Analysis of Development-Related Gene Expression in Cloned Bovine Blastocysts with Different Developmental Potential

Expression profile of developmental competence gene markers in comparison with prostaglandin F2α synthesis and action in the early- and late-cleaved pre-implantation bovine embryos

The kinetics of early cleavage stages can affect embryo quality. The bovine model of early- and late-cleaved embryos has been described in the literature and is deemed a useful tool in the field of oocyte developmental competence studies. The expression of genes demonstrating developmental potential differs between early- and late-cleaved embryos. Previously, we demonstrated that prostaglandin F_2α synthase (PGFS) and prostaglandin F_2α receptor (PTGFR) expression depend on the developmental stage and embryo quality. In the present study, we used the same model to determine the mRNA expression profile of developmentally important genes (IGF1R, IGF2R, PLAC8, OCT4, SOX2) in early, expanded and hatched blastocysts obtained from the early- and late-cleaved group of embryos, as well as to correlate the transcription levels of these embryonic gene markers with the transcription levels of PGFS and PTGFR. The mRNA expression of PGFS, PTGFR and factors described as gene markers of embryonic implantation ability and developmental competence genes was determined by real-time PCR. The obtained results were analysed using statistical software GraphPad prism 6.05. During the course of our analyses, we observed that the transcript abundance of most analysed genes tends to be higher in the late-rather than in the early cleaved group of embryos, as well as in B and/or C grade embryos rather than in A grade embryos. On the other hand, for the early cleaved group of blastocysts with cavity, we detected higher PLAC8 mRNA expression for grade A embryos compared with grade C embryos. It suggests that the mRNA expression level of genes depends on the quality of embryos but differs according to various factors including the method of production or culture method. Moreover, numerous correlations between analysed gene markers and PGF_2α synthase and PGF_2α receptor suggest that PGF_2α plays a role in the crucial steps of bovine embryo development.

Gene expression and lymphocyte population at the fetal-maternal interface in sheep pregnancies established by somatic cell nuclear transfer

The hypothesis of this study was that the leukocyte populations and expression levels of genes related to immune response, growth factors and apoptosis would be altered at the fetal-maternal interface in somatic cell nuclear transfer (SCNT)-generated sheep pregnancies. Placental and endometrial samples from sheep pregnancies established by SCNT and natural breeding (control) were collected at 45 days and at term. Expression of genes related to growth factors, apoptosis and immune response was examined using quantitative reverse transcription polymerase chain reaction. Endometrial leukocyte populations and major histocompatibility class I (MHC-I) protein expression were examined by immunohistochemistry. At term we observed altered expression of genes related to apoptosis, growth factors and immune response in placental and endometrial tissue of SCNT pregnancies. In Day-45 pregnancies there was less-pronounced abnormal expression and only genes related to apoptosis and growth factors were abnormal in the placenta. Endometrial gene expression profiles were similar to age-matched controls. Placental MHC-I protein expression was similar in SCNT and controls at 45 days but increased in the SCNT at term. The altered gene expression at the fetal-maternal interface likely contributes to the placental dysfunction and overgrowth observed in sheep SCNT pregnancies.

Mitogen-Activated Protein Kinase Activity Is Not Essential for the First Step of Nuclear Reprogramming in Bovine Somatic Cell Nuclear Transfer

For reprogramming a somatic nucleus during mammalian cloning, metaphase of the second meiotic division (MII) oocytes has been widely used as recipient cytoplasm. High activity of maturation-promoting factor (MPF) and mitogen-activated protein kinase (MAPK) is believed to accelerate the remodeling and/or reprogramming of a somatic nucleus introduced into the ooplasm by somatic cell nuclear transfer. We demonstrated previously that the first step in nuclear reprogramming is not directly regulated by MPF and MAPK because activated oocytes in which MPF activity is diminished and MAPK activity is maintained can develop to the blastocyst stage after receiving an M phase somatic nucleus in bovine cloning. In this study, our aim was to test whether MAPK activity is necessary for the first step in nuclear reprogramming and/or chromatin remodeling (phosphorylation of histone H3 at Ser3, trimethylation of histone H3 at Lys 9, and acetylation of histone H3 at Lys14) in bovine somatic cloning. We found that it was not necessary, and neither was MPF activity.

Differences in developmental competence and gene expression profiles between buffalo (Bubalus bubalis) preimplantation embryos cultured in three different embryo culture media

The objective of this study was to compare effects of in vitro culture systems on embryonic development and expression patterns of developmentally important genes in preimplantation buffalo embryos. After IVM/IVF presumptive zygotes were cultured in one of three systems: undefined TCM-199, mCR2aa medium supplemented with 10 % FBS and defined PVA-myo-inositol-phosphate-EGF medium. No (P > 0.05) differences at 2-cell, 4-cell and 8-cell to 16- cell stages were observed among the three cultured media used, however, increased (P < 0.05) blastocyst yield, cell number and hatching rate were found in defined medium compared to undefined media. The expression patterns of genes implicated in embryo metabolism (GLUT-1), anti-apoptosis (BCL-2), imprinting (IGF-2R), DNA methylation (DNMT-3A) and maternal recognition of pregnancy (IFNT) were increased (P < 0.05) in hatched blastocysts derived from defined medium compared to undefined media. In conclusion, serum-free, defined medium improved developmental competence of in vitro cultured buffalo embryos. Whether these differences in morphological development and gene expression have long-term effects on buffalo calves born after embryo transfer remains unknown. However, it is possible that early adaptations of the preimplantation embryo to its environment persist during fetal and post-natal development.

