Enhancement of Chromatin and Epigenetic Reprogramming in Porcine SCNT Embryos—Progresses and Perspectives

Optimizing gene editing in pigs: The role of electroporation and lipofection

The production of genetically modified pigs is becoming increasingly important in both the agricultural and biomedical fields. Optimization of these processes is a key objective to improve the precision, scalability and viability of genetically modified animals for research and commercial applications. Among the available techniques, electroporation and lipofection have emerged as promising alternatives to traditional methods such as microinjection and somatic cell nuclear transfer (SCNT) due to their simplicity, cost-effectiveness, and potential for high-throughput applications. These methods allow the direct delivery of CRISPR/Cas components into zygotes and embryos, reducing the technical expertise required and bypassing some of the challenges associated with cloning. This review examines the application, efficacy, and outcomes of electroporation and lipofection as gene editing techniques in porcine gametes and embryos. We provide a comprehensive synthesis of recent advances, compare their efficacy, and discuss their potential in agricultural and biomedical research. The principles and mechanisms of both methods are reviewed, highlighting their advantages, such as cost-effectiveness and ease of implementation, over traditional approaches such as microinjection. In addition, we address their limitations, including variability in efficiency, and discuss recent protocol optimizations aimed at improving reproducibility and applicability. By analyzing these developments, this review provides valuable insights into the evolving role of electroporation and lipofection in porcine genetic modification strategies.

Heterologous expression of bovine histone H1foo into porcine fibroblasts alters the transcriptome profile but not embryo development following nuclear transfer

PURPOSE

Somatic cell nuclear transfer (SCNT) is a valuable tool for investigating reprogramming mechanisms and creating animal clones for applications in production, conservation, companionship, and biomedical research. However, SCNT efficiency remains low. Expression of nuclear proteins associated with an undifferentiated chromatin state, such as the oocyte-specific variant of the linker histone H1 (H1foo), represents a strategy for improving reprogramming outcomes, but this approach has not been tested in the context of SCNT.

METHODS

Bovine H1foo (bH1foo) was transfected into porcine fibroblasts via electroporation for expression until SCNT. The transcriptomic profile of these cells was analyzed, and their potential as donor cells for SCNT was evaluated 48 h post-electroporation.

RESULTS

Strong nuclear localization of bH1foo persisted for 48 h post-electroporation. A total of 447 genes were differentially expressed, and lower levels of H3K4me3 and H3K27me3 were detected in bH1foo-expressing cells, indicating changes in chromatin remodeling and function. Embryo development and total cell number per blastocyst were similar between SCNT embryos produced with control and bH1foo-expressing cells. mRNA levels of genes involved in embryonic genome activation were comparable between embryos derived from control and bH1foo-expressing cells on days 3 and 4 of development, suggesting that bH1foo did not disrupt this critical process.

CONCLUSIONS

The heterologous expression of bovine H1foo altered the chromatin function of porcine fibroblasts without impairing development to the blastocyst stage following SCNT. These results highlight the potential of expressing nuclear proteins as a strategy to enhance cell reprogramming and cloning efficiency, including interspecies cloning applications.

Navigating gene editing in porcine embryos: Methods, challenges, and future perspectives

Gene editing technologies, particularly CRISPR/Cas9, have emerged as transformative tools in genetic modification, significantly advancing the use of porcine embryos in biomedical and agricultural research. This review comprehensively examines the various methodologies for gene editing and delivery methods, such as somatic cell nuclear transfer (SCNT), microinjection, electroporation, and lipofection. This review, focuses on the advantages or limitations of using different biological sources (in vivo- vs. in vitro oocytes/embryos). Male germ cell manipulation using sperm-mediated gene transfer (SMGT) and testis-mediated gene transfer (TMGT) represent innovative approaches for producing genetically modified animals. Although these technologies have revolutionized the genetic engineering field, all these strategies face challenges, including high rates of off-target events and mosaicism. This review emphasizes the need to refine these methods, with a focus on reducing mosaicism and improving editing accuracy. Further advancements are essential to unlocking the full potential of gene editing for both agricultural applications and biomedical innovations.

