The bHLH Transcription Factors OLIG2 and OLIG1 Couple Neuronal and Glial Subtype Specification

“Anderson1,2,3 Division of Biology 216-76 2 Howard Hughes Medical Institute California Institute of Technology V3 interneurons are generated from the p0, p1, p2, and Pasadena, California 91125 p3 domains, respectively (Briscoe et al., 2000; Jessell, 2000).”

“In heterozygotes, Olig2-hGFP -derived precursors gave is restricted to oligodendrocyte precursors (Lu et al., 2000; Zhou et al., 2000), nearly all OLIG2-positive cells rise to Islet1/2 (cid:2) motoneurons (Figure 3A, yellow cells) but not Chx10 (cid:2) V2 interneurons (Figure 3B).”

“These data sug-sophila proneural genes, such as the Neurogenins gest that Olig genes couple neuronal and glial subtype (Ngns) (Gradwohl et al., 1996; Ma et al., 1996; McCor-specification. mick et al., 1996) and Mash1 (Johnson et al., 1990 .”

“In heterozygotes, Olig2-hGFP -derived precursors gave is restricted to oligodendrocyte precursors (Lu et al., 2000; Zhou et al., 2000), nearly all OLIG2-positive cells rise to Islet1/2 (cid:2) motoneurons (Figure 3A, yellow cells) but not Chx10 (cid:2) V2 interneurons (Figure 3B).”

“After 7 days of differentiation, there were 2-fold fewer Tuj1-positive cells and 3-fold fewer cells expressing OLIG2, a marker of the oligodendrocyte lineage (Zhou and Anderson, 2002).”

“Expression of bHLH transcription factor Olig2, required for oligodendrocyte and motor neuron differentiation in the spinal cord (Lu et al., 2000, 2002; Zhou and Anderson, 2002), was also reduced in the subpallium of N11Cre/cGOF mutants (Figs.”

“One current candidate is the bHLH transcription factor Olig2, since it is expressed prior to SOX10 in oligodendrocyte progenitors and plays an essential role in oligodendrocyte differentiation (Lu et al., 2000; Zhou et al., 2000; Lu et al., 2002; Zhou and Anderson, 2002).”

“Studies from other vertebrates suggest that Olig2 inhibits astrocyte formation and that astrocytes do not normally develop from the olig2-expressing motoneuron and oligodendrocyte domain (Takebayashi et al., 2002; Zhou and Anderson, 2002).”

“Misexpression and loss-of-function studies have shown that Olig proteins activate Ngn2 expression (Novitch et al. 2001; Lu et al. 2002; Zhou and Anderson 2002).”

“In Olig1/2 double-knockout mice (Lu et al., 2002; Zhou and Anderson, 2002), an overactivation or loss of fibroblast growth factor receptor 3 (FGFR3) function resulted in alteration of the numbers of both oligodendrocytes and astrocytes (Lin et al., 2003; Oh et al., 2003; Pringle et al., 2003).”

“Recent studies have identified Olig1 and Olig2, novel bHLH transcription factors, as important intracellular signals to regulate the differentiation processes of oligodendrocytes.(45,46) We have recently transfected HB1.”

“Interestingly, qRT-PCR analysis revealed expression of NKX2-2 and OLIG1, two genes with essential roles in normal neuronal cell-fate specification and differentiation (Briscoe et al., 2000; Zhou and Anderson, 2002), was also diminished in miR-520g, as well as 517c-expressing hNSCs (Figure 5D).”

“In the ventral spinal cord, motoneuron and oligodendrocyte precursors expressed Olig bHLH proteins, which are structurally similar to proneural Ngns (Lu et al., 2000; Takebayashi et al., 2000; Zhou et al., 2000).”

“Olig2, an early marker of the lineage, is required for the specification of oligodendrocyte progenitors (OPCs) in most regions of the CNS and is thus ultimately required for the generation of mature oligodendrocytes (Lu et al., 2002; Zhou and Anderson, 2002; Ligon et al., 2006).”

