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First published online 7 July 2004
doi: 10.1242/dev.01204


Development 131, 3805-3819 (2004)
Published by The Company of Biologists 2004


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Sox2 deficiency causes neurodegeneration and impaired neurogenesis in the adult mouse brain

Anna L. M. Ferri1, Maurizio Cavallaro1, Daniela Braida2, Antonello Di Cristofano3, Annalisa Canta1, Annamaria Vezzani4, Sergio Ottolenghi1, Pier Paolo Pandolfi3, Mariaelvina Sala2, Silvia DeBiasi5 and Silvia K. Nicolis1,*

1 Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milano, Italy
2 Department of Pharmacology, Chemotherapy and Medical Toxicology, University of Milano, via Vanvitelli 32, 20129 Milano, Italy
3 Cancer Biology and Genetics Program, and Department of Pathology, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, Box 110, New York, NY 10021, USA
4 Department of Neuroscience, `Mario Negri' Institute of Pharmacological Research, via Eritrea 62, 20157 Milano, Italy
5 Department of Biomolecular Sciences and Biotechnology, University of Milano, via Celoria 26, 20133 Milano, Italy



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Fig. 1. Generation of an allelic series of Sox2 mutations by gene targeting. (A) A schematic diagram of the Sox2 locus (top) and targeting vector used to generate the Sox2{Delta}ENHneo regulatory mutant allele (middle) in ES cells. From this mutant allele, Sox2{Delta}ENH{Delta}neo is obtained by in vivo Cre-mediated excision of the neo cassette. The Sox2ß-geo null/reporter allele (bottom) was previously described (Zappone et al., 2000Go). The PGKneo and PGKTK cassettes are derived from the pPNT vector. ENH is the DNA region containing the brain enhancer described by Zappone et al. (Zappone et al., 2000Go); {alpha},ß and {gamma} are probes used for Southern analysis [for details of {alpha} and {gamma} see Zappone et al. (Zappone et al., 2000Go)], ß is an AccI-XbaI 750 nucleotide fragment within the Sox2 coding region; E, EcoRI; S, SalI; N, NotI; H3, HindIII; X, XhoI; Xb, XbaI. Grey triangles indicate loxP sites; arrows indicate PCR primers used for verifying PGKneo deletion. (B,C) Southern analysis of EcoRI (B) and XbaI (C) digests of ES cell clones. In B, probe {gamma} detects a 16 kb band from the wild-type allele, a 12.5 kb band from the Sox2{Delta}ENHneo allele, and a 6.5 kb band from the Sox2ß-geo allele. In C, probe ß detects a 14 kb band from the wild-type allele, and a 7.2 kb band from the Sox2{Delta}ENHneo allele. Cre-mediated in vivo deletion of the PGKneo cassette from the Sox2{Delta}ENHneo allele was diagnosed by PCR (see above) and confirmed by Southern analysis with both a neo probe and probe {alpha} (not shown).

 


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Fig. 2. Sox2ß-geo expression (X-gal staining, blue) in neural and forebrain development and in adult neural stem cells from Sox2ß-geo/+ mice. (A) Undifferentiated ES cells; (B) E7.5 neural plate stage. Right, anterior; left, posterior. A few blue cells are also visible at the base of the allantois, where the first appearance of primordial germ cells has been described. (C) E12.5 embryo; (D-G) coronal sections of forebrain at E11.5 (D), E12.5 (E) and E17.5 (F,G). In F, asterisks indicate developing thalamic nuclei, basolateral (more external) and centromedian and paraventricular (closer to the midline); black circle indicates the striatum. In G, the black arrowhead indicates the choroid plexus. GE, ganglionic eminence; LV, lateral ventricle. (H-Q) Adult brain. (H) Sagittal section with anterior to the left and posterior to the right. Brief X-gal reaction development. Note the intensely stained ventricle lining and rostral migratory stream. (I,J) Coronal sections (I is more posterior than J) after a prolonged X-gal reaction development. Asterisk and black arrowheads, thalamic nuclei; black circle, dorsal striatum; white circle, septum. (K,L) Interference contrast microscope view of lateral ventricle wall showing details from a section corresponding to that shown in J. Black arrow, ependymal staining; white arrows, subependymal staining. (M) Thalamic region detail, at a level slightly posterior to that shown in I (and corresponding to that shown in F; see F, I and J for symbols). (N) Hippocampus dentate gyrus (long X-gal reaction development). Arrows indicate the germinative layer; asterisks indicate the granule cell layer. (O) Neurospheres, the progeny of stem cells, grown in vitro from adult brain lateral ventricles in the presence of G418 for 5-12 passages (about 5-12 weeks) express lacZ in most cells. (P,Q) Cells obtained by differentiation of the clonal progeny of a single G418-resistant (i.e. Sox2 expressing) cell were probed with antibodies against (P) ß-tubulin III (neurones; red) and GFAP (astroglia; green), or (Q) GalC (oligodendroglia).

