes controlling cortical projection neuron fates raises the question of how the more narrowly conserved corticospinal and callosal projections evolved. We identify a microRNA cluster selectively expressed by corticospinal projection neurons and exclusive to placental mammals. One of these microRNAs promotes corticospinal fate via regulation of the callosal gene LMO4, suggesting a mechanism whereby microRNA regulation during development promotes evolution of neuronal diversity.

The corticospinal tract is unique to mammals and the corpus callosum is unique to placental mammals (eutherians). The emergence of these structures is thought to underpin the evolutionary acquisition of complex motor and cognitive skills. Corticospinal motor neurons (CSMN) and callosal projection neurons (CPN) are the archetypal projection neurons of the corticospinal tract and corpus callosum, respectively. Although a number of conserved transcriptional regulators of CSMN and CPN development have been identified in vertebrates, none are unique to mammals and most are coexpressed across multiple projection neuron subtypes. Here, we discover 17 CSMN-enriched microRNAs (miRNAs), 15 of which map to a single genomic cluster that is exclusive to eutherians. One of these, miR-409-3p, promotes CSMN subtype identity in part via repression of LMO4, a key transcriptional regulator of CPN development. In vivo, miR-409-3p is sufficient to convert deep-layer CPN into CSMN. This is a demonstration of an evolutionarily acquired miRNA in eutherians that refines cortical projection neuron subtype development. Our findings implicate miRNAs in the eutherians’ increase in neuronal subtype and projection diversity, the anatomic underpinnings of their complex behavior.

Translational Control during Mammalian Neocortex Development and Postembryonic Neuronal Function

The control of mRNA translation has key roles in the regulation of gene expression and biological processes such as mammalian cellular differentiation and identity. Methodological advances in the last decade have resulted in considerable progress towards understanding how translational control contributes to the regulation of diverse biological phenomena. In this review, we discuss recent findings in the involvement of translational control in the mammalian neocortex development and neuronal biology. We focus on regulatory mechanisms that modulate translational efficiency during neural stem cells self-renewal and differentiation, as well as in neuronal-related processes such as synapse, plasticity, and memory.

MicroRNA-7: expression and function in brain physiological and pathological processes

MicroRNAs (miRNAs) are a class of small non-coding RNAs that regulate gene expression at the post-transcriptional level and play critical roles in regulating physiological function, and are becoming worldwide research hot spot in brain development and diseases. However, the exact value of miRNAs in brain physiological and pathological processes remain to be fully elucidated, which is vital for the application of miRNAs as diagnostic, prognostic, and therapeutic biomarkers for brain diseases. MicroRNA-7 (miR-7), as a highly expressed miRNA molecule in the mammalian brain, is well documented to play a critical role in development of various diseases. Importantly, accumulating evidence has shown that miR-7 is involved in a range of developmental and pathological processes of brain. Expressively, miR-7, encoded by three genes located different chromosomes, is dominantly expressed in neurons with sensory or neurosecretory. Moreover, the expression of miR-7 is regulated at three levels including gene transcription, process of primary and precursor sequence and formation of mature sequence. Physiologically, miR-7 principally governs the physiological development of Pituitary gland, Optic nervous system and Cerebral cortex. Pathologically, miR-7 can regulate multiple genes thereby manipulating the process of various brain diseases including neurodegenerative diseases, neuroinflammation, and mental disorders and so on. These emerging studies have shown that miR-7, a representative member of miRNA family, might be a novel intrinsic regulatory molecule involved in the physiological and pathological process of brain. Therefore, in-depth studies on the role of miR-7 in brain physiology and pathology undoubtedly not only provide a light on the roles of miRNAs in brain development and diseases, but also are much helpful for ultimate development of therapeutic strategies against brain diseases. In this review, we provide an overview of current scientific knowledge regarding the expression and function of miR-7 in development and disease of brain and raise many issues involved in the relationship between miR-7 and brain physiological and pathological processes.

