Gatekeeper of pluripotency: a common Oct4 transcriptional network operates in mouse eggs and embryonic stem cells

Pyometra does not affect some molecular quality-related parameters of canine oocytes

Cystic endometrial hyperplasia-pyometra complex (CEH/P) significantly perturbs the reproductive performance of affected bitches and ovariohysterectomy (OHE) is a commonly applied treatment. Thus the only way to take advantage of the genetic potential of valuable females is application of assisted reproductive techniques (ART) mainly in vitro embryo production (IVP) or in some exceptional cases animal cloning by somatic cell nuclear transfer (SCNT). The aim of our study was to examine a potential effect of the CEH/P status on the quality of oocytes from females subjected to OHE. In total, 828 immature oocytes collected from ovaries of 33 bitches (21 control, 12 CEH/P) were subjected to genetic analyses (mRNA expression of two maternal-effect genes: GDF-9, OCT4 and mitochondrial DNA (mtDNA) content). Oocytes of CEH/P females were characterized by a higher mtDNA content (471 696) than gametes of their healthy counterparts (368 175; P<0.005). Transcripts for the two genes were detected in all samples and the mRNA level was not affected by the CEH/P status. In conclusion, the CEH/P complex does not exert a negative effect on oocyte quality reflected by the two parameters examined in this study.

The Caenorhabditis elegans homolog of human copper chaperone Atox1, CUC-1, aids in distal tip cell migration

Cell migration is a fundamental biological process involved in for example embryonic development, immune system and wound healing. Cell migration is also a key step in cancer metastasis and the human copper chaperone Atox1 was recently found to facilitate this process in breast cancer cells. To explore the role of the copper chaperone in other cell migration processes, we here investigated the putative involvement of an Atox1 homolog in Caenorhabditis elegans, CUC-1, in distal tip cell migration, which is a key process during the development of the C. elegans gonad. Using knock-out worms, in which the cuc-1 gene was removed by CRISPR-Cas9 technology, we probed life span, brood size, as well as distal tip cell migration in the absence or presence of supplemented copper. Upon scoring of gonads, we found that cuc-1 knock-out, but not wild-type, worms exhibited distal tip cell migration defects in approximately 10–15% of animals and, had a significantly reduced brood size. Importantly, the distal tip cell migration defect was rescued by a wild-type cuc-1 transgene provided to cuc-1 knock-out worms. The results obtained here for C. elegans CUC-1 imply that Atox1 homologs, in addition to their well-known cytoplasmic copper transport, may contribute to developmental cell migration processes.

Roles of OCT4 in pathways of embryonic development and cancer progression

Somatic cells may be reprogrammed to pluripotent state by ectopic expression of certain transcription factors; namely, OCT4, SOX2, KLF4 and c-MYC. However, the molecular and cellular mechanisms are not adequately understood, especially for human embryonic development. Studies during the last five years implicated importance of OCT4 in human zygotic genome activation (ZGA), patterns of OCT4 protein folding and role of specialized sequences in binding to DNA for modulation of gene expression during development. Epigenetic modulation of OCT4 gene and post translational modifications of OCT4 protein activity in the context of multiple cancers are important issues. A consensus is emerging that chromatin organization and epigenetic landscape play crucial roles for the interactions of transcription factors, including OCT4 with the promoters and/or regulatory sequences of genes associated with human embryonic development (ZGA through lineage specification) and that when the epigenome niche is deregulated OCT4 helps in cancer progression, and how OCT4 silencing in somatic cells of adult organisms may impact ageing.

Heat stress-induced alterations in the expression of genes associated with gonadal integrity of the teleost Puntius sophore

Temperature plays an important role on reproductive physiology of vertebrates including mammals, fish, and birds. It has varying effects on fish reproduction depending on the species; higher temperatures favor the spring-spawning species, while lower temperatures stimulate reproduction in autumn spawners. To evaluate the impact of high temperature on the reproductive physiology of minnow Puntius sophore, we carried out expression analysis of selected genes associated with gamete quality (hsp60, hsp70, hsp90, hsf1, vtg), pleuripotency (sox2, oct4, nanog), and sex determination (dmrt1) in gonads (ovary and testis) of P. sophore, heat stressed for different time periods (36 °C/7 days or 60 days) using real-time quantitative polymerase chain reaction (RT-qPCR). Expression of most of the hsp, vtg, and pleuripotency marker genes sox-2, oct-4, and nanog genes was downregulated in both ovary and testis of heat-stressed fish. The expression of dmrt-1 was upregulated in testis but downregulated in ovary of the heat-stressed fish which could be a male favoring effect of high temperature in P. sophore. This study suggests that the reproductive physiology and health of the nutrient dense P. sophore would be negatively affected by high temperature stress.

