Overexpression of mSim2 gene in the zona limitans of the diencephalon of segmental trisomy 16 Ts1Cje fetuses, a mouse model for trisomy 21: a novel whole-mount based RNA hybridization study

Trisomy 21 (Down syndrome) is the most common chromosomal abnormality associated with mental retardation in humans. Sim2, a human homologue of Drosophila sim gene, which acts as a master regulator of the early development of the fly central nervous system midline, is located on chromosome 21, in the Down syndrome critical region, and might therefore be involved in the pathogenesis of some of the morphological features and brain anomalies observed in Down syndrome. We report here the detailed expression pattern of murine mSim2 gene in Ts1Cje mice fetuses, a segmental trisomy 16 mouse model for trisomy 21, and its overexpression in the zona limitans of the diencephalon using a new quantitative method based on the whole-mount RNA hybridization technique.

Regional and cellular specificity of the expression of TPRD, the tetratricopeptide Down syndrome gene, during human embryonic development

The TPRD gene (tetratricopeptide (TPR) containing Down syndrome gene) is one of the candidate genes in the Down syndrome chromosomal region-1. Duplication of this gene may be the cause of major phenotypic features of Down syndrome. Here we show that the TPRD expression is developmentally regulated during human embryogenesis. At the earliest stages of development (Carnegie 8-12) TPRD expression is ubiquitous. At later developmental stages (Carnegie stages 14, 16 and 18), it becomes restricted to the nervous system, as is the case for the mtprd gene during mouse development. We extended our analysis of TPRD expression during fetal development of the human nervous system (13, 22 and 24 weeks). A new oblique illumination technique was used to compare signal intensity and cell density. Some regions of the nervous system such as the external cortical layers of the brain, and the inner neuroblastic layer of the eye, strongly express the TPRD gene.

Characterization of a novel gene, C21orf6, mapping to a critical region of chromosome 21q22.1 involved in the monosomy 21 phenotype and of its murine ortholog, orf5

Phenotypic and molecular analyses of patients with partial chromosome 21 monosomy enabled us to define a region, spanning 2.4 Mb between D21S190 and D21S226, associated with arthrogryposis, mental retardation, hypertonia, and several facial anomalies. The markers of the region were used to screen a total human PAC library (Ioannou, RZPD). We isolated 57 PACs, which formed primary contigs. EST clusters (UNIGENE collection) located in a 6-Mb interval, between D21S260 and D21S263, were mapped in individual bacterial clones. We mapped the WI-17843 cluster to the PAC clone J12100, which contains the two anchor markers LB10T and LA329. The open reading frame extends over 960 bp, with three putative start codons. The 1695-bp cDNA containing a polyadenylation signal should correspond to the full-length cDNA. From the genomic sequence, we deduced that the gene contained five exons and that there was a putative promoter sequence upstream from exon 1. In silico screening of DNA databases revealed similarity with a murine EST. The corresponding cDNA (1757 bp) sequence was very similar (>85%) to the human cDNA and had an open reading frame of 876 nucleotides. Somatic hybrid mapping localized the cDNA to mouse chromosome 16. EST analyses and RT-PCR indicated that the third exon in the human gene (exon 2 in the mouse) undergoes alternative splicing. Northern blot hybridization showed that the gene was ubiquitously expressed in humans and mice. The longest mouse clone was used to generate riboprobes, which were hybridized to murine embryos at stages E-9.5, E-10.5, E-12.5, E-13.5, and E-14.5-15, to study the pattern of expression during development. Ubiquitous labeling was observed, with strong signals restricted to limited areas of the telencephalon, the mesencephalon, and the interrhombomeric regions in the central nervous system, and other regions of the body such as the limb buds, branchial arches, and somites.

Overproduction of Cu/Zn-superoxide dismutase or Bcl-2 prevents the brain mitochondrial respiratory dysfunction induced by glutathione depletion

Recent work has focused attention on the role of oxidative stress in various acute and chronic neurodegenerative diseases. Low concentrations of the powerful antioxidant glutathione (GSH) and impaired brain energy metabolism, particularly in the substantia nigra, are key features of Parkinson's disease (PD). The main goal of this study was to better characterize the deleterious effects of brain GSH depletion on mitochondrial function. We depleted GSH in the brains of newborn wild-type (WT) and transgenic (Tg) mice overproducing either human Cu/Zn-superoxide dismutase (h-CuZnSOD) or human Bcl2 (h-Bcl-2), by subcutaneous injection of l-buthionine sulfoximine (BSO), a specific inhibitor of gamma-glutamylcysteine synthetase. GSH was 97% depleted in brain homogenates and 90% depleted in brain mitochondria for both WT and Tg mice. This depletion of brain GSH led to a decrease in the activity of the GSH-dependent antioxidant enzyme glutathione peroxidase, both in WT and in Tg animals. BSO treatment decreased the activities of respiratory complexes I, II, and IV in the brain homogenates of WT mice. BSO-treated h-CuZnSOD or h-Bcl-2 Tg mice had no respiratory chain deficiencies. Thus, brain GSH depletion leads to the impairment of mitochondrial respiratory chain activity. The protection of mitochondrial respiratory function by overproduction of Bcl-2 may result from a decrease in the generation of reactive oxygen species (ROS) or lipid peroxidation. The protection of mitochondria by overproduction of CuZnSOD is consistent with the involvement of superoxide or superoxide-derived ROS in the mitochondrial dysfunction caused by brain GSH depletion. This study demonstrates that the antioxidant balance is critical for maintenance of brain mitochondrial function, and its disruption may contribute to the pathogenesis of PD.

