ABSTRACT
Amyotrophic lateral sclerosis (ALS) is a fatal degenerative motor neuron disorder. Ten percent of cases are inherited; most involve unidentified genes. We report here 13 mutations in the fused in sarcoma/translated in liposarcoma (FUS/TLS) gene on chromosome 16 that were specific for familial ALS. The FUS/TLS protein binds to RNA, functions in diverse processes, and is normally located predominantly in the nucleus. In contrast, the mutant forms of FUS/TLS accumulated in the cytoplasm of neurons, a pathology that is similar to that of the gene TAR DNA-binding protein 43 (TDP43), whose mutations also cause ALS. Neuronal cytoplasmic protein aggregation and defective RNA metabolism thus appear to be common pathogenic mechanisms involved in ALS and possibly in other neurodegenerative disorders.
Subject(s)
Amyotrophic Lateral Sclerosis/genetics , Chromosomes, Human, Pair 16/genetics , Mutation, Missense , RNA-Binding Protein FUS/genetics , RNA-Binding Protein FUS/metabolism , Age of Onset , Amino Acid Substitution , Amyotrophic Lateral Sclerosis/metabolism , Amyotrophic Lateral Sclerosis/pathology , Animals , Brain/pathology , Cell Line, Tumor , Cell Nucleus/metabolism , Cytoplasm/metabolism , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , Exons , Female , Humans , Male , Mice , Motor Neurons/chemistry , Motor Neurons/metabolism , Motor Neurons/ultrastructure , Mutant Proteins/chemistry , Mutant Proteins/genetics , Mutant Proteins/metabolism , Neurons/metabolism , Neurons/ultrastructure , RNA/metabolism , RNA-Binding Protein FUS/chemistry , Recombinant Fusion Proteins/metabolism , Sequence Analysis, DNA , Spinal Cord/pathologyABSTRACT
OBJECTIVE: The GRIN3B gene encodes NR3B, a motoneuron-specific member of the NMDA type of ionotropic glutamate receptors. NR3B reduces the Ca(2+)-permeability as well as the overall current of the receptor response and may thereby protect motoneurons against glutamate-mediated excitotoxicity. We tested whether genetic dysfunction of GRIN3B is implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). METHODS: We searched for mutations in the GRIN3B coding region (3.1 kb) in 117 individuals with familial ALS and in 46 individuals with sporadic ALS. We genotyped the newly identified GRIN3B null allele and four "tag single nucleotide polymorphisms (SNPs)" at the GRIN3B locus in 342 individuals with sporadic ALS and in 374 matched controls. The GRIN3B null allele frequency was determined in 2,128 individuals from a worldwide panel of 42 populations. We furthermore compared the GRIN3B coding sequence in primates (human-macaque) and rodents (rat-mouse) to evaluate the molecular evolution of GRIN3B. RESULTS: Thirty-two SNPs, including 16 previously unreported SNPs, one 27-bp deletion, a polymorphic CAG repeat, and a 4-bp insertion (insCGTT), were identified. Mutational and case-control studies did not reveal variants that cause or modify disease in ALS. Intriguing is an insCGTT variant that truncates the protein at its amino terminus and results in a GRIN3B null allele. We demonstrated a global distribution of the null allele with allele frequencies ranging between 0 and 0.38, and we delineated a null allele specific haplotype of 9.89 kb. Comparative genomic analysis across four taxa demonstrated accelerated evolution of NR3B in primates. CONCLUSIONS: Our study supports the conclusions that 1) GRIN3B does not seem to be associated with familial or sporadic ALS, 2) the GRIN3B null allele is a common polymorphism, 3) the GRIN3B null allele has arisen once and early in human evolution, and 4) the GRIN3B gene belongs to a group of nervous system-related genes that have been subjected to faster evolution during evolution.
