We are very proud to present some of the articles which were most popular in the field over the last 12 months. The following list consists of a mix of articles that were cited well and articles which created a buzz on social media, upon publication in Mobile DNA.
Transposable elements in Drosophila
Vincent Mérel, Matthieu Boulesteix, Marie Fablet and Cristina Vieira
Mobile DNA 11, 23(2020)
Drosophila has been studied as a biological model for many years and many discoveries in biology rely on this species. Research on transposable elements (TEs) is not an exception. Drosophila has contributed significantly to our knowledge on the mechanisms of transposition and their regulation, but above all, it was one of the first organisms on which genetic and genomic studies of populations were done. In this review article, in a very broad way, we will approach the TEs of Drosophila with a historical hindsight as well as recent discoveries in the field.
Evolution of pogo, a separate superfamily of IS630-Tc1-mariner transposons, revealing recurrent domestication events in vertebrates
Bo Gao, Yali Wang, Mohamed Diaby, Wencheng Zong, Dan Shen, Saisai Wang, Cai Chen, Xiaoyan Wang and Chengyi Song
Mobile DNA 11, 25(2020)
Tc1/mariner and Zator, as two superfamilies of IS630-Tc1-mariner (ITm) group, have been well-defined. However, the molecular evolution and domestication of pogo transposons, once designated as an important family of the Tc1/mariner superfamily, are still poorly understood.
This is the first report to systematically reveal the evolutionary profiles of the pogo transposons, suggesting that pogo and Tc1/Mariner are two separate superfamilies of ITm group, and demonstrating the repeated domestications of pogo in vertebrates. These data indicate that pogo transposons have played important roles in shaping the genome and gene evolution of fungi and animals. This study expands our understanding of the diversity of pogo transposons and updates the classification of ITm group.
Transposons and satellite DNA: on the origin of the major satellite DNA family in the Chenopodium genome
Alexander Belyayev, Jiřina Josefiová, Michaela Jandová, Václav Mahelka, Karol Krak and Bohumil Mandák
Mobile DNA 11, 20(2020)
Extensive and complex links exist between transposable elements (TEs) and satellite DNA (satDNA), which are the two largest fractions of eukaryotic genome. These relationships have a crucial effect on genome structure, function and evolution. Here, we report a novel case of mutual relationships between TEs and satDNA. In the genomes of Chenopodium s. str. species, the deletion derivatives of tnp2 conserved domain of the newly discovered CACTA-like TE Jozin are involved in generating monomers of the most abundant satDNA family of the Chenopodium satellitome. The analysis of the relative positions of satDNA and different TEs utilizing assembled Illumina reads revealed several associations between satDNA arrays and the transposases of putative CACTA-like elements when an ~ 40 bp fragment of tnp2 served as the start monomer of the satDNA array. The high degree of identity of the consensus satDNA monomers of the investigated species and the tnp2 fragment (from 82.1 to 94.9%) provides evidence of the genesis of CficCl-61-40 satDNA family monomers from analogous regions of their respective parental elements. The results were confirmed via molecular genetic methods and Oxford Nanopore sequencing. The discovered phenomenon leads to the continuous replenishment of species genomes with new identical satDNA monomers, which in turn may increase species satellitomes similarity.
Comprehensive genomic analysis reveals dynamic evolution of endogenous retroviruses that code for retroviral-like protein domains
Mahoko Takahashi Ueda, Kirill Kryukov, Satomi Mitsuhashi, Hiroaki Mitsuhashi, Tadashi Imanishi and So Nakagawa
Mobile DNA 11, 29(2020)
Endogenous retroviruses (ERVs) are remnants of ancient retroviral infections of mammalian germline cells. A large proportion of ERVs lose their open reading frames (ORFs), while others retain them and become exapted by the host species. However, it remains unclear what proportion of ERVs possess ORFs (ERV-ORFs), become transcribed, and serve as candidates for co-opted genes.
Twenty years of transposable element analysis in the Arabidopsis thaliana genome
Mobile DNA 11, 28(2020)
Transposable elements (TEs) are mobile repetitive DNA sequences shown to be major drivers of genome evolution. As the first plant to have its genome sequenced and analyzed at the genomic scale, Arabidopsis thaliana has largely contributed to our TE knowledge.
