Selective degradation of maternal and embryonic transcripts in in vitro produced bovine oocytes and embryos using sequence specific double-stranded RNA

Combined Exogenous Activation of Bovine Oocytes: Effects on Maturation-Promoting Factor, Mitogen-Activated Protein Kinases, and Embryonic Competence

Oocyte activation via dual inhibition of protein synthesis and phosphorylation has improved in vitro embryo production in different mammalian species. In this study, we evaluated the effects of the combination of cycloheximide (CHX), dimethyl amino purine (DMAP), and anisomycin (ANY) on the activation of bovine oocytes, particularly on dynamics of MPF and MAPKs, embryonic developmental potential, and quality. The results showed that the cleavage and blastocyst rates, as well as levels of CCNB1, CDK1, p-CDK1Thr161, and p-CDK1Thr14-Tyr15, were similar among groups; ANY and ANY + CHX reduced the expression of ERK1/2 compared to DMAP-combinations (p < 0.05), whereas ANY + DMAP, CHX + DMAP, and ANY + CHX + DMAP reduced p-ERK1/2 compared to ANY and ANY + CHX treatments (p < 0.05). The quality of blastocysts in terms of cell counts, their allocation, and the numbers of TUNEL-positive cells did not differ among groups. However, transcript levels of POU5F1 were higher in embryos derived from ANY + CHX + DMAP treatment compared to other groups, while expression levels of CDX2 did not show differences. In addition, the BCL2A1/BAX ratio of the ANY + CHX + DMAP treatment was significantly low compared to the ANY treatment (p < 0.05) and did not differ significantly from the other treatments. In conclusion, oocyte activation by dual inhibition of protein synthesis and phosphorylation induces MPF inactivation without degradation of CCNB1, while MAPK inactivation occurs differentially between these inhibitors. Thus, although the combined use of these inhibitors does not affect early developmental competence in vitro, it positively impacts the expression of transcripts associated with embryonic quality.

Pluripotent Core in Bovine Embryos: A Review

Early development in mammals is characterized by the ability of each cell to produce a complete organism plus the extraembryonic, or placental, cells, defined as pluripotency. During subsequent development, pluripotency is lost, and cells begin to differentiate to a particular cell fate. This review summarizes the current knowledge of pluripotency features of bovine embryos cultured in vitro, focusing on the core of pluripotency genes (OCT4, NANOG, SOX2, and CDX2), and main chemical strategies for controlling pluripotent networks during early development. Finally, we discuss the applicability of manipulating pluripotency during the morula to blastocyst transition in cattle species.

Inhibition of Skp1-Cullin-F-box complexes during bovine oocyte maturation and preimplantation development leads to delayed development of embryos†

The mechanism of maternal protein degradation during preimplantation development has not been clarified yet. It is thought that a lot of maternal proteins are degraded by the ubiquitin-proteasome system. In this study, we focused on the role of the SCF (Skp1-Cullin-F-box) complexes during early bovine embryogenesis. We inhibited them using MLN4924, an inhibitor of SCF complex ligases controlled by neddylation. Oocytes maturated in MLN4924 could be fertilized, but we found no cumulus cell expansion and a high number of polyspermy after in vitro fertilization. We also found a statistically significant deterioration of development after MLN4924 treatment. After treatment with MLN4924 from the four-cell to late eight-cell stage, we found a statistically significant delay in their development; some of the treated embryos were, however, able to reach the blastocyst stage later. We found reduced levels of mRNA of EGA markers PAPOLA and U2AF1A, which can be related to this developmental delay. The cultivation with MLN4924 caused a significant increase in protein levels in MLN4924-treated oocytes and embryos; no such change was found in cumulus cells. To detect the proteins affected by MLN4924 treatment, we performed a Western blot analysis of selected proteins (SMAD4, ribosomal protein S6, centromeric protein E, P27, NFKB inhibitor alpha, RNA-binding motif protein 19). No statistically significant increase in protein levels was detected in either treated embryos or oocytes. In summary, our study shows that SCF ligases are necessary for the correct maturation of oocytes, cumulus cell expansion, fertilization, and early preimplantation development of cattle.

Symposium review: Embryo survival-A genomic perspective of the other side of fertility

The majority of embryonic loss in cattle occurs within the first 3 to 4 wk of pregnancy, and there are currently no accurate predictors of pregnancy outcome. Existing embryo quality assessment methods include morphological evaluation and embryo biopsy. These methods are not accurate and carry some health risks to the developing embryo, respectively. Therefore, there is need to identify noninvasive biomarkers such as microRNA that can predict embryo quality and pregnancy outcome. Furthermore, researchers need a better understanding of the dynamic interaction between the mother and the embryo. The transcriptome of the uterus shows plasticity that depends on the embryo type so that the expression level of some genes for in vivo embryos would be different from that of in vitro-produced embryos. Similarly, the embryonic transcriptome and epigenome change in response to different environmental factors such as stress, diet, disease, and physiological status of the mother. This embryo-mother crosstalk could be better understood by investigating the molecular signaling that occurs at different stages of embryonic development. Although transcriptomics is a useful tool to assess the roles of genes and pathways in embryo quality and maternal receptivity, it does not provide the exact functions of these genes, and it shows correlation rather than causality. Therefore, an in-depth functional genomic analysis is needed for better understanding of the molecular mechanisms controlling embryo development. In this review, we discuss recent genomic technologies such as RNA interference, gapmer technology, and genome editing techniques used in humans and livestock to elucidate the molecular mechanisms of genes affecting embryo development.

CoQ10 increases mitochondrial mass and polarization, ATP and Oct4 potency levels, and bovine oocyte MII during IVM while decreasing AMPK activity and oocyte death

PURPOSE

We tested whether mitochondrial electron transport chain electron carrier coenzyme Q10 (CoQ10) increases ATP during bovine IVM and increases %M2 oocytes, mitochondrial polarization/mass, and Oct4, and decreases pAMPK and oocyte death.

