Aberrant protein expression in the placenta of cloned mouse derived from embryonic stem cell

Aberrant Expression of TIMP-2 and PBEF Genes in the Placentae of Cloned Mice Due to Epigenetic Reprogramming Error

Cloned mice derived from somatic or ES cells show placental overgrowth (placentomegaly) at term. We had previously analyzed cloned and normal mouse placentae by using two-dimensional gel electrophoresis and mass spectrometry to identify differential protein expression patterns. Cloned placentae showed upregulation of tissue inhibitor of metalloproteinase-2 (TIMP-2), which is involved in extracellular matrix degradation and tissue remodeling, and downregulation of pre-B cell colony enhancing factor 1 (PBEF), which inhibits apoptosis and induces spontaneous labor. Here, we used Western blotting to further analyze the protein expression levels of TIMP-2 and PBEF in cloned placentae derived from cumulus cells, TSA-treated cumulus cells, intracytoplasmic sperm injection (ICSI), and natural mating (NM control). Cloned and TSA-treated cloned placentae had higher expression levels of TIMP-2 compared with NM control and ICSI-derived placentae, and there was a positive association between TIMP-2 expression and the placental weight of cloned mouse concepti. Conversely, PBEF protein expression was significantly lower in cloned and ICSI placentae compared to NM controls. To examine whether the observed differences were due to abnormal gene expression caused by faulty epigenetic reprogramming in clones, we investigated DNA methylation and histone modification in the promoter regions of the genes encoding TIMP-2 and PBEF. Sodium bisulfite sequencing did not reveal any difference in DNA methylation between cloned and NM control placentae. However, ChIP assays revealed that the level of H3-K9/K14 acetylation at the TIMP-2 locus was higher in cloned placentae than in NM controls, whereas acetylation of the PBEF promoter was lower in cloned and ICSI placenta versus NM controls. These results suggest that cloned placentae appear to suffer from failure of histone modification-based reprogramming in these (and potentially other) developmentally important genes, leading to aberrant expression of their protein products. These changes are likely to be involved in generating the abnormalities seen in cloned mouse placentae, including enlargement and/or a lack of proper placental function.

DNA Methylation Errors in Cloned Mouse Sperm by Germ Line Barrier Evasion

The germ line reprogramming barrier resets parental epigenetic modifications according to sex, conferring totipotency to mammalian embryos upon fertilization. However, it is not known whether epigenetic errors are committed during germ line reprogramming that are then transmitted to germ cells, and consequently to offspring. We addressed this question in the present study by performing a genome-wide DNA methylation analysis using a target postbisulfite sequencing method in order to identify DNA methylation errors in cloned mouse sperm. The sperm genomes of two somatic cell-cloned mice (CL1 and CL7) contained significantly higher numbers of differentially methylated CpG sites (P = 0.0045 and P = 0.0116). As a result, they had higher numbers of differentially methylated CpG islands. However, there was no evidence that these sites were transmitted to the sperm genome of offspring. These results suggest that DNA methylation errors resulting from embryo cloning are transmitted to the sperm genome by evading the germ line reprogramming barrier.

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.

Involvement of ubiquitin-proteasome system in icariin-induced cardiomyocyte differentiation of embryonic stem cells using two-dimensional gel electrophoresis

Icariin has been shown to significantly facilitate the differentiation of embryonic stem (ES) cells into cardiomyocytes in vitro. However, the mechanism underlying the icariin-induced cardiomyocyte differentiation is still not fully understood. In the present study, 52 differentially displayed proteins selected from two-dimensional electrophoresis gels were identified by MALDI-TOF mass spectrometry analysis. More than half of proteins could be assigned to six main categories: (1) protein synthesis, metabolism, processing and degradation, (2) stress response, (3) cytoskeleton proteins, (4) energy metabolism, (5) carbohydrate metabolism/transport, and (6) RNA/other nucleic acids metabolisms and transport, nuclear proteins. MALDI-TOF/MS showed that icariin treatment resulted in the induction of five ubiquitin-proteasome system (UPS)-related proteins, such as ubiquitin carboxy-terminal hydrolase L1 (UCH-L1), ubiquitin-conjugating enzyme E2N, proteasome 26S, proteasome subunit-alpha type 6, and proteasome subunit-alpha type 2 in the differentiated cardiomyocytes. These results implied that UPS might play an important role in the control of cardiomyocyte differentiation. Epoxomicin (a proteasome inhibitor) significantly reduced the cardiomyocyte differentiation rate of ES cells and proteasome activities, as well as inhibited NF-κB translocation into the nucleus, which were evidently reversed by presence of icariin. Meanwhile, icariin could significantly reverse the reduction of four proteins (proteasome subunit-alpha type 6, proteasome subunit-alpha type 2, UCH-L1, and ubiquitin-conjugating enzyme E2N) expressions owing to application of epoxomicin. These suggest UPS could be a means by which icariin may regulate expressions of key proteins that control cardiomyocyte differentiation. Taken together, these results indicated that UPS played an important role in ES cell differentiate into cardiomyocytes induced by icariin.

Epigenetic characterization of the PBEF and TIMP-2 genes in the developing placentae of normal mice

Reprogramming errors, which appear frequently in cloned animals, are reflected by aberrant gene expression. We previously reported the aberrant expression of TIMP-2 and PBEF in cloned placenta and differential expression of PBEF genes during pregnancy. To examine the epigenetic modifications that regulate dynamic gene expression in developing placentae, we herein analyzed the mRNA and protein expression levels of PBEF and TIMP-2 in the placentae of normal mice during pregnancy and then examined potential correlations with epigenetic modifications. DNA methylation pattern analysis revealed no difference, but ChIP assays using antibodies against H3-K9/K14 and H4-K5 histone acetylation revealed that the H3-K9/K14 acetylation levels, but not the H4-K5 acetylation levels, of the TIMP-2 and PBEF loci were significantly correlated with their gene expression levels during placentation in normal mice. These results suggest that epigenetic changes may regulate gene expression level in the developing placentae of normal mice and that inappropriate epigenetic reprogramming might be one cause of the abnormal placentae seen in cloned animals.