Fishing for answers with transposons

Clinical applications of gamma delta T cells with multivalent immunity

γδ T cells hold promise for adoptive immunotherapy because of their reactivity to bacteria, viruses, and tumors. However, these cells represent a small fraction (1–5%) of the peripheral T-cell pool and require activation and propagation to achieve clinical benefit. Aminobisphosphonates specifically expand the Vγ9Vδ2 subset of γδ T cells and have been used in clinical trials of cancer where objective responses were detected. The Vγ9Vδ2 T cell receptor (TCR) heterodimer binds multiple ligands and results in a multivalent attack by a monoclonal T cell population. Alternatively, populations of γδ T cells with oligoclonal or polyclonal TCR repertoire could be infused for broad-range specificity. However, this goal has been restricted by a lack of applicable expansion protocols for non-Vγ9Vδ2 cells. Recent advances using immobilized antigens, agonistic monoclonal antibodies (mAbs), tumor-derived artificial antigen presenting cells (aAPC), or combinations of activating mAbs and aAPC have been successful in expanding gamma delta T cells with oligoclonal or polyclonal TCR repertoires. Immobilized major histocompatibility complex Class-I chain-related A was a stimulus for γδ T cells expressing TCRδ1 isotypes, and plate-bound activating antibodies have expanded Vδ1 and Vδ2 cells ex vivo. Clinically sufficient quantities of TCRδ1, TCRδ2, and TCRδ1^negTCRδ2^neg have been produced following co-culture on aAPC, and these subsets displayed differences in memory phenotype and reactivity to tumors in vitro and in vivo. Gamma delta T cells are also amenable to genetic modification as evidenced by introduction of αβ TCRs, chimeric antigen receptors, and drug-resistance genes. This represents a promising future for the clinical application of oligoclonal or polyclonal γδ T cells in autologous and allogeneic settings that builds on current trials testing the safety and efficacy of Vγ9Vδ2 T cells.

A hyperactive sleeping beauty transposase enhances transgenesis in zebrafish embryos

Background

Transposons are useful molecular tools for transgenesis. The 'sleeping beauty' transposon is a synthetic member of the Tc1/mariner transposon family. Davidson et al. (2003) previously described a vector for zebrafish transgenesis consisting of the inverted repeats of 'sleeping beauty' flanking the gene to be transposed. Subsequently, there have been attempts to enhance the transpositional activity of 'sleeping beauty' by increasing the activity of its transposase. Recently, Mates et al. (2009) generated a hyperactive transposase giving a 100-fold increased transposition rate in mouse embryos.

Findings

The aim of this experiment was to determine whether this novel hyperactive transposase enhances transgenesis in zebrafish embryos. Using our previously characterised mitfa-amyloidβ-GFP transgene, we observed an eight-fold enhancement in transient transgenesis following detection of transgene expression in melanophores by whole mount in-situ hybridisation. However, high rates of defective embryogenesis were also observed.

Conclusion

The novel hyperactive 'sleeping beauty' transposase enhances the rate of transgenesis in zebrafish embryos.

Liver-directed gene therapy using the sleeping beauty transposon system

Sleeping Beauty (SB) is a transposon system genetically reconstructed from teleost fish that mediates chromosomal integration of DNA sequences by a cut-and-paste mechanism. SB has been shown to mediate transposition in a variety of cells and tissues, has been used for the generation of transgenic animals and has been tested as a vector for gene therapy in several animal models of human disease. Here, we describe methods that we have developed for testing SB-mediated transposition, first in cultured mammalian cells, and then in vivo using a combination of rapid, high-volume tail vein injection for DNA delivery to the liver along with in vivo bioluminescence imaging to monitor sustained luciferase gene expression in individual animals.

Lung-directed gene therapy in mice using the nonviral Sleeping Beauty transposon system

The Sleeping Beauty (SB) transposon is an integrative nonviral plasmid system. Here, we describe a protocol for SB-mediated transgene delivery using DNA/polyethyleneimine (PEI) complexes for long-term expression in mouse lungs. This protocol can be used for delivery of any plasmid-based vector system to mouse lungs, although long-term transgene expression will be obtained only when using the SB transposon or other integrating vector systems. The stages of this protocol are preparation of DNA-PEI complexes and injection of the complexes into the lateral tail vein of mice. We also provide protocols for assessing transgene expression using in vivo bioluminescence imaging and enzymatic assay of lung homogenates. The procedure can be completed within 24 h, starting from preparation of DNA-PEI complexes to analysis of transient transgene expression.

Insertional mutagenesis strategies in zebrafish

We review here some recent developments in the field of insertional mutagenesis in zebrafish. We highlight the advantages and limitations of the rich body of retroviral methodologies, and we focus on the mechanisms and concepts of new transposon-based mutagenesis approaches under development, including prospects for conditional 'gene trapping' and 'gene breaking' approaches.

