Author Correction: Consistent success in life-supporting porcine cardiac xenotransplantation.

In this Letter, Mayuko Kurome and Valeri Zakhartchenko have been added to the author list (affiliated with Institute of Molecular Animal Breeding and Biotechnology, Gene Center, LMU Munich, Munich, Germany). The author list and 'Author contributions' section have been corrected online; see accompanying Amendment.

Consistent success in life-supporting porcine cardiac xenotransplantation.

Heart transplantation is the only cure for patients with terminal cardiac failure, but the supply of allogeneic donor organs falls far short of the clinical need1-3. Xenotransplantation of genetically modified pig hearts has been discussed as a potential alternative4. Genetically multi-modified pig hearts that lack galactose-α1,3-galactose epitopes (α1,3-galactosyltransferase knockout) and express a human membrane cofactor protein (CD46) and human thrombomodulin have survived for up to 945 days after heterotopic abdominal transplantation in baboons5. This model demonstrated long-term acceptance of discordant xenografts with safe immunosuppression but did not predict their life-supporting function. Despite 25 years of extensive research, the maximum survival of a baboon after heart replacement with a porcine xenograft was only 57 days and this was achieved, to our knowledge, only once6. Here we show that α1,3-galactosyltransferase-knockout pig hearts that express human CD46 and thrombomodulin require non-ischaemic preservation with continuous perfusion and control of post-transplantation growth to ensure long-term orthotopic function of the xenograft in baboons, the most stringent preclinical xenotransplantation model. Consistent life-supporting function of xenografted hearts for up to 195 days is a milestone on the way to clinical cardiac xenotransplantation7.

Viable pigs after simultaneous inactivation of porcine MHC class I and three xenoreactive antigen genes GGTA1, CMAH and B4GALNT2.

BACKGROUND: Cell surface carbohydrate antigens play a major role in the rejection of porcine xenografts. The most important for human recipients are α-1,3 Gal (Galactose-alpha-1,3-galactose) causing hyperacute rejection, also Neu5Gc (N-glycolylneuraminic acid) and Sd(a) blood group antigens both of which are likely to elicit acute vascular rejection given the known human immune status. Porcine cells with knockouts of the three genes responsible, GGTA1, CMAH and B4GALNT2, revealed minimal xenoreactive antibody binding after incubation with human serum. However, human leucocyte antigen (HLA) antibodies cross-reacted with swine leucocyte antigen class I (SLA-I). We previously demonstrated efficient generation of pigs with multiple xeno-transgenes placed at a single genomic locus. Here we wished to assess whether key xenoreactive antigen genes can be simultaneously inactivated and if combination with the multi-transgenic background further reduces antibody deposition and complement activation. METHODS: Multiplex CRISPR/Cas9 gene editing and somatic cell nuclear transfer were used to generate pigs carrying functional knockouts of GGTA1, CMAH, B4GALNT2 and SLA class I. Fibroblasts derived from one- to four-fold knockout animals, and from multi-transgenic cells (human CD46, CD55, CD59, HO1 and A20) with the four-fold knockout were used to examine the effects on human IgG and IgM binding or complement activation in vitro. RESULTS: Pigs were generated carrying four-fold knockouts of important xenoreactive genes. In vitro assays revealed that combination of all four gene knockouts reduced human IgG and IgM binding to porcine kidney cells more effectively than single or double knockouts. The multi-transgenic background combined with GGTA1 knockout alone reduced C3b/c and C4b/c complement activation to such an extent that further knockouts had no significant additional effect. CONCLUSION: We showed that pigs carrying several xenoprotective transgenes and knockouts of xenoreactive antigens can be readily generated and these modifications will have significant effects on xenograft survival.

The expression of TAP1 candidate gene, but not its polymorphism and methylation, is associated with colonic polyp formation in a porcine model of human familial adenomatous polyposis.