Establishment of cell-based transposon-mediated transgenesis in cattle

Transposon-mediated transgenesis is a well-established tool for genome modification in small animal models. However, translation of this active transgenic method to large animals warrants further investigations. Here, the piggyBac (PB) and sleeping beauty (SB) transposon systems were assessed for stable gene transfer into the cattle genome. Bovine fibroblasts were transfected either with a helper-independent PB system or a binary SB system. Both transposons were highly active in bovine cells increasing the efficiency of DNA integration up to 88 times over basal nonfacilitated integrations in a colony formation assay. SB transposase catalyzed multiplex transgene integrations in fibroblast cells transfected with the helper vector and two donor vectors carrying different transgenes (fluorophore and neomycin resistance). Stably transfected fibroblasts were used for SCNT and on in vitro embryo culture, morphologically normal blastocysts that expressed the fluorophore were obtained with both transposon systems. The data indicate that transposition is a feasible approach for genetic engineering in the cattle genome.

Differential developmental competence and gene expression patterns in buffalo (Bubalus bubalis) nuclear transfer embryos reconstructed with fetal fibroblasts and amnion mesenchymal stem cells

The developmental ability and gene expression pattern at 8- to 16-cell and blastocyst stages of buffalo (Bubalus bubalis) nuclear transfer (NT) embryos from fetal fibroblasts (FFs), amnion mesenchymal stem cells (AMSCs) and in vitro fertilized (IVF) embryos were compared in the present studies. The in vitro expanded buffalo FFs showed a typical "S" shape growth curve with a doubling time of 41.4 h and stained positive for vimentin. The in vitro cultured undifferentiated AMSCs showed a doubling time of 39.5 h and stained positive for alkaline phosphatase, and these cells also showed expression of pluripotency markers (OCT 4, SOX 2, NANOG), and mesenchymal stem cell markers (CD29, CD44) and were negative for haematopoietic marker (CD34) genes at different passages. Further, when AMSCs were exposed to corresponding induction conditions, these cells differentiated into adipogenic, chondrogenic and osteogenic lineages which were confirmed through oil red O, alcian blue and alizarin staining, respectively. Donor cells at 3-4 passage were employed for NT. The cleavage rate was significantly (P < 0.05) higher in IVF than in FF-NT and AMSC-NT embryos (82.6 ± 8.2 vs. 64.6 ± 1.3 and 72.3 ± 2.2 %, respectively). However, blastocyst rates in IVF and AMSC-NT embryos (30.6 ± 2.7 and 28.9 ± 3.1 %) did not differ and were significantly (P < 0.05) higher than FF-NT (19.5 ± 1.8 %). Total cell number did not show significant (P > 0.05) differences between IVF and AMSC-NT embryos (186.7 ± 4.2, 171.2 ± 3.8, respectively) but were significantly (P < 0.05) higher than that from FF-NT (151.3 ± 4.1). Alterations in the expression pattern of genes implicated in transcription and pluripotency (OCT4, STAT3, NANOG), DNA methylation (DNMT1, DNMT3A), histone deacetylation (HDAC2), growth factor signaling and imprinting (IGF2, IGF2R), apoptosis (BAX, BCL2), metabolism (GLUT1) and oxidative stress (MnSOD) regulation were observed in cloned embryos. The transcripts or expression patterns in AMSC-NT embryos more closely followed that of the in vitro derived embryos compared with FF-NT embryos. The results demonstrate that multipotent amnion MSCs have a greater potential as donor cells than FFs in achieving enhanced production of cloned buffalo embryos.

Transcriptomic Features of Bovine Blastocysts Derived by Somatic Cell Nuclear Transfer

Reprogramming incompletely occurs in most somatic cell nuclear transfer (SCNT) embryos, which results in misregulation of developmentally important genes and subsequent embryonic malfunction and lethality. Here we examined transcriptome profiles in single bovine blastocysts derived by in vitro fertilization (IVF) and SCNT. Different types of donor cells, cumulus cell and ear-skin fibroblast, were used to derive cSCNT and fSCNT blastocysts, respectively. SCNT blastocysts expressed 13,606 genes on average, similar to IVF (13,542). Correlation analysis found that both cSCNT and fSCNT blastocyst groups had transcriptomic features distinctive from the IVF group, with the cSCNT transcriptomes closer to the IVF ones than the fSCNT. Gene expression analysis identified 56 underrepresented and 78 overrepresented differentially expressed genes in both SCNT groups. A 400-kb locus harboring zinc-finger protein family genes in chromosome 18 were found coordinately down-regulated in fSCNT blastocysts, showing a feature of reprogramming-resistant regions. Probing into different categories of genes important for blastocyst development revealed that genes involved in trophectoderm development frequently were underrepresented, and those encoding epigenetic modifiers tended to be overrepresented in SCNT blastocysts. Our effort to identify reprogramming-resistant, differentially expressed genes can help map reprogramming error-prone loci onto the genome and elucidate how to handle the stochastic events of reprogramming to improve cloning efficiency.