 


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Fig. 3. Sox2-expressing cells in the adult brain (DAB staining). (A,B) Origin of the rostral migratory stream in the top corner of the lateral ventricle. Both SOX2 immunostaining (brown) and Haematoxylin counterstaining (blue) of the same section identify a nuclear location. (C) SOX2 immunostaining of lateral ventricle ependyma. (D) SOX2 expression in choroid plexi. (E,F) SOX2-positive (brown) pyramidal cells in cortex (black arrowheads in E), with haematoxylin counterstaining (blue); F shows a higher magnification image. White arrowheads in E indicate SOX2-negative cells. (G) SOX2-positive cells in the striatum (brown). (H) Abundant SOX2-positive cells in the thalamus (brown) with light haematoxylin counterstaining (blue). (I) Occasional SOX2-positive cell (arrow) observed in the corpus callosum.

 


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Fig. 4. Double immunofluorescence characterization of Sox2-expressing cells in adult neurogenic regions (by confocal microscopy). Coronal sections from mice treated with BrdU for one week. (A-D'') Sections comprising the lateral ventricle were labelled with antibodies against SOX2 (green, A'-D'), BrdU (red, A'',B'') and GFAP (red, C'',D''). Co-expression of SOX2 and BrdU, or SOX2 and GFAP results in yellow staining in merged images (A-D). (A,C) Top corner of lateral ventricle, comprising the origin (top left of each panel) of the rostral migratory stream. In C, white arrowheads indicate some of the SOX2/GFAP double-positive cells in the rostral migratory region. (B) Detail of the ventricle wall, lining the striatum. (D) Magnification of a detail of the ventricle wall, adjacent to the striatum, showing a subependymal SOX2/GFAP double-positive cell [for the morphology of GFAP-positive cells in a similar region, see Doetsch (Doetsch, 2003Go)]. (E-G) Sections comprising the basal portion of the hippocampus dentate gyrus. (E) General view of anti-SOX2-labelled dentate gyrus (red). (F) Magnification of a SOX2-positive cell at the basis of the dentate gyrus. (G,H) SOX2/BrdU (G) and SOX2/GFAP (H) double-positive cells are located in the germinative zone at the basis of the dentate gyrus. (G',H') SOX2, green label; (G'') BrdU or (H'') GFAP, red label. (G,H) Yellow indicates double positivity. The position of the cell relative to the germinative cell layer (GCL) is indicated by a dotted white line, which represents the border between the GCL and the hilus (HIL).

 


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Fig. 5. Reduced viability and neurological abnormalities in Sox2ß-geo/{Delta}ENH mutants. (A) Survival of Sox2ß-geo/{Delta}ENH compound heterozygotes is decreased (n=50 embryos genotyped; n=510 adults genotyped). (B) Electroencephalography on Sox2ß-geo/{Delta}ENH (mut) and on wild-type (wt) control mice, performed in cortex (cx) and hippocampus (hip). Epileptic-like activity characterized by abnormal synchronized spikes is observed in mutant mice. These spikes appeared in clusters during the recording period and they were intermixed to basal activity similar to that observed in wild-type mice. (C,D) Effect of L-dopa and dopamine receptor agonists on circling and horizontal motility. (C) Decrease in the absolute number of turns (cumulative turns, mean±s.e.m.) and (D) decrease in cumulative horizontal counts (mean±s.e.m.), following administration of L-dopa (50 mg/kg, intraperitoneal injection), SKF 39383 (D1 receptor agonist, 56 mg/kg, subcutaneous) and quinpirole (QUINP; D2 receptor agonist, 3 mg/kg, subcutaneous). The number of turns and of counts were assessed for 30 minutes in wild-type (wt) and Sox2ß-geo/{Delta}ENH(ko) mutant mice. All drugs were given 10 minutes before the tests. A similar percentage decrease of turns was observed for each individual mouse after treatment, irrespective of the absolute basal number of turns. VEH, vehicle (saline). {circ}{circ}{circ}P<0.001 versus wild-type vehicle-treated group. P<0.05, P<0.01 and P<0.001 versus vehicle-treated mutant group, Tukey's multiple comparison test.

