Haipeng Xue

Oligodendrocyte and astrocyte development in rodents: An in situ and immunohistological analysis during embryonic development†

Lineally related multipotent neuroepithelial cells (NEP), neuronal restricted precursors (NRP), and glial restricted precursors (GRP) have been identified in the spinal cord. To determine the sequence of differentiation and identify lineage and stage‐specific markers, we have examined the spatiotemporal expression of established glial markers during rodent embryonic development and within fetal cell culture. In this report, we show that proliferating stem cells in the developing neural tube do not express any glial markers at E10.5. By E11, however, glial precursors have begun to differentiate and at least two regions of the ventral neural tube containing glial precursor cells can be distinguished, an Nkx2.2/Neurogenin 3 (Ngn3) domain and a platelet‐derived growth factor receptor alpha (PDGFRα)/Olig2/Sox10 domain. Radial glia, as identified by RC1 immunoreactivity, develop in concert with other glial precursors and can be distinguished by their morphology, spatial distribution, and antigen expression. Astrocytes as assessed by glial fibrillary acidic protein (GFAP) immunoreactivity are first detected at E16. A novel dorsal domain of CD44 immunoreactivity that can be distinguished from the more ventral glial precursor domains can be detected as early as E13.5. GLIA 40:25–43, 2002. Published 2002 Wiley‐Liss, Inc.

Creation of Engineered Human Embryonic Stem Cell Lines Using phiC31 Integrase

It has previously been shown that the phage‐derived phiC31 integrase can efficiently target native pseudo‐attachment sites in the genome of various species in cultured cells, as well as in vivo. To demonstrate its utility in human embryonic stem cells (hESC), we have created hESC‐derived clones containing expression constructs. Variant human embryonic stem cell lines BG01v and SA002 were used to derive lines expressing a green fluorescent protein (GFP) marker under control of either the human Oct4 promoter or the EF1α promoter. Stable clones were selected by antibiotic resistance and further characterized. The frequency of integration suggested candidate hot spots in the genome, which were mapped using a plasmid rescue strategy. The pseudo‐attP profile in hESC differed from those reported earlier in differentiated cells. Clones derived using this method retained the ability to differentiate into all three germ layers, and fidelity of expression of GFP was verified in differentiation assays. GFP expression driven by the Oct4 promoter recapitulated endogenous Oct4 expression, whereas persistent stable expression of GFP expression driven by the EF1α promoter was seen. Our results demonstrate the utility of phiC31 integrase to target pseudo‐attP sites in hESC and show that integrase‐mediated site‐specific integration can efficiently create stably expressing engineered human embryonic stem cell clones.

Microarray analysis of selected genes in neural stem and progenitor cells.

To access and compare gene expression in fetal neuroepithelial cells (NEPs) and progenitor cells, we have used microarrays containing approximately 500 known genes related to cell cycle regulation, apoptosis, growth and differentiation. We have identified 152 genes that are expressed in NEPs and 209 genes expressed by progenitor cells. The majority of genes (141) detected in NEPs are also present in progenitor populations. There are 68 genes specifically expressed in progenitors with little or no expression in NEPs, and a few genes that appear to be present exclusively in NEPs. Using cell sorting, RT–PCR, in situ hybridization or immunocytochemistry, we have examined the segregation of expression to neuronal and glial progenitors, and identified several that appeared to be enriched in neuronal (e.g. CDK5, neuropilin, EphrinB2, FGF11) or glial (e.g. CXCR4, RhoC, CD44, tenascin C) precursors. Our data provide a first report of gene expression profiles of neural stem and progenitor cells at early stages of development, and provide evidence for the potential roles of specific cell cycle regulators, chemokines, cytokines and extracellular matrix molecules in neural development and lineage segregation.

Genome wide profiling of human embryonic stem cells (hESCs), their derivatives and embryonal carcinoma cells to develop base profiles of U.S. Federal government approved hESC lines

BackgroundIn order to compare the gene expression profiles of human embryonic stem cell (hESC) lines and their differentiated progeny and to monitor feeder contaminations, we have examined gene expression in seven hESC lines and human fibroblast feeder cells using Illumina® bead arrays that contain probes for 24,131 transcript probes.ResultsA total of 48 different samples (including duplicates) grown in multiple laboratories under different conditions were analyzed and pairwise comparisons were performed in all groups. Hierarchical clustering showed that blinded duplicates were correctly identified as the closest related samples. hESC lines clustered together irrespective of the laboratory in which they were maintained. hESCs could be readily distinguished from embryoid bodies (EB) differentiated from them and the karyotypically abnormal hESC line BG01V. The embryonal carcinoma (EC) line NTera2 is a useful model for evaluating characteristics of hESCs. Expression of subsets of individual genes was validated by comparing with published databases, MPSS (Massively Parallel Signature Sequencing) libraries, and parallel analysis by microarray and RT-PCR.Conclusionwe show that Illuminas bead array platform is a reliable, reproducible and robust method for developing base global profiles of cells and identifying similarities and differences in large number of samples.

