“Calling Cards” for DNA-Binding Proteins in Mammalian Cells

Self Cite

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

Section: Resultsmentioning

confidence: 59%

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

Mitra

Kapusta

et al. 2012

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“…piggyBac inserts at target sites with the sequence TTAA but displays little selectivity for particular regions of the genome other than a modest preference for regions of DNase I sensitivity (16,17). A useful modification of PB would be to be able to guide integrations to safe harbor sites.…”

Section: Intmentioning

confidence: 99%

“…A useful modification of PB would be to be able to guide integrations to safe harbor sites. Others have shown that PB is distinguished by its ability to remain active when fused to a DNA binding domain and that such fusions can bias insertion toward cognate sites (10,16,18). Notably, Wilson and colleagues (19) fused a zinc finger protein (ZFP) targeted to the upstream promoter region of the cell-cycle checkpoint kinase 2 protein-coding gene CHEK2 to the native insect-derived piggyBac (iPB) transposase.…”

mentioning

confidence: 99%

piggyBac transposase tools for genome engineering

Burnight

Cooney

et al. 2013

210

193

The transposon piggyBac is being used increasingly for genetic studies. Here, we describe modified versions of piggyBac transposase that have potentially wide-ranging applications, such as reversible transgenesis and modified targeting of insertions. piggyBac is distinguished by its ability to excise precisely, restoring the donor site to its pretransposon state. This characteristic makes piggyBac useful for reversible transgenesis, a potentially valuable feature when generating induced pluripotent stem cells without permanent alterations to genomic sequence. To avoid further genome modification following piggyBac excision by reintegration, we generated an excision competent/integration defective (Exc + Int − ) transposase. Our findings also suggest the position of a target DNA-transposase interaction. Another goal of genome engineering is to develop reagents that can guide transgenes to preferred genomic regions. Others have shown that piggyBac transposase can be active when fused to a heterologous DNA-binding domain. An Exc + Int − transposase, the intrinsic targeting of which is defective, might also be a useful intermediate in generating a transposase whose integration activity could be rescued and redirected by fusion to a site-specific DNA-binding domain. We show that fusion to two designed zinc finger proteins rescued the Int − phenotype. Successful guided transgene integration into genomic DNA would have broad applications to gene therapy and molecular genetics. Thus, an Exc + Int − transposase is a potentially useful reagent for genome engineering and provides insight into the mechanism of transposase-target DNA interaction.NA "cut-and-paste" transposable elements are important tools for genome engineering, such as insertional mutagenesis and transgenesis. Research with the DNA transposon Sleeping Beauty, a "resurrected" transposon, has pioneered the use of DNA transposons in mammalian cells (1, 2). piggyBac is also a DNA transposon and a promising alternative to Sleeping Beauty. piggyBac, originally isolated from the cabbage looper moth Trichoplusia ni genome (3), has a large cargo size (4), is highly active in many cell types, and mediates long-term expression in mammalian cells in vivo (5-10). piggyBac is also distinguished by its ability to excise precisely (11), thus restoring the donor site to its pretransposon insertion sequence.Because it can excise precisely, piggyBac is especially useful if a transgene is only transiently required. Transient integration and expression of transcription factors are important approaches to generate transgene-free induced pluripotent stem cells (iPSCs) (12, 13) as well as directed differentiation of specific cell types for both research and clinical use. Removal of the transgenes is key for potential therapeutic applications of iPSCs. piggyBac has been used as a vector for reversible integration; however, reintegration of the transposon catalyzed by piggyBac (PB) transposase occurs in 40-50% of cells (14) Int− transposase whose excision frequency is five-to six-f...

“…The only inputs it requires are one expression profile of the initial state, one expression profile of cells in the target state, and an approximate transcriptional regulatory map indicating the direct targets of each TF. The network map can be derived from gene expression data by NetProphet (14) or other network inference algorithms, from TF binding motifs determined in vitro, or from in vivo binding data derived by methods such as chromatin immunoprecipitation sequencing (ChIP-seq) or Calling Cards (15,16). Unlike the CellNet recommendation system (8), NetSurgeon considers all genes that are DE between the initial and target states, not only those that increase, it considers interventions on all TFs whether or not they are DE, and it has no bias toward TFs with large numbers of targets.…”

Section: Significancementioning

confidence: 99%

Model-based transcriptome engineering promotes a fermentative transcriptional state in yeast

Michael

Maier

Brown

et al. 2016

The ability to rationally manipulate the transcriptional states of cells would be of great use in medicine and bioengineering. We have developed an algorithm, NetSurgeon, which uses genomewide gene-regulatory networks to identify interventions that force a cell toward a desired expression state. We first validated NetSurgeon extensively on existing datasets. Next, we used NetSurgeon to select transcription factor deletions aimed at improving ethanol production in Saccharomyces cerevisiae cultures that are catabolizing xylose. We reasoned that interventions that move the transcriptional state of cells using xylose toward that of cells producing large amounts of ethanol from glucose might improve xylose fermentation. Some of the interventions selected by NetSurgeon successfully promoted a fermentative transcriptional state in the absence of glucose, resulting in strains with a 2.7-fold increase in xylose import rates, a 4-fold improvement in xylose integration into central carbon metabolism, or a 1.3-fold increase in ethanol production rate. We conclude by presenting an integrated model of transcriptional regulation and metabolic flux that will enable future efforts aimed at improving xylose fermentation to prioritize functional regulators of central carbon metabolism.gene-regulatory networks | regulatory systems biology | transcriptome | engineering | Saccharomyces cerevisiae T he central premise of regulatory systems biology is that a systematic map of a cell's regulatory machinery will enable us to understand, predict, and rationally manipulate the cell's state or behavior. Manipulation of cellular state has many promising applications, including stem cell biology and regenerative medicine, biofuel production, and gene therapy. Progress toward cellular state control has been driven by both the systems biology and the synthetic biology research communities. Systems biology has produced whole-genome regulatory network maps (1), but relatively little research has focused on using these maps for predicting and manipulating cellular behavior (2). Regulatory synthetic biology has focused on creating molecular circuits that can be placed into a cell to control the transcription of a small number of transgenes, but genome-scale engineering of the cell's native regulatory apparatus is still rare, with most systems restricted to a limited set of controlled targets (3). Here, we demonstrate that transcription factor (TF) network mapping, gene expression profiling, and computational modeling can be integrated to rationally engineer transcriptional state. We call this activity, which bridges the gap between systems biology and synthetic biology, "transcriptome engineering