Olig2 transcription factor in the developing and injured forebrain; cell lineage and glial development

ALAS1 associated with goat kidding number trait was regulated by the transcription factor ASCL2 to affect granulosa cell proliferation

ALAS1 is a member of the α-oxoamine synthase family, which is the first rate-limiting enzyme for heme synthesis and is important for maintaining intracellular heme levels. In the ovary, ALAS1 is associated with the regulation of ovulation-related mitochondrial P450 cytochromes, steroid metabolism, and steroid hormone production. However, there are few studies on the relationship between ALAS1 and reproductive traits in goats. In this study, a mutation located in the promoter region of ALAS1 (g.48791372C>A) was found to be significantly (p < 0.05) associated with the kidding number of Yunshang black goats. Specifically, the mean kidding number in the first three litters and the kidding numbers of all three litters were significantly (p < 0.05) higher in individuals with the CA genotype or AA genotype than in those with the CC genotype. To further investigate the regulatory mechanism of ALAS1, the expression of ALAS1 in goat ovarian tissues with different genotypes was verified by real-time quantitative PCR. The results showed that the expression of ALAS1 was significantly higher in the ovaries of individuals with AA genotype than those with AC and CC genotypes (p < 0.01), and the expression trend of transcription factor ASCL2 was consistent with ALAS1. Additionally, the ALAS1 g.48791372C>A mutation created a new binding site for the transcription factor ASCL2. The luciferase activity assay indicated that the mutation increased the promoter activity of ALAS1. Overexpression of the transcription factor ASCL2 induced increased expression of ALAS1 in goat granulosa cells (p < 0.05). The opposite trend was shown for the inhibition of ASCL2 expression. The results of real-time quantitative PCR, EdU and Cell Counting Kit-8 assays indicated that the transcription factor ASCL2 increased the proliferation of goat granulosa cells by mediating the expression of ALAS1. In conclusion, the transcription factor ASCL2 positively regulated the transcriptional activity and expression levels of ALAS1, altering granulosa cell proliferation and the kidding number in goats.

Astroglial and oligodendroglial markers in the cuprizone animal model for de- and remyelination

Myelin loss with consecutive axon degeneration and impaired remyelination are the underlying causes of progressive disease in patients with multiple sclerosis. Astrocytes are suggested to play a major role in these processes. The unmasking of distinct astrocyte identities in health and disease would help to understand the pathophysiological mechanisms in which astrocytes are involved. However, the number of specific astrocyte markers is limited. Therefore, we performed immunohistochemical studies and analyzed various markers including GFAP, vimentin, S100B, ALDH1L1, and LCN2 during de- and remyelination using the toxic murine cuprizone animal model. Applying this animal model, we were able to confirm overlapping expression of vimentin and GFAP and highlighted the potential of ALDH1L1 as a pan-astrocytic marker, in agreement with previous data. Only a small population of GFAP-positive astrocytes in the corpus callosum highly up-regulated LCN2 at the peak of demyelination and S100B expression was found in a subset of oligodendroglia as well, thus S100B turned out to have a limited use as a particular astroglial marker. Additionally, numerous GFAP-positive astrocytes in the lateral corpus callosum did not express S100B, further strengthening findings of heterogeneity in the astrocytic population. In conclusion, our results acknowledged that GFAP, vimentin, LCN2, and ALDH1L1 serve as reliable marker to identify activated astrocytes during cuprizone-induced de- and remyelination. Moreover, there were clear regional and temporal differences in protein and mRNA expression levels and patterns of the studied markers, generally between gray and white matter structures.