In humans, the dysfunction of the adenomatous polyposis coli (APC) gene causes hereditary familial adenomatous polyposis (FAP) and increased risk of colorectal cancer (CRC). The severity of polyposis varies between individuals, but genetic basis for this is in large part unknown. This variability also occurs in our porcine model of FAP, based on an APC1311 mutation (orthologous to human APC1309). Since loss of TAP1 function can lead to CRC in humans, we searched for germline polymorphisms in APC1311/+ pigs with low (LP) and high (HP) levels of polyposis, as well as in wild-type pigs representing six breeds and a commercial line. The distribution of 40 identified polymorphic variants was similar in the LP and HP pigs. In contrast, the TAP1 transcript level was significantly higher in normal colon mucosa of HP pigs than in LP pigs. Moreover, six SNPs showed significant effects on TAP1 promoter activity, but no correlation with severity of polyposis was observed. Analysis of DNA methylation in the promoter region showed that one CpG site differed significantly between LP and HP pigs. We conclude that TAP1 genotype may not itself be associated with polyposis, but our findings concerning its expression suggest a role in the development of polyps.

Genetically Engineered Pigs to Study Cancer.

Recent decades have seen groundbreaking advances in cancer research. Genetically engineered animal models, mainly in mice, have contributed to a better understanding of the underlying mechanisms involved in cancer. However, mice are not ideal for translating basic research into studies closer to the clinic. There is a need for complementary information provided by non-rodent species. Pigs are well suited for translational biomedical research as they share many similarities with humans such as body and organ size, aspects of anatomy, physiology and pathophysiology and can provide valuable means of developing and testing novel diagnostic and therapeutic procedures. Porcine oncology is a new field, but it is clear that replication of key oncogenic mutation in pigs can usefully mimic several human cancers. This review briefly outlines the technology used to generate genetically modified pigs, provides an overview of existing cancer models, their applications and how the field may develop in the near future.

Assembling multiple xenoprotective transgenes in pigs.

This review gives a brief overview of the genetic modifications necessary for grafted porcine tissues and organs to overcome rejection in human recipients. It then focuses on the problem of generating and breeding herds of donor pigs carrying modified endogenous genes and multiple xenoprotective transgenes. A xenodonor pig optimised for human clinical use could well require the addition of ten or more xenoprotective transgenes. It is impractical to produce the required combination of transgene by cross-breeding animals bearing individual transgenes at unlinked genetic loci, because independent segregation means that huge numbers of pigs would be required to produce relatively few donor animals. A better approach is to colocate groups of transgenes at a single genomic locus. We outline current methods to assemble transgene arrays and consider their pros and cons. These include polycistronic expression systems, in vitro recombination of large DNA fragments in PAC and BAC vectors, transposon vectors, classical gene targeting by homologous recombination at permissive loci such as ROSA26, targeted transgene placement aided by gene editing systems such as CRISPR/Cas9, and transgene placement by site-specific recombination such as Min-tagging using the Bxb1recombinase.

Multiple genetically modified GTKO/hCD46/HLA-E/hß2-mg porcine hearts are protected from complement activation and natural killer cell infiltration during ex vivo perfusion with human blood.