Identification of beta-amyloid-responsive genes by RNA differential display: early induction of a DNA damage-inducible gene, gadd45

Alzheimer's disease is a neurodegenerative disorder characterized by the extracellular deposition in the brain of amyloid beta-peptide (A beta), presumed to play a pathogenic role. However, the precise molecular mechanisms of its neurotoxicity are not fully understood. Recent studies have suggested that it may exert its toxic effect via activation of transcription factors. We investigated A beta-responsive genes in human preneuron NT2 cells, at early stages of A beta (25-35) exposure, by RNA differential display. A beta induced the expression of (i) the growth arrest and DNA damage-inducible gene (gadd45) implicated in the DNA excision-repair process; (ii) a stress-signaling kinase gene encoding the mitogen-activated protein kinase/Erk kinase kinase-1 (MEKK1); (iii) a new growth factor-inducible immediate-early gene, CYR61, the product of which functions as an extracellular matrix signaling molecule; (iv) other immediate-early genes, such as c-jun and c-fos; (v) the gene encoding the basic fibroblast growth factor (bFGF); (vi) a gene encoding a constituent of the mitochondrial pyruvate dehydrogenase complex, the dihydrolipoamide dehydrogenase-binding protein (E3-BP); and (vii) an unidentified human gene (KIAA0099). A beta not only activates but also respresses genes: (i) the gene encoding "hinge" protein, a subunit of the mitochondrial cytochrome-c reductase and (ii) the SRp55 gene encoding a splicing factor involved in constitutive pre-mRNA splicing and alternative splice site selection. Our results underscored A beta-responsive genes that play key roles in the response (damage/recovery) of neuron cells to A beta exposure. In particular, the strong upregulation of gadd45, indicating DNA damage, was detected early in A beta cytotoxicity. This suggests that DNA strand breaks occurred rapidly in cells exposed to A beta, which may be a critical event in A beta neurotoxicity.

Developmentally regulated expression of mtprd, the murine ortholog of tprd, a gene from the Down syndrome chromosomal region 1

The gene tprd, which contains three tetratricopeptide domains, has been recently localized in the Down syndrome (DS) chromosomal region 1. We have cloned a cDNA encoding part of the murine ortholog of tprd and used it to characterize the expression pattern of this gene during development and at the adult stage. At E8.5 the expression is uniform. In the later stages of embryogenesis, although expression remains ubiquitous, a pattern of tissues with particularly high expression develops: the strong expression is restricted to non proliferating zones of the nervous system such as the external layer of the cortex, the spinal cord, the cranial and root ganglia and the nerves. In the brain of adult mouse the strongest signals are observed in layers II-III and V-VI of the cortex, in the hippocampus and in the cerebellum, which correspond to the abnormal brain regions seen in DS patients.

Transcriptional map of the 2.5-Mb CBR-ERG region of chromosome 21 involved in Down syndrome

The region of chromosome 21 between genes CBR and ERG (CBR-ERG region), which spans 2.5 Mb on 21q22.2, has been defined by analysis of patients with partial trisomy 21. It contributes significantly to the pathogenesis of many characteristics of Down syndrome, including morphological features, hypotonia, and mental retardation. Cosmid contigs covering 80% of the region were constructed and EcoRI maps produced. These cosmids were used for exon trapping and cDNA selection from three cDNA libraries (fetal brain, fetal liver, and adult skeletal muscle). Isolated exons and cDNAs were mapped on the EcoRI map, organized into contigs, sequenced, and used as probes for Northern blot analysis of RNA from fetal and adult tissues. We identified 27 genuine or highly probable transcriptional units evenly distributed along the CBR-ERG region. Eight of the transcriptional units are known genes.

A new inward rectifier potassium channel gene (KCNJ15) localized on chromosome 21 in the Down syndrome chromosome region 1 (DCR1)

The Down syndrome chromosome region-1 (DCR1) on subband q22.2 of chromosome 21 is thought to contain genes contributing to many features of the trisomy 21 phenotype, including dysmorphic features, hypotonia, and psychomotor delay. Isolation, mapping, and sequencing of trapped exons and captured cDNAs from cosmids of this region have revealed the presence of a gene (KCNJ15) encoding a potassium (K+) channel belonging to the family of inward rectifier K+ (Kir) channels. The amino acid sequence deduced from the 1125-bp open reading frame indicates that this gene is a member of the Kir4 subfamily; it has been named Kir4.2. It is expressed in kidney and lung during human development and in several adult tissues including kidney and brain. After Kir3.2 (GIRK2), Kir4.2 is the second K+ channel gene of this type described within the DCR1.

High-resolution physical mapping of a 6.7-Mb YAC contig spanning a region critical for the monosomy 21 phenotype in 21q21.3-q22.1

Deletion of genes from the chromosome 21 region between APP and SOD1 is a potential cause of some of the major phenotypic features of monosomy 21 patients. Fine physical mapping helps identify potential candidate genes. After selecting nonchimeric YACs by FISH analysis, we determined their marker contents by PCR and hybridization studies. Fifteen YACs were chosen and mapped by restriction enzyme analysis and labeling of end fragments. We localized 55 markers, including 31 STSs, 10 YAC ends, and 4 NotI linking clones, along a 6.7-Mb contig. This map facilitates transcriptional analysis of this region and construction of ready-to-sequence contigs. Furthermore, FISH mapping of two patients with partial monosomy 21 using YAC and cosmid clones allowed us to define more accurately the telomeric border of the critical region between markers S226 and S213.

