Analysis of variation in relative mRNA abundance for specific gene transcripts in single bovine oocytes and early embryos

Association of growth differentiation factor 9 expression with nuclear receptor and basic helix-loop-helix transcription factors in buffalo oocytes during in vitro maturation

Growth differentiation factor 9 (GDF9) is an oocyte-specific paracrine factor involved in bidirectional communication, which plays an important role in oocyte developmental competence. In spite of its vital role in reproduction, there is insufficient information about exact transcriptional control mechanism of GDF9. Hence, present study was undertaken with the aim to study the expression of basic helix-loop-helix (bHLH) transcription factors (TFs) such as the factor in the germline alpha (FIGLA), twist-related protein 1 (TWIST1) and upstream stimulating factor 1 and 2 (USF1 and USF2), and nuclear receptor (NR) superfamily TFs like germ cell nuclear factor (GCNF) and oestrogen receptor 2 (ESR2) under three different in vitro maturation (IVM) groups [follicle-stimulating hormone (FSH), insulin-like growth factor-1 (IGF1) and oestradiol)] along with all supplementation group as positive control, to understand their role in regulation of GDF9 expression. Buffalo cumulus-oocyte complexes were aspirated from abattoir-derived ovaries and matured in different IVM groups. Following maturation, TFs expression was studied at 8 h of maturation in all four different IVM groups and correlated with GDF9 expression. USF1 displayed positive whereas GCNF, TWIST1 and ESR2 revealed negative correlation with GDF9 expression. TWIST1 & ESR2 revealing negative correlation with GDF9 expression were found to be positively correlated amongst themselves also. GCNF & USF1 revealing highly significant correlation with GDF9 expression in an opposite manner were found to be negatively correlated. The present study concludes that the expression of GDF9 in buffalo oocytes remains under control through the involvement of NR and bHLH TFs.

Role of the Na+/K+-ATPase ion pump in male reproduction and embryo development

Na⁺/K⁺-ATPase was one of the first ion pumps studied because of its importance in maintaining osmotic and ionic balances between intracellular and extracellular environments, through the exchange of three Na⁺ ions out and two K⁺ ions into a cell. This enzyme, which comprises two main subunits (α and β), with or without an auxiliary polypeptide (γ), can have specific biochemical properties depending on the expression of associated isoforms (α1β1 and/or α2β1) in the cell. In addition to the importance of Na⁺/K⁺-ATPase in ensuring the function of many tissues (e.g. brain, heart and kidney), in the reproductive tract this protein is essential for embryo development because of its roles in blastocoel formation and embryo hatching. In the context of male reproduction, the discovery of a very specific subunit (α4), apparently restricted to male germ cells, only expressed after puberty and able to influence sperm function (e.g. motility and capacitation), opened a remarkable field for further investigations regarding sperm biology. Therefore, the present review focuses on the importance of Na⁺/K⁺-ATPase on male reproduction and embryo development.

Teofilina como agente capacitante do sêmen bovino

RESUMO Objetivou-se avaliar a teofilina como agente capacitante substituto ou associado à heparina sobre a reação acrossômica dos espermatozoides e o desenvolvimento de embriões produzidos in vitro. O experimento foi realizado com quatro touros e três tratamentos, totalizando 12 grupos experimentais. O sêmen dos touros foi avaliado nos tratamentos descritos a seguir: tratamento 1 (HEP): heparina - 10µg/mL; tratamento 2 (TEO): teofilina - 5mM; tratamento 3 (HEP + TEO): heparina (10µg/mL) + teofilina (5mM), por zero, seis, 12 e 18 horas, corados com trypan blue/Giemsa para avaliação da reação acrossômica. Para a produção dos embriões, os agentes capacitantes foram adicionados aos meios de fertilização. Na análise espermática, a taxa de reação acrossômica verdadeira foi maior (P<0,05) no tempo zero hora, enquanto para espermatozoides mortos, as maiores taxas (P<0,05) foram nos tempos de 12h (84,46±5,82) e 18h (86,75±4,19). A taxa de embriões produzidos (37,97±13) e a taxa de eclosão (33,50±14) foram maiores (P<0,05) para o tratamento HEP. Não foi observada diferença (P>0,05) entre touros na análise de reação acrossômica nem na PIVE. A utilização da teofilina foi tão eficiente quanto a da heparina na indução da reação acrossômica, no entanto resultou em menores taxas de produção embrionária.

Blastocyst recovery and multifactorial gene expression analysis in the wild guinea pig (Cavia aperea)

The expression of specific developmentally important genes in preimplantation embryos is an accepted marker for unraveling the influence of single factors in studies that are mostly related to artificial reproduction techniques. Such studies, however, often reveal high levels of heterogeneity between single embryos, independently of the influence of factors of interest. A possible explanation for this variation could be the large variety of physiological and environmental factors to which early embryos are exposed and their ability to react to them. Here, we investigated several potentially important parameters of development at the same time, in blastocysts of the wild guinea pig (Cavia aperea) generated in vivo after natural mating. The optimal time for flushing fully developed blastocysts was between 123 and 126 hours after mating. The abundance of POU5F1 (P = 0.042), BAX (P < 0.001), SLC2A1 (P = 0.017), and DNMT3A (P < 0.001) mRNA changed significantly over time after mating. The number of sibling embryos present influenced STAT3 levels significantly (P = 0.02). Levels of BAX and POU5F1 were significantly affected by season (P = 0.03 and 0.04). The temporal pattern of SLC2A1 levels was significantly altered both after feeding a protein-deficient diet (P = 0.04) and temperature treatment (P = 0.04) of the sire. In addition, the identity of the father had a significant influence on POU5F1 (P = 0.049) and STAT3 (P < 0.001) mRNA abundances. These data report that the expression of specific genes in early embryos reflects the entire heterogeneity of their surroundings and that it is a plastic reaction toward a multifactorial environment.

Molecular signatures of bovine embryo developmental competence

Assessment of the developmental capacity of early bovine embryos is still an obstacle. Therefore, the present paper reviews all current knowledge with respect to morphological criteria and environmental factors that affect embryo quality. The molecular signature of an oocyte or embryo is considered to reflect its quality and to predict its subsequent developmental capacity. Therefore, the primary aim of the present review is to provide an overview of reported correlations between molecular signatures and developmental competence. A secondary aim of this paper is to present some new strategies to enable concomitant evaluation of the molecular signatures of specific embryos and individual developmental capacity.

