Trichostatin A rescues the disrupted imprinting induced by somatic cell nuclear transfer in pigs

Combined Chaetocin/Trichostatin A Treatment Improves the Epigenetic Modification and Developmental Competence of Porcine Somatic Cell Nuclear Transfer Embryos

Developmental defects in somatic cell nuclear transfer (SCNT) embryos are principally attributable to incomplete epigenetic reprogramming. Small-molecule inhibitors such as histone methyltransferase inhibitors (HMTi) and histone deacetylase inhibitors (HDACi) have been used to improve reprogramming efficiency of SCNT embryos. However, their possible synergistic effect on epigenetic reprogramming has not been studied. In this study, we explored whether combined treatment with an HMTi (chaetocin) and an HDACi (trichostatin A; TSA) synergistically enhanced epigenetic reprogramming and the developmental competence of porcine SCNT embryos. Chaetocin, TSA, and the combination significantly increased the cleavage and blastocyst formation rate, hatching/hatched blastocyst rate, and cell numbers and survival rate compared to control embryos. In particular, the combined treatment improved the rate of development to blastocysts more so than chaetocin or TSA alone. TSA and combined chaetocin/TSA significantly reduced the H3K9me3 levels and increased the H3K9ac levels in SCNT embryos, although chaetocin alone significantly reduced only the H3K9me3 levels. Moreover, these inhibitors also decreased global DNA methylation in SCNT embryos. In addition, the expression of zygotic genome activation- and imprinting-related genes was increased by chaetocin or TSA, and more so by the combination, to levels similar to those of in vitro-fertilized embryos. These results suggest that combined chaetocin/TSA have synergistic effects on improving the developmental competences by regulating epigenetic reprogramming and correcting developmental potential-related gene expression in porcine SCNT embryos. Therefore, these strategies may contribute to the generation of transgenic pigs for biomedical research.

Optimizing 5-aza-2'-deoxycytidine treatment to enhance the development of porcine cloned embryos by inhibiting apoptosis and improving DNA methylation reprogramming

Apoptosis and incomplete DNA methylation reprogramming in cloned embryos reduce cloning efficiency. 5-aza-2'-deoxycytidine (5-aza-dC) is proven to regulate apoptosis and DNA methylation reprogramming, however, the treatment method and potential role of 5-aza-dC during cloned embryo development are still not well studied. This study displayed that treating donor cells with 5-aza-dC (AN group) significantly reduced the blastocyst rate, while treating cloned embryos (NA group) or both donor cells and cloned embryos (ANA group) significantly promoted the blastocyst formation, and the ANA group was the best treatment of 5-aza-dC to enhance the development of cloned embryos. Then, compared with the NT group, the ANA group showed the significantly enhanced nuclear remodeling. The apoptotic cell numbers and rates of blastocysts were significantly reduced, and the expression levels of significantly upregulated anti-apoptosis gene Bcl2l1 and downregulated pro-apoptosis genes Bax, P53 and Caspase3 were observed in the ANA group. Further study demonstrated that the transcription levels of DNA methylation reprogramming genes Dnmt1, Dnmt3a, Tet1 and Tet3 were significantly upregulated, and, significant genomic DNA remethylation, DNA demethylation of pluripotency gene Oct4, and DNA remethylation of tissue specific gene Thy1 were observed at the blastocyst stage in the ANA group. Embryo development related genes including Igf2, H19, Oct4, Nanog, Sox2, Eif1a, Cdx2 and ATP1b1 were significantly upregulated, and Thy1 and Col5a2 were remarkably silenced at the 4-cell and blastocyst stages in the ANA group. In conclusion, the best 5-aza-dC treatment enhanced the development of cloned embryos by inhibiting apoptosis and improving DNA methylation reprogramming.

