The presence of galactose alpha-1,3-galactose residues on the surface of pig cells is a major obstacle to successful xenotransplantation. Here, we report the production of four live pigs in which one allele of the alpha-1,3-galactosyltransferase locus has been knocked out. These pigs were produced by nuclear transfer technology; clonal fetal fibroblast cell lines were used as nuclear donors for embryos reconstructed with enucleated pig oocytes.

Since Beck, Katz, and Tucker (1998), the standard method for modeling time dependence in binary data has been to incorporate time dummies or splined time in logistic regressions. Although we agree with the need for modeling time dependence, we demonstrate that time dummies can induce estimation problems due to separation. Splines do not suffer from these problems. However, the complexity of splines has led substantive researchers (1) to use knot values that may be inappropriate for their data and (2) to ignore any substantive discussion concerning temporal dependence. We propose a relatively simple alternative: including t, t2, and t3 in the regression. This cubic polynomial approximation is trivial to implement—and, therefore, interpret—and it avoids problems such as quasi-complete separation. Monte Carlo analysis demonstrates that, for the types of hazards one often sees in substantive research, the polynomial approximation always outperforms time dummies and generally performs as well as splines or even more flexible autosmoothing procedures. Due to its simplicity, this method also accommodates nonproportional hazards in a straightforward way. We reanalyze Crowley and Skocpol (2001) using nonproportional hazards and find new empirical support for the historical-institutionalist perspective.

Hyperacute rejection of porcine organs by old world primate recipients is mediated through preformed antibodies against galactosyl-␣-1,3-galactose (Gal␣-1,3-Gal) epitopes expressed on the pig cell surface. Previously, we generated inbred miniature swine with a null allele of the ␣-1,3-galactosyltransferase locus (GGTA1) by nuclear transfer (NT) with gene-targeted fibroblasts. To expedite the generation of GGTA1 null pigs, we selected spontaneous null mutant cells from fibroblast cultures of heterozygous animals for use in another round of NT. An unexpectedly high rate of spontaneous loss of GGTA1 function was observed, with the vast majority of null cells resulting from loss of the WT allele. Healthy piglets, hemizygous and homozygous for the genetargeted allele, were produced by NT by using fibroblasts that had undergone deletional and crossover͞gene conversion events, respectively. Aside from loss of Gal␣-1,3-Gal epitopes, there were no obvious phenotypic differences between these null piglets and WT piglets from the same inbred lines. In fact, congenital abnormalities observed in the heterozygous NT animals did not reappear in the serially produced null animals.A ntibodies against galactosyl-␣-1,3-galactose (Gal␣-1,3-Gal) residues on cell surface glycoproteins of pig cells mediate hyperacute rejection of porcine organs in primate model recipients and are the most immediate barrier to successful clinical xenotransplantation (1, 2). High levels of preformed ''natural'' antibodies against the Gal␣-1,3-Gal epitope are found in humans and old world primates, following evolutionary loss of the corresponding galactosyltransferase activity (encoded by GGTA1) (3). The presence of these antibodies, along with the high density of Gal␣-1,3-Gal residues on most pig cells (4), suggests that elimination of GGTA1 function would provide a practical means of overcoming both hyperacute rejection and subsequent acute or chronic tissue damage associated with antibody binding to this epitope.The lack of GGTA1 function in humans and old world primates, along with the viability of GGTA1 knockout mice produced with embryonic stem cell technology (5, 6), suggested that a knockout strategy might be biologically feasible in pigs. The cloning of sheep (7) and subsequently pigs (8-10) by nuclear transfer with somatic cells has made attempts to knockout the GGTA1 locus in pigs technically feasible.We have previously reported the generation of GGTA1 heterozygous inbred miniature swine using nuclear transfer with gene-targeted fibroblasts (11). Starting with heterozygous fibroblasts from such animals, we now report the isolation of GGTA1 null cells with spontaneous loss of the WT allele. The rate of loss of heterozygosity (LOH) was several orders of magnitude greater than typically expected, an observation that may be related to the inbred background of the heterozygous animals. LOH resulted in some cases from deletion of the WT allele and in others from either somatic crossing over or gene conversion. Similarly high rates of somatic recombi...