Activation and Role of Astrocytes in Ischemic Stroke

Ischemic stroke refers to the disorder of blood supply of local brain tissue caused by various reasons. It has high morbidity and mortality worldwide. Astrocytes are the most abundant glial cells in the central nervous system (CNS). They are responsible for the homeostasis, nutrition, and protection of the CNS and play an essential role in many nervous system diseases’ physiological and pathological processes. After stroke injury, astrocytes are activated and play a protective role through the heterogeneous and gradual changes of their gene expression, morphology, proliferation, and function, that is, reactive astrocytes. However, the position of reactive astrocytes has always been a controversial topic. Many studies have shown that reactive astrocytes are a double-edged sword with both beneficial and harmful effects. It is worth noting that their different spatial and temporal expression determines astrocytes’ various functions. Here, we comprehensively review the different roles and mechanisms of astrocytes after ischemic stroke. In addition, the intracellular mechanism of astrocyte activation has also been involved. More importantly, due to the complex cascade reaction and action mechanism after ischemic stroke, the role of astrocytes is still difficult to define. Still, there is no doubt that astrocytes are one of the critical factors mediating the deterioration or improvement of ischemic stroke.

Olig2-astrocytes express neutral amino acid transporter SLC7A10 (Asc-1) in the adult brain

We have reported that the transcription factor Olig2 labels a subpopulation of astrocytes (Olig2-astrocytes), which show distribution patterns different from those of GFAP-expressing astrocytes (GFAP-astrocytes) in the adult brain. Here, to uncover the specific functions of Olig2-astrocytes, we first analyzed public single-cell RNA-seq databases of adult mouse brains. Unbiased classification of gene expression profiles and subsequent gene ontology analyses revealed that the majority of Olig2-astrocytes belonged to an astrocytic cluster that is enriched for transporter-related genes. SLC7A10 (also known as ASC-1) was one of the representative neutral amino acid transporter genes in the cluster. To complement the in silico data analyses, we differentially isolated Olig2- and GFAP-astrocytes from the same frozen section of the lateral globus pallidus using laser microdissection and compared their gene expression by quantitative reverse transcription PCR. We confirmed that Olig2 and GFAP mRNAs were preferentially expressed in the Olig2- and GFAP-astrocytes, respectively, indicating that the laser microdissection method yielded minimal cross-contamination between two types of cells. The Olig2-astrocytes expressed significantly higher levels of SLC7A10 mRNA than the GFAP-astrocytes, corroborating the in silico data. We next localized SLC7A10 protein by immunohistochemistry in the lateral globus pallidus, which was also genetically labeled for Olig2. SLC7A10 co-localized with Olig2-genetic labeling, especially on the fine processes of Olig2-astrocytes. These results are consistent with the recent discovery that SLC7A10 is expressed not only in neurons but also in a subset of astrocytes. Taken together, our findings suggest that SLC7A10 exerts specific functions in Olig2-astrocytes of the adult brain.

Olig2 knockdown alleviates hypoxic-ischemic brain damage in newborn rats

OBJECTIVES

Neuronal damage is an important pathological mechanism in neonatal hypoxic-ischemic brain damage (HIBD). We found in our previous studies that oligodendrocyte transcription factor 2 (Olig2) downregulation was able to increase cell survival in the brain. However, the specific mechanism has yet to be clarified.

METHODS

Sprague-Dawley rats aged 3 d were randomly divided into three groups: the normal control group, the Olig2-RNAi group, and the RNAi-negative control group. The normal control group received no treatment, the Olig2-RNAi group received the Olig2 RNAi adenovirus, and the RNAi-negative control group was given the control adenovirus after the completion of the HIBD model. Infarct lesions and their volumes were observed by triphenyltetrazolium chloride (TTC) staining 3 d after the completion of the adenovirus local injection. The condition of the tissue was characterized by hematoxylin-eosin staining 7 d after the model was established, and cell viability was determined by azure methylene blue staining. Subcellular damage was analyzed by transmission electron microscopy. Rotarod analysis was performed to detect moving behavior ability and an MWM assay was conducted to evaluate the memory.

RESULTS

TTC staining showed a smaller brain injury area in the Olig2-RNAi group than in the RNAi-negative control group. Hematoxylin-eosin staining indicated the presence of severe cell injury in the hippocampal region after HIBD, which improved after Olig2 knockdown. Azure methylene blue staining and electron microscopy results suggested that the cells improved after Olig2 knockdown. The rats stayed longer on the rotating rod, and their latency in the water maze test was gradually shortened relative to that of the rats in the Olig2-RNAi negative control group.

