44 LIMITATIONS OF PORCINE OOPLASM TO REPROGRAM BOVINE SOMATIC CELLS

The oocyte cytoplasm (ooplasm) constitutes a unique mixture of factors that are critical for successful reprogramming of haploid maternal and paternal genomes at fertilization as well as the diploid somatic cell genome after somatic cell nuclear transfer (SCNT). The 1-cell-stage embryos (produced by transfer of bovine fibroblast into porcine enucleated ooplast; interspecies SCNT, iSCNT) were processed at different time points (2, 4, 8, and 12 h post-activation, hpa) for detailed nuclear and nucleolar analysis by transmission electron microscopy (TEM; 4 to 5 embryos per group), and immunofluorescence (4 and 12 hpa) for visualization of nucleolar proteins related to transcription (upstream binding factor, UBF) and processing (fibrillarin; 8 to 9 embryos per group). The parameters of interspecies embryos were compared with porcine parthenogenetic (PA) counterparts (4 to 5 embryos per group for TEM analysis; 8 to 9 embryos per group for immunofluorescence analysis). At all evaluated time points, embryos in both groups displayed pronucleus-like nuclei with abundant euchromatin and characteristic porcine nucleolus precursor body (NPB), indicating maternal origin of nucleolar components. Fibrillarin was in both groups localized into shell-like intranuclear entities surrounding NPB. On the contrary, UBF in PA embryos was at 12 hpa colocalized with fibrillarin, whereas in iSCNT embryos, UBF staining was absent at both time points. Despite the similar morphology and localization of processing factor fibrillarin, striking differences in localization of transcription factor UBF suggest limitation of porcine ooplasm to mediate initial phases of nucleolar remodelling. This work was supported by VEGA 1/0077/11.

327 PRODUCTION OF TRIPLE TRANSGENIC hHO-1/GGTA-1–/–/hCD55 TRANSGENIC PIGS USING SLEEPING BEAUTY TRANSPOSITION AND ZINC-FINGER NUCLEASES

Advances in xenotransplantation (pig-to-baboon or human transplantation) require multi-transgenic pigs with a homozygous knockout (KO) of the α1,3-galactosyltransferase gene (GGTA-1, encoding for Gal-epitopes) to control the hyperacute rejection response. To achieve prolonged survival of the porcine xenograft, transgenic expression of additional immune modulatory genes on the GGTA-1–/– background is considered the solution of choice. The acute vascular rejection (AVR) is primarily caused by endothelial cell activation and leads to rejection of GGTA-1–/– pig organs. Here, we set out to produce triple transgenic pigs with high expression of the human complement regulatory gene hCD55 (human decay acceleration factor, hDAF) and the anti-apoptotic and anti-inflammatory gene human heme oxygenase-1 (hHO-1), respectively. Porcine ear fibroblasts carrying a hHO-1 transgene (Petersen et al. 2011 Xenotransplantation 18, 355–368) were transfected with zinc-finger nucleases (ZFN) targeting the GGTA-1 gene, leading to a biallelic KO of the GGTA-1 gene in ~1% of the transfected cells (Hauschild et al. 2011 Proc. Natl. Acad. Sci. USA 108, 15 010). Somatic cell nuclear transfer (SCNT) was accomplished with cells from double transgenic cell line (hHO-1/GGTA-1–/–), and one pregnancy was terminated to obtain fetal cell cultures. Fluorescence-activated cell sorting (FACS) analysis revealed that all 11 fetuses (C6F1-F11) were lacking Gal-epitopes. One pure fetal cell culture (C6F5) was used for co-transfection with the newly designed SB-CAGGS-hDAF-Puror transposon, based on the Sleeping Beauty transposon plasmid pT2/HB, together with the SB transposase 100X plasmid (both kindly provided by Dr. Zoltan Ivics). After 14 days of selection with puromycin, cell colonies were picked and expanded to obtain cells for analysis and as a backup for SCNT. The PCR amplification with hDAF-specific primers revealed that ~50% of picked colonies had integrated the transgene. Two hDAF-positive colonies were pooled and used for SCNT. One pregnancy was sacrificed and 4 hHO-1/GGTA-1–/–/hCD55 fetuses were obtained for real-time PCR analysis and subsequent use in SCNT. Real-time PCR showed elevated hCD55 expression representing a 0.9-fold (0.7- to 1.0-fold) expression of the housekeeping gene glyceraldehyde 3-phosphate dehydrogenase (GAPDH), while FACS analysis confirmed absence of Gal-epitopes in all 4 fetuses. Binding of human-specific anti-CD55 antibodies showed high expression of hCD55 by FACS measurement. Triple transgenic fetuses C8F2 and C8F4 showed higher expression of hCD55 by real-time PCR and by FACS analysis compared with fetuses C8F1 and C8F3. Fetuses C8F3 and C8F4 were used for re-cloning experiments to produce live offspring, which will further be characterised and used in transplantation experiments. This work underlines the importance of new genomic technologies to further improve the efficiency of the generation of transgenic pigs suitable for xenotransplantation.

