Distinct expression patterns for type II topoisomerases IIA and IIB in the early foetal human telencephalon

New Views of the DNA Repair Protein Ataxia-Telangiectasia Mutated in Central Neurons: Contribution in Synaptic Dysfunctions of Neurodevelopmental and Neurodegenerative Diseases

Ataxia-Telangiectasia Mutated (ATM) is a serine/threonine protein kinase principally known to orchestrate DNA repair processes upon DNA double-strand breaks (DSBs). Mutations in the Atm gene lead to Ataxia-Telangiectasia (AT), a recessive disorder characterized by ataxic movements consequent to cerebellar atrophy or dysfunction, along with immune alterations, genomic instability, and predisposition to cancer. AT patients show variable phenotypes ranging from neurologic abnormalities and cognitive impairments to more recently described neuropsychiatric features pointing to symptoms hardly ascribable to the canonical functions of ATM in DNA damage response (DDR). Indeed, evidence suggests that cognitive abilities rely on the proper functioning of DSB machinery and specific synaptic changes in central neurons of ATM-deficient mice unveiled unexpected roles of ATM at the synapse. Thus, in the present review, upon a brief recall of DNA damage responses, we focus our attention on the role of ATM in neuronal physiology and pathology and we discuss recent findings showing structural and functional changes in hippocampal and cortical synapses of AT mouse models. Collectively, a deeper knowledge of ATM-dependent mechanisms in neurons is necessary not only for a better comprehension of AT neurological phenotypes, but also for a higher understanding of the pathological mechanisms in neurodevelopmental and degenerative disorders involving ATM dysfunctions.

A custom-made AAV1 variant (AAV1-T593K) enables efficient transduction of Japanese quail neurons in vitro and in vivo

The widespread use of rodents in neuroscience has prompted the development of optimized viral variants for transduction of brain cells, in vivo. However, many of the viruses developed are less efficient in other model organisms, with birds being among the most resistant to transduction by current viral tools. Resultantly, the use of genetically-encoded tools and methods in avian species is markedly lower than in rodents; likely holding the field back. We sought to bridge this gap by developing custom viruses towards the transduction of brain cells of the Japanese quail. We first develop a protocol for culturing primary neurons and glia from quail embryos, followed by characterization of cultures via immunostaining, single cell mRNA sequencing, patch clamp electrophysiology and calcium imaging. We then leveraged the cultures for the rapid screening of various viruses, only to find that all yielded poor to no infection of cells in vitro. However, few infected neurons were obtained by AAV1 and AAV2. Scrutiny of the sequence of the AAV receptor found in quails led us to rationally design a custom-made AAV variant (AAV1-T593K; AAV1*) that exhibits improved transduction efficiencies in vitro and in vivo (14- and five-fold, respectively). Together, we present unique culturing method, transcriptomic profiles of quail's brain cells and a custom-tailored AAV1 for transduction of quail neurons in vitro and in vivo.

Human cortical spheroids with a high diversity of innately developing brain cell types

BACKGROUND

Three-dimensional (3D) human brain spheroids are instrumental to study central nervous system (CNS) development and (dys)function. Yet, in current brain spheroid models the limited variety of cell types hampers an integrated exploration of CNS (disease) mechanisms.

METHODS

Here we report a 5-month culture protocol that reproducibly generates H9 embryonic stem cell-derived human cortical spheroids (hCSs) with a large cell-type variety.

RESULTS

We established the presence of not only neuroectoderm-derived neural progenitor populations, mature excitatory and inhibitory neurons, astrocytes and oligodendrocyte (precursor) cells, but also mesoderm-derived microglia and endothelial cell populations in the hCSs via RNA-sequencing, qPCR, immunocytochemistry and transmission electron microscopy. Transcriptomic analysis revealed resemblance between the 5-months-old hCSs and dorsal frontal rather than inferior regions of human fetal brains of 19-26 weeks of gestational age. Pro-inflammatory stimulation of the generated hCSs induced a neuroinflammatory response, offering a proof-of-principle of the applicability of the spheroids.

CONCLUSIONS

Our protocol provides a 3D human brain cell model containing a wide variety of innately developing neuroectoderm- as well as mesoderm-derived cell types, furnishing a versatile platform for comprehensive examination of intercellular CNS communication and neurological disease mechanisms.

