Identification of a novel gene set in human cumulus cells predictive of an oocyte's pregnancy potential.

OBJECTIVE: To identify a gene expression signature in human cumulus cells (CCs) predictive of pregnancy outcome across multiple clinics, taking into account the clinic and patient variations inherent in IVF practice. DESIGN: Retrospective analysis of single human cumulus-oocyte complexes with the use of a combined microarray and quantitative reverse-transcription polymerase chain reaction (qRT-PCR) approach. SETTING: Multiple private IVF clinics. PATIENT(S): Fifty-eight patients. Samples from 55 patients underwent qRT-PCR analysis, and samples from 27 patients resulted in live birth. INTERVENTION(S): Gene expression analysis for correlation with pregnancy outcome on individual human CCs collected immediately after oocyte retrieval. Pregnancy prediction analysis used leave-one-out cross-validation with weighted voting. MAIN OUTCOME MEASURE(S): Combinatorial expression of 12 genes in 101 samples from 58 patients. RESULT(S): We found a set of 12 genes predictive of pregnancy outcome based on their expression levels in CCs. This pregnancy prediction model had an accuracy of 78%, a sensitivity of 72%, a specificity of 84%, a positive predictive value of 81%, and a negative predictive value of 76%. Receiver operating characteristic analysis found an area under the curve of 0.763 ± 0.079, significantly greater than 0.5 (random chance prediction). CONCLUSION(S): Gene expression analysis in human CCs should be considered in identifying oocytes with a high potential to lead to pregnancy in IVF-ET.

Alteration of gene expression in human cumulus cells as a potential indicator of oocyte aneuploidy.

BACKGROUND: Human female meiosis is particularly error prone, leading to the generation of aneuploidy, a problem which increases dramatically with advancing age. Despite being of great clinical importance, the genesis of oocyte aneuploidy remains poorly understood. Cumulus cells (CCs) surround oocytes in antral follicles and play a crucial role in regulating their maturation. During this investigation, we aimed to obtain an insight into the follicular environment of oocytes that become aneuploid and identify non-invasive markers of oocyte chromosome status and competence. METHODS: Microarray comparative genomic hybridization was used to assess oocyte ploidy. Expression of 96 genes was examined via a large real-time PCR experiment in 51 CC samples, whereas an additional 26 CC clumps were used for a more focused real-time PCR experiment assessing just three genes. Gene selection was based on the results of a previous microarray analysis comparing the transcriptome of CCs from normal and aneuploid oocytes. RESULTS: Fifty eight of the investigated genes were confirmed to be expressed in CCs. Patterns of expression were generally similar among all CC samples, regardless of the chromosomal status of the corresponding oocyte. However, two genes, SPSB2 and TP53I3, were both significantly down-regulated in CCs from chromosomally abnormal oocytes (P<0.05). The expression of SPSB2 was also found to display a strong trend towards up-regulation in the CCs of oocytes that produced a healthy live birth (P=0.054). CONCLUSIONS: In the current study, SPSB2 and TP53I3 exhibited highly significant differences in their expression between CCs of normal and chromosomally abnormal oocytes. SPSB2 is involved in intracellular signalling and homeostasis, whereas TP53I3 regulates carbohydrate metabolism and apoptosis. We speculate that both these genes might have the potential to serve as non-invasive markers of oocyte aneuploidy.

Bovine ooplasm partially remodels primate somatic nuclei following somatic cell nuclear transfer.

Interspecies somatic cell nuclear transfer (iSCNT) has the potential to become a useful tool to address basic questions about the nucleus-cytoplasm interactions between species. It has also been proposed as an alternative for the preservation of endangered species and to derive autologous embryonic stem cells. Using chimpanzee/ bovine iSCNT as our experimental model we studied the early epigenetic events that take place soon after cell fusion until embryonic genome activation (EGA). Our analysis suggested partial EGA in iSCNT embryos at the eight-cell stage, as indicated by Br-UTP incorporation and expression of chimpanzee embryonic genes. Oct4, Stella, Crabp1, CCNE2, CXCL6, PTGER4, H2AFZ, c-MYC, KLF4, and GAPDH transcripts were expressed, while Nanog, Glut1, DSC2, USF2, Adrbk1, and Lin28 failed to be activated. Although development of iSCNT embryos did not progress beyond the 8- to 16-cell stage, chromatin remodeling events, monitored by H3K27 methylation, H4K5 acetylation, and global DNA methylation, were similar in both intra- and interspecies SCNT embryos. However, bisulfite sequencing indicated incomplete demethylation of Oct4 and Nanog promoters in eight-cell iSCNT embryos. ATP production levels were significantly higher in bovine SCNT embryos than in iSCNT embryos, TUNEL assays did not reveal any difference in the apoptotic status of the nuclei from both types of embryos. Collectively, our results suggest that bovine ooplasm can partially remodel chimpanzee somatic nuclei, and provides insight into some of the current barriers iSCNT must overcome if further embryonic development is to be expected.

