Sigrid Müller

HLA-E/human beta2-microglobulin transgenic pigs: protection against xenogeneic human anti-pig natural killer cell cytotoxicity

Background. Natural killer (NK) cells participate in pig-to-primate xenograft rejection both by antibody-dependent and -independent mechanisms. A majority of human NK cells express the inhibitory receptor CD94/NKG2A, which binds specifically to human leukocyte antigen (HLA)-E, a trimeric complex consisting of the HLA-E heavy chain, &bgr;2-microglobulin (&bgr;2m), and a peptide derived from the leader sequence of some major histocompatibility complex class I molecules. Methods. To use this mechanism for protection of pig tissues against human NK cell-mediated cytotoxicity, we generated transgenic pigs by pronuclear microinjection of genomic fragments of HLA-E with an HLA-B7 signal sequence and of human &bgr;2-microglobulin (hu&bgr;2m) into zygotes. Results. Three transgenic founder pigs were generated. Northern blot analysis of RNA from peripheral blood mononuclear cells revealed the presence of the expected transcript sizes for both transgenes in two of the three founders. The founder with the highest expression and his offspring were characterized in detail. Fluorescence-activated cell sorting (FACS) and Western blot analyses demonstrated consistent expression of HLA-E and hu&bgr;2m in peripheral blood mononuclear cells. Immunohistochemistry revealed the presence of HLA-E and hu&bgr;2m on endothelial cells of many organs, including heart and kidney. In vitro studies showed that lymphoblasts and endothelial cells derived from HLA-E/hu&bgr;2m transgenic pigs are effectively protected against human NK cell-mediated cytotoxicity, depending on the level of CD94/NKG2A expression on the NK cells. Further, HLA-E/hu&bgr;2m expression on porcine endothelial cells inhibited the secretion of interferon (IFN)-&ggr; by co-cultured human NK cells. Conclusions. This novel approach against cell-mediated xenogeneic responses has important implications for the generation of multitransgenic pigs as organ donors for clinical xenotransplantation.

Stable Production of Human Insulin-like Growth Factor 1 (IGF-1) in the Milk of Hemi- and Homozygous Transgenic Rabbits Over Several Generations

One transgenic rabbit line was generated carrying a fusion gene consisting of the cDNA for human IGF-1 fused to a mammary gland specific expression cassette derived from bovine alpha-S1-casein sequences. Transgene expression was shown to be strictly tissue and lactation period specific. The transgenic rabbit line was bred for six generations. All transgenic animals showed stable production of biologically active IGF-1 over the generations and no apparent effect on the physiological or reproductive performance was observed. The absence of adverse effects on homozygous transgenic rabbits suggested the absence of insertional mutagenesis. Eight hemizygous transgenic offspring analysed produced on average 363 ± 12μg/ml (ranging from 223 ± 61 to 484 ± 39 μg/ml) mature human IGF-1 in their milk, whereas three homozygous animals produced on average 543 ± 41 μg/ml (ranging from 360 ± 15 to 678 ± 80 μg/ml). Homozygous huIGF-1 females clearly showed a significantly increased production performance of the recombinant protein.

Nuclear-cytoplasmic interactions affect in utero developmental capacity, phenotype, and cellular metabolism of bovine nuclear transfer fetuses