Deep Insights in Circular RNAs: from biogenesis to therapeutics

Abstract

Circular RNAs (circRNAs) have emerged as a universal novel class of eukaryotic non-coding RNA (ncRNA) molecules and are becoming a new research hotspot in RNA biology. They form a covalent loop without 5′ cap and 3′ tail, unlike their linear counterparts. Endogenous circRNAs in mammalian cells are abundantly conserved and discovered so far. In the biogenesis of circRNAs exonic, intronic, reverse complementary sequences or RNA-binding proteins (RBPs) play a very important role. Interestingly, the majority of them are highly conserved, stable, resistant to RNase R and show developmental-stage/tissue-specific expression. CircRNAs play multifunctional roles as microRNA (miRNA) sponges, regulators of transcription and post-transcription, parental gene expression and translation of proteins in various diseased conditions. Growing evidence shows that circRNAs play an important role in neurological disorders, atherosclerotic vascular disease, and cancer and potentially serve as diagnostic or predictive biomarkers due to its abundance in various biological samples. Here, we review the biogenesis, properties, functions, and impact of circRNAs on various diseases.

Graphical Abstract

Cell-free microRNAs in Parkinson's disease: potential biomarkers that provide new insights into disease pathogenesis

MicroRNAs (miRNAs) are master post-transcriptional regulators of gene expression and their specific footprints reflect disease conditions. Over the last few years, several primary reports have described the deregulation of cell-free miRNAs in Parkinson's disease (PD), however, results have been rather inconsistent due to preanalytical and analytical challenges. This study integrated the data across twenty-four reports to identify steadily deregulated miRNAs that may assist in the path towards biomarker development and molecular characterization of the underlying pathology. Stringent KEGG pathway analysis of the miRNA targets revealed FoxO, Prolactin, TNF, and ErbB signaling pathways as the most significantly enriched categories while Gene Ontology analysis revealed that the protein targets are mostly associated with transcription. Chromosomal location of the consistently deregulated miRNAs revealed that over a third of them were clustered at the same location at Chr14q32 suggesting that they are co-regulated by specific transcription factors. This genomic region is inherently unstable due to expanded TGG repeats and responsible for human abnormalities. Stringent analysis of transcription factor sites surrounding the deregulated miRNAs revealed that CREB1, CEBPB and MAZ sites existed in approximately half of the miRNAs, including all of the miRNAs located at Chr14q32. Additional studies are now needed to determine the biomarker potential of the consistently deregulated miRNAs in PD and the therapeutic implications of these bioinformatics insights.

Estrogen Abolishes the Repression Role of gga-miR-221-5p Targeting ELOVL6 and SQLE to Promote Lipid Synthesis in Chicken Liver

Few studies have been conducted regarding the biological function and regulation role of gga-miR-221-5p in the liver. We compared the conservation of miR-221-5p among species and investigated the expression pattern of gga-miR-221-5p, validating the direct target genes of gga-miR-221-5p by dual luciferase reporter assay, the biological function of gga-miR-221-5p in the liver was studied by gga-miR-221-5p overexpression and inhibition. Furthermore, we explored the regulation of gga-miR-221-5p and its target genes by treatment with estrogen and estrogen antagonists in vivo and in vitro. The results showed that miR-221-5p was highly conserved among species, expressed in all tested tissues and significantly downregulated in peak-laying hen liver compared to pre-laying hen liver. Gga-miR-221-5p could directly target the expression of elongase of very long chain fatty acids 6 (ELOVL6) and squalene epoxidase (SQLE) genes to affect triglyceride and total cholesterol content in the liver. 17β-estradiol could significantly inhibit the expression of gga-miR-221-5p but promote the expression of ELOVL6 and SQLE genes. In conclusion, the highly conservative gga-miR-221-5p could directly target ELOVL6 and SQLE mRNAs to affect the level of intracellular triglyceride and total cholesterol. Meanwhile, 17β-estradiol could repress the expression of gga-miR-221-5p but increase the expression of ELOVL6 and SQLE, therefore promoting the synthesis of intracellular triglyceride and cholesterol levels in the liver of egg-laying chicken.