METHODS

Bovine oocytes were aspirated from ovaries and cultured in IVM media for 24 h with 0, 20, 40, or 60 μM CoQ10. Oocytes were assayed for ATP by luciferase-based luminescence. Oocyte micrographs were quantitated for Oct4, pAMPK (i.e., activity), polarization by JC1 staining, and mitochondrial mass by MitoTracker Green staining.

RESULTS

CoQ10 at 40 μM was optimal. Oocytes at 40 μM enabled 1.9-fold more ATP than 0 μM CoQ10. There was 4.3-fold less oocyte death, 1.7-fold more mitochondrial charge polarization, and 3.1-fold more mitochondrial mass at 40 μM than at 0 μM CoQ10. Increased ATP was associated with 2.2-fold lower AMPK thr172P activation and 2.1-fold higher nuclear Oct4 stemness/potency protein at 40 μM than at 0 μM CoQ10. CoQ10 is hydrophobic, and at all doses, 50% was lost from media into oil by ~ 12 h. Replenishing CoQ10 at 12 h did not significantly diminish dead oocytes.

CONCLUSIONS

The data suggest that CoQ10 improves mitochondrial function in IVM where unwanted stress, higher AMPK activity, and Oct4 potency loss are induced.

MicroRNA-130b is involved in bovine granulosa and cumulus cells function, oocyte maturation and blastocyst formation

Background

Oocyte maturation and preimplantation embryo development are controlled by array of genes that are post-transcriptionally regulated by microRNAs. With respect to this, previously, we identified altered expression of microRNA-130b (miR-130b) during oocyte maturation. Here, we aimed to investigate the role of miR-130b in bovine granulosa and cumulus cell function, oocyte maturation and preimplantation embryo development using gain- and loss-of- function approach.

Methods

For this study, the granulosa cells, cumulus cells and the oocytes were collected from ovaries obtained from slaughterhouse. The genes targeted by miR-130b were identified using dual-luciferase reporter assay. The role of miR-130b in granulosa and cumulus cell function was investigated by increasing and inhibiting its expression in in vitro cultured cells using miR-130b precursor and inhibitor, respectively while the role of miR-130b on oocyte development, immature oocytes were microinjected with miR-130b precursor and inhibitor and the polar body extrusion, the proportion of oocytes reaching to metaphase II stage and the mitochondrial were determined in each oocyte group 22 h after microinjection. Moreover, to investigate the role of miR-130b during preimplantation embryo development, zygote stage embryos were microinjected with miR-130b precursor or inhibitor and the cleavage rate, morula and blastocyst formation was analyzed in embryos derived from each zygote group after in vitro culture.

Results

The luciferase assay showed that SMAD5 and MSK1 genes were identified as the direct targets of miR-130b. Overexpression of miR-130b increased the granulosa and cumulus cell proliferation, while inhibition showed the opposite phenotype. Apart from these, modulation of miR-130b altered the lactate production and cholesterol biosynthesis in cumulus cells. Furthermore, inhibition of miR-130b expression during oocyte in vitro maturation reduced the first polar body extrusion, the proportion of oocytes reaching to metaphase II stage and the mitochondrial activity, while inhibition of miR-130b during preimplantation embryo development significantly reduced morula and blastocyst formation.

Conclusion

This study demonstrated that in vitro functional modulation of miR-130b affected granulosa and cumulus cell proliferation and survival, oocyte maturation, morula and blastocyst formation suggesting that miR-130b is involved in bovine oocyte maturation and preimplantation embryo development.

Electronic supplementary material

The online version of this article (doi:10.1186/s13048-017-0336-1) contains supplementary material, which is available to authorized users.

Targeted Gene Knockdown in Early Embryos Using siRNA

RNA interference is a convenient and highly effective technique to investigate the biological function of genes. Adequately designed RNA molecules introduced into an oocyte are able to bind specific endogenous mRNAs and trigger their degradation. Subsequent fertilization of these oocytes will result in the generation of embryos in which the expression of the gene of interest is downregulated, and following the degradation of maternal proteins the role of the gene product can be studied. Here, we describe the approach how post-transcriptional gene silencing can be achieved in oocytes and early embryos using siRNA.

Low level of mono(2-ethylhexyl) phthalate reduces oocyte developmental competence in association with impaired gene expression

Di-(2-ethylhexyl) phthalate (DEHP) and its metabolite, mono-(2-ethylhexyl) phthalate (MEHP), are reproductive toxicants. However, disruptive effects of MEHP at low concentrations on the oocyte and developing blastocyst are unknown. Previously, we detected low levels of MEHP in follicular fluid aspirated from DEHP-treated cows associated with reduced estradiol levels. Moreover, the MEHP concentrations found were similar to those reported for follicular fluid aspirated from women who have undergone IVF cycles. In the current study, we used an in vitro embryo production model to examine the effect of MEHP at low levels on oocyte developmental competence. We set up several experiments to mimic the follicular fluid content, i.e., low MEHP level and low estradiol. For all experiments, cumulus oocyte complexes (COCs) were aspirated from bovine ovaries, then matured in vitro in standard oocyte maturation medium (OMM) supplemented with: MEHP at a range levels (20-1000nM) or with estradiol at a range levels (0-2000ng/ml). Then, oocytes were fertilized and cultured for an additional 7days to allow blastocyst development. Findings revealed that MEHP at low levels impairs oocyte developmental competence in a dose-dependent manner (P<0.05) and that estradiol by itself does not impair it. Accordingly, in another set of experiments, COCs were matured in vitro with MEHP at two choosen concentrations (20 or 1000nM) with or without estradiol, fertilized and cultured for 7days. Samples of mature oocytes and their derived blastocysts were subjected to quantitative real-time PCR to examine the profiles of selected genes (CYC1, MT-CO1, ATP5B, POU5F1, SOX2 and DNMT3b). Maturation of COCs with MEHP (20 or 1000nM) affected gene expression in the mature oocyte. Maturation of COCs with MEHP (20 or 1000nM) in the absence of estradiol reduced oocyte developmental competence (P<0.05). A differential carryover effect on transcript abundance was recorded in blastocysts developed from MEHP-treated oocytes. In the presence of estradiol, increased expression was recorded for CYC1, ATP5B, SOX2 and DNMT3b. In the absence of estradiol, decreased expression was recorded, with a significant effect for 1000nM MEHP (P<0.05). Taken together, the findings suggest that low levels of phthalate must be taken into consideration in risk assessments.