Activation of bovine somatic cell nuclear transfer embryos by PLCZ cRNA injection.

The production of cloned animals by the transfer of a differentiated somatic cell into an enucleated oocyte circumvents fertilization. During fertilization, the sperm delivers a sperm-specific phospholipase C (PLCZ) that is responsible for triggering Ca(2)(+) oscillations and oocyte activation. During bovine somatic cell nuclear transfer (SCNT), oocyte activation is artificially achieved by combined chemical treatments that induce a monotonic rise in intracellular Ca(2)(+) and inhibit either phosphorylation or protein synthesis. In this study, we tested the hypothesis that activation of bovine nuclear transfer embryos by PLCZ improves nuclear reprogramming. Injection of PLCZ cRNA into bovine SCNT units induced Ca(2)(+) oscillations similar to those observed after fertilization and supported high rates of blastocyst development similar to that seen in embryos produced by IVF. Furthermore, gene expression analysis at the eight-cell and blastocyst stages revealed a similar expression pattern for a number of genes in both groups of embryos. Lastly, levels of trimethylated lysine 27 at histone H3 in blastocysts were higher in bovine nuclear transfer embryos activated using cycloheximide and 6-dimethylaminopurine (DMAP) than in those activated using PLCZ or derived from IVF. These results demonstrate that exogenous PLCZ can be used to activate bovine SCNT-derived embryos and support the hypothesis that a fertilization-like activation response can enhance some aspects of nuclear reprogramming.

Polycomb gene expression and histone H3 lysine 27 trimethylation changes during bovine preimplantation development.

Trimethylation of histone H3 at lysine 27 (H3K27me3) is established by polycomb group genes and is associated with stable and heritable gene silencing. The aim of this study was to characterize the expression of polycomb genes and the dynamics of H3K27me3 during bovine oocyte maturation and preimplantation development. Oocytes and in vitro-produced embryos were collected at different stages of development. Polycomb gene expression was analyzed by real-time quantitative RT-PCR and immunofluorescence. Global H3K27me3 levels were determined by semiquantitative immunofluorescence. Transcripts for EZH2, EED, and SUZ12 were detected at all stages analyzed, with EZH2 levels being the highest of the three at early stages of development. By the time the embryo reached the blastocyst stage, the level of PcG gene mRNA levels significantly increased. Immunofluorescence staining indicated nuclear expression of EZH2 at all stages while nuclear localized EED and SUZ12 were only evident at the morula and blastocyst stages. Semiquantitative analysis of H3K27me3 levels showed that nuclear fluorescence intensity was the highest in immature oocytes, which steadily decreased after fertilization to reach a nadir at the eight-cell stage, and then increased at the blastocyst stage. These results suggest that the absence of polycomb repressive complex 2 proteins localized to the nucleus of early embryos could be responsible for the gradual decrease in H3K27me3 during early preimplantation development.

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.

Parthenogenetic activation of bovine oocytes using bovine and murine phospholipase C zeta.

BACKGROUND: During natural fertilization, sperm fusion with the oocyte induces long lasting intracellular calcium oscillations which in turn are responsible for oocyte activation. PLCZ1 has been identified as the factor that the sperm delivers into the egg to induce such a response. We tested the hypothesis that PLCZ1 cRNA injection can be used to activate bovine oocytes. RESULTS: Mouse and bovine PLCZ1 cRNAs were injected into matured bovine oocytes at different concentrations. Within the concentrations tested, mouse PLCZ1 injection activated bovine oocytes at a maximum rate when the pipette concentration of cRNA ranged from 0.25 to 1 mug/muL, while bovine PLCZ1 was optimal at 0.1 mug/muL. At their most effective concentrations, PLCZ1 induced parthenogenetic development at rates similar to those observed using other activation stimuli such as Ionomycin/CHX and Ionomycin/DMAP. Injection of mouse and bovine PLCZ1 cRNA induced dose-dependent sperm-like calcium oscillations whose frequency increased over time. Injection of bovine and mouse PLCZ1 cRNA also induced IP3R-1 degradation, although bovine PLCZ1 cRNA evoked greater receptor degradation than its mouse counterpart. CONCLUSION: Injection of PLCZ1 cRNA efficiently activated bovine oocytes by inducing a sperm-like calcium oscillatory pattern. Importantly, the high rate of aneuploidy encountered in parthenogenetic embryos activated by certain chemical means was not observed in PLCZ1 activated embryos.

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.

Interspecies nuclear transfer: implications for embryonic stem cell biology.

Accessibility of human oocytes for research poses a serious ethical challenge to society. This fact categorically holds true when pursuing some of the most promising areas of research, such as somatic cell nuclear transfer and embryonic stem cell studies. One approach to overcoming this limitation is to use an oocyte from one species and a somatic cell from another. Recently, several attempts to capture the promises of this approach have met with varying success, ranging from establishing human embryonic stem cells to obtaining live offspring in animals. This review focuses on the challenges and opportunities presented by the formidable task of overcoming biological differences among species.