CONCLUSION

Olig2 knockdown can promote the repair of hypoxic-ischemic brain damage in newborn rats.

Quantitative Cellular Changes in the Thalamus of Patients with Multiple System Atrophy

The thalamus is a brain region consisting of anatomical and functional connections between various spinal, subcortical, and cortical regions, which has a putative role in the clinical manifestation of Multiple System Atrophy (MSA). Previous stereological studies have reported significant anatomical alterations in diverse brain regions of MSA patients, including the cerebral cortex, basal ganglia and white matter, but no quantitative studies have examined the thalamus. To establish the extent of thalamic involvement, we applied stereological methods to estimate the total number of neurons and glial cells (oligodendrocytes, astrocytes and microglia) as well as the volume in two thalamic sub-regions, the mediodorsal nucleus (MDT) and the anterior principal nucleus (APn), in brains from ten MSA patients and 11 healthy control subjects. Compared to healthy controls, MSA patients had significantly fewer neurons (26%) in the MDT, but not the APn. We also found significantly more astrocytes (32%) and microglia (54%) in the MDT, with no such changes in the APn. Finally, we saw no group differences in the total number of oligodendrocytes. Our findings show a region-specific loss of thalamic neurons that occurs without loss of oligodendrocytes, whereas thalamic microgliosis seems to occur alongside astrogliosis. These pathological changes in the thalamus may contribute to the cognitive impairment seen in most patients with MSA.

A novel population of Hopx-dependent basal radial glial cells in the developing mouse neocortex

A specific subpopulation of neural progenitor cells, the basal radial glial cells (bRGCs) of the outer subventricular zone (OSVZ), are thought to have a key role in the evolutionary expansion of the mammalian neocortex. In the developing lissencephalic mouse neocortex, bRGCs exist at low abundance and show significant molecular differences from bRGCs in developing gyrencephalic species. Here, we demonstrate that the developing mouse medial neocortex (medNcx), in contrast to the canonically studied lateral neocortex (latNcx), exhibits an OSVZ and an abundance of bRGCs similar to that in developing gyrencephalic neocortex. Unlike bRGCs in developing mouse latNcx, the bRGCs in medNcx exhibit human bRGC-like gene expression, including expression of Hopx, a human bRGC marker. Disruption of Hopx expression in mouse embryonic medNcx and forced Hopx expression in mouse embryonic latNcx demonstrate that Hopx is required and sufficient, respectively, for bRGC abundance as found in the developing gyrencephalic neocortex. Taken together, our data identify a novel bRGC subpopulation in developing mouse medNcx that is highly related to bRGCs of developing gyrencephalic neocortex.

Variants of the OLIG2 Gene are Associated with Cerebral Palsy in Chinese Han Infants with Hypoxic-Ischemic Encephalopathy

Cerebral palsy (CP) is a leading cause of neurological disability among young children. Congenial and adverse perinatal clinical conditions, such as genetic factors, perinatal infection, and asphyxia, are risk factors for CP. Oligodendrocyte transcription factor (OLIG2) is a protein that is expressed in brain oligodendrocyte cells and is involved in neuron repair after brain injury. In this study, we employed a Chinese Han cohort of 763 CP infants and 738 healthy controls to study the association of OLIG2 gene polymorphisms with CP. We found marginal association of the SNP rs6517135 with CP (p = 0.044) at the genotype level, and the association was greatly strengthened when we focused on the subgroup of CP infants who suffered from hypoxic-ischemic encephalopathy (HIE) after birth, with p = 0.003 (OR = 0.558) at the allele level and p = 0.007 at the genotype level, indicating a risk-associated role of the T allele of the SNP rs6517135 under HIE conditions. The haplotype CTTG for rs6517135-rs1005573-rs6517137-rs9653711 in OLIG2 was also significantly associated with the occurrence of CP in infants with HIE (p = 0.01, OR = 0.521). Our results indicate that in the Han Chinese population, the polymorphisms of OLIG2 were associated with CP, especially in patients who had suffered HIE injury. This finding could be used to develop personalized care for infants with high susceptibility to CP.