Subject(s)
Alleles , Motor Neuron Disease/genetics , Motor Neurons/physiology , Receptors, N-Methyl-D-Aspartate/genetics , Case-Control Studies , DNA Mutational Analysis , Gene Frequency , Genetic Predisposition to Disease/genetics , Genetics, Population , Genotype , Haplotypes , Humans , Linkage Disequilibrium , Motor Neuron Disease/diagnosis , Motor Neuron Disease/physiopathology , Polymorphism, Single Nucleotide/genetics , Superoxide Dismutase/genetics , Superoxide Dismutase-1ABSTRACT
OBJECTIVE: To perform genetic linkage analysis in a family affected with ALS and frontotemporal dementia (FTD). METHODS: The authors performed a genome-wide linkage analysis of a four-generation, 50-member Scandinavian family in which five individuals were diagnosed with ALS and nine with FTD. Linkage calculations assuming autosomal dominant inheritance of a single neurodegenerative disease manifesting as either ALS or FTD with age-dependent penetrance were performed. Further analyses for ALS alone and FTD alone were performed. A parametric logarithm of odds (lod) score of 2.0 or greater was required for further study of a potential locus and crossover (haplotype) analysis. RESULTS: A new ALS-FTD locus was identified between markers D9s1870 and D9s1791 on human chromosome 9p21.3-p13.3. A maximum multipoint lod score of 3.00 was obtained between markers D9s1121 and D9s2154. Crossover analysis indicates this region covers approximately 21.8 cM, or 14Mb. CONCLUSIONS: A locus on chromosome 9p21.3-p13.3 is linked to ALS-FTD.
Subject(s)
Amyotrophic Lateral Sclerosis/genetics , Chromosomes, Human, Pair 9/genetics , Dementia/genetics , Genetic Predisposition to Disease/genetics , Quantitative Trait Loci/genetics , Aged , Female , Genetic Linkage/genetics , Genetic Markers/genetics , Haplotypes/genetics , Humans , Male , Middle Aged , PedigreeABSTRACT
Amyotrophic lateral sclerosis 2 (ALS2) is an autosomal recessive form of juvenile ALS and has been mapped to human chromosome 2q33. Here we report the identification of two independent deletion mutations linked to ALS2 in the coding exons of the new gene ALS2. These deletion mutations result in frameshifts that generate premature stop codons. ALS2 is expressed in various tissues and cells, including neurons throughout the brain and spinal cord, and encodes a protein containing multiple domains that have homology to RanGEF as well as RhoGEF. Deletion mutations are predicted to cause a loss of protein function, providing strong evidence that ALS2 is the causative gene underlying this form of ALS.
Subject(s)
Amyotrophic Lateral Sclerosis/genetics , GTP Phosphohydrolases/metabolism , Guanine Nucleotide Exchange Factors/genetics , Mutation , Amino Acid Sequence , Animals , Chromosome Mapping , Chromosomes, Human, Pair 2 , Female , Guanine Nucleotide Exchange Factors/chemistry , Humans , Male , Mice , Molecular Sequence Data , Polymorphism, Genetic , Sequence Homology, Amino AcidABSTRACT
CONTEXT: Occasionally, 2 or more major neurodegenerative diseases arise simultaneously. An understanding of the genetic bases of combined disorders, such as amyotrophic lateral sclerosis (ALS) with frontotemporal dementia (FTD), will likely provide insight into mechanisms of these and related neurodegenerative diseases. OBJECTIVE: To identify loci that contain genes whose defects cause ALS. DESIGN: A genome-wide linkage analysis of 2 data sets from an ongoing study begun in the mid-1980s at 4 university research centers. SUBJECTS: An initial subset of 16 families (549 people) potentially informative for genetic analysis, in which 2 or more individuals were diagnosed as having ALS, identified from a Boston data set of 400 families and 4 families potentially informative (244 people) subsequently identified from a Chicago data set of more than 300 families to test a hypothesis based on findings from the Boston families. MAIN OUTCOME MEASURES: Linkage calculations assuming autosomal dominant inheritance with age-dependent penetrance (a parametric logarithm-of-odds [lod] score of 1.0 or greater required for further study of a potential locus); crossover analysis involving the ALS-FTD locus. RESULTS: In a set of families in which persons develop both ALS and FTD or either ALS or FTD alone, a genetic locus that is linked to ALS with FTD located between markers D9S301 and D9S167 was identified on human chromosome 9q21-q22. Families with ALS alone did not show linkage to this locus. Crossover analysis indicates this region covers approximately 17 cM. CONCLUSION: These data suggest that a defective gene located in the chromosome 9q21-q22 region may be linked to ALS with FTD. JAMA. 2000;284:1664-1669.