 


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Fig. 6. Morphological alterations of the brain in Sox2ß-geo/{Delta}ENH mutants. (A) Dorsal view of wild-type (top) and mutant (bottom) brains. The shrinkage of the medial-posterior cortex is particularly visible in this mutant. (B-F) Coronal sections through adult forebrain of a normal (top) and a mutant (bottom) mouse. Sections were matched between normal and mutant brains on the basis of the correspondence of characteristic anatomical landmarks (hippocampus, thalamic nuclei and fibre tracts). Left, anteriormost; right, posteriormost. Asterisk indicates thalamic nuclei (see Fig. 2F). Black circle, dorsal striatum; white circle, septum; arrowhead and arrow in E, corpus callosum. Black arrow in F-H marks the diminished extension of the cortex. (G-I) Coronal sections at E14.5 (G,H) and P0 (I) of normal (top) and mutant (bottom) brains. Note, in G and H, the ventricles of the mutant are normal, and the thalamus and striatum sizes are essentially normal, in contrast to the reduced cortex (particularly visible in H).

 


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Fig. 7. Degeneration and pathological cytoplasmic aggregates in mutant neurones, and abnormality of mutant ependyma and choroid plexi. (A-D) Degenerating neurones. (A) Semithin section stained with Toluidine Blue showing abundant shrunken and hyperchromic degenerating cells in the thalamus (centromedian nucleus) of mutant mice. The same cell abnormalities were observed in dorsal striatum and septum (not shown). (B) Detail of A. White asterisks indicate healthy neurones; black asterisks indicate shrunken and hyperchromatic pathological neurones. (C,D) Electron microscopy of hyperchromatic cell. Note the high electron density of the cytoplasm and nucleus, the cytoplasmic and nuclear membrane irregularities, and the dilated Golgi cisternae (indicated by arrows). N, nucleus; M, mitochondria. Scale bars: 2.5 µm in C; 0.5 µm in D. (E-L) Intraneuronal aggregates. (E) Semithin section stained with Toluidine Blue showing abundant intraneuronal perinuclear aggregates in the thalamus (ventrobasal nuclei) of mutant mice. The inclusions in the cells at the far left and lower right are similar to those shown by electron microscopy in F and G, respectively. Arrowheads point to aggregates. V, blood vessel. (F,G,H) Electron microscopy of aggregates. Asterisks indicate the central clearer region, seen at higher magnification in H. The inclusions show abundant filamentous content, with a filament diameter of 9-10 µm. Scale bars: 1 µm in F,G; 0.2 µm in H. (I) Semithin section showing inclusion-containing and normal neurones, stained with Toluidine Blue. Arrow indicates aggregate showing typical perinuclear location. (J-L) Immunohistochemistry (on paraffin sections) with anti-neurofilament (SMI 32; J) and anti-ubiquitin (K,L) antibodies. Positive staining was also observed with SMI 31 (anti-phosphorylated neurofilaments) antibody (not shown). Arrows indicate immunostained intraneuronal aggregates. Note the normal morphology of the aggregate-containing neurones in J and K, and the pathological morphology of the hyperchromatic aggregate-containing neurone in L (see text). In K, note the weaker immunostaining (light brown) in the cell on the right. (M,N) Wild-type (M) and mutant (N) ependyma. Black diamond indicates lipidic inclusions; arrows indicate cilia. N, nucleus. (O,P) Wild-type (O) and mutant (P) choroid plexi. Left, apical microvilli; right, basal membrane, with numerous infoldings (asterisk) in the mutant. Arrowheads point to basal membrane.

