Epigenetic Modification Agents Improve Gene-Specific Methylation Reprogramming in Porcine Cloned Embryos

Astaxanthin enhances the development of bovine cloned embryos by inhibiting apoptosis and improving DNA methylation reprogramming of pluripotency genes

Low cloning efficiency limits the wide application of somatic cell nuclear transfer technology. Apoptosis and incomplete DNA methylation reprogramming of pluripotency genes are considered as the main causes for low cloning efficiency. Astaxanthin (AST), a powerfully antioxidative and antiapoptotic carotenoid, is recently shown to improve the development of early embryos, however, the potential role of AST during the development of cloned embryos remains unclear. This study displayed that treating cloned embryos with AST significantly increased the blastocyst rate and total blastocyst cell number in a concentration dependent manner, and also alleviated the damage of H2O2 to the development of cloned embryos. In addition, compared with the control group, AST significantly reduced the apoptotic cell number and rate in cloned blastocysts, and the significantly upregulated expression of anti-apoptotic gene Bcl2l1 and antioxidative genes (Sod1 and Gpx4) and downregulated transcription of pro-apoptotic genes (Bax, P53 and Caspase3) were observed in the AST group. Moreover, AST treatment facilitated DNA demethylation of pluripotency genes (Pou5f1, Nanog and Sox2), in accompany with the improved transcription levels of DNA methylation reprogramming genes (Tet1, Tet3, Dnmt1, Dnmt3a and Dnmt3b) in cloned embryos, and then, the significantly upregulated expression levels of embryo development related genes including Pou5f1, Nanog, Sox2 and Cdx2 were observed in comparison with the control group. In conclusion, these results revealed that astaxanthin enhanced the developmental potential of bovine cloned embryos by inhibiting apoptosis and improving DNA methylation reprogramming of pluripotency genes, and provided a promising approach to improve cloning efficiency.

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

Over the last 25 years, cloned animals have been produced by transferring somatic cell nuclei into enucleated oocytes (SCNT) in more than 20 mammalian species. Among domestic animals, pigs are likely the leading species in the number of clones produced by SCNT. The greater interest in pig cloning has two main reasons, its relevance for food production and as its use as a suitable model in biomedical applications. Recognized progress in animal cloning has been attained over time, but the overall efficiency of SCNT in pigs remains very low, based on the rate of healthy, live born piglets following embryo transfer. Accumulating evidence from studies in mice and other species indicate that new strategies for promoting chromatin and epigenetic reprogramming may represent the beginning of a new era for pig cloning.

Recurrent transcriptional responses in AML and MDS patients treated with decitabine

The molecular events responsible for decitabine responses in myelodysplastic syndrome and acute myeloid leukemia patients are poorly understood. Decitabine has a short serum half-life and limited stability in tissue culture. Therefore, theoretical pharmacologic differences may exist between patient molecular changes in vitro and the consequences of in vivo treatment. To systematically identify the global genomic and transcriptomic alterations induced by decitabine in vivo, we evaluated primary bone marrow samples that were collected during patient treatment and applied whole-genome bisulfite sequencing, RNA-sequencing, and single-cell RNA sequencing. Decitabine induced global, reversible hypomethylation after 10 days of therapy in all patients, which was associated with induction of interferon-induced pathways, the expression of endogenous retroviral elements, and inhibition of erythroid-related transcripts, recapitulating many effects seen previously in in vitro studies. However, at relapse after decitabine treatment, interferon-induced transcripts remained elevated relative to day 0, but erythroid-related transcripts now were more highly expressed than at day 0. Clinical responses were not correlated with epigenetic or transcriptional signatures, although sample size and interpatient variance restricted the statistical power required for capturing smaller effects. Collectively, these data define global hypomethylation by decitabine and find that erythroid-related pathways may be relevant because they are inhibited by therapy and reverse at relapse.