Subject(s)
Amyotrophic Lateral Sclerosis/genetics , Chromosomes, Human, Pair 9 , Dementia/genetics , Aged , Aged, 80 and over , Amyotrophic Lateral Sclerosis/complications , Dementia/complications , Genetic Linkage , Haplotypes , Humans , Lod Score , Microsatellite Repeats , Middle Aged , Pedigree , Polymerase Chain ReactionABSTRACT
OBJECTIVES: 1) To confirm linkage of hereditary sensory neuropathy type 1 (HSN-I) to human chromosome 9q22 in a large American family of German origin. 2) To construct a yeast artificial chromosome (YAC) contig spanning the HSN-I candidate interval. 3) To investigate the HSN-I contig for potential candidate genes. BACKGROUND: HSN-I is a rare peripheral neuropathy characterized by loss of temperature sensation, ulceration and osteomyelitis of the digits, and subtle distal weakness. A gene for HSN-I has previously been mapped to human chromosome 9q22.1-q22.3 between markers D9S318 and D9S176 in an 8-cM interval in four Australian families. METHODS: In a large German-American family with HSN-I, genome-wide linkage analysis was performed on 68 family members extending over five generations and including 17 affected members. Genotyping was performed with PCR, and the resulting genotypes were analyzed with two-point linkage analysis with Fastlink. A YAC contig was constructed based on the Whitehead Institute YAC contig WC9.3. RESULTS: Two-point linkage analysis resulted in a maximum lod score of 8.2 at theta = 0 for marker D9S1815. Haplotype analysis locates the HSN-I gene between markers D9S1797 and D9S197. Using YAC clones from the Centre d'Etude du Polymorphism Humain YAC Library, we constructed a YAC contig spanning these markers. Based on the radiation hybrid map of the human genome, we estimate that the size of this interval is less than 2,500 kb. CONCLUSIONS: Our study confirms linkage of a putative HSN-I gene to chromosome 9q22, considerably narrows the HSN-I locus, and provides a basis for identification of the HSN-I gene.
Subject(s)
Chromosomes, Human, Pair 9/genetics , Genetic Linkage , Hereditary Sensory and Autonomic Neuropathies/genetics , Chromosome Mapping , Female , Haplotypes , Humans , Male , PedigreeABSTRACT
Miyoshi myopathy (MM) is an adult onset, recessive inherited distal muscular dystrophy that we have mapped to human chromosome 2p13. We recently constructed a 3-Mb P1-derived artificial chromosome (PAC) contig spanning the MM candidate region. This clarified the order of genetic markers across the MM locus, provided five new polymorphic markers within it and narrowed the locus to approximately 2 Mb. Five skeletal muscle expressed sequence tags (ESTs) map in this region. We report that one of these is located in a novel, full-length 6.9-kb muscle cDNA, and we designate the corresponding protein 'dysferlin'. We describe nine mutations in the dysferlin gene in nine families; five are predicted to prevent dysferlin expression. Identical mutations in the dysferlin gene can produce more than one myopathy phenotype (MM, limb girdle dystrophy, distal myopathy with anterior tibial onset).
Subject(s)
Membrane Proteins , Muscle Proteins/genetics , Muscular Dystrophies/genetics , Mutation , Adult , Amino Acid Sequence , Blotting, Northern , Cloning, Molecular , Dysferlin , Female , Gene Expression , Genetic Markers , Humans , Male , Molecular Sequence Data , Muscle Proteins/chemistry , Muscle Proteins/metabolism , Muscle, Skeletal/metabolism , Polymorphism, Genetic , Polymorphism, Single-Stranded ConformationalABSTRACT
Recently, variant mRNA transcripts for the astroglial glutamate transporter EAAT2 have been detected in brain tissues of 60% of patients with sporadic amyotrophic lateral sclerosis (SALS). We have tested the hypothesis that the gene for EAAT2 may be defective in some ALS cases. In 16 familial ALS (FALS) pedigrees without mutations in SOD1, we failed to detect genetic linkage to the EAAT2 locus. We next characterized the genomic organization of the EAAT2 gene and used single-strand conformation polymorphism analysis of genomic DNA to identify one novel mutation in a single SALS patient and two novel mutations in 2 affected FALS siblings. In the SALS patient, the mutation substitutes serine for an asparagine that might be involved in N-linked glycosylation of the EAAT2 protein. In the 2 affected individuals in the FALS family, we detected both a mutation in the 5' end of intron 7 and a silent G --> A transition at codon 234 in exon 5. It remains unclear whether this intron 7 mutation is related to the defective mRNA splicing. These studies indicate that germline mutations in the EAAT2 gene are infrequent and do not explain the presence of variant mRNA transcripts of EAAT2 in more than one-half of ALS cases.