Rapid fluorescence in situ hybridization on interphasic nuclei to discriminate between homozygous and heterozygous transgenic mice

Homozygous and heterozygous transgenic mice of the Tg152 line overexpressing the human copper/zinc superoxide dismutase (hSOD-1) were rapidly differentiated by fluorescence in situ hybridization (FISH) using interphase lymphocyte nuclei. We have devised a simple and fast method for preparing interphase nuclei with very small quantities of whole mouse blood, avoiding several steps of the classical FISH technique. Lymphocyte separation and cell culture were not required. This technique provides an excellent tool for the unambiguous detection of homozygous and heterozygous transgenic mice in a litter. It can be used to check young animals since 2 microliters of whole blood is sufficient. We also show that in this transgenic line numerous copies of the hSOD-1 transgene are integrated at a single autosomal locus, in tandem head-to-tail organization.

Transgenic mice overexpressing the human Cu/Zn-SOD gene: ultrastructural studies of a premature thymic involution model of Down's syndrome (trisomy 21)

It has been suggested that the overexpression of copper-zinc superoxide dismutase (SOD-1) in Down's syndrome (DS) patients may be involved in expression of some of the phenotypic characteristics observed in these patients. To explore the possible role of SOD-1 overexpression in the premature thymic involution and immunologic disorders observed in DS patients, transgenic mice overexpressing the human SOD-1 gene have been generated and their thymuses have been studied at the ultrastructural level. Our observations show premature involution of the thymus in SOD-1 transgenic mice, with a strong modification of the thymic microenvironment starting at approximately 3-4 months of age. The thymic microenvironment in 7-month-old transgenic mice is similar to that observed in 20-month-old control mice. We suggest that these results are consistent with the role of SOD-1 overexpression in the early thymic involution observed in DS patients. These transgenic mice provide an interesting model to investigate the deleterious effect of increased dosage of some chromosome 21 genes such as SOD-1 in the pathogenesis of DS.

Down syndrome-critical region contains a gene homologous to Drosophila sim expressed during rat and human central nervous system development

Many features of Down syndrome might result from the overdosage of only a few genes located in a critical region of chromosome 21. To search for these genes, cosmids mapping in this region were isolated and used for trapping exons. One of the trapped exons obtained has a sequence very similar to part of the Drosophila single-minded (sim) gene, a master regulator of the early development of the fly central nervous system midline. Mapping data indicated that this exonic sequence is only present in the Down syndrome-critical region in the human genome. Hybridization of this exonic sequence with human fetal kidney poly(A)+ RNA revealed two transcripts of 6 and 4.3 kb. In situ hybridization of a probe derived from this exon with human and rat fetuses showed that the corresponding gene is expressed during early fetal life in the central nervous system and in other tissues, including the facial, skull, palate, and vertebra primordia. The expression pattern of this gene suggests that it might be involved in the pathogenesis of some of the morphological features and brain anomalies observed in Down syndrome.

Molecular mapping of 21 features associated with partial monosomy 21: involvement of the APP-SOD1 region

We compared the phenotypes, karyotypes, and molecular data for six cases of partial monosomy 21. Regions of chromosome 21, the deletion of which corresponds to particular features of monosomy 21, were thereby defined. Five such regions were identified for 21 features. Ten of the features could be assigned to the region flanked by genes APP and SOD1: six facial features, transverse palmar crease, arthrogryposis-like symptoms, hypertonia, and contribution to mental retardation. This region, covering the interface of bands 21q21-21q22.1, is 4.7-6.4 Mb long and contains the gene encoding the glutamate receptor subunit GluR5 (GRIK1).

Genomic organization of the human cystathionine beta-synthase gene: evidence for various cDNAs

A CBS cDNA isolated from an adult liver cDNA library was cloned and sequenced. The 5' untranslated region (5'-UTR) contains a sequence which is only partially common (88nt) with that previously published (3). It is expressed as a 2.5kb species mostly in liver and pancreas and faintly in brain, heart, kidney and lung and as a 3.7 kb in pancreas and liver. The human cystathionine beta-synthase gene (CBS) was isolated from a cosmid genomic library and its structure was determined. The CBS gene is at least 23 kb long and is composed of 17 exons. The organization of the human gene is different from that of the rat especially in the 5'-UTR. In the rat gene the ATG is present in exon 1, conversely in the human gene first the ATG is present in exon 3 and second the 5'-UTR contains two different exons 1 (E1a and E1b) linked with exon 2.

3.6-Mb genomic and YAC physical map of the Down syndrome chromosome region on chromosome 21

The Down syndrome chromosome region (DCR) on chromosome 21 has been shown to contain a gene(s) important in the pathogenesis of Down syndrome. We constructed a long-range restriction map of the D21S55-D21S65 region covering the proximal part of the DCR. Pulsed-field gel electrophoresis of lymphocyte DNA digested with three rare cutting enzymes. NotI, NruI, and MluI, was used to establish two physical linkage groups of 5 and 7 markers, respectively, spanning 4.6 Mb on the NotI map. Mapping analysis of 40 YACs allowed the selection of 13 YACs covering 95% of the D21S55-D21S65 region and spanning 3.6 Mb. The restriction maps of these YACs and their positioning on the genomic map allowed 19 markers to be ordered, including 4 NotI linking clones, 9 polymorphic markers, the CBR gene, and the AML1 gene. The distances between markers could also be estimated. This physical map and the location of eight NotI sites between D21S55 and D21S17 should facilitate the isolation of previously unidentified genes in this region.

