Validation of reference genes for quantitative RT-PCR studies in porcine oocytes and preimplantation embryos

<p>Abstract</p> <p>Background</p> <p>In the developing embryo, total RNA abundance fluctuates caused by functional RNA degradation and zygotic genome activation. These variations in the transcriptome in early development complicate the choice of good reference genes for gene expression studies by quantitative real time polymerase chain reaction.</p> <p>Results</p> <p>In order to identify stably expressed genes for normalisation of quantitative data, within early stages of development, transcription levels were examined of 7 frequently used reference genes (<it>B2M, BACT, GAPDH, H2A, PGK1, SI8</it>, and <it>UBC</it>) at different stages of early porcine embryonic development (germinal vesicle, metaphase-2, 2-cell, 4-cell, early blastocyst, expanded blastocyst). Analysis of transcription profiling by geNorm software revealed that <it>GAPDH, PGK1, S18</it>, and <it>UBC </it>showed high stability in early porcine embryonic development, while transcription levels of <it>B2M, BACT</it>, and <it>H2A </it>were highly regulated.</p> <p>Conclusion</p> <p>Good reference genes that reflect total RNA content were identified in early embryonic development from oocyte to blastocyst. A selection of either <it>GAPDH </it>or <it>PGK1</it>, together with ribosomal protein <it>S18 </it>(<it>S18</it>), and <it>UBC </it>is proposed as reference genes, but the use of <it>B2M, BACT</it>, or <it>H2A </it>is discouraged.</p

Sperm DNA damage causes genomic instability in early embryonic development

Genomic instability is common in human embryos, but the underlying causes are largely unknown. Here, we examined the consequences of sperm DNA damage on the embryonic genome by single-cell whole-genome sequencing of individual blastomeres from bovine embryos produced with sperm damaged by γ-radiation. Sperm DNA damage primarily leads to fragmentation of the paternal chromosomes followed by random distribution of the chromosomal fragments over the two sister cells in the first cell division. An unexpected secondary effect of sperm DNA damage is the induction of direct unequal cleavages, which include the poorly understood heterogoneic cell divisions. As a result, chaotic mosaicism is common in embryos derived from fertilizations with damaged sperm. The mosaic aneuploidies, uniparental disomies, and de novo structural variation induced by sperm DNA damage may compromise fertility and lead to rare congenital disorders when embryos escape developmental arrest

Cell Lineage Specific Distribution of H3K27 Trimethylation Accumulation in an In Vitro Model for Human Implantation

Female mammals inactivate one of their two X-chromosomes to compensate for the difference in gene-dosage with males that have just one X-chromosome. X-chromosome inactivation is initiated by the expression of the non-coding RNA Xist, which coats the X-chromosome in cis and triggers gene silencing. In early mouse development the paternal X-chromosome is initially inactivated in all cells of cleavage stage embryos (imprinted X-inactivation) followed by reactivation of the inactivated paternal X-chromosome exclusively in the epiblast precursors of blastocysts, resulting temporarily in the presence of two active X-chromosomes in this specific lineage. Shortly thereafter, epiblast cells randomly inactivate either the maternal or the paternal X-chromosome. XCI is accompanied by the accumulation of histone 3 lysine 27 trimethylation (H3K27me3) marks on the condensed X-chromosome. It is still poorly understood how XCI is regulated during early human development. Here we have investigated lineage development and the distribution of H3K27me3 foci in human embryos derived from an in-vitro model for human implantation. In this system, embryos are co-cultured on decidualized endometrial stromal cells up to day 8, which allows the culture period to be extended for an additional two days. We demonstrate that after the co-culture period, the inner cell masses have relatively high cell numbers and that the GATA4-positive hypoblast lineage and OCT4-positive epiblast cell lineage in these embryos have segregated. H3K27me3 foci were observed in ∼25% of the trophectoderm cells and in ∼7.5% of the hypoblast cells, but not in epiblast cells. In contrast with day 8 embryos derived from the co-cultures, foci of H3K27me3 were not observed in embryos at day 5 of development derived from regular IVF-cultures. These findings indicate that the dynamics of H3K27me3 accumulation on the X-chromosome in human development is regulated in a lineage specific fashion

A Distinct Expression Pattern in Mammalian Testes Indicates a Conserved Role for NANOG in Spermatogenesis

BACKGROUND: NANOG is a key player in pluripotency and its expression is restricted to pluripotent cells of the inner cell mass, the epiblast and to primordial germ cells. Spermatogenesis is closely associated with pluripotency, because through this process highly specialized sperm cells are produced that contribute to the formation of totipotent zygotes. Nevertheless, it is unknown if NANOG plays a role in this process. METHODOLOGY/PRINCIPAL FINDINGS: In the current study, NANOG expression was examined in testes of various mammals, including mouse and human. Nanog mRNA and NANOG protein were detected by RT-PCR, immunohistochemistry, and western blotting. Furthermore, eGFP expression was detected in the testis of a transgenic Nanog eGFP-reporter mouse. Surprisingly, although NANOG expression has previously been associated with undifferentiated cells with stem cell potential, expression in the testis was observed in pachytene spermatocytes and in the first steps of haploid germ cell maturation (spermiogenesis). Weak expression in type A spermatogonia was also observed. CONCLUSIONS: The findings of the current study strongly suggest a conserved role for NANOG in meiotic and post-meiotic stages of male germ cell developmen