Subject(s)
Amyotrophic Lateral Sclerosis/genetics , Genetic Linkage , Point Mutation , Receptors, Neurotransmitter/genetics , Transcription, Genetic/genetics , Animals , Base Sequence , Excitatory Amino Acid Transporter 2 , Exons/genetics , Genome, Human , Humans , Mice , Molecular Sequence Data , Pedigree , Polymorphism, Single-Stranded Conformational , RNA Splicing/geneticsABSTRACT
Miyoshi myopathy (MM) and limb-girdle muscular dystrophy subtype 2B (LGMD2B) map to the same region on chromosome 2p13. To facilitate the cloning of the defective gene causing these two diseases, we used a combination of chromosome walking and expressed sequence tag (EST) screening and identified 864 P1-derived artificial chromosomes (PACs) whose inserts map to the MM/LGMD2B candidate region and surrounding areas. Among them, 139 are from a chromosome 2-specific PAC library and 725 are from a total genomic PAC library. A 3-Mb contig spanning the candidate region for MM/LGMD2B was assembled. This contig contains 200 PACs, 10 known genetic markers, 5 new polymorphic markers, 57 sequence tagged sites (STSs) generated from PAC end fragments, and 4 random STSs. In addition, we mapped 24 ESTs to this contig and excluded 37 ESTs from the contig, thus eliminating them as candidate MM/LGMD2B genes. The high-resolution, sequence-ready PAC contig for the MM/LGMD2B region provides a backbone for the identification of the disease gene(s) and for clarification of the relationship between the two diseases.
Subject(s)
Chromosomes, Human, Pair 2 , Muscular Dystrophies/genetics , Humans , In Situ Hybridization, FluorescenceABSTRACT
Amyotrophic lateral sclerosis (ALS) is a progressive degenerative neuromuscular disease that shows familial, autosomal dominant inheritance in 10%-15% of cases. Previous genetic analysis of one large family linked a recessive form of familial ALS (FALS-AR type 3) to the chromosome 2q33-35 region. Using additional polymorphic markers, we have narrowed the size of the linked region to approximately 1.7 cM by linkage and haplotype analysis. We have also established a yeast artificial chromosome contig across the locus that covers an approximate physical distance of 3 million bases. Based on this contig, genes and expressed sequences that map near the 2q33 region have been examined to determine whether they are located within this ALS2 candidate locus. Five identified genes and 34 expressed sequence tags map within the region defined by crossover analysis and merit further consideration as candidate genes for this disease.
Subject(s)
Chromosomes, Human, Pair 2 , Genes, Recessive , Motor Neuron Disease/genetics , Chromosome Mapping , Chromosomes, Artificial, Yeast , Contig Mapping , Female , Genetic Markers , Humans , Male , Pedigree , Polymerase Chain ReactionABSTRACT
We registered 366 families in a study of dominantly inherited amyotrophic lateral sclerosis. Two hundred ninety families were screened for mutations in the gene encoding copper-zinc cytosolic superoxide dismutase (SOD1). Mutations were detected in 68 families. The most common SOD1 mutation is an alanine for valine substitution in codon 4 (50%). We present clinical and genetic data concerning 112 families with 395 affected individuals. The clinical characteristics of patients with familial amyotrophic lateral sclerosis arising from SOD1 mutations are similar to those lacking SOD1 defects. Mean age at onset was earlier (Wilcoxon test, p = 0.004) in the SOD1 group (46.9 years [standard deviation, 12.5] vs 50.5 years [11.5] in the non-SOD1 group). Bulbar onset was associated with a later onset age. The presence of either of two mutations, G37R and L38V, predicted an earlier age at onset. Kaplan-Meier plots demonstrated shorter survival in the SOD1 group compared with the non-SOD1 group at early survival times (Wilcoxon test, p = 0.0007). The presence of one mutation, A4V, correlated with shorter survival. G37R, G41D, and G93C mutations predicted longer survival. This information suggests it will be productive to investigate other genetic determinants in amyotrophic lateral sclerosis and to use epidemiological characteristics of the disease to help discern molecular mechanisms of motor neuron cell death.