The trade network in the dairy industry and its implication for the spread of contamination

In case of an outbreak of a foodborne disease, administrative decisions in the context of crisis management are only efficient if they follow standard practices and are specifically adapted to the outbreak situation in a timely manner. These goals are hard to achieve. The complexity of national and global trade structures obscures a clear view of trade flows and, consequently, it is often impossible to unravel complex trade links quickly. Furthermore, increasing public concerns about possible health hazards caused by global trade put additional pressure on decision makers. The aim of this paper was to unveil the specific trade structures of the German milk supply chain, to highlight how these structures could affect the spatial spread of a hypothetical contaminant, and to quantify the risk of the contaminant reaching the consumer. To achieve this goal, the vertical and horizontal trade links between milk producers, dairies, and consumers were taken into account. The horizontal flow of milk between dairies (inter-dairy trade), which is intended to compensate a temporary over- or undersupply of milk, is of special importance in this respect. We hypothesized that the extent of inter-dairy trade would significantly influence the spatial spread of contaminated milk and the contamination risk. This hypothesis was tested using a computer simulation model that predicts the hypothetical spread of a contaminant via trade of milk. The model parameters were estimated using trade data collected in 2004 and 2010. The results of our study indicate that inter-dairy trade significantly influenced the contamination risk. Compared with a scenario with no inter-dairy trade, the risk that contaminated milk will reach the consumer was up to 4 times higher, even with moderate inter-dairy trade. The contamination risk depended on the extent of inter-dairy trade in a nonlinear way and reached its maximum asymptotically when inter-dairy trade increased. The contamination risk exhibited considerable spatial variation, which could be utilized to implement more accurate food control interventions in times of crisis caused by a foodborne disease.

Validation of self-reported erythema: comparison of self-reports, researcher assessment and objective measurements in sun worshippers and skiers

BACKGROUND

Most epidemiological data of sunburn related to skin cancer have come from self-reporting in diaries and questionnaires. We thought it important to validate the reliability of such data.

OBJECTIVE

To validate the quality of self-reported erythema by sun worshippers and skiers, and to validate the ability to determine erythema visually compared with objectively measured erythema.

METHODS

The skin in a group of sun worshippers in Tenerife and of skiers in Austria was closely monitored over a week. The participants used a diary to record any erythema assessed on different skin sites and underwent a twice daily skin examination by researchers who assessed erythema on the same sites. Lastly, the erythema assessment was validated by objective measurements.

RESULTS

We found that the participants' agreed with researchers' assessment of erythema in only 57-61% of cases, and that the researchers detected up to 28% more of the objectively measured erythema than the participants did. We also found that, even for the trained eye (researchers), it was difficult to detect an increase in erythema as only 71-91% of those cases with an increase >15 in measured erythema percentage were detected in the evening. Possibly, detection was impeded by a simultaneous increase in pigmentation.

CONCLUSION

Self-assessment of erythema from diaries is unreliable. Erythema is considerably underestimated and possibly neglected. Even for the trained eye, it can be difficult to detect erythema.

