Drosophila muller f elements maintain a distinct set of genomic properties over 40 million years of evolution

Genomic changes following the reversal of a Y chromosome to an autosome in Drosophila pseudoobscura

Robertsonian translocations resulting in fusions between sex chromosomes and autosomes shape karyotype evolution by creating new sex chromosomes from autosomes. These translocations can also reverse sex chromosomes back into autosomes, which is especially intriguing given the dramatic differences between autosomes and sex chromosomes. To study the genomic events following a Y chromosome reversal, we investigated an autosome‐Y translocation in Drosophila pseudoobscura. The ancestral Y chromosome fused to a small autosome (the dot chromosome) approximately 10–15 Mya. We used single molecule real‐time sequencing reads to assemble the D. pseudoobscura dot chromosome, including this Y‐to‐dot translocation. We find that the intervening sequence between the ancestral Y and the rest of the dot chromosome is only ∼78 Kb and is not repeat‐dense, suggesting that the centromere now falls outside, rather than between, the fused chromosomes. The Y‐to‐dot region is 100 times smaller than the D. melanogaster Y chromosome, owing to changes in repeat landscape. However, we do not find a consistent reduction in intron sizes across the Y‐to‐dot region. Instead, deletions in intergenic regions and possibly a small ancestral Y chromosome size may explain the compact size of the Y‐to‐dot translocation.

Transmission of Metabolic Dysfunction Across Generations

Recent human and animal studies investigating the roles of the genome, epigenome, and environmental cues have identified associations between offspring predisposition to life-long obesity/metabolic disease and epigenetic modifications such as DNA methylation. This review explores the mechanisms by which maternal exposures impair the health of not only the next generation but also potentially future generations of offspring.

The GEP: Crowd-Sourcing Big Data Analysis with Undergraduates

The era of 'big data' is also the era of abundant data, creating new opportunities for student-scientist research partnerships. By coordinating undergraduate efforts, the Genomics Education Partnership produces high-quality annotated data sets and analyses that could not be generated otherwise, leading to scientific publications while providing many students with research experience.

Helitrons shaping the genomic architecture of Drosophila: enrichment of DINE-TR1 in α- and β-heterochromatin, satellite DNA emergence, and piRNA expression

Drosophila INterspersed Elements (DINEs) constitute an abundant but poorly understood group of Helitrons present in several Drosophila species. The general structure of DINEs includes two conserved blocks that may or not contain a region with tandem repeats in between. These central tandem repeats (CTRs) are similar within species but highly divergent between species. It has been assumed that CTRs have independent origins. Herein, we identify a subset of DINEs, termed DINE-TR1, which contain homologous CTRs of approximately 150 bp. We found DINE-TR1 in the sequenced genomes of several Drosophila species and in Bactrocera tryoni (Acalyptratae, Diptera). However, interspecific high sequence identity (∼ 88 %) is limited to the first ∼ 30 bp of each tandem repeat, implying that evolutionary constraints operate differently over the monomer length. DINE-TR1 is unevenly distributed across the Drosophila phylogeny. Nevertheless, sequence analysis suggests vertical transmission. We found that CTRs within DINE-TR1 have independently expanded into satellite DNA-like arrays at least twice within Drosophila. By analyzing the genome of Drosophila virilis and Drosophila americana, we show that DINE-TR1 is highly abundant in pericentromeric heterochromatin boundaries, some telomeric regions and in the Y chromosome. It is also present in the centromeric region of one autosome from D. virilis and dispersed throughout several euchromatic sites in both species. We further found that DINE-TR1 is abundant at piRNA clusters, and small DINE-TR1-derived RNA transcripts (∼25 nt) are predominantly expressed in the testes and the ovaries, suggesting active targeting by the piRNA machinery. These features suggest potential piRNA-mediated regulatory roles for DINEs at local and genome-wide scales in Drosophila.

