Article Figures & Data
Figures
- Figure 1.
Olig2 expression in the SVZ. A, Diagram of coronal and parasagittal planes highlighting the SVZ (B) and RMS (C) (both green), respectively. SVZ-derived glial precursors migrate radially within a coronal plane into adjacent forebrain areas, whereas SVZ-derived neuronal progenitors migrate rostrally in a parasagittal plane to the olfactory bulb. D, Transcriptional regulators directing the formation of neuronal and glial lineages in SVZ cells are not known. E-G, Olig2 expression in Zebrin II+ (border) and Zebrin II- (middle) SVZ cells, as indicated by immunostaining of P6 mouse forebrain. The inset in E depicts the area of photomicrographs shown in E and F. The boxed area in F is magnified in G. H-J, Olig2 is expressed in Dlx2+ (central) SVZ progenitors. The inset in H depicts the area of the photomicrograph shown in H and I. The boxed area in I is magnified in J. K, Cells within the RMS do not express Olig2. lv, Lateral ventricle; wm, white matter.
- Figure 2.
Developing astrocytes and oligodendrocytes express Olig2. A, Cortical radial glia with an intermediate morphology (arrowheads), indicative of a transformation into astrocytes, express Zebrin II and Olig2 (P3, coronal section through murine cerebral cortex). B-D, Olig2 and Zebrin II are expressed robustly in developing astrocytes (P6, murine cerebral cortex) at early stages of differentiation before GFAP expression (B, arrowheads) and at later stages as GFAP is upregulated (B, asterisk). The cell marked with an asterisk in B is magnified to show perinuclear GFAP (C) and Zebrin II (D) immunolabeling with respect to nuclear Olig2 expression. E-G, Mature and fully arborized astrocytes (P6, murine cerebral cortex) expressing high amounts of GFAP and Zebrin II (E, arrowheads) consistently appeared to express lower levels of Olig2 than astrocytes with immature morphologies that express less GFAP (E, asterisk). H, I, CNPase+/Olig2+ oligodendrocytes in parasagittal sections of P6 mouse forebrain. J, K, Developing astrocytes in the hGFAP-GFP mouse (P7) forebrain coexpress GFP and Olig2. L, M, Astrocytes in the mOlig2-I-eGFP mouse forebrain (P6, cortex) coexpress GFAP, GFP, and Olig2. O, Cell cultures generated from P3 mouse SVZ contained many vimentin+/Olig2+, immature astrocytes after 4 div. P, After 8 div, cultures were mostly comprised of mature, GFAP+ astrocytes. Olig2 immunoreactivity in these mature astrocytes was markedly reduced. Q, Summary of Olig2 expression with respect to glial cell lineages in the postnatal forebrain.
- Figure 3.
Olig2 is expressed exclusively by SVZ-derived glia. A, GFP expression 2 d after stereotactic injection of replication-deficient retrovirus (pNIT-eGFP) into P2/P3 rat SVZ. See F for the site of injection and distribution of infected cells at 4 dpi. B, C, At 4 dpi, GFP+/Olig2+ cells with oligodendrocyte (B) and astrocyte (C) morphologies were observed in the parenchyma (the asterisk in C indicates a blood vessel enwrapped by an astrocyte). D, E, SVZ-derived neuroblasts do not express Olig2 as they migrate in the RMS, which is outlined for clarity. The boxed area is magnified in E. F, Distribution of SVZ cells transduced with GFP. The red box indicates the area of the photomicrograph in D. G-I, SVZ-derived interneuronal precursors remain Olig2-within the olfactory bulb. The boxed area in G is magnified in H. I, The red box indicates the area of the photomicrograph in G. lv, Lateral ventricle; wm, white matter; str, striatum.
- Figure 4.