BACKGROUND: In pig-to-human xenotransplantation, early cellular rejection reactions are mediated by natural killer cells (NK cells). Human NK cells are inhibited by HLA-E via CD94/NKG2A receptors. To protect porcine grafts against human NK cell responses, transgenic GTKO pigs expressing hCD46 and HLA-E have been generated. The aim of this study was to test the effect of this genetic modification on xenogeneic, and in particular human NK cell response, using an ex vivo perfusion model of pig hearts with human blood. METHODS: Cardiopleged and explanted genetically modified (gm) pig hearts (GTKO/hCD46/HLA-E/hß2-microglobulin) and wild-type (wt) controls (n = 6 each) were reperfused and tested in an 8 hours ex vivo perfusion system using freshly drawn human blood. Cardiac function was evaluated during a 165-minute period in working heart mode. Myocardial damage, antibody deposition, complement activation, and coagulation parameters were evaluated histologically at the end of perfusion. The number of NK cells in the perfusate was determined by flow cytometry at baseline and at 8 hours; tissue infiltration by NK cells was quantified by immunofluorescence microscopy using NKp46 staining of frozen sections. RESULTS: Deposition of IgG (1.2 ± 1 × 107 vs 8.8 ± 2.9 × 106 ; P < .01), IgM (4.4 ± 3.7 × 106 vs 1.7 ± 1.2 × 106 ; P < .01), and the complement activation product C4b/c (3.5 ± 1.3 × 106 vs 2.3 × 106  ± 9.4 × 105 ; P > .01) was lower in gm than wt hearts. NK cell percentages of leukocytes in the perfusate decreased from 0.94 ± 0.77% to 0.21 ± 0.25% (P = .04) during xenoperfusion of wt hearts. In contrast, the ratio of NK cells did not decrease significantly in the gm hearts. In this group, NK cell myocardial infiltration after 480 minutes of perfusion was lower than in wt organs (2.5 ± 3.7 × 104 /mm3 vs 1.3 ± 1.4 × 105 /mm3 ; P = .0001). The function of gm hearts was better preserved compared to wt organs, as demonstrated by higher cardiac index during the first 2 hours of ex vivo perfusion. CONCLUSION: GTKO, hCD46, and HLA-E expression in porcine hearts reduced complement deposition, complement dependent injury, and myocardial NK cell infiltration during perfusion with human blood. This tested combination of genetic modifications may minimize damage from acute human-anti-pig rejection reactions and improve myocardial function after xenotransplantation.

Strong xenoprotective function by single-copy transgenes placed sequentially at a permissive locus.

BACKGROUND: Multiple xenoprotective transgenes are best grouped at a single locus to avoid segregation during breeding and simplify production of donor animals. METHODS: We used transgene stacking to place a human CD55 transgene adjacent to a human heme oxygenase 1 construct at the porcine ROSA26 locus. A transgenic pig was analyzed by PCR, RT-PCR, droplet digital PCR, immunohistochemistry, immunofluorescence, and flow cytometry. Resistance to complement-mediated cell lysis and caspase 3/7 activation were determined in vitro. RESULTS: The ROSA26 locus was retargeted efficiently, and animals were generated by nuclear transfer. RNA and protein analyses revealed abundant expression in all organs analyzed, including pancreatic beta cells. Transgenic porcine kidney fibroblasts were almost completely protected against complement-mediated lysis and showed reduced caspase 3/7 activation. CONCLUSION: Step-by-step placement enables highly expressed single-copy xenoprotective transgenes to be grouped at porcine ROSA26.

Maternal placenta modulates a deleterious fetal mutation.

Intrauterine growth restriction (IUGR) is caused by dysregulation of placental metabolism. Paternally inherited IUGR mutations in the fetus influence maternal physiology via the placenta. However, it is not known whether the maternal placenta also affects the extent of IUGR in such fetuses. In cattle and other ruminants, maternal-fetal communication occurs primarily at the placentomes. We previously identified a 3΄ deletion in the noncoding MER1 repeat containing imprinted transcript 1 (MIMT1) gene that, when inherited from the sire, causes IUGR and late abortion in Ayshire cattle with variable levels of severity. Here, we compared the transcriptome and genomic imprinting in fetal and maternal placentome components of wild-type and MIMT1Del/WT fetuses before IUGR became apparent, to identify key early events. Transcriptome analysis revealed fewer differentially expressed genes in maternal than fetal MIMT1Del/WT placentome. AST1, within the PEG3 domain, was the only gene consistently reduced in IUGR in both fetal and maternal samples. Several genes showed an imprinting pattern associated with IUGR, of which only secernin 3 (SCRN3) and paternally expressed 3 (PEG3) were differentially imprinted in both placentome components. Loss of strictly monoallelic, allele-specific expression (∼80:20) of PEG3 in the maternal MIMT1Del/WT placenta could be associated with incomplete penetrance of MIMT1Del. Our data show that dysregulation of the PEG3 domain is involved in IUGR, but also reveal that maternal placental tissues may affect the penetrance of the paternally inherited IUGR mutation.

Complement C3 inhibitor Cp40 attenuates xenoreactions in pig hearts perfused with human blood.