Depolarization-Associated CircRNA Regulate Neural Gene Expression and in Some Cases May Function as Templates for Translation

Circular RNAs (circRNAs) are a relatively new class of RNA transcript with high abundance in the mammalian brain. Here, we show that circRNAs expression in differentiated neuroblastoma cells were significantly altered after depolarization with 107 upregulated and 47 downregulated circRNAs. This coincided with a global alteration in the expression of microRNA (miRNA) (n = 269) and mRNA (n = 1511) in depolarized cells, suggesting a regulatory axis of circRNA–miRNA–mRNA is involved in the cellular response to neural activity. In support of this, our in silico analysis revealed that the circular transcripts had the capacity to influence mRNA expression through interaction with common miRNAs. Loss-of-function of a highly expressed circRNA, circ-EXOC6B, resulted in altered expression of numerous mRNAs enriched in processes related to the EXOC6B function, suggesting that circRNAs may specifically regulate the genes acting in relation to their host genes. We also found that a subset of circRNAs, particularly in depolarized cells, were associated with ribosomes, suggesting they may be translated into protein. Overall, these data support a role for circRNAs in the modification of gene regulation associated with neuronal activity.

Exploring the Regulatory Role of Circular RNAs in Neurodegenerative Disorders

Circular RNAs (circRNAs) are a distinctive class of regulatory non-coding RNAs characterised by the presence of covalently closed ends. They are evolutionary conserved molecules, and although detected in different tissues, circRNAs resulted specifically enriched in the nervous system. Recent studies have shown that circRNAs are dynamically modulated during neuronal development and aging, that circRNAs are enriched at synaptic levels and resulted modulated after synaptic plasticity induction. This has suggested that circRNAs might play an important role in neuronal specification and activity. Despite the exact function of circRNAs is still poorly understood, emerging evidence indicates that circRNAs have important regulatory functions that might extensively contribute to the dynamic modulation of gene expression that supports neuronal pathways. More interestingly, deregulation of circRNAs expression has been linked with various pathological conditions. In this review, we describe current advances in the field of circRNA biogenesis and function in the nervous system both in physiological and in pathological conditions, and we specifically lay out their association with neurodegenerative diseases. Furthermore, we discuss the opportunity to exploit circRNAs for innovative therapeutic approaches and, due to their high stability, to use circRNAs as suitable biomarkers for diagnosis and disease progression.

MicroRNA-Based Separation of Cortico-Fugal Projection Neuron-Like Cells Derived From Embryonic Stem Cells

The purification of pluripotent stem cell-derived cortico-fugal projection neurons (PSC-CFuPNs) is useful for disease modeling and cell therapies related to the dysfunction of cortical motor neurons, such as amyotrophic lateral sclerosis (ALS) or stroke. However, no CFuPN-specific surface markers for the purification are known. Recently, microRNAs (miRNAs) have been reported as alternatives to surface markers. Here, we investigated this possibility by applying the miRNA switch, an mRNA technology, to enrich PSC-CFuPNs. An array study of miRNAs in mouse fetal brain tissue revealed that CFuPNs highly express miRNA-124-3p at E14.5 and E16.5. In response, we designed a miRNA switched that responds to miRNA-124-3p and applied it to mouse embryonic stem cell (ESC)-derived cortical neurons. Flow cytometry and quantitative polymerase chain reaction (qPCR) analyses showed the miRNA-124-3p switch enriched CFuPN-like cells from this population. Immunocytechemical analysis confirmed vGlut1/Emx1/Bcl11b triple positive CFuPN-like cells were increased from 6.5 to 42%. Thus, our miRNA-124-3p switch can uniquely enrich live CFuPN-like cells from mouse ESC-derived cortical neurons.