The Necessity of OCT-4 and CDX2 for Early Development and Gene Expression Involved in Differentiation of Inner Cell Mass and Trophectoderm Lineages in Bovine Embryos

The functions of POU class 5 transcription factor 1 (Oct-4) and caudal-type homeobox 2 (Cdx2) in the differentiation of the murine inner cell mass (ICM) and trophectoderm (TE) have been described in detail. However, little is known about the roles of OCT-4 and CDX2 in preimplantation bovine embryos. To elucidate their functions during early development in bovine embryos, we performed OCT-4 and CDX2 downregulation using RNA interference. We injected OCT-4- or CDX2-specific short interfering RNAs (siRNAs) into bovine zygotes. The rate of blastocyst development of OCT-4-downregulated embryos was lower compared with uninjected or control siRNA-injected embryos. Gene expression analysis revealed decreased CDX2 and fibroblast growth factor 4 expression in OCT-4-downregulated embryos. CDX2-downregulated embryos developed to the blastocyst stage; however, in most cases, blastocoel formation was delayed. Gene expression analysis revealed decreased GATA3 expression and elevated NANOG expression in CDX2-downregulated embryos. In conclusion, OCT-4 and CDX2 are essential for early development and gene expression involved in differentiation of ICM and TE lineages in bovine embryos.

Follicular progesterone concentrations and messenger RNA expression of MATER and OCT-4 in immature bovine oocytes as predictors of developmental competence

The ability of bovine embryos to develop to the blastocyst stage and to implant and generate healthy offspring depends greatly on the competence of the oocyte. Oocyte competence is attributed to its close communication with the follicular environment and to its capacity to synthesize and store substantial amounts of messenger RNA. Higher developmental competence of bovine oocytes has been associated with both the expression of a cohort of developmental genes and the concentration of sex steroids in the follicular fluid. The aim of this study was to identify differences in the expression of FST in cumulus cells and OCT-4 and MATER in oocytes and the influence of the follicular progesterone and follicular estrogen concentration on the competence of bovine oocytes retrieved 30 minutes or 4 hours after slaughter. Cumulus-oocyte complexes (COCs) were left in postmortem ovaries for 30 minutes (group I) or 4 hours (group II) at 30 °C. Aspirated oocytes were then subjected to IVM, IVF, and IVC or were evaluated for MATER and OCT-4 messenger RNA abundance by quantitative real-time polymerase chain reaction. Total RNA was isolated from pools of 100 oocytes for each experimental replicate. Progesterone and estradiol concentration in follicular fluid was evaluated by immunoassay using an IMMULITE 2000 analyzer. Three repeats of in vitro embryo production were performed with a total of 455 (group I) and 470 (group II) COCs. There were no significant differences between the cleavage rates (72 hours postinsemination [hpi]) between both groups (63.5% vs. 69.1%). However, blastocyst (168 hpi) and hatching (216 hpi) rates were higher (P < 0.05) in group II compared with those of group I (21.3% vs. 30.7% and 27.6% vs. 51.5%, respectively). Group II oocytes exhibited the highest MATER and OCT-4 abundance (P < 0.05). Follicular estradiol concentration was not different between both the groups, whereas the progesterone concentration was lower (P ≤ 0.05) in group II follicles. These results indicate that retrieving COCs 4 hours after slaughter could increase bovine in vitro developmental competence, which is linked to higher levels of oocyte MATER and OCT-4 transcripts and lower follicular progesterone concentration. Moreover, the results of the present study contribute to the identification of factors involved in the developmental competence of immature oocytes.

Knockdown of p66Shc by siRNA injection rescues arsenite-induced developmental retardation in mouse preimplantation embryos

Two-cell arrest plays a principal role in the elevated levels of embryo loss during the first week of development in mouse. Previously, we have shown that arsenic can apparently induce 2-cell arrest in mouse preimplantation embryo and the expression of oxidative stress adaptor protein p66(Shc) is up-regulated in this process. In the present study, we demonstrated that microinjection of p66(Shc) siRNA into the pronucleus of zygotes resulted in a markedly decrease in both mRNA and protein levels of p66(Shc). The arsenite-induced 2-cell arrests, along with a reduction in the levels of reactive oxygen species (ROS), were significantly inhibited and the number of embryos developing to morula stage concurrently increased upon p66(shc) siRNA microinjection. These findings indicate that knockdown of p66(shc) improves the developmental competence of arsenite-exposed embryos in vitro by increasing the resistance to oxidative stress. In addition, we highlight the utility of single-embryo analysis in preimplantation embryos.

Knockdown of CDKN1C (p57(kip2)) and PHLDA2 results in developmental changes in bovine pre-implantation embryos

Imprinted genes have been implicated in early embryonic, placental, and neonatal development and alterations in expression levels of these genes can lead to growth abnormalities and embryonic lethality. However, little is known about the functions of bovine imprinted genes during the pre-implantation period. Therefore, the objective of this study was to assess the influence of altered expression of imprinted genes on developmental progress of embryos using small interfering RNA (siRNA). Expression levels of 18 imprinted genes (MAGEL2, UBE3A, IGF2R, NAP1L5, TSSC4, PEG3, NDN, CDKN1C, PHLDA2, MKRN3, USP29, NNAT, PEG10, RTL1, IGF2, H19, MIM1, and XIST) were compared between embryos reaching the blastocyst stage and growth-arrested embryos (degenerates) using quantitative real-time PCR (qRT-PCR). Ten genes were found to be differentially expressed between blastocysts and degenerates. The CDKN1C gene showed the highest upregulation in blastocysts whereas PHLDA2 was highly expressed in degenerates. To assess whether the observed differential gene expression was causative or resultant of embryo degeneration, these genes were selected for functional analysis using siRNA. Injection of siRNA specific to PHLDA2 into one-cell zygotes resulted in a substantial increase in blastocyst development, whereas injection of CDKN1C-specific siRNA resulted in a 45% reduction (P = 0.0006) in blastocyst development. RNA-Seq analysis of CDKN1C-siRNA-injected vs. non-injected embryos revealed 51 differentially expressed genes with functions in apoptosis, lipid metabolism, differentiation, and cell cycle regulation. Gene ontology analysis revealed nine pathways related to cell signaling, metabolism, and nucleic acid processing. Overall, our results show that proper expression levels of the imprinted genes CDKN1C and PHLDA2 are critical for embryo development, which suggests that these genes can be used as markers for normal blastocyst formation.

