The N-Terminal Part of the 1A Domain of Desmin Is a Hot Spot Region for Putative Pathogenic DES Mutations Affecting Filament Assembly.

Desmin is the major intermediate filament protein of all three muscle cell types, and connects different cell organelles and multi-protein complexes such as the cardiac desmosomes. Several pathogenic mutations in the DES gene cause different skeletal and cardiac myopathies. However, the significance of the majority of DES missense variants is currently unknown, since functional data are lacking. To determine whether desmin missense mutations within the highly conserved 1A coil domain cause a filament assembly defect, we generated a set of variants with unknown significance and systematically analyzed the filament assembly using confocal microscopy in transfected SW-13, H9c2 cells and cardiomyocytes derived from induced pluripotent stem cells. We found that mutations in the N-terminal part of the 1A coil domain affect filament assembly, leading to cytoplasmic desmin aggregation. In contrast, mutant desmin in the C-terminal part of the 1A coil domain forms filamentous structures comparable to wild-type desmin. Our findings suggest that the N-terminal part of the 1A coil domain is a hot spot for pathogenic desmin mutations, which affect desmin filament assembly. This study may have relevance for the genetic counselling of patients carrying variants in the 1A coil domain of the DES gene.

Identification and re-addressing of a transcriptionally permissive locus in the porcine genome.

Recently, we established the Sleeping Beauty transposon system for germ line competent transgenesis in the pig. Here, we extend this approach to re-target a transposon-tagged locus for a site-specific gene knock-in, and generated a syngeneic cohort of piglets carrying either the original transposon or the re-targeted event. A Cre-loxP-mediated cassette exchange of the tagging transposon with a different reporter gene was performed, followed by flow cytometric sorting and somatic cell nuclear transfer of recombined cells. In parallel, the original cells were employed in somatic cell nuclear transfer to generate clone siblings, thereby resulting in a clone cohort of piglets carrying different reporter transposons at an identical chromosomal location. Importantly, this strategy supersedes the need for an antibiotic selection marker. This approach expands the arsenal of genome engineering technologies in domestic animals, and will facilitate the development of large animal models for human diseases. Potentially, the syngeneic cohort of pigs will be instrumental for vital tracking of transplanted cells in pre-clinical assessments of novel cell therapies.

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.

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.

Genotype-independent transmission of transgenic fluorophore protein by boar spermatozoa.

Recently, we generated transposon-transgenic boars (Sus scrofa), which carry three monomeric copies of a fluorophore marker gene. Amazingly, a ubiquitous fluorophore expression in somatic, as well as in germ cells was found. Here, we characterized the prominent fluorophore load in mature spermatozoa of these animals. Sperm samples were analyzed for general fertility parameters, sorted according to X and Y chromosome-bearing sperm fractions, assessed for potential detrimental effects of the reporter, and used for inseminations into estrous sows. Independent of their genotype, all spermatozoa were uniformly fluorescent with a subcellular compartmentalization of the fluorophore protein in postacrosomal sheath, mid piece and tail. Transmission of the fluorophore protein to fertilized oocytes was shown by confocal microscopic analysis of zygotes. The monomeric copies of the transgene segregated during meiosis, rendering a certain fraction of the spermatozoa non-transgenic (about 10% based on analysis of 74 F1 offspring). The genotype-independent transmission of the fluorophore protein by spermatozoa to oocytes represents a non-genetic contribution to the mammalian embryo.

Germline transgenic pigs by Sleeping Beauty transposition in porcine zygotes and targeted integration in the pig genome.

Genetic engineering can expand the utility of pigs for modeling human diseases, and for developing advanced therapeutic approaches. However, the inefficient production of transgenic pigs represents a technological bottleneck. Here, we assessed the hyperactive Sleeping Beauty (SB100X) transposon system for enzyme-catalyzed transgene integration into the embryonic porcine genome. The components of the transposon vector system were microinjected as circular plasmids into the cytoplasm of porcine zygotes, resulting in high frequencies of transgenic fetuses and piglets. The transgenic animals showed normal development and persistent reporter gene expression for >12 months. Molecular hallmarks of transposition were confirmed by analysis of 25 genomic insertion sites. We demonstrate germ-line transmission, segregation of individual transposons, and continued, copy number-dependent transgene expression in F1-offspring. In addition, we demonstrate target-selected gene insertion into transposon-tagged genomic loci by Cre-loxP-based cassette exchange in somatic cells followed by nuclear transfer. Transposase-catalyzed transgenesis in a large mammalian species expands the arsenal of transgenic technologies for use in domestic animals and will facilitate the development of large animal models for human diseases.

Transgenic expression of the human A20 gene in cloned pigs provides protection against apoptotic and inflammatory stimuli.

BACKGROUND: Porcine organs with transgenic expression of anti-apoptotic and anti-inflammatory genes like the human A20 gene (hA20), a tumor necrosis factor-alpha (TNF-alpha)-inducible gene, may control the acute vascular rejection (AVR) of porcine xenografts. The human A20 molecule possesses protective features against inflammatory and apoptotic stimuli in various cell types including endothelial cells, rendering it a promising candidate for transgenic pig production in the context of xenotransplantation. Here, we produced pigs transgenic for hA20 and investigated whether hA20-transgenic porcine aortic endothelial cells (PAECs) were resistant against the induction of apoptosis in vitro and to what extent hA20-transgenic porcine hearts were protected against ischemia/reperfusion (I/R) injury. METHODS: Porcine fetal fibroblasts (PFFs) were transfected with the vector pCAGGSEhA20-IRESNEO containing a chicken beta-actin/rabbit beta-globin (CAGGS)-promoter element, known to provide ubiquitous gene expression in both mice and pigs. Transfected PFFs were then used in somatic cell nuclear transfer (SCNT). Three hA20-transgenic pigs were killed for PAEC isolation and organ mRNA and protein expression analysis by reverse transcriptase-polymerase chain reaction (RT-PCR), Northern and Western Blotting. PAECs were tested for susceptibility to apoptosis after TNF-alpha challenging and triggering of the CD95(Fas)/CD95Ligand pathway. Five transgenic and three wild type animals were subjected to an I/R experiment followed by measurement of infarct size, myeloperoxidase (MPO) activity and subendocardial segmental shortening (SES) to assess protective effects of hA20 in the porcine myocardium. RESULTS: The hA20-transgenic pigs developed normally and expression of hA20 was found in skeletal muscle, heart and PAECs. Cultured human A20-transgenic PAECs showed significantly reduced apoptosis when compared to their wild type counterparts and were less susceptible to the induction of cell death by CD95(Fas)L. Only partial protection of hA20-transgenic pig hearts was observed after I/R. While infarct size did not differ between the two groups after ischemic assault, hA20-transgenic porcine hearts showed significantly lower MPO activity and better hemodynamic performance (determined as SES) than their wild type counterparts. CONCLUSIONS: The hA20 gene was for the first time functionally expressed in transgenic pigs. Although the CAGGS is a ubiquitous promoter element, expression was restricted to heart, skeletal muscle and PAECs of transgenic animals. Cultivated hA20-transgenic PAECs were protected against TNF-alpha-mediated apoptosis, and partially protected against CD95(Fas)L-mediated cell death; cardiomyocytes were partially protected in I/R. These findings reveal hA20 as a promising molecule for controlling AVR in multi-transgenic pigs for xenotransplantation studies.