Abstract We generated a clone of bovine somatic cell nuclear transfer embryos using oocyte pools from defined maternal sources to study nuclear-cytoplasmic interactions. Nucleocytoplasmic hybrids were reconstructed with Bos taurus (Brown Swiss) granulosa cells and oocytes that contained B. taurus A (Simmental), B. taurus B (Simmental), or Bos indicus (Dwarf Zebu) cytoplasm. Another set of embryos was reconstructed with randomly selected Brown Swiss (B. taurus R) oocytes. Embryo transfer resulted in nine (12.5%), nine (13.8%), three (50%), and 11 (16.7%) Day 80 fetuses, of which eight (11.1%), three (4.6%), three (50%), and 10 (15.2%) were viable, respectively. The proportion of viable fetuses was affected by cytoplasm (likelihood ratio test, P < 0.02) and was higher for embryos with B. indicus cytoplasm than for the B. taurus A (P < 0.05) and B (P < 0.01) groups. Furthermore, the proportion of surviving Day 80 fetuses was reduced for B. taurus B as compared with B. taurus A and B. taurus R cytoplasm (P < 0.05 and P < 0.02). Body weight of nucleocytoplasmic hybrid fetuses was not significantly different from Brown Swiss control fetuses produced by artificial insemination (AI), but fetuses reconstructed with random cytoplasts of the same breed as the nuclear donor exhibited overgrowth (P < 0.01) and a higher coefficient of variation in weight. Furthermore, body weight, crown rump length, thorax circumference (P < 0.05), and femur length (P < 0.01) of fetuses with B. taurus A cytoplasm differed from fetuses with B. taurus R cytoplasms. Fetal skin, heart, and liver cells with B. indicus cytoplasm showed a greater increase in number per time period (P < 0.001) and oxygen consumption rate per cell (skin and liver, P < 0.001; heart, P < 0.08) in comparison with their counterparts with B. taurus A cytoplasm. These data point to complex oocyte cytoplasm-dependent epigenetic modifications and/or nuclear DNA-mitochondrial DNA interactions with relevance to nuclear transfer and other reproductive technologies such as ooplasmic transfer in human assisted reproduction.

Primary culture of porcine PGCs requires LIF and porcine membrane-bound stem cell factor.

We studied the effect of murine leukaemia inhibitory factor (LIF), human basic fibroblast growth factor (bFGF) and porcine stem cell factor (SCF) on the survival and/or proliferation of porcine primordial germ cells (PGCs) obtained from 27-day-old embryos in vitro. PGCs were cultured in embryonic stem cell (ESC) medium supplemented with or without either LIF (1000 IU/ml) alone or LIF together with bFGF (10 ng/ml). They were seeded on mitotically inactivated feeder cells, either STO or transfected STO cells (STO#8), expressing the membrane-bound form of porcine SCF. PGCs were identified by their alkaline phosphatase (AP) activity and counted after 1, 3 and 5 days in culture. After 1 day of culture, PGCs cultured on STO#8 cells showed significantly higher survival than PGCs cultured on STO cells (p < 0.05). The combined effect of SCF and LIF caused a significant increase in PGC number by day 3 of culture when PGCs were cultured on either STO cells (p < 0.01) or STO#8 (p < 0.001). When SCF and LIF were used together with bFGF no increase in the PGC number was observed. Our results suggest that the membrane-bound form of porcine SCF plays a pivotal role in the primary culture of porcine PGCs and that bFGF is not required in vitro.

Quantification of Leukocyte Genomic 5-Methylcytosine Levels Reveals Epigenetic Plasticity in Healthy Adult Cloned Cattle

Successful somatic cell nuclear transfer (SCNT) requires epigenetic reprogramming of a differentiated donor cell nucleus. Incorrect reprogramming of epigenetic markings such as DNA methylation is associated with compromised prenatal development and postnatal abnormalities. Clones that survive into adulthood, in contrast, are assumed to possess a normalized epigenome corresponding to their normal phenotype. To address this point, we used capillary electrophoresis to measure 5-methylcytosine (5mC) levels in leukocyte DNA of 38 healthy female bovine clones that represented five genotypes from the Simmental breed and four genotypes from the Holstein breed. The estimated variance in 5mC level within clone genotypes of both breeds [0.104, 95% confidence interval (CI): 0.070-0.168] was higher than between clone genotypes (0, CI: 0-0.047). We quantified the contribution of SCNT to this unexpected variability by comparing the 19 Simmental clones with 12 female Simmental monozygotic twin pairs of similar age. In Simmental clones, the estimated variability within genotype (0.0636, CI: 0.0358-0.127) was clearly higher than in twin pairs (0.0091, CI: 0.0047-0.0229). In clones, variability within genotype (0.0636) was again higher than between genotypes (0, CI: 0-0.077). Twins, in contrast, showed lower variability within genotypes (0.0091) than between genotypes (0.0136, CI: 0.00250-0.0428). Importantly, the absolute deviations of 5mC values of individual SCNT clones from their genotype means were fivefold increased in comparison to twins. Further comparisons with noncloned controls revealed DNA hypermethylation in most of the clones. The clone-specific variability in DNA methylation and DNA hypermethylation clearly show that healthy adult SCNT clones must be considered as epigenome variants.