A comparative study on expression profile of developmentally important genes during pre-implantation stages in buffalo hand-made cloned embryos derived from adult fibroblasts and amniotic fluid derived stem cells

Abnormal gene expression in somatic cell nuclear transfer embryos due to aberrant epigenetic modifications of the donor nucleus may account for much of the observed diminished viability and developmental abnormalities. The present study compared the developmentally important gene expression pattern at 4-cell, 8- to 16-cell, morula, and blastocyst stages of buffalo nuclear transfer (NT) embryos from adult fibroblasts (AFs) and amniotic fluid stem cells (AFSCs). In vitro fertilized embryos were used as control embryos. Alterations in the expression pattern of genes implicated in transcription and pluripotency (OCT4, STAT3, NANOG), DNA methylation (DNMT1, DNMT3A), histone deacetylation (HDAC2), growth factor signaling, and imprinting (IGF2, IGF2R), apoptosis (BAX, BCL2), oxidative stress (MnSOD), metabolism (GLUT1) regulation were observed in cloned embryos. The expression of transcripts in AFSC-NT embryos more closely followed that of the in vitro fertilized embryos compared with AF-NT embryos. It is concluded that AFSCs with a relatively undifferentiated genome may serve as suitable donors which could be reprogrammed more efficiently to reactivate expression of early embryonic genes in buffalo NT.

Expression profile of developmentally important genes between hand-made cloned buffalo embryos produced from reprogramming of donor cell with oocytes extract and selection of recipient cytoplast through brilliant cresyl blue staining and in vitro fertilized embryos

PURPOSE

To compare the expression profile of developmentally important genes between hand-made cloned buffalo embryos produced from reprogramming of donor cell with oocyte extracts and selection of recipient cytoplast through brilliant cresyl blue staining and in vitro fertilized (IVF) embryos.

METHODS

Hand-made cloned embryos were produced using oocyte extracts treated donor cells and brilliant cresyl blue (BCB) stained recipient cytoplasts. IVF embryos were produced by culturing 15-20 COCs in BO capacitated sperms from frozen thawed buffalo semen and the mRNA expression patterns of genes implicated in metabolism (GLUT1), pluripotency (OCT4), DNA methylation (DNMT1), pro- apoptosis (BAX) and anti-apoptosis (BCL2) were evaluated at 8- to16- cell stage embryos.

RESULTS

A significantly (P < 0.05) higher number of 8- to16- cell and blastocyst stages (73.9 %, 32.8 %, respectively) were reported in hand-made cloning (HMC) as compared to in vitro fertilization (49.2 %, 24.2 %, respectively). The amount of RNA recovered from 8- to 16- cell embryos of HMC and in vitro fertilization did not appear to be influenced by the method of embryo generation (3.76 ± 0.61 and 3.82 ± 0.62 ng/μl for HMC and in vitro fertilization embryos, respectively). There were no differences in the expression of the mRNA transcripts of genes (GLUT1, OCT4, DNMT1, BAX and BCL2) were analysed by real-time PCR between hand-made cloned and IVF embryos.

CONCLUSIONS

Pre-treatment of donor cells with oocyte extracts and selection of developmentally competent oocytes through BCB staining for recipient cytoplast preparations may enhance expression of developmentally important genes GLUT1, OCT4, DNMT1, BAX, and BCL2 in hand-made cloned embryos at levels similar to IVF counterparts. These results also support the notion that if developmental differences observed in HMC and in vitro fertilization produced foetuses and neonates are the results of aberrant gene expression during the pre-implantation stage, those differences in expression are subtle or appear after the maternal to zygotic transition stage of development.

Transcriptome profile of bovine elongated conceptus obtained from SCNT and IVP pregnancies

In the present study we analyzed the gene expression changes induced by somatic cell nuclear transfer (SCNT) and in vitro production (IVP) in bovine elongated embryos using Affymetrix bovine genome array. For this, Day-16 bovine embryos from SCNT, IVP, and artificial insemination (AI) were recovered from recipients and used for transcriptome analysis. Despite comparable in vivo development rates, considerable reduction in elongation size was observed in SCNT compared to non-cloned embryos (93.3 mm for SCNT vs. 186.6 mm and 196.3 mm for IVP and AI embryos, respectively). Gene expression analysis revealed that the transcript levels of 477 genes, which are involved in various pathways including arginine and proline or glycerolipid and fatty acid metabolism, were significantly altered in SCNT compared to AI embryos. Similarly, 365 genes were differentially expressed in IVP embryos compared to AI. Thus, several pathways including TNRF-1 signaling and tight junction pathways were affected. To predict whether the altered transcripts were associated with culture condition or errors in transcriptional reprogramming, unique or common differentially expressed genes were analyzed in SCNT and IVP embryos compared to AI or fibroblast donor cells. Accordingly, 71 transcripts were found to be not transcriptionally reprogrammed, as their expression resembled the donor cells more than AI embryos; the remaining transcripts were either partially or incompletely reprogrammed. In conclusion, the present study identified deviations in elongation size, gene expression, and the corresponding molecular pathways in Day-16 SCNT and IVP conceptuses compared to their AI counterparts, which may subsequently be associated with the outcome of fetal development.

