Nuclear targeting defect of SMN lacking the C-terminus in a mouse model of spinal muscular atrophy.

Deletion of the murine survival of motor neuron gene (SMN) exon 7, the most frequent mutation found in spinal muscular atrophy (SMA) patients, directed to neurons but not to skeletal muscle, enabled generation of a mouse model of SMA providing evidence that motor neurons are the primary target of the gene defect. Moreover, the mutated SMN protein (SMNDeltaC15) is dramatically reduced in the motor neuron nuclei and causes a lack of gems associated with large aggregates of coilin, a coiled-body-specific protein. These results identify the lack of the nuclear targeting of SMN as the biochemical defect in SMA.

Gene targeting restricted to mouse striated muscle lineage.

Spatially and temporally regulated somatic mutations can be achieved by using the Cre/LoxP recombination system of bacteriophage P1. In order to develop gene knockouts restricted to striated muscle, we generated a transgenic mouse line expressing Cre recombinase under the control of the human alpha-skeletal actin promoter. Specific excision of a loxP-flanked gene was demonstrated in striated muscle, heart and skeletal muscle, in a pattern very similar to the expression of the endogenous alpha-skeletal actin gene. Therefore, the reported transgenic line can be used to target inactivation or activation of a given gene to the skeletal muscle lineage.

Abnormal methylation does not prevent X inactivation in ICF patients.

DNA undermethylation is a characteristic feature of ICF syndrome and has been implicated in the formation of the juxtacentromeric chromosomal abnormalities of this rare syndrome. We have previously shown that in female ICF patients the inactive X chromosome (Xi) is also undermethylated. This result was unexpected since female ICF patients are not more severely affected than male patients. Here we show that CpG island methylation is abnormal in some ICF patients but in other ICF patients, the difference in methylation pattern between Xi and Xa (active X) is maintained. The consequences of Xi undermethylation on gene expression were investigated by enzyme assays. They showed that significant gene expression did not correlate with CpG island methylation status. The widespread Xi undermethylation does not affect overall Xi replication timing and does not prevent Barr body formation suggesting that a normal methylation pattern is not required for normal chromatin organization of Xi. Molecular investigation of some X-chromosome intron regions showed that the methylation changes in ICF female patients extend to non CpG islands sequences. Our results suggest that the genetic alteration of DNA methylation in ICF syndrome has little consequence on X chromosome gene expression and chromatin organization.

The promoters of the survival motor neuron gene (SMN) and its copy (SMNc) share common regulatory elements.

Spinal muscular atrophy (SMA) is a common autosomal recessive neuromuscular disorder characterized by degeneration of motor neurons of the spinal cord. The survival motor neuron gene (SMN) has been recognized as the disease-causing gene. SMN is duplicated, and the almost identical copy gene (SMNc) remains functional in patients with SMA. The expression level of SMNc is tightly correlated with the clinical severity of the disease. Here, we define the transcription initiation site, delineate the region containing promoter activity, and analyze the sequence of the promoter region of both SMN and SMNc. We show that the promoter sequence and activity of the two genes are quasi identical, providing strong evidence for similar transcription regulation of the two genes. Therefore, the difference in the level of protein encoded by SMN and SMNc is the result of either different regulatory region(s) further apart or different posttranscriptional regulation. Interestingly, sequence analysis of the promoter region revealed several consensus binding sites for transcription factors. Therefore, the identification of transcription factors involved in the regulation of SMNc gene expression may lead to attractive strategies for therapy in SMA.

Human colorectal cancer (CRC) antigen CO17-1A/GA733 encoded by adenovirus inhibits growth of established CRC cells in mice.

The human colorectal carcinoma (CRC)-associated Ag CO17-1A/GA733, originally defined by mAbs CO17-1A and GA733, has been a useful target in passive immunotherapy of CRC patients with mAb and in active immunotherapy with anti-idiotypic Abs mimicking the CO17-1A or GA733 epitope. Both approaches have targeted single epitopes. We investigated the capacity of full-length CO17-1A/GA733 Ag expressing multiple potentially immunogenic epitopes and encoded by recombinant adenovirus 5 (Ad5 GA733-2) to induce humoral, cellular, and/or protective immunity in mice. Ad5 GA733-2 induced Ag-specific Abs that reacted predominantly to CO17-1A- and GA733-unrelated epitopes on the Ag and lysed Ag-positive CRC targets in conjunction with effector cells. Ad5 GA733-2-immune mice developed Ag-specific, proliferative lymphocytes of Th1 type and cytolytic lymphocytes. The use of Ad5 GA733-2 to immunize mice bearing established syngeneic CRC cells transfected with the human Ag induced significant and specific tumor regression. Cured mice resisted rechallenge with human CO17-1A/GA733 Ag-negative parental CRC cells, suggesting that targeting the human Ag on the murine transfectants induced protective immunity to other Ag expressed by the parental tumor. These results may explain the high potency of the recombinant vaccine. Thus, rAd5 GA733-2 may have potential as a vaccine for CRC patients.

alpha-satellite DNA methylation in normal individuals and in ICF patients: heterogeneous methylation of constitutive heterochromatin in adult and fetal tissues.