Translating neural stem cells to neurons in the mammalian brain

The mammalian neocortex underlies our perception of sensory information, performance of motor activities, and higher-order cognition. During mammalian embryogenesis, radial glial precursor cells sequentially give rise to diverse populations of excitatory cortical neurons, followed by astrocytes and oligodendrocytes. A subpopulation of these embryonic neural precursors persists into adulthood as neural stem cells, which give rise to inhibitory interneurons and glia. Although the intrinsic mechanisms instructing the genesis of these distinct progeny have been well-studied, most work to date has focused on transcriptional, epigenetic, and cell-cycle control. Recent studies, however, have shown that posttranscriptional mechanisms also regulate the cell fate choices of transcriptionally primed neural precursors during cortical development. These mechanisms are mediated primarily by RNA-binding proteins and microRNAs that coordinately regulate mRNA translation, stability, splicing, and localization. Together, these findings point to an extensive network of posttranscriptional control and provide insight into both normal cortical development and disease. They also add another layer of complexity to brain development and raise important biological questions for future investigation.

Investigation of Circulating Serum MicroRNA-328-3p and MicroRNA-3135a Expression as Promising Novel Biomarkers for Autism Spectrum Disorder

Circulating microRNAs (miRNAs) are emerging as promising diagnostic biomarkers for autism spectrum disorder (ASD), but their usefulness for detecting ASD remains unclear. Nowadays, development of promising biomarkers for ASD remains a challenge. Recently, dysregulation of the miRNAs expression in postmortem brain tissue, serum and peripheral blood, have been associated with ASD. Circulating miRNAs are known to be secreted by a number of different cells and can interpose delivery of information into receiver cells, thus affecting their functions. Based on this fact, it is supposed that serum miRNAs could be a novel class of biomarkers for prognosis or diagnosis of pathological disorders including ASD. In the current research, we investigated whether the expression patterns of circulating miRNAs showed dysregulation in subjects diagnosed with ASD. Expression levels of serum miR-328-3p and miR-3135a were analyzed by quantitative reverse transcription polymerase chain reaction (qRT-PCR) method of subjects diagnosed with ASD in comparison with healthy control subjects. Our data showed that miR-328-3p and miR-3135a were substantially down-regulated in ASD patients than in those of healthy control subjects. Moreover, target gene analysis of altered serum miRNAs displayed that these molecules targeted 162 genes denoted as unique validated targets in the miRWalk database, 71 of which appear to participate in biological pathways involved in synaptic pathways and neurodegenerative condition such as Alzheimer, Huntington and Parkinson diseases. Finally, the results strongly suggested that dys-regulated serum miRNAs might be involved in molecular pathways associated with ASD and miR-328-3p and miR-3135a have the potential to be promising novel biomarkers for ASD.

The Epigenetic Factor Landscape of Developing Neocortex Is Regulated by Transcription Factors Pax6→ Tbr2→ Tbr1

Epigenetic factors (EFs) regulate multiple aspects of cerebral cortex development, including proliferation, differentiation, laminar fate, and regional identity. The same neurodevelopmental processes are also regulated by transcription factors (TFs), notably the Pax6→ Tbr2→ Tbr1 cascade expressed sequentially in radial glial progenitors (RGPs), intermediate progenitors, and postmitotic projection neurons, respectively. Here, we studied the EF landscape and its regulation in embryonic mouse neocortex. Microarray and in situ hybridization assays revealed that many EF genes are expressed in specific cortical cell types, such as intermediate progenitors, or in rostrocaudal gradients. Furthermore, many EF genes are directly bound and transcriptionally regulated by Pax6, Tbr2, or Tbr1, as determined by chromatin immunoprecipitation-sequencing and gene expression analysis of TF mutant cortices. Our analysis demonstrated that Pax6, Tbr2, and Tbr1 form a direct feedforward genetic cascade, with direct feedback repression. Results also revealed that each TF regulates multiple EF genes that control DNA methylation, histone marks, chromatin remodeling, and non-coding RNA. For example, Tbr1 activates Rybp and Auts2 to promote the formation of non-canonical Polycomb repressive complex 1 (PRC1). Also, Pax6, Tbr2, and Tbr1 collectively drive massive changes in the subunit isoform composition of BAF chromatin remodeling complexes during differentiation: for example, a novel switch from Bcl7c (Baf40c) to Bcl7a (Baf40a), the latter directly activated by Tbr2. Of 11 subunits predominantly in neuronal BAF, 7 were transcriptionally activated by Pax6, Tbr2, or Tbr1. Using EFs, Pax6→ Tbr2→ Tbr1 effect persistent changes of gene expression in cell lineages, to propagate features such as regional and laminar identity from progenitors to neurons.