Subject(s)
Amyotrophic Lateral Sclerosis/epidemiology , Amyotrophic Lateral Sclerosis/genetics , Mutation/genetics , Superoxide Dismutase/genetics , Adult , Age of Onset , Female , Humans , Male , Middle AgedABSTRACT
Although reactive oxygen species are natural metabolic products, they can be toxic to cells and are implicated in some neurodegenerative disease. Cytosolic Cu, Zn superoxide dismutase normally defends against damage by reactive oxygen species; however, mutant forms of the enzyme might instead contribute to damage of motor neurons n some amyotrophic lateral sclerosis patients. Possible mechanisms of oxidative injury to neurons are discussed with reference to cytosolic Cu, Zn superoxide dismutase mutations and other factors which might enhance oxygen radical toxicity.
Subject(s)
Amyotrophic Lateral Sclerosis/genetics , Reactive Oxygen Species/metabolism , Superoxide Dismutase/genetics , Amyotrophic Lateral Sclerosis/enzymology , Animals , Cell Death/genetics , DNA Mutational Analysis , Humans , Hydroxyl Radical/metabolism , Mice , Motor Neurons/enzymology , Superoxide Dismutase/deficiencyABSTRACT
Autosomal dominant inheritance is exhibited by about 10% of cases of amyotrophic lateral sclerosis (ALS), a paralytic disorder characterized by the death of motor neurons in the brain and spinal cord. A subgroup of these familial cases are linked to mutations in the gene which codes for Cu/Zn superoxide dismutase (SOD1). We report three additional mutations occurring in the SOD1 gene in ALS patients and two single base pair variant changes. The single base pair change in an ALS family causes a glycine 93 to valine substitution, which is the fifth distinct amino acid change reported for the glycine 93 residue. One missense mutation in exon 5 would substitute neutral valine for the negatively-charged aspartate 124 (aspartate 124 to valine). An individual with an apparently sporadic case of ALS carries a three base pair deletion in exon 5 of the SOD1 gene. These three mutations bring to 38 the total number of distinct SOD1 mutations associated with familial ALS.
Subject(s)
Amyotrophic Lateral Sclerosis/genetics , Point Mutation/genetics , Polymorphism, Genetic , Superoxide Dismutase/genetics , Amyotrophic Lateral Sclerosis/enzymology , Family Health , Humans , Polymorphism, Single-Stranded Conformational , Sequence Analysis, DNAABSTRACT
About 10% of cases of amyotrophic lateral sclerosis (ALS), a paralytic disorder characterized by death of motor neurons in the brain and spinal cord, exhibit autosomal dominant inheritance. A subgroup of these familial cases are caused by mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1). We report here three additional mutations occurring in the SOD1 gene in three families with ALS. Two of these changes are missense mutations in exon 5 of the SOD1 gene, resulting in leucine 144 to serine and alanine 145 to threonine substitutions. The third, a single base pair change in intron 4 immediately upstream of exon 5, results in an alternatively spliced mRNA. The alternate transcript conserves the open reading frame of exon 5, producing an SOD1 protein with three amino acids inserted between exons 4 and 5 (following residue 118). These three mutations bring to 29 the total number of distinct SOD1 mutations associated with familial ALS.
Subject(s)
Amyotrophic Lateral Sclerosis/genetics , Mutation , Superoxide Dismutase/genetics , Adult , Age of Onset , Aged , Base Sequence , Exons/genetics , Genes, Dominant , Humans , Middle Aged , Molecular Sequence Data , Open Reading Frames , Polymerase Chain Reaction , Polymorphism, Single-Stranded Conformational , RNA SplicingABSTRACT
Increased levels of CuZn superoxide dismutase (SOD-1) are cytoprotective in experimental models of neurological disorders associated with free radical toxicity (e.g. stroke, trauma). Targeted delivery of SOD-1 to central nervous system neurons may therefore be therapeutic in such diseases. The nontoxic C-fragment of tetanus toxin (TTC) possesses the nerve cell binding/transport properties of tetanus holotoxin and has been used as a vector to enhance the neuronal uptake of proteins including enzymes. We have now produced a recombinant, hybrid protein in Escherichia coli tandemly joining human SOD-1 to TTC. The expressed hybrid protein (SOD:Tet450) has a subunit molecular mass of 68 kDa and is recognized by both anti-SOD-1 and anti-TTC antibodies. Calculated per mol, SOD:Tet450 has approximately 60% of the expected SOD-1 enzymatic activity. Analysis of the hybrid protein's interaction with the neuron-like cell line, N18-RE-105, and cultured hippocampal neurons by enzyme immunoassay for human SOD-1 revealed that SOD:Tet451 association with cells was neuron-specific and dose-dependent. The hybrid protein was also internalized, but there was substantial loss of internalized hybrid protein over the first 24 h. Hybrid protein associated with cells remained enzymatically active. These results suggest that human SOD-1 and TTC retain their respective functional properties when expressed together as a single peptide. SOD:Tet451 may prove to be a useful agent for the targeted delivery of SOD-1 to neurons.