Fetal-derived fibroblast cells were transduced with replication defective vectors containing the enhanced green fluorescent protein (EGFP). The transgenic cells were treated with colchicine, which theoretically would synchronize the cells into G2/M stage, and then used as donor nuclei for nuclear transfer. The donor cells were transferred into the perivitalline space of enucleated in vitro matured porcine oocytes, and fused and activated with electrical pulses. A total of 8.3% and 28.6% of reconstructed oocytes showed nuclear envelope breakdown and premature chromosome condensation 0.5 and 2 hr after activation, respectively. Percentage of pronuclear formation was 62.5, 12 hr after activation. Most (91.4%) of the 1-cell embryos with pronuclei did not extrude a polar body. Most (77.2%) embryos on day 5 were diploid. Within 2 hr after fusion, strong fluorescence was detectable in most reconstructed oocytes (92.3%). The fluorescence in all NT embryos became weak 15 hr after fusion and disappeared when culture to 48 hr. But from day 3, cleaved embryos at the 2- to 4-cell stage started to express EGFP again. On day 7, 85.8% of cleaved embryos expressed EGFP. A total of 9.4% of reconstructed embryos developed to blastocyst stage and 71.5% of the blastoctysts expressed EGFP. After 200 reconstructed 1-cell stage embryos were transferred into four surrogate gilts, three recipients were found to be pregnant. One of them maintained to term and delivered a healthy transgenic piglet expressing EGFP. Our data suggest that the combination of transduction of somatic cells by a replication defective vector with the nuclear transfer of colchicine-treated donors is an alternative to produce transgenic pigs. Furthermore, the tissues expressing EGFP from descendents of this pig may be very useful in future studies using pigs that require genetically marked cells.

Little existing work has systematically examined the factors that help terrorist groups survive or contribute to their failure. State support for terrorist groups is commonly thought to be a factor that helps groups to survive. I demonstrate with newly collected data that state sponsorship is not always helpful to terrorist groups. The resources provided by sponsors increase a group's ability to maintain itself internally. However, when a group has a sponsor that provides it with safe haven, the risk of the group being forcefully eliminated by the target increases. I argue that sponsors that provide safe haven can have incentives to provide information to the target about the groups to avoid potential costs from target military operations within their territory. The key empirical findings suggest that state sponsorship is a less serious problem for target states than many previously thought.

We argue that new international borders are rarely new. We propose that when states choose new borders they use previous administrative frontiers to solve a difficult short-term bargaining problem and a long-term coordination problem. With a unique new set of data collected specifically for this project, we systematically examine the new international borders of the twentieth century resulting from secession, partition, and the use of force. New international borders, we find, are drawn not according to principles of “nationalism” or defensible borders, but rather according to previous administrative frontiers. How borders are drawn has important consequences for international stability: borders drawn along previously existing internal or external administrative frontiers experience fewer future territorial disputes and have a much lower risk of militarized confrontation if a dispute emerges.

The authors study the influence of domestic political dissent and violence on incumbent dictators and their regimes. They argue that elite with an interest in preserving the regime hold dictators accountable when there is a significant increase in terrorism. To pinpoint the accountability of dictators to elite who are strongly invested in the current regime, the authors make a novel theoretical distinction between reshuffling coups that change the leader but leave the regime intact and regime-change coups that completely change the set of elites atop the regime. Using a new data set that distinguishes between these two coup types, the authors provide robust evidence that terrorism is a consistent predictor of reshuffling coups, whereas forms of dissent that require broader public participation and support, such as protests and insurgencies, are associated with regime-change coup attempts. This article is the first to show that incumbent dictators are held accountable for terrorist campaigns that occur on their watch.

This study focuses on processes employed by organisational managers making strategic investment decisions (SIDs) in an environment of extreme uncertainty in post-revolution Egypt.Our study illustrates how significant social, political and economic uncertainty impacts upon the utility of capital investment appraisal techniques employed in management accounting decision-making. To engage in this analysis, we employ strong structuration theory as a lens to examine how local Egyptian managers (agents-in-focus) respond to the impact of emergent structures that emanate from the post-revolutionary context in their strategic investment decision-making (SIDM). Our empirical evidence includes focused interviews with twenty-one local managers to understand the experience of accounting for decision-making under extreme uncertainty. Our analysis demonstrates that non-financial considerations and objectives take precedence over the technical 'accounting' measures, for example net present value (NPV) in post-revolution SIDM processes. In particular, recognising and responding to shifting labour power and short-term sacrifices (such as rejecting merger opportunities) become comparatively more important than the pre-supposed rationality of the NPV criteria. However, as multinational corporations insist on the calculation of NPV by their Egyptian subsidiaries, local managers reproduce the imperfect NPV as a communication tool in relation to capital investment decisions, whilst resisting its persuasiveness in favour of more qualitative criteria.