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PubMed1992

Antibodies to the p70/p80 (Ku) antigens in systemic lupus erythematosus.

The Ku (p70/p80) autoantigen, a heterodimer consisting of 70 kDa (p70) and 80 kDa (p80) protein subunits, is one of a group of DNA-associated autoantigens identified as targets of autoantibodies produced by patients with SLE and related disorders. Many of these DNA-protein antigens are involved in organizing the genome into transcriptionally active (euchromatin) and inactive (heterochromatin) domains. The bulk of available evidence indicates that the Ku antigen is also involved in organizing the genome, although its precise role remains unclear. Molecular cloning of the protein subunits of Ku has revealed that the structure of p70 resembles that of certain transcriptional activator proteins, and there is some evidence in vitro that Ku may increase transcriptional activity from at least two promoters. Moreover, examination of the distribution of Ku in the polytene chromosomes of insects suggests an association with transcriptionally active chromatin. The DNA-binding domain of Ku has been localized to the C-terminus of p70, whereas p80 does not appear to bind DNA, and may be involved in interactions with other proteins. Epitope mapping and mutagenesis experiments have shown that the immunodominant epitope of p70 lies within the DNA-binding domain. Surprisingly, this autoepitope is not conserved between humans and mice, raising the possibility that the interaction of Ku with DNA might exhibit species specific functional differences. At least seven additional autoepitopes have been identified on the Ku particle, located on p70, p80, or both subunits. Autoantibodies to p70, p80, and DNA are produced tandemly by patients with SLE, providing evidence for an antigen-driven immune response targeting the entire Ku particle. The multiple specificities of anti-Ku autoantibodies and the tandem production of antibodies to the various constituents of the Ku particle are consistent with a role of either "molecular mimicry" or "intermolecular help" in the generation of autoimmunity to this antigen.

Animals↗
PubMed1970

Chromosome number variation in a stick insect Didymuria violescens (Leach).

Seven major races, with diploid numbers ranging from 26 to 40, and three types of sex-chromosome mechanism were found in the Australian phasmatid Didymuria violescens (Leach). The differences between chromosome complements are mainly due to translocations between autosomes, and to translocations between autosomes and sex chromosomes. The geographic pattern of chromosome variation and the characteristics of hybrids implicate chromosomal rearrangements in mechanisms of speciation.

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PubMed1998

Multiple origins of cytologically identical chromosome inversions in the Anopheles gambiae complex.

For more than 60 years, evolutionary cytogeneticists have been using naturally occurring chromosomal inversions to infer phylogenetic histories, especially in insects with polytene chromosomes. The validity of this method is predicated on the assumption that inversions arise only once in the history of a lineage, so that sharing a particular inversion implies shared common ancestry. This assumption of monophyly has been generally validated by independent data. We present the first clear evidence that naturally occurring inversions, identical at the level of light microscopic examination of polytene chromosomes, may not always be monophyletic. The evidence comes from DNA sequence analyses of regions within or very near the breakpoints of an inversion called the 2La that is found in the Anopheles gambiae complex. Two species, A. merus and A. arabiensis, which are fixed for the "same" inversion, do not cluster with each other in a phylogenetic analysis of the DNA sequences within the 2La. Rather, A. merus 2La is most closely related to strains of A. gambiae homozygous for the 2L+. A. gambiae and A. merus are sister taxa, the immediate ancestor was evidently homozygous 2L+, and A. merus became fixed for an inversion cytologically identical to that in A. arabiensis. A. gambiae is polymorphic for 2La/2L+, and the 2La in this species is nearly identical at the DNA level to that in A. arabiensis, consistent with the growing evidence that introgression has or is occurring between these two most important vectors of malaria in the world. The parallel evolution of the "same" inversion may be promoted by the presence of selectively important genes within the breakpoints.

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PubMed2003

Telomeric and interstitial telomeric sequences in holokinetic chromosomes of Lepidoptera: telomeric DNA mediates association between postpachytene bivalents in achiasmatic meiosis of females.