Oligodendrocyte precursor cells in the mouse optic nerve originate in the preoptic area

The present study aims to examine the origin of oligodendrocyte progenitor cells (OPCs) in the mouse optic nerve (ON) by labeling OPCs in the fetal forebrain. The labeling of OPCs in the ON was performed by injection of a retrovirus vector carrying the lacZ gene into the lateral ventricle, or by inducible Cre/loxP of Olig2-positive cells. The retrovirus labeling revealed that ventricular zone-derived cells of the fetal forebrain relocated to the ON and differentiated into oligodendrocytes. In addition, lineage tracing of Olig2-positive cells and whole-mount staining of PDGFRα-positive cells demonstrated that OPCs appeared by E12.5 in the preoptic area, and spread caudally to enter the ON. Our results also suggest that OPCs generated during the early stage are depleted from the ON after maturation.

Oligodendrocyte generation during mouse development

Oligodendrocytes (OLs) are glial cells, which generate myelin in the central nervous system. Their interesting developmental features attract many neurobiologists eager to study cell differentiation, gene expression regulation, or dynamic morphogenesis. Their primary role in protecting the axons has major impacts in the medical research field: in multiple sclerosis, a demyelinating disease in which remyelination is blocked. Oligodendrogenesis is involved in higher brain function including motor skill learning and cognitive function. Here, we review advances in the research on OL development and highlight areas where questions remain to be answered in both developmental biology and neurobiology related aspects.

Disruption of neurogenesis and cortical development in transgenic mice misexpressing Olig2, a gene in the Down syndrome critical region

The basic helix-loop-helix (bHLH) transcription factor Olig2 is crucial for mammalian central nervous system development. Human ortholog OLIG2 is located in the Down syndrome critical region in trisomy 21. To investigate the effect of Olig2 misexpression on brain development, we generated a developmentally regulated Olig2-overexpressing transgenic line with a Cre/loxP system. The transgenic mice with Olig2 misexpression in cortical neural stem/progenitor cells exhibited microcephaly, cortical dyslamination, hippocampus malformation, and profound motor deficits. Ectopic misexpression of Olig2 impaired cortical progenitor proliferation and caused precocious cell cycle exit. Massive neuronal cell death was detected in the developing cortex of Olig2-misexpressing mice. In addition, Olig2 misexpression led to a significant downregulation of neuronal specification factors including Ngn1, Ngn2 and Pax6, and a defect in cortical neurogenesis. Chromatin-immunoprecipitation and sequencing (ChIP-Seq) analysis indicates that Olig2 directly targets the promoter and/or enhancer regions of Nfatc4, Dscr1/Rcan1 and Dyrk1a, the critical neurogenic genes that contribute to Down syndrome phenotypes, and inhibits their expression. Together, our study suggests that Olig2 misexpression in neural stem cells elicits neurogenesis defects and neuronal cell death, which may contribute to developmental disorders including Down syndrome, where OLIG2 is triplicated on chromosomal 21.

Oligodendroglial Development: New Roles for Chromatin Accessibility

In the central nervous system, the generation of mature oligodendrocytes from their progenitors is a critical step in myelination, which is essential for normal nervous system function. Thus, understanding the regulatory mechanism underlying oligodendroglial development is of great importance, especially for the development of new therapeutic strategies that promote remyelination in demyelinating diseases, such as multiple sclerosis. Previous studies have focused on genetic patterns and revealed a network of cell signaling pathways and related transcription factors involved in oligodendroglial lineage development. Recently, epigenetic regulation, which refers to regulation of gene expression by adjusting the environment of the genes has been shown to play a profound role during oligodendroglial development. In this review, we summarize the recent data demonstrating the effects of chromatin modification and remodeling in regulating oligodendroglial development and discuss the use of high-throughput analysis and bio-informatics in future studies.