The methylation profile of ten alpha-satellites was investigated in normal individuals and in ICF (Immunodeficiency, Centromeric instability, Facial abnormalities) patients. Two out of three ICF patients showed modified methylation of these sequences, reproducing a placental profile. CENP-B boxes, the binding sites of centromeric protein B, were always skewed toward nonmethylation. Unexpected results were observed in normal individuals: in somatic adult tissues the methylation pattern of alpha-satellite DNA varied between chromosomes, and in fetal tissues these satellites were homogeneously undermethylated. Detailed methylation analysis of CENP-B boxes revealed that unmethylated alpha-satellite units coexist with thoroughly methylated regions. These observations showed that the two major components of constitutive heterochromatin are differently methylated in normal somatic and fetal tissues, since classical satellites are consistently methylated. The definite changes in the methylation profile of heterochromatin in somatic chromosomes and the asynchronous timing of methylation of classical and alpha-satellites during development may reflect specific roles of highly repeated sequences in genomic organization.

Cloning and characterization of p52, the fifth subunit of the core of the transcription/DNA repair factor TFIIH.

TFIIH is a multiprotein factor involved in transcription and DNA repair and is implicated in DNA repair/transcription deficiency disorders such as xeroderma pigmentosum, Cockayne syndrome and trichothiodystrophy. Eight out of the nine genes encoding the subunits forming TFIIH have already been cloned. We report here the identification, cDNA cloning and gene structure of the 52 kDa polypeptide and its homology with the yeast counterpart TFB2. This protein, along with p89/XPB, p62, p44 and p34, forms the core of TFIIH. Moreover, using in vitro reconstituted transcription and nucleotide excision repair (NER) assays and microinjection experiments, we demonstrate that p52 is directly involved in both transcription and DNA repair mechanisms in vitro and in vivo.

Undermethylation of Alu sequences in ICF syndrome: molecular and in situ analysis.

The methylation status of young Alu sequences was investigated in four ICF patients. In fibroblast and leukocyte DNAs, Alu repeats were either undermethylated (HhaI and HpaII digestion) or demethylated (BstUI digestion), in contrast with the methylated status of Alus in control subjects. The methylation profile exhibited in ICF patients reproduces the normal profile of placental or sperm DNA. High-sensitivity immunocytochemical detection of HhaI and HpaII restriction sites on metaphase chromosomes provided further evidence of this undermethylation. The DNA methylation defect in ICF patients, first detected in satellite DNAs (constitutive heterochromatin) and CpG islands of genes on the inactive X chromosome (facultative heterochromatin), thus includes Alu sequences that are widely distributed throughout the human genome.

The gene encoding p44, a subunit of the transcription factor TFIIH, is involved in large-scale deletions associated with Werdnig-Hoffmann disease.

Mutations of the survival motor neurone gene (SMN) are associated with spinal muscular atrophy (SMA), a frequent lethal autosomal recessive disorder. In spite of this, no phenotype-genotype correlation was observed, since the SMN gene is lacking in the majority of patients affected with either the severe form (type I) or the milder forms (types II and III). Here, we show that the gene encoding p44, a subunit of the basal transcription factor TFIIH, is duplicated in the SMA region and that the p44 gene products (p44t and p44c) differ by three amino acid changes. Gene analysis of a total of 94 unrelated SMA patients revealed that the p44t gene is involved in large-scale deletions associated with Werdnig-Hoffmann disease (type I). The TFIIH polypeptide composition as well as transcription and DNA repair activities are normal in patients lacking the p44t gene on both mutant chromosomes, suggesting that the p44t gene is not critical for the development of SMA.

Three new dinucleotide repeat polymorphisms on human chromosome 9: D9S970, D9S971, and D9S972.

Three human chromosome 9-specific cosmid recombinants containing (CA)n microsatellites are described. Three microsatellite loci, D9S970, D9S971, and D9S972, were observed to have heterozygosities of 0.78, 0.84, and 0.82, respectively. Subchromosomal localizations were determined by R-banding and fluorescence in situ hybridization.

cDNA, gene structure, and chromosomal localization of human GAR1 (CNCG3L), a homolog of the third subunit of bovine photoreceptor cGMP-gated channel.