232 GENERATION OF TRANSGENIC PIGS CARRYING A SMALL INTERFERING RNA VECTOR DIRECTED AGAINST TISSUE FACTOR EXPRESSION

The acute vascular rejection (AVR) remains the main hurdle for long-term survival of a porcine xenograft after transplantation into primates. Immunological reactions and molecular incompatibilities can lead to endothelial activation and microvascular thrombosis. Knock-down of tissue factor (TF) could be a promising mechanism to prevent AVR. Tissue factor is a key molecule of the extrinsic coagulation pathway. It functions as cell surface receptor for coagulation factor VIIa and thereby initiates thrombin formation. Since TF knockout was lethal in the mouse model (Toomey et al. 1996 Blood 88, 1583–1587), we tested different small interfering (si) RNAs in their efficiency to knock down TF in a porcine cell line. Two siRNAs reduced the mRNA level of TF to <3% compared with wild type controls as determined by RT-PCR. Subsequently, porcine fetal fibroblasts (PFF) were co-transfected with constructs coding for one of the most promising siRNAs and a DsRed vector, which confers neomycin resistance and red fluorescence. Transfected cells were selected with neomycin for 14 days and checked for the occurrence of fluorescence. Integration of the siRNA vector was confirmed by PCR. Cell clones positive for TF knock-down siRNA served as donor cells for somatic cell nuclear transfer (SCNT). Successfully reconstructed embryos were transferred to synchronised recipient sows. Eight transfers resulted in 4 pregnancies. One foster animal was sacrificed on Day 35 of gestation. All of the 3 resulting fetuses had integrated the TF knock-down siRNA as shown by PCR and will be used for recloning. Additionally, we plan to determine vector integration by Southern blot analysis and siRNA and TF expression level by real time-PCR. The remaining 3 sows will be allowed to carry to full term for further investigations. The functionality of the knock-down will be tested in a tumo necrosis factor-α induced assay using cultured endothelial cells of knock-down piglets and of wild type counterparts because exposure to inflammation mediators stimulates expression of TF and adhesion molecules in the endothelium. Our genetically modified TF transgenic pigs can be combined with already existing genetic modifications to generate multi-transgenic pigs. This model would be of great importance to prolong xenograft survival and move porcine xenografts to the preclinical level. This project was funded by the EU project ‘Xenome’ (LSHB-CT-2006-037377).

233 GENDER-UNSPECIFIC KNOCKOUT OF THE GGTA1 GENE IN PIGS USING ZINC FINGER NUCLEASES

A knockout (KO) of the porcine α1,3-galactosyltransferase (GGTA1) gene is crucial for controlling the hyperacute rejection after pig-to-human xenotransplantation. Porcine kidney and cardiac xenografts from Gal-KO pigs showed prolonged survival after transplantation into baboons. Unfortunately, knockouts produced by conventional targeting (homologous recombination) are rare events and normally do not lead to biallelic KO. Zinc-finger nucleases (ZFN) have been shown to be much more efficient by inducing mutations via specific cleavage followed by nonhomologous end joining (NHEJ). Zinc-finger nucleases do not require antibiotic selection. Here, we used designed ZFN to specifically target exon 9 of the GGTA1 gene encoding the catalytic domain of the Gal-transferase. Recently, we generated female pigs with a GGTA1-KO using ZFN (Hauschild et al. 2011 PNAS 108, 12 013–12 017). Here, we investigated whether cells of a male cell line are susceptible to ZFN-mediated genome editing in a comparable manner. Male porcine fetal fibroblasts (3 × 106) were co-transfected with a ZFN-plasmid pair (7.5 μg each) by electroporation at 250 V and 400 μF. One week after transfection, a Cel-I assay revealed a NHEJ rate of 5.7% of all alleles in the cell population. After magnetic bead selection, Gal-expression was analysed by fluorescence-activated cell sorting (FACS) using fluorescein isothiocyanate (FITC)-conjugated isolectin-B4. Ninety-five percent of the cells were free of Gal epitopes, indicating a biallelic KO. These Gal-negative cells served as donor cells in somatic cell nuclear transfer (SCNT). In total, 507 transgenic embryos were transferred into 6 recipient sows. By obtaining live animals by SCNT after transfer of male ZFN-GGTA1-KO embryos, we will have produced female and male ZFN-KO pigs, which can be used for further breeding experiments to circumvent the extensive and relative inefficient recloning method. These results show that ZFN work independent of the sex of the cells and that a biallelic Gal-KO can be produced in male cells by using the ZFN technology. This technology could benefit both agriculture and biomedicine and establishes the pig as a model for human diseases.

The German milky way: trade structure of the milk industry and possible consequences of a food crisis

The aim of this paper is to analyze the structure of the trade network between milk producers, dairies and milk collection companies in Germany through a network analysis using suitable centrality measures. The study shows that structures exist among the relevant enterprises which are critical for the spread of a contamination in the German milk trade network. The results may be used to improve food security