Epigenetic Reprogramming During Somatic Cell Nuclear Transfer: Recent Progress and Future Directions

Somatic cell nuclear transfer (SCNT) has broad applications but is limited by low cloning efficiency. In this review, we mainly focus on SCNT-mediated epigenetic reprogramming in livestock and also describe mice data for reference. This review presents the factors contributing to low cloning efficiency, demonstrates that incomplete epigenetic reprogramming leads to the low developmental potential of cloned embryos, and further describes the regulation of epigenetic reprogramming by long non-coding RNAs, which is a new research perspective in the field of SCNT-mediated epigenetic reprogramming. In conclusion, this review provides new insights into the epigenetic regulatory mechanism during SCNT-mediated nuclear reprogramming, which could have great implications for improving cloning efficiency.

Increased pregnancy losses following serial somatic cell nuclear transfer in goats

Serial cloning by somatic cell nuclear transfer (SCNT) is a critical tool for the expansion of precious transgenic lines or resetting the lifespan of primary transgenic cells for multiple genetic modifications. We successfully produced second-generation cloned goats using donor neonatal fibroblasts from first-generation clones. However, our attempts to produce any third-generation clones failed. SCNT efficiency decreased progressively with the clonal generations. The rate of pregnancy loss was significantly greater in recloning groups (P<0.05). While no pregnancy loss was observed during the first round of SCNT, 14 out of 21 pregnancies aborted in the second round of SCNT and all pregnancies aborted in the third round of SCNT. In this retrospective study, we also investigated the expression of 21 developmentally important genes in muscle tissue of cloned (G1) and recloned (G2) offspring. The expression of most of these genes in live clones was found to be largely comparable to naturally reproduced control goats, but fibroblast growth factor 10 (FGF10), methyl CpG binding protein 2 (MECP2) and growth factor receptor bound protein 10 (GRB10) were differentially expressed (P<0.05) in G2 goats compared with G1 and controls. To study the effects of serial cloning on DNA methylation, the methylation pattern of differentially methylated regions in imprinted genes H19 and insulin like growth factor 2 receptor (IGF2R) were also analysed. Aberrant H19 DNA methylation patterns were detected in G1 and G2 clones.

XIST Derepression in Active X Chromosome Hinders Pig Somatic Cell Nuclear Transfer

Pig cloning by somatic cell nuclear transfer (SCNT) remains extremely inefficient, and many cloned embryos undergo abnormal development. Here, by profiling transcriptome expression, we observed dysregulated chromosome-wide gene expression in every chromosome and identified a considerable number of genes that are aberrantly expressed in the abnormal cloned embryos. In particular, XIST, a long non-coding RNA gene, showed high ectopic expression in abnormal embryos. We also proved that nullification of the XIST gene in donor cells can normalize aberrant gene expression in cloned embryos and enhance long-term development capacity of the embryos. Furthermore, the increased quality of XIST-deficient embryos was associated with the global H3K9me3 reduction. Injection of H3K9me demethylase Kdm4A into NT embryos could improve the development of pre-implantation stage embryos. However, Kdm4A addition also induced XIST derepression in the active X chromosome and thus was not able to enhance the in vivo long-term developmental capacity of porcine NT embryos.

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Normal and abnormal pig SCNT embryos featured different transcriptome patterns

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Disrupting XIST gene in donor cells could enhance pig NT embryo development capacity

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Kdm4A injection was able to improve development of pig pre-implantation stage embryos

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Kdm4A addition caused XIST derepression and failed to improve pig cloning efficiency

Imprinting disorder in donor cells is detrimental to the development of cloned embryos in pigs