Blastocyst implantation failure relates to impaired translational machinery gene expression

Oocyte quality is a well-established determinant of embryonic fate. However, the molecular participants and biological markers that affect and may predict adequate embryonic development are largely elusive. Our aim was to identify the components of the oocyte molecular machinery that part take in the production of a healthy embryo. For this purpose, we used an animal model, generated by us previously, the oocytes of which do not express Cx43 (Cx43(del/del)). In these mice, oogenesis appears normal, fertilisation does occur, early embryonic development is successful but implantation fails. We used magnetic resonance imaging analysis combined with histological examination to characterise the embryonic developmental incompetence. Reciprocal embryo transfer confirmed that the blastocyst evolved from the Cx43(del/del) oocyte is responsible for the implantation disorder. In order to unveil the genes, the impaired expression of which brings about the development of defective embryos, we carried out a genomic screening of both the oocytes and the resulting blastocysts. This microarray analysis revealed a low expression of Egr1, Rpl21 and Eif4a1 in Cx43(del/del) oocytes and downregulation of Rpl15 and Eif4g2 in the resulting blastocysts. We propose that global deficiencies in genes related to the expression of ribosomal proteins and translation initiation factors in apparently normal oocytes bring about accumulation of defects, which significantly compromise their developmental capacity. The blastocysts resulting from such oocytes, which grow within a confined space until implantation, may be unable to generate enough biological mass to allow their expansion. This information could be implicated to diagnosis and treatment of infertility, particularly to IVF.

Kinetics of GDF9 expression in buffalo oocytes during in vitro maturation and their associated development ability

The capacity of fully grown oocytes to regulate their own microenvironment by secreted paracrine factors contribute to their developmental competence. In spite of growing evidence about the vital role of Growth Differentiation Factor 9 (GDF9) in determination of oocyte developmental competence, there is insufficient information about time dependent behavior of its expression during in vitro maturation (IVM) to have definite understanding about at what time point during IVM it plays most crucial role. The study reports the kinetics of GDF9 expression under four different IVM supplement conditions in buffalo oocytes and their concomitant development rate up to blastocyst. Oocytes matured under an ideal media condition with all supplements and those cultured with only FSH resulted in significantly higher cumulus expansion, nuclear maturation, cleavage and blastocyst rates. GDF9 expression at both mRNA and protein levels at different time points of IVM revealed that magnitude of mRNA abundance at 8h of IVM was most important towards imparting development competence to buffalo oocytes. Appearance of GDF9 protein in maturing oocytes was found asynchronous with mRNA appearance in the time course of IVM suggesting possible posttranscriptional regulation of this gene under dynamic oocyte cumulus cell communication process. Abundance of mature GDF9 protein at 16 h was most consistently related with all oocyte development parameters.

A novel approach to sexing bovine blastocysts using male-specific gene expression

When examining gene expression profiles for the purposes of assessing embryo quality, it is imperative that sex be considered, because many embryonic transcripts have sex-related expression patterns. The objective of this study was to systematically examine eight Y chromosome linked genes (DDX3Y, EIF1AY, HSFY, SRY, TSPY, USP9Y, ZFY, and ZRSR2Y) to characterize their expression in bovine blastocysts and to examine the usefulness of this expression for the purpose of RNA-based embryo sexing. In order to examine the expression of these genes, pools of blastocysts (groups of 10 and 20) as well as single embryos (N = 50) were analyzed with reverse transcriptase polymerase chain reaction (RT-PCR) and reverse transcriptase quantitative PCR (RT-qPCR). Of the 50 single embryos, 32 were concurrently sexed with DNA-based methods. Transcripts of DDX3Y, EIF1AY, TSPY, USP9Y, ZFY and ZRSR2Y were detected in the pooled and single blastocysts, but no transcripts were detected for HSFY or SRY. After performing DNA-based sexing experiments, we concluded that this expression was restricted to the male embryos. The consistency of the expression varied according to the gene as well as the specific primer set. Three genes were expressed in the full set of male embryos, DDX3Y, USP9Y, and ZRSR2Y and therefore represent good candidates for RNA-based sexing methods.

Gene expression profiling of pluripotency and differentiation-related markers in cat oocytes and preimplantation embryos

During mammalian preimplantation development, two successive differentiation events lead to the establishment of three committed lineages with separate fates: the trophectoderm, the primitive endoderm and the pluripotent epiblast. In the mouse embryo, the molecular mechanisms underlying these two cell fate decisions have been studied extensively, leading to the identification of lineage-specific transcription factors. Species-specific differences in expression patterns of key regulatory genes have been reported, raising questions regarding their role in different species. The aim of the present study was to characterise the gene expression patterns of pluripotency (OCT4, SOX2, NANOG) and differentiation (CDX2, GATA6)-related markers during feline early development using reverse transcription–quantitative polymerase chain reaction. In addition, we assessed the impact of in vitro development on gene expression by comparing transcript levels of the genes investigated between in vitro and in vivo blastocysts. To normalise quantitative data within different preimplantation embryo stages, we first validated a set of stable reference genes. Transcript levels of all genes investigated were present and changed over the course of preimplantation development; a highly significant embryo-stage effect on gene expression was observed. Transcript levels of OCT4 were significantly reduced in in vitro blastocysts compared with their in vivo counterparts. None of the other genes investigated showed altered expression under in vitro conditions. The different gene expression patterns of OCT4, SOX2, CDX2 and GATA6 in cat embryos resembled those described in mouse embryos, indicative of a preserved role for these genes during early segregation. However, because of the absence of any upregulation of NANOG transcription levels after embryonic genome activation, it is unlikely that NANOG is a key regular of lineage segregation. Such results support the hypothesis that the behaviour of early lineage markers can be species specific. The present study also revealed a pool of maternal NANOG mRNA transcripts, the role of which remains to be elucidated. Comparing transcription levels of these genes between in vivo and in vitro blastocysts revealed low levels of OCT4 mRNA in the latter, which may contribute to the reduced developmental competence of embryos under suboptimal conditions.