Recent progress in bovine somatic cell nuclear transfer

Bovine somatic cell nuclear transfer (SCNT) embryos can develop to the blastocyst stage at a rate similar to that of embryos produced by in vitro fertilization. However, the full-term developmental rate of SCNT embryos is very low, owing to the high embryonic and fetal losses after embryo transfer. In addition, increased birth weight and postnatal mortality are observed at high rates in cloned calves. The low efficiency of SCNT is probably attributed to incomplete reprogramming of the donor nucleus and most of the developmental problems of clones are thought to be caused by epigenetic defects. Applications of SCNT will depend on improvement in the efficiency of production of healthy cloned calves. In this review, we discuss problems and recent progress in bovine SCNT.

Epigenetic status and full-term development of bovine cloned embryos treated with trichostatin A

We examined the comprehensive epigenetic status, including histone H3 and H4 acetylation, DNA methylation and level of mRNA transcripts of bovine somatic cell nuclear transfer (SCNT) embryos treated with trichostatin A (TSA), along with their full-term developmental efficacy. Treatment with 50 nM TSA enhanced early developmental competence; increased acetylation of two histones, H3K9K14 and H4K8, at the blastocyst stage; and maintained the DNA methylation status of the satelliteI sequence in bovine SCNT embryos. The difference in IGFBP-3 transcript levels between in vivo and SCNT embryos disappeared in SCNT embryos after treatment with 50 nM TSA. Pregnancy, full-term developmental competence and body weight at birth of offspring did not differ between SCNT embryos treated with 50 nM TSA and untreated embryos. These results suggest that treatment with TSA improves preimplantation development and changes the epigenetic status but does not promote the full-term development competence in bovine SCNT embryos.

Aberrant expression patterns of genes involved in segregation of inner cell mass and trophectoderm lineages in bovine embryos derived from somatic cell nuclear transfer

High rates of embryonic, fetal, or placental abnormalities have consistently been observed in bovine cloning. Segregation of inner cell mass (ICM) and trophectoderm (TE) lineages in early embryos is an important process for fetal and placental formation. In mouse embryos, differentiation of ICM and TE is regulated by various transcription factors, such as OCT-4, CDX2, and TEAD4, but molecular mechanisms that regulate differentiation in bovine embryos remain unknown. To clarify gene transcripts involved in segregation of ICM and TE lineages in bovine embryos, we examined the relative abundances of OCT-4, CDX2, TEAD4, GATA3, NANOG, and FGF4 transcripts in blastocyst embryos derived from in vitro fertilization (IVF). Furthermore, transcript levels of such genes in bovine embryos derived from somatic cell nuclear transfer (NT-SC) and in vivo (Vivo) were also compared. OCT-4, NANOG, and FGF4 transcript levels in IVF embryos were significantly higher in ICM than in TE. In contrast, the CDX2 transcript level was lower in ICM than in TE. In NT-SC embryos at the blastocyst stage, transcript levels of all genes except CDX2 were lower than that in Vivo embryos. In the elongated stage, expression levels of the six genes did not differ between NT-SC and Vivo embryos. We observed aberrant expression patterns of various genes involved in segregation of ICM and TE lineages in bovine NT-SC embryos. These results raise the possibility that abnormalities in the cloned fetus and placenta are related to the aberrant expression of genes involved in segregation and differentiation process in the early developmental stage.

Comparative potential of cultured skin fibroblast, cumulus, and granulosa cell to produce somatic cell nuclear transfer (SCNT) preimplantation embryos in buffaloes (Bubalus bubalis) in relation to gene expressions

To improve the efficiency of somatic cell nuclear transfer (SCNT)-derived embryos in buffaloes (Bubalus bubalis), skin fibroblast, cumulus, and granulosa cells were cultured up to the 15th passage and cloned embryos were produced from each cell type. At the 15th passage the cumulative population doublings (CPDs) in cumulus cells was higher (60.78) than skin fibroblast (57.12) and granulosa (56.05) cell lines. Gene expression of chromatin remodelling proteins, that is, HDAC1, DNMT1, DNMT3a, and DNMT3b, were comparable at all five passages (P-3, P-6, P-9, P-12, and P-15) groups in cumulus cells but different in skin fibroblast and granulosa cells. Cleavage and blastocyst production rate in cumulus (65.9 and 27.4%)-derived embryos was higher than skin fibroblast (63.8 and 24.3%) and granulosa (62.5 and 22.3%)-derived embryos. Expressions of HDAC1, DNMT1, and DNMT3a mRNA in cumulus-derived blastocysts were similar to IVF blastocysts (control), whereas skin fibroblast and granulosa-derived blastocysts expression was significantly different (p < or = 0.05). DNMT3b mRNA expression in all the three donor cell types and IVF control were similar. The expression pattern of these genes showed the effect of donor cell type with different epigenetic reprogramming capabilities for SCNT embryo production rate. Overall, results indicated that cumulus cells are the best nuclear donor for SCNT.