Imprinting disorder during somatic cell nuclear transfer usually leads to the abnormality of cloned animals and low cloning efficiency. However, little is known about the role of donor cell imprinting in the development of cloned embryos. Here, we demonstrated that the imprinting (H19/Igf2) in porcine fetus fibroblasts derived from the morphologically abnormal cloned fetuses (the abnormal imprinting group) was more hypomethylated, and accordingly, significantly higher H19 transcription and lower Igf2 expression occurred in comparison with those in fibroblasts derived from morphologically normal cloned fetuses (the normal imprinting group) or donor fetus fibroblasts (the control group). When these fibroblasts were used as donor cells, the abnormal imprinting group displayed an even lower imprinting methylation level, in correspondence to the significantly downregulated expression of Dnmt1, Dnmt3a and Zfp57, and a markedly reduced blastocyst rate, while the normal imprinting group took on the similar patterns of imprinting, gene expression and embryo development to the control group. When 5-aza-dC was applied to reduce the fibroblasts imprinting methylation level in the normal imprinting group, cloned embryos displayed the more severely impaired imprinting and significantly lower blastocyst rate. While the upregulated H19 transcription in the abnormal imprinting group was knocked down, the imprinting statuses were partly rescued, and the cleavage and blastocyst rates significantly increased in cloned embryos. In all, donor cell imprinting disorder reduced the developmental efficiency of cloned embryos. This work provides a new insight into understanding the molecular mechanism of donor cells regulating the cloned embryo development.

Human lactoferrin efficiently targeted into caprine beta-lactoglobulin locus with transcription activator-like effector nucleases

Objective

To create genetically modified goat as a biopharming source of recombinant human lacotoferrin (hLF) with transcription activator-like effector nucleases.

Methods

TALENs and targeting vector were transferred into cultured fibroblasts to insert hLF cDNA in the goat beta-lactoglobulin (BLG) locus with homology-directed repair. The gene targeted efficiency was checked using sequencing and TE7I assay. The bi-allelic gene targeted colonies were isolated and confirmed with polymerase chain reaction, and used as donor cells for somatic cell nuclear transfer (SCNT).

Results

The targeted efficiency for BLG gene was approximately 10%. Among 12 Bi-allelic gene targeted colonies, five were used in first round SCNT and 4 recipients (23%) were confirmed pregnant at 30 d. In second round SCNT, 7 (53%), 4 (31%), and 3 (23%) recipients were confirmed to be pregnant by ultrasound on 30 d, 60 d, and 90 d.

Conclusion

This finding signifies the combined use of TALENs and SCNT can generate bi-allelic knock-in fibroblasts that can be cloned in a fetus. Therefore, it might lay the foundation for transgenic hLF goat generation and possible use of their mammary gland as a bioreactor for large-scale production of recombinant hLF.

Ovulation Statuses of Surrogate Gilts Are Associated with the Efficiency of Excellent Pig Cloning

Somatic cell nuclear transfer (SCNT) is an assisted reproductive technique that can produce multiple copies of excellent livestock. However, low cloning efficiency limits the application of SCNT. In this study, we systematically investigated the major influencing factors related to the overall cloning efficiency in pigs. Here, 13620 cloned embryos derived from excellent pigs were transferred into 79 surrogate gilts, and 119 live cloned piglets were eventually generated. During cloning, group of cloned embryos derived from excellent Landrace or Large white pigs presented no significant differences of cleavage and blastocyst rates, blastocyst cell numbers, surrogate pregnancy and delivery rates, average numbers of piglets born and alive and cloning efficiencies, and group of 101-150, 151-200 or 201-250 cloned embryos transferred per surrogate also displayed a similar developmental efficiency. When estrus stage of surrogate gilts was compared, group of embryo transfer on Day 2 of estrus showed significantly higher pregnancy rate, delivery rate, average number of piglets born, average alive piglet number or cloning efficiency than group on Day 1, Day 3, Day 4 or Day 5, respectively (P<0.05). And, in comparison with the preovulation and postovulation groups, group of surrogate gilts during periovulation displayed a significantly higher overall cloning efficiency (P<0.05). Further investigation of surrogate estrus stage and ovulation status displayed that ovulation status was the real factor underlying estrus stage to determine the overall cloning efficiency. And more, follicle puncture for preovulation, not transfer position shallowed for preovulation or deepened for postovulation, significantly improved the average number of piglets alive and cloning efficiency (P<0.05). In conclusion, our results demonstrated that ovulation status of surrogate gilts was the fundamental factor determining the overall cloning efficiency of excellent pigs, and follicle puncture, not transfer position change, improved cloning efficiency. This work would have important implications in preserving and breeding excellent livestock and improving the overall cloning efficiency.