Differential gene expression and developmental competence in in vitro produced bovine embryos

The embryonic developmental block occurs at the 8-cell stage in cattle and is characterized by a lengthening of the cell cycle and an increased number of embryos that stop development. The maternal-embryonic transition arises at the same stage resulting in the transcription of many genes. Gene expression studies during this stage may contribute to the understanding of the physiological mechanisms involved in the maternal-embryonic transition. Herein we identified genes differentially expressed between embryos with high or low developmental competence to reach the blastocyst stage using differential display PCR. Embryos were analysed according to developmental kinetics: fast cleavage embryos showing 8 cells at 48 h post insemination (hpi) with high potential of development (F8), and embryos with slow cleavage presenting 4 cells at 48 hpi (S4) and 8 cells at 90 hpi (S8), both with reduced rates of development to blastocyst. The fluorescence DDPCR method was applied and allowed the recovery of 176 differentially expressed bands with similar proportion between high and low development potential groups (52% to F8 and 48% in S4 and S8 groups). A total of 27 isolated fragments were cloned and sequenced, confirming the expected primer sequences and allowing the identification of 27 gene transcripts. PI3KCA and ITM2B were chosen for relative quantification of mRNA using real-time PCR and showed a kinetic and a time-related pattern of expression respectively. The observed results suggest the existence of two different embryonic genome activation mechanisms: fast-developing embryos activate genes related to embryonic development, and slow-developing embryos activate genes related to cellular survival and/or death.

RFD Award Lecture 2009. In vitro maturation of farm animal oocytes: a useful tool for investigating the mechanisms leading to full-term development

Due to logistical and economic reasons, assisted reproduction of domestic animals has been based mostly on the use of oocytes isolated from ovaries collected at the slaughterhouse. In order to propagate valuable or rare genetic material, perform somatic cell nuclear transfer or generate genetically modified animals, it is essential to obtain fully competent oocytes that will allow full-term development of the in vitro-produced embryos. Such a need makes clear the crucial role played by oocyte quality. In fact, it is easy to compromise the oocyte's developmental potential but it is impossible to restore once it has been lost. Almost three decades after the first cow, sheep, goat, horse and pig in vitro-generated offspring were born, a large body of information has accumulated on the mechanisms regulating oocyte competence and on how the latter may be preserved during all the required manipulations. The amount of knowledge is far from complete and many laboratories are actively working to further expand it. In this review we will highlight the aspects of the ongoing research in which we have been actively involved.

A link between the interleukin-6/Stat3 anti-apoptotic pathway and microRNA-21 in preimplantation mouse embryos

Signal transducers and activators of transcription-3 (Stat3) plays a central role in interleukin-6 (IL-6)-mediated cell proliferation by inhibiting apoptosis in a variety of cell types. MicroRNA-21 (miRNA-21), a ubiquitous miRNA, acts as an anti-apoptotic factor that seems to be indirectly but strictly linked to Stat3. In order to determine whether the IL-6 induced Stat3 anti-apoptosis pathway is linked with miRNA-21, we first determined the effects of recombinant mouse IL-6 on Stat3 expression, mouse embryo viability, and the mRNA levels of apoptosis related genes and miRNA-21 during mouse embryo development in vitro. Addition of 10 or 100 ng/ml of recombinant IL-6 to the culture medium did not affect the developmental ability of 2-cell stage embryos into blastocysts. However, total cell number was significantly increased and apoptosis was reduced in blastocyst stage embryos cultured in the presence of 100 ng/ml of recombinant IL-6. Furthermore, addition of recombinant IL-6 to the culture medium significantly increased the copy numbers of anti-apoptotic miRNA-21, up-regulated Bcl2l1, and down-regulated casp3. Similarly, the injection of mature miRNA-21 into cells up-regulated Bcl2l1 and down-regulated casp3. These results suggest that the induction of the Stat3 anti-apoptotic pathway by IL-6 is linked to miRNA-21 expression, which possibly results in the regulation of cell apoptosis in early mouse embryo development.

Improvement of in vitro oocyte maturation with lectin supplementation and expression analysis of Cx43, GDF-9, FGF-4 and Fibronectin mRNA transcripts in Buffalo (Bubalus bubalis)

PURPOSE

To optimize In vitro maturation (IVM) of quality oocytes for embryo production through IVF and SCNT.

METHODS

Buffalo oocytes were in vitro matured in the presence of the pokeweed lectin (Phytolacca americana), a potent lymphocyte mitogen. Lectin was supplemented in TCM + 10% FBS at the doses of 0, 1, 5, 10, 15, 20 and 40 microg/ml and cumulus expansion and gene expression patterns were characterized.

RESULTS

The degree of cumulus expansion in different lectin treatment levels improved from 1.1 at 1 Ag/ml level to 3.60 at 10 microg/ml level and then decreased in higher concentration 20 microg/ml (1.66) and 40 microg/ml (0.64). IVF embryos showed highest cleavage rate (88.8%) in 10 microg/ml lectin treatment. Expression of all mRNA transcript studied (Cx43, GDF 9, FGF-4 and Fibronectin) was positively correlated with cumulus expansion and polar body extrusion.

CONCLUSIONS

Mitogenic lectin supplemented maturation media improves oocyte quality for in vitro embryo production.

High mobility group box 1 (HMGB1) is implicated in preimplantation embryo development in the mouse

High mobility group box 1 (HMGB1) regulates multiple cell functions, including transcription, DNA repair, differentiation, and apoptosis. In order to obtain insight into the role of HMGB1 in embryo development, we first evaluated its gene expression levels in mouse preimplantation embryos. Quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) revealed high expression levels in zygotes, and expression steadily increased after zygotic genome activation when normalized to the rabbit Globin mRNA. Indirect immunocytochemistry showed that the HMGB1 protein was also produced in mouse embryos. Injection of a small interfering RNA (siRNA) specific for HMGB1 into zygotes specifically reduced both mRNA expression (P < 0.001) and protein synthesis of HMGB1 in early embryos developed in vitro. Injection of siRNA into the zygote did not affect development to the blastocyst stage, but significantly decreased cell numbers (P < 0.01) in the blastocyst and increased caspase3 (Casp3, P < 0.05) gene expression and apoptosis (P < 0.005). Addition of recombinant HMGB1 (Sigma, H-4652) into the culture medium enhanced the development of zygote stage mouse embryos to blastocysts, in the absence of BSA supplementation. These findings suggest that endogenous and exogenous HMGB1 are implicated in preimplantation embryo development in the mouse.