"Ficus johannis Boiss. leaves ethanolic extract ameliorate streptozotocin-induced diabetes in rats by upregulating the expressions of GCK, GLUT4, and IGF and downregulating G6P"

The leaves of Ficus johannis Boiss (F. johannis), commonly known as Fig tree, Anjir, and Teen, are used by the folk medicinal practitioners in Iran for controlling hyperglycemia in diabetic patients. This study investigated the pharmacological basis for antidiabetic effect of the ethanolic extract of F. johannis leaves using in vitro and in vivo experimental models. Qualitative screening of phytochemicals, estimation of total phenolic and flavonoid contents, and in vitro antioxidant and α-amylase inhibition assays were performed. Moreover, the High-performance liquid chromatography (HPLC) quantification, acute toxicity, glucose tolerance, and in vivo antidiabetic effect along with the evaluation of gene expressions involved in diabetes mellitus were carried out. Significant quantities of phenolic (71.208 ± 2.89 mgg^-1 GAE) and flavonoid (26.38 ± 3.53 mgg^-1 QE) were present. Inhibitory concentration (IC₅₀) of the plant extract exhibited an excellent in vitro antioxidant (IC₅₀ = 33.81 µg/mL) and α-amylase (IC₅₀ = 12.18 µg/mL) inhibitory potential. The HPLC analysis confirmed the gallic acid (257.79 mgg^-1) as main constituent of the extract followed by kaempferol (22.86 mgg^-1), myricetin (0.16 mgg^-1), and quercetin (3.22 mgg^-1). Ethanolic extract displayed glucose tolerance in normo-glycemic rats. Streptozotocin-induced hyperglycemia declined dose dependently in the extract treated rats with improvement in lipid profile and liver and renal function biomarkers. The F. johannis-treated groups showed an increase in mRNA expressions of glucose transporter 4 (GLUT-4), glucokinase, insulin growth like factor 1 and peroxisomal proliferator activating receptor gamma in pancreas. However, the Glucose-6-phosphatase was downregulated. Present study suggests that the ethanolic extract of F. johannis leaves demonstrates a good anti-diabetic profile by improving insulin sensitivity, GLUT-4 translocation, and carbohydrate metabolism while inhibiting lipogenesis.

Topoisomerase IIA in adult NSCs regulates SVZ neurogenesis by transcriptional activation of Usp37

Topoisomerase IIA (TOP2a) has traditionally been known as an important nuclear enzyme that resolves entanglements and relieves torsional stress of DNA double strands. However, its function in genomic transcriptional regulation remains largely unknown, especially during adult neurogenesis. Here, we show that TOP2a is preferentially expressed in neurogenic niches in the brain of adult mice, such as the subventricular zone (SVZ). Conditional knockout of Top2a in adult neural stem cells (NSCs) of the SVZ significantly inhibits their self-renewal and proliferation, and ultimately reduces neurogenesis. To gain insight into the molecular mechanisms by which TOP2a regulates adult NSCs, we perform RNA-sequencing (RNA-Seq) plus chromatin immunoprecipitation sequencing (ChIP-Seq) and identify ubiquitin-specific protease 37 (Usp37) as a direct TOP2a target gene. Importantly, overexpression of Usp37 is sufficient to rescue the impaired self-renewal ability of adult NSCs caused by Top2a knockdown. Taken together, this proof-of-principle study illustrates a TOP2a/Usp37-mediated novel molecular mechanism in adult neurogenesis, which will significantly expand our understanding of the function of topoisomerase in the adult brain.

Upregulation of CCNB2 and Its Perspective Mechanisms in Cerebral Ischemic Stroke and All Subtypes of Lung Cancer: A Comprehensive Study

Cyclin B2 (CCNB2) belongs to type B cell cycle family protein, which is located on chromosome 15q22, and it binds to cyclin-dependent kinases (CDKs) to regulate their activities. In this study, 103 high-throughput datasets related to all subtypes of lung cancer (LC) and cerebral ischemic stroke (CIS) with the data of CCNB2 expression were collected. The analysis of standard mean deviation (SMD) and summary receiver operating characteristic (SROC) reflecting expression status demonstrated significant up-regulation of CCNB2 in LC and CIS (Lung adenocarcinoma: SMD = 1.40, 95%CI [0.98–1.83], SROC = 0.92, 95%CI [0.89–0.94]. Lung squamous cell carcinoma: SMD = 2.56, 95%CI [1.64–3.48]. SROC = 0.97, 95%CI [0.95–0.98]. Lung small cell carcinoma: SMD = 3.01, 95%CI [2.01–4.01]. SROC = 0.98, 95%CI [0.97–0.99]. CIS: SMD = 0.29, 95%CI [0.05–0.53], SROC = 0.68, 95%CI [0.63–0.71]). Simultaneously, protein-protein interaction (PPI) analysis indicated that CCNB2 is the hub molecule of crossed high-expressed genes in CIS and LC. Through Multiscale embedded gene co-expression network analysis (MEGENA), a gene module of CIS including 76 genes was obtained and function enrichment analysis of the CCNB2 module genes implied that CCNB2 may participate in the processes in the formation of CIS and tissue damage caused by CIS, such as “cell cycle,” “protein kinase activity,” and “glycosphingolipid biosynthesis.” Afterward, via single-cell RNA-seq analysis, CCNB2 was found up-regulated on GABAergic neurons in brain organoids as well as T cells expressing proliferative molecules in LUAD. Concurrently, the expression of CCNB2 distributed similarly to TOP2A as a module marker of cell proliferation in cell cluster. These findings can help in the field of the pathogenesis of LC-related CIS and neuron repair after CIS damage.