Production of Pigs From Porcine Embryos Generated in vitro

Generating porcine embryos in vitro is a critical process for creating genetically modified pigs as agricultural and biomedical models; however, these embryo technologies have been scarcely applied by the swine industry. Currently, the primary issue with in vitro-produced porcine embryos is low pregnancy rate after transfer and small litter size, which may be exasperated by micromanipulation procedures. Thus, in this review, we discuss improvements that have been made to the in vitro porcine embryo production system to increase the number of live piglets per pregnancy as well as abnormalities in the embryos and piglets that may arise from in vitro culture and manipulation techniques. Furthermore, we examine areas related to embryo production and transfer where improvements are warranted that will have direct applications for increasing pregnancy rate after transfer and the number of live born piglets per litter.

Sex difference in adrenal developmental toxicity induced by dexamethasone and its intrauterine programming mechanism

Dexamethasone is widely used to treat preterm labor and related diseases. However, prenatal dexamethasone treatment (PDT) can cause multiorgan developmental toxicities in offspring. Our previous study found that the occurrence of fetal-originated diseases was associated with adrenal developmental programming alterations in offspring. Here, we investigated the effects of PDT on adrenal function in offspring and its intrauterine programming mechanism. A rat model of PDT was established to observe the alterations of adrenal steroidogenesis in offspring. Furthermore, we confirmed the sex differences of adrenal steroidogenesis and its molecular mechanism combined with in vivo and in vitro experiments. PDT caused a decrease in adrenal steroidogenic function in fetal rats, but it was decreased in males and increased in females after birth. Meanwhile, the adrenal H3K14ac level and expression of 11β-hydroxysteroid dehydrogenase 2 (11β-HSD2) in PDT offspring were decreased in males and increased in females, suggesting that 11β-HSD2 might mediate sex differences in adrenal function. We further confirmed that dexamethasone inhibited the H3K14ac level and expression of 11β-HSD2 through the GR/SP1/p300 pathway. After bilateral testectomy or ovariectomy of adult PDT offspring rats, adrenal 11β-HSD2 expression and steroidogenic function were both reduced. Using rat primary fetal adrenal cells, the differential expression of AR and ERβ was proven to be involved in regulating the sex difference in 11β-HSD2 expression. This study demonstrated the sex difference in adrenal steroidogenic function of PDT offspring after birth and elucidated a sex hormone receptor-dependent epigenetically regulating mechanism for adrenal 11β-HSD2 programming alteration.

Nuclear Transfer Arrest Embryos Show Massive Dysregulation of Genes Involved in Transcription Pathways

Somatic cell nuclear transfer (SCNT) technology can reprogram terminally differentiated cell nuclei into a totipotent state. However, the underlying molecular barriers of SCNT embryo development remain incompletely elucidated. Here, we observed that transcription-related pathways were incompletely activated in nuclear transfer arrest (NTA) embryos compared to normal SCNT embryos and in vivo fertilized (WT) embryos, which hinders the development of SCNT embryos. We further revealed the transcription pathway associated gene regulatory networks (GRNs) and found the aberrant transcription pathways can lead to the massive dysregulation of genes in NTA embryos. The predicted target genes of transcription pathways contain a series of crucial factors in WT embryos, which play an important role in catabolic process, pluripotency regulation, epigenetic modification and signal transduction. In NTA embryos, however, these genes were varying degrees of inhibition and show a defect in synergy. Overall, our research found that the incomplete activation of transcription pathways is another potential molecular barrier for SCNT embryos besides the incomplete reprogramming of epigenetic modifications, broadening the understanding of molecular mechanism of SCNT embryonic development.