Genetic reprogramming of transcription factor ap-2gamma in bovine somatic cell nuclear transfer preimplantation embryos and placentomes

Bovine somatic cell nuclear transfer (SCNT) efficiency remains very low despite a tremendous amount of research devoted to its improvement over the past decade. Frequent early and mid-gestational losses are commonly accompanied by placental abnormalities. A transcription factor, activating protein AP-2gamma, has been shown to be necessary for proper placental development in the mouse. We first evaluated the expression of the gene coding for AP-2gamma (Tfap2c) in several bovine fibroblast donor cell lines and found it was not expressed. Subsequently we determined the expression profile of Tfap2c in oocytes and various stages of preimplantation in vitro fertilized (IVF) embryos. Tfap2c was undetectable in oocytes and early embryos, and was detectable at relatively high levels in morula and blastocyst IVF embryos. The lack of expression in oocytes and donor cells means Tfap2c must be induced in the zygote at the morula stage in properly reprogrammed embryos. SCNT embryos expressed Tfap2c at the eight-cell stage, 2 days earlier than control embryos. Control embryos first expressed Tfap2c at the morula stage, and at this stage Tfap2c was significantly lower in the SCNT embryos. No differences in expression were detected at the blastocyst stage. To determine whether Tfap2c was properly reprogrammed in the placenta of SCNT pregnancies, we evaluated its expression in cotyledons and caruncles of SCNT and control pregnancies between days 55 and 90 gestation. Expression of Tfap2c in caruncles significantly increased between days 55 and 90, while expression in cotyledons was relatively consistent over that same period. Expression levels in SCNT tissues were not different from controls. This data indicates Tfap2c expression is altered in early preimplantation SCNT embryos, which may have developmental consequences resulting from genes influenced by Tfap2c, but expression was not different at the blastocyst stage and in placentomes.

In vitro culture and somatic cell nuclear transfer affect imprinting of SNRPN gene in pre- and post-implantation stages of development in cattle

Background

Embryo in vitro manipulations during early development are thought to increase mortality by altering the epigenetic regulation of some imprinted genes. Using a bovine interspecies model with a single nucleotide polymorphism, we assessed the imprinting status of the small nuclear ribonucleoprotein polypeptide N (SNRPN) gene in bovine embryos produced by artificial insemination (AI), in vitro culture (IVF) and somatic cell nuclear transfer (SCNT) and correlated allelic expression with the DNA methylation patterns of a differentially methylated region (DMR) located on the SNRPN promoter.

Results

In the AI group, SNRPN maternal expression is silenced at day 17 and 40 of development and a third of the alleles analyzed are methylated in the DMR. In the IVF group, maternal transcripts were identified at day 17 but methylation levels were similar to the AI group. However, day-40 fetuses in the IVF group showed significantly less methylation when compared to the AI group and SNRPN expression was mostly paternal in all fetal tissues studied, except in placenta. Finally, the SCNT group presented severe loss of DMR methylation in both day-17 embryos and 40 fetuses and biallelic expression was observed in all stages and tissues analyzed.

Conclusion

Together these results suggest that artificial reproductive techniques, such as prolonged in vitro culture and SCNT, lead to abnormal reprogramming of imprinting of SNRPN gene by altering methylation levels at this locus.

Trichostatin A improves histone acetylation in bovine somatic cell nuclear transfer early embryos

Epigenetic aberrancies likely preclude correct and complete nuclear reprogramming following somatic cell nuclear transfer (SCNT), and may underlie the observed reduced viability of cloned embryos. In the present study, we tested the effects of the histone deacetylase inhibitor (HDACi), trichostatin A (TSA), on development and histone acetylation of cloned bovine preimplantation embryos. Our results indicated that treating activated reconstructed SCNT embryos with 50 nM TSA for 13 h produced eight-cell embryos with levels of acetylation of histone H4 at lysine 5 (AcH4K5) similar to fertilized counterparts and significantly greater than in control NT embryos (p < 0.005). Further, TSA treatment resulted in SCNT embryos with preimplantation developmental potential similar to fertilized counterparts, as no difference was observed in cleavage and blastocyst rates or in blastocyst total cell number (p > 0.05). Measurement of eight selected developmentally important genes in single blastocysts showed a similar expression profile among the three treatment groups, with the exception of Nanog, Cdx2, and DNMT3b, whose expression levels were higher in TSA-treated NT than in in vitro fertilized (IVF) embryos. Data presented herein demonstrate that TSA can improve at least one epigenetic mark in early cloned bovine embryos. However, evaluation of development to full-term is necessary to ascertain whether this effect reflects a true increase in developmental potential.