 


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Fig. 8. Reduced cell proliferation and impaired neurogenesis in adult mutant neurogenic regions. (A) Decreased BrdU labelling in mutant (right) versus wild-type (left) hippocampus dentate gyrus (DG, top) and lateral ventricle (LV, bottom). BrdU immunoreactivity was revealed by diaminobenzydine (DAB) staining (brown) in the hippocampus, and by rhodamine fluorescence (red) in the lateral ventricle. In the lateral ventricle, the upper panel shows the top lateral corner, and the lower panel shows the ventrolateral wall of the ventricle. (B) Quantitation of BrdU labelling. The average number of BrdU-positive cells in wild-type mice was set equal to 100. Each bar corresponds to the total number of BrdU-positive nuclei in the lateral ventricle walls (LV, left) or in the hippocampus dentate gyrus germinative layer (DG, right) of an individual mouse (white bars, wild type; black bars, mutants). (C) Double fluorescence immunohistochemistry for BrdU (red) and calbindin (CB, green, marking mature granule neurones) on hippocampus dentate gyrus (confocal microscopy). Mice were treated with BrdU for 12 days. BrdU/CB double-positive cells (yellow) are newborn neurones still retaining the label (BrdU) of a recently divided precursor. White arrows indicate BrdU-positive, CB-negative precursors at the base of the granule cell layer; the white arrowhead indicates a BrdU/CB double-positive cell within the granule cell layer (yellow). Quantitative assessment is shown in E. (D) Double fluorescence immunocytochemistry for BrdU (red) and ß-tubulin (green, marking neuroblasts) on dissociated cells from the periventricular region of the lateral ventricle of mice treated with BrdU for 7 days (blue, DAPI nuclear staining). Note that ß-tubulin staining is cytoplasmic. An example of five different cells, stained with all three labels and viewed as a merged image, is shown on the left (ß-tub, BrdU, DAPI). The corresponding single fluorescence images are shown in the panels to the right. Double-positivity for BrdU and ß-tubulin results in a pink nuclear image (due to overlap of the red BrdU staining with the blue DAPI) partially surrounded by a blue-green halo (top left cell). Single positivity for BrdU results in a pink image (top right cell), whereas single positivity for ß-tubulin results in a blue-green colour (bottom left cell). At the bottom right, note the doublet consisting of a doubly positive cell and a single ß-tubulin-positive cell. (E) Quantitation of BrdU/CB double-positive cells (left histogram), and of the proportion of CB-positive cells among BrdU-positive cells, in the dentate gyrus of wild-type (white bars) and mutant (black bars) mice (see C). The average number of BrdU/CB double-positive cells counted in wild-type mice was 71 (5 sections per mouse counted), and was set equal to 100 (left histogram). The average proportion of CB-positive cells among BrdU-positive cells was 31% in wild-type mice. Each bar corresponds to one mouse, identified by numbers on the x axis (see also panel B). (F) Quantitation of BrdU/ß-tubulin double-positive cells in dissociated periventricular cells of the lateral ventricle from wild-type and mutant mice (see panel D). The average value for wild-type mice (corresponding to 60 double-positive cells/four chambered wells counted) was set equal to 100.

 


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Fig. 9. Nestin- and GFAP-positive early precursors are severely reduced in mutant hippocampus. (A,C) Immunofluorescence detection of radially oriented nestin-expressing cells (bright green; white arrowheads) in wild-type (A) and mutant (C) hippocampus. (B,B',D,D') Immunohistochemical detection (DAB, brown) of GFAP-expressing cells in wild-type (B) and mutant (D) hippocampus. Note, in the enlargement of the boxed areas (B',D'), the severe reduction of GFAP-positive radially oriented cells within the dentate gyrus. (E,F) Double immunofluorescence detection of nestin (E,E',F,F'; green)/GFAP (E,E'',F,F''; red) double-positive precursor cells in the hippocampus dentate gyrus of wild-type (E) and mutant (F) mice. Double-positive cells are indicated by white arrowheads. The dotted lines define the dentate gyrus region. HIL, hilus.

 

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© The Company of Biologists Ltd 2004