Investigating Markers of Reprogramming Potential in Somatic Cell Lines Derived from Matched Donors

Somatic cell biobanking and related technologies, somatic cell nuclear transfer (SCNT), and induction of pluripotent stem cells offer significant promise for wildlife conservation, but have yet to achieve optimal success. Inefficiency and variability in outcome have been linked to incomplete nuclear reprogramming, highlighting the importance of donor cell contribution. Studies show significant differences in SCNT outcome in donor cell lines within and between individuals, highlighting the necessity for a standardized characterization method to evaluate cell line reprogramming potential. Stringently standardized bovine fibroblast cell lines were generated and assessed for inter- and intraindividual variability on cellular (morphology, chromosome number, apoptotic incidence; Experiment 1) and molecular (pluripotency and epigenetic-related gene expression; Experiment 2) levels encompassing putative biomarkers of reprogramming potential. Cellular parameters were similar across cell lines. While some statistically significant differences were observed in DNMT1, DNMT3B, and HAT1, but not HDAC1, their biological relevance could not be determined with the information at hand. This study lays the foundation for understanding cellular characteristics in cultured cell lines; however, further studies are required to determine any correlation with reprogramming potential.

GR/Sp3/HDAC1/UGDH signaling participated in the maternal dexamethasone-induced dysplasia of the rat fetal growth plate

Maternal dexamethasone decreases the body length of the newborn. However, whether dexamethasone inhibits the development of the growth plate of the fetal long bone is still unknown. Here, we found that lengths of fetal femur and growth plate were both shorter in the fetuses with maternal dexamethasone (0.2 mg/kg.d from gestation day 9 to 20), with a decreased proteoglycan content of the growth plate in the fetal rat. Notable decreases in both the gene expression and H3K9 acetylation of UDP-glucose dehydrogenase (Ugdh) gene, which codes a key enzyme in the proteoglycan biosynthesis in the chondrocyte, were also observed. Meanwhile, up-regulation of glucocorticoid receptor (GR), specific protein 3 (Sp3), and histone deacetylase 1 (Hdac1) gene expression were detected in the fetal growth plate. Similar changes were also observed in the chondrogenic rat bone marrow stromal cells (BMSCs) with excessive exogenous dexamethasone. However, antagonizing GR with RU486 and silencing Hdac1 or Sp3 with specific siRNAs could all stimulate the H3K9 acetylation and gene expression of Ugdh previously inhibited by dexamethasone. Meanwhile, dexamethasone also induced the nuclear translocation of GR, which further directly bound to the Ugdh promoter and interacted with HDAC1 and Sp3, respectively. Collectively, our study revealed that maternal dexamethasone induced the direct binding of GR to the Ugdh promoter of the chondrocyte in the rat fetal growth plate, which recruited HDAC1 and Sp3, induced deacetylation of the H3K9, and subsequently inhibited Ugdh gene expression. Such changes further led to attenuated proteoglycan synthesis in the developing chondrocyte and therefore disrupted the development of growth plate and fetal long bone.

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.

The multiple roles of Thy-1 in cell differentiation and regeneration

Thy-1 is a 25-37 kDa glycophosphatidylinositol (GPI)-anchored cell surface protein that was discovered more than 50 years ago. Recent findings have suggested that Thy-1 is expressed on thymocytes, mesenchymal stem cells (MSCs), cancer stem cells, hematopoietic stem cells, fibroblasts, myofibroblasts, endothelial cells, neuronal smooth muscle cells, and pan T cells. Thy-1 plays vital roles in cell migration, adhesion, differentiation, transdifferentiation, apoptosis, mechanotransduction, and cell division, which in turn are involved in tumor development, pulmonary fibrosis, neurite outgrowth, and T cell activation. Studies have increasingly indicated a significant role of Thy-1 in cell differentiation and regeneration. However, despite recent research, many questions remain regarding the roles of Thy-1 in cell differentiation and regeneration. This review aimed to summarize the roles of Thy-1 in cell differentiation and regeneration. Furthermore, since Thy-1 is an outer leaflet membrane protein anchored by GPI, we attempted to address how Thy-1 regulates intracellular pathways through cis and trans signals. Due to the complexity and mystery surrounding the issue, we also summarized the Thy-1-related pathways in different biological processes, and this might provide novel insights in the field of cell differentiation and regeneration.

