DNA polymorphism in the human Thy-1 gene

Novel homozygous ataxia‑telangiectasia (A‑T) mutated gene mutation identified in a Chinese pedigree with A‑T

Ataxia‑telangiectasia (A‑T) syndrome is a rare autosomal recessive disorder mainly caused by mutations in the A‑T mutated (ATM) gene. However, the genomic abnormalities and their consequences associated with the pathogenesis of A‑T syndrome remain to be fully elucidated. In the present study, a whole‑exome sequencing analysis of a family with A‑T syndrome was performed, revealing a novel homozygous deletion mutation [namely, NM_000051.3:c.50_72+7del,p.Asp18_Lys24delins(23)] in ATM in three affected siblings, which was inherited from their carrier parents who exhibited a normal phenotype in this pedigree. The identified mutation spans the exon 2 and intron 2 regions of the ATM gene, causing a splicing aberration that resulted in a 30‑bp deletion in exon 2 and intron 2, as well as a 71‑bp insertion in intron 2 in the splicing process, which was confirmed by reverse transcription‑polymerase chain reaction and sequencing analysis. The change in the three‑dimensional structure of the protein caused by the mutation in ATM may affect the functions associated with telomere length maintenance and DNA damage repair. Taken together, the present study reported a novel homozygous deletion mutation in the ATM gene resulting in A‑T syndrome in a Chinese pedigree and expanded on the spectrum of known causative mutations of the ATM gene.

Atrophy, oxidative switching and ultrastructural defects in skeletal muscle of the ataxia telangiectasia mouse model

Ataxia telangiectasia is a rare, multi system disease caused by ATM kinase deficiency. Atm-knockout mice recapitulate premature aging, immunodeficiency, cancer predisposition, growth retardation and motor defects, but not cerebellar neurodegeneration and ataxia. We explored whether Atm loss is responsible for skeletal muscle defects by investigating myofiber morphology, oxidative/glycolytic activity, myocyte ultrastructural architecture and neuromuscular junctions. Atm-knockout mice showed reduced muscle and fiber size. Atrophy, protein synthesis impairment and a switch from glycolytic to oxidative fibers were detected, along with an increase of in expression of slow and fast myosin types (Myh7, and Myh2 and Myh4, respectively) in tibialis anterior and solei muscles isolated from Atm-knockout mice. Transmission electron microscopy of tibialis anterior revealed misalignments of Z-lines and sarcomeres and mitochondria abnormalities that were associated with an increase in reactive oxygen species. Moreover, neuromuscular junctions appeared larger and more complex than those in Atm wild-type mice, but with preserved presynaptic terminals. In conclusion, we report for the first time that Atm-knockout mice have clear morphological skeletal muscle defects that will be relevant for the investigation of the oxidative stress response, motor alteration and the interplay with peripheral nervous system in ataxia telangiectasia.

Atm reactivation reverses ataxia telangiectasia phenotypes in vivo

Hereditary deficiencies in DNA damage signaling are invariably associated with cancer predisposition, immunodeficiency, radiation sensitivity, gonadal abnormalities, premature aging, and tissue degeneration. ATM kinase has been established as a central player in DNA double-strand break repair and its deficiency causes ataxia telangiectasia, a rare, multi-system disease with no cure. So ATM represents a highly attractive target for the development of novel types of gene therapy or transplantation strategies. Atm tamoxifen-inducible mouse models were generated to explore whether Atm reconstitution is able to restore Atm function in an Atm-deficient background. Body weight, immunodeficiency, spermatogenesis, and radioresistance were recovered in transgenic mice within 1 month from Atm induction. Notably, life span was doubled after Atm restoration, mice were protected from thymoma and no cerebellar defects were observed. Atm signaling was functional after DNA damage in vivo and in vitro. In summary, we propose a new Atm mouse model to investigate novel therapeutic strategies for ATM activation in ataxia telangiectasia disease.

Investigations into the molecular effects of single nucleotide polymorphism

OBJECTIVES

DNA sequences are very rich in short repeats and their pattern can be altered by point mutations. We wanted to investigate the effect of single nucleotide polymorphism (SNP) on the pattern of short DNA repeats and its biological consequences.

METHODS

Analysis of the pattern of short DNA repeats of the Thy-1 sequence with and without SNP. Searching for DNA-binding factors in any region of significance.

RESULTS

Comparing the pattern of short repeats in the Thy-1 gene sequences of Turkish patients with ataxia telangiectasia (AT) with the "wild type" sequence from the DNA database, we identified a missing 8-bp repeat element due to an SNP in position 1271 (intron II) in AT-DNA sequences. Only the mutated sequence had the potential for the formation of a stem loop in DNA or pre-mRNA. In super-shift experiments we found that DNA oligomers covering the area of this SNP formed a complex with proteins amongst which we identified the proliferating cell nuclear antigen (PCNA) protein.

CONCLUSION

SNPs have the potential to alter DNA or pre-mRNA conformation. Although no SNP-depeding formation of the DNA-protein complex was evident, future investigations could reveal differential molecular mechanisms of cellular regulation.