Effects of pre-mating nutrition on mRNA levels of developmentally relevant genes in sheep oocytes and granulosa cells

The present study was designed to investigate the relationship between pre-mating nutrition and the relative amounts of a panel of developmentally relevant genes in ovine oocytes and granulosa cells. Cast age ewes were fed a ration providing 0.5x (0.5 M) or 1.5x (1.5 M) live weight maintenance requirements for 2 weeks before slaughter. The ewes were synchronized and superovulated with FSH and pregnant mares serum gonadotropin. At slaughter, oocytes and granulosa cells were aspirated from follicles >2 mm in diameter and the relative abundance of 8 and 17 transcripts in oocytes and granulosa cells respectively were analyzed by semi-quantitative RT-PCR. In the oocytes, no differences between groups were observed for five transcripts (GDF9, BMP15, c-kit, glucose transporter 1 (SLC2A1), and hexokinase 1), but a lower amount of glucose transporter 3 (SLC2A3), sodium/glucose cotransporter 1 (SLC5A1), and Na(+)/K(+) ATPase mRNAs was detected in the 0.5 M group. Increased expression of PTGS2, HAS2, and the leptin receptor long form was observed in granulosa cells from the 0.5 M group. No differences between groups were observed for the other transcripts (early growth response factor-1, estrogen receptor-alpha, LH and FSH receptors, gremlin 1, pentraxin 3, KIT ligand, glucose transporters 1, 3, and 8, IGF1, IGF1 receptor, leptin receptor, and tumor necrosis factor-stimulated gene 6). Expression of leptin and sodium/glucose cotransporter 1 was not detected in both groups. The present data indicate that pre-mating nutrition is associated with alteration in the mRNA content in oocytes and surrounding follicle cells in ewes, which may account for the reduced reproductive performance typical of ewes that are fed a restricted ration for a short period of time before mating.

Bovine oocytes and early embryos express Staufen and ELAVL RNA-binding proteins

RNA-binding proteins (RBP) influence RNA editing, localization, stability and translation and may contribute to oocyte developmental competence by regulating the stability and turnover of oogenetic mRNAs. The expression of Staufen 1 and 2 and ELAVL1, ELAVL2 RNA-binding proteins during cow early development was characterized. Cumulus–oocyte complexes were collected from slaughterhouse ovaries, matured, inseminated and subjected to embryo culturein vitro. Oocyte or preimplantation embryo pools were processed for RT-PCR and whole-mount immunofluorescence analysis of mRNA expression and protein distribution. STAU1 and STAU2 and ELAVL1 mRNAs and proteins were detected throughout cow preimplantation development from the germinal vesicle (GV) oocyte to the blastocyst stage. ELAVL2 mRNAs were detectable from the GV to the morula stage, whereas ELAVL2 protein was in all stages examined and localized to both cytoplasm and nuclei. The findings provide a foundation for investigating the role of RBPs during mammalian oocyte maturation and early embryogenesis.

Increased messenger ribonucleic acid expression of the cyclin-dependent kinase inhibitor p27Kip1 in cleavage-stage human embryos exhibiting developmental arrest

OBJECTIVE

To quantify p27 messenger RNA (mRNA) levels in human arrested and normally developing embryos and nonfertilized oocytes to determine whether the p27 protein abundance, reported in cleavage-stage embryos exhibiting developmental arrest, is regulated at the mRNA expression level.

DESIGN

Real-time reverse transcription quantitative polymerase chain reaction was used to quantify the expression of p27 in three samples: arrested embryos (group A, n = 29), normally developing embryos (group D, n = 34), and nonfertilized oocytes (group O, n = 20).

SETTING

Research laboratory working closely with a clinical IVF practice.

PATIENT(S)

Oocytes and embryos were obtained from patients undergoing assisted fertilization.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Quantification of mRNA transcripts.

RESULT(S)

The amount of p27 mRNA was statistically significantly higher in group A (mean +/- SEM, 86,143 +/- 42,496 relative units [RU]) compared with groups D (10,680 +/- 3,850 RU) and O (3,555 +/- 1,458 RU). Furthermore, in a group of 13 two- to four-cell arrested embryos, high levels of p27 mRNA (51,481 +/- 31,120 RU) were found in comparison with the nonfertilized oocyte group (3,555 +/- 1,458 RU).

CONCLUSION(S)

Cleavage-stage human embryos exhibiting developmental arrest show increased p27 mRNA expression. This probably is due to increased transcriptional activity.

Expression stability of two housekeeping genes (18S rRNA and G3PDH) during in vitro maturation of follicular oocytes in buffalo (Bubalus bubalis)

The present study was undertaken to evaluate the expression stability of two housekeeping genes (HKGs), 18S rRNA and G3PDH during in vitro maturation (IVM) of oocytes in buffalo, which qualifies their use as internal controls for valid qRT-PCR estimation of other oocyte transcripts. A semi quantitative RT-PCR system was used with optimised qRT-PCR parameters at exponential PCR cycle for evaluation of temporal expression pattern of these genes over 24 h of IVM. 18S rRNA was found more stable in its expression pattern than G3PDH.

Using the histone H2a transcript as an endogenous standard to study relative transcript abundance during bovine early development

The requirement for sample standardization is basic to any relative RNA abundance assessment. In 2002, we published on the RNA abundance profiling of several housekeeping targets during early bovine embryonic development. It was then concluded that histone H2a was the most stable transcript across the studied developmental period. Since that time, several teams have applied this information, yet neglected to use the published set of primers. Here, we show that these other primer sets do not target the same histone H2a variant. Within the present report, the RNA abundance profiles of their respective targets, for example, histone H2a.1, H2a.z, and H2a.o were measured in developmental series spanning the immature oocyte to the blastocyst stage embryo. In order to more clearly define the conditions that impact the RNA abundance level measurement of these candidates, the state of polyadenylation and the origin of the transcript either from de novo transcription or from maternal stocks were taken into consideration. The histone H2a.z transcript is principally regulated by de novo transcription following embryonic genome activation, whereas the levels of H2a.1 and H2a.o variants are largely of maternal origin, conferring a more stable profile throughout the studied developmental window. The histone H2a.z was found solely in a polyadenylated state whereas the H2a.1 and H2a.o were found to be more abundant in a nonadenylated form. The presence of serum in the in vitro embryo production system also had some impact on the histone H2a.1 RNA level at the blastocyst stage.