S-adenosylhomocysteine treatment of adult female fibroblasts alters X-chromosome inactivation and improves in vitro embryo development after somatic cell nuclear transfer

The poor outcome of somatic cell nuclear transfer (SCNT) is thought to be a consequence of incomplete reprogramming of the donor cell. The objective of this study was to investigate the effects of treatment withS-adenosylhomocysteine (SAH) a DNA demethylation agent, on DNA methylation levels and X-chromosome inactivation status of bovine female fibroblast donor cells and the subsequent impact on developmental potential after SCNT. Compared with non-treated controls, the cells treated with SAH revealed (i) significantly (P<0.05) reduced global DNA methylation, (ii) significantly (∼1.5-fold) increased telomerase activity, (iii) diminished distribution signals of methylated histones H3-3mK9 and H3-3mK27 on the presumptive inactive X-chromosome (Xi), (iv) alteration in the replication pattern of the Xi, and (v) elevation of transcript levels for X-chromosome linked genes,ANT3,MECP2,XIAP,XIST, andHPRT. SCNT embryos produced with SAH-treated donor cells compared with those derived from untreated donor cells revealed (i) similar cleavage frequencies, (ii) significant elevation in the frequencies of development of cleaved embryos to hatched blastocyst stage, and (iii) 1.5-fold increase in telomerase activity. We concluded that SAH induces global DNA demethylation that partially reactivates the Xi, and that a hypomethylated genome may facilitate the nuclear reprogramming process.

Aberrant gene expression in deceased transgenic cloned calves

Several transgenic cloned species have been obtained; however, the efficiency of transgenic cloning remains very low, even lower than cloning. Many experiments have demonstrated abnormal growth and development, and inappropriate gene expression in cloned animals. In this study, we examined the expression of 19 development-related genes in lungs of three normal controls and three aberrant transgenic cloned calves. Results showed in transgenic cloned calves, 84.2% genes had decreased expression levels, however, 5.3% genes had increased levels. This study suggests transgenic cloning and the aberrant expression would cause abnormal growth and development in transgenic cloned calves. To our knowledge, this is the first time that gene expression was examined in transgenic cloned cattle. These findings may have some implications in understanding the low efficiency of the transgenic cloning.

Aberrant epigenetic changes and gene expression in cloned cattle dying around birth

Background

Aberrant reprogramming of donor somatic cell nuclei may result in many severe problems in animal cloning. To assess the extent of abnormal epigenetic modifications and gene expression in clones, we simultaneously examined DNA methylation, histone H4 acetylation and expression of six genes (β-actin, VEGF, oct4, TERT, H19 and Igf2) and a repetitive sequence (art2) in five organs (heart, liver, spleen, lung and kidney) from two cloned cattle groups that had died at different stages. In the ED group (early death, n = 3), the cloned cattle died in the perinatal period. The cattle in the LD group (late death, n = 3) died after the perinatal period. Normally reproduced cattle served as a control group (n = 3).

Results

Aberrant DNA methylation, histone H4 acetylation and gene expression were observed in both cloned groups. The ED group showed relatively fewer severe DNA methylation abnormalities (p < 0.05) but more abnormal histone H4 acetylations (p < 0.05) and more abnormal expression (p < 0.05) of the selected genes compared to the LD group. However, our data also suggest no widespread gene expression abnormalities in the organs of the dead clones.

Conclusion

Deaths of clones may be ascribed to abnormal expression of a very limited number of genes.

Identification of genes aberrantly expressed in mouse embryonic stem cell-cloned blastocysts

During development, cloned embryos often undergo embryonic arrest at any stage of embryogenesis, leading to diverse morphological abnormalities. The long-term effects resulting from embryo cloning procedures would manifest after birth as early death, obesity, various functional disorders, and so forth. Despite extensive studies, the parameters affecting the developmental features of cloned embryos remain unclear. The present study carried out extensive gene expression analysis to screen a cluster of genes aberrantly expressed in embryonic stem cell-cloned blastocysts. Differential screening of cDNA subtraction libraries revealed 224 differentially expressed genes in the cloned blastocysts: eighty-five were identified by the BLAST search as known genes performing a wide range of functions. To confirm their differential expression, quantitative gene expression analyses were performed by real-time PCR using single blastocysts. The genes Skp1a, Canx, Ctsd, Timd2, and Psmc6 were significantly up-regulated, whereas Aqp3, Ak3l1, Rhot1, Sf3b3, Nid1, mt-Rnr2, mt-Nd1, mt-Cytb, and mt-Co2 were significantly down-regulated in the majority of embryonic stem cell-cloned embryos. Our results suggest that an extraordinarily high frequency of multiple functional disorders caused by the aberrant expression of various genes in the blastocyst stage is involved in developmental arrest and various other disorders in cloned embryos.

