Genotype-independent transmission of transgenic fluorophore protein by boar spermatozoa

Intratesticular injection followed by electroporation allows gene transfer in caprine spermatogenic cells

The production of transgenic livestock is constrained due to the limited success of currently available methods for transgenesis. Testis mediated gene transfer (TMGT) is an emerging method that shows a high success rate in generating transgenic mice. In this study, we report a newly developed protocol for electroporation-aided TMGT to produce a transgenic goat. The injectable volume and concentration of the transgene were first standardized, and then electroporation conditions were optimized in vitro. In vivo experiments were performed by injecting a transgenic construct (pIRES2-EGFP; enhanced green fluorescent protein) into the testicular interstitium followed by electroporation. Immunohistochemistry, quantitative real-time PCR (qPCR) and western blotting analyses confirmed the successful transfer of the transgene into seminiferous tubules and testicular cells. Furthermore, chromosomal integration of the transgene and its expression in sperm were evaluated d60 and d120 post-electroporation. Our protocol neither altered the seminal characteristics nor the fertilization capacity of the sperm cells. In vitro fertilization using transgenic sperm generated fluorescent embryos. Finally, natural mating of a pre-founder buck produced a transgenic baby goat. The present study demonstrates the first successful report of an electroporation-aided TMGT method for gene transfer in goats.

Transposon-Based Reporter Marking Provides Functional Evidence for Intercellular Bridges in the Male Germline of Rabbits

The Sleeping Beauty transposon system was established as a robust and efficient method for germline transgenesis in different mammalian species. The generation of transgenic mice, rats, rabbits and swine carrying an identical Venus reporter construct delivered by transposon-mediated gene transfer enables comparative studies of gene expression in these lines of mammalian models. Whereas comparable expression patterns of the Venus reporter were found in somatic tissues, preliminary studies suggested that a striking difference in reporter expression may exist in mature spermatozoa of these species. Here we clearly show the differential expression of Venus reporter protein during spermatogenesis of the two compared species, the laboratory rabbit and mice. We provide evidence for the functionality of intercellular bridges in the male germline and genotype-independent transgenic phenotype of rabbit spermatids. Our data suggest that the reporter rabbit line may be a suitable tool to identify molecular mechanisms in testicular development, and may contribute to develop better animal models for male infertility in men.

Expression of Active Fluorophore Proteins in the Milk of Transgenic Pigs Bypassing the Secretory Pathway

We describe the expression of recombinant fluorescent proteins in the milk of two lines of transgenic pigs generated by Sleeping Beauty transposon-mediated genetic engineering. The Sleeping Beauty transposon consisted of an ubiquitously active CAGGS promoter driving a fluorophore cDNA, encoding either Venus or mCherry. Importantly, the fluorophore cDNAs did not encode for a signal peptide for the secretory pathway, and in previous studies of the transgenic animals a cytoplasmic localization of the fluorophore proteins was found. Unexpectedly, milk samples from lactating sows contained high levels of bioactive Venus or mCherry fluorophores. A detailed analysis suggested that exfoliated cells of the mammary epithelium carried the recombinant proteins passively into the milk. This is the first description of reporter fluorophore expression in the milk of livestock, and the findings may contribute to the development of an alternative concept for the production of bioactive recombinant proteins in the udder.

Cytoplasmic injection of murine zygotes with Sleeping Beauty transposon plasmids and minicircles results in the efficient generation of germline transgenic mice

Transgenesis in the mouse is an essential tool for the understanding of gene function and genome organization. Here, we describe a simplified microinjection protocol for efficient germline transgenesis and sustained transgene expression in the mouse model employing binary Sleeping Beauty transposon constructs of different topology. The protocol is based on co-injection of supercoiled plasmids or minicircles, encoding the Sleeping Beauty transposase and a transposon construct, into the cytoplasm of murine zygotes. Importantly, this simplified injection avoids the mechanical penetration of the vulnerable pronuclear membrane, resulting in higher survival rates of treated embryos and a more rapid pace of injections. Upon translation of the transposase, transposase-catalyzed transposition into the genome results in stable transgenic animals carrying monomeric transgenes. In summary, cytoplasmic injection of binary transposon constructs is a feasible, plasmid-based, and simplified microinjection method to generate genetically modified mice. The modular design of the components allows the multiplexing of different transposons, and the generation of multi-transposon transgenic mice in a single step.