333 OCT-4 EXPRESSION ANALYSIS IN F0 AND F1 PORCINE OG2 TRANSGENICS

OG2 transgenic pigs provide a new large animal model in which to study Oct-4 expression and the derivation, migration and maintenance of pluripotent cells. They may also prove to be a valuable tool for the development of cell-based therapies. The OG2 transgene consists of the genomic sequence of the murine Oct-4 gene with the enhanced green fluorescence protein (EGFP) reporter gene inserted between the promoter and the coding sequences. As previously reported, 11 OG2 founder animals were produced (7 male and 4 female). Two of the OG2-F0 transgenic boars were mated with 3 wild-type sows and with 2 OG2-F0 transgenic sows. The pregnancy of 1 wild-type sow was terminated at Day 5 after fertilization, and approximately 60% (14/23) of the flushed blastocysts expressed EGFP, demonstrating germ line transmission. The remaining 2 wild-type sows delivered 21 piglets, of which 11 were transgenic. The 2 OG2-F0 sows delivered 9 piglets, all of which were transgenic. Transgenesis and tissue-specific expression of the transgene were determined by Southern blotting, Northern blotting, and real-time PCR analysis. Germ cell-specific expression of the OG2 construct was confirmed in both F0 and F1 transgenics by fluorescence microscopy. Testis isolated from male transgenic piglets exhibited weak EGFP fluorescence in some cells within the seminiferous tubules, whereas testis tissue from adult transgenic boars gave strong EGFP expression in pre-spermatogonial cells. In contrast, fluorescence-activated cell sorting (FACS) analysis and fluorescence microscopy of ejaculated spermatozoa from 3 mature OG2-F0 boars displayed no EGFP fluorescence, as expected. Northern blot analysis of EGFP mRNA revealed stronger EGFP expression in the testis of adult transgenic pigs than in the testis from transgenic piglets. No EGFP mRNA was detected in other organs or in control testis isolated from wild-type piglets. Real-time PCR and Northern blot analysis showed that the time course and signal intensity of EGFP expression in OG2 testis paralleled expression of the endogenous Oct-4 gene in both transgenic and in wild-type testis, confirming that there is indeed stronger expression of Oct-4 in the adult testis than in testis from younger animals. We conclude that the OG2 founders exhibit germline transmission and that the offspring express EGFP in a pattern that faithfully mimics expression of the endogenous Oct-4 gene, thus providing a marker for pluripotent cells. We are currently using FACS to isolate EGFP-positive germ cells (pre-spermatogonial stem cells) from the testis of OG2 boars for further characterisation. Funded by BMBF.

37 LIMITATION OF BOVINE OOPLASM IN REPROGRAMMING OF PORCINE SOMATIC CELLS

Ooplasm posses several, undefined factors allowing for reprogramming of somatic genome into pluripotent state. However, it is presently unknown if and to what extent the ooplasm is able to interact with a transferred somatic cell from another species in the context of interspecies somatic cell nuclear transfer (SCNT). The 1-cell stage embryos were processed at different time points (2, 4, 8, and 12 h post-activation) for detailed nuclear and nucleolar analysis by TEM, and immunofluorescence for visualisation of nucleolar proteins related to transcription (UBF) and processing (fibrillarin). The embryos produced by SCNT of porcine fibroblast into non-activated bovine ooplasm were compared to bovine parthenogenetic counterparts. In the absence of morphological remodelling features (premature chromatin condensation, nuclear envelope break-down), intergeneric embryos showed bovine nuclear and nucleolar precursor body (NPB) morphology. The somatic cell introduced into the bovine ooplasm displayed intranuclear activity at the post-translational level signalling a universal function of ooplasmic factors. The lack of distinct UBF localization in intergeneric embryos, however, suggests failures in sequence-specific interactions between the ooplasm and transferred cell from another genus. We conclude that sperm or a somatic cell of the same species is required for successful embryonic development. Clonet MRTN-CT-2006-035468; MedRat LSHG-CT-2006-518240; PluriSys FP7-HEALTH-2007-223485; DFG, Alexander von Humboldt fellowship, VEGA 1/0057/08; VEGA 1/0012/10.

38 DNA METHYLATION IN PORCINE PREIMPLANTATION EMBRYOS DEVELOPED IN VIVO AND PRODUCED BY IN VITRO FERTILIZATION, PARTHENOGENETIC ACTIVATION, AND SOMATIC CELL NUCLEAR TRANSFER