Mapping of the Down syndrome phenotype on chromosome 21 at the molecular level

Phenotypic and molecular analysis of individuals with partial trisomy 21 can be used to determine which regions of chromosome 21 are involved in the pathogenesis of specific features of Down's Syndrome. Using dosage analysis of 27 sequences we defined, at the molecular level, the extent of the chromosome 21 duplication in ten individuals with partial trisomy 21. Phenotype-genotype correlations led to the definition of minimal regions, the duplications of which are linked to the expression of 23 clinical features of Down's Syndrome. The D21S55 region or Down's Syndrome Chromosome Region 1 (DCR1) (1/20 of the long arm), on 21q22.2-21q22.3 proximal, is involved in four cardinal features of the disease: mental retardation, growth retardation, muscular hypotonia and joint hyperlaxity, and in eight of the 18 more common morphological anomalies of the face, hands and feet. Overlapping the DCR1, the D21S55-MX1 region or DCR2 (1/10 of the long arm), spanning 21q21.2 down to the 1/4th proximal part of 21q22.3, is involved in the features defined by the DCR1 plus congenital heart defect and five additional morphological anomalies. Thus, our results indicate that duplication of a relatively small region of chromosome 21 plays a critical role in the pathogenesis of the Down's phenotype.

Hippocampal mossy fiber changes in mice transgenic for the human copper-zinc superoxide dismutase gene

The copper-zinc superoxide dismutase (SOD-1) gene, located on chromosome 21 and triplicated in Down's syndrome (DS), is suspected to be involved in the neuropathology observed in Alzheimer's disease (AD), DS and physiological aging. In order to explore the effect of an overproduction of SOD-1 in the mouse hippocampus, we investigated the Timm-stained mossy fiber (MF) innervation in the hippocampus of transgenic mice for the human SOD-1 gene (hSOD-1 mice). The results showed a decrease of the MF projection area in the hSOD-1 mice overexpressing the SOD-1 protein. These findings suggest that free radicals could play a role in this particular synaptic loss.

Preferential expression of superoxide dismutase messenger RNA in melanized neurons in human mesencephalon

The copper-zinc-dependent superoxide dismutase messenger RNA expression was studied at cellular level by in situ hybridization, using a 35S-labelled complementary DNA probe homologous to human copper-zinc-dependent superoxide dismutase messenger RNA, in the dopaminergic neuron-containing areas of the human mesencephalon (the substantia nigra pars compacta, ventral tegmental area, central gray substance and peri- and retrorubral region corresponding to catecholaminergic cell group A8). The autoradiographic labelling signal was localized in neurons. No detectable hybridization signal could be found in the glial cells. Copper-zinc-dependent superoxide dismutase messenger RNA was detected in melanin-containing neurons as well as in non-melanized neurons. Quantification at cellular level, taking the autoradiographic silver grain density as an index of the abundance of copper-zinc-dependent superoxide dismutase messenger RNA, indicated that hybridization level was higher in the melanized than in the non-melanized neurons within a region. Among melanized neurons, cellular copper-zinc-dependent superoxide dismutase messenger RNA content was lowest in the neurons of the substantia nigra. No significant difference in levels of transcripts was evidenced between the groups of non-melanized neurons. The data suggest that the abundance of copper-zinc-dependent superoxide dismutase messenger RNA is higher in the mesencephalic neurons containing neuromelanin compared to other neurons. Thus, the melanized neurons have a particular defence system against oxygen toxicity, which may represent a basis for their preferential vulnerability to Parkinson's disease.

Partial physical map of human chromosome 21 from fibroblast and lymphocyte DNA

A partial physical map of the human chromosome 21 including 26 genes and anonymous sequences was established by pulsed-field gel electrophoresis analysis of restriction fragments obtained from lymphocyte and fibroblast DNAs. The sizes of the restriction fragments obtained by total digestion with eight different enzymes were compared in these two tissues. Differences resulting from the variations in the methylation state of the restriction sites were frequently observed. These differences and partial digestions were used to estimate the order and the distances between genes and sequences. Six linkage groups were defined: D21S13-D21S16, D21S1-D21S11, D21S65-D21S17, (D21S55,ERG)-ETS2, BCEI-D21S19-D21S42-D21S113-CBS-CRYA1, and COL6A2-S100B. For six intergenic distances the resolution of previous maps was significantly increased.

Molecular mapping of twenty-four features of Down syndrome on chromosome 21

To determine which regions of chromosome 21 are involved in the pathogenesis of specific features of Down syndrome, we analysed, phenotypically and molecularly, 10 patients with partial trisomy 21. Six minimal regions for 24 features were defined by genotype-phenotype correlations. Nineteen of these features could be assigned to just 2 regions: short stature, joint hyperlaxity, hypotonia, major contribution to mental retardation and 9 anomalies of the face, hand and foot to the region D21S55, or Down syndrome chromosome region (DCR), located on q22.2 or very proximal q22.3, and spanning 0.4-3 Mb; 6 facial and dermatoglyphic anomalies to the region D21S55-MX1, including the DCR and spanning a maximum of 6 Mb on q22.2 and part of q22.3. Thus, the complex phenotype that constitutes Down syndrome may in large part simply result from the overdosage of only one or a few genes within the DCR and/or region D21S55-MX1.

Mapping the Down syndrome chromosome region. Establishment of a YAC contig spanning 1.2 megabases

The triplication of a region of chromosome 21 around D21S55 in 21q22.2-22.3 has been involved in the main features of Down syndrome including mental retardation (Down syndrome chromosome region: DCR). To improve the physical map of this region, we screened yeast artificial chromosome (YAC) libraries with ETS2 and ERG sequences. Five selected clones were analyzed by AluPCR, pulsed-field gel electrophoresis, and in situ hybridization. A 1.2-Mg contig, encompassing the protooncogenes ETS2 and ERG, was identified, its restriction map established and compared to the genomic map. ERG is distal to D21S55 and proximal to ETS2. ERG and ETS2 genes are 400 kb apart and in opposite orientations. The contig contains the distal boundary and part of the DCR. Three putative HTF islands were identified.