Evidence that nucleocytoplasmic Olig2 translocation mediates brain-injury-induced differentiation of glial precursors to astrocytes

The mechanisms by which neural and glial progenitor cells in the adult brain respond to tissue injury are unknown. We studied the responses of these cells to stab wound injury in rats and in two transgenic mouse models in which Y/GFP is driven either by Sox2 (a neural stem cell marker) or by Tα‐1 (which marks newly born neurons). The response of neural progenitors was low in all nonneurogenic regions, and no neurogenesis occurred at the injury site. Glial progenitors expressing Olig2 and NG2 showed the greatest response. The appearance of these progenitors preceded the appearance of reactive astrocytes. Surprisingly, we found evidence of the translocation of the transcription factor Olig2 into cytoplasm in the first week after injury, a mechanism that is known to mediate the differentiation of astrocytes during brain development. Translocation of Olig2, down‐regulation of NG2, and increased glial fibrillary acidic protein expression were recapitulated in vitro after exposure of glial progenitors to serum components or bone morphogentic protein by up‐regulation of Notch‐1. The glial differentiation and Olig2 translocation could be blocked by inhibition of Notch‐1 with the γ‐secretase inhibitor DAPT. Together, these data indicate that the prompt maturation of numerous Olig2+ glial progenitors to astrocytes underlies the repair process after a traumatic injury. In contrast, neural stem cells and neuronal progenitor cells appear to play only a minor role in the injured adult CNS.

Role of astroglia in Down’s syndrome revealed by patient-derived human-induced pluripotent stem cells

Down’s syndrome (DS), caused by trisomy of human chromosome 21, is the most common genetic cause of intellectual disability. Here we use induced pluripotent stem cells (iPSCs) derived from DS patients to identify a role for astrocytes in DS pathogenesis. DS astroglia exhibit higher levels of reactive oxygen species and lower levels of synaptogenic molecules. Astrocyte-conditioned medium collected from DS astroglia causes toxicity to neurons, and fails to promote neuronal ion channel maturation and synapse formation. Transplantation studies show that DS astroglia do not promote neurogenesis of endogenous neural stem cells in vivo. We also observed abnormal gene expression profiles from DS astroglia. Finally, we show that the FDA-approved antibiotic drug, minocycline, partially corrects the pathological phenotypes of DS astroglia by specifically modulating the expression of S100B, GFAP, inducible nitric oxide synthase, and thrombospondins 1 and 2 in DS astroglia. Our studies shed light on the pathogenesis and possible treatment of DS by targeting astrocytes with a clinically available drug. Down’s syndrome is characterized by intellectual disability and other neuropathological symptoms. Here, the authors show that astroglia derived from induced pluripotent stem cells from Down’s syndrome patients impair the development of neurons, and that this can be attenuated with the drug minocycline.

A Targeted Neuroglial Reporter Line Generated by Homologous Recombination in Human Embryonic Stem Cells

In this study, we targeted Olig2, a basic helix‐loop‐helix transcription factor that plays an important role in motoneuron and oligodendrocyte development, in human embryonic stem cell (hESC) line BG01 by homologous recombination. One allele of Olig2 locus was replaced by a green fluorescent protein (GFP) cassette with a targeting efficiency of 5.7%. Targeted clone R‐Olig2 (like the other clones) retained pluripotency, typical hESC morphology, and a normal parental karyotype 46,XY. Most importantly, GFP expression recapitulated endogenous Olig2 expression when R‐Olig2 was induced by sonic hedgehog and retinoic acid, and GFP‐positive cells could be purified by fluorescence‐activated cell sorting. Consistent with previous reports on rodents, early GFP‐expressing cells appeared biased to a neuronal fate, whereas late GFP‐expressing cells appeared biased to an oligodendrocytic fate. This was corroborated by myoblast coculture, transplantation into the rat spinal cords, and whole genome expression profiling. The present work reports an hESC reporter line generated by homologous recombination targeting a neural lineage‐specific gene, which can be differentiated and sorted to obtain pure neural progenitor populations. STEM CELLS 2009;27:1836–1846