TOP2B Is Required to Maintain the Adrenergic Neural Phenotype and for ATRA-Induced Differentiation of SH-SY5Y Neuroblastoma Cells

The neuroblastoma cell line SH-SY5Y is widely used to study retinoic acid (RA)-induced gene expression and differentiation and as a tool to study neurodegenerative disorders. SH-SY5Y cells predominantly exhibit adrenergic neuronal properties, but they can also exist in an epigenetically interconvertible alternative state with more mesenchymal characteristics; as a result, these cells can be used to study gene regulation circuitry controlling neuroblastoma phenotype. Using a combination of pharmacological inhibition and targeted gene inactivation, we have probed the requirement for DNA topoisomerase IIB (TOP2B) in RA-induced gene expression and differentiation and in the balance between adrenergic neuronal versus mesenchymal transcription programmes. We found that expression of many, but not all genes that are rapidly induced by ATRA in SH-SY5Y cells was significantly reduced in the TOP2B null cells; these genes include BCL2, CYP26A1, CRABP2, and NTRK2. Comparing gene expression profiles in wild-type versus TOP2B null cells, we found that long genes and genes expressed at a high level in WT SH-SY5Y cells were disproportionately dependent on TOP2B. Notably, TOP2B null SH-SY5Y cells upregulated mesenchymal markers vimentin (VIM) and fibronectin (FN1) and components of the NOTCH signalling pathway. Enrichment analysis and comparison with the transcription profiles of other neuroblastoma-derived cell lines supported the conclusion that TOP2B is required to fully maintain the adrenergic neural-like transcriptional signature of SH-SY5Y cells and to suppress the alternative mesenchymal epithelial-like epigenetic state.

Interneuron origin and molecular diversity in the human fetal brain

Precise generation of excitatory neurons and inhibitory interneurons is crucial for proper formation and function of neural circuits in the mammalian brain. Because of the size and complexity of the human brain, it is a challenge to reveal the rich diversity of interneurons. To decipher origin and diversity of interneurons in the human fetal subpallium, here we show molecular features of diverse subtypes of interneuron progenitors and precursors by conducting single-cell RNA sequencing and in situ sequencing. Interneuron precursors in the medial and lateral ganglionic eminence simultaneously procure temporal and spatial identity through expressing a combination of specific sets of RNA transcripts. Acquisition of various interneuron subtypes in adult human brains occurs even at fetal stages. Our study uncovers complex molecular signatures of interneuron progenitors and precursors in the human fetal subpallium and highlights the logic and programs in the origin and lineage specification of various interneurons.

TOP2B's contributions to transcription

Transcription is regulated and mediated by multiprotein complexes in a chromatin context. Transcription causes changes in DNA topology which is modulated by DNA topoisomerases, enzymes that catalyse changes in DNA topology via transient breaking and re-joining of one or both strands of the phosphodiester backbone. Mammals have six DNA topoisomerases, this review focuses on one, DNA topoisomerase II beta (TOP2B). In the absence of TOP2B transcription of many developmentally regulated genes is altered. Long genes seem particularly susceptible to the lack of TOP2B. Biochemical studies of the role of TOP2B in transcription regulated by ligands such as nuclear hormones, growth factors and insulin has revealed PARP1 associated with TOP2B and also PRKDC, XRCC5 and XRCC6. Analysis of publicly available databases of protein interactions confirms these interactions and illustrates interactions with other key transcriptional regulators including TRIM28. TOP2B has been shown to interact with proteins involved in chromosome organisation including CTCF and RAD21. Comparison of publicly available Chip-seq datasets reveals the location at which these proteins interact with genes. The availability of resources such as large datasets of protein-protein interactions, e.g. BioGrid and IntAct and protein-DNA interactions such as Chip-seq in GEO enables scientists to extend models and propose new hypotheses.

Generation of striatal neurons from human induced pluripotent stem cells by controlling extrinsic signals with small molecules

Human induced pluripotent stem cells (hiPSCs) are powerful tools for modeling human brain development and treating neurodegenerative diseases. Here we established a robust protocol with high scalability for generating striatal medium spiny neurons (MSNs) from hiPSCs using small molecules under two- and three-dimensional culture conditions. Using this protocol, GSH2⁺ lateral ganglionic eminence (LGE) progenitors were generated in two-dimensional culture by Sonic hedgehog signaling activation using purmorphamine, WNT signaling inhibition using XAV939, and dual-SMAD inhibition using LDN193189 and A83-01. Quantitative PCR analysis revealed sequential expression of LGE and striatal genes during differentiation. These LGE progenitors subsequently gave rise to DARPP32⁺ MSNs exhibiting spontaneous and evoked monophasic spiking activity. Applying this protocol in three-dimensional culture, we generated striatal neurospheres with gene expression profiles and cell layer organization resembling that of the developing striatum, including distinct ventricular and subventricular zones and DARPP32⁺ neurons at the surface. This protocol provides a useful experimental model for studying striatal development and yields cells potentially applicable for regenerative medicine to treat striatum-related disorders such as Huntington's disease.

