Transposable elements （TEs） are self-replicating, mobile DNA sequences which constitute a significant fraction of eukaryotic genomes. They are generally considered selfish DNA, as their replication and random insert...Transposable elements （TEs） are self-replicating, mobile DNA sequences which constitute a significant fraction of eukaryotic genomes. They are generally considered selfish DNA, as their replication and random insertion may have deleterious effects on genome functionalities, although some beneficial effects and evolutionary potential have been recognized. Short interspersed elements （SINEs） are non-autonomous TEs with a modular structure： a small RNA-related head, a body, and a long interspersed element-related tail. Despite their high turnover rate and de novo emergence, the body may retain highly conserved domains （HCDs） shared among divergent SINE families： in metazoans, at least nine HCD-SINEs have been recognized. Data mining on public molecular databases allowed the retrieval of 16 new HCD-SINE families from cnidarian, molluscs, arthropods, and vertebrates. Tracking the ancestry of HCDs on the metazoan phylogeny revealed that some of them date back to the Radiata-Bilateria split. Moreover, phylogenetic and age versus divergence analyses of the most ancient HCDs suggested that long-term vertical inheritance is the rule, with few horizontal transfer events. We suggest that the evolutionary conservation of HCDs may be linked to their potential to serve as recombination hotspots. This indirectly affects host genomes by maintaining active and diverse SINE lineages, whose insertions may impact （either positively or negatively） on the evolution of the genome.展开更多
Transposable elements （TEs） are selfish genetic elements whose self-replication is contrasted by the host genome. In this context, host reproductive strategies are predicted to impact on both TEs load and activity. ...Transposable elements （TEs） are selfish genetic elements whose self-replication is contrasted by the host genome. In this context, host reproductive strategies are predicted to impact on both TEs load and activity. The presence and insertion distribution of the non- LTR retrotransposon R2 was here studied in populations of the strictly bisexual Bacillus grandii maretimi and of the obligatory parthenogenetic Bacillus atticus atticus. Further- more, data were also obtained from the offspring of selected B. a. atticus females. At the population level, the gonochoric B. g. maretimi showed a significantly higher R2 load than the obligatory parthenogenetic B. a. atticus. The comparison with bisexual and unisexual Bacillus rossius populations showed that their values were higher than those recorded for B. a. atticus and similar, or even higher, than those of B. g. maretimi. Consistently, an R2 load reduction is scored in B. a. atticus offspring even if with a great variance. On the whole, data here produced indicate that in the obligatory unisexual B. a. atticus R2 is active and that mechanisms of molecular turnover are effective. Furthermore, progeny analyses show that, at variance of the facultative parthenogenetic B. rossius, the R2 activ- ity is held at a lower rate. Modeling parental-offspring inheritance, suggests that in B. a. atticus recombination plays a major role in eliminating insertions rather than selection, as previously suggested for unisexual B. rossius progeny, even if in both cases a high variance is observed. In addition to this, mechanisms of R2 silencing or chances of clonal selection cannot be ruled out.展开更多
文摘Transposable elements （TEs） are self-replicating, mobile DNA sequences which constitute a significant fraction of eukaryotic genomes. They are generally considered selfish DNA, as their replication and random insertion may have deleterious effects on genome functionalities, although some beneficial effects and evolutionary potential have been recognized. Short interspersed elements （SINEs） are non-autonomous TEs with a modular structure： a small RNA-related head, a body, and a long interspersed element-related tail. Despite their high turnover rate and de novo emergence, the body may retain highly conserved domains （HCDs） shared among divergent SINE families： in metazoans, at least nine HCD-SINEs have been recognized. Data mining on public molecular databases allowed the retrieval of 16 new HCD-SINE families from cnidarian, molluscs, arthropods, and vertebrates. Tracking the ancestry of HCDs on the metazoan phylogeny revealed that some of them date back to the Radiata-Bilateria split. Moreover, phylogenetic and age versus divergence analyses of the most ancient HCDs suggested that long-term vertical inheritance is the rule, with few horizontal transfer events. We suggest that the evolutionary conservation of HCDs may be linked to their potential to serve as recombination hotspots. This indirectly affects host genomes by maintaining active and diverse SINE lineages, whose insertions may impact （either positively or negatively） on the evolution of the genome.
文摘Transposable elements （TEs） are selfish genetic elements whose self-replication is contrasted by the host genome. In this context, host reproductive strategies are predicted to impact on both TEs load and activity. The presence and insertion distribution of the non- LTR retrotransposon R2 was here studied in populations of the strictly bisexual Bacillus grandii maretimi and of the obligatory parthenogenetic Bacillus atticus atticus. Further- more, data were also obtained from the offspring of selected B. a. atticus females. At the population level, the gonochoric B. g. maretimi showed a significantly higher R2 load than the obligatory parthenogenetic B. a. atticus. The comparison with bisexual and unisexual Bacillus rossius populations showed that their values were higher than those recorded for B. a. atticus and similar, or even higher, than those of B. g. maretimi. Consistently, an R2 load reduction is scored in B. a. atticus offspring even if with a great variance. On the whole, data here produced indicate that in the obligatory unisexual B. a. atticus R2 is active and that mechanisms of molecular turnover are effective. Furthermore, progeny analyses show that, at variance of the facultative parthenogenetic B. rossius, the R2 activ- ity is held at a lower rate. Modeling parental-offspring inheritance, suggests that in B. a. atticus recombination plays a major role in eliminating insertions rather than selection, as previously suggested for unisexual B. rossius progeny, even if in both cases a high variance is observed. In addition to this, mechanisms of R2 silencing or chances of clonal selection cannot be ruled out.