Cdc42 is implicated in polarity during meiotic resumption and blastocyst formation in the mouse

Cell division cycle 42 (Cdc42), a member of the Rho family of small guanosine triphosphatase (GTPase) proteins, regulates multiple cell functions, including: motility, proliferation, apoptosis, and cell morphology. In order to obtain insight into the role of Cdc42 in meiotic resumption and embryo development, we first evaluated its gene expression levels in mouse oocytes and embryos during in vitro development. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) revealed high-expression levels in GV stage oocytes that steadily decreased up to the 2-cell (2C) stage embryo, and then expression increased during morulae and blastocyst formation. Indirect Immunocytochemistry also showed protein synthesis of CDC42 in the mouse oocytes and early embryos. Introducing small interference RNA (siRNA) of Cdc42 into germinal vesicle stage oocytes or zygotes specifically reduced both mRNA expression and protein synthesis of CDC42 in in vitro developed metaphase II oocytes and early embryos. Meiotic maturation and cytoskeleton assembly were significantly altered following siRNA injection into germinal vesicle stage oocytes. Injection of siRNA into the zygote did not affect cleavage or cell numbers in morulae, but significantly decreased in vitro development to the morula or blastocyst. These findings suggest that gene expression of Cdc42 is involved in meiotic resumption and blastocyst formation in the mouse, possibly through maintaining polarity.

Universal reference method for real-time PCR gene expression analysis of preimplantation embryos

Real-time PCR expression profiling in individual preimplantation embryos poses two main challenges. First, the amount of RNA from blastocysts (between 100 and 200 cells) is too small to quantify, and secondly, a reference gene with stable expression across preimplantation embryos produced by different reproductive technologies is required. We have developed a method using RNA and DNA spikes that allows for accurate normalization of gene expression without the use of an internal housekeeping gene in preimplantation blastocysts. Prior to the simultaneous extraction of RNA and DNA, plant-specific RNA and DNA spikes are added to the tissue. After synthesis of cDNA, target gene transcript and the exogenous RNA spike are measured using real-time PCR. To account for differences in the number of cells in each sample, the genomic gene copies of 18S-DNA are measured by quantitative PCR and normalized to the DNA spike. While the DNA spike accounts for extraction efficiency, the 18S genomic target indicates the number of cells prior to extraction. The values obtained from normalizing the target gene to the RNA spike can be adjusted for cell number, allowing the RNA spike to be used as reference gene. This universal reference approach allows the use of an exogenous spike as a pseudo-housekeeping gene for normalization of gene expression data.

Development of a Competitive Quantitative PCR Strategy for Evaluating the Expression Stability of 18s rRNA during In Vitro Maturation of Buffalo (Bubalus bubalis) Follicular Oocytes

The present work describes the development of a quantitative competitive PCR strategy for quantifying the relative abundance of 18s rRNA transcripts in buffalo oocytes during in vitro maturation (IVM). As a method, the competitive PCR overcomes some of the shortcomings of conventional reverse transcriptase polymerase chain reaction (RT-PCR) procedure making it a more authentic quantitative method. A composite primer based approach was used to generate the competitor cDNA to be used as external control. Validity of the method for its efficiency was demonstrated by quantitative analysis of the competition parameters. Using this method the relative abundance of buffalo oocyte 18s rRNA transcript over the period of IVM was found to vary within a narrow range of 0.93-1.06 folds which establishes the accuracy of the method and reflects the stability of its expression during IVM. This qualifies the use of this house keeping gene as a valid internal control in studies investigating the gene expression pattern in buffalo oocytes. The competitive PCR approach described in this study could be used for quantification of other transcripts from a limited number of oocytes where a conventional RT-PCR method is either difficult to use or multiplexing it with highly abundant house keeping genes is apparently problematic.

Developmental competence of bovine oocytes is not related to apoptosis incidence in oocytes, cumulus cells and blastocysts

The number of follicles undergoing atresia in an ovary is very high, and isolation of cumulus-oocyte complexes (COCs) from such atretic follicles may impair subsequent embryo development in vitro. Our aim was to study if stringent selection by morphological assessment of COCs can improve embryo development, and to evaluate whether oocyte diameter is related with apoptotic ratio in oocytes and blastocysts. COCs from slaughtered cattle were recovered by follicle aspiration and classified depending on oocyte diameter: (A) <110 microm; (B) 110-120 microm; (C) >120 microm. COCs were matured, fertilized and cultured in vitro. Early and late stages of apoptosis were detected by Annexin-V and TUNEL staining, respectively, in denuded oocytes, COCs and blastocysts. Immature oocytes from Group A showed higher apoptotic ratio assessed by TUNEL assay, and the COCs corresponding to this group also showed a higher proportion of apoptotic cumulus cells. After maturation, no differences were present in the incidence of apoptosis among oocytes from different groups, but COCs corresponding to the largest diameter showed less apoptotic cumulus cells. In addition, the percentage of apoptotic oocytes decreased during in vitro maturation in all groups. Apoptotic cell ratio (ACR) in blastocysts was not related to oocyte diameter. In conclusion, oocyte selection and oocyte morphological evaluation prior to maturation was not sufficient to select non-atretic oocytes. When oocyte diameter was used as an additional selection the embryonic developmental potential increased together with oocyte diameter, but this improvement was not related to a lower incidence of apoptosis in the largest oocytes.

Temporal expression of transcripts related to embryo quality in bovine embryos cultured from the two-cell to blastocyst stage in vitro or in vivo

The post-fertilization embryo culture environment can have a dramatic effect on the pattern of gene expression in the embryo and it is widely acknowledged that bovine embryos derived from in vitro culture are of inferior quality to those derived in vivo. The objective of this study was to examine temporal variation in the mRNA abundance of several transcription and translation factors known to differ between blastocysts produced following culture in vitro and in vivo. Embryos were recovered from two in vitro culture systems SOF1 or SOF2 at five developmental stages: 2- to 4-cell, 8-cell, 16-cell, morula, and blastocyst. In vivo embryos were produced from superovulated and artificially inseminated heifers and recovered at approximately 40 hr or 3, 4, 5, and 7 days postinsemination. Blastocysts were also produced following in vitro maturation, in vitro fertilization and culture in the ewe oviduct. Analysis of relative transcript abundance for FOXO3A, EEF1G, HMG2, and REA was performed using quantitative real-time PCR. Irrespective of culture environment each transcript followed, approximately the same general pattern of expression where relative abundance decreased dramatically from the 2- to 4-cell stage to 8-cell stage and increased from the morula to blastocyst stage (P < 0.05). Transcripts for GNBL2 were not observed between the 2- and 16-cell stage of development. Relatively high expression at the 2- to 4-cell indicated that these transcripts are most likely of maternal origin produced in the oocyte during growth and final maturation. A culture-induced change in mRNA abundance of transcription and translation factors was evident in embryos that were produced not only between in vivo and in vitro culture environments but also between different in vitro culture systems.

