Biology subjects

Metzger, G. A.

Publications and source records attributed to Metzger, G. A..

3 recordsLinked to original sources

bioRxiv2022

Evolutionary insights from profiling LINE-1 activity at allelic resolution in a single human genome

Transposable elements including LINE-1 (Long INterspersed Element-1) impact genome variation, function, regulation, and disease. LINE-1s seem to have expanded as distinct consecutive lineages, but the drivers of lineage emergence and disappearance are unknown. Reference genomes provide a snapshot of LINE-1 evolution; however, the ongoing retrotransposition of LINE-1s in humans is not evident in these mosaic assemblies. Utilizing long-read-based haploid assemblies, we identified the sequence and location of all the youngest LINE-1s in these genomes at allelic resolution. We cloned and assayed the in vitro retrotransposition activity of the subset of LINE-1s with intact open reading frames and found 34 were measurably active. Yet, among individuals, these same LINE-1s varied in their presence, allelic sequences, and activity. Using a measure of in vivo retrotransposition of closely related groups of LINE-1, we found that recently retrotransposed LINE-1s tend to be active in vitro and polymorphic in the population. However, for a considerable number of LINE-1s, their measured in vitro activity and inferred in vivo fitness were uncorrelated, regardless of their frequency in the population. Some of these unexpected patterns come from rare allelic forms of old LINE-1s that retain activity, suggesting older LINE-1 lineages can persist much longer than expected. Finally, some LINE-1s showed mutations that were potentially adaptive, increasing their replication in the genome. These key mutations specific to LINE-1s with both in vitro activity and in vivo fitness represent promising candidates for the future mechanistic investigation of the drivers of LINE-1 evolution which may contribute to disease susceptibility.

genetics↗

bioRxiv2022

Biofilms preserve transmissibility of a multi-drug resistance plasmid

Self-transmissible multidrug resistance (MDR) plasmids are a major health concern because they can spread antibiotic resistance to pathogens. Even though most pathogens form biofilms, little is known about how MDR plasmids persist and evolve in biofilms. We hypothesize that (i) biofilms act as refugia of MDR plasmids by retaining them in the absence of antibiotics longer than well-mixed planktonic populations, and that (ii) the evolutionary trajectories that account for the improvement of plasmid persistence over time differ between biofilms and planktonic populations. In this study, we evolved Acinetobacter baumannii with an MDR plasmid in biofilm and planktonic populations with and without antibiotic selection. In the absence of selection biofilm populations were better able to maintain the MDR plasmid than planktonic populations. In planktonic populations plasmid persistence improved rapidly but was accompanied by a loss of genes required for the horizonal transfer of plasmids. In contrast, in biofilms most plasmids retained their transfer genes, but on average plasmid persistence improved less over time. Our results showed that biofilms can act as refugia of MDR plasmids and favor the horizontal mode of plasmid transfer, which has important implications for the spread of MDR.

microbiology↗

bioRxiv2019

Characterization of LINE-1 transposons in a human genome at allelic resolution

The activity of the retrotransposon LINE-1 has created a substantial portion of the human genome. Most of this sequence comprises fractured and debilitated LINE-1s. An accurate approximation of the number, location, and sequence of the LINE-1 elements present in any single genome has proven elusive due to the difficulty of assembling and phasing the repetitive and polymorphic regions of the human genome. Through an in-depth analysis of publicly-available, deep, long-read assemblies of nearly homozygous human genomes, we defined the location and sequence of all intact LINE-1s in these assemblies. We found 148 and 142 intact LINE-1s in two nearly homozygous assemblies. A combination of these assemblies suggests a diploid human genome contains at least 50% more intact LINE-1s than previous estimates - in this case, 290 intact LINE-1s at 194 loci. We think this is the best approximation, to date, of the number of intact LINE-1s in a single diploid human genome. In addition to counting intact LINE-1 elements, we resolved the sequence of each element, including some LINE-1 elements in unassembled, presumably centromeric regions of the genome. A comparison of the intact LINE-1s in each assembly shows the specific pattern of variation between these genomes, including LINE-1s that remain intact in only one genome, allelic variation in shared intact LINE-1s, and LINE-1s that are unique (presumably young) insertions in only one genome. We found that many old elements (> 6 million years old) remain intact, and comparison of the young and intact LINE-1s across assemblies reinforces the notion that only a small portion of all LINE-1 sequences that may be intact in the genomes of the human population has been uncovered. This dataset provides the first nearly comprehensive estimate of LINE-1 diversity within an individual, an important dataset in the quest to understand the functional consequences of sequence variation in LINE-1 and the complete set of LINE-1s in the human population.

genomics↗