Gene expression profiling of the uterus with embryos cloned by somatic cell nuclear transfer on day 30 of pregnancy

Conceptus-derived cytokines interleukin-1β and interferon-γ induce the expression of acute phase protein serum amyloid A3 in endometrial epithelia at the time of conceptus implantation in pigs

OBJECTIVE

Serum amyloid A3 (SAA3), an acute phase response protein, plays important roles in opsonization, antimicrobial activity, chemotactic activity, and immunomodulation, but its expression, regulation, and function at the maternal-conceptus interface in pigs are not fully understood. Therefore, we determined the expression of SAA3 in the endometrium throughout the estrous cycle and at the maternal-conceptus interface during pregnancy.

METHODS

Endometrial tissues from pigs at various stages of the estrous cycle and pregnancy and with conceptuses derived from somatic cell nuclear transfer (SCNT), conceptus tissues during early pregnancy, and chorioallantoic tissues during mid- to late pregnancy were obtained and the expression of SAA3 was analyzed. The effects of the steroid hormones, interleukin-1β (IL1B), and interferon-γ (IFNG) on the expression of SAA3 were determined in endometrial explant cultures.

RESULTS

SAA3 was expressed in the endometrium during the estrous cycle and pregnancy, with the highest level on day 12 of pregnancy. The expression of SAA3 in the endometrium was significantly higher on day 12 of pregnancy than during the estrous cycle. Early-stage conceptuses and chorioallantoic tissues during mid to late pregnancy also expressed SAA3. The expression of SAA3 was primarily localized to luminal epithelial cells in the endometrium. In endometrial explant cultures, the expression of SAA3 was induced by increasing doses of IL1B and IFNG. Furthermore, the expression of SAA3 decreased significantly in the endometria of pigs carrying conceptuses derived from SCNT on day 12 of pregnancy.

CONCLUSION

These results suggest that the expression of SAA3 in the endometrium during the implantation period increases in response to conceptus-derived IL1B and IFNG. The failure of those appropriate interactions between the implanting conceptus and the endometrium leads to dysregulation of endometrial SAA3 expression, which could result in pregnancy failure. In addition, SAA3 could be a specific endometrial epithelial marker for conceptus implantation in pigs.

Calcium-binding proteins S100A8, S100A9, and S100A12: expression and regulation at the maternal-conceptus Interface in pigs†

Among the many calcium-binding proteins, S100A8, S100A9, and S100A12 play important roles in inflammation, innate immunity, and antimicrobial function, but their expression, regulation, and function at the maternal-conceptus interface in pigs are not fully understood. Therefore, we determined the expression and regulation of S100A8, S100A9, S100A12, and their receptor AGER at the maternal-conceptus interface in pigs. We found that S100A8, S100A9, and S100A12 mRNAs were expressed in the endometrium during the estrous cycle and pregnancy, with the greatest levels on Day (D) 12 of pregnancy, and AGER appeared at greater levels on D15 and D30 of pregnancy than on other days. The expression of S100A8, S100A9, and S100A12 was predominantly localized to epithelial cells in the endometrium, and they were detected in early-stage conceptus and later chorioallantoic tissues during pregnancy. AGER expression was localized to endometrial epithelial and stromal cells and chorionic epithelial cells. In endometrial explant tissues, the expression of S100A8, S100A9, and S100A12 was induced by estrogen, S100A8 by interleukin-1β, and AGER by interferon-γ. We further found that on D12 of pregnancy, the expression of S100A8, S100A9, and S100A12 decreased significantly in the endometria of gilts carrying conceptuses derived from somatic cell nuclear transfer. These results indicate that the expression of S100A8, S100A9, and S100A12 is dynamically regulated in response to conceptus-derived signals at the maternal-conceptus interface, suggesting that S100A8, S100A9, and S100A12 could play a critical role in regulating endometrial epithelial cell function and conceptus implantation to support the establishment and maintenance of pregnancy in pigs.