Immune system cell markers in the northern brown bandicoot, Isoodon macrourus

This is the first study to report the presence of T and B lymphocyte markers and antigen presenting-like molecules in a marsupial bandicoot. Intra-cytoplasmic markers for CD3 and CD5, as well as surface Thy-1.1 and CD1a molecules were located in lymphocytes of T dependent regions of immuno-lymphoid tissue in the northern brown bandicoot using immunohistochemical techniques. Similarly, intra-cytoplasmic domains of CD79a, CD79b molecules and surface IgG molecules enabled characterisation of B lymphocytes and plasma cells. The phenotypic expression of these molecules parallels findings in eutherians, suggesting firstly the conservation of lineage epitopes for T and B subsets and secondly, the potential for similar functional properties of immune system cells between marsupials and eutherians. In addition, the presence of MHC class II and CD1a molecules on dendritic-like cells may indicate similar mechanisms for antigen processing and presentation as reported in eutherians. The use of such immune system cell markers will enable functional studies to characterise the marsupial immune system as well as ontogeny studies of immune competence.

Detection of MspI RFLP in human THY1 gene by the polymerase chain reaction

THY1 gene encodes a cell surface glycoprotein predominantly expressed in brain and peripheral nerves. Human THY1 gene region on chromosome 11q23 has been implicated in susceptibility to type 1 diabetes (Wong et al., 1991). Two primers derived from the sequences flanking the polymorphic MspI site in intron 2 of the human THY1 gene (Gatti et al., 1988) were selected for RCP to amplify a 566 bp fragment that spans the MspI polymorphism. Polymorphism was detected by MspI digestion of the PCR product.

Genetic linkage analysis and homology relationships of genes located on human chromosome 11q

We have used DNA polymorphisms detected by probes for 11q to order 16 genes and to determine the genetic distances between them. Our map includes the genes for CD20, tyrosinase, progesterone receptor, stromelysin, collagenase, N-CAM, dopamine-D2 receptor, apolipoproteins AI-CIII-AIV, CD3-epsilon, -delta, and -gamma, porphobilinogen deaminase, thy-1, and ets-1. These genes have previously been sequenced as well as placed on the 11q cytogenetic map, which now makes them anchor points between the cytogenetic, genetic, and physical maps of this region. The ordering and distances between these genes are of immediate use in testing hypotheses of candidate genes for human genetic diseases associated with chromosome 11q. A comparison between our genetic map and similar maps from other species defines regions of homologous synteny that may be useful in mapping human genetic disease genes localized to the 11q region. Analysis of such homology provides additional bases for speculation of the evolutionary histories of gene families in this region.

A primary linkage map of the human chromosome 11q22-23 region

We have constructed a genetic map of the human chromosomal region 11q22-23 by multipoint linkage analysis of 13 DNA polymorphisms that we have condensed into eight loci. An analysis for linkage disequilibrium between tightly linked probe/enzyme systems allows us to make specific recommendations for future DNA typing at these loci. The resulting sex-averaged multipoint map spans approximately 80 cM and differs considerably from previously reported genetic maps of this region. Our mathematically derived "most likely order" of the markers is compatible with physical mapping data using somatic cell hybrids. The known localizations of at least 14 functional genes and several disease loci to 11q22-23, including ataxia telangiectasia, make the mapping of this region especially relevant to studies of disease pathogenesis.

Speculations on ataxia-telangiectasia: defective regulation of the immunoglobulin gene superfamily

In this short article, Raymond Peterson and Jane Funkhouser develop the argument that the common molecular mechanism linking the various clinical manifestations of ataxia-telangiectasia (AT) is a defect in the regulation of the immunoglobulin (Ig) gene superfamily. They propose that the AT gene codes for a protein essential for the orderly expression of this gene family, perhaps regulating the gene rearrangement process that appears to be a unique characteristic of this system. Members of the Ig gene superfamily play a major role in the development and operation of the immune and nervous systems, and any perturbation of their expression would be anticipated to produce a panoply of signs and symptoms, such as those characterizing the AT phenotype.

Localization of an ataxia-telangiectasia gene to chromosome 11q22-23

Ataxia-telangiectasia (AT) is a human autosomal recessive disorder of childhood characterized by: (1) progressive cerebellar ataxia with degeneration of Purkinje cells; (2) hypersensitivity of fibroblasts and lymphocytes to ionizing radiation; (3) a 61-fold and 184-fold increased cancer incidence in white and black patients, respectively; (4) non-random chromosomal rearrangements in lymphocytes; (5) thymic hypoplasia with cellular and humoral (IgA and IgG2) immunodeficiencies; (6) elevated serum level of alphafetoprotein; (7) premature ageing; and (8) endocrine disorders, such as insulin-resistant diabetes mellitus. A DNA processing or repair protein is the suspected common denominator in this pathology. Heterozygotes are generally healthy; however, the sensitivity of their cultured cells to ionizing radiation is intermediate between normal individuals and that of affected homozygotes. Furthermore, heterozygous females are at an increased risk of breast cancer. These findings, when coupled with an estimated carrier frequency of 0.5-5.0%, suggest that (1) as many as one in five women with breast cancer may carry the AT gene and that (2) the increased radiation sensitivity of AT heterozygotes may be causing radiation therapists to reduce the doses of radiation used for treating cancer in all patients. To identify the genetic defect responsible for this multifaceted disorder, and to provide effective carrier detection, we performed a genetic linkage analysis of 31 families with AT-affected members. This has allowed us to localize a gene for AT to chromosomal region 11q22-23.