Genetic Background, Maternal Age, and Interaction Effects Mediate Rates of Crossing Over in Drosophila melanogaster Females.
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ABSTRACT:
SUBMITTER: Hunter CM
PROVIDER: S-EPMC4856091 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:BACKGROUND: Variation at the level of gene expression is abundant in natural populations and is thought to contribute to the adaptive divergence of populations and species. Gene expression also differs considerably between males and females. Here we report a microarray analysis of gene expression variation among females of 16 Drosophila melanogaster strains derived from natural populations, including eight strains from the putative ancestral range in sub-Saharan Africa and eight strains from Europe. Gene expression variation among males of the same strains was reported previously. RESULTS: We detected relatively low levels of expression polymorphism within populations, but much higher expression divergence between populations. A total of 569 genes showed a significant expression difference between the African and European populations at a false discovery rate of 5%. Genes with significant over-expression in Europe included the insecticide resistance gene Cyp6g1, as well as genes involved in proteolysis and olfaction. Genes with functions in carbohydrate metabolism and vision were significantly over-expressed in the African population. There was little overlap between genes expressed differently between populations in females and males. CONCLUSIONS: Our results suggest that adaptive changes in gene expression have accompanied the out-of-Africa migration of D. melanogaster. Comparison of female and male expression data indicates that the vast majority of genes differing in expression between populations do so in only one sex and suggests that most regulatory adaptation has been sex-specific.
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Project description:Meiotic crossing over ensures proper segregation of homologous chromosomes and generates genotypic diversity. Despite these functions, little is known about the genetic factors and population genetic forces involved in the evolution of recombination rate differences among species. The dicistronic meiosis gene, mei-217/mei-218, mediates most of the species differences in crossover rate and patterning during female meiosis between the closely related fruitfly species, Drosophila melanogaster and D. mauritiana The MEI-218 protein is one of several meiosis-specific mini-chromosome maintenance (mei-MCM) proteins that form a multi-protein complex essential to crossover formation, whereas the BLM helicase acts as an anti-crossover protein. Here we study the molecular evolution of five genes- mei-218, the other three known members of the mei-MCM complex, and Blm- over the phylogenies of three Drosophila species groups- melanogaster, obscura, and virilis We then use transgenic assays in D. melanogaster to test if molecular evolution at mei-218 has functional consequences for crossing over using alleles from the distantly related species D. pseudoobscura and D. virilis Our molecular evolutionary analyses reveal recurrent positive selection at two mei-MCM genes. Our transgenic assays show that sequence divergence among mei-218 alleles from D. melanogaster, D. pseudoobscura, and D. virilis has functional consequences for crossing over. In a D. melanogaster genetic background, the D. pseudoobscura mei-218 allele nearly rescues wildtype crossover rates but alters crossover patterning, whereas the D. virilis mei-218 allele conversely rescues wildtype crossover patterning but not crossover rates. These experiments demonstrate functional divergence at mei-218 and suggest that crossover rate and patterning are separable functions.
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Project description:A correlation between diversity levels and rates of recombination is predicted both by models of positive selection, such as hitchhiking associated with the rapid fixation of advantageous mutations, and by models of purifying selection against strongly deleterious mutations (commonly referred to as "background selection"). With parameter values appropriate for Drosophila populations, only the first class of models predicts a marked skew in the frequency spectrum of linked neutral variants, relative to a neutral model. Here, we consider 29 loci scattered throughout the Drosophila melanogaster genome. We show that, in African populations, a summary of the frequency spectrum of polymorphic mutations is positively correlated with the meiotic rate of crossing over. This pattern is demonstrated to be unlikely under a model of background selection. Models of weakly deleterious selection are not expected to produce both the observed correlation and the extent to which nucleotide diversity is reduced in regions of low (but nonzero) recombination. Thus, of existing models, hitchhiking due to the recurrent fixation of advantageous variants is the most plausible explanation for the data.
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Project description:Genomic imprinting occurs when expression of an allele differs based on the sex of the parent that transmitted the allele. In D. melanogaster, imprinting can occur, but its impact on allelic expression genome-wide is unclear. Here, we search for imprinted genes in D. melanogaster using RNA-seq to compare allele-specific expression between pools of 7- to 10-day-old adult female progeny from reciprocal crosses. We identified 119 genes with allelic expression consistent with imprinting, and these genes showed significant clustering within the genome. Surprisingly, additional analysis of several of these genes showed that either genomic heterogeneity or high levels of intrinsic noise caused imprinting-like allelic expression. Consequently, our data provide no convincing evidence of imprinting for D. melanogaster genes in their native genomic context. Elucidating sources of false-positive signals for imprinting in allele-specific RNA-seq data, as done here, is critical given the growing popularity of this method for identifying imprinted genes.
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