Subject(s)
Hippocampus/metabolism , Immunotoxins/metabolism , Neurons/metabolism , Peptide Fragments/metabolism , Superoxide Dismutase/metabolism , Tetanus Toxin/metabolism , Animals , Base Sequence , Biological Transport , Blotting, Western , Cell Line , Cells, Cultured , Cloning, Molecular , DNA Primers , Electrophoresis, Polyacrylamide Gel , Humans , Immunohistochemistry , Immunotoxins/administration & dosage , Kinetics , Molecular Sequence Data , Peptide Fragments/administration & dosage , Peptide Fragments/biosynthesis , Polymerase Chain Reaction , Protein Multimerization , Rats , Restriction Mapping , Superoxide Dismutase/administration & dosage , Superoxide Dismutase/biosynthesis , Tetanus Toxin/administration & dosage , Tetanus Toxin/biosynthesisABSTRACT
Mutations in the gene for Cu/Zn superoxide dismutase (SOD1) have been detected in some families with an autosomal dominant form of amyotrophic lateral sclerosis; these mutations appear to reduce the activity of this enzyme. To determine whether decreased SOD activity could contribute to motor neuron loss, SOD1 was inhibited chronically with either antisense oligodeoxynucleotides or diethyldithiocarbamate in spinal cord organotypic cultures. Chronic inhibition of SOD resulted in the apoptotic degeneration of spinal neurons, including motor neurons, over several weeks. Motor neuron loss was markedly potentiated by the inhibition of glutamate transport. In this paradigm, motor neuron toxicity could be entirely prevented by the antioxidant N-acetylcysteine and, to a lesser extent, by the non-N-methyl-D-aspartate glutamate receptor antagonist 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride. These data support the hypothesis that the loss of motor neurons in familial amyotrophic lateral sclerosis could be due to a reduction in SOD1 activity, possibly potentiated by inefficient glutamate transport.
Subject(s)
Anti-Anxiety Agents , Antioxidants/pharmacology , Apoptosis/physiology , Benzodiazepines/pharmacology , Ditiocarb/pharmacology , Motor Neurons/cytology , Motor Neurons/physiology , Oligonucleotides, Antisense/pharmacology , Spinal Cord/cytology , Spinal Cord/physiology , Superoxide Dismutase/antagonists & inhibitors , Acetylcysteine/pharmacology , Amyotrophic Lateral Sclerosis/genetics , Animals , Animals, Newborn , Apoptosis/drug effects , Base Sequence , Biological Transport/drug effects , Choline O-Acetyltransferase/metabolism , Chromans/pharmacology , Glutamates/metabolism , Glutamic Acid , Humans , Molecular Sequence Data , Motor Neurons/drug effects , Nerve Degeneration , Neurotoxins/antagonists & inhibitors , Organ Culture Techniques , Piperazines/pharmacology , Rats , Superoxide Dismutase/geneticsABSTRACT
The message for the zinc finger gene Rex-1 (Zfp-42) is expressed in undifferentiated murine F9 teratocarcinoma cells and embryonic stem cells. Expression of Rex-1 is reduced at the transcriptional level when F9 cells are induced by the addition of retinoic acid (RA) to differentiate. We have isolated genomic DNA for the Rex-1 gene (Zfp-42), characterized the gene's structure, and mapped the gene to mouse chromosome 8. Promoter elements contributing to the regulation of the Rex-1 promoter in F9 cells have been identified. A region required for Rex-1 promoter activity in F9 stem cells contains an octamer motif (ATTTGCAT) which is a binding site for octamer transcription factor members of the POU domain family of DNA-binding proteins. Rex-1 reporter plasmids including this octamer site also exhibited reduced expression in F9 cells treated with RA. Thus, the octamer motif is a regulatory element required for the activity of the Rex-1 promoter in F9 stem cells, and this motif contributes to the negative regulation by RA of the transcription of the Rex-1 gene. As an initial confirmation of the in vivo relevance of the isolated fragment, a larger Rex-1 promoter fragment, also containing the octamer site, was able to promote expression of the bacterial lacZ gene in mouse embryos at the morula stage.