Fusion of single-cell transcriptome and DNA-binding data, for genomic network inference in cortical development

BACKGROUND

Network models are well-established as very useful computational-statistical tools in cell biology. However, a genomic network model based only on gene expression data can, by definition, only infer gene co-expression networks. Hence, in order to infer gene regulatory patterns, it is necessary to also include data related to binding of regulatory factors to DNA.

RESULTS

We propose a new dynamic genomic network model, for inferring patterns of genomic regulatory influence in dynamic processes such as development. Our model fuses experiment-specific gene expression data with publicly available DNA-binding data. The method we propose is computationally efficient, and can be applied to genome-wide data with tens of thousands of transcripts. Thus, our method is well suited for use as an exploratory tool for genome-wide data. We apply our method to data from human fetal cortical development, and our findings confirm genomic regulatory patterns which are recognised as being fundamental to neuronal development.

CONCLUSIONS

Our method provides a mathematical/computational toolbox which, when coupled with targeted experiments, will reveal and confirm important new functional genomic regulatory processes in mammalian development.

Full function of exon junction complex factor, Rbm8a, is critical for interneuron development

The formation of the nervous system requires a balance between proliferation, differentiation, and migration of neural progenitors (NPs). Mutations in genes regulating development impede neurogenesis and lead to neuropsychiatric diseases, including autism spectrum disorders (ASDs) and schizophrenia (SZ). Recently, mutations in nonsense-mediated mRNA decay genes have been associated with ASDs, intellectual disability (ID), and SZ. Here, we examine the function of a gene in the exon junction complex, Rbm8a, in the cortical development. When Rbm8a is selectively knocked out in neural stem cells, the resulting mice exhibit microcephaly, early postnatal lethality, and altered distribution of excitatory neurons in the neocortex. Moreover, Rbm8a haploinsufficiency in the central nervous system decreases cell proliferation in the ganglionic eminences. Parvalbumin+ and neuropeptide Y+ interneurons in the cortex are significantly reduced, and distribution of interneurons are altered. Consistently, neurons in the cortex of conditional knockout (cKO) mice show a significant decrease in GABA frequency. Transcriptomic analysis revealed differentially expressed genes enriched in telencephalon development and mitosis. To further investigate the role of Rbm8a in interneuron differentiation, conditional KO of Rbm8a in NKX2.1 interneuron progenitor cells reduces progenitor proliferation and alters interneuron distributions. Taken together, these data reveal a critical role of Rbm8a in interneuron development, and establish that perturbation of this gene leads to profound cortical deficits.

Deciphering the Proteome Dynamics during Development of Neurons Derived from Induced Pluripotent Stem Cells

Neuronal development is a complex multistep process that shapes neurons by progressing though several typical stages, including axon outgrowth, dendrite formation, and synaptogenesis. Knowledge of the mechanisms of neuronal development is mostly derived from the study of animal models. Advances in stem cell technology now enable us to generate neurons from human induced pluripotent stem cells (iPSCs). Here we provide a mass spectrometry-based quantitative proteomic signature of human iPSC-derived neurons, i.e., iPSC-derived induced glutamatergic neurons and iPSC-derived motor neurons, throughout neuronal differentiation. Tandem mass tag 10-plex labeling was carried out to perform proteomic profiling of cells at different time points. Our analysis reveals significant expression changes (FDR < 0.001) of several key proteins during the differentiation process, e.g., proteins involved in the Wnt and Notch signaling pathways. Overall, our data provide a rich resource of information on protein expression during human iPSC neuron differentiation.

Contributions of DNA Damage to Alzheimer's Disease

Alzheimer’s disease (AD) is the most common type of neurodegenerative disease. Its typical pathology consists of extracellular amyloid-β (Aβ) plaques and intracellular tau neurofibrillary tangles. Mutations in the APP, PSEN1, and PSEN2 genes increase Aβ production and aggregation, and thus cause early onset or familial AD. Even with this strong genetic evidence, recent studies support AD to result from complex etiological alterations. Among them, aging is the strongest risk factor for the vast majority of AD cases: Sporadic late onset AD (LOAD). Accumulation of DNA damage is a well-established aging factor. In this regard, a large amount of evidence reveals DNA damage as a critical pathological cause of AD. Clinically, DNA damage is accumulated in brains of AD patients. Genetically, defects in DNA damage repair resulted from mutations in the BRAC1 and other DNA damage repair genes occur in AD brain and facilitate the pathogenesis. Abnormalities in DNA damage repair can be used as diagnostic biomarkers for AD. In this review, we discuss the association, the causative potential, and the biomarker values of DNA damage in AD pathogenesis.

A de novo TOP2B variant associated with global developmental delay and autism spectrum disorder

Background

TOP2B encodes type II topoisomerase beta, which controls topological changes during DNA transcription. TOP2B is expressed in the developing nervous system and is involved in brain development and neural differentiation. Recently, a de novo missense TOP2B variant (c.187C>T) has been identified in an individual with neurodevelopmental disorder (NDD). However, the association between TOP2B variants and NDDs remains uncertain.