Atypical chemokine receptors 1, 2, 3 and 4: Expression and regulation in the endometrium during the estrous cycle and pregnancy and with somatic cell nucleus transfer-cloned embryos in pigs

Atypical chemokine receptor (ACKR) 1, ACKR2, ACKR3, and ACKR4, chemokine decoy receptors that lack G-protein-mediated signaling pathways, internalize and degrade chemokines to control their availability and function. Chemokines play important roles in the endometrium during the estrous cycle and pregnancy, but the expression and regulation of ACKRs have not been determined in pigs. Therefore, we examined the expression of ACKRs in the endometrium throughout the estrous cycle and pregnancy and in conceptus tissues in pigs. ACKR1, ACKR2, ACKR3, and ACKR4 mRNA was expressed in the endometrium, with higher levels of ACKR3 on day 12 of the estrous cycle than in pregnancy and higher levels of ACKR4 on day 15 of pregnancy than in the estrous cycle. ACKR1, ACKR2, and ACKR3, but not ACKR4, mRNA was detected in conceptus and chorioallantoic tissues during pregnancy. ACKR2 and ACKR3 mRNA and ACKR4 protein were mainly localized to luminal epithelial cells and weakly to glandular epithelial cells in the endometrium. Increasing doses of progesterone increased the expression of ACKR2 and ACKR4 and decreased the expression of ACKR3 in endometrial tissues. On day 12 of pregnancy, the expression of ACKR4 mRNA was lower in the endometria of gilts with somatic cell nucleus transfer-derived conceptuses than in the endometria of gilts carrying conceptuses derived from natural mating. These results indicate that the expression of ACKRs is dynamically regulated at the maternal-conceptus interface, suggesting that ACKR proteins might play critical roles in regulating endometrial chemokines to support the establishment and maintenance of pregnancy in pigs.

Analysis of stage-specific expression of the toll-like receptor family in the porcine endometrium throughout the estrous cycle and pregnancy

Toll-like receptors (TLRs) play critical roles in innate immunity by regulating antimicrobial responses in mucosal tissues. The expression and function of TLRs in female reproductive tissues have been studied in several species, but the expression and function of TLRs and MYD88, an adaptor molecule in the TLR signaling pathway, at the maternal-conceptus interface are not well understood in pigs. Thus, we determined the expression of TLR1 - TLR10 and MYD88 in the endometrium, conceptus, and chorioallantoic tissues of pigs. TLR1 - TLR10 and MYD88 mRNAs were expressed in the endometrium during the estrous cycle and pregnancy in a stage-dependent manner. TLR and MYD88 mRNAs were also detected in early stage conceptuses and chorioallantoic tissues from Day 30 to term pregnancy. The expression of TLR2, TLR4, TLR5, and TLR7 was localized to epithelial and stromal cells in endometrial and chorioallantoic tissues. Increasing doses of P₄, but not E₂, induced the expression of TLR4, TLR5, TLR6, TLR7, and TLR8, while interferon-γ increased the expression of TLR2 and TLR7 in endometrial explant tissues. Expression of TLR3, TLR5, TLR6, TLR7, and MYD88 was higher in the endometrium with somatic cell nucleus transfer-derived conceptuses than conceptuses derived from natural mating on Day 12. These results indicate that the expression of TLR1 - TLR10 and MYD88 is dynamically regulated at the maternal-conceptus interface in pigs, suggesting that TLRs expressed in the endometrium and the placenta may play a critical role in regulating mucosal immune responses to support the establishment and maintenance of pregnancy.

Endometrial response to conceptus-derived estrogen and interleukin-1β at the time of implantation in pigs

The establishment of pregnancy is a complex process that requires a well-coordinated interaction between the implanting conceptus and the maternal uterus. In pigs, the conceptus undergoes dramatic morphological and functional changes at the time of implantation and introduces various factors, including estrogens and cytokines, interleukin-1β2 (IL1B2), interferon-γ (IFNG), and IFN-δ (IFND), into the uterine lumen. In response to ovarian steroid hormones and conceptus-derived factors, the uterine endometrium becomes receptive to the implanting conceptus by changing its expression of cell adhesion molecules, secretory activity, and immune response. Conceptus-derived estrogens act as a signal for maternal recognition of pregnancy by changing the direction of prostaglandin (PG) F_2α from the uterine vasculature to the uterine lumen. Estrogens also induce the expression of many endometrial genes, including genes related to growth factors, the synthesis and transport of PGs, and immunity. IL1B2, a pro-inflammatory cytokine, is produced by the elongating conceptus. The direct effect of IL1B2 on endometrial function is not fully understood. IL1B activates the expression of endometrial genes, including the genes involved in IL1B signaling and PG synthesis and transport. In addition, estrogen or IL1B stimulates endometrial expression of IFN signaling molecules, suggesting that estrogen and IL1B act cooperatively in priming the endometrial function of conceptus-produced IFNG and IFND that, in turn, modulate endometrial immune response during early pregnancy. This review addresses information about maternal-conceptus interactions with respect to endometrial gene expression in response to conceptus-derived factors, focusing on the roles of estrogen and IL1B during early pregnancy in pigs.