New chromosome 21 DNA markers isolated by pulsed field gel electrophoresis from an ETS2-containing Down syndrome chromosomal region

To generate new chromosome 21 markers in a region that is critical for the pathogenesis of Down syndrome (D21S55-MX1), we used pulsed field gel electrophoresis (PFGE) to isolate a 600-kb NruI DNA fragment from the WA17 hybrid cell line, which has retained chromosome 21 as the only human material. This fragment, which contains the oncogene ETS2, was used to construct a partial genomic library. Among the 14 unique sequences that were isolated, 3 were polymorphic markers and contained sequences that are conserved in mammals. Five of these markers mapped on the ETS2-containing NruI fragment and allowed us to define an 800-kb high-resolution PFGE map.

No significant effect of monosomy for distal 21q22.3 on the Down syndrome phenotype in "mirror" duplications of chromosome 21

Three Down syndrome patients for whom karyotypic analysis showed a "mirror" (reverse tandem) duplication of chromosome 21 were studied by phenotypic, cytogenetic, and molecular methods. On high-resolution R-banding analysis performed in two cases, the size of the fusion 21q22.3 band was apparently less than twice the size of the normal 21q22.3, suggesting a partial deletion of distal 21q. The evaluation of eight chromosome 21 single-copy sequences of the 21q22 region--namely, SOD1, D21S15, D21S42, CRYA1, PFKL, CD18, COL6A1, and S100B--by a slot blot method showed in all three cases a partial deletion of 21q22.3 and partial monosomy. The translocation breakpoints were different in each patient, and in two cases the rearranged chromosome was found to be asymmetrical. The molecular definition of the monosomy 21 in each patient was, respectively, COL6A1-S100B, CD18-S100B, and PFKL-S100B. DNA polymorphism analysis indicated in all cases a homozygosity of the duplicated material. The duplicated region was maternal in two patients and paternal in one patient. These data suggest that the reverse tandem chromosomes did not result from a telomeric fusion between chromosomes 21 but from a translocation between sister chromatids. The phenotypes of these patients did not differ significantly from that of individuals with full trisomy 21, except in one case with large ears with an unfolded helix. The fact that monosomy of distal 21q22.3 in these patients resulted in a phenotype very similar to Down syndrome suggests that the duplication of the genes located in this part of chromosome 21 is not necessary for the pathogenesis of the Down syndrome features observed in these patients, including most of the facial and hand features, muscular hypotonia, cardiopathy of the Fallot tetralogy type, and part of the mental retardation.

De novo t(X;21)(q28;q11) in a girl with phenotypic features of Williams-Beuren syndrome

We describe a female infant with mental retardation and some of the phenotypic features of Williams-Beuren syndrome. Chromosome analysis showed t(X;21)(q28;q11). Diagnosis, inactivation of the X chromosome, and possible involvement of the translocation breakpoints in the pathogenesis of this syndrome are discussed.

Age-related changes in antioxidant enzymes and lipid peroxidation in brains of control and transgenic mice overexpressing copper-zinc superoxide dismutase

The aim of our study was first to obtain a comprehensive profile of the brain antioxidant defense potential and peroxidative damage during aging. We investigated copper-zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), seleno-dependent glutathione peroxidase (GSH-PX), glutathione reductase (GSSG-R) activities, endogenous and in vitro stimulated lipid peroxidation in 40 brains of control mice divided into 3 age groups: 2 months (young), 12 months (middle-aged) and 28 months (old). We found a positive correlation between age and activities of CuZnSOD (r = 0.47; P < 0.01) and GSH-PX (r = 0.72; P < 0.0001). CuZnSOD and GSH-PX activities are independently regulated during brain aging since temporal changes of these two enzymes do not correlate. No modification in MnSOD activity and basal lipid peroxidation was observed as a function of age. Nevertheless, stimulated lipid peroxidation was significantly higher at 12 months (6.53 +/- 0.71 mumole MDA/g tissue) than at 2 months (5.69 +/- 0.90) and significantly lower at 28 months (5.13 +/- 0.33) than at 12 months. Second, we used genetic manipulations to construct transgenic mice that specifically overexpress CuZnSOD to understand the role of CuZnSOD in neuronal aging. The human CuZnSOD transgene expression was stable during aging. The increased CuZnSOD activity in the brain (1.9-fold) of transgenic mice resulted in an enhanced rate of basal lipid peroxidation and in increased MnSOD activity in the 3 age groups. Other antioxidant enzymes did not exhibit modifications indicating the independence of the regulation between CuZnSOD and glutathione-related enzymes probably due to their different cellular localization in the brain.

Gene-dosage mapping of 30 DNA markers on chromosome 21

Using a slot-blot method for the dosage of single-copy sequences, the copy numbers of 30 chromosome 21 markers were assessed in the blood DNA of 11 patients with partial trisomy or monosomy 21 and in the DNA of a patient-derived human-hamster hybrid cell line carrying a microduplication of chromosome 21. The physical order of these markers on chromosome 21 was thereby determined.