Glutamate transporter expression and function in human glial progenitors

Glutamate is the major neurotransmitter of the brain, whose extracellular levels are tightly controlled by glutamate transporters. Five glutamate transporters in the human brain (EAAT1–5) are present on both astroglia and neurons. We characterize the profile of three different human astroglial progenitors in vitro: human glial restricted precursors (HGRP), human astrocyte precursors (HAPC), and early‐differentiated astrocytes. EAAT 1, EAAT3, and EAAT4 are all expressed in GRPs with a subsequent upregulation of EAAT1 following differentiation of GRPs into GRP‐derived astrocytes in the presence of bone morphogenic protein (BMP‐4). This corresponds to a significant increase in the glutamate transport capacity of these cells. EAAT2, the transporter responsible for the bulk of glutamate transport in the adult brain, is not expressed as a full‐length protein, nor does it appear to have functional significance (as determined by the EAAT2 inhibitor dihydrokainate) in these precursors. A splice variant of EAAT2, termed EAAT2b, does appear to be present in low levels, however. EAAT3 and EAAT4 expression is reduced as glial maturation progresses both in astrocyte precursors and early‐differentiated astrocytes and is consistent with their role in adult tissues as primarily neuronal glutamate transporters. These human glial precursors offer several advantages as tools for understanding glial biology because they can be passaged extensively in the presence of mitogens, afford the potential to study the temporal changes in glutamate transporter expression in a tightly controlled fashion, and are cultured in the absence of neuronal coculture, allowing for the independent study of astroglial biology.

Adult glial precursor proliferation in mutant SOD1G93A mice

The focus of most neurodegenerative disease studies has been on neuronal death in particular subpopulations of the central nervous system. The associated response of glial populations has been ascribed the term “reactive astrocytosis.” This has been defined as the proliferation of astrocytes accompanied by cellular hypertrophy and changes in gene expression following injury to the central nervous system. Yet the significance of that response to disease course is debated. In both human ALS and in the SOD1G93A mouse model of ALS, reactive astrocytosis is a hallmark of the disease—particularly at endstage. The brain also harbors immature progenitors which have the capacity for differentiation into both glial and neuronal lineages. We examined whether glial progenitors in the adult spinal cord of SOD1G93A mice become activated and contribute the astroglial response observed in this model. We found that the glial progenitor proteoglycan NG2 is increased in parallel with GFAP during the symptomatic phase of the disease and that there is a differential in vitro response of SOD1G93A glial progenitors to inflammatory cytokines when compared to wildtype mouse glial progenitors. This response was accompanied by the proliferation of glial progenitors but not mature GFAP+ astrocytes, through the translocation of the transcription factor Olig2 from the nucleus to the cytoplasm—resulting in astrocyte differentiation. These data suggest that adult glial progenitors from SOD1G93A mice differentially respond to inflammatory cytokines and contribute to the observed reactive astrocytosis observed in SOD1G93A mouse lumbar spinal cord.

Cytoplasmic translocation of Olig2 in adult glial progenitors marks the generation of reactive astrocytes following autoimmune inflammation.

The injury response in the brain involves complex interplay between neural and immune components. Following inflammatory insults to the adult CNS, formation of an astroglial scar often impedes functional repair. Glial progenitor cells expressing the nuclear transcription factor Olig2 possibly generate astrocytes in response to various types of injuries; however, the mechanisms underlying this differentiation are unclear. In a model of immune-mediated injury (MOG(35-55)-experimental autoimmune encephalomyelitis), we show that the conversion from progenitor to reactive astrocyte is marked by the translocation of Olig2 into the cytoplasm. Evidence of this process is found for months after disease initiation in the absence of new inflammatory infiltrates. A proportion of cells with cytoplasmic Olig2 was found to express NG2 or Nkx2.2, but only Nkx2.2 was occasionally retained by GFAP+ cells. We further show that differentiation to astrocytes is induced in glial progenitors in vitro through exposure to the pro-inflammatory cytokine IFN-gamma, but not to TNF-alpha. Together, these data ascribe a pivotal role to Olig2+ glial precursor cells in the adult CNS, linking autoimmune inflammation and glial scar formation.