Methods

Trio‐based whole‐exome sequencing was performed on a 7‐year‐old girl, presenting muscle hypotonia, stereotypic hand movements, epilepsy, global developmental delay, and autism spectrum disorder. Brain magnetic resonance images were normal. She was unable to walk independently and spoke no meaningful words.

Results

We found a de novo variant in TOP2B (NM_001330700.1:c.187C>T, p.(His63Tyr)), which is identical to the previous case. The clinical features of the two individuals with the c.187C>T variant overlapped.

Conclusion

Our study supports the finding that TOP2B variants may cause NDDs.

Smoothed Potential MD Simulations for Dissociation Kinetics of Etoposide To Unravel Isoform Specificity in Targeting Human Topoisomerase II

Human type II topoisomerases (TopoII) are essential for controlling DNA topology within the cell. For this reason, there are a number of TopoII-targeted anticancer drugs that act by inducing DNA cleavage mediated by both TopoII isoforms (TopoIIα and TopoIIβ) in cells. However, recent studies suggest that specific poisoning of TopoIIα may be a safer strategy for treating cancer. This is because poisoning of TopoIIβ appears to be linked to the generation of secondary leukemia in patients. We recently reported that enzyme-mediated DNA cleavage complexes (in which TopoII is covalently linked to the cleaved DNA during catalysis) formed in the presence of the anticancer drug etoposide persisted approximately 3-fold longer with TopoIIα than TopoIIβ. Notably, enhanced drug-target residence time may reduce the adverse effects of specific TopoIIα poisons. However, it is still not clear how to design drugs that are specific for the α isoform. In this study, we report the results of classical molecular dynamics (MD) simulations to comparatively analyze the molecular interactions formed within the TopoII/DNA/etoposide complex with both isoforms. We also used smoothed potential MD to estimate etoposide dissociation kinetics from the two isoform complexes. These extensive classical and enhanced sampling simulations revealed stabilizing interactions of etoposide with two serine residues (Ser763 and Ser800) in TopoIIα. These interactions are missing in TopoIIβ, where both amino acids are alanine residues. This may explain the greater persistence of etoposide-stabilized cleavage complexes formed with Topo TopoIIα. These findings could be useful for the rational design of specific TopoIIα poisons.

Expression of ventral telencephalon transcription factors ASCL1 and DLX2 in the early fetal human cerebral cortex

In rodent ventral telencephalon, diffusible morphogens induce expression of the proneural transcription factor ASCL1, which in turn induces expression of the transcription factor DLX2 that controls differentiation of cortical interneuron precursors and their tangential migration to the cerebral cortex. RNAseq analysis of human fetal samples of dorsal telencephalon revealed consistently high cortical expression of ASCL1 and increasing expression of DLX2 between 7.5 and 17 post-conceptional weeks (PCW). We explored whether cortical expression of these genes represented a population of intracortically derived interneuron precursors. Immunohistochemistry revealed an ASCL1+ /DLX2+ population of progenitor cells in the human ganglionic eminences between 6.5 and 12 PCW, but in the cortex there also existed a population of ASCL1+ /DLX2- progenitors in the subventricular zone (SVZ) that largely co-expressed cortical markers PAX6 or TBR2, although a few ASCL1+ /PAX6- progenitors were observed in the ventricular zone (VZ) and ASCL1+ cells expressing the interneuron marker GAD67 were present in the SVZ. Although rare in the VZ, DLX2+ cells progressively increased in number between 8 and 12 PCW across the cortical wall and the majority co-expressed LHX6 and originated either in the MGE, migrating to the lateral cortex, or from the septum, populating the medial wall. A minority co-expressed COUP-TFII, which identifies cells from the caudal ganglionic eminence (CGE). By 19 PCW, a significant increase in expression of DLX2 and ASCL1 was observed in the cortical VZ with a small proportion expressing both proteins. The DLX2+ cells did not co-express a cell division marker, so were not progenitors. The majority of DLX2+ cells throughout the cortical plate expressed COUP-TFII rather than LHX6+ . As the VZ declined as a proliferative zone it appeared to be re-defined as a migration pathway for COUP-TFII+ /DLX2+ interneurons from CGE to cortex. Therefore, in developing human cortex, ASCL1 expression predominantly marks a population of intermediate progenitors giving rise to glutamatergic neurons. DLX2 expression predominantly defines post-mitotic interneuron precursors.

