Multiple waves of recent DNA transposon activity in the bat, Myotis lucifugus

Abstract

DNA transposons, or class 2 transposable elements, have successfully propagated in a wide variety of genomes. However, it is widely believed that DNA transposon activity has ceased in mammalian genomes for at least the last 40 million years. We recently reported evidence for the relatively recent activity of hAT and Helitron elements, two distinct groups of DNA transposons, in the lineage of the vespertilionid bat Myotis lucifugus. Here, we describe seven additional families that have also been recently active in the bat lineage. Early vespertilionid genome evolution was dominated by the activity of Helitrons, mariner-like and Tc2-like elements. This was followed by the colonization of Tc1-like elements, and by a more recent explosion of hAT-like elements. Finally, and most recently, piggyBac-like elements have amplified within the Myotis genome and our results indicate that one of these families is probably still expanding in natural populations. Together, these data suggest that there has been tremendous recent activity of various DNA transposons in the bat lineage that far exceeds those previously reported for any mammalian lineage. The diverse and recent populations of DNA transposons in genus Myotis will provide an unprecedented opportunity to study the impact of this class of elements on mammalian genome evolution and to better understand what makes some species more susceptible to invasion by genomic parasites than others.

Transposable elements and an epigenetic basis for punctuated equilibria

“…(95) In addition, a major episode of diversification in Myotis, the most species-rich mammalian genus, corresponds to a period of intense activity of Tc1-like elements $12-13 Mya. (90) These findings suggest that TEs played a role in a unique event in mammalian evolution, the colonization of an aerial adaptive zone.…”

“…Genomes in both orders have experienced repeated episodes of bombardment by a succession of TE families. (37,89,90) DNA transposons, which exist largely as fossils in extant mammals, are inferred to have been intensely active during the emergence of primates at the end of the Cretaceous, 80-65 Mya. (89) It is estimated that 74,000 of the 98,300 primatespecific DNA transposons fixed in the human genome integrated during this interval.…”

“…This peculiarity extends to mobile elements present in bat genomes. (90,95) Beginning with an explosive amplification of Helitrons $40 Mya, vespertilionid bat genomes have experienced waves of TE expansion by a progression of DNA transposon families. As in primates, episodes of TE expansion are associated with cladogenesis.…”

Phylogenetic and Functional Characterization of the hAT Transposon Superfamily

“…None of the hAT elements in the human genome, however, are known to have been active during the past 50 million years (Lander et al 2001). In contrast, in the genome of the little brown bat, Myotis lucifugus, there has been a marked expansion of DNA transposons with hAT transposons being the most abundant and recent component of this expansion (Ray et al 2008). No active hAT transposons have been recovered from the genome of M. lucifugus, but the abundance of these and other DNA transposons indicates that some mammals have retained the ability to support high DNA transposon activity (Ray et al 2008).…”

Distribution of complete and defective copies of the Tol1 transposable element in natural populations of the medaka fish Oryzias latipes

“…Accelerated expansion of genome sequence information has revealed that DNA-based transposable elements exhibited intense activity in the period of mammalian radiation (Pace and Feschotte,, 2007), and that DNAbased elements have been active until recently in some lineages of mammals, such as the bat, bushbaby, opossum and mouse (Ray et al, 2007(Ray et al, , 2008Pace et al, 2008). Among the several known transposable element families, the hAT family is central to the results in these reports.…”