Exploration of the Drosophila buzzatii transposable element content suggests underestimation of repeats in Drosophila genomes

Background

Many new Drosophila genomes have been sequenced in recent years using new-generation sequencing platforms and assembly methods. Transposable elements (TEs), being repetitive sequences, are often misassembled, especially in the genomes sequenced with short reads. Consequently, the mobile fraction of many of the new genomes has not been analyzed in detail or compared with that of other genomes sequenced with different methods, which could shed light into the understanding of genome and TE evolution. Here we compare the TE content of three genomes: D. buzzatii st-1, j-19, and D. mojavensis.

Results

We have sequenced a new D. buzzatii genome (j-19) that complements the D. buzzatii reference genome (st-1) already published, and compared their TE contents with that of D. mojavensis. We found an underestimation of TE sequences in Drosophila genus NGS-genomes when compared to Sanger-genomes. To be able to compare genomes sequenced with different technologies, we developed a coverage-based method and applied it to the D. buzzatii st-1 and j-19 genome. Between 10.85 and 11.16 % of the D. buzzatii st-1 genome is made up of TEs, between 7 and 7,5 % of D. buzzatii j-19 genome, while TEs represent 15.35 % of the D. mojavensis genome. Helitrons are the most abundant order in the three genomes.

Conclusions

TEs in D. buzzatii are less abundant than in D. mojavensis, as expected according to the genome size and TE content positive correlation. However, TEs alone do not explain the genome size difference. TEs accumulate in the dot chromosomes and proximal regions of D. buzzatii and D. mojavensis chromosomes. We also report a significantly higher TE density in D. buzzatii and D. mojavensis X chromosomes, which is not expected under the current models. Our easy-to-use correction method allowed us to identify recently active families in D. buzzatii st-1 belonging to the LTR-retrotransposon superfamily Gypsy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2648-8) contains supplementary material, which is available to authorized users.

Crowdsourced Data Indicate Widespread Multidrug Resistance in Skin Flora of Healthy Young Adults

In a laboratory exercise for undergraduate biology majors, students plated bacteria from swabs of their facial skin under conditions that selected for coagulase-negative Staphylococcus; added disks containing the antibiotics penicillin, oxacillin, tetracycline, and erythromycin; and measured zones of inhibition. Students also recorded demographic and lifestyle variables and merged this information with similar data collected from 9,000 other students who had contributed to the database from 2003 to 2011. Minimum inhibitory concentration (MIC) testing performed at the Harborview Medical Center Microbiology Laboratory (Seattle, WA) indicated a high degree of accuracy for student-generated data; species identification with a matrix-assisted laser desorption ionization (MALDI) Biotyper revealed that over 88% of the cells analyzed by students were S. epidermidis or S. capitus. The overall frequency of resistant cells was high, ranging from 13.2% of sampled bacteria resistant to oxacillin to 61.7% resistant to penicillin. Stepwise logistic regressions suggested that recent antibiotic use was strongly associated with resistance to three of the four antibiotics tested (p = 0.0003 for penicillin, p << 0.0001 for erythromycin and tetracycline), and that age, gender, use of acne medication, use of antibacterial soaps, or makeup use were associated with resistance to at least one of the four antibiotics. Furthermore, drug resistance to one antibiotic was closely linked to resistance to the other three antibiotics in every case (all p values << 0.0001), suggesting the involvement of multidrug-resistant strains. The data reported here suggest that citizen science could not only provide an important educational experience for undergraduates, but potentially play a role in efforts to expand antibiotic resistance (ABR) surveillance.

Insights from a Convocation: Integrating Discovery-Based Research into the Undergraduate Curriculum

The National Academies of Sciences, Engineering, and Medicine organized a convocation in 2015 to explore and elucidate opportunities, barriers, and realities of course-based undergraduate research experiences, known as CUREs, as a potentially integral component of undergraduate science, technology, engineering, and mathematics education. This paper summarizes the convocation and resulting report.