Atractylenolide Ⅲ partially alleviates tunicamycin-induced damage in porcine oocytes during in vitro maturation by reducing oxidative stress

Assisted reproductive technology (ART) is widely used to address infertility and enhance reproductive outcomes in livestock. Among various ART techniques, in vitro maturation (IVM) is commonly used to obtain high-quality oocytes but is susceptible to oxidative stress. In traditional Chinese medicine, Rhizoma Atractylodis Macrocephalae (Bai Zhu) is used to enhance maternal and fetal health. Atractylenolide Ⅲ (AⅢ), a major component of Bai Zhu, has shown both antioxidant properties and oxidative stress induction, leading to controversy. This study used porcine oocytes as a model to investigate the effects of AⅢ under tunicamycin (TM)-induced oxidative stress. During IVM, oocytes were treated with various concentrations of AⅢ and a constant dose of TM. AⅢ promoted oocyte maturation and cumulus cell expansion, with the optimal concentration being 1 mg/L. AⅢ reduced reactive oxygen species (ROS) and malondialdehyde (MDA) levels, indicating reduced oxidative damage. Mitochondrial function and membrane potential (MMP) were preserved in AⅢ-treated oocytes. Additionally, AIII could alleviate TM-induced endoplasmic reticulum (ER) stress, as shown by decreased mRNA expression of ER stress markers. Following parthenogenetic activation (PA), AⅢ-treated oocytes exhibited increased cleavage and blastocyst formation rates with reduced apoptosis compared to the TM group. These findings suggest that AⅢ protects against oxidative stress, improving oocyte quality and developmental potential, with potential applications in ART.

From genome to epigenome: Who is a predominant player in the molecular hallmarks determining epigenetic mechanisms underlying ontogenesis?

Genetic factors are one of the basic determinants affecting ontogenesis in mammals. Nevertheless, on the one hand, epigenetic factors have been found to exert the preponderant and insightful impact on the intracellular mechanistic networks related to not only initiation and suppression, but also up- and downregulation of gene expression in all the phases of ontogenetic development in a variety of mammalian species. On the other hand, impairments in the epigenetic mechanisms underlying reprogramming of transcriptional activity of genes (termed epimutations) not only give rise to a broad spectrum of acute and chronic developmental abnormalities in mammalian embryos, foetuses and neonates, but also contribute to premature/expedited senescence or neoplastic transformation of cells and even neurodegenerative and mental disorders. The current article is focused on the unveiling the present knowledge aimed at the identification, classification and characterization of epigenetic agents as well as multifaceted interpretation of current and coming trends targeted at recognizing the epigenetic background of proper ontogenesis in mammals. Moreover, the next objective of this paper is to unravel the mechanistic insights into a wide array of disturbances leading to molecular imbalance taking place during epigenetic reprogramming of genomic DNA. The above-indicated imbalance seems to play a predominant role in the initiation and progression of anatomo-, histo-, and physiopathological processes throughout ontogenetic development. Conclusively, different modalities of epigenetically assisted therapeutic procedures that have been exemplified in the current article, might be the powerful and promiseful tools reliable and feasible in the medical treatments of several diseases triggered by dysfunctions in the epigenetic landscapes, e.g., myelodysplastic syndromes or epilepsy.

Tetraploid embryo aggregation produces high-quality blastocysts with an increased trophectoderm in pigs

Tetraploid complementation is an ideal method for demonstrating the differentiation potential of pluripotent stem cells. In this study, we selected the most efficient tetraploid production method for porcine embryos and investigated whether tetraploid blastomere aggregation could enhance the quality of tetraploid embryos. Three methods were investigated to produce tetraploid embryos: First, tetraploid embryos were produced using electro-fusion of two-cell stage parthenogenetic blastomere (FUTP). Second, somatic cell was injected into the mature oocyte and fused to produce tetraploid embryos. Third, oocytes were matured with Cytochalasin B (CB) for the late 22 h of in vitro maturation to inhibit the first polar body (PB1). Following that, non-PB1 oocytes were treated with CB for 4 h after parthenogenetic activation. There was no significant difference in the blastocyst development rate and tetraploid production rate of the embryos produced through the three methods. However, FUTP-derived blastocysts had a significantly lower percentage of apoptotic cells compared to other methods. The developmental competence of embryos, expression of trophectoderm cell marker genes, and distribution of YAP1 protein were investigated in tetraploid embryos produced using the FUTP method. The FUTP method most effectively prevented apoptosis during porcine tetraploid embryo formation. Tetraploid aggregation-derived blastocysts have a high proportion of trophectoderm with increased expression of the CDX2 mRNA and high YAP1 intensity. High-quality blastocysts derived from a tetraploid embryo aggregation can serve as suitable source material for testing the differentiation potential of pluripotent stem cells for blastocyst complementation in pigs.