Effects of downregulating oct-4 transcript by RNA interference on early development of porcine embryos

The objective of this study was to investigate the role of the POU family transcription factor, Oct-4, in the early development of porcine embryos. We attempted Oct-4 downregulation of porcine early embryos by RNA interference, and evaluated Oct-4 suppression of developmental competencies and gene transcripts in porcine embryos. Injection of specific siRNA resulted in a distinct decrease in Oct-4 mRNA and protein expression in porcine embryos until at least the morula stage. Although the porcine embryos injected with Oct-4 siRNA were able to develop to the morula stage, these embryos failed to form blastocysts. Gene transcripts of caudal-like transcription factor (Cdx2) and fibroblast growth factor 4 (Fgf4), which were involved in segregation of the trophectderm and functionalization of the inner cell mass, were unchanged by Oct-4 siRNA injection. Our results indicated that Oct-4 is an important factor for porcine embryos and, in particular, for the regulation of porcine blastocyst formation.

Effect of di-(2-ethylhexyl) phthalate and mono-(2-ethylhexyl) phthalate on in vitro developmental competence of bovine oocytes

In the last decade, potential exposure of humans and animals to industrial chemicals and pesticides has been a growing concern. In the present study, di-(2-ethylhexyl) phthalate (DEHP) and mono-(2-ethylhexyl) phthalate (MEHP) were used to model the effects of endocrine-disrupting compounds and their risk in relation to early embryonic losses. Exposure of cumulus oocyte complexes during maturation to 50 μM MEHP reduced the proportion of oocytes that underwent nuclear maturation (p < 0.05) and increased the proportion of apoptotic oocytes (p < 0.05). Furthermore, phthalates reduced cleavage rate in the MEHP-treated group (p < 0.05) and the proportion of embryos developing to the blastocyst stage in both DEHP- and MEHP-treated groups (p < 0.05). The total cell count for blastocysts developing from MEHP-treated oocytes was lower than in controls (p < 0.05). Exposure of oocytes to MEHP during maturation reduced (p < 0.05) the expression of ASAH1 (an anti-apoptotic factor), CCNA2 (involved in cell cycle control), and POU5F1 (responsible for pluripotency) in matured oocytes. Furthermore, the reduced mRNA expression of POU5F1 and ASAH1 lasted into two-cell stage embryos (p < 0.05). Phthalate-induced alterations in POU5F1, ASAH1, and CCNA2 expression might explain in part the reduced developmental competence of MEHP-treated oocytes.

Bovine preimplantation embryos with silenced nucleophosmin mRNA are able to develop until the blastocyst stage

This study was conducted to investigate the effect of silencing nucleophosmin in the development of in vitro-produced bovine embryos. Nucleophosmin is an abundant multifunctional nucleolar phosphoprotein that participates, for example, in ribosome biogenesis or centrosome duplication control. We showed that although the transcription of embryonic nucleophosmin started already at late eight-cell stage, maternal protein was stored throughout the whole preimplantation development and was sufficient for the progression to the blastocyst stage. At the beginning of embryogenesis, translation occurs on maternally derived ribosomes, the functionally active nucleoli emerge during the fourth cell cycle in bovines. We found that nucleophosmin localisation reflected the nucleolar formation during bovine preimplantation development. The protein was detectable from the beginning of embryonic development. Before embryonic genome activation, it was dispersed throughout the nucleoplasm. The typical nucleolar localisation emerged with the formation of active nucleoli. At the blastocyst stage, nucleophosmin tended to localise especially to the trophectoderm. To see for how long is maternal nucleophosmin preserved, we silenced the nucleophosmin mRNA using RNA interference approach. Although a large portion of nucleophosmin was degraded in embryos with silenced nucleophosmin mRNA, an amount sufficient for normal development was preserved and we detected only a temporal delay in nucleophosmin relocalisation to nucleoli. Moreover, we observed no defects in nuclear shape or cytoskeleton previously found in somatic cells and only a non-significant decrease in embryonic developmental competence. Thus, our results show that the preserved amount of maternal nucleophosmin is sufficient for preimplantation development of bovine embryo.

Gas6 downregulation impaired cytoplasmic maturation and pronuclear formation independent to the MPF activity

Previously, we found that the growth arrest-specific gene 6 (Gas6) is more highly expressed in germinal vesicle (GV) oocytes than in metaphase II (MII) oocytes using annealing control primer (ACP)-PCR technology. The current study was undertaken to investigate the role of Gas6 in oocyte maturation and fertilization using RNA interference (RNAi). Interestingly, despite the specific and marked decrease in Gas6 mRNA and protein expression in GVs after Gas6 RNAi, nuclear maturation including spindle structures and chromosome segregation was not affected. The only discernible effect induced by Gas6 RNAi was a change in maturation promoting factor (MPF) activity. After parthenogenetic activation, Gas6 RNAi-treated oocytes at the MII stage had not developed further and arrested at MII (90.0%). After stimulation with Sr(2+), Gas6-silenced MII oocytes had markedly reduced Ca(2+) oscillation and exhibited no exocytosis of cortical granules. In these oocytes, sperm penetration occurred during fertilization but not pronucleus (PN) formation. By roscovitine and colcemid treatment, we found that the Gas6 knockdown affected cytoplasmic maturation directly, independent to the changed MPF activity. These results strongly suggest that 1) the Gas6 signaling itself is important to the cytoplasmic maturation, but not nuclear maturation, and 2) the decreased Gas6 expression and decreased MPF activity separately or mutually influence sperm head decondensation and PN formation.