Acquisition of oocyte competence to develop as an embryo: integrated nuclear and cytoplasmic events

Infertility affects ~7% of couples of reproductive age with little change in incidence in the last two decades. ART, as well as other interventions, have made major strides in correcting this condition. However, and in spite of advancements in the field, the age of the female partner remains a main factor for a successful outcome. A better understanding of the final stages of gamete maturation yielding an egg that can sustain embryo development and a pregnancy to term remains a major area for improvement in the field. This review will summarize the major cellular and molecular events unfolding at the oocyte-to-embryo transition. We will provide an update on the most important processes/pathways currently understood as the basis of developmental competence, including the molecular processes involved in mRNA storage, its recruitment to the translational machinery, and its degradation. We will discuss the hypothesis that the translational programme of maternal mRNAs plays a key role in establishing developmental competence. These regulations are essential to assemble the machinery that is used to establish a totipotent zygote. This hypothesis further supports the view that embryogenesis begins during oogenesis. A better understanding of the events required for developmental competence will guide the development of novel strategies to monitor and improve the success rate of IVF. Using this information, it will be possible to develop new biomarkers that may be used to better predict oocyte quality and in selection of the best egg for IVF.

Sperm-derived factors enhance the in vitro developmental potential of haploid parthenotes

Parthenotes are characterized by poor in vitro developmental potential either due to the ploidy status or the absence of paternal factors. In the present study, we demonstrate the beneficial role of sperm-derived factors (SDF) on the in vitro development of mouse parthenotes. Mature (MII) oocytes collected from superovulated Swiss albino mice were activated using strontium chloride (SrCl2) in the presence or absence of various concentrations of SDF in M16 medium. The presence of SDF in activation medium did not have any significant influence on the activation rate. However, a significant increase in the developmental potential of the embryos and increased blastocyst rate (P < 0.01) was observed at 50 µg/ml concentration. Furthermore, the activated oocytes from this group exhibited early cleavage and cortical distribution of cortical granules that was similar to that of normally fertilized zygotes. Culturing 2-cell stage parthenotes in the presence of SDF significantly improved the developmental potential (P < 0.05) indicating that they also play a significant role in embryo development. In conclusion, artificial activation of oocytes with SDF can improve the developmental potential of parthenotes in vitro.

Copper chaperone ATOX1 regulates pluripotency factor OCT4 in preimplantation mouse embryos

Despite of the importance of copper (Cu) during pregnancy, the roles of Cu-binding proteins during early embryonic development are unknown. The Cu chaperone ATOX1 was recently suggested to have additional functions related to transcription and cancer. When we analyzed single-cell RNA transcript data from early mouse embryos, Atox1 transcript levels increased dramatically at the 8-cell stage and, at 16- and 32-cell embryo stages, matched those of Oct4 which expresses a transcription factor essential for pluripotency in the inner cell mass. To explore this, we probed Atox1 expression during the first week of development of mouse embryos. ATOX1 appeared ubiquitously expressed throughout the cells until compaction; in subsequent embryo stages, ATOX1 relocalized to cytoplasmic perinuclear domains in the inner cell mass. Silencing of Oct4 did not affect Atox1 expression, but silencing of Atox1 at the 2-cell stage strongly diminished Oct4 expression in 16-cell embryos.

Characterization of the POU5F1 Homologue in Nile Tilapia: From Expression Pattern to Biological Activity

POU5F1 (OCT4) is a crucial transcription factor for induction and maintenance of cellular pluripotency, as well as survival of germ cells in mammals. However, the homologues of POU5F1 in teleost fish, including zebrafish and medaka, now named Pou5f3, exhibit considerable differences in expression pattern and pluripotency-maintaining activity. To what extent the POU5F1 homologues are conserved in vertebrates has been unclear. In this study, we report that the POU5F1 homologue from the Nile tilapia (Oreochromis niloticus), OnPou5f3, displays an expression pattern and biological activity somewhat different from those in zebrafish or medaka. The expression of Onpou5f3 at both mRNA and protein levels was abundant in early development embryos until blastula stages, barely detectable as proceeding, and then displayed a transiently strong expression domain in the brain region during neurula stages similar to zebrafish but not medaka. Afterward, OnPou5f3 appeared as germline-restricted (including primordial germ cells and female and male gonad germ cells) expression just like medaka. Notably, OnPou5f3 depletion through morpholino oligos caused blastula blockage or lethality and failure of survival and proliferation of blastula cell-derived cells. These findings indicate that equivalent POU5F1-like expression and activity of Pou5f3 might be conserved accompanying with species-specific expression pattern during evolution. Our study provides insight into the evolutionary conservation of the POU5F1 homologues across vertebrates.