Mutations in TOP2B cause autosomal-dominant hereditary hearing loss via inhibition of the PI3K-Akt signalling pathway

Hereditary hearing impairment is a clinically and genetically heterogeneous disease. Whole-exome sequencing was performed on seven affected and six unaffected members in a large Chinese family with autosomal-dominant nonsyndromic hearing loss. The pathogenic variant of the gene encoding human topoisomerase IIβ TOP2B (c.G4837C:p.D1613H) was cosegregated with hearing loss in this pedigree and another two variants of TOP2B were detected in 66 sporadic patients with hearing loss. top2b knockdown led to significant defects in zebrafish inner ears and caused downregulation of akt which resulted in inactivation of PI3K-Akt signalling. As a result, supporting cell and hair cell numbers were reduced through inhibition of the PI3K-Akt pathway. Therefore, we hypothesized that mutations in TOP2B can cause autosomal-dominant nonsyndromic hearing impairment through inhibition of the PI3K-Akt signalling pathway. DATABASE: The whole-exome sequence data in the study are available at the Sequence Read Archive database (NCBI) under the accession numbers SRR9050868, SRR9050867, SRR90508676, SRR90508675, SRR90508674, SRR90508673, SRR90508672, SRR90508671, SRR90508679, SRR90508670, SRR9050859. SRR9050858 and SRR9050857, respectively.

Thalamocortical Afferents Innervate the Cortical Subplate much Earlier in Development in Primate than in Rodent

The current model, based on rodent data, proposes that thalamocortical afferents (TCA) innervate the subplate towards the end of cortical neurogenesis. This implies that the laminar identity of cortical neurons is specified by intrinsic instructions rather than information of thalamic origin. In order to determine whether this mechanism is conserved in the primates, we examined the growth of thalamocortical (TCA) and corticofugal afferents in early human and monkey fetal development. In the human, TCA, identified by secretagogin, calbindin, and ROBO1 immunoreactivity, were observed in the internal capsule of the ventral telencephalon as early as 7-7.5 PCW, crossing the pallial/subpallial boundary (PSB) by 8 PCW before the calretinin immunoreactive corticofugal fibers do. Furthermore, TCA were observed to be passing through the intermediate zone and innervating the presubplate of the dorsolateral cortex, and already by 10-12 PCW TCAs were occupying much of the cortex. Observations at equivalent stages in the marmoset confirmed that this pattern is conserved across primates. Therefore, our results demonstrate that in primates, TCAs innervate the cortical presubplate at earlier stages than previously demonstrated by acetylcholinesterase histochemistry, suggesting that pioneer thalamic afferents may contribute to early cortical circuitry that can participate in defining cortical neuron phenotypes.

TOP2B: The First Thirty Years

Type II DNA topoisomerases (EC 5.99.1.3) are enzymes that catalyse topological changes in DNA in an ATP dependent manner. Strand passage reactions involve passing one double stranded DNA duplex (transported helix) through a transient enzyme-bridged break in another (gated helix). This activity is required for a range of cellular processes including transcription. Vertebrates have two isoforms: topoisomerase IIα and β. Topoisomerase IIβ was first reported in 1987. Here we review the research on DNA topoisomerase IIβ over the 30 years since its discovery.

The role of E2F1-topoIIβ signaling in regulation of cell cycle exit and neuronal differentiation of human SH-SY5Y cells

This study aims to test the role of E2F1-topoIIβ signaling in neuronal differentiation of SH-SY5Y cells. With retinoic acid (RA) induction, a high percentage of cells were found to be arrested at the G₀/G₁ phase, with decreased levels of cyclinD1, CDK4, phosphorylation status of pRb and E2F1, in addition to an elevated level of p27. The cells were shown to differentiate into neuronal phenotypes characterized by highly expressed neuronal markers, MAP2 and enriched topoIIβ, and remarkable neurite outgrowth. Exogenously forced E2F1 expression with a specific E2F1 plasmid led to suppression of topoIIβ expression and disruption of the neuronal differentiation of SH-SY5Y cells. On further examination using the ChIP assay, we found that E2F1 bound directly to the promoter region of topoIIβ, and its binding ability was inversely correlated with topoIIβ expression in response to RA induction. Thus, our findings suggest that E2F1-topoIIβ signaling may play a role in regulation of cell cycle exit and neuronal differentiation.

Human neural stem cells dispersed in artificial ECM form cerebral organoids when grafted in vivo

Human neural stem cells (hNSC) derived from induced pluripotent stem cells can be differentiated into neurons that could be used for transplantation to repair brain injury. In this study we dispersed such hNSC in a three-dimensional artificial extracellular matrix (aECM) and compared their differentiation in vitro and following grafting into the sensorimotor cortex (SMC) of postnatal day (P)14 rat pups lesioned by localised injection of endothelin-1 at P12. After 10-43 days of in vitro differentiation, a few cells remained as PAX6⁺ neuroprogenitors but many more resembled post-mitotic neurons expressing doublecortin, β-tubulin and MAP2. These cells remained dispersed throughout the ECM, but with extended long processes for over 50 μm. In vivo, by 1 month post grafting, cells expressing human specific markers instead organised into cerebral organoids: columns of tightly packed PAX6 co-expressing progenitor cells arranged around small tubular lumen in rosettes, with a looser network of cells with processes around the outside co-expressing markers of immature neurons including doublecortin, and CTIP2 characteristic of corticofugal neurons. Host cells also invaded the graft including microglia, astrocytes and endothelial cells forming blood vessels. By 10 weeks post-grafting, the organoids had disappeared and the aECM had started to break down with fewer transplanted cells remaining. In vitro, cerebral organoids form in rotating incubators that force oxygen and nutrients to the centre of the structures. We have shown that cerebral organoids can form in vivo; intrinsic factors may direct their organisation including infiltration by host blood vessels.

