Cloned Transgenic Swine Via In Vitro Production and Cryopreservation1

Somatic cell nuclear transfer in pigs: recent achievements and future possibilities

During the past 6 years, considerable advancement has been achieved in experimental embryology of pigs. This process was mainly generated by the rapidly increasing need for transgenic pigs for biomedical research purposes, both for future xenotransplantation to replace damaged human organs or tissues, and for creating authentic animal models for human diseases to study aetiology, pathogenesis and possible therapy. Theoretically, among various possibilities, an established somatic cell nuclear transfer system with genetically engineered donor cells seems to be an efficient and reliable approach to achieve this goal. However, as the result of unfortunate coincidence of known and unknown factors, porcine embryology had been a handicapped branch of reproductive research in domestic animals and a very intensive and focused research was required to eliminate or minimise this handicap. This review summarises recent achievements both in the background technologies (maturation, activation, embryo culture) and the actual performance of the nuclear replacement. Recent simplified methods for in vivo development after embryo transfer are also discussed. Finally, several fields of potential application for human medical purposes are discussed. The authors conclude that although in this early phase of research no direct evidence can be provided about the practical use of transgenic pigs produced by somatic cell nuclear transfer as organ donors or disease models, the future chances even in medium term are good, and at least proportional with the efforts and sums that are invested into this research area worldwide.

Simplified cryopreservation of porcine cloned blastocysts

Recently, a non-invasive delipation (lipid removal) method combined with ultrarapid vitrification has been used successfully for in vitro produced (IVP) porcine embryos. In the present study, this method was combined with parthenogenesis and a recent form of somatic cell nuclear transfer (SCNT) - handmade cloning (HMC) - to establish a simplified and efficient cryopreservation system for porcine cloned embryos. In Experiment 1, zonae pellucidae of oocytes were partially digested with pronase, followed by centrifugation to polarize lipid particles. Ninety percent (173/192) oocytes were successfully delipated in this way. Parthenogenetic activation (PA) after complete removal of zona resulted in similar blastocyst rates in delipated vs. control oocytes (28+/-7% vs. 28+/-5%, respectively). Subsequent vitrification of produced blastocysts with the Cryotop technique resulted in higher survival rates in the delipated group compared to the control group (85+/-6% vs. 32+/-7%, respectively; P<0.01). In Experiment 2, delipated oocytes were used for HMC with normal oocytes as control. Partial zona digestion was further applied before enucleation both in delipated and control groups, to bisect oocyte successfully. Although the blastocyst rate of reconstructed embryos was similar between groups derived from delipated vs. control oocytes (21+/-6% and 23+/-6%, respectively), after vitrification higher survival rates were achieved in the delipated groups than in controls (79+/-6% vs. 32+/-8%, respectively). Our results prove that porcine embryos produced from delipated oocytes by PA or HMC can be cryopreserved effectively by ultrarapid vitrification. Further experiments are required to assess the in vivo developmental competence of the cloned-vitrified embryos.

The effectiveness of the stereomicroscopic evaluation of embryo quality in vitrified-warmed porcine blastocysts: an ultrastructural and cell death study

The objective of this study was to analyze the validity of the stereomicroscopic evaluation of vitrified-warmed (V-W) porcine blastocysts. Unhatched blastocysts were obtained from Large-white gilts (n=10). Blastocysts (n=156) were vitrified using the Open Pulled Straw technology. After warming, V-W blastocysts were cultured for 24h (V24). Then, their developmental progression was morphologically assessed by stereomicroscopy and classified as: V24 viable re-expanded blastocysts; V24 viable hatched blastocysts or V24 degenerated. Blastocysts which re-expanded or hatched after warming were considered viable. Some fresh blastocysts were not vitrified and were evaluated after 24h in culture (F24). By stereomicroscopic analysis all the fresh blastocysts were considered viable. Some F24, V24 re-expanded viable, V24 hatched viable and V24 degenerated blastocysts were processed for transmission electron microscopy (n=13, 19, 9 and 9, respectively) or assessed by TUNEL for cell-death evaluation (n=16, 21, 11 and 21, respectively). All V24 hatched blastocysts showed similar ultrastructure to fresh blastocysts. However, some V24 re-expanded blastocysts considered viable (6/19) revealed ultrastructural alterations. Degenerated V24 blastocysts showed ultrastructural disintegration. Hatched V24 blastocysts did not differ (p>0.05) from F24 hatched blastocysts with regard to the ratio of dead cells (2.8+/-0.5% versus 1.9+/-0.3%, respectively). However, V24 expanded blastocysts had higher (p<0.01) cell death levels (4.3+/-3.4%) than those observed in the F24 expanded blastocysts (1.1+/-0.3%). The degenerated blastocysts showed the highest cell-death index (19.4+/-6.3%). In summary, V-W blastocyst hatching during in vitro culture appears to coincide with good ultrastructure and low cell-death index, suggesting that the hatching rate assessed by stereomicroscopy is more appropriate than embryo re-expansion for an evaluation of V-W blastocyst quality.

Cloned transgenic heart-healthy pork?

Here I comment on the production and uses of swine that express a humanized fat-1 gene. The gene product is a fatty acid desaturase that converts omega-6 fatty acids to omega-3 fatty acids. Omega-3 fatty acids have been implicated as being important for reproductive success, maintaining a healthy cardiovascular system, sustaining a functional immune system, and even preventing depression and cancer. The descendants of these hfat-1 transgenic swine will be very useful as models of the human condition, and if they are permitted to enter the food chain, they may improve human health.