BACKGROUND: The complement system plays a crucial role in acute xenogeneic reactions after cardiac transplantation. We used an ex vivo perfusion model to investigate the effect of Cp40, a compstatin analog and potent inhibitor of complement at the level of C3. METHODS: Fifteen wild-type pig hearts were explanted, cardiopleged, and reperfused ex vivo after 150 minutes of cold ischemia. Hearts were challenged in a biventricular working heart mode to evaluate cardiac perfusion and function. In the treatment group (n=5), the complement cascade was blocked at the level of C3 using Cp40, using diluted human blood. Untreated human and porcine blood was used for controls. RESULTS: Throughout the perfusion, C3 activation was inhibited when Cp40 was used (mean of all time points: 1.11 ± 0.34% vs 3.12 ± 0.48% control activation; P<.01). Compared to xenoperfused controls, the cardiac index improved significantly in the treated group (6.5 ± 4.2 vs 3.5 ± 4.8 mL/min/g; P=.03, 180 minutes perfusion), while the concentration of lactate dehydrogenase as a maker for cell degradation was reduced in the perfusate (583 ± 187 U/mL vs 2108 ± 1145 U/mL, P=.02). Histological examination revealed less hemorrhage and edema, and immunohistochemistry confirmed less complement fragment deposition than in untreated xenoperfused controls. CONCLUSIONS: Cp40 efficiently prevents C3 activation of the complement system, resulting in reduced cell damage and preserved function in wild-type porcine hearts xenoperfused ex vivo. We suggest that this compstatin analog, which blocks all main pathways of complement activation, could be a beneficial perioperative treatment in preclinical and in future clinical xenotransplantation.

Hemodynamic and perioperative management in two different preclinical pig-to-baboon cardiac xenotransplantation models.

BACKGROUND: The perioperative phase of preclinical cardiac xenotransplantations significantly affects the experimental outcome. Moderate or even severe hemodynamic and respiratory impairment occurs frequently in baboons after receiving a cardiac transplant. The perioperative management of such postoperative instability is very demanding, especially in the experimental setting. We compared perioperative changes of hemodynamic and laboratory findings during orthotopic and heterotopic thoracic cardiac xenotransplantations and describe our monitoring, treatment and intensive care. METHODS: Twenty-eight pig-to-baboon cardiac xenotransplantations were performed using either the orthotopic (oHTx, n=5) or heterotopic thoracic (htHTx; n=23) technique. In both techniques, cardioplegia and an intraoperative cardiopulmonary bypass (CPB) were required. Preoperatively, intensive care (eg, transfusions, catecholamine therapy) was provided and fast extubation was targeted. A central venous catheter, a femoral arterial thermodilution catheter, a telemetric pressure transmitter and transthoracic echocardiography were used to monitor the animal. Baboon jackets with a tethering system were used to continuously apply medication postoperatively and permit blood sampling, also after extubation of the animal and transfer into the cage. Perioperative survival, hemodynamics, catecholamine doses, respiratory function and weaning from respirator were compared. Perioperative organ damage was evaluated based on laboratory findings 12 hours after transplantation. RESULTS: Recipients could be weaned from CPB in the 20 htHTx and all five oHTx experiments, and three htHTx procedures were terminated during the operation. The time of cardiopulmonary bypass was significantly lower in the heterotopic group (oHTx median 171 [157-193] minutes; htHTx median 144 [100-190] minutes; P=.02). In 17 htHTx procedures, no inotropics were used, whereas epinephrine had to be administered in four of the five oHTx experiments; the mean time of catecholamine support was longer in the oHTx group (oHTx 972±348 minutes vs htHTx 111±92 minutes; P<.01). After htHTx, weaning off the respirator was possible in 19 of 20 cases (one died due to pneumothorax). After oHTx, three of the five baboons could be weaned off the respirator; in these cases, the arterial saturation was higher compared with the extubated baboons after htHTx (oHTx 99±1% vs htHTx 91±4%, P=.01). Intraoperative blood loss was similar between the two groups, and hemostasis was impaired after all procedures, but relevant postoperative bleeding never occurred. CONCLUSION: Intensive intra- and postoperative monitoring and care is required in both transplantation techniques as a requirement for successful weaning from CPB and respirator. After htHTx, the animals needed less catecholamines and were hemodynamically more stable. Even though pulmonary function was often impaired after htHTx, weaning from the respirator and extubation was more successful in this group.

