Recent studies have identified stem cells in brain cancer. However, their relationship to normal CNS progenitors, including dependence on common lineage-restricted pathways, is unclear. We observe expression of the CNS-restricted transcription factor, OLIG2, in human glioma stem and progenitor cells reminiscent of type C transit-amplifying cells in germinal zones of the adult brain. Olig2 function is required for proliferation of neural progenitors and for glioma formation in a genetically relevant murine model. Moreover, we show p21(WAF1/CIP1), a tumor suppressor and inhibitor of stem cell proliferation, is directly repressed by OLIG2 in neural progenitors and gliomas. Our findings identify an Olig2-regulated lineage-restricted pathway critical for proliferation of normal and tumorigenic CNS stem cells.

SUMMARY High-grade gliomas are notoriously insensitive to radiation and genotoxic drugs. Paradoxically, the p53 gene is structurally intact in the majority of these tumors. Resistance to genotoxic modalities in p53-positive gliomas is generally attributed to attenuation of p53 functions by mutations of other components within the p53 signaling axis, such as p14Arf, MDM2 and ATM, but this explanation is not entirely satisfactory. We show here that the central nervous system (CNS) restricted transcription factor Olig2 affects a key post-translational modification of p53 in both normal and malignant neural progenitors and thereby antagonizes the interaction of p53 with promoter elements of multiple target genes. In the absence of Olig2 function, even attenuated levels of p53 are adequate for biological responses to genotoxic damage.

SUMMARY Gliomas comprise heterogeneous malignant glial and stromal cells. While blood vessel co-option is a potential mechanism to escape anti-angiogenic therapy, the relevance of glial phenotype in this process is unclear. We show that Olig2+ oligodendrocyte precursor-like glioma cells invade by single-cell vessel co-option and preserve the blood-brain barrier (BBB). Conversely, Olig2-negative glioma cells form dense perivascular collections and promote angiogenesis and BBB breakdown, leading to innate immune cell activation. Experimentally, Olig2 promotes Wnt7b expression, a finding that correlates in human glioma profiling. Targeted Wnt7a/7b deletion or pharmacologic Wnt inhibition blocks Olig2+ glioma single-cell vessel co-option and enhances responses to temozolomide. Finally, Olig2 and Wnt7 become upregulated after anti-VEGF treatment in preclinical models and patients. Thus, glial-encoded pathways regulate distinct glioma-vascular microenvironmental interactions.

Summary The basic helix-loop-helix transcription factors oligodendrocyte transcription factor 1 (OLIG1) and OLIG2 are structurally similar and, to a first approximation, coordinately expressed in the developing CNS and postnatal brain. Notwithstanding these similarities, it was apparent from early on after their discovery that OLIG1 and OLIG2 have non-overlapping developmental functions in patterning, neuron subtype specification and the formation of oligodendrocytes. Here, we summarize more recent insights into the separate functions of these transcription factors in the postnatal brain during repair processes and in neurological disease states, including multiple sclerosis and malignant glioma. We discuss how the unique biological functions of OLIG1 and OLIG2 may reflect their distinct genetic targets, co-regulator proteins and/or post-translational modifications.

Summary The bHLH transcription factors that regulate early development of the central nervous system can generally be classified as either anti-neural or pro-neural. Initial expression of anti-neural factors prevents cell cycle exit and thereby expands the pool of neural progenitors. Subsequent (and typically transient) expression of pro-neural factors promotes cell cycle exit, subtype specification and differentiation. Against this backdrop, the bHLH transcription factor Olig2 in the oligodendrocyte lineage is unorthodox, showing anti-neural functions in multipotent CNS progenitor cells but also sustained expression and pro-neural functions in formation of oligodendrocytes. We show here that the proliferative function of Olig2 is controlled by developmentally regulated phosphorylation of a conserved triple serine motif within the amino terminal domain. In the phosphorylated state, Olig2 maintains anti-neural (i.e. pro-mitotic) functions that are reflected in human glioma cells and in a genetically defined murine model of primary glioma.

The yeast 2 micron plasmid achieves high fidelity segregation by coupling its partitioning pathway to that of the chromosomes. Mutations affecting distinct steps of chromosome segregation cause the plasmid to missegregate in tandem with the chromosomes. In the absence of the plasmid stability system, consisting of the Rep1 and Rep2 proteins and the STB DNA, plasmid and chromosome segregations are uncoupled. The Rep proteins, acting in concert, recruit the yeast cohesin complex to the STB locus. The periodicity of cohesin association and dissociation is nearly identical for the plasmid and the chromosomes. The timely disassembly of cohesin is a prerequisite for plasmid segregation. Cohesin-mediated pairing and unpairing likely provides a counting mechanism for evenly partitioning plasmids either in association with or independently of the chromosomes.