A novel functional role for the oocyte-specific transcription factor newborn ovary homeobox (NOBOX) during early embryonic development in cattle

Newborn ovary homeobox (NOBOX) is an oocyte-specific transcription factor essential for folliculogenesis and expression of many germ cell-specific genes in mice. Here we report the characterization of the bovine NOBOX gene and its role in early embryogenesis. The cloned cDNA for bovine NOBOX contains an open reading frame encoding a protein of 500 amino acids with a conserved homeodomain. mRNA for NOBOX is preferentially expressed in ovaries and undetectable by RT-PCR in somatic tissues examined. NOBOX protein is present in oocytes throughout folliculogenesis. NOBOX is expressed in a stage-specific manner during oocyte maturation and early embryonic development and of maternal origin. Knockdown of NOBOX in early embryos using small interfering RNA demonstrated that NOBOX is required for embryonic development to the blastocyst stage. Depletion of NOBOX in early embryos caused significant down-regulation of genes associated with transcriptional regulation, signal transduction, and cell cycle regulation during embryonic genome activation. In addition, NOBOX depletion in early embryos reduced expression of pluripotency genes (POU5F1/OCT4 and NANOG) and number of inner cell mass cells in embryos that reached the blastocyst stage. This study demonstrates that NOBOX is an essential maternal-derived transcription factor during bovine early embryogenesis, which functions in regulation of embryonic genome activation, pluripotency gene expression, and blastocyst cell allocation.

Dicer is a key player in oocyte maturation

OBJECTIVE

Apply Dicer siRNA to study functions of Dicer and miRNA during oogenesis.

MATERIALS AND METHODS

Mouse oocytes were injected with Dicer siRNA and negative control siRNA and then matured in vitro. After IVM, oocytes were examined for maturation rates, spindle and chromosomal organization, and various gene expressions.

RESULTS

Dicer siRNA significantly reduced maturation rates, increased abnormal spindle and chromosomal organization, and reduced the transcripts of Dicer miRNAs, spindle formation proteins (plk1 and AURKA) and spindle check points (Bub1, Bublb). Depletion of bulb16 markedly prohibited the first polar body extrusion and increased the incidence of misaligned chromosomes and abnormal meiotic spindle assembly.

CONCLUSION

Dicer siRNA triggered a cascade reduction for gene expressions starting from Dicer to miRNAs than to spindle assembly proteins and checkpoints which led to abnormal spindle and chromosomal organization. Thus, Dicer and miRNA appeared to play an important role during oogenesis and were essential for meiotic completion.

Seasonal effects on gene expression, cleavage timing, and developmental competence of bovine preimplantation embryos

We examined the association between season and expression of genes involved in early embryonic development with an emphasis on cleavage rate and timing of the first embryonic cleavage. In Exp. 1, oocytes were aspirated during the cold (Dec–Apr) and hot (May–Nov) seasons. Matured oocytes were chemically activated and culturedin vitro. The developmental peak to the two- and four-cell stages occurred earlier, with a higher proportion of first-cleaved embryos, during the cold season relative to the hot season (P<0.01). In Exp. 2, a time-lapse system was employed to characterize the delayed cleavage noted for the hot season. Cleavage to the two-cell stage occurred in two distinct waves: early cleavage occurred between 18 and 25 h post activation, and late cleavage occurred between 27 and 40 h post activation. In Exp. 3, oocytes were aspirated during the cold and hot seasons, maturedin vitro, fertilized, and cultured for 8 days. In each season, early- and late-cleaved two-cell stage embryos were collected. Total RNA was isolated, and semi-quantitative and real-time PCRs were carried out with primers forGDF9,POU5F1, andGAPDHusing18S rRNAas the reference gene. In both seasons, the expression of all examined genes was higher (P<0.05) in early- versus late-cleaved embryos.POU5F1expression was higher (P<0.05) in early-cleaved embryos developed in the cold season versus the hot season counterparts. The findings suggest a deleterious seasonal effect on oocyte developmental competence with delayed cleavage and variation in gene expression.

Suppression of the transcription factor MSX1 gene delays bovine preimplantation embryo development in vitro

This study was conducted to investigate the effect of suppressing transcription factor geneMSX1on the development ofin vitroproduced bovine oocytes and embryos, and identify its potential target genes regulated by this gene. Injection of long double-stranded RNA (LdsRNA) and small interfering RNA (siRNA) at germinal vesicle stage oocyte reducedMSX1mRNA expression by 73 and 37% respectively at metaphase II stage compared with non-injected controls. Similarly, injection of the same anti-sense oligomers at zygote stage reducedMSX1mRNA expression by 52 and 33% at 8-cell stage compared with non-injected controls. Protein expression was also reduced in LdsRNA- and siRNA-injected groups compared with non-injected controls at both stages. Blastocysts rates were 33, 28, 20 and 18% in non-injected control, scrambled RNA (scRNA), LdsRNA- and siRNA-injected groups respectively. Cleavage rates were also significantly reduced in Smartpool siRNA (SpsiRNA)-injected group (53.76%) compared with scRNA-injected group (57.76%) and non-injected control group (61%). Large-scale gene expression analysis showed that 135 genes were differentially regulated in SpsiRNA-injected group compared with non-injected controls, of which 54 and 81 were down- and up-regulated respectively due to suppression ofMSX1. Additionally, sequence homology mapping and gene enrichment analysis with known human pathway information identified several functional modules that were affected due to suppression ofMSX1. In conclusion, suppression ofMSX1affects oocyte maturation, embryo cleavage rate and the expression of several genes, suggesting its potential role in the development of bovine preimplantation embryos.