The present report describes 20 years of accumulated TE knowledge gained through the study of the Arabidopsis genome and covers the known TE families, their relative abundance, and their genomic distribution. It presents our knowledge of the different TE family activities, mobility, population and long-term evolutionary dynamics. Finally, the role of TE as substrates for new genes and their impact on gene expression is illustrated through a few selected demonstrative cases. Promising future directions for TE studies in this species conclude the review.
Identification and characterisation of endogenous Avian Leukosis Virus subgroup E (ALVE) insertions in chicken whole genome sequencing data
Andrew S. Mason, Ashlee R. Lund, Paul M. Hocking, Janet E. Fulton and David W. Burt
Mobile DNA 11, 22(2020)
Endogenous retroviruses (ERVs) are the remnants of retroviral infections which can elicit prolonged genomic and immunological stress on their host organism. In chickens, endogenous Avian Leukosis Virus subgroup E (ALVE) expression has been associated with reductions in muscle growth rate and egg production, as well as providing the potential for novel recombinant viruses. However, ALVEs can remain in commercial stock due to their incomplete identification and association with desirable traits, such as ALVE21 and slow feathering. The availability of whole genome sequencing (WGS) data facilitates high-throughput identification and characterisation of these retroviral remnants.
LINE-1 ORF1p does not determine substrate preference for human/orangutan SVA and gibbon LAVA
Mobile DNA 11, 27(2020)
Non-autonomous VNTR (Variable Number of Tandem Repeats) composite retrotransposons – SVA (SINE-R-VNTR-Alu) and LAVA (L1-Alu-VNTR-Alu) – are specific to hominoid primates. SVA expanded in great apes, LAVA in gibbon. Both SVA and LAVA have been shown to be mobilized by the autonomous LINE-1 (L1)-encoded protein machinery in a cell-based assay in trans. The efficiency of human SVA retrotransposition in vitro has, however, been considerably lower than would be expected based on recent pedigree-based in vivo estimates. The VNTR composite elements across hominoids – gibbon LAVA, orangutan SVA_A descendants and hominine SVA_D descendants – display characteristic structures of the 5′ Alu-like domain and the VNTR. Different partner L1 subfamilies are currently active in each of the lineages. The possibility that the lineage-specific types of VNTR composites evolved in response to evolutionary changes in their autonomous partners, particularly in the nucleic acid binding L1 ORF1-encoded protein, has not been addressed.
IS982 and kin: new insights into an old IS family
Nancy Fayad, Mireille Kallassy Awad and Jacques Mahillon
Mobile DNA 11, 24(2020)
Insertion sequences (IS) are ubiquitous transposable elements with a very simple organization: two inverted repeats flanking a transposase coding gene. IS982 is one of 26 insertion sequence families known so far. With 70 registered members in the ISFinder database, this family remains somewhat unexplored, despite the association of many of its members with important features such as antibiotic resistance. IS982 has a fairly simple organization with a mean length of ca. 1 Kb, two inverted repeats with conserved 5′ AC 3′ ends flanking a transposase coding gene and direct repeats of variable lengths. Its transposase has a RNAse-H like chemistry with an atypical DDE motif.
In this study, we first highlight the current knowledge on the IS982 family by dissecting its registered members and their characteristics. Secondly, we bring new insights into this old, yet uncharted IS family, by exploring its registered elements, as well as the genomic and proteomic databases of bacterial and archaeal strains. This probing showed that the presence and distribution of this family goes far beyond the clear-cut registry of ISFinder database.
Phylogenetic analysis of the Tc1/mariner superfamily reveals the unexplored diversity of pogo-like elements
Mathilde Dupeyron, Tobias Baril, Chris Bass and Alexander Hayward
Mobile DNA 11, 21(2020)
Tc1/mariner transposons are widespread DNA transposable elements (TEs) that have made important contributions to the evolution of host genomic complexity in metazoans. However, the evolution and diversity of the Tc1/mariner superfamily remains poorly understood. Following recent developments in genome sequencing and the availability of a wealth of new genomes, Tc1/mariner TEs have been identified in many new taxa across the eukaryotic tree of life. To date, the majority of studies focussing on Tc1/mariner elements have considered only a single host lineage or just a small number of host lineages. Thus, much remains to be learnt about the evolution of Tc1/mariner TEs by performing analyses that consider elements that originate from across host diversity.