Transposons as tools for enhancer trap screens in vertebrates

DNA transposons are efficient tools in transgenesis and have therefore become popular in the analysis of the regulatory genome in vertebrates via enhancer trap screens. Here, I discuss recent progress in this field of research, with a focus on the application of one of these transposons, namely the medaka fish derived Tol2, to enhancer trapping in zebrafish, and how this approach compares with others that have a similar objective.

Meganuclease and transposon mediated transgenesis in medaka

From among a plethora of various gene delivery methods, the researcher must choose the right one according to availability for a given species and the precise application the transgenic animal is intended for. Here we review the progress in meganuclease and Sleeping Beauty transposon mediated transgenesis over recent years with a focus on medaka and zebrafish. We present a side-by-side comparison of these two approaches based on their biologic properties and provide interesting perspectives for future experiments and applications, which are different for the two techniques because of their distinct modes of action.

Site-directed gene integration in transgenic zebrafish mediated by cre recombinase using a combination of mutant lox sites

With current gene-transfer techniques in fish, insertion of DNA into the genome occurs randomly and in many instances at multiple sites. Associated position effects, copy number differences, and multiple gene interactions make gene expression experiments difficult to interpret and fish phenotype less predictable. To meet different fish engineering needs, we describe here a gene targeting model in zebrafish. At first, four target zebrafish lines, each harboring a single genomic lox71 target site, were generated by zebrafish transgenesis. The zygotes of transgenic zebrafish lines were coinjected with capped Cre mRNA and a knockin vector pZklox66RFP. Site-specific integration event happened from one target zebrafish line. In this line two integrant zebrafish were obtained from more than 80,000 targeted embryos (integrating efficiency about 10(-4) to 10(-5)) and confirmed to have a sole copy of the integrating DNA at the target genome site. Genomic polymerase chain reaction analysis and DNA sequencing verified the correct gene target events where lox71 and lox66 have accurately recombined into double mutant lox72 and wild-type loxP. Each integrant zebrafish chosen for analysis harbored the transgene rfp at the designated egfp concatenates. Although the Cre-mediated recombination is site specific, it is dependent on a randomly placed target site. That is, a genomic target cannot be preselected for integration based solely on its sequence. Conclusively, an rfp reporter gene was successfully inserted into the egfp target locus of zebrafish genome by Cre-lox-mediated recombination. This site-directed knockin system using the lox71/lox66 combination should be a promising gene-targeting platform serving various purposes in fish genetic engineering.

Sleeping beauty transposon-mediated nonviral gene therapy

Safe and effective delivery of genetic material to mammalian tissues would significantly expand the therapeutic possibilities for a large number of medical conditions. Unfortunately, the promise of gene therapy has been hampered by technical challenges, the induction of immune responses, and inadequate expression over time. Despite these setbacks, progress continues to be made and the anticipated benefits may come to fruition for certain disorders. In terms of delivery, nonviral vector systems are particularly attractive as they are simple to produce, can be stored for long periods of time, and induce no specific immune responses. A significant drawback to nonviral systems has been the lack of persistent expression, as plasmids are lost or degraded when delivered to living tissues. The recent application of integrating transposons to nonviral gene delivery has significantly helped to overcome this obstacle, because it allows for genomic integration and long-term expression. Recent advances in transposon-based vector systems hold promise as new technologies that may unlock the potential of gene therapy; however, technical and safety issues still need refinement.

Pluripotency and chimera competence of an embryonic stem cell line from the sea perch (Lateolabrax japonicus)

A stable GFP-expressing (GFP(+)LJES1) cell strain was developed from the LJES1 cells obtained from sea perch (Lateolabrax japonicus,) embryos. GFP(+)LJES1 cells were induced in vitro by RA to differentiate into a variety of cell types and also had the ability to form embryoid body-like structures in suspension culture. To determine the differentiation potential of LJES1 cells in vivo, GFP(+)LJES1 cells were transplanted into sea perch and zebrafish embryos at mid-blastula stage. Twenty out of 478 transplanted sea perch embryos contained GFP-expressing LJES1 cells 24 h after microinjection. Fifteen chimera embryos developed into fry. In these chimeras, the GFP(+)LJES1 cells contributed to a variety of tissues including the head and trunk. In zebrafish, 221 embryos were microinjected with GFP(+)LJES1 cells and 22 chimera embryos and fries expressing GFP were obtained. Donor GFP(+)LJES1 cells contributed to various tissues in head and trunk of zebrafish embryos and hatched fry.