Suppression of keratin 18 gene expression in bovine blastocysts by RNA interference

The expression of the cytoskeleton protein Keratin 18 (KRT18) starts at the onset of bovine blastocyst formation. KRT18 is solely expressed in the trophectoderm and can therefore be used as a marker for trophectodermal differentiation. In the present study, the expression of KRT18 was suppressed by RNA interference to probe its functional importance in bovine blastocyst formation. Microinjection of KRT18 double-stranded RNA into the cytoplasm of zygotes resulted in reduced KRT18 mRNA (76% reduction) and protein expression at the blastocyst stage and a lower developmental competence (41% reduction in the percentage of blastocyst formation) compared with non-injected and phosphate-buffered saline (PBS)-injected controls. KRT18 downregulation was associated with reduced mRNA expression of KRT8, the binding partner of KRT18, but had no effect on the expression of KRT19, CDH1 and DSP, other genes involved in intermediate filament and cytoskeleton formation. The results of the present study demonstrated that KRT18 knockdown in preimplantation embryos results in reduced blastocyst formation, but no further morphological aberrations were observed with regard to the biological function of KRT18. These observations could be due to the function of KRT18 being replaced by that of another gene, the surviving blastocysts expressing the minimum level of KRT18 required for normal blastocyst development or the possibility that further aberrations may occur later in development.

Depletion of BIRC6 leads to retarded bovine early embryonic development and blastocyst formation in vitro

Baculoviral inhibitors of apoptosis repeat-containing 6 (BIRC6) is believed to inhibit apoptosis by targeting key cell-death proteins. To understand its involvement during bovine preimplantation embryo development, two consecutive experiments were conducted by targeted knockdown of its mRNA and protein using RNA interference. In Experiment 1, the effect of BIRC6 knockdown during the early stages of preimplantation embryo development was assessed by injecting zygotes with long double-stranded RNA (ldsRNA) and short hairpin RNA (shRNA) against BIRC6 mRNA followed by in vitro culturing until 96 h post insemination (hpi). The results showed that in RNA-injected zygote groups, reduced levels of BIRC6 mRNA and protein were accompanied by an increase (P < 0.05) in the proportion of 2- and 4-cell and uncleaved embryos and a corresponding decrease (P < 0.05) in the number of 8-cell embryos. In Experiment 2, the effect of BIRC6 knockdown on blastocyst formation, blastocyst total cell number and the extent of apoptosis was investigated. Consequently, zygotes injected with ldsRNA and shRNA resulted in lower (P < 0.05) blastocyst formation and total blastocyst cell number. Moreover, the apoptotic cell ratio, CASPASE 3 and 7 activity, BAX to BCL-2 ratio and levels of SMAC and CASPASE 9 were higher in blastocysts derived from the ldsRNA and shRNA groups, suggesting increased apoptosis in those blastocysts. The results of this study reveal the importance of BIRC6 expression for embryo survival during bovine preimplantation embryo development. However, whether BIRC6 is essential for implantation and fetal development during bovine pregnancy needs further research.

In vitro suppression of the MMP-3 gene in normal and cytokine-treated human chondrosarcoma using small interfering RNA

Background

Matrix metalloproteinase (MMPs) synthesized and secreted from connective tissue cells have been thought to participate in degradation of the extracellular matrix. Increased MMPs activities that degrade proteoglycans have been measured in osteoarthritis cartilage. This study aims to suppress the expression of the MMP-3 gene in in vitro human chondrosarcoma using siRNA.

Methods

Cells were categorized into four groups: control (G.1); transfection solution treated (G.2); negative control siRNA treated (G.3); and MMP-3 siRNA treated (G.4). All four groups were further subdivided into two groups - treated and non-treated with IL-1β- following culture for 48 and 72 h. We observed the effects of gene suppression according to cell morphology, glycosaminoglycan (GAG) and hyaluronan (HA) production, and gene expression by using real-time polymerase chain reaction (PCR).

Results

In IL-1β treated cells the apoptosis rate in G.4 was found to be lower than in all other groups, while viability and mitotic rate were higher than in all other groups (p < 0.05). The production of GAG and HA in G.4 was significantly higher than the control group (p < 0.05). MMP-3 gene expression was downregulated significantly (p < 0.05).

Conclusion

MMP-3 specific siRNA can inhibit the expression of MMP-3 in chondrosarcoma. This suggests that MMP-3 siRNA has the potential to be a useful preventive and therapeutic agent for osteoarthritis.

Gene expression in early expanded parthenogenetic and in vitro fertilized bovine blastocysts

Mammalian oocytes can undergo artificial parthenogenesis in vitro and develop to the blastocyst stage. In this study, using real-time PCR, we analyzed the expression of genes representative of essential events in development. In vitro matured oocytes were either fertilized or activated with ionomycin + 6-DMAP and cultured in simple medium. The pluripotency-related gene Oct3/4 was downregulated in parthenotes, while the de novo methylation DNMT3A gene was unchanged. Among the pregnancy recognition genes, IFN-t was upregulated, PGRMC1 was downregulated and PLAC8 was unchanged in parthenotes. Among the metabolism genes, SLC2A1 was downregulated, while AKR1B1, COX2, H6PD and TXN were upregulated in parthenotes; there was no difference in SLC2A5. Among the genes involved in compaction/blastulation, GJA1 expression increased in parthenotes, but no differences were detected within ATP1A1 and CDH1. Expression of p66(shc) and the Bax/Bcl2 ratio were higher in parthenotes, and there was no difference in p53. Parthenotes and embryos may differ in the way they stimulate apoptosis, with a preponderant role for p66(shc) within parthenotes. Differentially affected functions may also include pluripotency, de novo methylation and early embryonic signalling.

Silencing CENPF in bovine preimplantation embryo induces arrest at 8-cell stage

Identification of genes that are important for normal preimplantation development is essential for understanding the basics of early mammalian embryogenesis. In our previous study, we have shown that CENPF (mitosin) is differentially expressed during preimplantation development of bovine embryos. CENPF is a centromere-kinetochore complex protein that plays a crucial role in the cell division of somatic cells. To our best knowledge, no study has yet been done on either bovine model, or oocytes and preimplantation embryos. In this study, we focused on the fate of bovine embryos after injection of CENPF double-stranded RNA (dsRNA) into the zygotes. An average decrease of CENPF mRNA abundance by 94.9% or more and an extensive decline in immunofluorescence staining intensity was detected relative to controls. There was no disparity between individual groups in the developmental competence before the 8-cell stage. However, the developmental competence rapidly decreased then and only 28.1% of CENPF dsRNA injected 8-cell embryos were able to develop further (uninjected control: 71.8%; green fluorescent protein dsRNA injected control: 72.0%). In conclusion, these results show that depletion of CENPF mRNA in preimplantation bovine embryos leads to dramatic decrease of developmental competence after embryonic genome activation.