The impact of ovarian stimulation for IVF on the developing embryo

The use of assisted reproductive technologies (ART) has been increasing over the past three decades, and, in developed countries, ART account for 1-3% of annual births. In an attempt to compensate for inefficiencies in IVF procedures, patients undergo ovarian stimulation using high doses of exogenous gonadotrophins to allow retrieval of multiple oocytes in a single cycle. Although ovarian stimulation has an important role in ART, it may also have detrimental effects on oogenesis, embryo quality, endometrial receptivity and perinatal outcomes. In this review, we consider the evidence for these effects and address possible underlying mechanisms. We conclude that such mechanisms are still poorly understood, and further knowledge is needed in order to increase the safety of ovarian stimulation and to reduce potential effects on embryo development and implantation, which will ultimately be translated into increased pregnancy rates and healthy offspring.<br/

Validation of reference genes for quantitative RT-PCR studies in porcine oocytes and preimplantation embryos

BACKGROUND: In the developing embryo, total RNA abundance fluctuates caused by functional RNA degradation and zygotic genome activation. These variations in the transcriptome in early development complicate the choice of good reference genes for gene expression studies by quantitative real time polymerase chain reaction. RESULTS: In order to identify stably expressed genes for normalisation of quantitative data, within early stages of development, transcription levels were examined of 7 frequently used reference genes (B2M, BACT, GAPDH, H2A, PGK1, SI8, and UBC) at different stages of early porcine embryonic development (germinal vesicle, metaphase-2, 2-cell, 4-cell, early blastocyst, expanded blastocyst). Analysis of transcription profiling by geNorm software revealed that GAPDH, PGK1, S18, and UBC showed high stability in early porcine embryonic development, while transcription levels of B2M, BACT, and H2A were highly regulated. CONCLUSION: Good reference genes that reflect total RNA content were identified in early embryonic development from oocyte to blastocyst. A selection of either GAPDH or PGK1, together with ribosomal protein S18 (S18), and UBC is proposed as reference genes, but the use of B2M, BACT, or H2A is discouraged

Altered expression of pluripotency and early lineage segregation genes in IVP equine embryos

Compared to their in vivo counterparts, in vitro produced (IVP) horse embryos are smaller, have fewer cells, show developmental delay and, while pregnancy rates are comparable, may be more prone to pre-implantation failure (1,2). During mouse blastocyst formation, Oct4 and Cdx2 are essential for inner cell mass (ICM) and trophectoderm delineation respectively, while differential expression of Nanog and Gata6 determines which ICM cells form pluripotent epiblast or primitive endoderm respectively (3). Expression of these genes and other pluripotency markers (DPPA4, ESRRB, GDF3, SALL4, SOX2 and TERT) was used to examine the effects of IVP on early horse embryo development. Morulae, early and expanded blastocysts were recovered non-surgically from mares, or produced in vitro by ICSI of oocytes from slaughtered mares (n = 5, 7 and 9 per group at the respective stages). Gene expression was quantified by real-time PCR (4). Expression of most pluripotency genes decreased during the morula-to-early blastocyst (ESRRB and GDF3) or early-to-expanded blastocyst (DPPA4, NANOG, OCT4 and SOX2) transitions in vivo; consistent with a decreasing proportion of pluripotent (epiblast) cells. Expanded blastocysts showed reduced GATA6 and increased CDX2 expression presumably reflecting completion of primitive endoderm segregation, and trophectoderm proliferation. In IVP embryos, GDF3, TERT and GATA6 expression was undetectable, and SALL4 reduced. IVP morulae had undetectable CDX2 expression and reduced OCT4 compared to in vivo morulae. Additionally, the expected down-regulation of OCT4 and upregulation of CDX2 during blastocyst expansion was not observed in vitro, while down-regulation of some pluripotency genes was delayed (ESRRB) or advanced (NANOG and SOX2). In summary, IVP embryos show an altered expression pattern for genes associated with cell lineage segregation. Whether this primarily reflects developmental retardation or indicates changes in the proportion of cells entering the 3 cell lineages remains to be investigated, as does the significance for developmental competence.\ud \ud 1. Stout T.A.E. (2006) Equine Veterinary Journal 38: 467-478.\ud 2. Galli C. et al. (2007) Animal Reproduction Science 98: 39-55.\ud 3. Ralston A. and Rossant J. (2005) Clinical Genetics 68: 106-112.\ud 4. Paris D.B.B.P. et al. (2011) Reproduction, Fertility and Development 23: 353-363