Postmortem findings in cloned and transgenic piglets dead before weaning

Important factors contributing to the well-known high mortality of piglets produced by SCNT are gross malformations of vital organs. The aim of the present retrospective study was to describe malformations found in cloned piglets, transgenic or not, dying or culled before weaning on Day 28. Large White (LW) embryos were transferred to 78 LW recipients, while 72 recipients received Göttingen embryos (67 transgenic and five not transgenic) and 56 received Yucatan embryos (43 transgenic and 13 not transgenic). Overall pregnancy rate was 76%, and there were more abortions in recipients with minipig embryos than in those with LW embryos (26% and 24% vs. 6%). Piglets (n = 815) were born from 128 sows with 6.5 ± 0.4 full-born piglets per litter. The overall rate of stillborn piglets was 21% of all born with the number of stillborn piglets ranging from one to nine in a litter. The mortality of the surviving piglets during the first month was 48%. Thus, altogether 58% of the full-born piglets died before weaning. In 87 of the 128 litters (68%), one to 12 of the piglets showed major or minor malformations. Malformations were found in 232 piglets (29.5% of all born). A single malformation was registered in 152 piglets, but several piglets showed two (n = 58) or more (n = 23) malformations (7.4% and 2.8% of all born, respectively). A significantly higher malformation rate was found in transgenic Göttingen and Yucatan piglets (32% and 46% of all born, respectively) than in nontransgenic LW (17%). There was a gender difference in the transgenic minipigs because male piglets had a higher rate of malformations (49.1%) than females (29.7%). The most common defects in the cloned piglets were in the digestive (12.2%), circulatory (9.4%), reproductive (11.3%), and musculoskeletal (9.1%) systems. Malformations of the musculoskeletal system were most frequent in Göttingen (16.3% vs. approximately 5.5% in the two other breeds), whereas abnormal cardiopulmonary systems were most frequent in Yucatan piglets (26.9% vs. 2.1% in LW and 5.3% in Göttingen). In conclusion, these results show that pig cloning results in a considerable loss of piglets and that many of these can be related to various malformations that all are also seen in noncloned piglets. Because approximately half of the cloned piglets still survive, even with eventual unknown minor malformations, use of pigs as models for human diseases is still realistic. However, continued efforts are needed to further reduce the level of malformations.

Regulation of S100G Expression in the Uterine Endometrium during Early Pregnancy in Pigs

Calcium ions play an important role in the establishment and maintenance of pregnancy, but molecular and cellular regulatory mechanisms of calcium ion action in the uterine endometrium are not fully understood in pigs. Previously, we have shown that calcium regulatory molecules, transient receptor potential vanilloid type 5 (TRPV6) and calbindin-D9k (S100G), are expressed in the uterine endometrium during the estrous cycle and pregnancy in a pregnancy status- and stage-specific manner, and that estrogen of conceptus origin increases endometrial TRPV6 expression. However, regulation of S100G expression in the uterine endometrium and conceptus expression of S100G has been not determined during early pregnancy. Thus, we investigated regulation of S100G expression by estrogen and interleukin-1β (IL1B) in the uterine endometrium and conceptus expression of S100G during early pregnancy in pigs. We obtained uterine endometrial tissues from day (D) 12 of the estrous cycle and treated with combinations of steroid hormones, estradiol-17β (E2) and progesterone (P4), and increasing doses of IL1B. Real-time RT-PCR analysis showed that E2 and IL1B increased S100G mRNA levels in the uterine endometrium, and conceptuses expressed S100G mRNA during early pregnancy, as determined by RT-PCR analysis. To determine if endometrial expression of S100G mRNA during the implantation period was affected by the somatic cell nuclear transfer (SCNT) procedure, we compared S100G mRNA levels in the uterine endometrium from gilts with SCNT-derived conceptuses with those from gilts with conceptuses derived from natural mating on D12 of pregnancy. Real-time RT-PCR analysis showed that levels of S100G mRNA in the uterine endometrium from gilts carrying SCNT-derived conceptuses was significantly lower than those from gilts carrying conceptuses derived from natural mating. These results showed that S100G expression in the uterine endometrium was regulated by estrogen and IL1B of conceptus origin, and affected by the SCNT procedure during early pregnancy. These suggest that conceptus signals regulate S100G, an intracellular calcium transport protein, for the establishment of pregnancy in pigs.