Biological differences between in vitro produced bovine embryos and parthenotes

Parthenotes may represent an alternate ethical source of stem cells, once biological differences between parthenotes and embryos can be understood. In this study, we analyzed development, trophectoderm (TE) differentiation, apoptosis/necrosis, and ploidy in parthenotes and in vitro produced bovine embryos. Subsequently, using real-time PCR, we analyzed the expression of genes expected to underlie the observed differences at the blastocyst stage. In vitro matured oocytes were either fertilized or activated with ionomycin +6-DMAP and cultured in simple medium. Parthenotes showed enhanced blastocyst development and diploidy and reduced TE cell counts. Apoptotic and necrotic indexes did not vary, but parthenotes evidenced a higher relative proportion of apoptotic cells between inner cell mass and TE. The pluripotence-related POU5F1 and the methylation DNMT3A genes were downregulated in parthenotes. Among pregnancy recognition genes, TP-1 was upregulated in parthenotes, while PGRMC1 and PLAC8 did not change. Expression of p66(shc) and BAX/BCL2 ratio were higher, and p53 lower, in parthenotes. Among metabolism genes, SLC2A1 was downregulated, while AKR1B1, PTGS2, H6PD, and TXN were upregulated in parthenotes, and SLC2A5 did not differ. Among genes involved in compaction/blastulation, GJA1 was downregulated in parthenotes, but no differences were detected within ATP1A1 and CDH1. Within parthenotes, the expression levels of SLC2A1, TP-1, and H6PD, and possibly AKR1B1, resemble patterns described in female embryos. The pro-apoptotic profile is more pronounced in parthenotes than in embryos, which may differ in their way to channel apoptotic stimuli, through p66(shc) and p53 respectively, and in their mechanisms to control pluripotency and de novo methylation.

Spatio-Temporal Expression Patterns of Aurora Kinases A, B, and C and Cytoplasmic Polyadenylation-Element-Binding Protein in Bovine Oocytes During Meiotic Maturation1

Maturation of immature bovine oocytes requires cytoplasmic polyadenylation and synthesis of a number of proteins involved in meiotic progression and metaphase-II arrest. Aurora serine-threonine kinases--localized in centrosomes, chromosomes, and midbody--regulate chromosome segregation and cytokinesis in somatic cells. In frog and mouse oocytes, Aurora A regulates polyadenylation-dependent translation of several mRNAs such as MOS and CCNB1, presumably by phosphorylating CPEB, and Aurora B phosphorylates histone H3 during meiosis. We analyzed the expression of three Aurora kinase genes--AURKA, AURKB, and AURKC--in bovine oocytes during meiosis by reverse transcription followed by quantitative real-time PCR and immunodetection. Aurora A was the most abundant form in oocytes, both at mRNA and protein levels. AURKA protein progressively accumulated in the oocyte cytoplasm during antral follicle growth and in vitro maturation. AURKB associated with metaphase chromosomes. AURKB, AURKC, and Thr-phosphorylated AURKA were detected at a contractile ring/midbody during the first polar body extrusion. CPEB, localized in oocyte cytoplasm, was hyperphosphorylated during prophase/metaphase-I transition. Most CPEB degraded in metaphase-II oocytes and remnants remained localized in a contractile ring. Roscovitine, U0126, and metformin inhibited meiotic divisions; they all induced a decrease of CCNB1 and phospho-MAPK3/1 levels and prevented CPEB degradation. However, only metformin depleted AURKA. The Aurora kinase inhibitor VX680 at 100 nmol/L did not inhibit meiosis but led to multinuclear oocytes due to the failure of the polar body extrusion. Thus, in bovine oocyte meiosis, massive destruction of CPEB accompanies metaphase-I/II transition, and Aurora kinases participate in regulating segregation of the chromosomes, maintenance of metaphase-II, and formation of the first polar body.

Opportunities and challenges in applying genomics to the study of oogenesis and folliculogenesis in farm animals

Ovarian oogenesis and folliculogenesis are complex and coordinated biological processes which require a series of events that induce morphological and functional changes within the follicle, leading to cell differentiation and oocyte development. In this context, the challenge of the researchers is to describe the dynamics of gene expression in the different compartments and their interactions during the follicular programme. In recent years, high-throughput arrays have become a powerful tool with which to compare the whole population of transcripts in a single experiment. Here, we review the challenges of applying genomics to this model in farm animal species. The first limitation lies in limited the availability of biological material, which makes the study of the follicle compartments (oocyte, granulosa cells and thecal cells) or early embryo much more difficult. The concept of observing all transcripts at once is very attractive but despite progress in sequencing, the genome annotation remains very incomplete in non-model species. Particularly, oogenesis and early embryo development relate to the high proportion of unknown expressed sequence tags. Then, it is important to consider post-transcriptional and translational regulation to understand the role of these genes. Ultimately, these new inferred insights will still have to be validated by functional approaches. In addition toin vitroorex vivofunctional approaches, both ‘natural mutant’ ewe models and RNA interference represent, at the moment, the best hope for functional genomics. Advances in our understanding of reproductive physiology should be facilitated by gene expression data exchange and translation into a better understanding of the underlying biological phenomena.

RNA silencing in mammalian oocytes and early embryos

RNA silencing is a common term for homology-dependent silencing phenomena found in the majority of eukaryotic species. RNA silencing pathways share several conserved components. The common denominator of these pathways is the presence of specific, short (21-25 nt) RNA molecules generated from different double-stranded RNA substrates by a specific RNase III activity. Short RNA molecules serve as a template for sequence-specific effects including transcriptional silencing, mRNA degradation, and inhibition of translation. This review will discuss possible roles of RNA silencing pathways in mouse oocytes and early embryos as well as the use of RNA silencing for experimental inhibition of gene expression in this model system.