Glioblastoma (GBM) is one of the deadliest forms of cancer. Despite many treatment options, prognosis of GBM remains dismal with a 5-year survival rate of 4.7%. Even then, tumors often recur after treatment. Tumor recurrence is hypothesized to be driven by glioma stem cell (GSC) populations which are highly tumorigenic, invasive, and resistant to several forms of therapy. GSCs are often concentrated around the tumor vasculature, referred to as the vascular niche, which are known to provide microenvironmental cues to maintain GSC stemness, promote invasion, and resistance to therapies. In this work, we developed a 3D organotypic microfluidic platform, integrated with hydrogel-based biomaterials, to mimic the GSC vascular niche and study the influence of endothelial cells (ECs) on patient-derived GSC behavior and identify signaling cues that mediate their invasion and phenotype. The established microvascular network enhanced GSC migration within a 3D hydrogel, promoted invasive morphology as well as maintained GSC proliferation rates and phenotype (Nestin, SOX2, CD44). Notably, we compared migration behavior to in vivo mice model and found similar invasive morphology suggesting that our microfluidic system could represent a physiologically relevant in vivo microenvironment. Moreover, we confirmed that CXCL12-CXCR4 signaling is involved in promoting GSC invasion in a 3D vascular microenvironment by utilizing a CXCR4 antagonist (AMD3100), while also demonstrating the effectiveness of the microfluidic as a drug screening assay. Our model presents a potential ex vivo platform for studying the interplay of GSCs with its surrounding microenvironment as well as development of future therapeutic strategies tailored toward disrupting key molecular pathways involved in GSC regulatory mechanisms.

The 2m circle is a highly persistent "selfish" DNA element resident in the Saccharomyces cerevisiae nucleus whose stability approaches that of the chromosomes. The plasmid partitioning system, consisting of two plasmid-encoded proteins, Rep1p and Rep2p, and a cis-acting locus, STB, apparently feeds into the chromosome segregation pathway. The Rep proteins assist the recruitment of the yeast cohesin complex to STB during the S phase, presumably to apportion the replicated plasmid molecules equally to daughter cells. The DNAprotein and protein-protein interactions of the partitioning system, as well as the chromatin organization at STB, are important for cohesin recruitment. Rep1p variants that are incompetent in binding to Rep2p, STB, or both fail to assist the assembly of the cohesin complex at STB and are nonfunctional in plasmid maintenance. Preventing the cohesin-STB association without impeding Rep1p-Rep2p-STB interactions also causes plasmid missegregation. During the yeast cell cycle, the Rep1p and Rep2p proteins are expelled from STB during a short interval between the late G 1 and early S phases. This dissociation and reassociation event ensures that cohesin loading at STB is replication dependent and is coordinated with chromosomal cohesin recruitment. In an rsc2⌬ yeast strain lacking a specific chromatin remodeling complex and exhibiting a high degree of plasmid loss, neither Rep1p nor the cohesin complex can be recruited to STB. The phenotypes of the Rep1p mutations and of the rsc2⌬ mutant are consistent with the role of cohesin in plasmid partitioning being analogous to that in chromosome partitioning.The 2m circle of Saccharomyces cerevisiae is a high-copynumber selfish extrachromosomal DNA element that resides in the nucleus and propagates itself stably in the cell population (2, 29). The plasmid does not seem to confer any selective advantage to its host under normal laboratory growth conditions, nor does it pose any noticeable disadvantage as long as the copy number does not rise significantly above the steadystate value of approximately 60 per cell. The stability of the plasmid approaches that of the yeast chromosomes, with the loss rate being as low as 10 Ϫ4 to 10 Ϫ5 per cell per generation. The structural organization of the plasmid and its genetic potential are devoted to two goals: (i) efficient plasmid segregation during cell division and (ii) the maintenance of the plasmid copy number with only modest deviations from the mean.The presence of a typical yeast replication origin in its sequence permits each plasmid molecule to be replicated once per cell cycle (35). A stability system consisting of two plasmidencoded proteins (Rep1p and Rep2p) and a cis-acting partitioning locus (STB) mediates equal or nearly equal distribution of the replicated molecules into daughter cells. The direct observation of reporter plasmids tagged with fluorescence indicates that the plasmid molecules are organized into a tightknit cluster in the nucleus and segregate as a cluster. Hence, the copy number relevant ...