Functional characterization of piggyBat from the bat Myotis lucifugus unveils an active mammalian DNA transposon

Abstract

A revelation of the genomic age has been the contributions of the mobile DNA segments called transposable elements to chromosome structure, function, and evolution in virtually all organisms. Substantial fractions of vertebrate genomes derive from transposable elements, being dominated by retroelements that move via RNA intermediates. Although many of these elements have been inactivated by mutation, several active retroelements remain. Vertebrate genomes also contain substantial quantities and a high diversity of cut-and-paste DNA transposons, but no active representative of this class has been identified in mammals. Here we show that a cut-and-paste element called piggyBat, which has recently invaded the genome of the little brown bat (Myotis lucifugus) and is a member of the piggyBac superfamily, is active in its native form in transposition assays in bat and human cultured cells, as well as in the yeast Saccharomyces cerevisiae. Our study suggests that some DNA transposons are still actively shaping some mammalian genomes and reveals an unprecedented opportunity to study the mechanism, regulation, and genomic impact of cut-and-paste transposition in a natural mammalian host. genome evolution | mobile genetic element

piggyBacTransposon

“…These preferential integrations into the open chromatin structure were also observed in piggyBat transposon (the M. lucifugus-derived piggyBac-like element) in both human cells and bat fibroblasts (27). Interestingly, the piggyBat transposons are accumulated in genic regions of the bat genome, indicating that the in vitro studies using human or mouse cell lines truly reflect native transposition patterns.…”

“…Thus far, piggyBac-like sequences have been found in the genomes of a wide range of organisms including fungi, plants, insects, crustaceans, urochordates, amphibians, fishes, and mammals (22). In addition, active or apparently intact full-length piggyBac-like transposons have been identified in another moth Macdunnoughia crassisigna (23), silkworm (24), ants (25), Xenopus (26), and the bat Myotis lucifugus (27).…”

“…Animals in which expression of the domesticated gene was knocked down by RNAi exhibited deficiency in initiating genome rearrangement in the developing macronucleus. Furthermore, both proteins carry a conserved DDD motif and the TPB2 gene product has been shown to have an endonuclease activity in vitro (27). In addition to RAG1 recombinase, the domesticated piggyBac transposases in ciliates provide another example that the catalytic activity of transposases is utilized by the host organisms.…”

“…Recently, the full-length piggyBac1_ML element was cloned and tested for its transposition activity. Similar to T. ni piggyBac, the batderived piggyBac transposon (named piggyBat) is able to transpose in yeast, bat, and human cells, albeit at a 2-to-10 times lower frequency than T. ni piggyBac (27). Cloning of the piggyBat element represented the first isolation of mammalian piggyBac derivative.…”

“…For example, a large fraction of the nonautonomous piggyBac1_ML element (npiggy_156 and npiggy_239) is identical in sequence (34). Thirty-four full-length copies of the piggyBac1_ML element identified in the M. lucifugus genome show >99% nucleotide identity (27). Recently, the full-length piggyBac1_ML element was cloned and tested for its transposition activity.…”