DPF2 regulates OCT4 protein level and nuclear distribution

The amount of transcription factor OCT4 is strictly regulated. A tight regulation of OCT4 levels is crucial for mammalian embryonic development and oncogenesis. However, the mechanisms underlying regulation of OCT4 protein expression and nuclear distribution are largely unknown. Here, we report that DPF2, a plant homeodomain (PHD) finger protein, is upregulated during H9 cell differentiation induced by retinoic acid. Endogenous interaction between DPF2 and OCT4 in P19 cells was revealed by an immunoprecipitation assay. GST-pull down assay proved that OCT4 protein in H9 cells and recombinant OCT4 can precipitate with DPF2 in vitro. In vitro ubiquitination assay demonstrated DPF2 might serve as an E3 ligase. Knock down of dpf2 using siRNA increased OCT4 protein level and stability in P19 cells. DPF2 siRNAs also up-regulates OCT4 but not NANOG in H9 cells. However, RA fails to downregulates OCT4 protein level in cells infected by lenitviruses containing DPF2 siRNA. Moreover, overexpression of both DPF2 and OCT4 in 293 cells proved the DPF2-OCT4 interaction. DPF2 but not PHD2 mutant DPF2 enhanced ubiquitination and degradation of OCT4 in 293 cells co-expressed DPF2 and OCT4. Both wild type DPF2 and PHD2 mutant DPF2 redistributes nuclear OCT4 without affecting DPF2-OCT4 interaction. Further analysis indicated that DPF2 decreases monomeric and mono-ubiquitinated OCT4, assembles poly-ubiquitin chains on OCT4 mainly through Ub-K48 linkage. These findings contribute to an understanding of how OCT4 protein level and nuclear distribution is regulated by its associated protein.

Maternal-zygotic knockout reveals a critical role of Cdx2 in the morula to blastocyst transition

The first lineage segregation in the mouse embryo generates the inner cell mass (ICM), which gives rise to the pluripotent epiblast and therefore the future embryo, and the trophectoderm (TE), which will build the placenta. The TE lineage depends on the transcription factor Cdx2. However, when Cdx2 first starts to act remains unclear. Embryos with zygotic deletion of Cdx2 develop normally until the late blastocyst stage leading to the conclusion that Cdx2 is important for the maintenance but not specification of the TE. In contrast, down-regulation of Cdx2 transcripts from the early embryo stage results in defects in TE specification before the blastocyst stage. Here, to unambiguously address at which developmental stage Cdx2 becomes first required, we genetically deleted Cdx2 from the oocyte stage using a Zp3-Cre/loxP strategy. Careful assessment of a large cohort of Cdx2 maternal-zygotic null embryos, all individually filmed, examined and genotyped, reveals an earlier lethal phenotype than observed in Cdx2 zygotic null embryos that develop until the late blastocyst stage. The developmental failure of Cdx2 maternal-zygotic null embryos is associated with cell death and failure of TE specification, starting at the morula stage. These results indicate that Cdx2 is important for the correct specification of TE from the morula stage onwards and that both maternal and zygotic pools of Cdx2 are required for correct pre-implantation embryogenesis.

Time-lapse dynamics of the mouse oocyte chromatin organisation during meiotic resumption

In the mammalian oocyte, distinct patterns of centromeres and pericentromeric heterochromatin localisation correlate with the gamete's developmental competence. Mouse antral oocytes display two main types of chromatin organisation: SN oocytes, with a ring of Hoechst-positive chromatin surrounding the nucleolus, and NSN oocytes lacking this ring. When matured to MII and fertilised, only SN oocytes develop beyond the 2-cell, and reach full term. To give detailed information on the dynamics of the SN or NSN chromatin during meiosis resumption, we performed a 9 hr time-lapse observation. The main significant differences recorded are: (1) reduction of the nuclear area only in SN oocytes; (2) ~17 min delay of GVBD in NSN oocytes; (3) chromatin condensation, after GVBD, in SN oocytes; (4) formation of 4-5 CHCs in SN oocytes; (5) increase of the perivitelline space, ~57 min later in NSN oocytes; (6) formation of a rosette-like disposition of CHCs, ~84 min later in SN oocytes; (7) appearance of the MI plate ~40 min later in NSN oocytes. Overall, we described a pathway of transition from the GV to the MII stage that is punctuated of discrete recordable events showing their specificity and occurring with different time kinetics in the two types of oocytes.