ABSTRACT
The conserved heterochromatic location of centromeres in higher eukaryotes suggests that intrinsic properties of heterochromatin are important for chromosome inheritance. Based on this hypothesis, mutations in Drosophila melanogaster that alter heterochromatin-induced gene silencing were tested for effects on chromosome inheritance. Here we describe the characterization of the Su(var)2-10 locus, initially identified as a Suppressor of Position-Effect Variegation. Su(var)2-10 is required for viability, and mutations cause both minichromosome and endogenous chromosome inheritance defects. Mitotic chromosomes are improperly condensed in mutants, and polytene chromosomes are structurally abnormal and disorganized in the nucleus. Su(var)2-10 encodes a member of the PIAS protein family, a group of highly conserved proteins that control diverse functions. SU(VAR)2-10 proteins colocalize with nuclear lamin in interphase, and little to no SU(VAR)2-10 is found on condensed mitotic chromosomes. SU(VAR)2-10 is present at some polytene chromosome telomeres, and FISH analyses in mutant polytene nuclei revealed defects in telomere clustering and telomere-nuclear-lamina associations. We propose that Su(var2-10 controls multiple aspects of chromosome structure and function by establishing/maintaining chromosome organization in interphase nuclei.
Subject(s)
Carrier Proteins/genetics , Chromatin/genetics , Chromosome Structures/genetics , Drosophila/genetics , Proteins/genetics , Repressor Proteins/genetics , Animals , Blotting, Western , Carrier Proteins/metabolism , Cell Nucleus/genetics , Cell Nucleus/metabolism , Cell Nucleus/ultrastructure , Chromatin/metabolism , Chromatin/ultrastructure , Chromosome Structures/metabolism , Chromosome Structures/ultrastructure , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , Drosophila/cytology , Drosophila/metabolism , Fluorescent Antibody Technique , Gene Silencing , In Situ Hybridization, Fluorescence , Kruppel-Like Transcription Factors , Mitosis/genetics , Nuclear Proteins/genetics , Nuclear Proteins/metabolism , Polymerase Chain Reaction , Protein Inhibitors of Activated STAT , Proteins/metabolism , Repressor Proteins/metabolism , Telomere/genetics , Telomere/metabolism , Telomere/ultrastructure , Transcription Factors/genetics , Transcription Factors/metabolism , Ubiquitin-Protein LigasesABSTRACT
The segregation of homologous chromosomes from one another is the essence of meiosis. In many organisms, accurate segregation is ensured by the formation of chiasmata resulting from crossing over. Drosophila melanogaster females use this type of recombination-based system, but they also have mechanisms for segregating achiasmate chromosomes with high fidelity. We describe a P-element mutagenesis and screen in a sensitized genetic background to detect mutations that impair meiotic chromosome pairing, recombination, or segregation. Our screen identified two new recombination-deficient mutations: mei-P22, which fully eliminates meiotic recombination, and mei-P26, which decreases meiotic exchange by 70% in a polar fashion. We also recovered an unusual allele of the ncd gene, whose wild-type product is required for proper structure and function of the meiotic spindle. However, the screen yielded primarily mutants specifically defective in the segregation of achiasmate chromosomes. Although most of these are alleles of previously undescribed genes, five were in the known genes alphaTubulin67C, CycE, push, and Trl. The five mutations in known genes produce novel phenotypes for those genes.
Subject(s)
DNA Transposable Elements/genetics , Drosophila melanogaster/genetics , Genes, Insect , Meiosis/genetics , Animals , Chromosomes/genetics , DNA/genetics , Female , Heterochromatin , Male , Metaphase , Mutation , Nondisjunction, Genetic , Phenotype , Recombination, Genetic , Research Design , X Chromosome/geneticsABSTRACT
Centromeres and the associated kinetochores are involved in essential aspects of chromosome transmission. Recent advances have included the identification and understanding of proteins that have a pivotal role in centromere structure, kinetochore formation, and the coordination of chromosome inheritance with the cell cycle in several organisms. A picture is beginning to emerge of the centromere-kinetechore as a complex and dynamic structure with conservation of function at the protein level across diverse species.
Subject(s)
Centromere/metabolism , Chromosomal Proteins, Non-Histone/metabolism , Animals , Cell Cycle/genetics , Microtubules/metabolismABSTRACT
The D. melanogaster mei-41 gene is required for DNA repair, mitotic chromosome stability, and normal levels of meiotic recombination in oocytes. Here we show that the predicted mei-41 protein is similar in sequence to the ATM (ataxia telangiectasia) protein from humans and to the yeast rad3 and Mec1p proteins. There is also extensive functional overlap between mei-41 and ATM. Like ATM-deficient cells, mei-41 cells are exquisitely sensitive to ionizing radiation and display high levels of mitotic chromosome instability. We also demonstrate that mei-41 cells, like ATM-deficient cells, fail to show an irradiation-induced delay in the entry into mitosis that is characteristic of normal cells. Thus, the mei-41 gene of Drosophila may be considered to be a functional homolog of the human ATM gene.