PEG3 domain gene expression in maternal and foetal placenta in intrauterine growth restricted bovine foetuses.

We used a genetic (MIMT1(Del)) model of intrauterine growth restriction to investigate dysregulation of PEG3 domain gene expression in bovine foetal and maternal placenta. ZIM2, APEG3 and PEG3 expressions were similarly reduced in MIMT1(Del/) (WT) foetal placenta, suggesting coordinated regulation. Methylation of DNA CpG sites associated with these genes showed no differences, but differences in the levels of MIMT1 RNA methylation at three CpG sites were found in foetal placenta. Our data are consistent with the presence of a bidirectional promoter 5' of MIMT1 and suggest a regulatory role for the MIMT1 non-coding transcript. PEG3 domain expression on the maternal placenta side was not affected by the foetal mutation.

Non-invasive assessment of porcine oocyte quality by supravital staining of cumulus-oocyte complexes with lissamine green B.

We evaluated the usefulness of lissamine green B (LB) staining of cumulus-oocyte complexes (COC) as a non-invasive method of predicting maturational and developmental competence of slaughterhouse-derived porcine oocytes cultured in vitro. Cumulus cells of freshly aspirated COCs were evaluated either morphologically on the basis of thickness of cumulus cell layers, or stained with LB, which penetrates only non-viable cells. The extent of cumulus cell staining was taken as an inverse indicator of membrane integrity. The two methods of COC grading were then examined as predictors of nuclear maturation and development after parthenogenetic activation. In both cases LB staining proved a more reliable indicator than morphological assessment (P < 0.05). The relationship between LB staining and cumulus cell apoptosis was also examined. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay for DNA fragmentation revealed that oocytes within COCs graded as low quality by either LB staining or visual morphology showed significantly greater DNA fragmentation (P < 0.05) than higher grades, and that LB and visual grading were of similar predictive value. Expression of the stress response gene TP53 showed significantly higher expression in COCs graded as low quality by LB staining. However expression of the apoptosis-associated genes BAK and CASP3 was not significantly different between high or low grade COCs, suggesting that mRNA expression of BAK and CASP3 is not a reliable method of detecting apoptosis in porcine COCs. Evaluation of cumulus cell membrane integrity by lissamine green B staining thus provides a useful new tool to gain information about the maturational and developmental competence of porcine oocytes.

Viable pigs with a conditionally-activated oncogenic KRAS mutation.

Oncogenic mutations of KRAS play a major role in human carcinogenesis. Here we describe viable gene-targeted pigs carrying a latent KRAS (G12D) mutant allele that can be activated by Cre recombination. These have been produced as part of a program to model human cancers in pigs by replicating genetic lesions known to initiate and drive human disease. Cre-activated KRAS (G12D) animals add to a growing set of gene-targeted pigs that includes a Cre-activated oncogenic mutant TP53, a Cre-responsive dual fluorescent reporter and two truncating mutations of APC (adenomatous polyposis coli). These alleles can be combined and activated in various tissues to produce new models for cancer research.

Pre-clinical heterotopic intrathoracic heart xenotransplantation: a possibly useful clinical technique.