Influence of gold, silver and gold-silver alloy nanoparticles on germ cell function and embryo development

The use of engineered nanoparticles has risen exponentially over the last decade. Applications are manifold and include utilisation in industrial goods as well as medical and consumer products. Gold and silver nanoparticles play an important role in the current increase of nanoparticle usage. However, our understanding concerning possible side effects of this increased exposure to particles, which are frequently in the same size regime as medium sized biomolecules and accessorily possess highly active surfaces, is still incomplete. That particularly applies to reproductive aspects, were defects can be passed onto following generations. This review gives a brief overview of the most recent findings concerning reprotoxicological effects. The here presented data elucidate how composition, size and surface modification of nanoparticles influence viablility and functionality of reproduction relevant cells derived from various animal models. While in vitro cultured embryos displayed no toxic effects after the microinjection of gold and silver nanoparticles, sperm fertility parameters deteriorated after co-incubation with ligand free gold nanoparticles. However, the effect could be alleviated by bio-coating the nanoparticles, which even applies to silver and silver-rich alloy nanoparticles. The most sensitive test system appeared to be in vitro oocyte maturation showing a dose-dependent response towards protein (BSA) coated gold-silver alloy and silver nanoparticles leading up to complete arrest of maturation. Recent biodistribution studies confirmed that nanoparticles gain access to the ovaries and also penetrate the blood-testis and placental barrier. Thus, the design of nanoparticles with increased biosafety is highly relevant for biomedical applications.

Current progress of genetically engineered pig models for biomedical research

The first transgenic pigs were generated for agricultural purposes about three decades ago. Since then, the micromanipulation techniques of pig oocytes and embryos expanded from pronuclear injection of foreign DNA to somatic cell nuclear transfer, intracytoplasmic sperm injection-mediated gene transfer, lentiviral transduction, and cytoplasmic injection. Mechanistically, the passive transgenesis approach based on random integration of foreign DNA was developed to active genetic engineering techniques based on the transient activity of ectopic enzymes, such as transposases, recombinases, and programmable nucleases. Whole-genome sequencing and annotation of advanced genome maps of the pig complemented these developments. The full implementation of these tools promises to immensely increase the efficiency and, in parallel, to reduce the costs for the generation of genetically engineered pigs. Today, the major application of genetically engineered pigs is found in the field of biomedical disease modeling. It is anticipated that genetically engineered pigs will increasingly be used in biomedical research, since this model shows several similarities to humans with regard to physiology, metabolism, genome organization, pathology, and aging.

Assessment of fetal cell chimerism in transgenic pig lines generated by Sleeping beauty transposition

Human cells migrate between mother and fetus during pregnancy and persist in the respective host for long-term after birth. Fetal microchimerism occurs also in twins sharing a common placenta or chorion. Whether microchimerism occurs in multiparous mammals such as the domestic pig, where fetuses have separate placentas and chorions, is not well understood. Here, we assessed cell chimerism in litters of wild-type sows inseminated with semen of transposon transgenic boars. Segregation of three independent monomeric transposons ensured an excess of transgenic over non-transgenic offspring in every litter. Transgenic siblings (n = 35) showed robust ubiquitous expression of the reporter transposon encoding a fluorescent protein, and provided an unique resource to assess a potential cell trafficking to non-transgenic littermates (n = 7) or mothers (n = 4). Sensitive flow cytometry, fluorescence microscopy, and real-time PCR provided no evidence for microchimerism in porcine littermates, or piglets and their mothers in both blood and solid organs. These data indicate that the epitheliochorial structure of the porcine placenta effectively prevents cellular exchange during gestation.