Analysis of ENPP2 in the Uterine Endometrium of Pigs Carrying Somatic Cell Nuclear Transfer Cloned Embryos

Somatic cell nuclear transfer (SCNT) is a useful tool for animal cloning, but the efficiency of producing viable offspring by SCNT is very low. To improve this efficiency in the production of cloned pigs, it is critical to understand the interactions between uterine function and cloned embryos during implantation. Lysophosphatidic acid (LPA) is a lipid mediator that plays an important role in the establishment of pregnancy in pigs; however, LPA production in the uterine endometrium of pigs carrying SCNT-cloned conceptuses has not been determined. Therefore, we investigated expression of ENPP2, an LPA-generating enzyme, in the uterine endometrium of gilts with conceptuses derived from SCNT during the implantation period. Uterine endometrial tissue and uterine flushing were obtained from gilts carrying SCNT-derived conceptuses and from gilts carrying conceptuses resulting from natural mating on d 12 of pregnancy. Our results demonstrated no difference in the level of ENPP2 mRNA expression in the uterine endometrium between gilts carrying SCNT-derived conceptuses and gilts carrying naturally-conceived conceptuses, but secretion of ENPP2 protein into the uterine lumen did decrease significantly in pigs with SCNT-derived conceptuses. These results indicate that expression and secretion of ENPP2, which are critical for appropriate LPA production and successful pregnancy, are dysregulated in the uterine endometrium of pigs carrying SCNT-derived conceptuses.

Microarray Analysis of Gene Expression in the Uterine Endometrium during the Implantation Period in Pigs

During embryo implantation in pigs, the uterine endometrium undergoes dramatic morphological and functional changes accompanied with dynamic gene expression. Since the greatest amount of embryonic losses occur during this period, it is essential to understand the expression and function of genes in the uterine endometrium. Although many reports have studied gene expression in the uterine endometrium during the estrous cycle and pregnancy, the pattern of global gene expression in the uterine endometrium in response to the presence of a conceptus (embryo/fetus and associated extraembryonic membranes) has not been completely determined. To better understand the expression of pregnancy-specific genes in the endometrium during the implantation period, we analyzed global gene expression in the endometrium on day (D) 12 and D15 of pregnancy and the estrous cycle using a microarray technique in order to identify differentially expressed endometrial genes between D12 of pregnancy and D12 of the estrous cycle and between D15 of pregnancy and D15 of the estrous cycle. Results showed that the global pattern of gene expression varied with pregnancy status. Among 23,937 genes analyzed, 99 and 213 up-regulated genes and 92 and 231 down-regulated genes were identified as differentially expressed genes (DEGs) in the uterine endometrium on D12 and D15 of pregnancy compared to D12 and D15 of the estrous cycle, respectively. Functional annotation clustering analysis showed that those DEGs included genes involved in immunity, steroidogenesis, cell-to-cell interaction, and tissue remodeling. These findings suggest that the implantation process regulates differential endometrial gene expression to support the establishment of pregnancy in pigs. Further analysis of the genes identified in this study will provide insight into the cellular and molecular bases of the implantation process in pigs.

Comparative proteomic analysis of hearts of adult SCNT Bama miniature pigs (Sus scrofa)

This study aims to determine the effects of SCNT on cardiac development of SCNT pigs through proteomic methods. Heart proteins from three adult SCNTs and two normal reproductive Bama miniature pigs were extracted, separated, and identified via comparative proteomic methods, including two-dimensional gel electrophoresis, mass spectrometry, and Western blot. Eleven differentially expressed spots were identified as differentially expressed proteins, of which five spots were upregulated proteins such as cardiac myosin heavy chain, cathepsin D, and heat shock protein beta-1 (HSP27). By contrast, six spots were downregulated proteins such as alpha skeletal muscle and actin. The results also demonstrated that nuclear transfer might result in abnormal expression of some important proteins in hearts from SCNT pigs, and affect the cardiac development in SCNT pigs' survival.