Contrasting effects of in vitro fertilization and nuclear transfer on the expression of mtDNA replication factors

Mitochondrial DNA (mtDNA) is normally only inherited through the oocyte. However, nuclear transfer (NT), the fusion of a donor cell with an enucleated oocyte, can transmit both donor cell and recipient oocyte mtDNA. mtDNA replication is under the control of nuclear-encoded replication factors, such as polymerase gamma (POLG) and mitochondrial transcription factor A (TFAM). These are first expressed during late preimplantation embryo development. To account for the persistence of donor cell mtDNA, even when introduced at residual levels (mtDNA(R)), we hypothesized that POLG and TFAM would be upregulated in intra- and interspecific (ovine-ovine) and intergeneric (caprine-ovine) NT embryos when compared to in vitro fertilized (IVF) embryos. For the intra- and interspecific crosses, PolGA (catalytic subunit), PolGB (accessory subunit), and TFAM mRNA were expressed at the 2-cell stage in both nondepleted (mtDNA(+)) and mtDNA(R) embryos with protein being expressed up to the 16-cell stage for POLGA and TFAM. However, at the 16-cell stage, there was significantly more PolGA expression in the mtDNA(R) embryos compared to their mtDNA(+) counterparts. Expression for all three genes first matched IVF embryos at the blastocyst stage. In the intergeneric model, POLG was upregulated during preimplantation development. Although these embryos did not persist further than the 16+-cell stage, significantly more mtDNA(R) embryos reached this stage. However, the vast majority of these embryos were homoplasmic for recipient oocyte mtDNA. The upreglation in mtDNA replication factors was most likely due to the donor cells still expressing these factors prior to NT.

Transcriptional reprogramming of somatic cell nuclei during preimplantation development of cloned bovine embryos

While somatic cell nuclear transfer (SCNT) techniques have been successfully implemented in several species to produce cloned embryos and offspring, the efficiencies of the procedures are extremely low, possibly due to insufficient reprogramming of somatic nuclei. Employing GeneChip microarrays, we describe global gene expression analysis of bovine in vitro fertilized (IVF) and SCNT blastocysts as well as respective donor cell lines to characterize differences in their transcription profiles. Gene expression profiles of our donor cell lines were significantly different from each other; however, the SCNT and IVF blastocysts displayed surprisingly similar gene expression profiles, suggesting that a major reprogramming activity had been exerted on the somatic nuclei. Despite this remarkable phenomenon, a small set of genes appears to be aberrantly expressed and may affect critical developmental processes responsible for the failures observed in SCNT embryos. Our data provide the most comprehensive transcriptome database of bovine IVF and SCNT blastocysts to date.

Universal reference method for real-time PCR gene expression analysis of preimplantation embryos

Real-time PCR expression profiling in individual preimplantation embryos poses two main challenges. First, the amount of RNA from blastocysts (between 100 and 200 cells) is too small to quantify, and secondly, a reference gene with stable expression across preimplantation embryos produced by different reproductive technologies is required. We have developed a method using RNA and DNA spikes that allows for accurate normalization of gene expression without the use of an internal housekeeping gene in preimplantation blastocysts. Prior to the simultaneous extraction of RNA and DNA, plant-specific RNA and DNA spikes are added to the tissue. After synthesis of cDNA, target gene transcript and the exogenous RNA spike are measured using real-time PCR. To account for differences in the number of cells in each sample, the genomic gene copies of 18S-DNA are measured by quantitative PCR and normalized to the DNA spike. While the DNA spike accounts for extraction efficiency, the 18S genomic target indicates the number of cells prior to extraction. The values obtained from normalizing the target gene to the RNA spike can be adjusted for cell number, allowing the RNA spike to be used as reference gene. This universal reference approach allows the use of an exogenous spike as a pseudo-housekeeping gene for normalization of gene expression data.

Effect of the Timing of First Cleavage on In Vitro Developmental Potential of Nuclear-Transferred Bovine Oocytes Receiving Cumulus and Fibroblast Cells

The aim of the present study was to examine whether cumulus and fibroblast cell nuclear-transferred oocytes, which have high and low potential to develop into normal calves, respectively, are different in terms of in their patterns of timing of first cleavage and in their relationships between timing of first cleavage and in vitro developmental potential. The timing of first cleavage was similar in both types of nuclear-transferred and in vitro fertilized oocytes. More than 86% of the oocytes cleaved within 24 h after activation or in vitro fertilization; these oocytes contributed to more than 98% of the total number of blastocysts in all three groups. The potential of oocytes that cleaved at different intervals to develop into blastocysts differed among the groups. The developmental potential of the cumulus cell nuclear-transferred oocytes and in vitro fertilized oocytes decreased with the increase in time required for cleavage. Fibroblast cell nuclear-transferred oocytes that cleaved at 20 h, an intermediate cleaving time, had higher potential to develop into blastocysts. The results of the present study suggest that the type of donor nucleus used for nuclear transfer affects the timing of first cleavage.

