The Evolutionary History And Genomic Impact Of Mammalian Dna Transposons

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Title: The Evolutionary History And Genomic Impact Of Mammalian Dna Transposons
Author: Pace, John Kelly
Abstract: Transposable elements (TEs ) are mobile repetitive sequences that make up large fractions of mammalian genomes , including at least 45 % of the human genome . Class 2 , or DNA intermediate transposons , which make up approximately 3 % of human nuclear DNA , have typically been overlooked in analyses of mammalian genomes and therefore remain poorly understood . Here , we carried out the first large -scale analysis of the evolutionary history of DNA transposons throughout eutherian mammal evolution . The analysis included 18 mammals from all major branches of the eutherian tree including Afrotheria , Laurasiatheria , primates , rodents and Xenarthra . We combined three different computational methods : average divergence of the TE family from the ancestral consensus sequence , nested insertion analysis and cross -species genomic analysis of orthologous loci to determine the average age of each TE family , when the family was active and in which species . The combination of these methods , the latter two of which do not rely upon calibration of a molecular clock , allowed us to trace the evolutionary history of the 249 currently recognizable eutherian DNA transposon families for which at least 100 copies of the TE could be identified . Our analysis revealed that , contrary to previous assumptions , the horizontal transfer (HT ) of DNA transposons is a widespread and common phenomenon in eutherians . We report strong evidence for the HT of 13 different autonomous TE families that were horizontally transferred into 13 of the 18 eutherian species surveyed , typically invading multiple species lineages . In each case , the infiltration of the TE family was an independent event that resulted in lineage -specific activity , producing distinct bursts of transposition . Together , these bursts were responsible for the insertion of between 2 ,300 and 222 ,000 copies of new elements and the addition of up to 39 megabases of nuclear DNA per species . We discovered a general , eutherian -wide slowdown in the number of horizontal transfers and lineage -specific activity of DNA transposons over the past 100 million years , with only 2 different families of TEs invading 4 of the 18 species within the past 40 million years .
URI: http : / /hdl .handle .net /10106 /1897
Date: 2009-09-16

Citation

The Evolutionary History And Genomic Impact Of Mammalian Dna Transposons. Available electronically from http : / /hdl .handle .net /10106 /1897 .

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