A unique glutamic acid-rich protein was previously identified in bovine rod photoreceptors (Sugimoto et al., 1991, Proc. Natl. Acad. Sci. USA 88: 3116-3119) and later suggested to be a third subunit (gamma) of the rod cGMP-gated cation channel (Chen et al., 1994, Proc. Natl. Acad. Sci. USA 91: 11757-11761). Here, we report on the characterization of the GAR1 gene encoding a human homolog of bovine gamma. Sequence analysis of cDNA clones encoding human gamma revealed an open reading frame predicting a protein of 299 amino acids (approximately 32 kDa), half the size of the bovine gamma subunit. Comparison of the N-terminal half of bovine gamma with the predicted human gamma sequence revealed 90% identity within the first 31 amino acids, and only 60% homology was found throughout the remainder of the protein sequence. As in bovine gamma, the predicted isoelectric point of the human protein is very acidic despite the absence of the bovine C-terminal glutamic acid-rich domain. The integrity of the cDNA sequence was confirmed by analysis of several overlapping genomic clones that span the GAR1 gene. The protein coding region of the gene consists of 12 exons spanning approximately 11 kb with exon sequence identical to that of the cDNA clones. PCR of somatic cell hybrid DNA with primer pairs that amplify a portion of the GAR1 gene (locus designation CNCG3L) demonstrate localization to chromosome 16. The location of the gene was further delimited by fluorescence in situ hybridization placing the gene at 16q13.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal methylation pattern in constitutive and facultative (X inactive chromosome) heterochromatin of ICF patients.

We have investigated the distribution of DNA methylation in chromosomes and nuclei of normal individuals and ICF (Immunodeficiency, Centromeric instability and Facial abnormalities) syndrome patients, using 5-methylcytosine monoclonal antibody. In this syndrome, DNA digestion with methyl-sensitive enzymes has previously shown a specific hypomethylation of classical satellites located in constitutive heterochromatin. The chromosome methylation pattern confirms this hypomethylation showing in addition a clear undermethylation of facultative heterochromatin (X inactive chromosome). Antibodies give, in normal and ICF chromosomes, a non-uniform labeling of euchromatin, generating a weak R-like banding pattern on chromosomes. This pattern reflects an unequal distribution of DNA methylation over the genome disclosing another aspect of chromosome organization. The breakpoints of chromosome rearrangements and the heterochromatin stretchings observed in ICF patients were analyzed by means of in situ hybridization. These chromosome modifications involve hypomethylated classical DNA satellite sequences. The underlying hypomethylation, associated with an abnormal chromatin organization, may predispose to chromosome instability.

Human retinal guanylate cyclase (GUC2D) maps to chromosome 17p13.1.

3',5'-Cyclic guanosine monophosphate is the intracellular second messenger regulating phototransduction in mammals. The level of cGMP in photoreceptor cells is controlled by the cGMP-hydrolyzing enzyme cGMP phosphodiesterase and the cGMP-producing enzyme guanylate cyclase. Identification of a photoreceptor-specific guanylate cyclase (retGC) that may function in visual transduction was recently reported. As an initial step in assessing the potential for defects in the retGC (GUC2D) gene to be causal of hereditary retinal disease, we have determined its chromosome location. A 720-bp region of the human GUC2D locus was amplified with exon-specific primers. The amplified product contains three introns, two intact exons, and part of two additional exons, suggesting a high degree of structural complexity. PCR analysis of human-rodent somatic cell hybrids was used to map the GUC2D locus to chromosome 17. This assignment was confirmed and a more precise localization to 17p13.1 was obtained by fluorescence in situ hybridization.

Baculovirus recombinant expressing a secreted form of a transmembrane carcinoma-associated antigen.

GA733-2 is a monoclonal antibody-defined, 40-kDa glycoprotein antigen that is associated with carcinomas of various origins. Hydrophobicity analysis of the protein sequence predicted by complementary DNA (cDNA) has suggested that the GA733-2 antigen is a type I membrane protein. In this study, the polymerase chain reaction was used in a strategy to omit cDNA sequences for the transmembrane and cytoplasmic domains, thereby converting the extracellular domain into a secretory protein. Full-length and truncated cDNAs were cloned into the baculovirus transfer vector pVL1392 and introduced into Autographa californica nuclear polyhedrosis virus by homologous recombination. The full-length cDNA baculovirus recombinant directed the expression of a 40-kDa glycoprotein that was confined to infected Spodoptera frugiperda cells, whereas cells infected with the truncated cDNA baculovirus recombinant abundantly secreted a 31-kDa glycoprotein into the culture medium. Recombinant secretory antigen displayed an in vitro immunoreactivity to monoclonal antibody and an in vivo immunogenicity in mice that were similar to native antigen. The facile purification of mg quantities of carcinoma-associated antigen will enable an evaluation of its immunogenicity in cancer patients.