DNA topoisomerase IIβ stimulates neurite outgrowth in neural differentiated human mesenchymal stem cells through regulation of Rho-GTPases (RhoA/Rock2 pathway) and Nurr1 expression

Background

DNA topoisomerase IIβ (topo IIβ) is known to regulate neural differentiation by inducing the neuronal genes responsible for critical neural differentiation events such as neurite outgrowth and axon guidance. However, the pathways of axon growth controlled by topo IIβ have not been clarified yet. Microarray results of our previous study have shown that topo IIβ silencing in neural differentiated primary human mesenchymal stem cells (hMSCs) significantly alters the expression pattern of genes involved in neural polarity, axonal growth, and guidance, including Rho-GTPases. This study aims to further analyze the regulatory role of topo IIβ on the process of axon growth via regulation of Rho-GTPases.

Methods and results

For this purpose, topo IIβ was silenced in neurally differentiated hMSCs. Cells lost their morphology because of topo IIβ deficiency, becoming enlarged and flattened. Additionally, a reduction in both neural differentiation efficiency and neurite length, upregulation in RhoA and Rock2, downregulation in Cdc42 gene expression were detected. On the other hand, cells were transfected with topo IIβ gene to elucidate the possible neuroprotective effect of topo IIβ overexpression on neural-induced hMSCs. Topo IIβ overexpression prompted all the cells to exhibit neural cell morphology as characterized by longer neurites. RhoA and Rock2 expressions were downregulated, whereas Cdc42 expression was upregulated. Nurr1 expression level correlated with topo IIβ in both topo IIβ-overexpressed and -silenced cells. Furthermore, differential translocation of Rho-GTPases was detected by immunostaining in response to topo IIβ.

Conclusion

Our results suggest that topo IIβ deficiency could give rise to neurodegeneration through dysregulation of Rho-GTPases. However, further in-vivo research is needed to demonstrate if re-regulation of Rho GTPases by topo IIβ overexpression could be a neuroprotective treatment in the case of neurodegenerative diseases.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0859-4) contains supplementary material, which is available to authorized users.

A comparative study of the neural stem cell niche in the adult hypothalamus of human, mouse, rat and gray mouse lemur (Microcebus murinus)

The adult brain contains niches of neural stem cells that continuously add new neurons to selected circuits throughout life. Two niches have been extensively studied in various mammalian species including humans, the subventricular zone of the lateral ventricles and the subgranular zone of the hippocampal dentate gyrus. Recently, studies conducted mainly in rodents have identified a third neurogenic niche in the adult hypothalamus. In order to evaluate whether a neural stem cell niche also exists in the adult hypothalamus in humans, we performed multiple immunofluorescence labeling to assess the expression of a panel of neural stem/progenitor cell (NPC) markers (Sox2, nestin, vimentin, GLAST, GFAP) in the human hypothalamus and compared them with the mouse, rat and a non-human primate species, the gray mouse lemur (Microcebus murinus). Our results show that the adult human hypothalamus contains four distinct populations of cells that express the five NPC markers: (a) a ribbon of small stellate cells that lines the third ventricular wall behind a hypocellular gap, similar to that found along the lateral ventricles, (b) ependymal cells, (c) tanycytes, which line the floor of the third ventricle in the tuberal region, and (d) a population of small stellate cells in the suprachiasmatic nucleus. In the mouse, rat and mouse lemur hypothalamus, co-expression of NPC markers is primarily restricted to tanycytes, and these species lack a ventricular ribbon. Our work thus identifies four cell populations with the antigenic profile of NPCs in the adult human hypothalamus, of which three appear specific to humans.

The Transcription Factors COUP-TFI and COUP-TFII have Distinct Roles in Arealisation and GABAergic Interneuron Specification in the Early Human Fetal Telencephalon