The oxidative stress adaptor p66Shc is required for permanent embryo arrest in vitro

BACKGROUND

Excessive developmental failure occurs during the first week of in vitro embryo development due to elevated levels of cell death and arrest. We hypothesize that permanently arrested embryos enter a stress-induced "senescence-like" state that is dependent on the oxidative stress-adaptor and lifespan determinant protein p66Shc. The aim of this study was to selectively diminish p66Shc gene expression in bovine oocytes and embryos using post-transcriptional gene silencing by RNA-mediated interference to study the effects of p66Shc knockdown on in vitro fertilized bovine embryos.

RESULTS

Approximately 12,000-24,000 short hairpin (sh)RNAi molecules specific for p66Shc were microinjected into bovine germinal vesicle stage oocytes or zygotes. Experiments were comprised of a control group undergoing IVF alone and two groups microinjected with and without p66Shc shRNAi molecules prior to IVF. The amount of p66Shc mRNA quantified by Real Time PCR was significantly (P < 0.001) lowered upon p66Shc shRNAi microinjection. This reduction was selective for p66Shc mRNA, as both histone H2a and p53 mRNA levels were not altered. The relative signal strength of p66Shc immuno-fluorescence revealed a significant reduction in the number of pixels for p66Shc shRNAi microinjected groups compared to controls (P < 0.05). A significant decrease (P < 0.001) in the incidence of arrested embryos upon p66Shc shRNAi microinjection was detected compared to IVF and microinjected controls along with significant reductions (P < 0.001) in both cleavage divisions and blastocyst development. No significant differences in p66Shc mRNA levels (P = 0.314) were observed among the three groups at the blastocyst stage.

CONCLUSION

These results show that p66Shc is involved in the regulation of embryo development specifically in mediating early cleavage arrest and facilitating development to the blastocyst stage for in vitro produced bovine embryos.

Selective degradation of transcripts in mammalian oocytes and embryos

During the last decade several gene expression analysis studies have been carried out to investigate the transcriptional profile of bovine embryos in response to various culture and treatments conditions. Despite this fact, the function of a large number of genes in mammalian embryogenesis has not yet been investigated or is not known. The conventional gene-knockout experiments have been used extensively to study the function of genes in mammalian embryogenesis. However, these studies are relatively slow and cannot keep pace with the rapid accumulation of new sequence information produced by various genome projects. For this, the posttranscriptional gene silencing (PTGS) by double-stranded RNA (dsRNA), or RNA interference (RNAi), has emerged as a new tool for studying gene function in an increasing number of organisms. The present review will focus on recent developments in the use of RNAi for selective degradation of transcripts in mammalian embryos to elucidate their function in early development.

Suppression of connexin 43 and E-cadherin transcripts in in vitro derived bovine embryos following culture in vitro or in vivo in the homologous bovine oviduct

In this study, a combination of RNAi and endoscopic transfer to the oviduct of synchronized heifers has been used to investigate the effect of suppression of Cx43 and E-cadherin on the development, mRNA and protein expression of bovine blastocysts cultured in vitro or in vivo. In vitro matured and fertilized bovine zygotes were randomly assigned to one of four groups namely: Connexin43 dsRNA-injected (n = 790), E-cadherin dsRNA-injected (n = 775), water-injected (n = 774), and noninjected controls (n = 652). Following 2 days in vitro culture, 4- and 8-cell stage embryos from each treatment group were used for culture in vitro or in vivo. About half of the 4-8-cell stage embryos from each treatment group were transferred to the oviduct of synchronized heifers, while the remainder were further cultured in vitro. Embryos from in vivo culture were flushed from recipients on the fourth day post transfer (= Day 7 post insemination). Blastocyst stage embryos from both culture systems were used for mRNA and protein expression analysis. Irrespective of treatment or culture conditions, microinjection resulted in a decline in the proportion of embryos reaching the blastocyst stage. Significantly, lower blastocyst development was observed in E-cadherin and water-injected embryos following in vivo culture compared to the noninjected controls, while intermediate results were obtained following injection with Cx43 dsRNA. Both mRNA and protein products of the target genes were suppressed but the efficiency of suppression of the target genes varied depending on the initial level of transcript abundance, which is known to be greatly affected by the culture environment.

Development and pattern of mRNA relative abundance of bovine embryos cultured in the isolated mouse oviduct in organ culture

The aim of this study was to examine the development of bovine zygotes in isolated mouse oviducts (IMO) and the quality of the blastocysts produced. In vitro produced bovine zygotes were transferred into the ampullae of the IMO and cultured in SOF or KSOM. Control embryos were cultured in droplets of the same media. Following 6 days of culture, blastocysts were processed for nuclei counts or mRNA abundance. Culture in the IMO did not affect the proportion of zygotes developing to the blastocyst stage compared to the respective control droplets (SOF: 17.7 +/- 3.2% vs. 18.8 +/- 2.7%; KSOM: 20.7 +/- 2.6% vs. 22.2 +/- 2.8%). Culture in the IMO in KSOM resulted in an increased number of inner cell mass (ICM) nuclei; however, total nuclei number or incidence of apoptosis was unaffected. Culture in the IMO in SOF resulted in an increase (P < 0.05) in abundance of transcripts in blastocysts for Oct-4 and SOX, and reduced abundance of Glut-1, Na/K, Cx43, and survivin compared to blastocysts derived from culture in SOF alone. In contrast, culture in the IMO in KSOM resulted in increased abundance of transcripts for Glut-1, Cx43, Oct-4, and survivin and reduced expression of Na/K and SOX compared to KSOM alone. Transcripts for G6PDH, IFN-tau, and E-Cad were unaffected. These data confirm that the IMO is capable of supporting development of bovine embryos. Depending on the basal medium used, the pattern of transcript abundance in embryos derived from the IMO is similar to that of in vivo derived embryos.