Melatonin Enhances the Development of Porcine Cloned Embryos by Improving DNA Methylation Reprogramming

Incomplete DNA methylation reprogramming in cloned embryos leads to poor cloning efficiency. Melatonin has been proven to improve the development of cloned embryos, however, the role of melatonin during somatic cell nuclear transfer remains unclear. This work demonstrated that 10^-7 M melatonin significantly enhanced the developmental progress, reduced the arrested rate before zygotic genome activation, and upregulated the blastocyst rate of cloned embryos. Melatonin also promoted the pseudo-pronucleus formation, increased blastocyst cell number, and reduced embryo apoptosis through upregulating the expression of antiapoptosis factors while downregulating the transcription of proapoptosis genes. Further study displayed that DNA methylation reprogramming related genes were greatly improved in cloned embryos when treated with melatonin; then, melatonin effectively promoted genomic DNA demethylation and DNA remethylation, DNA demethylation of pluripotency related gene Oct4, DNA methylation maintenance of imprinted gene H19/Igf2, and DNA remethylation of tissue-specific gene Thy1 in cloned embryos. Thus, zygotic genome activation related gene Eif1a, pluripotency related genes Oct4, Nanog, and Sox2, imprinted genes Igf2 and H19, and blastocyst quality related genes Cdx2 and ATP1b1 were remarkably upregulated, and tissue-specific genes Thy1 and Col5a2 were considerably silenced. In conclusion, melatonin enhanced the development of cloned embryos by ameliorating DNA methylation reprogramming. This work reveals that melatonin can regulate DNA methylation reprogramming and provides a novel insight to improve cloning efficiency.

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.

Enhancement of in Vitro Developmental Outcome of Cloned Goat Embryos After Epigenetic Modulation of Somatic Cell-Inherited Nuclear Genome with Trichostatin A

In this study, the effect of trichostatin A (TSA)-mediated epigenomic modulation of nuclear donor cells on the in vitro developmental potential of caprine somatic cell cloned embryos was examined. The enucleated ex vivo-matured oocytes were subzonally injected with adult ear skin-derived fibroblast cells exposed or not exposed to TSA (at a concentration of 50 nM). The experiment was designed on the basis of three different approaches to TSA-dependent modulation of donor cell-descended genome: before being used for somatic cell nuclear transfer/SCNT (Group I); immediately after activation of nuclear-transferred (NT) oocytes (Group II); or combined treatment both before being used for SCNT and after activation of NT oocytes (Group III). In the control Group IV, donor cell nuclei have not been treated with TSA at any stage of the experimental design. In TSA-treated Groups I and II and untreated Group IV, cleavage activities of cloned embryos were at the similar levels (80.6%, 79.8% and 77.1%, respectively). But, significant difference was observed between Groups III and IV (85.3 vs. 77.1%). Moreover, in the experimental Groups I and III, the percentages of cloned embryos that reached the blastocyst stages remarkably increased as compared to those noticed in the control Group IV (31.2% vs. 36.7% vs. 18.9%, respectively). In turn, among embryos assigned to Group II, blastocyst formation rate was only slightly higher than that in the control Group IV, but the differences were not statistically significant (25.8% vs. 18.9%). To sum up, TSA-based epigenomic modulation of somatic cell-inherited nuclear genome gave rise to increased competences of caprine cloned embryos to complete their development to blastocyst stages. In particular, sequential TSA-mediated modulation of both nuclear donor cells and activated NT oocytes led to improvement in the blastocyst yields of cloned goat embryos, which can result from enhanced donor cell nuclear reprogrammability.