Counter-Balance Between Gli3 and miR-7 Is Required for Proper Morphogenesis and Size Control of the Mouse Brain

Brain morphogenesis requires precise regulation of multiple genes to control specification of distinct neural progenitors (NPs) and neuronal production. Dysregulation of these genes results in severe brain malformation such as macrocephaly and microcephaly. Despite studies of the effect of individual pathogenic genes, the counter-balance between multiple factors in controlling brain size remains unclear. Here we show that cortical deletion of Gli3 results in enlarged brain and folding structures in the cortical midline at the postnatal stage, which is mainly caused by the increased percentage of intermediate progenitors (IPs) and newborn neurons. In addition, dysregulation of neuronal migration also contributes to the folding defects in the cortical midline region. Knockdown of microRNA (miRNA) miR-7 can rescue abnormal brain morphology in Gli3 knockout mice by recovering progenitor specification, neuronal production and migration through a counter-balance of the Gli3 activity. Moreover, miR-7 likely exerts its function through silencing target gene Pax6. Our results indicate that proper brain morphogenesis is an outcome of interactive regulations of multiple molecules such as Gli3 and miR-7. Because miRNAs are easy to synthesize and deliver, miR-7 could be a potential therapeutic means to macrocephaly caused by Gli3-deficiency.

Elucidating sex differences in response to cerebral ischemia: immunoregulatory mechanisms and the role of microRNAs

Cerebral ischemia remains a major cause of death and disability worldwide, yet therapeutic options remain limited. Differences in sex and age play an important role in the final outcome in response to cerebral ischemia in both experimental and clinical studies: males have a higher risk and worse outcome than females at younger ages and this trend reverses in older ages. Although the molecular mechanisms underlying sex dimorphism are complex and are still not well understood, studies suggest steroid hormones, sex chromosomes, differential cell death and immune pathways, and sex-specific microRNAs may contribute to the outcome following cerebral ischemia. This review focuses on differential effects between males and females on cell death and immunological pathways in response to cerebral ischemia, the central role of innate sex differences in steroid hormone signaling, and upstreamregulation of sexually dimorphic gene expression by microRNAs.

A Network of Noncoding Regulatory RNAs Acts in the Mammalian Brain

Noncoding RNAs (ncRNAs) play increasingly appreciated gene-regulatory roles. Here, we describe a regulatory network centered on four ncRNAs-a long ncRNA, a circular RNA, and two microRNAs-using gene editing in mice to probe the molecular consequences of disrupting key components of this network. The long ncRNA Cyrano uses an extensively paired site to miR-7 to trigger destruction of this microRNA. Cyrano-directed miR-7 degradation is much more effective than previously described examples of target-directed microRNA degradation, which come primarily from studies of artificial and viral RNAs. By reducing miR-7 levels, Cyrano prevents repression of miR-7-targeted mRNAs and enables accumulation of Cdr1as, a circular RNA known to regulate neuronal activity. Without Cyrano, excess miR-7 causes cytoplasmic destruction of Cdr1as in neurons, in part through enhanced slicing of Cdr1as by a second miRNA, miR-671. Thus, several types of ncRNAs can collaborate to establish a sophisticated regulatory network.