Transposable element abundance correlates with mode of transmission in microsporidian parasites
Nathalia Rammé Medeiros de Albuquerque, Dieter Ebert and Karen Luisa Haag
Mobile DNA 11, 19(2020)
The extreme genome reduction and physiological simplicity of some microsporidia has been attributed to their intracellular, obligate parasitic lifestyle. Although not all microsporidian genomes are small (size range from about 2 to 50 MB), it is suggested that the size of their genomes has been streamlined by natural selection. We explore the hypothesis that vertical transmission in microsporidia produces population bottlenecks, and thus reduces the effectiveness of natural selection. Here we compare the transposable element (TE) content of 47 microsporidian genomes, and show that genome size is positively correlated with the amount of TEs, and that species that experience vertical transmission have larger genomes with higher proportion of TEs. Our findings are consistent with earlier studies inferring that nonadaptive processes play an important role in microsporidian evolution.
The Dfam community resource of transposable element families, sequence models, and genome annotations
Jessica Storer, Robert Hubley, Jeb Rosen, Travis J. Wheeler and Arian F. Smit
Mobile DNA 12, 2(2021)
Dfam is an open access database of repetitive DNA families, sequence models, and genome annotations. The 3.0–3.3 releases of Dfam (https://dfam.org) represent an evolution from a proof-of-principle collection of transposable element families in model organisms into a community resource for a broad range of species, and for both curated and uncurated datasets. In addition, releases since Dfam 3.0 provide auxiliary consensus sequence models, transposable element protein alignments, and a formalized classification system to support the growing diversity of organisms represented in the resource. The latest release includes 266,740 new de novo generated transposable element families from 336 species contributed by the EBI. This expansion demonstrates the utility of many of Dfam’s new features and provides insight into the long term challenges ahead for improving de novo generated transposable element datasets.
Genomic properties of variably methylated retrotransposons in mouse
Jessica L. Elmer, Amir D. Hay, Noah J. Kessler, Tessa M. Bertozzi, Eve A. C. Ainscough and Anne C. Ferguson-Smith
Mobile DNA 12, 6(2021)
Transposable elements (TEs) are enriched in cytosine methylation, preventing their mobility within the genome. We previously identified a genome-wide repertoire of candidate intracisternal A particle (IAP) TEs in mice that exhibit inter-individual variability in this methylation (VM-IAPs) with implications for genome function.
Our findings indicate that a recently evolved interplay between genetic sequence, CTCF binding, and DNA methylation at young TEs can result in inter-individual variability in transcriptional outcomes with implications for phenotypic variation.
RIP-seq reveals LINE-1 ORF1p association with p-body enriched mRNAs
Erica M. Briggs, Wilson McKerrow, Paolo Mita, Jef D. Boeke, Susan K. Logan and David Fenyö
Mobile DNA 12, 5(2021)
Long INterspersed Element-1 (LINE-1) is an autonomous retroelement able to “copy-and-paste” itself into new loci of the host genome through a process called retrotransposition. The LINE-1 bicistronic mRNA codes for two proteins, ORF1p, a nucleic acid chaperone, and ORF2p, a protein with endonuclease and reverse transcriptase activity. Both proteins bind LINE-1 mRNA in cis and are necessary for retrotransposition. While LINE-1 transcription is usually repressed in most healthy somatic cells through a plethora of mechanisms, ORF1p expression has been observed in nearly 50% of tumors, and new LINE-1 insertions have been documented in a similar fraction of tumors, including prostate cancer.
Transposable element-derived sequences in vertebrate development
Ema Etchegaray, Magali Naville, Jean-Nicolas Volff and Zofia Haftek-Terreau
Mobile DNA 12, 1(2021)
Transposable elements (TEs) are major components of all vertebrate genomes that can cause deleterious insertions and genomic instability. However, depending on the specific genomic context of their insertion site, TE sequences can sometimes get positively selected, leading to what are called “exaptation” events. TE sequence exaptation constitutes an important source of novelties for gene, genome and organism evolution, giving rise to new regulatory sequences, protein-coding exons/genes and non-coding RNAs, which can play various roles beneficial to the host. In this review, we focus on the development of vertebrates, which present many derived traits such as bones, adaptive immunity and a complex brain. We illustrate how TE-derived sequences have given rise to developmental innovations in vertebrates and how they thereby contributed to the evolutionary success of this lineage.