Zebularine significantly improves the preimplantation development of ovine somatic cell nuclear transfer embryos

Aberrant DNA methylation reduces the developmental competence of mammalian somatic cell nuclear transfer (SCNT) embryos. Thus, hypomethylation-associated drugs are beneficial for improving reprogramming efficiency. Therefore, in the present study we investigated the effect of zebularine, a relatively novel DNA methyltransferase inhibitor, on the developmental potential of ovine SCNT embryos. First, reduced overall DNA methylation patterns and gene-specific DNA methylation levels at the promoter regions of pluripotency genes (octamer-binding transcription factor 4 (Oct4), SRY (sex determining region Y)-box 2 (Sox2) and Nanog) were found in zebularine-treated cumulus cells. In addition, the DNA methylation levels in SCNT embryos derived from zebularine-treated cumulus cells were significantly reduced at the 2-, 4-, 8-cell, and blastocyst stages compared with their corresponding controls (P<0.05). The blastocyst rate was significantly improved in SCNT embryos reconstructed by the cumulus donor cells treated with 5nM zebularine for 12h compared with the control group (25.4±1.6 vs 11.8±1.7%, P<0.05). Moreover, the abundance of Oct4 and Sox2 mRNA was significantly increased during the preimplantation stages after zebularine treatment (P<0.05). In conclusion, the results indicate that, in an ovine model, zebularine decreases overall DNA methylation levels in donor cumulus cells and reconstructed embryos, downregulates the DNA methylation profile in the promoter region of pluripotency genes in donor cells and ultimately elevates the expression of pluripotency genes in the reconstructed embryos, which can lead to improved development of SCNT embryos.

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.

Expression of pluripotency-related genes is highly dependent on trichostatin A-assisted epigenomic modulation of porcine mesenchymal stem cells analysed for apoptosis and subsequently used for generating cloned embryos

The present study sought to examine whether trichostatin A (TSA)-assisted epigenetic transformation of porcine bone marrow (BM)-derived mesenchymal stem cells (BM-MSCs) affects the transcriptional activities of pluripotency-related genes (Oct4, Nanog, c-Myc, Sox2 and Rex1), multipotent stemness-related gene (Nestin) and anti-apoptotic/anti-senescence-related gene (Survivin). Epigenetically transformed or non-transformed BM-MSCs that had been transcriptionally profiled by qRT-PCR and had been analysed for different stages of apoptosis progression provided a source of nuclear donor cells for the in vitro production of cloned pig embryos. TSA-mediated epigenomic modulation has been found to enhance the multipotency extent, stemness and intracellular anti-ageing properties of porcine BM-MSCs. This has been confirmed by the relative abundances for Nanog, c-Myc Rex1, Sox2 and Survivin mRNAs in TSA-exposed BM-MSCs that turned out to be significantly higher than those of TSA-unexposed BM-MSCs. Additionally, TSA-assisted epigenomic modulation of BM-MSCs did not impact the caspase-8 activity, Bax protein expression and the incidence of TUNEL-positive cells. In conclusion, the considerably elevated quantitative profiles of Sox2, Rex1, c-Myc, Nanog and Survivin mRNA transcripts seem to trigger improved reprogrammability of TSA-treated BM-MSC nuclei in cloned pig embryos that thereby displayed remarkably increased blastocyst formation rates as compared to those noticed for embryos derived from TSA-untreated BM-MSCs.

Use of trichostatin A alters the expression of HDAC3 and KAT2 and improves in vitro development of bovine embryos cloned using less methylated mesenchymal stem cells

The aim of this work was to investigate the methylation and hydroxymethylation status of mesenchymal stem cells (MSC) from amniotic fluid (MSC-AF), adipose tissue (MSC-AT) and fibroblasts (FIB-control) and to verify the effect of trichostatin A (TSA) on gene expression and development of cloned bovine embryos produced using these cells. Characterization of MSC from two animals (BOV1 and BOV2) was performed by flow cytometry, immunophenotyping and analysis of cellular differentiation genes expression. The cells were used in the nuclear transfer in the absence or presence of 50 nM TSA for 20 hr in embryo culture. Expression of HDAC1, HDAC3 and KAT2A genes was measured in embryos by qRT-PCR. Methylation results showed difference between animals, with MSC from BOV2 demonstrating lower methylation rate than BOV1. Meanwhile, MSC-AF were less hydroxymethylated for both animals. MSC-AF from BOV2 produced 44.92 ± 8.88% of blastocysts when embryos were exposed to TSA and similar to embryo rate of MSC-AT also treated with TSA (37.96 ± 15.80%). However, when methylation was lower in FIB compared to MSC, as found in BOV1, the use of TSA was not sufficient to increase embryo production. MSC-AF embryos expressed less HDAC3 when treated with TSA, and expression of KAT2A was higher in embryos produced with all MSC and treated with TSA than embryos produced with FIB. The use of MSC less methylated and more hydroxymethylated in combination with embryo incubation with TSA can induce lower expression of HDAC3 and higher expression of KAT2A in the embryos and consequently improve bovine embryo production.