Cellular clones and transgenic mice overexpressing copper-zinc superoxide dismutase: models for the study of free radical metabolism and aging

Down's Syndrome (DS), the most frequent of congenital birth defects, results from the trisomy of the chromosome numbered 21 in all cells of affected patients. This disease is characterized by developmental anomalies, mental retardation and features of rapid aging, particularly in the brain where the occurrence of Alzheimer's disease (AD) is observed in all trisomy 21 patients over the age of 35. Elucidation of the biological mechanisms leading to brain aging in DS might provide new insight into the understanding of brain aging and AD in normal people. Copper-zinc superoxide dismutase (CuZnSOD) is one of the genes encoded by chromosome 21. As a consequence of gene dosage excess, CuZnSOD activity and protein are increased by 50% in all DS tissues. The level of CuZnSOD protein and mRNA is particularly high in hippocampal pyramidal neurons susceptible to degenerative processes in AD and in dopaminergic melanized-neurons vulnerable in Parkinson's disease. Increased CuZnSOD activity in these age-related neurodegenerative disorders might result in H2O2 overproduction and subsequently promote peroxidative damages within cells. Increase of seleno-dependent glutathione peroxidase (Se-GPx) in DS cells supports this concept. In order to test this hypothesis, cell and animal models of CuZnSOD overexpression have been designed. In cells transfected with the human CuZnSOD gene, and increased Se-GPx activity is observed, a situation which mimics DS. In mice transgenic for the human CuZnSOD, the expression pattern of the transgene in the brain is similar to that in humans, and we can observe an increased peroxidation in this tissue. These data, like others in the literature, support the hypothesis that excess CuZnSOD induces an imbalance in the regulation of oxygen-derived free radical production which might result in peroxidative brain damage and possibly contribute to accelerated aging and age-related neuropathology.

Age-correlated modifications of copper-zinc superoxide dismutase and glutathione-related enzyme activities in human erythrocytes

To obtain a comprehensive profile of the erythrocyte antioxidant defense potential during aging, we investigated copper-zinc superoxide dismutase (CuZn-SOD), seleno-dependent glutathione peroxidase (GSH-Px), glutathione reductase (GSSG-RD), and glutathione-S-transferase (GSH-S-T) activities in human erythrocytes from 167 apparently healthy subjects, ages one month to 63 years (102 females, 65 males). We found a negative correlation between age and activities of CuZn-SOD (r = 0.362, P less than 0.001), GSSG-RD (r = 0.549, P less than 0.001), and GSH-S-T (r = 0.575, P less than 0.001). In contrast, we found a positive correlation between age and GSH-Px activity (r = 0.401, P less than 0.001). To evaluate aging changes, we divided the subjects into five groups: Group 1 (newborn-age one year), Group 2 (1-11 years), Group 3 (11-25 years), Group 4 (25-40 years), and Group 5 (40-63 years). Significant age-related modifications in erythrocyte enzyme activities appeared in Group 3 for CuZn-SOD, GSSG-RD, and GSH-Px activity, whereas for GSH-S-T activity age-related modifications appeared in Group 2. We found no sex-related differences in erythrocyte CuZn-SOD, GSSG-RD, GSH-Px, and GSH-S-T activities.

Cytogenetic and molecular analysis of a de novo tandem duplication of chromosome 21

We have characterised by cytogenetic and molecular analysis a de novo tandem duplication of chromosome 21. High resolution chromosome examination of lymphocytes revealed the following karyotype in 90% of the cells: 46,XY,dir dup (21)(pter----q22.300::q11.205----qter). Of these cells, 10% showed a normal karyotype. Gene dosage of chromosome 21 sequences by a slot blot method indicated that the duplication extends from D21S16 to D21S55. In situ hybridization with probes close to the borders of the duplicated segment confirmed the gene dosage data and gave results consistent with a true tandem duplication of chromosome 21. Pulsed field gel electrophoresis of the patient's DNA showed an abnormal restriction band common to D21S55 and D21S16, confirming that the junction point between the two homologous parts of the tandem chromosome brings these two sequences into proximity. Restriction fragment length polymorphism analysis indicated that the abnormal chromosome was maternal in origin and that the rearrangement of chromosome 21 could not have occurred at a post-zygotic stage of development but resulted from a recombination event during maternal gametogenesis. The possible mechanisms of formation of the abnormal chromosome are discussed, as is the presence of cells with normal chromosomes 21, in the patient.

Accurate evaluation of the sizes of DNA fragments (from 30 to 4700 kb) in pulse field gel electrophoresis

Construction of long-range genomic maps by pulse field gel electrophoresis requires optimum resolution of large DNA fragments. Using the transverse-alternating field electrophoresis system, we describe a method to accurately evaluate the sizes of fragments generated by rare-cutter digestions within the 30-4700-kb range. A protocol generating large (greater than 1000 kb) molecules by partial digestion is also reported.

Reduced protein kinase C activity in sporadic Alzheimer's disease fibroblasts

A decrease in the protein kinase C immunoreactivity and an altered protein phosphorylation have been reported in patients with Alzheimer's disease, but discordant results have been obtained from determinations of protein kinase C activity. By assaying the calcium- and phospholipid-dependent phosphorylation of a lysine-rich histone after detergent extraction, we have determined the total protein kinase C activity in fibroblasts from patients with sporadic Alzheimer's disease, age-matched controls and young subjects. The activity was not significantly different between young and aged controls, whereas it was significantly lower (0.70 +/- 0.12 vs 1.16 +/- 0.23 nmol/min/mg protein, P less than 0.01) in the patients. The total amount of protein kinase C estimated from the binding of phorbol dibutyrate to intact cells was also significantly lower (1.70 +/- 0.41 vs 2.48 +/- 0.54 pmol/mg protein, P less than 0.01). This decrease in protein kinase C activity suggests that abnormal protein phosphorylation might play a role in the pathogenesis of the disease.