Extraordinary conservation of entire chromosomes in insects over long evolutionary periods

Comparison of the genomes of different Drosophila species has shown that six different chromosomes, the so-called ''Muller elements," constitute the building blocks for all Drosophila species. Here, we confirm previous results suggesting that this conservation of the Muller elements extends far beyond Drosophila, to at least tephritid fruit flies, thought to have diverged from drosophilids 60-70 mYr ago. Less than 10 percent of genes differ in chromosome location between the two insect groups. Within chromosomes, however, the order is highly scrambled, as expected from the comparison between Drosophila species. The data also support the notion that the sex chromosomes of tephritid flies originated from an ancestor of the dot chromosome 4 of Drosophila. Overall, therefore, no new chromosome has been created for perhaps a billion generations over the two evolutionary lines. This stability at the chromosome level, which appears to extend to all Diptera including mosquitoes, is in stark contrast to other groups such as mammals, birds, fish and plants, in which chromosome numbers and organization vary enormously among species that have diverged over much fewer generations.

No Accumulation of Transposable Elements in Asexual Arthropods

Transposable elements (TEs) and other repetitive DNA can accumulate in the absence of recombination, a process contributing to the degeneration of Y-chromosomes and other nonrecombining genome portions. A similar accumulation of repetitive DNA is expected for asexually reproducing species, given their entire genome is effectively nonrecombining. We tested this expectation by comparing the whole-genome TE loads of five asexual arthropod lineages and their sexual relatives, including asexual and sexual lineages of crustaceans (Daphnia water fleas), insects (Leptopilina wasps), and mites (Oribatida). Surprisingly, there was no evidence for increased TE load in genomes of asexual as compared to sexual lineages, neither for all classes of repetitive elements combined nor for specific TE families. Our study therefore suggests that nonrecombining genomes do not accumulate TEs like nonrecombining genomic regions of sexual lineages. Even if a slight but undetected increase of TEs were caused by asexual reproduction, it appears to be negligible compared to variance between species caused by processes unrelated to reproductive mode. It remains to be determined if molecular mechanisms underlying genome regulation in asexuals hamper TE activity. Alternatively, the differences in TE dynamics between nonrecombining genomes in asexual lineages versus nonrecombining genome portions in sexual species might stem from selection for benign TEs in asexual lineages because of the lack of genetic conflict between TEs and their hosts and/or because asexual lineages may only arise from sexual ancestors with particularly low TE loads.

An off-the-shelf, authentic, and versatile undergraduate molecular biology practical course

We provide a prepackaged molecular biology course, which has a broad context and is scalable to large numbers of students. It is provided complete with technical setup guidance, a reliable assessment regime, and can be readily implemented without any development necessary. Framed as a forensic examination of blue/white cloning plasmids, the course is a versatile workbench, adaptable to different degree subjects, and can be easily modified to undertake novel research as part of its teaching activities. Course activities include DNA extraction, RFLP, PCR, DNA sequencing, gel electrophoresis, and transformation, alongside a range of basic microbiology techniques. Students particularly appreciated the relevance of the practical to professional practice and the authenticity of the experimental work.

Population Genomics of Infectious and Integrated Wolbachia pipientis Genomes in Drosophila ananassae

Coevolution between Drosophila and its endosymbiont Wolbachia pipientis has many intriguing aspects. For example, Drosophila ananassae hosts two forms of W. pipientis genomes: One being the infectious bacterial genome and the other integrated into the host nuclear genome. Here, we characterize the infectious and integrated genomes of W. pipientis infecting D. ananassae (wAna), by genome sequencing 15 strains of D. ananassae that have either the infectious or integrated wAna genomes. Results indicate evolutionarily stable maternal transmission for the infectious wAna genome suggesting a relatively long-term coevolution with its host. In contrast, the integrated wAna genome showed pseudogene-like characteristics accumulating many variants that are predicted to have deleterious effects if present in an infectious bacterial genome. Phylogenomic analysis of sequence variation together with genotyping by polymerase chain reaction of large structural variations indicated several wAna variants among the eight infectious wAna genomes. In contrast, only a single wAna variant was found among the seven integrated wAna genomes examined in lines from Africa, south Asia, and south Pacific islands suggesting that the integration occurred once from a single infectious wAna genome and then spread geographically. Further analysis revealed that for all D. ananassae we examined with the integrated wAna genomes, the majority of the integrated wAna genomic regions is represented in at least two copies suggesting a double integration or single integration followed by an integrated genome duplication. The possible evolutionary mechanism underlying the widespread geographical presence of the duplicate integration of the wAna genome is an intriguing question remaining to be answered.