DNA de- and re-methylation are crucial for reprogramming of the differentiated parental/somatic genome in the ooplasm. The presented research was aimed at analysis of the DNA methylation dynamics in porcine preimplantation embryos developed in vivo (IV) and produced in vitro by IVF, somatic cell nuclear transfer (SCNT), and parthenogenetic activation (PA). Embryos of early and late 1-cell, 2-, 4-, and 8-cell, and early and late blastocysts stages obtained by the mentioned methods were fixed in 4% paraformaldehyde and subjected to immunocytochemistry using anti-5MetC (Mouse monoclonal, Abcam, Cambridge, MA, USA) antibody. DNA was labelled using Hoechst 33258 (Sigma, Copenhagen, Denmark). Epifluorescence microscopy (Leica Microsystems, Wetzlar, Germany) images were subjected to NIH imageJ software to measure the DNA methylation/DNA content signal by manually outlining the nuclei (n = 2003) of the embryos. The data were analysed using PROC-GLM statistical procedure in SAS 9.1 (SAS Institute Inc., Cary, NC, USA), least square means were compared and P-values were used to decide the significant differences within and between different groups of embryos. The 1-cell stages lacked active demethylation of paternal genome in IV and IVF embryos. Embryos produced under in vitro conditions presented higher levels of DNA methylation than IV. A lineage specific DNA methylation (hypermethylation of inner cell mass and hypomethylation of trophectoderm) observed in porcine IV late blastocysts was absent in PA and SCNT blastocysts despite the occurrence of de novo methylation in early blastocysts. SCNT early (50%) and late (14%) blastocysts presented DNA methylation pattern similar to IV early and late blastocysts, respectively. Concluding, DNA methylation patterns are strongly impaired under in vitro conditions in porcine preimplantation embryos.

329 GENETIC TARGETING OF THE PORCINE α1,3-GALACTOSYLTRANSFERASE GENE IN FETAL FIBROBLAST CELLS USING ZINC FINGER NUCLEASES

Hyperacute rejection after porcine-to-human xenotransplantation is caused by binding of preformed human antibodies against Gal-epitopes on the surface of porcine cells. Organs from Gal-negative pigs have shown prolonged survival after transplantation into baboons. Knocking out a gene by conventional gene targeting frequency is extremely inefficient (homologous recombination = 0.0001 to 0.001%; Denning et al. 2001). Recent publications in rats (Geurts et al. 2009) show that the gene knockout via zinc finger nuclease (ZFN)-driven nonhomologous end joining (NHEJ) can be enhanced 10 000-fold over conventional approaches, making it feasible to generate a biallelic gene knockout with one ZFN application. Here, we used ZFN technology to generate porcine cells that carry a ZFN-mediated knockout of the Gal gene to use these cells as donor cells in somatic cell nuclear transfer (SCNT) to obtain live offspring. One primary porcine fetal fibroblast cell line was transfected by electroporation (n = 6) with a pair of ZFN plasmids designed to target the DNA sequence encoding the catalytic domain located in exon 9 of the α1,3-gal locus. Transfected cells were incubated (7 days at a combination of 30°C and 37°C) and analysed for Gal expression by fluorescence activated cell sorting (FACS) using fluorescein isothiocyanate (FITC)-conjugated isolectin-B4. On average, 1.4% (± 0.3%; n = 6) of the cells were free of Gal epitopes, indicating a biallelic knockout. DNA mutation detection analysis (Cel-I assay) of cell cultures gave a mean frequency of 3.5% NHEJ (± 1.3%; n = 6) giving the fraction of mutant alleles within the cell population. One cell line with 1% Gal-negative cells was sorted by a magnetic Dynabead-based separation method to select for Gal-negative cells (Fujimura et al. 2008). Because of the limited amount of Gal-negative cells within the cell population, we chose to select the cells with magnetic beads. This method is gentler to the cells and leads to a higher plating efficiency after sorting compared with FACS. The sorted cells could be easily expanded and will serve as donor cells in SCNT to show the feasibility of generating knockout pigs via ZFN-mediated gene knockout. This study demonstrates that ZFN technology is an applicable tool to produce genetically modified porcine cells for use as donors in SCNT and to speed the creation of pig models for xenotransplantation and human diseases.

A new tool for the navigated placement of intracerebral chemotherapy catheters

OBJECTIVE

The aim of this report is to illustrate a method for the precise placement of chemotherapeutic delivery catheters with the aid of computer-assisted navigation systems.

MATERIALS AND METHODS

We have developed a cannula which can be referenced to our navigation system (BrainLab (®)) to advance and position catheters. The cannula has a length of 10 cm. In the case of a ventricular puncture, CSF will drain through holes at the tip and a side port of the cannula to caution the surgeon. The cannula is fixed to the BrainLab (®) adapter ML and navigated with a BrainLab (®) vector vision (®) system. Using the puncture software, the placement is planned and executed. After placing the cannula as planned, the mandrin is removed and the primed catheter moved forward. When resistance is felt the cannula is withdrawn over the catheter. Further catheters can be placed similarly.