Analysis of legumain and cystatin 6 expression at the maternal-fetal interface in pigs

Cathepsins (CTSs), a family of lysosomal cysteine proteases, and their inhibitors, cystatins (CSTs), play a critical role in endometrial and placental tissue remodeling during the establishment and maintenance of pregnancy in many species including rodents, sheep, cow, and pigs. In this study, we determined expression of legumain (LGMN), a cathepsinmember, and its inhibitor, CST6, at the maternal-fetal interface in pigs. Expression of both LGMN and CST6 mRNAs increased during mid- to late pregnancy in the uterine endometrium. LGMN and CST6 mRNAs localized to luminal epithelial cells (LE) and glandular epithelial cells (GE) and to the chorionic membrane (CM), with a strong intensity in GE and the CM for LGMN and in the CM for CST6 during pregnancy. LGMN protein was detected at molecular weights (MW) of approximately 50,000 and 37,000, and the abundance of the37,000-MW LGMN protein increased during mid- to latepregnancy. CST6 protein was also highly expressed in the uterine endometrium in mid- to latepregnancy. LGMN protein localized to LE, GE, and the CM during pregnancy. LGMN and CST6 were aberrantly expressed in the uterine endometrium from gilts with somatic cell nuclear transfer-derived conceptuses at term compared to those of gilts carrying conceptuses derived from natural mating. These results demonstrated that LGMN and CST6 were expressed in the uterine endometrium in a cell-type and stage-specific manner, suggesting that the LGMN and CST6 system at the maternal-fetal interface may play an important role in the establishment and maintenance of pregnancy in pigs.

Swine leukocyte antigen-DQ expression and its regulation by interferon-gamma at the maternal-fetal interface in pigs

Successful pregnancy requires an appropriate intrauterine immune response to the conceptus, which is a semiallograft within the uterus. We reported that swine leukocyte antigen-DQA (SLA-DQA), a major histocompatibility complex (MHC) class II gene, is expressed in the uterine endometrium at the time of conceptus implantation in pigs. Because MHC molecules play critical roles in the immune system, SLA-DQ was hypothesized to be involved in immune regulation during pregnancy. Therefore, we examined expression of SLA-DQ in uterine endometrial tissues obtained during the estrous cycle and pregnancy. SLA-DQA and SLA-DQB mRNAs were detected as 1.3-kb and 1.2-kb bands, respectively. Real-time RT-PCR analysis indicated that SLA-DQA and SLA-DQB mRNA expression was affected by day and pregnancy status, with the highest expression on Day 15 of pregnancy. SLA-DQ was localized primarily to subepithelial stromal cells and endothelial cells of the uterus. Using endometrial explant cultures from Day 12 of the estrous cycle, we determined that expression of SLA-DQA and SLA-DQB mRNAs increased in response to interferon-gamma (IFNG), which is produced by pig conceptus trophectoderm between Days 14 and 18 of pregnancy. The abundance of SLA-DQ protein was less in endometria from gilts with conceptuses resulting from somatic cell nuclear transfer compared with endometria from gilts with conceptuses resulting from natural mating. These results support our hypothesis that SLA-DQ is expressed in response to IFNG from the conceptus, and likely regulates immune response at the maternal-fetal interface to support the maintenance of pregnancy in pigs.

Exploring the application of high-throughput genomics technologies in the field of maternal-embryo communication

Deciphering the complex molecular dialogue between the maternal tract and embryo is crucial to increasing our understanding of pregnancy failure, infertility problems and in the modulation of embryo development, which has consequences through adulthood. High-throughput genomic technologies have been applied to look for a holistic view of the molecular interactions occurring during this dialogue. Among these technologies, microarrays have been widely used, being one of the most popular tools in maternal-embryo communication. Today, next generation sequencing technologies are dwarfing the capabilities of microarrays. The application of these new technologies has broadened to almost all areas of genomics research, because of their massive sequencing capacity. We review the current status of high-throughput genomic technologies and their application to maternal-embryo communication research. We also survey next generation technologies and their huge potential in many research areas. Given the diversity of unanswered questions in the field of maternal-embryo communication and the wide range of possibilities that these technologies offer, here we discuss future perspectives on the use of these technologies to enhance maternal-embryo research.

