| 1. |
- Guichard, Etienne, et al.
(författare)
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Impact of non-LTR retrotransposons in the differentiation and evolution of anatomically modern humans
- 2018
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Ingår i: Mobile DNA. - : BMC. - 1759-8753. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Background: Transposable elements are biologically important components of eukaryote genomes. In particular, non-LTR retrotransposons (N-LTRrs) played a key role in shaping the human genome throughout evolution. In this study, we compared retrotransposon insertions differentially present in the genomes of Anatomically Modern Humans, Neanderthals, Denisovans and Chimpanzees, in order to assess the possible impact of retrotransposition in the differentiation of the human lineage. Results: We first identified species-specific N-LTRrs and established their distribution in present day human populations. These analyses shortlisted a group of N-LTRr insertions that were found exclusively in Anatomically Modern Humans. These insertions are associated with an increase in the number of transcriptional/splicing variants of those genes they inserted in. The analysis of the functionality of genes containing human-specific N-LTRr insertions reflects changes that occurred during human evolution. In particular, the expression of genes containing the most recent N-LTRr insertions is enriched in the brain, especially in undifferentiated neurons, and these genes associate in networks related to neuron maturation and migration. Additionally, we identified candidate N-LTRr insertions that have likely produced new functional variants exclusive to modern humans, whose genomic loci show traces of positive selection. Conclusions: Our results strongly suggest that N-LTRr impacted our differentiation as a species, most likely inducing an increase in neural complexity, and have been a constant source of genomic variability all throughout the evolution of the human lineage.
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| 2. |
- Peona, Valentina, et al.
(författare)
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How complete are "complete" genome assemblies? : An avian perspective
- 2018
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Ingår i: Molecular Ecology Resources. - : John Wiley & Sons. - 1755-098X .- 1755-0998. ; 18:6, s. 1188-1195
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Tidskriftsartikel (refereegranskat)abstract
- The genomics revolution has led to the sequencing of a large variety of non-model organisms often referred to as 'whole' or 'complete' genome assemblies. But how complete are these, really? Here we use birds as an example for non-model vertebrates and find that, although suitable in principle for genomic studies, the current standard of short-read assemblies misses a significant proportion of the expected genome size (7 to 42%; mean 20 ± 9%). In particular, regions with strongly deviating nucleotide composition (e.g., guanine-cytosine-[GC]-rich) and regions highly enriched in repetitive DNA (e.g., transposable elements and satellite DNA) are usually underrepresented in assemblies. However, long-read sequencing technologies successfully characterize many of these underrepresented GC-rich or repeat-rich regions in several bird genomes. For instance, only ~2% of the expected total base pairs are missing in the last chicken reference (galGal5). These assemblies still contain thousands of gaps (i.e., fragmented sequences) because some chromosomal structures (e.g., centromeres) likely contain arrays of repetitive DNA that are too long to bridge with currently available technologies. We discuss how to minimize the number of assembly gaps by combining the latest available technologies with complementary strengths. Finally, we emphasize the importance of knowing the location, size, and potential content of assembly gaps when making population genetic inferences about adjacent genomic regions.
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| 3. |
- Ricci, Marco, et al.
(författare)
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Transposable Elements Activity is Positively Related to Rate of Speciation in Mammals
- 2018
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Ingår i: Journal of Molecular Evolution. - : Springer. - 0022-2844 .- 1432-1432. ; 86:5, s. 303-310
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Tidskriftsartikel (refereegranskat)abstract
- Transposable elements (TEs) play an essential role in shaping eukaryotic genomes and generating variability. Speciation and TE activity bursts could be strongly related in mammals, in which simple gradualistic models of differentiation do not account for the currently observed species variability. In order to test this hypothesis, we designed two parameters: the Density of insertion (DI) and the Relative rate of speciation (RRS). DI is the ratio between the number of TE insertions in a genome and its size, whereas the RRS is a conditional parameter designed to identify potential speciation bursts. Thus, by analyzing TE insertions in mammals, we defined the genomes as "hot" (high DI) and "cold" (low DI). Then, comparing TE activity among 29 taxonomical families of the whole Mammalia class, 16 intra-order pairs of mammalian species, and four superorders of Eutheria, we showed that taxa with high rates of speciation are associated with "hot" genomes, whereas taxa with low ones are associated with "cold" genomes. These results suggest a remarkable correlation between TE activity and speciation, also being consistent with patterns describing variable rates of differentiation and accounting for the different time frames of the speciation bursts.
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