Cloning horses by somatic cell nuclear transfer: Effects of oocyte source on development to foaling

The cloning of horses is a commercial reality, yet the availability of oocytes for cloned embryo production remains a major limitation. Immature oocytes collected from abattoir-sourced ovaries or from live mares by ovum pick-up (OPU) have both been used to generate cloned foals. However, the reported cloning efficiencies are difficult to compare due to the different somatic cell nuclear transfer (SCNT) techniques and conditions used. The objective of this retrospective study was to compare the in vitro and in vivo development of equine SCNT embryos produced using oocytes recovered from abattoir-sourced ovaries and from live mares by OPU. A total of 1,128 oocytes were obtained, of which 668 were abattoir-derived and 460 were OPU-derived. The methods used for in vitro maturation and SCNT were identical for both oocyte groups, and the embryos were cultured in Dulbecco's Modified Eagle's Medium/Nutrient Mixture F-12 Ham medium supplemented with 10% fetal calf serum. Embryo development in vitro was assessed, and Day 7 blastocysts were transferred to recipient mares. The embryos were transferred fresh when possible, and a cohort of vitrified-thawed OPU-derived blastocysts was also transferred. Pregnancy outcomes were recorded at Days 14, 42 and 90 of gestation and at foaling. The rates of cleavage (68.7 ± 3.9% vs 62.4 ± 4.7%) and development to the blastocyst stage (34.6 ± 3.3% vs 25.6 ± 2.0%) were superior for OPU-derived embryos compared with abattoir-derived embryos (P < 0.05). Following transfer of Day 7 blastocysts to a total of 77 recipient mares, the pregnancy rates at Days 14 and 42 of gestation were 37.7% and 27.3%, respectively. Beyond Day 42, the percentages of recipient mares that still had a viable conceptus at Day 90 (84.6% vs 37.5%) and gave birth to a healthy foal (61.5% vs 12.5%) were greater for the OPU group compared with the abattoir group (P < 0.05). Surprisingly, more favourable pregnancy outcomes were achieved when blastocysts were vitrified for later transfer, probably because the uterine receptivity of the recipient mares was more ideal. A total of 12 cloned foals were born, 9 of which were viable. Given the differences observed between the two oocyte groups, the use of OPU-harvested oocytes for generating cloned foals is clearly advantageous. Continued research is essential to better understand the oocyte deficiencies and increase the efficiency of equine cloning.

Somatic Cell Nuclear Transfer in Pigs

Somatic cell nuclear transfer (SCNT) has been successfully applied to clone animals of several species. Pigs are one of the main livestock species for food production and are also important for biomedical research due to their physiopathological similarities with humans. In the past 20 years, clones of several swine breeds have been produced for a variety of purposes, including biomedical and agricultural applications. In this chapter, we describe a protocol to produce cloned pigs by SCNT.

Simultaneous Inhibition of Histone Deacetylases and RNA Synthesis Enables Totipotency Reprogramming in Pig SCNT Embryos

Combining somatic cell nuclear transfer (SCNT) with genome editing technologies has emerged as a powerful platform for the creation of unique swine lineages for agricultural and biomedical applications. However, successful application of this research platform is still hampered by the low efficiency of these technologies, particularly in attaining complete cell reprogramming for the production of cloned pigs. Treating SCNT embryos with histone deacetylase inhibitors (HDACis), such as Scriptaid, has been routinely used to facilitate chromatin reprogramming after nuclear transfer. While increasing histone acetylation leads to a more relaxed chromatin configuration that facilitates the access of reprogramming factors and DNA repair machinery, it may also promote the expression of genes that are unnecessary or detrimental for normal embryo development. In this study, we evaluated the impact of inhibiting both histone deacetylases and RNA synthesis on pre- and post-implantation development of pig SCNT embryos. Our findings revealed that transcription can be inhibited for up to 40 h of development in porcine embryos, produced either by activation, fertilization or SCNT, without detrimentally affecting their capacity to form a blastocyst and their average number of cells at this developmental stage. Importantly, inhibiting RNA synthesis during HDACi treatment resulted in SCNT blastocysts with a greater number of cells and more abundant transcripts for genes related to embryo genome activation on days 2, 3 and 4 of development, compared to SCNT embryos that were treated with HDACi only. In addition, concomitant inhibition of histone deacetylases and RNA synthesis promoted the full reprograming of somatic cells, as evidenced by the normal fetal and full-term development of SCNT embryos. This combined treatment may improve the efficiency of the genome-editing + SCNT platform in swine, which should be further tested by transferring more SCNT embryos and evaluating the health and growth performance of the cloned pigs.

Molecular Mechanism and Application of Somatic Cell Cloning in Mammals-Past, Present and Future

Thus far, nearly 25 mammalian species have been cloned by intra- or interspecies somatic cell nuclear transfer (SCNT) [...].