RESULTS

Initial phantom tests showed a good target accuracy. Clinically we have used the cannula in 7 cases with good accuracy.

CONCLUSION

This newly designed tool is easy to handle and well integrated into the navigation system. It provides the means to place catheters precisely to the planned position. Potentially it can be combined with every navigation system using adaptable reference systems.

Characterization of the metabolic phenotype of chronically activated lymphocytes

Activated lymphocytes proliferate, secrete cytokines, and can make antibodies. Normally activated B and T cells meet the bioenergetic demand for these processes by up-regulating aerobic glycolysis. In contrast, several lines of evidence suggest that pathogenic lymphocytes in autoimmune diseases like lupus meet ATP demands through oxidative phosphorylation. Using (13)C-glucose as a stable tracer, we found that splenocytes from mice with lupus derive the same fraction of lactate from glucose as control animals, suggesting comparable levels of glycolysis and non-oxidative ATP production. However, lupus splenocytes increase glucose oxidation by 40% over healthy control animals. The ratio between pentose phosphate cycle (PPC) activity and glycolysis is the same for each group, indicating that increased glucose oxidation is due to increased activity of the TCA cycle in lupus splenocytes. Repetitive stimulation of cultured human T cells was used to model chronic lymphocyte activation, a phenotype associated with lupus. Chronically activated T cells rely primarily on oxidative metabolism for ATP synthesis suggesting that chronic antigen stimulation may be the basis for the metabolic findings observed in lupus mice. Identification of disease-related bioenergetic phenotypes should contribute to new diagnostic and therapeutic strategies for immune diseases.

429 GENERATION OF Oct4-EGFP TRANSGENIC PIGS FOR MONITORING REPROGRAMMING AND PLURIPOTENCY

The Oct4 gene is an essential transcription factor for maintenance of pluripotency in mammals. Here, we report the production of cloned transgenic pigs carrying a genomic construct encompassing murine Oct4 regulatory regions and driving an enhanced green fluorescent protein (Oct4-EGFP) construct. We employed fetal porcine fibroblasts, stably co-transfected with neomycin and the mouse Oct4-EGFP construct, for somatic cell nuclear transfer to reconstruct transgenic embryos. The cloned embryos (811 embryos) were surgically transferred into the oviducts of 8 recipient animals. Two pregnancies were terminated at Day 25 for recovery of fetuses and the others delivered a total of 23 piglets, of which 11 survived the postpartum period. A detailed analysis showed that the Oct4-EGFP construct was active in cloned pig blastocysts from Days 5 to 6. EGFP fluorescence was found exclusively in the primordial germ cells of Day 25 fetuses, whereas somatic tissues did not express the transgene. We could also detect expression of Oct4-EGFP in individual cells of the postnatal testis. Testis-specific expression was confirmed by Northern blotting. We fused transgenic porcine fibroblasts with murine embryonic stem cells to analyze reactivation of the Oct4-EGFP transgene under experimental reprogramming conditions. The fused hybrids displayed stem cell morphology and a high proliferation rate and started to express EGFP fluorescence 72 h after fusion. In conclusion, we report the production of viable Oct4-EGFP transgenic piglets that express EGFP exclusively in germ line and pluripotent cells. This transgenic pig line is a valuable tool for derivation and maintenance of porcine embryonic stem cells and will be of utmost interest for reprogramming studies and for preclinical testing of stem cell therapies in a large animal model. Funded by BMBF.

A novel system of polymorphic and diverse NK cell receptors in primates

There are two main classes of natural killer (NK) cell receptors in mammals, the killer cell immunoglobulin-like receptors (KIR) and the structurally unrelated killer cell lectin-like receptors (KLR). While KIR represent the most diverse group of NK receptors in all primates studied to date, including humans, apes, and Old and New World monkeys, KLR represent the functional equivalent in rodents. Here, we report a first digression from this rule in lemurs, where the KLR (CD94/NKG2) rather than KIR constitute the most diverse group of NK cell receptors. We demonstrate that natural selection contributed to such diversification in lemurs and particularly targeted KLR residues interacting with the peptide presented by MHC class I ligands. We further show that lemurs lack a strict ortholog or functional equivalent of MHC-E, the ligands of non-polymorphic KLR in "higher" primates. Our data support the existence of a hitherto unknown system of polymorphic and diverse NK cell receptors in primates and of combinatorial diversity as a novel mechanism to increase NK cell receptor repertoire.