Nuclear Transfer: Preservation of a Nuclear Genome at the Expense of Its Associated mtDNA Genome(s)

Nuclear transfer technology has uses across theoretical and applied applications, but advances are restricted by continued poor success rates and health problems associated with live offspring. Development of reconstructed embryos is dependent upon numerous interlinking factors relating both to the donor cell and the recipient oocyte. For example, abnormalities in gene expression following somatic cell nuclear transfer (SCNT) have been linked with an inability of the oocyte cytoplasm to sufficiently epigenetically reprogram the nucleus. Furthermore, influences on the propagation of mitochondria and mitochondrial DNA (mtDNA) could be of great importance in determining the early developmental potential of NT embryos and contributing to their genetic identity. mtDNA encodes some of the subunits of the electron transfer chain, responsible for cellular ATP production. The remaining subunits and those factors required for mtDNA replication, transcription and translation are encoded by the nucleus, necessitating precise intergenomic communication. Additionally, regulation of mtDNA copy number, via the processes of mtDNA transcription and replication, is essential for normal preimplantation embryo development and differentiation. Unimaternal transmission following natural fertilization usually results in the presence of a single identical population of mtDNA, homoplasmy. Heteroplasmy can result if mixed populations of mtDNA genomes co-exist. Many abnormalities observed in NT embryos, fetuses, and offspring may be caused by deficiencies in OXPHOS, perhaps resulting in part from heteroplasmic mtDNA populations. Additionally, incompatibilities between the somatic nucleus and the cytoplast may be exacerbated by increased genetic divergence between the two genomes. It is important to ensure that the nucleus is capable of sufficiently regulating mtDNA, requiring a level of compatibility between the two genomes, which may be a function of evolutionary distance. We suggest that abnormal expression of factors such as TFAM and POLG in NT embryos will prematurely drive mtDNA replication, hence impacting on early development.

Changes in the mRNA transcripts of insulin-like growth factor ligand, receptors and binding proteins in bovine blastocysts and elongated embryos derived from somatic cell nuclear transfer

The objective of this study was to determine changes in the transcription of insulin-like growth factor (IGF)-related genes in blastocyst (BC)- and elongated (EL)-stage embryos produced by nuclear transfer using somatic cells (NT-SC). Bovine BC (day 7)- and EL (day 15)-stage embryos were obtained from NT-SC or in vivo production (Vivo). The relative abundance of mRNA was examined by RT- real-time PCR. The transcript of IGF-II was only detected at the EL stage in both the NT-SC and Vivo embryos. The level of transcription of the IGF-I receptor (r) in the NT-SC embryos was decreased at the EL stage and was significantly (P<0.05) lower than at the BC stage. In contrast, the IGF-IIr levels did not differ significantly between the NT-SC and Vivo embryos, regardless of the developmental stage. IGF-binding protein (IGFBP)-2 levels were markedly decreased in the NT-SC and Vivo embryos at the EL stage (P<0.05). The IGFBP-3 level in Vivo was significantly (P<0.05) increased at the EL stage compared with at the BC stage. However, the IGFBP-3 levels in NT-SC embryos were unchanged and lower (P<0.05) than in the Vivo embryos at the EL stage. These results suggest that there are differences in the levels and changes in the transcription of IGF-related genes in bovine embryos produced by NT-SC compared with those produced by Vivo.

Comparative Studies on the mRNA Expression of Development-Related Genes in an Individual Mouse Blastocyst with Different Developmental Potential

The evaluation of embryo morphology, widely used for selecting mammalian embryos before transfer, is not an adequate standard for selecting nuclear-transferred (NT) embryos. To search for markers useful for predicting the potential of NT embryos to develop into young, we examined the relation between the morphology of embryos with different developmental potential and gene expression of Oct 4, Nanog, Stat3, FGF4, Stella, and Sox2. In the present study, we examined pronuclear-exchanged blastocysts and morula blastomere, embryonic stem (ES) cell, and cumulus cell NT blastocysts, and in vivo-developed and in vitro-developed blastocysts. Based on the small variations in the gene expression levels among the in vivo-developed blastocysts, and the significant differences in gene expression between in vivo-developed (high developmental potential), and ES cell and cumulus cell NT blastocysts (low developmental potential), down-regulation of Sox2 and Oct4 genes is considered to be a candidate marker for the low potential of NT embryos to develop into young.

Gene expression in bovine nuclear transfer embryos in relation to donor cell efficiency in producing live offspring

Developmental abnormalities associated with the cloning process suggest that reprogramming of donor nuclei into an embryonic state may not be fully completed in most of the cloned animals. One of the areas of interest in this regard, is the analysis of gene expression patterns in nuclear transfer (NT) embryos to dissect the processes that failed and develop means to overcome the limitations imposed by these factors. In this study, we investigated expression patterns of histone deacetylase-1, -2, -3 (HDAC-1, -2, -3), DNA methyltransferase-3a (DNMT3A), and octamer binding protein-4 gene (OCT4) in donor cells with different cloning efficiencies and NT embryos derived from these cells employing a real-time RT-PCR assay. All genes investigated followed altered expression patterns in NT embryos when compared to IVF-derived embryos. In general, expression of HDAC genes was elevated especially at the compact morula stage and comparable to in vitro fertilized (IVF) embryos at the hatched blastocyst stage. DNMT3A expression in NT embryos was lower than IVF embryos at all stages. Oct-4 transcript levels were also reduced in cloned compared to IVF embryos at the compact morula and blastocyst stages. This difference disappeared at the hatched blastocyst stage. There was a donor cell effect on the expression patterns of all genes investigated. These results demonstrate altered gene expression patterns for certain genes, in cloned cattle embryos from our donor cells of different efficiency in producing live offspring. Therefore we suggest that differences in expression of developmentally important genes during early embryo development may characterize the efficiency of donor cells in producing live offspring.