Telomeres, besides their main role in the protection and maintenance of chromosome ends, have several other vital functions in the cell cycle. We studied their role in the achiasmatic meiosis of female Lepidoptera, insects with holokinetic chromosomes. By fluorescence in-situ hybridization (FISH) with the insect telomeric probe, (TTAGG)n, we mapped the distribution of telomeric and interstitial telomeric sequences (ITS) in female meiotic chromosomes of two species, Orgyia antiqua with a reduced chromosome number (2n = 28) and Ephestia kuehniella mutants, possessing a radiation-induced chromosome fusion in the genome (2n = 59). In addition to the strong typical telomeric signals, O. antiqua displayed weaker hybridization signals in interstitial sites of pachytene bivalents. The observed ITS most probably reflect remnants of chromosomal rearrangements and support the hypothesis that the Orgyia karyotype had arisen by multiple fusions of ancestral chromosomes. On the other hand, the absence of ITS in the chromosome fusion of Ephestia indicated the loss of telomeres before the two original chromosomes fused. When the telomeric probe was amplified by enzymatic reaction with tyramid, the number of ITS observed increased in Orgyia, and a few ITS were also observed in several chromosomes of Ephestia but not in the fused chromosome. This suggests that the genomes of both species also contain ITS other than those originating from chromosome fusions. The analysis of female meiotic prophase I revealed non-homologous associations of postpachytene bivalents mediated by telomeric DNA, which were not observed in the pachytene stage. Surprisingly, in early postpachytene nuclei the telomeric associations also involved ITS, whereas later postpachytene nuclei displayed chains of bivalents interconnected only by true telomeres. This finding favours a hypothesis that telomeric associations between bivalents play a role in chromosome segregation in the achiasmatic meiosis of female Lepidoptera.

Animals↗
PubMed1999

Persistent Hz-1 virus infection in insect cells: evidence for insertion of viral DNA into host chromosomes and viral infection in a latent status.

Persistent/latent viral infections of insect cells are a prominent though poorly understood phenomenon. In this study, the long-term association between the Hz-1 virus and insect host cells, conventionally referred to as persistent viral infection, is described. With the aid of a newly developed fluorescent cell-labeling system, we found that productive viral replication occurs by spontaneous viral reactivation in fewer than 0.2% of persistently infected cell lines over a 5-day period. Once viral reactivation takes place, the host cell dies. The persistently infected cells contain various amounts of viral DNA, and, in an extreme case, up to 16% of the total DNA isolated from infected cells could be of viral origin. Both pulsed-field gel electrophoresis and in situ hybridization experiments showed that some of these viral DNA molecules are inserted into the host chromosomes but that the rest of viral DNA copies are free from host chromosomes. Thus, Hz-1 virus is the first nonretroviral insect virus known to insert its genome into the host chromosome during the infection process. These data also suggest that the previously described persistent infection of Hz-1 virus in insect cells should be more accurately referred to as latent viral infection.

Animals↗
PubMed2007

Update of the Anopheles gambiae PEST genome assembly.

BACKGROUND: The genome of Anopheles gambiae, the major vector of malaria, was sequenced and assembled in 2002. This initial genome assembly and analysis made available to the scientific community was complicated by the presence of assembly issues, such as scaffolds with no chromosomal location, no sequence data for the Y chromosome, haplotype polymorphisms resulting in two different genome assemblies in limited regions and contaminating bacterial DNA. RESULTS: Polytene chromosome in situ hybridization with cDNA clones was used to place 15 unmapped scaffolds (sizes totaling 5.34 Mbp) in the pericentromeric regions of the chromosomes and oriented a further 9 scaffolds. Additional analysis by in situ hybridization of bacterial artificial chromosome (BAC) clones placed 1.32 Mbp (5 scaffolds) in the physical gaps between scaffolds on euchromatic parts of the chromosomes. The Y chromosome sequence information (0.18 Mbp) remains highly incomplete and fragmented among 55 short scaffolds. Analysis of BAC end sequences showed that 22 inter-scaffold gaps were spanned by BAC clones. Unmapped scaffolds were also aligned to the chromosome assemblies in silico, identifying regions totaling 8.18 Mbp (144 scaffolds) that are probably represented in the genome project by two alternative assemblies. An additional 3.53 Mbp of alternative assembly was identified within mapped scaffolds. Scaffolds comprising 1.97 Mbp (679 small scaffolds) were identified as probably derived from contaminating bacterial DNA. In total, about 33% of previously unmapped sequences were placed on the chromosomes. CONCLUSION: This study has used new approaches to improve the physical map and assembly of the A. gambiae genome.

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