BACKGROUND: As a step towards clinical cardiac xenotransplantation, our experimental heterotopic intrathoracic xenotransplantation model offers a beating and ejecting donor heart while retaining the recipient's native organ as a backup in case of graft failure. Clinically applicable immunosuppressive regimens (IS) were investigated first, then treatments known to be effective in hypersensitized patients or those with recalcitrant rejection reactions. METHODS: Consecutive experiments were carried out between 2009 and 2013. Twenty-one genetically modified pigs (GGTA1-knockout/hCD46/± thrombomodulin, in one case HLA-E instead) were used as donors. In all experiments, two cycles of immunoabsorption reduced preformed antibodies. Recipient baboons were divided into two groups according to IS regimen: In group one (n = 10), pre-treatment started either one (anti-CD20) or four weeks (anti-CD20 plus the proteasome inhibitor bortezomib) prior to transplantation. The extended conventional (as for allotransplantation) immunosuppressive maintenance regimen included anti-thymocyte globuline, tacrolimus, mycophenolate mofetil, methylprednisolone and weekly anti-CD20. In group two (n = 11), myeloablative pre-treatment as in multiple myeloma patients (long and short regimens) was added to extended conventional IS; postoperative total thoracic and abdominal lymphoid irradiation (TLI; single dose of 600 cGY) was used to further reduce antibody-producing cells. RESULTS: In the perioperative course, the surgical technique was safely applied: 19 baboons were weaned off extracorporeal circulation and 17 extubated. Nine animals were lost in the early postoperative course due to causes unrelated to surgical technique or IS regimen. Excluding these early failures, median graft survival times of group 1 and 2 were 18.5 (12-50) days and 16 (7-35) days. Necropsy examination of group 1 donor organs revealed hypertrophy of the left ventricular wall in the six longer-lasting grafts; myocardial histology confirmed pre-clinical suspicion of humoral rejection, which was not inhibited by the extended conventional IS including intensified treatments, and signs of thrombotic microangiopathy. Grafts of group 2 presented with only mild-to-moderate features of humoral rejection and thrombotic microangiopathy, except in one case of delayed rejection on day 17. The other experiments in this group were terminated because of untreatable pulmonary oedema, recurring ventricular fibrillation, Aspergillus sepsis, as well as a combination of a large donor organ and late toxic side effects due to TLI. CONCLUSIONS: Longer-term results were difficult to achieve in this model due to the IS regimens used. However, we conclude that heterotopic intrathoracic heart transplantation may be an option for clinical xenotransplantation.

Xenotransplantation of Cells, Tissues, Organs and the German Research Foundation Transregio Collaborative Research Centre 127.

Human organ transplantation is the therapy of choice for end-stage organ failure. However, the demand for organs far exceeds the donation rate, and many patients die while waiting for a donor. Clinical xenotransplantation using discordant species, particularly pigs, offers a possible solution to this critical shortfall. Xenotransplantation can also increase the availability of cells, such as neurons, and tissues such as cornea, insulin producing pancreatic islets and heart valves. However, the immunological barriers and biochemical disparities between pigs and primates (human) lead to rejection reactions despite the use of common immunosuppressive drugs. These result in graft vessel destruction, haemorrhage, oedema, thrombus formation, and transplant loss. Our consortium is pursuing a broad range of strategies to overcome these obstacles. These include genetic modification of the donor animals to knock out genes responsible for xenoreactive surface epitopes and to express multiple xenoprotective molecules such as the human complement regulators CD46, 55, 59, thrombomodulin and others. We are using (new) drugs including complement inhibitors (e.g. to inhibit C3 binding), anti-CD20, 40, 40L, and also employing physical protection methods such as macro-encapsulation of pancreatic islets. Regarding safety, a major objective is to assure that possible infections are not transmitted to recipients. While the aims are ambitious, recent successes in preclinical studies suggest that xenotransplantation is soon to become a clinical reality.

In frame exon skipping in UBE3B is associated with developmental disorders and increased mortality in cattle.