“Olig1 and Olig2 are expressed in the spinal motor neuron progenitor domain and are necessary for the generation of motor neurons and oligodendrocytes from this regio”

“Mice mutant for Olig2 completely lack OPCs in the embryonic spinal cord whereas a few OPCs remain in the brain because of the compensatory activity of Olig1 (Lu et al., 2002; Zhou and Anderson, 2002).”

“…of Olig1 and Olig2 in the spinal cord To better understand the lineage relationships of motoneurons and oligodendrocytes, we first extended previous work on the analysis of Olig1 and Olig2 expression in the developing spinal cord (Lu et al., 2000; Novitch et al., 2001; Zhou et al., 2000).”

“2 (Lu et al., 2002; Nieto et al., 2001; Qi et al., 2001; Takebayashi et al., 2002; Zhou and Anderson, 2002; Zhou et al., 2001).”

“The basic helix-loop-helix (bHLH) transcription factor Olig2 is essential for the formation of motoneurons and oligodendrocytes in the developing spinal cord (Lu et al., 2002; Takebayashi et al., 2002; Zhou and Anderson, 2002); however, its functions in astrocyte development remain elusive, particularly in the develop…”

“Olig2 was originally characterized as a key regulator for the differentiation of progenitor motor neurons (pMN) into either motor neurons or oligodendrocytes (Lee et al., 2005; Lu et al., 2002; Park et al., 2002; Zhou and Anderson, 2002).”

“Several Mof regulated ‘bivalent genes’ (e.g. Olig1 and Fgf15) have been shown to play important roles in ES differentiation (Fischer et al., 2011; Zhou and Anderson, 2002), further supporting the importance of Mof in ESC regulation.”

“Another model predicts that astrocytes and oligodendrocytes develop from separate progenitors (Lu et al., 2002; Zhou and Anderson, 2002; Pringle et al., 2003; Gabay et al., 2003).”

“Often, multiple tissue-specific bHLH factors are necessary for tissue differentiation, and double deficiencies have shown synergistic effects and more profound phenotypic changes as compared to the single knockouts (Kruger et al., 2006; Zhou and Anderson, 2002).”

“Previous lineage-tracing analyses of Olig-expressing progenitors using Olig1-Cre ROSA26R and Olig2-GFP mice have suggested that Olig1- and Olig2-expressing cells generate only motoneurons and oligodendrocytes and do not produce astrocytes (Lu et al., 2002; Zhou and Anderson, 2002 ).”

“As a result, pMN no longer generates motoneurones followed by OLPs, but instead produces V2 interneurones followed by astrocytes (Zhou and Anderson, 2002; Takebayashi et al., 2002).”

“…raised the possibility that differential bHLH protein expression creates a combinatorial code wherein cells that express both Olig2 and Ngn2 develop as motoneurons and those that express only Olig2, following Ngn2 downregulation, develop as OPCs (Zhou and Anderson, 2002; Zhou et al., 2001).”

“and expression of EGFP with nuclear-localization sequence”

“Recently, single and compound null alleles of these genes have been generate”

“These genes encode transcription factors that have been implicated in neurogenesis and oligodendrogenesis [131–133].”

“Moreover, the oligodendroglial shift induced by the overexpression of OLIG1 and OLIG2 in Twin-DS-iPSC-derived cells is in accordance with the pivotal role of these HSA21 genes in specifying oligodendrocyte lineage in the central nervous system of vertebrate (Zhou & Anderson, 2002).”

“RESEARCH ARTICLE Development 136 (9) D E V E LO P M E N T FGF2 increases pre-OPCs by inhibiting motoneuron differentiation In rodents, OLIG2-expressing spinal progenitors are a source of both motoneurons and OPCs (Lu et al., 2002; Zhou and Anderson, 2002).”

“The specification of these precursors is controlled by floor plate signals in the ventral spinal cord, notably sonic hedgehog (Shh), which induces expression of transcription factors necessary for the stages of OL development (Lu et al., 2000; Zhou et al., 2000; Zhou and Anderson, 2002).”