Liver-directed microRNA-7a depletion induces nonalcoholic fatty liver disease by stabilizing YY1-mediated lipogenic pathways in zebrafish

Nonalcoholic fatty liver disease (NAFLD) has been associated with the function and changes in expression levels of microRNAs (miRs). MiR-7 has been proven to play an important role in many cellular processes; however, its functions in the context of liver lipogenesis remain unknown. We applied the microRNA-sponge (miR-SP) technology and generated transgenic miR-7a-SP models (hC7aSP and bC7aSP), which disrupted the activities of hepatic miR-7a and induced the early onset of NAFLD and nonalcoholic steatohepatitis (NASH) in zebrafish. We identified a novel miR-7a target, YY1, and demonstrated novel miR-7a functions to regulate zebrafish hepatic lipid metabolism by controlling YY1 stabilization through the regulation of the expression of lipogenic signaling pathways. Correspondingly, liver specific miR-7a depletion functionally promoted lipid accumulation in hC7ASP livers. NASH hC7aSP increased the expression of inflammatory genes (il-1b, il-6, tnf-α, ifn-γ, nfkb2, and NF-kB) and endoplasmic reticulum stress markers (atf6, ern2, ire1, perk, hspa5 and ddit3). Molecular analysis revealed that miR-7a-SP can stabilize YY1 expression and contribute to the accumulation of hepatic triglycerides by reducing the CHOP-10 expression in the hC7aSP and then inducing the transactivation of C/EBP-α and PPAR-γ expression. PPAR-γ antagonists and miR-7a mimic treatment ameliorate hC7aSP NASH phenotypes.

CONCLUSION

Our results suggest that miR-7a-SP acts as a lipid enhancer by directly increasing YY1 stability to disrupt CHOP-10-dependent suppression of lipogenic pathways, resulting in increased lipid accumulation. MiR-7a expression improves liver steatosis and steatohepatitis in hC7aSPs, which suggests a novel strategy for the prevention and early treatment of NASH in humans.

Evolution of New miRNAs and Cerebro-Cortical Development

The noncoding portion of the genome, including microRNAs, has been fertile evolutionary soil for cortical development in primates. A major contribution to cortical expansion in primates is the generation of novel precursor cell populations. Because miRNA expression profiles track closely with cell identity, it is likely that numerous novel microRNAs have contributed to cellular diversity in the brain. The tools to determine the genomic context within which novel microRNAs emerge and how they become integrated into molecular circuitry are now in hand.

Role of RNA modifications in brain and behavior

Much progress in our understanding of RNA metabolism has been made since the first RNA nucleoside modification was identified in 1957. Many of these modifications are found in noncoding RNAs but recent interest has focused on coding RNAs. Here, we summarize current knowledge of cellular consequences of RNA modifications, with a special emphasis on neuropsychiatric disorders. We present evidence for the existence of an "RNA code," similar to the histone code, that fine-tunes gene expression in the nervous system by using combinations of different RNA modifications. Unlike the relatively stable genetic code, this combinatorial RNA epigenetic code, or epitranscriptome, may be dynamically reprogrammed as a cause or consequence of psychiatric disorders. We discuss potential mechanisms linking disregulation of the epitranscriptome with brain disorders and identify potential new avenues of research.

Cohesive Regulation of Neural Progenitor Development by microRNA miR-26, Its Host Gene Ctdsp and Target Gene Emx2 in the Mouse Embryonic Cerebral Cortex

Proper proliferation and differentiation of neural progenitors (NPs) in the developing cerebral cortex are critical for normal brain formation and function. Emerging evidence has shown the importance of microRNAs (miRNAs) in regulating cortical development and the etiology of neurological disorders. Here we show that miR-26 is co-expressed with its host gene Ctdsp in the mouse embryonic cortex. We demonstrate that similar to its host gene Ctdsp2, miR-26 positively regulates proliferation of NPs through controlling the cell-cycle progression, by using miR-26 overexpression and sponge approaches. On the contrary, miR-26 target gene Emx2 limits expansion of cortical NPs, and promotes transcription of miR-26 host gene Ctdsp. Our study suggests that miR-26, its target Emx2 and its host gene Ctdsp cohesively regulate proliferation of NPs during the mouse cortical development.