Development of the prethalamus is crucial for thalamocortical projection formation and is regulated by Olig2

Thalamocortical axons (TCAs) pass through the prethalamus in the first step of their neural circuit formation. Although it has been supposed that the prethalamus is an intermediate target for thalamocortical projection formation, much less is known about the molecular mechanisms of this targeting. Here, we demonstrated the functional implications of the prethalamus in the formation of this neural circuit. We show that Olig2 transcription factor, which is expressed in the ventricular zone (VZ) of prosomere 3, regulates prethalamus formation, and loss of Olig2 results in reduced prethalamus size in early development, which is accompanied by expansion of the thalamic eminence (TE). Extension of TCAs is disorganized in the Olig2-KO dorsal thalamus, and initial elongation of TCAs is retarded in the Olig2-KO forebrain. Microarray analysis demonstrated upregulation of several axon guidance molecules, including Epha3 and Epha5, in the Olig2-KO basal forebrain. In situ hybridization showed that the prethalamus in the wild type excluded the expression of Epha3 and Epha5, whereas loss of Olig2 resulted in reduction of this Ephas-negative area and the corresponding expansion of the Ephas-positive TE. Dissociated cultures of thalamic progenitor cells demonstrated that substrate-bound EphA3 suppresses neurite extension from dorsal thalamic neurons. These results indicate that Olig2 is involved in correct formation of the prethalamus, which leads to exclusion of the EphA3-expressing region and is crucial for proper TCA formation. Our observation is the first report showing the molecular mechanisms underlying how the prethalamus acts on initial thalamocortical projection formation.

Risk variant of oligodendrocyte lineage transcription factor 2 is associated with reduced white matter integrity

The oligodendrocyte lineage transcription factor 2 (OLIG2) regulates the genesis of oligodendrocytes, the brain cells responsible for axonal myelination. Although it has been associated with psychiatric and neurological disorders, the impact of this gene on white matter integrity has never been investigated in humans. Using diffusion tensor imaging, we examined the effect of a single nucleotide polymorphism (rs1059004) in OLIG2 previously associated with reduced gene expression, and with psychiatric disorders on fractional anisotropy in 78 healthy subjects. We found that the risk allele (A) was associated with reduced white matter integrity in the corona radiata bilaterally. This is consistent with evidence that it is a schizophrenia susceptibility gene, and suggests that it may confer increased risk through an effect on neuroanatomical connectivity.

Early activation of microglia triggers long-lasting impairment of adult neurogenesis in the olfactory bulb

Microglia, the innate immune cells of the brain, engulf and eliminate cellular debris during brain injury and disease. Recent observations have extended their roles to the healthy brain, but the functional impact of activated microglia on neural plasticity has so far been elusive. To explore this issue, we investigated the role of microglia in the function of the adult olfactory bulb network in which both sensory afferents and local microcircuits are continuously molded by the arrival of adult-born neurons. We show here that the adult olfactory bulb hosts a large population of resident microglial cells. Deafferentation of the olfactory bulb resulted in a transient activation of microglia and a concomitant reduction of adult olfactory bulb neurogenesis. One day after sensory deafferentation, microglial cells proliferate in the olfactory bulb, and their numbers peaked at day 3, and reversed at day 7 after lesion. Similar lesions performed on immunodeficient mice demonstrate that the both innate and adaptive lymphocyte responses are dispensable for the lesion-induced microglial proliferation and activation. In contrast, when mice were treated with an antiinflammatory drug to prevent microglial activation, olfactory deafferentation did not reduce adult neurogenesis, showing that activated microglial cells per se, and not the lack of sensory experience, relates to the survival of adult-born neurons. We conclude that the status of the resident microglia in the olfactory bulb is an important factor directly regulating the survival of immature adult-born neurons.

Ablation of proliferating cells in the CNS exacerbates motor neuron disease caused by mutant superoxide dismutase

Proliferation of glia and immune cells is a common pathological feature of many neurodegenerative diseases including amyotrophic lateral sclerosis (ALS). Here, to investigate the role of proliferating cells in motor neuron disease, SOD1(G93A) transgenic mice were treated intracerebroventicularly (i.c.v.) with the anti-mitotic drug cytosine arabinoside (Ara-C). I.c.v. delivery of Ara-C accelerated disease progression in SOD1(G93A) mouse model of ALS. Ara-C treatment caused substantial decreases in the number of microglia, NG2+ progenitors, Olig2+ cells and CD3+ T cells in the lumbar spinal cord of symptomatic SOD1(G93A) transgenic mice. Exacerbation of disease was also associated with significant alterations in the expression inflammatory molecules IL-1β, IL-6, TGF-β and the growth factor IGF-1.