SVZ progenitors transduced with Olig2 differentiate exclusively into astrocytes and oligodendrocytes. A-C, Parasagittal section of rat forebrain at 4 dpi, showing cells transduced with Olig2-ires-eGFP. The boxed area in A is magnified in B, highlighting differentiated glial cells within the SVZ/RMS. C, Distribution of cells expressing Olig2-ires-eGFP at 4 dpi. Thered box indicates the area of SVZ and proximal RMS shown in A. D, Infected cells differentiated ectopically in the SVZ, adjacent to the lateral ventricles. E-K, More than 70% of infected cells exhibited the morphology of oligodendrocytes (E) and expressed the oligodendrocyte-specific markers NG2 (F-H) and CC1 (I-K). L-N, Approximately 20% of infected cells exhibited astrocyte morphologies and expressed GFAP (asterisk). lv, Lateral ventricle; wm, white matter; str, striatum.
- Figure 5.
Distribution of SVZ cells expressing X-ires-eGFP and Olig2-ires-eGFP. A-D, Retroviral constructs used to transduce SVZ cells with GFP (A) or Olig2-GFP (C) and quantified distributions of cells misexpressing GFP (B) or Olig2-ires-GFP (D), presented as a percentage of infected cells per brain located in each area (mean ± SEM). OB, Olfactory bulb; WM, white matter; CTX, cerebral cortex.
- Figure 6.
A dominant-interfering form of Olig2 blocks glial differentiation. A, B, SVZ cells misexpressing Olig2 bHLH exhibited normal migration to the olfactory bulb via the RMS (A), which is outlined for clarity. The distribution of total infected cells at 4 dpi is shown in B. The red box indicates the area of RMS pictured (A). Infected cells also colonized the white matter and cerebral cortex, but glial differentiation was blocked in >90% of cells (data not shown). C-E, However, ∼25% of infected cells in the white matter and cortex ectopically expressed the neuronal marker NeuN, suggesting a potential respecification along a neuronal lineage. wm, White matter.
- Figure 7.
An antimorphic activator form of Olig2 promotes neurogenesis in SVZ cells. A-C, Expression of an Olig2bHLH-VP16 activator fusion construct limited the migration of SVZ cells. Cells migrated short distances into the proximal RMS, white matter, and layer 6 of the cerebral cortex. The boxed area in A, containing infected SVZ cells, is magnified in B. The distribution of infected cells is shown in C. D-I, More than 75% of infected cells expressed the neuronal markers Map2 (D-F) and NeuN (G-I). J-O, Approximately 30% of cells in the white matter and SVZ/RMS expressed interneuron-specific markers such as calbindin (J-L) and calretinin (M-O). WM/VI, White matter/layer 6 border; LV, lateral ventricle.
Additional Files
Supplemental data
Files in this Data Supplement:
- supplemental material - Supplemental Figure S1: Specificity of Olig2 antibody. Immunohistochemical analysis of spinal cord sections taken from e10.5 Olig2+/- control and Olig2-/- mutant mouse embryos.
- supplemental material - Supplemental Figure 2: Model of SVZ Cell Specification within the Neonatal Forebrain Olig2 represses a neuronal phenotype in SVZ progenitors, allowing or promoting the emergence of glioblasts. Previous in vivo clonal analyses suggest that while a percentage of these glial precursors will remain uncommitted for a period of time, others will become committed to an astrocyte or oligodendrocyte-specific lineage almost immediately following their emigration from the SVZ. SVZ progenitors negative for Olig2 become specified as interneuronal precursors, ultimately differentiating into olfactory interneurons. Transcription factors directing SVZ progenitors to a neuronal fate, potential targets for Olig2 repressor activity, are yet unknown. Olig2 expression is downregulated in maturing astrocytes but maintained in oligodendrocytes. While constitutive Olig2 expression appears to promote oligodendrocyte differentiation, perhaps even prematurely, it may alternatively inhibit the final stages of astrocyte maturation. In summary, Olig2 directs a pan-glial versus neuronal cell fate decision in SVZ progenitors. Furthermore, it may serve two different roles in maturing glial cells by promoting oligodendrocyte differentiation and regulating of astrocyte maturation.
