Effect of intercalating mutagens on crossing-over inDrosophila melanogaster females

Drosophila Model for the Analysis of Genesis of LIM-kinase 1-Dependent Williams-Beuren Syndrome Cognitive Phenotypes: INDELs, Transposable Elements of the Tc1/Mariner Superfamily and MicroRNAs

Genomic disorders, the syndromes with multiple manifestations, may occur sporadically due to unequal recombination in chromosomal regions with specific architecture. Therefore, each patient may carry an individual structural variant of DNA sequence (SV) with small insertions and deletions (INDELs) sometimes less than 10 bp. The transposable elements of the Tc1/mariner superfamily are often associated with hotspots for homologous recombination involved in human genetic disorders, such as Williams Beuren Syndromes (WBS) with LIM-kinase 1-dependent cognitive defects. The Drosophila melanogaster mutant agnts3 has unusual architecture of the agnostic locus harboring LIMK1: it is a hotspot of chromosome breaks, ectopic contacts, underreplication, and recombination. Here, we present the analysis of LIMK1-containing locus sequencing data in agnts3 and three D. melanogaster wild-type strains-Canton-S, Berlin, and Oregon-R. We found multiple strain-specific SVs, namely, single base changes and small INDEls. The specific feature of agnts3 is 28 bp A/T-rich insertion in intron 1 of LIMK1 and the insertion of mobile S-element from Tc1/mariner superfamily residing ~460 bp downstream LIMK1 3'UTR. Neither of SVs leads to amino acid substitutions in agnts3 LIMK1. However, they apparently affect the nucleosome distribution, non-canonical DNA structure formation and transcriptional factors binding. Interestingly, the overall expression of miRNAs including the biomarkers for human neurological diseases, is drastically reduced in agnts3 relative to the wild-type strains. Thus, LIMK1 DNA structure per se, as well as the pronounced changes in total miRNAs profile, probably lead to LIMK1 dysregulation and complex behavioral dysfunctions observed in agnts3 making this mutant a simple plausible Drosophila model for WBS.

Effects of chemical and physical agents on recombination events in cells of the germ line of male and female Drosophila melanogaster

Genotoxic agents can induce mutations as well as recombination in the genetic material. The fruit fly Drosophila melanogaster was one of the first assay systems to test physical and chemical agents for recombinogenic effects. Such effects can be observed in cells of the germ line as well as in somatic cells. At present information is available on 54 agents, among them 48 chemicals that have been tested in cells of the germ line of males and/or females. Effects on meiotic recombination in female germ cells cannot simply be classified as positive or negative since for a number of agents, depending on the chromosome region studied, recombination frequencies may be increased, unaffected or decreased. The male germ line of D. melanogaster represents a unique situation because meiotic recombination does not occur. Among 25 agents tested in male germ cells 24 did induce male recombination, among them alkylating, intercalating and cross-linking agents, direct-acting ones as well as compounds needing metabolic activation. With several compounds the frequency of induced recombination is highest in the heterochromatic regions near the centromeres. In brood pattern analyses, e.g., after exposure of adult males to ionizing radiation, the first appearance of crossover progeny is indicative of the sampling of exposed spermatocytes. In premeiotic cells of the male and the female germ line mitotic recombination can occur. Upon clonal expansion of the recombinant cells, clusters of identical crossovers can be observed.