Sex selection of sperm in farm animals: status report and developmental prospects

Pre-selection of spermatozoa based on the relative DNA difference between X- and Y-chromosome bearing populations by flow cytometry is an established method that has been introduced into commercial cattle production. Although several important improvements have increased the sort efficiency, the fertilising ability of sexed spermatozoa based on offspring per insemination is still behind farmers' expectations. The main stress factors, especially on mitochondria, that reduce the lifespan of spermatozoa are described, and new technical as well as biological solutions to maintain the natural sperm integrity and to increase the sorting efficiency are discussed. Among these methods are the identification of Y-chromosome bearing spermatozoa by bi-functionalised gold nanoparticles and triplex hybridisationin vivoas well as new laser-controlled deflection system that replaces the deflection of spermatozoa in the electrostatic field. Additionally, as well as a new nonsurgical transfer system of spermatozoa into the oviduct of cows has been developed and allows a significant reduction of spermatozoa per transfer. Altogether, the improvements made in the recent years will allow a broader use of sex-sorted spermatozoa even in those species that require more cells than cows and sheep.

Ectopic expression of human telomerase RNA component results in increased telomerase activity and elongated telomeres in bovine blastocysts

Telomeres play an important role in aging, and are critical for the regenerative capacity of mammalian cells. The holoenzyme telomerase rebuilds telomeres and is composed of two components, the catalytic protein telomerase reverse transcriptase (TERT) and the telomerase RNA (TERC). TERC is ubiquitously expressed in somatic cells and is thought to have no regulatory effects on telomerase activity. Transgenic expression of human TERT (hTERT) in bovine somatic and embryonic cells extends telomere length and enhances telomerase activity. To obtain further insight into the regulatory capacity of the two telomerase components, we have studied the ability of hTERC and hTERT to increase telomerase activity and telomere length in bovine embryos. Expression plasmids for the human RNA component (hTERC) and/or the catalytic subunit of human telomerase (hTERT), respectively, were injected into the cytoplasm of in vitro-produced bovine zygotes. Ectopic expression of hTERC increased telomerase activity and telomere length in bovine blastocysts. Coexpression of hTERT and hTERC did not result in further telomere elongation when compared to the hTERC group. These data indicate that TERC is one of the limiting factors of telomerase activity in bovine blastocysts, and further establish bovine preimplantation embryos as a useful model to modulate telomere length with impact for basic embryology and derivation of pluripotent cells.

Assessment of fecundity and germ line transmission in two transgenic pig lines produced by sleeping beauty transposition

Recently, we described a simplified injection method for producing transgenic pigs using a non-autonomous Sleeping Beauty transposon system. The founder animals showed ubiquitous expression of the Venus fluorophore in almost all cell types. To assess, whether expression of the reporter fluorophore affects animal welfare or fecundity, we analyzed reproductive parameters of two founder boars, germ line transmission, and organ and cell specific transgene expression in animals of the F1 and F2 generation. Molecular analysis of ejaculated sperm cells suggested three monomeric integrations of the Venus transposon in both founders. To test germ line transmission of the three monomeric transposon integrations, wild-type sows were artificially inseminated. The offspring were nursed to sexual maturity and hemizygous lines were established. A clear segregation of the monomeric transposons following the Mendelian rules was observed in the F1 and F2 offspring. Apparently, almost all somatic cells, as well as oocytes and spermatozoa, expressed the Venus fluorophore at cell-type specific levels. No detrimental effects of Venus expression on animal health or fecundity were found. Importantly, all hemizygous lines expressed the fluorophore in comparable levels, and no case of transgene silencing or variegated expression was found after germ line transmission, suggesting that the insertions occurred at transcriptionally permissive loci. The results show that Sleeping Beauty transposase-catalyzed transposition is a promising approach for stable genetic modification of the pig genome.

Rapid non-invasive genotyping of reporter transgenic mammals

Here we describe a non-invasive method for rapid and highly reproducible genotyping of transgenic mammals with ubiquitous expression of fluorophore reporters. Hair samples from transgenic mice and pigs with systemic expression of the fluorophore reporter Venus were analyzed with a fluorescence microscope in few minutes. The hair samples can be preserved for long-term storage at ambient temperature conditions. This non-invasive method is useful for genotyping of transgenic large animals and contributes to animal welfare by reducing stress and discomfort of the animals during sample collection.