“During CNS development, Olig2 is expressed in progenitor cells that give rise to neurons and to myelinating oligodendrocytes (Lu et al., 2002; Takebayashi et al., 2002; Zhou and Anderson, 2002).”

“Olig2 directs early OPC specification and differentiation (Lu et al., 2002; Yue et al., 2006; Zhou and Anderson, 2002); similarly, Olig1, whose expression is elevated during OPC differentiation, promotes oligodendrocyte maturation and is required for repair of demyelinated lesions (Arnett et al.”

“OLIG2, a member of a family of transcription factors of the bHLH type, plays a major role in neuroectodermal progenitor/oligodendrocyte development [26, 51] and is frequently expressed in gliomas of both oligodendroglial and astrocytic morphologies [24, 25].”

“…repressor function is both necessary and sufficient to stimulate the expression of a number of downstream homeodomain transcription factors that provide MNs with their unique character (Mizuguchi et al. 2001; Novitch et al. 2001b; Lu et al. 2002; Zhou & Anderson 2002; Takebayashi et al. 2002a).”

“2 (Qi et al., 2001; Sun et al., 2001; Zhou et al., 2001; Zhou and Anderson, 2002; Stolt et al., 2003, 2004; Arnett et al., 2004; Kitada and Rowitch, 2006; Liu et al., 2007; Cai et al., 2010).”

“…cord, however, may develop into neurons rather than OPCs (Marquardt and Pfaff, 2001; Mizuguchi et al., 2001; Novitch et al., 2001; Sun et al., 2001; Zhou et al., 2001): if Olig2 is inactivated, neither motor neurons nor OPCs develop in the spinal cord (Lu et al., 2002; Zhou and Anderson, 2002).”

“Olig2 lossand gain-of-function studies provided compelling support of its requirement in oligodendrocyte specification (Lu et al., 2000, 2002; Zhou et al., 2000; Zhou and Anderson, 2002; Liu et al., 2007; Maire et al., 2010).”

“Olig2 is expressed in a progenitor domain of the ventral spinal cord that generates initially motoneurons and, subsequently, oligodendrocytes, and is required for the specification of both cell types (Novitch et al. 2001; Zhou et al. 2001; Lu et al. 2002; Takebayashi et al. 2002a; Zhou and Anderson 2002).”

“The Olig1 and Olig2 genes encode transcription factors that have been implicated in neurogenesis and oligodendrogenesis (Takebayashi et al., 2000; Lu et al., 2002; Zhou and Anderson, 2002).”

“Olig2 inactivation during development leads to a reduced production of OPCs in most CNS regions (Lu et al., 2002; Zhou and Anderson, 2002; Ligon et al., 2006) and induction of Olig2 expression in neuroepithelium leads to an increased generation of OPCs in the CNS (Maire et al., 2010).”

“However, not all oligodendrocytes arise from Ascl1 expressing cells since the earliest oligodendrocytes arise in the ventral neural tube from non-Ascl1 cells (Lu et al., 2002; Sugimori et al., 2008; Zhou and Anderson, 2002).”

“Yet the effects of T3 loss on CNS myelination are not nearly as severe as mutations that directly and completely impair OL differentiation, such as ablation of SOX10, OLIG1/2, or MRF (Emery et al., 2009; Stolt et al., 2002; Zhou and Anderson, 2002).”

“The different binding specificities of these FGF isoforms for the three FGF receptors found in the CNS (FGFR1-3) suggests that the effect is mediated predominantly through FGFR1 (MacArthur et al., 1995; Ornitz et al., 1996; Belluardo et al., 1997; Igarashi et al., 1998; Beer et al., 2000; Ohuchi et al., 2000; Ford-Per…”

“Analysis of mice lacking Olig1 or Olig2, and double-homozygous Olig1/Olig2 mutants, has further shown that OLIG expression is obligatory for oligodendrocyte and motoneurone formation (Lu et al., 2002; Zhou and Anderson, 2002).”