CDK7 and miR-210 Co-regulate Cell-Cycle Progression of Neural Progenitors in the Developing Neocortex

The molecular mechanisms regulating neural progenitor (NP) proliferation are fundamental in establishing the cytoarchitecture of the mammalian neocortex. The rate of cell-cycle progression and a fine-tuned balance between cell-cycle re-entry and exit determine the numbers of both NPs and neurons as well as postmitotic neuronal laminar distribution in the cortical wall. Here, we demonstrate that the microRNA (miRNA) miR-210 is required for normal mouse NP cell-cycle progression. Overexpression of miR-210 promotes premature cell-cycle exit and terminal differentiation in NPs, resulting in an increase in early-born postmitotic neurons. Conversely, miR-210 knockdown promotes an increase in the radial glial cell population and delayed differentiation, resulting in an increase in late-born postmitotic neurons. Moreover, the cyclin-dependent kinase CDK7 is regulated by miR-210 and is necessary for normal NP cell-cycle progression. Our findings demonstrate that miRNAs are essential for normal NP proliferation and cell-cycle progress during neocortical development.

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miR-210 level is essential for cell-cycle progression in cortical neural progenitors

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Cdk7 and miR-210 control neural progenitor proliferation

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miR-210 promotes premature cell-cycle exit and differentiation in neural progenitors

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miR-210 expression induces a deep-layer neuronal fate in the neocortex

MicroRNA-7-5p mediates the signaling of hepatocyte growth factor to suppress oncogenes in the MCF-10A mammary epithelial cell

MicroRNA-7 (miR-7) is a non-coding RNA of 23-nucleotides that has been shown to act as a tumor suppressor in various cancers including breast cancer. Although there have been copious studies on the action mechanisms of miR-7, little is known about how the miR is controlled in the mammary cell. In this study, we performed a genome-wide expression analysis in miR-7-transfected MCF-10A breast cell line to explore the upstream regulators of miR-7. Analysis of the dysregulated target gene pool predicted hepatocyte growth factor (HGF) as the most plausible upstream regulator of miR-7. MiR-7 was upregulated in MCF-10A cells by HGF, and subsequently downregulated upon treatment with siRNA against HGF. However, the expression of HGF did not significantly change through either an upregulation or downregulation of miR-7 expression, suggesting that HGF acts upstream of miR-7. In addition, the target genes of miR-7, such as EGFR, KLF4, FAK, PAK1 and SET8, which are all known oncogenes, were downregulated in HGF-treated MCF-10A; in contrast, knocking down HGF recovered their expression. These results indicate that miR-7 mediates the activity of HGF to suppress oncogenic proteins, which inhibits the development of normal cells, at least MCF-10A, into cancerous cells.

RNA on the brain: emerging layers of post-transcriptional regulation in cerebral cortex development

Embryonic development is a critical period during which neurons of the brain are generated and organized. In the developing cerebral cortex, this requires complex processes of neural progenitor proliferation, neuronal differentiation, and migration. Each step relies upon highly regulated control of gene expression. In particular, RNA splicing, stability, localization, and translation have emerged as key post-transcriptional regulatory nodes of mouse corticogenesis. Trans-regulators of RNA metabolism, including microRNAs (miRs) and RNA-binding proteins (RBPs), orchestrate diverse steps of cortical development. These trans-factors function either individually or cooperatively to influence RNAs, often of similar classes, termed RNA regulons. New technological advances raise the potential for an increasingly sophisticated understanding of post-transcriptional control in the developing neocortex. Many RNA-binding factors are also implicated in neurodevelopmental diseases of the cortex. Therefore, elucidating how RBPs and miRs converge to influence mRNA expression in progenitors and neurons will give valuable insights into mechanisms of cortical development and disease. WIREs Dev Biol 2018, 7:e290. doi: 10.1002/wdev.290 This article is categorized under: Gene Expression and Transcriptional Hierarchies > Regulatory RNA Nervous System Development > Vertebrates: Regional Development Adult Stem Cells, Tissue Renewal, and Regeneration > Stem Cells and Disease.