In human telencephalon at 8-12 postconceptional weeks, ribonucleic acid quantitative sequencing and immunohistochemistry revealed cortical chicken ovalbumin upstream promotor-transcription factor 1 (COUP-TFI) expression in a high ventro-posterior to low anterior gradient except for raised immunoreactivity in the anterior ventral pallium. Unlike in mouse, COUP-TFI and SP8 were extensively co-expressed in dorsal sensory neocortex and dorsal hippocampus whereas COUPTFI/COUPTFII co-expression defined ventral temporal cortex and ventral hippocampus. In the ganglionic eminences (GEs) COUP-TFI immunoreactivity demarcated the proliferative zones of caudal GE (CGE), dorsal medial GE (MGE), MGE/lateral GE (LGE) boundary, and ventral LGE whereas COUP-TFII was limited to ventral CGE and the MGE/LGE boundary. Co-labeling with gamma amino butyric acidergic interneuron markers revealed that COUP-TFI was expressed in subpopulations of either MGE-derived (SOX6+) or CGE-derived (calretinin+/SP8+) interneurons. COUP-TFII was mainly confined to CGE-derived interneurons. Twice as many GAD67+ cortical cells co-labeled for COUP-TFI than for COUP-TFII. A fifth of COUP-TFI cells also co-expressed COUP-TFII, and cells expressing either transcription factor followed posterior or anterio-lateral pathways into the cortex, therefore, a segregation of migration pathways according to COUP-TF expression as proposed in mouse was not observed. In cultures differentiated from isolated human cortical progenitors, many cells expressed either COUP-TF and 30% also co-expressed GABA, however no cells expressed NKX2.1. This suggests interneurons could be generated intracortically from progenitors expressing either COUP-TF.

Genetic and Molecular Approaches to Study Neuronal Migration in the Developing Cerebral Cortex

The migration of neuronal cells in the developing cerebral cortex is essential for proper development of the brain and brain networks. Disturbances in this process, due to genetic abnormalities or exogenous factors, leads to aberrant brain formation, brain network formation, and brain function. In the last decade, there has been extensive research in the field of neuronal migration. In this review, we describe different methods and approaches to assess and study neuronal migration in the developing cerebral cortex. First, we discuss several genetic methods, techniques and genetic models that have been used to study neuronal migration in the developing cortex. Second, we describe several molecular approaches to study aberrant neuronal migration in the cortex which can be used to elucidate the underlying mechanisms of neuronal migration. Finally, we describe model systems to investigate and assess the potential toxicity effect of prenatal exposure to environmental chemicals on proper brain formation and neuronal migration.

Neurexins 1-3 Each Have a Distinct Pattern of Expression in the Early Developing Human Cerebral Cortex

Neurexins (NRXNs) are presynaptic terminal proteins and candidate neurodevelopmental disorder susceptibility genes; mutations presumably upset synaptic stabilization and function. However, analysis of human cortical tissue samples by RNAseq and quantitative real-time PCR at 8-12 postconceptional weeks, prior to extensive synapse formation, showed expression of all three NRXNs as well as several potential binding partners. However, the levels of expression were not identical; NRXN1 increased with age and NRXN2 levels were consistently higher than for NRXN3. Immunohistochemistry for each NRXN also revealed different expression patterns at this stage of development. NRXN1 and NRXN3 immunoreactivity was generally strongest in the cortical plate and increased in the ventricular zone with age, but was weak in the synaptogenic presubplate (pSP) and marginal zone. On the other hand, NRXN2 colocalized with synaptophysin in neurites of the pSP, but especially with GAP43 and CASK in growing axons of the intermediate zone. Alternative splicing modifies the role of NRXNs and we found evidence by RNAseq for exon skipping at splice site 4 and concomitant expression of KHDBRS proteins which control this splicing. NRXN2 may play a part in early cortical synaptogenesis, but NRXNs could have diverse roles in development including axon guidance, and intercellular communication between proliferating cells and/or migrating neurons.

Distinct cortical and sub-cortical neurogenic domains for GABAergic interneuron precursor transcription factors NKX2.1, OLIG2 and COUP-TFII in early fetal human telencephalon

The extent of similarities and differences between cortical GABAergic interneuron generation in rodent and primate telencephalon remains contentious. We examined expression of three interneuron precursor transcription factors, alongside other markers, using immunohistochemistry on 8–12 post-conceptional weeks (PCW) human telencephalon sections. NKX2.1, OLIG2, and COUP-TFII expression occupied distinct (although overlapping) neurogenic domains which extended into the cortex and revealed three CGE compartments: lateral, medial, and ventral. NKX2.1 expression was very largely confined to the MGE, medial CGE, and ventral septum confirming that, at this developmental stage, interneuron generation from NKX2.1+ precursors closely resembles the process observed in rodents. OLIG2 immunoreactivity was observed in GABAergic cells of the proliferative zones of the MGE and septum, but not necessarily co-expressed with NKX2.1, and OLIG2 expression was also extensively seen in the LGE, CGE, and cortex. At 8 PCW, OLIG2+ cells were only present in the medial and anterior cortical wall suggesting a migratory pathway for interneuron precursors via the septum into the medial cortex. By 12 PCW, OLIG2+ cells were present throughout the cortex and many were actively dividing but without co-expressing cortical progenitor markers. Dividing COUP-TFII+ progenitor cells were localized to ventral CGE as previously described but were also numerous in adjacent ventral cortex; in both the cases, COUP-TFII was co-expressed with PAX6 in proliferative zones and TBR1 or calretinin in post-mitotic cortical neurons. Thus COUP-TFII+ progenitors gave rise to pyramidal cells, but also interneurons which not only migrated posteriorly into the cortex from ventral CGE but also anteriorly via the LGE.