Dnmt1s in donor cells is a barrier to SCNT-mediated DNA methylation reprogramming in pigs

Low development of somatic cell nuclear transfer embryos could be due to the incomplete DNA methylation reprogramming, and Dnmt1s existing in donor cells may be one cause of this disrupted DNA methylation reprogramming. However, the reprogramming pattern of Dnmt1s and its effect on DNA methylation reprogramming in cloned embryos remain poorly understood. Here, we displayed that along with the significantly higher Dnmt1 expression at the zygotic gene activation stage of cloned embryos, genomic methylation level was markedly upregulated, and the arrested rate was significantly higher compared with their in vitro fertilization counterparts. Then, we demonstrated that Dnmt1s, not Dnmt1o, methylation and expression levels in cloned embryos were significantly higher from the 1-cell to 4-cell stage but markedly lower at the blastocyst stage. When Dnmt1s in donor cells was appropriately removed, more cloned embryos passed through the zygotic gene activation stage and the blastocyst rate significantly increased. Furthermore, Dnmt1s knockdown significantly improved itself and genomic methylation reconstruction in cloned embryos. Finally, we found that Dnmt1s removal significantly promoted the demethylation and expression of pluripotent genes in cloned embryos. Taken together, these data suggest that Dnmt1s in donor cells is a critical barrier to somatic cell nuclear transfer mediated DNA methylation reprogramming, impairing the development of cloned embryos.

Human histone deacetylase 6 shows strong preference for tubulin dimers over assembled microtubules

Human histone deacetylase 6 (HDAC6) is the major deacetylase responsible for removing the acetyl group from Lys40 of α-tubulin (αK40), which is located lumenally in polymerized microtubules. Here, we provide a detailed kinetic analysis of tubulin deacetylation and HDAC6/microtubule interactions using individual purified components. Our data unequivocally show that free tubulin dimers represent the preferred HDAC6 substrate, with a K _M value of 0.23 µM and a deacetylation rate over 1,500-fold higher than that of assembled microtubules. We attribute the lower deacetylation rate of microtubules to both longitudinal and lateral lattice interactions within tubulin polymers. Using TIRF microscopy, we directly visualized stochastic binding of HDAC6 to assembled microtubules without any detectable preferential binding to microtubule tips. Likewise, indirect immunofluorescence microscopy revealed that microtubule deacetylation by HDAC6 is carried out stochastically along the whole microtubule length, rather than from the open extremities. Our data thus complement prior studies on tubulin acetylation and further strengthen the rationale for the correlation between tubulin acetylation and microtubule age.

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.

MicroRNA-148a overexpression improves the early development of porcine somatic cell nuclear transfer embryos

Incomplete epigenetic reprogramming of donor cell nuclei is one of the main contributors to the low efficiency of somatic cell nuclear transfer (SCNT). To improve the success of SCNT, somatic cell DNA methylation levels must be reduced to those levels found in totipotent embryonic cells. Recent studies have demonstrated that miR-148a can affect DNA methylation via DNMT1 modulation in various cancers. Therefore, the focus of this study was to examine the influence of miR-148a on DNA methylation in donor cells and in SCNT embryo development. Thus, a stable cell line overexpressing miR-148a was established and used to produce SCNT embryos. Upon examination, DNMT1 was found to be a miR-148a target in porcine fetal fibroblasts (PFF). Furthermore, miR-148a overexpression in PFFs significantly decreased DNMT1 expression and global DNA methylation levels (P < 0.05). Moreover, miRNA-148a expression levels in SCNT embryos were significantly lower at the 2-cell and 4-cell stages when compared to IVF and parthenogenetic embryos. The group overexpressing miRNA-148a also showed a significant increase in blastocyst formation and total cell numbers (P < 0.05). Additionally, miR-148a overexpression altered the immunofluorescence signal of 5-mC and H3K9ac, and enhanced pluripotent gene (Oct4 and Nanog) expression levels during embryo development. These results indicate that miR-148a overexpression enhances the developmental potential of SCNT embryos and modifies epigenetic status.