Single-cell protein analysis of a single mouse embryo by two-dimensional capillary electrophoresis

The characterization of protein expression from a single-cell mouse embryo using two-dimensional capillary electrophoresis (2D-CE) is described. These zygotes were obtained from Hsf1 gene knockout mice. Single zygotes were lysed off-column and proteins were fluorescently labeled using the fluorogenic dye 3-(2-furoyl)quinoline-2-carboxaldehyde (FQ). After injection, analytes were separated first according to molecular weight using capillary sieving electrophoresis (CSE) and then by micellar electrokinetic capillary chromatography (MEKC) to obtain protein expression fingerprints. Analytes were detected in a sheath flow cuvette using laser-induced fluorescence. In a 1-h 2D-CE separation, over 100 components were resolved with a spot capacity of 380.

Potential and limitations of bovine-specific arrays for the analysis of mRNA levels in early development: preliminary analysis using a bovine embryonic array

New insights into the early development of large mammals are becoming available through the measurement of differential mRNA levels in oocytes and preimplantation embryos. These advances in knowledge are rapidly picking up in pace, mainly owing to the advantages brought by new molecular biology approaches being developed. The possibility of amplifying the starting material and therefore making measurements in single embryo units is now feasible. With these tools, the evaluation of variations in gene expression patterns during the preimplantation period or the impact of culture on mRNA levels is now possible. However, it is important to keep in mind that these methods still have limitations associated with sample preparation or the use of the appropriate controls. Even proper methods of analysis are very important to achieve the full benefit of the application of these tools. The present paper describes some of the potential, as well as limitations, of mRNA level analysis in early embryos, especially for microarray analysis. We have generated a bovine cDNA array (>2000 clones) that contains expressed sequence tags (ESTs) collected from various preimplantation development stages. Using this chip, we have initiated the characterisation of global mRNA level patterns of several key developmental stages from the immature oocyte to the blastocyst stage. As expected, the hybridisation results indicate very different expression profiles involving hundreds of genes when comparing oocyte and blastocyst samples to a reference mRNA sample made from a pool of ESTs from pooled somatic tissues. Although this array is still in its preliminary stage and the EST bank has not been processed to contain only unigenes, it is already a very useful tool for discovering candidate genes that may play important roles during early embryonic life.

Gene Expression of Cox5a, 5b, or 6b1 and Their Roles in Preimplantation Mouse Embryos1

To investigate the role of nuclear encoded genes in mitochondrial function during oocyte maturation and early embryogenesis we examined the expression pattern and function of the cytochrome oxidase (Cox) subunits, Cox5a, 5b, and 6b1 during oocyte maturation and early embryo development. Transcription of Cox5a, 5b, or 6b1 was observed in oocytes and during early development; their expression levels were abundant in mature oocytes (MII) and zygotes (1C), and lowest at the 2-cell stage (2C), gradually increasing from 4-cell to blastocyst stage. Immunocytochemical studies revealed that COX5A, 5B, or 6B1 proteins were expressed in all blastomeres of the blastocyst. Silencing of mRNA expression by RNA interference (siRNA) did not inhibit oocyte maturation or developmental events up to the morula and blastocyst stages, but disrupted mitochondrial distribution. Significantly higher apoptosis and lower cell numbers were observed in siRNA-treated blastocysts. Real time RT-PCR revealed that silencing of Cox5a, 5b, or 6b1 did not alter mRNA levels of Bcl-xL (Bcl2l1), but increased transcription levels of proapoptotic genes, Bax and caspase 3 (Casp3). Furthermore, mRNA and protein levels of E-cadherin (CDH1) were decreased in siRNA microinjected blastocysts. These results suggest that gene expression of the Cox subunits, Cox5a, 5b, and 6b1 is not required for embryo developmental events up to the blastocyst stage. The loss of these genes leads to mitochondrial dysfunction that results in apoptosis of the blastocyst stage embryos.

Relations between relative mRNA abundance and developmental competence of ovine oocytes

The present study was conducted to investigate the relation between in vitro developmental competence and the expression of a panel of developmentally important genes in germinal vesicle (GV) stage oocytes. One-month-old prepubertal and adult sheep oocytes were used as models of low and high quality gametes, respectively. Cumulus-oocyte complexes (COCs) derived from lambs and ewes were in vitro matured and fertilized, and their cleavage rate at 22, 26, and 32 hr post fertilization and the blastocyst yield were observed to assess their developmental potential. In parallel, the relative abundance (RA) of 11 genes was analyzed by semi-quantitative Reverse Transcription Polymerase Chain Reaction (RT-PCR) assay in the two groups of oocytes. We observed similar maturation and fertilization rates in the two groups, but a significant lower rate of cleaved prepubertal oocytes (P < 0.05), a general delay in the timing of their first division (P < 0.01), and a lower blastocysts production (P < 0.05). The analysis of gene expression evidenced no difference in the RA of four transcripts [superoxide dismutase (SOD), ubiquitin, beta-actin, cyclin B] in the two classes of oocytes, but a statistically lower RA of seven messenger RNAs (mRNA) [Na(+)K(+)ATPase, p34(cdc2), Glucose-transporter I (Glut-1), Activin, Zona Occludens Protein 2 (PanZO2), Poli(A)Polymerase (PAP), E-Cadherin (E-Cad)] in the prepubertal oocytes compared to the adult ones. The present data show for the first time in the ovine species that the lower developmental competence is associated with deficiencies in the mRNAs storage during the oocyte growth.