Tcf3 function is required for the inhibition of oligodendroglial fate specification in the spinal cord of zebrafish embryos

The generation of various subtypes of neurons and glial cells at the right time and place is crucial for the proper development of the vertebrate CNS. Although the mechanisms and factors for the regulation of neuronal diversity in the CNS have been well studied, the mechanisms regulating the sequential production of neuronal and glial cells from neural precursors remain poorly understood. This study shows that Tcf3, a member of the Lef/Tcf family of proteins, is required to inhibit the premature oligodendroglial fate specification of spinal cord precursors using the transgenic zebrafish, which expresses a dominant repressor form of Tcf3 under the control of a heat-shock inducible promoter. In addition, the data revealed that Tcf3 function in oligodendroglial fate specification is mediated independently of canonical Wnt signaling. Altogether, these results show a novel function for Tcf3 in regulating the timing of oligodendroglial fate specification in the spinal cord.

Role of transcription factors in neurogenesis after cerebral ischemia

Studies have revealed that the adult mammalian brain has the capacity to regenerate some neurons after cerebral ischemia. And this perspective on neurogenesis adds to the conceptual framework for strategies for the repair of ischemia-induced brain injury, that is, if the effect of ischemia-induced neurogenesis is enhanced, then the recovery of brain function after stroke can be promoted. Neurogenesis is a multistep process that requires the proliferation of neural stem/progenitor cells, migration and that new cells differentiate, survive and integrate into existing neural networks. For that to occur, the same concerted action of various factors is needed, especially transcription factors which regulate the expression of many moleculars and interact with them to promote neurogenesis. This review article gives a brief overview of some transcription factors (NF-κB, Hes, STAT3, AP-1, CREB, HIF1, Pax6, Tcf/Lef, Gli, Sox2, Olig2, Dlx2, TLX, Bmi-1) in ischemia-induced neurogenesis.

Spontaneous reactive astrogliosis in the dentate gyrus of Bax-deficient mice

Astrocytes play critical roles in many aspects of brain functions via modulation of neurotransmission, metabolism, and structural remodeling in response to physiological or pathological stimuli. Activation of astrocytes is a common phenomenon in many brain pathologies such as stroke, trauma, and neurodegenerative diseases. In this study, we found that gene deletion of the pro-apoptotic gene Bax (Bax-knockout) resulted in a spontaneous reactive astrogliosis in the dentate gyrus, as evidenced by the increased number/volume of astrocytes and cytoplasmic localization of the Olig2 protein. On the other hand, there was no evidence for microglial activation in the dentate gyrus of Bax-knockout mice. Previously, we reported that Bax-knockout mice failed to execute programmed cell death of adult-produced neurons, but the surplus neurons eventually impaired normal synaptic connections and dendritic arborization of dentate gyrus neurons. Therefore, we propose that the reactive astrocytes in the Bax knockout mice may play a role in tissue remodeling of the dentate gyrus following a failure in the programmed cell death of adult-produced neurons.

Control of neuronal migration through rostral migration stream in mice

During the nervous system development, immature neuroblasts have a strong potential to migrate toward their destination. In the adult brain, new neurons are continuously generated in the neurogenic niche located near the ventricle, and the newly generated cells actively migrate toward their destination, olfactory bulb, via highly specialized migratory route called rostral migratory stream (RMS). Neuroblasts in the RMS form chains by their homophilic interactions, and the neuroblasts in chains continually migrate through the tunnels formed by meshwork of astrocytes, glial tube. This review focuses on the development and structure of RMS and the regulation of neuroblast migration in the RMS. Better understanding of RMS migration may be crucial for improving functional replacement therapy by supplying endogenous neuronal cells to the injury sites more efficiently.