Increased SOD1 enzymatic activity and gene modifications in orangutans: evolutionary implications

Superoxide dismutase CuZn (SOD1) enzymatic activity was measured in five orangutans (Pongo pygmaeus, PPY) and compared to that of man, chimpanzee, and gorilla. It was found to be increased by a factor of two in one orangutan (Ralfina) and by a factor of 1.5 in the four others. In situ hybridization of the SOD1 cDNA human probe showed a heterozygous intra-chromosomal rearrangement of pair PPY XXI, possibly an insertion, in Ralfina. Southern blotting showed that the SOD1 gene is modified in the three orangutans that were investigated and that a further modification of the 5'-end of the gene had occurred in Ralfina. The evolutionary implications of these observations are discussed.

Neuronal-specific expression of human copper-zinc superoxide dismutase gene in transgenic mice: animal model of gene dosage effects in Down's syndrome

It has been suggested that copper-zinc superoxide dismutase (CuZn SOD) increment, by accelerating hydrogen peroxide formation, might promote oxidative damage within trisomy 21 cells and might be involved in the various neurobiological abnormalities found in Down's syndrome such as premature aging and Alzheimer-type neurological lesions. In order to test this hypothesis, we have developed strains of transgenic mice carrying the human CuZn SOD gene. The human transgene expression resulted in increased CuZn SOD activity predominantly in the brain (1.93 fold). Immunohistochemical and in situ hybridization analysis of brain sections revealed that human CuZn SOD protein and mRNA was preferentially expressed in neurons, particularly in pyramidal cells of Ammon's horn and granule cells of gyrus dentate. The amount of thiobarbituric acid (TBA)-reactive material was significantly higher in transgenic brains compared to controls, strongly suggesting an increased level of peroxidation in vivo. These results support the notion that CuZn SOD gene dosage effect could play a role in the pathogenesis of rapid aging features in the brain of Down's syndrome patients.

Expression of human Cu-Zn superoxide dismutase gene in transgenic mice: model for gene dosage effect in Down syndrome

It was suggested that increased Cu-Zn superoxide dismutase (SOD-1) might be involved in the various biological abnormalities found in Down's syndrome (DS) such as premature aging and Alzheimer-type neurological lesions. As a model system for testing this hypothesis we have developed two strains of transgenic mice carrying only one copy of the human SOD-1 gene. In the first strain (TG1), no expression has been found by northern blot analysis. The second strain (TG2) exhibited human SOD-1 mRNA and increased SOD-1 activity in the brain (1.93 fold), in the heart (1.69 fold), thymus (1.49 fold) and to a lesser extent in muscle (1.25 fold), liver (1.19 fold), kidney (1.18 fold), spleen (1.35 fold), lung (1.26 fold) and erythrocytes (1.09 fold). In this strain, increased SOD-1 activity in the brain did not induce modifications in the seleno-dependent glutathione peroxidase, glutathione reductase and glutathione S-transferase activities. In brain homogenates, we have focused our studies on Tau proteins which are known to be the major antigenic components of paired helical filaments (PHF), both in DS and Alzheimer's disease. Our results suggested that, in our experimental conditions, the overexpression of SOD-1 did not induce the modifications of Tau proteins similar to those seen during neurofibrillary degeneration.

Neuronal localization of copper-zinc superoxide dismutase protein and mRNA within the human hippocampus from control and Alzheimer's disease brains

The distribution of cells containing copper-zinc superoxide dismutase (CuZn SOD) protein and mRNA was studied in hippocampi from normal humans and patients with Alzheimer's disease (AD) by using immunohistochemistry and in situ hybridization. Using antisera against native and denatured CuZn SOD protein, we have determined that immunostaining was intense in pyramidal neurons of the cornu ammonis, in granule cells of the dentate gyrus and very weak in other cells. In the hippocampus of an Alzheimer's patient, successive immunostaining of the same tissue section by antiCuZn SOD and antipaired helical filaments antisera show that both normal and degenerating cells were labeled by the antiCuZn SOD antiserum. Thus, large pyramidal neurons which are susceptible to degenerative processes in AD have the property to contain high amount of CuZn SOD protein. In situ hybridization was performed on paraformaldehyde-fixed hippocampus sections of normal human brains and AD brains with a 35 S labeled DNA probe homologous to human CuZn SOD mRNA. Our results show that CuZn SOD transcripts are present at high abundance in pyramidal neurons of the CA1-CA4 fields, subiculum, and in granule cells of the dentate gyrus. This cellular distribution is similar to that obtained with the antiCuZn SOD antiserum. This might indicate that biochemical pathways leading to superoxide radicals generation are specially active in these neurons, requiring an active transcription of CuZn-SOD gene.

Slot blot method for the quantification of DNA sequences and mapping of chromosome rearrangements: application to chromosome 21

As an alternative to the methods of gene dosage based on either RFLP studies or Southern blots using specific and reference probes, we designed a "slot blot" method for the evaluation of the copy number of unique chromosome 21 sequences. Varying amounts of denatured DNA from a normal control, a trisomy 21 patient, and the subject to be analyzed were loaded on the same membrane. Successive hybridizations with reference probes and chromosome 21 probes were then carried out. Intensities of the signals on autoradiograms were quantified by densitometric scanning. Graphic and statistical analysis of the linear regressions between reference and chromosome 21 probe signals were performed, and the conclusion that the DNA from the studied subject had two or three copies for a given chromosome 21 sequence was assessed by statistical comparison of the slopes. As a test for the validation of this method, 10 coded blood DNAs from five normal controls and from five trisomy 21 patients were analyzed, by using two reference (COL1A1 and COL1A2) and two chromosome 21 (D21S11 and D21S17) probes. Among the 10 DNAs analyzed, it was possible to diagnose, with 100% accuracy, normal controls and trisomic 21 individuals. Application of this methodology to the mapping of partial chromosome 21 rearrangements is presented.