Transcription profile during maternal to zygotic transition in the mouse embryo

To gain insight into early embryo development, we used microarray technology to compare gene expression profiles in metaphase II oocytes and one- (1C), two- (2C) and four-cell (4C) embryos. Differences in spot intensities were normalised and grouped using Avadis Prophetic software platform (version 3.3; Strand Genomics, Bangalore, India) and categories were based on the PANTHER and Gene Ontology classification systems. We examined 6927 genes and identified those preferentially expressed in 1C or 2C embryos. We found 1261 genes that were more highly expressed (P < 0.05) in 1C compared with 2C embryos and 1480 genes showing enhanced expression in 2C embryos. Similarly, we investigated 6581 genes present in 2C and 4C embryos and identified 841 that are expressed to a greater extent at the 2C stage and 905 that are more highly expressed at the 4C stage. Using PANTHER classification, genes that were upregulated and downregulated in 2C embryos compared with 1C and 4C embryos were grouped according to their protein functions, which included developmental processes, electron transport, lipid, fatty acid and steroid metabolism, nucleoside, nucleotide and nucleic acid metabolism, protein metabolism and modification, signal transduction and transport, among others. Real time reverse transcription–polymerase chain reaction was performed to confirm differential expression of 14 selected genes. The identification of the genes being expressed will provide insight into the complex gene regulatory networks affecting zygotic genome activation and further development.

Characterization of linker histone H1FOO during bovine in vitro embryo development

Linker histones H1 are involved in various mechanisms, such as chromatin organization and gene transcription. In different organisms, a unique subtype can be found in the oocyte, however its function remains unclear. To assess the potential involvement of this oocyte linker histone (H1FOO) in chromatin modulation, we have cloned and sequenced the bovine H1FOO cDNA and followed its mRNA profile by quantitative RT-PCR in the oocyte and throughout bovine early embryo development. The highest level of mRNA was found in the germinal vesicle (GV) oocyte and diminished constantly throughout embryo development. In the 16-cell embryo and blastocyst, respectively, the mRNA levels were 200 and 2,000 times lower than in the GV oocyte. A specific antibody raised against bovine H1FOO was used to establish protein distribution in the oocyte and preimplantation embryo by immunocytochemistry. In the GV and metaphase II (MII) oocyte, as well as in the 1-, 2- and 4-cell embryo, H1FOO was localized in the cytoplasm and nucleus. The protein was uniformly spread within the cytoplasm, while it was concentrated onto the chromatin in the nucleus. In the 8- to 16-cell embryo, H1FOO's presence diminished in the cytoplasm, although it was still strongly expressed in nucleus. In the morula and blastocyst stages, the protein was totally lacking. By its position on chromatin, H1FOO could not only be involved in chromatin conformation but could also participate in activation or repression of genes during oogenesis and embryo development before embryonic genome activation.

Apoptosis in cumulus cells, but not in oocytes, may influence bovine embryonic developmental competence

Aim of our study was to clarify if the occurrence of apoptosis in oocytes and cumulus cells is correlated to bovine oocyte developmental competence. The cumulus-oocyte complexes (COCs) were selected according to cumulus status: G1 with more than five layers of compact cumulus cells, G2 with one to five layers of compact cumulus cells and G3 with expanded cumulus cells. The degree of apoptosis in cumulus cells and oocytes measured by caspase staining and TUNEL assay before and after maturation, and 24 h post-insemination was compared to the cleavage, blastocyst formation and hatching rates of each group. Highest cleavage, blastocyst and hatching rates were found in cumulus-oocyte complexes with more than five layers of compact cumulus cells, but no apoptosis was detected in immature or in vitro matured oocytes, regardless of the cumulus status. Many cumulus cells contained active caspases before maturation, but caspase activity declined dramatically after maturation. TUNEL positive cells were rarely observed in each cumulus-oocyte complex upon oocyte recovery, but a huge increase of them was seen after in vitro maturation. Significantly more TUNEL and caspase positive cells were found in G2 cumulus-oocyte complexes. Our results suggest that: (i) oocyte apoptosis does not account for the inferior oocyte quality of G2 and G3; (ii) apoptosis occurs in cumulus cells regardless of the number and compactness of cumulus cells; and (iii) the degree of apoptosis in the compact cumulus-oocyte complexes (G1 and G2) is negatively correlated to the developmental competence of oocyte.

A qualitative look at multiplex gene expression of single cells using capillary electrophoresis

We demonstrate the first use of capillary electrophoresis with laser-induced fluorescence (CE-LIF) for the qualitative analysis of single-cell multiplex products of the reverse transcriptase-polymerase chain reaction (RT-PCR). The expression of both estrogen receptor alpha (ERalpha) and beta-actin in individual MCF-7 cells was monitored using a one-pot reaction. Reverse transcription and a single round of touch-down PCR, performed in a multiplex format, were used to generate fragment sizes of 318 bp and 838 bp, for ERalpha and beta-actin, respectively. A replaceable hydroxypropylmethylcellulose sieving matrix was used to effect a size-based separation of ethidium bromide-bound DNA. As titration of RT-PCR reaction components did not appreciably influence multiplex product generation, the use of additives, including bovine serum albumin (BSA) and herring sperm DNA, was explored. The addition of BSA to the RT-PCR mixture only resulted in efficient amplification of beta-actin, whereas the DNA carrier allowed co-amplification of both ERalpha and beta-actin. Furthermore, the sensitivity of our CE-LIF method eliminated the need for a second round of nested PCR, typically required when RT-PCR products are analyzed using gel electrophoresis.

Effect of serum and cumulus cell expansion on marker gene transcripts in bovine cumulus-oocyte complexes during maturation in vitro

OBJECTIVE

To determine the distribution of transcripts encoding the FSH receptor (FSHr), LH receptor (LHr), connexin 43 (Cx43), cyclooxygenase-2 (COX-2), and prostaglandin E(2) receptors 2 and 3 (EP2 and EP3) within bovine cumulus-oocyte complexes (COCs) and denuded oocytes and investigate the influence of gonadotropins, serum, and cumulus cell expansion on the abundance of transcripts encoding these genes.

DESIGN

Prospective controlled animal study.

SETTING

University research laboratory.

PATIENT(S)

Animal models for human studies.

INTERVENTION(S)

Cumulus-oocyte complexes were treated in culture with serum and gonadotropin-supplemented media to examine the effects to mRNA transcript levels.

MAIN OUTCOME MEASURE(S)

Variation in mRNA transcript levels.