Functional integration of complex miRNA networks in central and peripheral lesion and axonal regeneration

New players are emerging in the game of peripheral and central nervous system injury since their physiopathological mechanisms remain partially elusive. These mechanisms are characterized by several molecules whose activation and/or modification following a trauma is often controlled at transcriptional level. In this scenario, microRNAs (miRNAs/miRs) have been identified as main actors in coordinating important molecular pathways in nerve or spinal cord injury (SCI). miRNAs are small non-coding RNAs whose functionality at network level is now emerging as a new level of complexity. Indeed they can act as an organized network to provide a precise control of several biological processes. Here we describe the functional synergy of some miRNAs in case of SCI and peripheral damage. In particular we show how several small RNAs can cooperate in influencing simultaneously the molecular pathways orchestrating axon regeneration, inflammation, apoptosis and remyelination. We report about the networks for which miRNA-target bindings have been experimentally demonstrated or inferred based on target prediction data: in both cases, the connection between one miRNA and its downstream pathway is derived from a validated observation or is predicted from the literature. Hence, we discuss the importance of miRNAs in some pathological processes focusing on their functional structure as participating in a cooperative and/or convergence network.

Human-specific genomic signatures of neocortical expansion

Neocortex evolutionary expansion is primarily due to increased proliferative capacity of neural progenitor cells during cortical development. Exploiting insights into the cell biology of cortical progenitors gained during the past two decades, recent studies uncovered a variety of gene expression differences that underlie differential cortical progenitor behavior. These comprise both, differences between cortical areas that likely provide a molecular basis for cortical folding, and differences across species thought to be responsible for increases in neocortex size. Human-specific signatures have been identified for gene regulatory elements, non-coding gene products, and protein-encoding genes, and have been functionally examined in in vivo as well as novel in vitro model systems.

ZIKA virus elicits P53 activation and genotoxic stress in human neural progenitors similar to mutations involved in severe forms of genetic microcephaly

Epidemiological evidence from the current outbreak of Zika virus (ZIKV) and recent studies in animal models indicate a strong causal link between ZIKV and microcephaly. ZIKV infection induces cell-cycle arrest and apoptosis in proliferating neural progenitors. However, the mechanisms leading to these phenotypes are still largely obscure. In this report, we explored the possible similarities between transcriptional responses induced by ZIKV in human neural progenitors and those elicited by three different genetic mutations leading to severe forms of microcephaly in mice. We found that the strongest similarity between all these conditions is the activation of common P53 downstream genes. In agreement with these observations, we report that ZIKV infection increases total P53 levels and nuclear accumulation, as well as P53 Ser15 phosphorylation, correlated with genotoxic stress and apoptosis induction. Interestingly, increased P53 activation and apoptosis are induced not only in cells expressing high levels of viral antigens but also in cells showing low or undetectable levels of the same proteins. These results indicate that P53 activation is an early and specific event in ZIKV-infected cells, which could result from cell-autonomous and/or non-cell-autonomous mechanisms. Moreover, we highlight a small group of P53 effector proteins that could act as critical mediators, not only in ZIKV-induced microcephaly but also in many genetic microcephaly syndromes.

MicroRNA-34/449 controls mitotic spindle orientation during mammalian cortex development

Correct orientation of the mitotic spindle determines the plane of cellular cleavage and is crucial for organ development. In the developing cerebral cortex, spindle orientation defects result in severe neurodevelopmental disorders, but the precise mechanisms that control this important event are not fully understood. Here, we use a combination of high-content screening and mouse genetics to identify the miR-34/449 family as key regulators of mitotic spindle orientation in the developing cerebral cortex. By screening through all cortically expressed miRNAs in HeLa cells, we show that several members of the miR-34/449 family control mitotic duration and spindle rotation. Analysis of miR-34/449 knockout (KO) mouse embryos demonstrates significant spindle misorientation phenotypes in cortical progenitors, resulting in an excess of radial glia cells at the expense of intermediate progenitors and a significant delay in neurogenesis. We identify the junction adhesion molecule-A (JAM-A) as a key target for miR-34/449 in the developing cortex that might be responsible for those defects. Our data indicate that miRNA-dependent regulation of mitotic spindle orientation is crucial for cell fate specification during mammalian neurogenesis.