Maternal endometrial oedema may increase perinatal mortality of cloned and transgenic piglets

The perinatal mortality of cloned animals is a well-known problem. In the present retrospective study, we report on mortality of cloned transgenic or non-transgenic piglets produced as part of several investigations. Large White (LW) sows (n = 105) received hand-made cloned LW or minipig blastocysts and delivered either spontaneously or after prostaglandin induction followed by either Caesarean section or vaginal birth. The overall pregnancy rate was 62%, with 26% of pregnancies terminating before term. This resulted in 48 deliveries. The terminated pregnancies consisted of 12 abortions that occurred at 35 ± 2 days gestation and five sows that went to term without returning to heat and then by surgery showed the uterus without fetal content. The gestation length was for sows with LW piglets that delivered by Caesarean section or vaginally was 115.7 ± 0.3 and 117.6 ± 0.4 days, respectively. In sows with minipiglets, the gestation length for those delivered by Caesarean section or vaginally 114.4 ± 0.2 and 115.5 ± 0.3 days, respectively. Of the 34 sows that delivered vaginally, 28 gave birth after induction, whereas 6 farrowed spontaneously. Of the 14 sows that delivered after Caesarean section and in the five empty sows, the endometrium and placenta showed severe oedema. Piglet mortality following vaginal delivery was higher than after Caesarean section (31% v. 10%, respectively; P < 0.001). When vaginal delivery occurred spontaneously, the stillborn rate was greater than after induced delivery (56% v. 24%, respectively; P < 0.0001). Internal organ weights were recorded for seven cloned LW piglets and six normal piglets. The relative weight of the heart, liver, kidneys and small intestine was found to be reduced in the cloned piglets (P < 0.05). The present study demonstrates extensive endometrial oedema in sows pregnant with cloned and transgenic piglets, as well as in empty recipients, at term. The growth of certain organs in some of the cloned piglets was reduced and the rate of stillborn piglets was greater in cloned and transgenic piglets delivered vaginally, possibly because of oedema of the fetal-maternal interface.

Identification of differentially expressed genes in the uterine endometrium on day 12 of the estrous cycle and pregnancy in pigs

Maternal recognition of pregnancy in pigs occurs approximately on Day (D) 12 of pregnancy and is critical for embryo implantation. The presence of the conceptus in the uterine lumen during this period changes uterine endometrial function to prepare for attachment of the conceptus to the endometrial epithelial cells and maintain luteal function in the ovary. Although much is known about endometrial gene expression, the genes expressed in the uterine endometria and the cellular and molecular mechanisms of those gene products during the period of implantation and maternal recognition of pregnancy in pigs are still not completely defined. To better understand the interactions between the maternal uterus and conceptus during the implantation process, we searched genes differentially expressed in the endometria on D12 of pregnancy compared to those on D12 of the estrous cycle. A new reverse transcription-polymerase chain reaction (RT-PCR)-based method that involves annealing control primers (ACPs) was employed. Using 120 ACPs, we sequenced 12 differentially expressed genes (DEGs) and identified those genes using the Basic Local Alignment Search Tool (BLAST). Northern blot hybridization analysis confirmed the differential expression of those DEGs in the uterine endometrium. In situ hybridization analysis determined the cell-type specific expression of the DEGs in the uterine endometrium. Further analysis of the DEGs found in this study will provide insights into the cellular and molecular basis of maternal and fetal interactions during the period of maternal recognition of pregnancy in the pig. Mol. Reprod. Dev. 76: 75-84, 2009. (c) 2008 Wiley-Liss, Inc.

Altered gene expression in cloned piglets

Studies on cloned pigs are scant compared with those in mice and cattle. Expression profiles of cloned pig embryos on full-term cloned pigs are even more limited owing to the limited availability of DNA microarray technology in the pig. We have conducted expression profile comparisons between pigs from somatic cell nuclear transfer and pigs from conventional breeding at birth and 1 month of age. Differentially expressed genes that are subjected to DNA methylation were also examined for their DNA methylation status. These data will be presented in the 2009 Annual Meeting of the International Embryo Transfer Society in San Diego. In the present review, we focus on summarising existing findings on epigenetic and other changes in cloned embryo, cloned pigs and their offspring by conventional breeding.