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.

Teneurins are ancient cell–cell adhesion receptors that are vital for brain development and synapse organisation. They originated in early metazoan evolution through a horizontal gene transfer event when a bacterial YD-repeat toxin fused to a eukaryotic receptor. We present X-ray crystallography and cryo-EM structures of two Teneurins, revealing a ~200 kDa extracellular super-fold in which eight sub-domains form an intricate structure centred on a spiralling YD-repeat shell. An alternatively spliced loop, which is implicated in homophilic Teneurin interaction and specificity, is exposed and thus poised for interaction. The N-terminal side of the shell is ‘plugged’ via a fibronectin-plug domain combination, which defines a new class of YD proteins. Unexpectedly, we find that these proteins are widespread amongst modern bacteria, suggesting early metazoan receptor evolution from a distinct class of proteins, which today includes both bacterial proteins and eukaryotic Teneurins.

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.

Diffuse intrinsic pontine glioma (DIPG) is a fatal malignancy because of its diffuse infiltrative growth pattern. Translational research suffers from the lack of a representative DIPG animal model. Hence, human E98 glioma cells were stereotactically injected into the pons of nude mice. The E98 DIPG tumors presented a strikingly similar histhopathology to autopsy material of a DIPG patient, including diffuse and perivascular growth, brainstem- and supratentorial invasiveness and leptomeningeal growth. Magnetic resonance imaging (MRI) was effectively employed to image the E98 DIPG tumor. [(18) F] 3'-deoxy-3'-[(18) F]fluorothymidine (FLT) positron emission tomography (PET) imaging was applied to assess the subcutaneous (s.c.) E98 tumor proliferation status but no orthotopic DIPG activity could be visualized. Next, E98 cells were cultured in vitro and engineered to express firefly luciferase and mCherry (E98-Fluc-mCherry). These cultured E98-Fluc-mCherry cells developed focal pontine glioma when injected into the pons directly. However, the diffuse E98 DIPG infiltrative phenotype was restored when cells were injected into the pons immediately after an intermediate s.c. passage. The diffuse E98-Fluc-mCherry model was subsequently used to test escalating doses of irradiation, applying the bioluminescent Fluc signal to monitor tumor recurrence over time. Altogether, we here describe an accurate DIPG mouse model that can be of clinical relevance for testing experimental therapeutics in vivo.

Summary Abnormal GABAergic interneuron density, and imbalance of excitatory versus inhibitory tone, is thought to result in epilepsy, neurodevelopmental disorders and psychiatric disease. Recent studies indicate that interneuron cortical density is determined primarily by the size of the precursor pool in the embryonic telencephalon. However, factors essential to regulate interneuron allocation from telencephalic multipotent precursors are poorly understood. Here we report that Olig1 represses production of GABAergic interneurons throughout the mouse brain. Olig1 deletion in mutant mice results in ectopic expression and upregulation of Dlx1/2 genes in the ventral medial ganglionic eminences and adjacent regions of the septum resulting in a ~30% increase in adult cortical interneuron numbers. We show that Olig1 directly represses the Dlx1/2 I12b intergenic enhancer and that Dlx1/2 functions genetically downstream of Olig1. These findings establish Olig1 as an essential repressor of Dlx1/2 and interneuron production in developing mammalian brain.

Low pH-induced ligand release and receptor recycling are important steps for endocytosis. The transmembrane protein sortilin, a β-propeller containing endocytosis receptor, internalizes a diverse set of ligands with roles in cell differentiation and homeostasis. The molecular mechanisms of pH-mediated ligand release and sortilin recycling are unresolved. Here we present crystal structures that show the sortilin luminal segment (s-sortilin) undergoes a conformational change and dimerizes at low pH. The conformational change, within all three sortilin luminal domains, provides an altered surface and the dimers sterically shield a large interface while bringing the two s-sortilin C-termini into close proximity. Biophysical and cell-based assays show that members of two different ligand families, (pro)neurotrophins and neurotensin, preferentially bind the sortilin monomer. This indicates that sortilin dimerization and conformational change discharges ligands and triggers recycling. More generally, this work may reveal a double mechanism for low pH-induced ligand release by endocytosis receptors.

The bHLH transcription factor Olig2 is expressed in cycling neural progenitor cells but also in terminally differentiated

Glioblastoma multiforme (GBM) is a devastating form of brain cancer for which there is no effective treatment. Here, we report a novel approach to brain tumor therapy through genetic modification of normal brain cells to block tumor growth and effect tumor regression. Previous studies have focused on the use of vector-based gene therapy for GBM by direct intratumoral injection with expression of therapeutic proteins by tumor cells themselves. However, as antitumor proteins are generally lethal to tumor cells, the therapeutic reservoir is rapidly depleted, allowing escape of residual tumor cells. Moreover, it has been difficult to achieve consistent transduction of these highly heterogeneous tumors. In our studies, we found that transduction of normal cells in the brain with an adeno-associated virus (AAV) vector encoding interferon-β (IFN-β) was sufficient to completely prevent tumor growth in orthotopic xenograft models of GBM, even in the contralateral hemisphere. In addition, complete eradication of established tumors was achieved through expression of IFN-β by neurons using a neuronal-restricted promoter. To our knowledge this is the first direct demonstration of the efficacy of targeting gene delivery exclusively to normal brain cells for brain tumor therapy.