ABSTRACT
Telomeres are the stable ends of linear chromosomes in eukaryotes. These complex protein-nucleic acid structures are essential to maintain genomic stability and the integrity of linear chromosomes. We identified a new mutation in Drosophila that causes a high frequency of end-to-end fusions of chromosomes during mitosis and meiosis. Linear chromosomal ends appear to be essential for fusions to take place. These fusions do not resolve, leading to cycles of chromosomal breakage and rejoining and severe genome rearrangements. The gene is essential for normal cell proliferation and mutant tissue shows significant apoptosis. Our analysis suggests that the function encoded by the mutant gene is required to protect the linear ends of chromosomes.
Subject(s)
Drosophila melanogaster/genetics , Genes, Insect , Mutation , Telomere/genetics , Animals , Apoptosis/genetics , Cell Division/genetics , Chromobox Protein Homolog 5 , Chromosomal Proteins, Non-Histone/metabolism , DNA Damage , DNA Repair/genetics , DNA Replication/genetics , Drosophila melanogaster/cytology , Drosophila melanogaster/metabolism , Gene Rearrangement , In Situ Hybridization, Fluorescence , Male , Mitosis/genetics , Neurons/cytology , Phenotype , Spermatogenesis/geneticsABSTRACT
We have isolated a Hoppel-like transposon from heterochromatin of the second chromosome of Drosophila melanogaster and used a conserved DNA sequence between the different elements of this family to determine their distribution in both mitotic and polytene chromosomes. The hybridization pattern of polytene chromosomes extends throughout the entire chromocentre, as well as a substantial portion of the fourth chromosome. Analysis of different wild-type strains of D. melanogaster shows variation in euchromatic insertion sites, although most insertions are found near the chromocentre. The positions and the number of heterochromatic clusters of Hoppel on mitotic chromosomes are conserved among the several strains analysed. Accurate mapping of this element was achieved by in situ hybridization on D. melanogaster mitotic chromosomes that had previously been banded with Hoechst 33258. To evaluate the evolutionary stability of this pattern, different species were analysed by in situ hybridization and Southern blotting. We conclude that Hoppel has a conserved distribution in mitotic heterochromatin within the D. melanogaster subgroup, established around 5 million years ago. The overall conservation of heterochormatic organization supports the notion that heterochormatin does perform important structural and functional roles.