Localization of copper-zinc superoxide dismutase mRNA in human hippocampus by in situ hybridization

The cellular localization of copper-zinc superoxide dismutase (CuZn SOD) mRNA was determined in the human hippocampus by in situ hybridization with a 35S-labelled DNA probe complementary to human CuZn SOD mRNA. A positive hybridization signal was detected in pyramidal cell layers CA1-CA4 of Ammon's horn (CA), pyramidal cells of subiculum and in the granule cells of the dentate gyrus. The fact that CuZn SOD gene expression is important in neurones which are preferentially vulnerable in neurodegenerative processes such as Alzheimer's disease, suggests a role played by oxygen free radicals in the mechanism of nerve cell death.

Preferential localization of copper zinc superoxide dismutase in the vulnerable cortical neurons in Alzheimer's disease

The distribution of cells containing CuZn superoxide dismutase (CuZn SOD) was determined in hippocampi and associative cortex from normal and Alzheimer's individuals by using antisera against native and denatured CuZn SOD proteins. Immunostaining was intense in large pyramidal neurons, moderate in hippocampal granule cells and very weak in other cells. In the hippocampus of an Alzheimer's patient, successive immunostaining of the same tissue section by anti CuZn SOD and anti paired helical filaments antisera show that both normal and degenerating cells are labelled by the anti CuZn SOD antiserum. Thus, large pyramidal neurons which are potentially susceptible to degenerative processes in AD have the property to contain higher amounts of CuZn SOD than other brain cells.

Expression of transfected human CuZn superoxide dismutase gene in mouse L cells and NS20Y neuroblastoma cells induces enhancement of glutathione peroxidase activity

The human CuZn superoxide dismutase (superoxide dismutase 1) a key enzyme in the metabolism of oxygen free-radicals, is encoded by a gene located on chromosome 21 in the region 21 q 22.1 known to be involved in Down's syndrome. A gene dosage effect for this enzyme has been reported in trisomy 21. To assess the biological consequences of superoxide dismutase 1 overproduction within cells, the human superoxide dismutase 1 gene and a human superoxide dismutase 1 cDNA were introduced into mouse L cells and NS20Y neuroblastoma cells. Both cell types expressed elevated levels (up to 3-fold) of enzymatically active human superoxide dismutase 1. These human superoxide dismutase 1 overproducers, especially neuronal cell lines, showed an increased activity in the selenodependent glutathione peroxidase. These data are consistent with the possibility that gene dosage of superoxide dismutase 1 contributes to oxygen metabolism modifications previously described in Down's syndrome.

Cloning and sequencing of a rat CuZn superoxide dismutase cDNA. Correlation between CuZn superoxide dismutase mRNA level and enzyme activity in rat and mouse tissues

The molecular cloning and nucleotide sequence of a cDNA clone (pR SOD) for rat CuZn superoxide dismutase (CuZnSOD) is reported. Nucleotide sequence homology with human superoxide dismutase is 86% for the coding region and 71% for the 3' untranslated region. The deduced amino acid sequence is given and the homologies with the sequences reported for other species are presented. Northern blot analysis of total RNA from various rat and mouse tissues and from two mouse cell lines show that pR SOD hybridizes with one mRNA species of about 0.7 kb. The amount of CuZnSOD mRNA in each tissue, measured by densitometry of the Northern blot autoradiograms, correlates with the enzymatic activity based on protein content. These results indicate that the control of CuZnSOD activity in mammalian tissues is largely dependent on the regulation of CuZnSOD mRNA levels. In human liver, fibroblasts and FG2 hepatoma cells, two CuZnSOD mRNAs (0.7 kb and 0.9 kb) are observed. The level of CuZnSOD mRNA in FG2 is 25% that of the liver and four times more abundant than in fibroblasts.

Submicroscopic duplication of chromosome 21 and trisomy 21 phenotype (Down syndrome)

A patient with the phenotype of trisomy 21 (Down syndrome) was found to have a normal karyotype in blood lymphocytes and fibroblasts. Assessment of the chromosome 21 markers SOD1, CBS, ETS2, D21S11, and BCEI showed partial trisomy by duplication of a chromosome segment carrying the SOD1, CBS, and ETS2 loci and flanked by the BCEI and D21S11 loci, which are not duplicated. This submicroscopic duplication at the interface of 21q21 and 21q22.1 reduces to about 2000-3000 kb the critical segment the trisomy of which is responsible for the phenotype of trisomy 21.

Beta amyloid gene duplication in Alzheimer's disease and karyotypically normal Down syndrome

With the recently cloned complementary DNA probe, lambda Am4 for the chromosome 21 gene encoding brain amyloid polypeptide (beta amyloid protein) of Alzheimer's disease, leukocyte DNA from three patients with sporadic Alzheimer's disease and two patients with karyotypically normal Down syndrome was found to contain three copies of this gene. Because a small region of chromosome 21 containing the ets-2 gene is duplicated in patients with Alzheimer's disease, as well as in karyotypically normal Down syndrome, duplication of a subsection of the critical segment of chromosome 21 that is duplicated in Down syndrome may be the genetic defect in Alzheimer's disease.