“OLIG2 initiates developmental oligodendrogenesis upstreamof SOX10,with the expression of SOX10marking the irreversible commitment to the oligodendrocyte lineage (15, 16).”

“2, Pax6 and Mnr2; and the bHLH proteins Olig1/2 and Ngn2 (Briscoe et al., 2000; Ericson et al., 1997; Lu et al., 2002; Marquardt and Pfaff, 2001; Mizuguchi et al., 2001; Novitch et al., 2001; Scardigli et al., 2001; Tanabe et al., 1998; Vallstedt et al., 2001; Zhou and Anderson, 2002).”

“We discuss 2002; Zhou and Anderson, 2002).”

“Furthermore, Olig1 and Olig2 play a role in the association of neurons and oligodendrocytes during development (27, 28 ).”

“As an example, when Olig2 is fused to the repressor domain of Engrailed, this fusion protein, but not an activating Olig2-VP16 fusion protein, recapitulates the function of native Olig2 by specifying neural fate in the chick spinal cord (Zhou and Anderson, 2002).”

“Dorsally-derived OPCs are also seen in the hindbrain (Vallstedt et al., 2005) and telencephalon (Kessaris et al., 2006); however, whether BMP affects OG specification in these regions will require further research.”

“Of relevance here, is the finding that the bHLH protein Olig2 has a pattern of expression and role in motor neuron specification imilar to that invoked for MNR2 (Novitch et al., 2001; Mizuguchi et al., 2001; Zhou et al., 2000; Zhou and Anderson, 2002; Lu et al., 2002).”

“Midline expression of olig2 at 2 dpf, a marker of oligodendrocyte and motor neuron progenitors (Lu et al., 2002; Takebayashi et al., 2002; Zhou and Anderson, 2002 ), is disrupted in all three mutants (Fig. 2C), suggesting that the reduction in mbp expression results from disruption of early steps in oligodendrocyte fa…”

“…transcription factor (bHLH) Olig2 is essential for the specification and maturation of oligodendrocytes in the spinal cord and forebrain (Zhou and Anderson, 2002; Lu et al., 2002; Takebayashi et al., 2002; Muroyama et al., 2005; Yue et al., 2006; Ligon et al., 2006; Maire et al., 2010).”

“Olig2 in glial cells inhibits astrocyte differentiation, thereby allowing the cells to maintain an undifferentiated state or to develop into myelinating oligodendrocytes (28).”

“2; Lu et al. 2002, 2000; Zhou and Anderson 2002; Zhou et al. 2000).”

“…precedes the expression of the early OL progenitor markers PDGFR-␣ and NG2, consistent with results in the rodent spinal cord (Zhou et al., 2000; Lu et al., 2002; Takebayashi et al., 2002; Zhou and Anderson, 2002; Liu and Rao, 2004) and forebrain (Spassky et al., 1998; Tekki-Kessaris et al., 2001).”

“S147 Phosphorylation Is Dispensable for the OL-Inducing Activity of OLIG2 In the spinal cords of Olig2 null mice, expression of the OLP markers PDGFRa and SOX10 is completely absent (Lu et al., 2002; Takebayashi et al., 2002; Zhou and Anderson, 2002), demonstrating an essential role for OLIG2 in OL lineage specificati…”

“bHLH transcription factor, Olig2, and develop Wrst into motor neurons) [52, 108].”

“…proteins promote astrocytes and inhibit oligodendrocytes (Gross et al., 1996; Mekki-Dauriac et al., 2002; Gomes et al., 2003), whereas Olig2 promotes formation of oligodendrocytes and inhibits formation of astrocytes (Zhou and Anderson, 2002; Fukuda et al., 2004; Setoguchi and Kondo, 2004).”

“Despite the functional versatility of glial cells and the fact that they significantly outnumber neurons in most parts of the CNS, we know relatively little about their intrinsic diversity and how this arises during development.”