TSA and BIX-01294 Induced Normal DNA and Histone Methylation and Increased Protein Expression in Porcine Somatic Cell Nuclear Transfer Embryos

The poor efficiency of animal cloning is mainly attributed to the defects in epigenetic reprogramming of donor cells' chromatins during early embryonic development. Previous studies indicated that inhibition of histone deacetylases or methyltransferase, such as G9A, using Trichostatin A (TSA) or BIX-01294 significantly enhanced the developmental efficiency of porcine somatic cell nuclear transfer (SCNT) embryos. However, potential mechanisms underlying the improved early developmental competence of SCNT embryos exposed to TSA and BIX-01294 are largely unclear. Here we found that 50 nM TSA or 1.0 μM BIX-01294 treatment alone for 24 h significantly elevated the blastocyst rate (P < 0.05), while further improvement was not observed under combined treatment condition. Furthermore, co-treatment or TSA treatment alone significantly reduced H3K9me2 level at the 4-cell stage, which is comparable with that in in vivo and in vitro fertilized counterparts. However, only co-treatment significantly decreased the levels of 5mC and H3K9me2 in trophectoderm lineage and subsequently increased the expression of OCT4 and CDX2 associated with ICM and TE lineage differentiation. Altogether, these results demonstrate that co-treatment of TSA and BIX-01294 enhances the early developmental competence of porcine SCNT embryos via improvements in epigenetic status and protein expression.

Genome-Wide Dynamic Profiling of Histone Methylation during Nuclear Transfer-Mediated Porcine Somatic Cell Reprogramming

The low full-term developmental efficiency of porcine somatic cell nuclear transfer (SCNT) embryos is mainly attributed to imperfect epigenetic reprogramming in the early embryos. However, dynamic expression patterns of histone methylation involved in epigenetic reprogramming progression during porcine SCNT embryo early development remain to be unknown. In this study, we characterized and compared the expression patterns of multiple histone methylation markers including transcriptionally repressive (H3K9me2, H3K9me3, H3K27me2, H3K27me3, H4K20me2 and H4K20me3) and active modifications (H3K4me2, H3K4me3, H3K36me2, H3K36me3, H3K79me2 and H3K79me3) in SCNT early embryos from different developmental stages with that from in vitro fertilization (IVF) counterparts. We found that the expression level of H3K9me2, H3K9me3 and H4K20me3 of SCNT embryos from 1-cell to 4-cell stages was significantly higher than that in the IVF embryos. We also detected a symmetric distribution pattern of H3K9me2 between inner cell mass (ICM) and trophectoderm (TE) in SCNT blastocysts. The expression level of H3K9me2 in both lineages from SCNT expanded blastocyst onwards was significantly higher than that in IVF counterparts. The expression level of H4K20me2 was significantly lower in SCNT embryos from morula to blastocyst stage compared with IVF embryos. However, no aberrant dynamic reprogramming of H3K27me2/3 occurred during early developmental stages of SCNT embryos. The expression of H3K4me3 was higher in SCNT embryos at 4-cell stage than that of IVF embryos. H3K4me2 expression in SCNT embryos from 8-cell stage to blastocyst stage was lower than that in the IVF embryos. Dynamic patterns of other active histone methylation markers were similar between SCNT and IVF embryos. Taken together, histone methylation exhibited developmentally stage-specific abnormal expression patterns in porcine SCNT early embryos.

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.