BACKGROUND: Inherited developmental diseases can cause severe animal welfare and economic problems in dairy cattle. The use of a small number of bulls for artificial insemination (AI) carries a risk that recessive defects rapidly enrich in the population. In recent years, an increasing number of Finnish Ayrshire calves have been identified with signs of ptosis, intellectual disability, retarded growth and mortality, which constitute an inherited disorder classified as PIRM syndrome. RESULTS: We established a cohort of nine PIRM-affected calves and 38 unaffected half-siblings and performed a genome-wide association study (GWAS) to map the disease to a 700-kb region on bovine chromosome 17 (p = 1.55 × 10-9). Whole genome re-sequencing of an unaffected carrier, its affected progeny and 43 other unaffected animals from another breed identified a G > A substitution mutation at the last nucleotide of exon 23 in the ubiquitin protein ligase E3B encoding gene (UBE3B). UBE3B transcript analysis revealed in-frame exon skipping in the affected animals resulting in an altered protein lacking 40 amino acids, of which 20 are located in the conserved HECT-domain, the catalytic site of the UBE3B protein. Mutation screening in 129 Ayrshire AI bulls currently used in Finland indicated a high carrier frequency (17.1%). We also found that PIRM syndrome might be connected to the recently identified AH1 haplotype, which has a frequency of 26.1% in the United States Ayrshire population. CONCLUSION: We describe PIRM syndrome in cattle, which is associated with the mutated UBE3B gene. The bovine phenotype resembles human Kaufman oculocerebrofacial syndrome, which is also caused by mutations in UBE3B. PIRM syndrome might be connected with the recently identified AH1 haplotype, which is associated with reduced fertility in the US Ayrshire population. This study enables the development of a genetic test to efficiently reduce the high frequency of mutant UBE3B in Ayrshires, significantly improving animal health and reducing economic loss.

Non-CpG hypermethylation in placenta of mutation-induced intrauterine growth restricted bovine foetuses.

The existence of non-CpG methylation in mammalian DNA has mainly been observed in embryonic stem cells, but its functional significance is uncertain. We found an age-dependent non-CpG hypermethylation in DMR at the 3' end of the MIMT1 in the placenta of intrauterine growth restricted foetuses in cattle. Data suggest that this DMR play a role in epigenetic regulation of the PEG3 domain.

A porcine model of familial adenomatous polyposis.

We created gene-targeted pigs with mutations in the adenomatous polyposis coli (APC) gene (APC) that are orthologous to those responsible for human familial adenomatous polyposis (FAP). One-year-old pigs with the APC(1311) mutation (orthologous to human APC(1309)) have aberrant crypt foci and low- and high-grade dysplastic adenomas in the large intestine, similar to the precancerous lesions that develop in patients with FAP. Dysplastic adenomas accumulate ß-catenin and lose heterozygosity of APC. This large-animal, genetic model of FAP will be useful in the development of diagnostics and therapeutics for colorectal cancer. DNA sequence data: NCBI accession number GU951771.

Factors influencing the efficiency of generating genetically engineered pigs by nuclear transfer: multi-factorial analysis of a large data set.

BACKGROUND: Somatic cell nuclear transfer (SCNT) using genetically engineered donor cells is currently the most widely used strategy to generate tailored pig models for biomedical research. Although this approach facilitates a similar spectrum of genetic modifications as in rodent models, the outcome in terms of live cloned piglets is quite variable. In this study, we aimed at a comprehensive analysis of environmental and experimental factors that are substantially influencing the efficiency of generating genetically engineered pigs. Based on a considerably large data set from 274 SCNT experiments (in total 18,649 reconstructed embryos transferred into 193 recipients), performed over a period of three years, we assessed the relative contribution of season, type of genetic modification, donor cell source, number of cloning rounds, and pre-selection of cloned embryos for early development to the cloning efficiency. RESULTS: 109 (56%) recipients became pregnant and 85 (78%) of them gave birth to offspring. Out of 318 cloned piglets, 243 (76%) were alive, but only 97 (40%) were clinically healthy and showed normal development. The proportion of stillborn piglets was 24% (75/318), and another 31% (100/318) of the cloned piglets died soon after birth. The overall cloning efficiency, defined as the number of offspring born per SCNT embryos transferred, including only recipients that delivered, was 3.95%. SCNT experiments performed during winter using fetal fibroblasts or kidney cells after additive gene transfer resulted in the highest number of live and healthy offspring, while two or more rounds of cloning and nuclear transfer experiments performed during summer decreased the number of healthy offspring. CONCLUSION: Although the effects of individual factors may be different between various laboratories, our results and analysis strategy will help to identify and optimize the factors, which are most critical to cloning success in programs aiming at the generation of genetically engineered pig models.