Subject(s)
DNA-Binding Proteins/genetics , DNA/metabolism , Gene Expression Regulation, Neoplastic/drug effects , Transcription, Genetic , Tretinoin/pharmacology , Zinc Fingers/genetics , Animals , Base Sequence , Binding Sites , Chloramphenicol O-Acetyltransferase/genetics , Chloramphenicol O-Acetyltransferase/metabolism , DNA/genetics , DNA-Binding Proteins/biosynthesis , Exons , Genomic Library , Mice , Mice, Inbred BALB C , Molecular Sequence Data , Oligodeoxyribonucleotides , Polymerase Chain Reaction/methods , Promoter Regions, Genetic , Spleen/physiology , Teratoma , Transfection , Tumor Cells, CulturedABSTRACT
We have previously isolated a cDNA clone for a gene whose expression is reduced by retinoic acid (RA) treatment of F9 embryonal carcinoma cells. The nucleotide sequence indicated that this gene, Rex-1, encodes a zinc-finger protein and thus may be a transcriptional regulator. The Rex-1 message level is high in two lines of embryonic stem cells (CCE and D3) and is reduced when D3 cells are induced to differentiate using four different growth conditions. As expected for a stem-cell-specific message, Rex-1 mRNA is present in the inner cell mass (ICM) of the day 4.5 mouse blastocyst. It is also present in the polar trophoblast of the blastocyst. One and two days later, Rex-1 message is found in the ectoplacental cone and extraembryonic ectoderm of the egg cylinder (trophoblast-derived tissues), but its abundance is much reduced in the embryonic ectoderm which is directly descended from the ICM. Rex-1 is expressed in the day 18 placenta (murine gestation is 18 days), a tissue which is largely derived from trophoblast. The only tested adult tissue that contains detectable amounts of Rex-1 mRNA is the testis. In situ hybridization and northern analyses of RNA from germ-cell-deficient mouse testis and stage-specific germ cell preparations suggest that Rex-1 expression is limited to spermatocytes (germ cells undergoing meiosis). These results suggest that Rex-1 is involved in trophoblast development and spermatogenesis, and is a useful marker for studies of early cell fate determination in the ICM.
Subject(s)
Blastocyst/physiology , Gene Expression Regulation/genetics , Gene Expression/physiology , Spermatocytes/physiology , Tretinoin/pharmacology , Trophoblasts/physiology , Zinc Fingers/genetics , Animals , Autoradiography , Blotting, Northern , Male , Mice , Mice, Inbred Strains , Placenta/physiology , RNA, Messenger/analysisABSTRACT
In the presence of retinoic acid (RA), cultured F9 murine teratocarcinoma stem cells differentiate into nontumorigenic cells resembling the extraembryonic endoderm of the early mouse embryo. By differential hybridization screening of an F9 cell cDNA library, we isolated a 1,745-nucleotide cDNA for a gene, REX-1 (for reduced expression), whose steady-state mRNA level began to decline in F9 cells in monolayer culture within 12 h after the addition of RA. By 48 to 96 h after RA treatment of F9 cells in monolayer culture, the REX-1 steady-state mRNA level was more than sevenfold lower than the level in undifferentiated F9 stem cells. The REX-1 mRNA decrease did not result from the reduction in cell growth rate associated with the differentiation process, since the REX-1 mRNA level did not decline in F9 cells that were partially growth arrested after 48 h of isoleucine deprivation. The RA-associated REX-1 mRNA decrease resulted primarily from a reduction in the transcription rate of the REX-1 gene in the presence of RA. In contrast to results in F9 cells, we have been unable thus far to detect REX-1 mRNA in day 7.5 to 12.5 mouse embryo RNA samples or in the P19 teratocarcinoma stem cell line. The putative REX-1 protein identified by DNA sequence analysis contains four repeats of the zinc finger nucleic acid-binding motif and a potential acidic activator domain, suggesting that REX-1 encodes a regulatory protein. The REX-1 gene is not identical to the previously reported murine genes that encode zinc finger-containing proteins.