Repeat structure of the catfish genome: a genomic and transcriptomic assessment of Tc1-like transposon elements in channel catfish (Ictalurus punctatus)

We have assessed the distribution and diversity of members of the Tc1/mariner superfamily of transposable elements in the channel catfish (Ictalurus punctatus) genome as well as evaluating the extent of transcription of Tc1 transposases in the species. Through use of PCR amplification and sequencing, assessment of random BAC end sequences (BES) equivalent to 1.2% genome coverage, and screening of over 45,000 catfish ESTs, a significant proportion of Tc1-like elements and their associated transcripts were captured. Up to 4.2% of the catfish genome in base pairs appears to be composed of Tc1-like transposon-related sequences and a significant fraction of the catfish cellular mRNA, approximately 0.6%, was transcribed from transposon-related sequences in both sense and antisense orientations. Based on results of repeat-masking, as much as 10% of BAC end sequences from catfish, which is a random survey of the genome, contain some remnant of Tc1 elements, suggesting that these elements are present in the catfish genome as numerous, small remnants of the transposons. Phylogenetic analysis allowed comparison of catfish Tc1 transposase types with those found in other vertebrate and invertebrate species. In spite of the existence of many types of Tc1-like sequences that are not yet able to be placed in clades with strong statistical support, it is clear that multiple families of Tc1-like elements exist in channel catfish.

Efficient transfection strategy for the spatiotemporal control of gene expression in zebrafish

Functional analyses of gene function by knockdown and expression approaches strongly enhance the genetic study of development. In vivo application of the introduction of inhibitors of gene expression, mRNA, and expression constructs in the target region make it possible to perform region- and stage-specific regulation of gene function in a simple manner. As a basic tool for the conditional regulation of gene expression in target tissue, we present methods for the efficient introduction of antisense morpholino oligonucleotide (MO), mRNA, and expression plasmid constructs into early and later stage zebrafish embryo and larva. Lipofection of a neuron-specific expression construct plasmid encoding green fluorescent protein (GFP) into optic vesicle resulted in clear GFP expression in the retinotectal pathway in hatched larva. Co-lipofection of MO and GFP mRNA to the presumptive head region resulted in brain-specific knockdown of the gene in mid-stage embryos.

Fish transposons and their potential use in aquaculture

A large part of repetitive DNA of vertebrate genomes have been identified as transposon elements (TEs) or mobile sequences. Although TEs detected to date in most vertebrates are inactivated, active TEs have been found in fish and a salmonid TE has been successfully reactivated by molecular genetic manipulation from inactive genomic copies (Sleeping Beauty, SB). Progress in the understanding of the dynamics, control and evolution of fish TEs will allow the insertion of selected sequences into the fish genomes of germ cells to obtain transgenics or to identify genes important for growth and/or of somatic cells to improve DNA vaccination. Expectations are high for new possible applications to fish of this well developed technology for mammals. Here, we review the present state of knowledge of inactive and active fish TEs and briefly discuss how their possible future applications might be used to improve fish production in aquaculture.

RNA as a source of transposase for Sleeping Beauty-mediated gene insertion and expression in somatic cells and tissues

Sleeping Beauty (SB) is a DNA transposon capable of mediating gene insertion and long-term expression in vertebrate cells when co-delivered with a source of transposase. In all previous reports of SB-mediated gene insertion in somatic cells, the transposase component has been provided by expression of a co-delivered DNA molecule that has the potential for integration into the host cell genome. Integration and continued expression of a gene encoding SB transposase could be problematic if it led to transposon re-mobilization and reintegration. We addressed this potential problem by supplying the transposase-encoding molecule in the form of mRNA. We show that transposase-encoding mRNA can effectively mediate transposition in vitro in HT1080 cells and in vivo in mouse liver following co-delivery with a recoverable transposon or with a luciferase transposon. We conclude that in vitro-transcribed mRNA can be used as an effective source of transposase for SB-mediated transposition in mammalian cells and tissues.

Sleeping Beauty Transposon‐Mediated Gene Therapy for Prolonged Expression

The Sleeping Beauty (SB) transposon system represents a new vector for non-viral gene transfer that melds advantages of viruses and other forms of naked DNA transfer. The transposon itself is comprised of two inverted terminal repeats of about 340 base pairs each. The SB system directs precise transfer of specific constructs from a donor plasmid into a mammalian chromosome. The excision of the transposon from a donor plasmid and integration into a chromosomal site is mediated by Sleeping Beauty transposase, which can be delivered to cells vita its gene or its mRNA. As a result of its integration in chromosomes, and its lack of viral sequences that are often detected by poorly understood cellular defense mechanisms, a gene in a chromosomally integrated transposon can be expressed over the lifetime of a cell. SB transposons integrate nearly randomly into chromosomes at TA-dinucleotide base pairs although the sequences flanking the TAs can influence the probability of integration at a given site. Although random integration of vectors into human genomes is often thought to raise significant safety issues, evidence to date does not indicate that random insertions of SB transposons represent risks that are equal to those of viral vectors. Here we review the activities of the SB system in mice used as a model for human gene therapy, methods of delivery of the SB system, and its efficacy in ameliorating disorders that model human disease.