RESULT(S)

Luteinizing hormone receptor, FSHr, and EP3 mRNAs were detected in intact COCs and not in cumulus cell-denuded oocytes, whereas Cx43, COX-2, and EP2 mRNAs were found in both COCs and oocytes. The relative abundance of marker gene mRNAs did not vary in media containing no additives or FSH alone, independent of whether the media induced cumulus cell expansion. However, the presence of serum in maturation media significantly decreased expression of all mRNAs except LHr.

CONCLUSION(S)

The relative abundance of COC mRNAs is altered by serum in the maturation medium, which may signify long-term consequences for embryonic development.

Oocyte and embryo quality: effect of origin, culture conditions and gene expression patterns

In general, the majority of immature bovine oocytes fail to develop to the blastocyst stage following maturation, fertilization and culture in vitro. The evidence suggests that while culture conditions during in vitro embryo production can impact on the developmental potential of the early embryo, the intrinsic quality of the oocyte is the key factor determining the proportion of oocytes developing to the blastocyst stage. In addition, evidence suggests that the period of post-fertilization embryo culture is the most critical in determining blastocyst quality. This paper reviews the current literature, with emphasis on the bovine model, demonstrating evidence for an effect of oocyte origin and/or in vitro maturation conditions on the developmental capacity and gene expression patterns in the oocyte. Furthermore, the well-documented effects of post-fertilization culture environment on embryo gene expression and quality are highlighted.

Amplification of representative cDNA pools from single human oocytes and pronucleate embryos

In the human embryo, gene expression studies have been hindered by the scarcity of material and the fact that in vitro fertilisation (IVF) embryos available for research are usually of poor quality and are, therefore, not representative of normal development. This has led most authors to study individual human embryos, using conventional RT-PCR strategies, which permit analysis of only a few genes. Variability in the expression of genes between individual embryos is characteristic of these studies. In this study, a global RT-PCR strategy has been used, allowing the analysis of an almost infinite number of genes from a single embryo. We have used oocytes, which failed to fertilise and representative pronucleate embryos donated from cycles in which the patient conceived, to investigate possible variability in transcript abundance between individual embryos. We have screened oocytes and embryos for a panel of genes including beta-actin (expressed in 24/28 oocytes, 6/6 pronuclear embryos), the integrins beta1 (17/28 oocytes, 6/6 pronuclear embryos) and beta5 (8/28 oocytes, 5/6 pronuclear embryos), and the apoptotic regulators BCL-2 (20/28 oocytes, 2/6 pronuclear embryos) and BAX (21/28 oocytes, 5/6 pronuclear embryos). The expression of the pro-apoptotic regulator BAX increased in human oocytes following prolonged periods of culture. Overall, patterns of gene transcript presence showed variation between embryos and this was independent of either zona removal or lysis conditions. Pronucleate embryos showed less variation, however, even sibling embryos from the patient did not express an identical subset of genes.

Tight junction messenger RNA expression levels in bovine embryos are dependent upon the ability to compact and in vitro culture methods

We have established a transcription map of individual bovine embryos using semiquantitative reverse transcriptase-polymerase chain reaction to detect the levels of six marker genes involved in early embryo differentiation. The critical step of compaction during preimplantation development is often not accomplished or it takes place for only a short period in in vitro generated embryos, which may result in reduced viability. Compaction is accompanied by the assembly of intercellular tight junctions (TJs) as a barrier against the extraembryonic environment and as a prerequisite for blastocele formation. In the present study, we have related the expression of TJ gene mRNA in individual bovine embryos to their developmental stage, their competence to undergo a clear period of compaction before blastocyst formation, and their in vitro or in vivo origin. Our results indicate that embryos that showed a detectable and well-formed compaction period in vitro are of similar quality to their in vivo counterparts. Starting from the same amount of maternal message, in vivo and in vitro development differ most during the critical period of the major switch from maternal to embryonic genomic control before a dramatic increase of TJ mRNAs occurs upon blastocyst formation. Failure to compact in vitro results in significant reduction of specific transcript levels, in a manner that depends on culture conditions, which may contribute to reduced viability. We conclude that TJ mRNA expression levels are sensitive to environmental conditions that may influence the developmental potential of bovine blastocysts.

Responsiveness of bovine cumulus-oocyte-complexes (COC) to porcine and recombinant human FSH, and the effect of COC quality on gonadotropin receptor and Cx43 marker gene mRNAs during maturation in vitro

Substantially less development to the blastocyst stage occurs in vitro than in vivo and this may be due to deficiencies in oocyte competence. Although a large proportion of bovine oocytes undergo spontaneous nuclear maturation, less is known about requirements for proper cytoplasmic maturation. Commonly, supraphysiological concentrations of FSH and LH are added to maturation media to improve cumulus expansion, fertilization and embryonic development. Therefore, various concentrations of porcine FSH (pFSH) and recombinant human FSH (rhFSH) were investigated for their effect on bovine cumulus expansion in vitro. Expression of FSHr, LHr and Cx43 mRNAs was determined in cumulus-oocyte complexes to determine whether they would be useful markers of oocyte competence. In serum-free media, only 1000 ng/ml pFSH induced marked cumulus expansion, but the effect of 100 ng/ml pFSH was amplified in the presence of 10% serum. In contrast, cumulus expansion occurred with 1 ng/ml rhFSH in the absence of serum. FSHr mRNA was highest at 0-6 h of maturation, then abundance decreased. Similarly, Cx43 mRNA expression was highest from 0-6 h but decreased by 24 h of maturation. However, the relative abundance of LHr mRNA did not change from 6-24 h of maturation. Decreased levels of FSHr, LHr and Cx43 mRNAs were detected in COCs of poorer quality. In conclusion, expansion of bovine cumulus occurred at low doses of rhFSH in serum-free media. In summary, FSHr, LHr and Cx43 mRNA abundance reflects COC quality and FSHr and Cx43 mRNA expression changes during in vitro maturation; these genes may be useful markers of oocyte developmental competence.

Use of heterologous complementary DNA array screening to analyze bovine oocyte transcriptome and its evolution during in vitro maturation

We have analyzed gene expression in bovine oocytes before and after in vitro maturation (IVM) using heterologous hybridization onto cDNA array. Total RNA was purified from pools of over 200 oocytes either immediately after aspiration from follicles at the surface of slaughterhouse cow ovaries or following in vitro maturation. Radiolabeled cDNA probes were generated by reverse-transcription followed by linear PCR amplification and were hybridized to Atlas human cDNA arrays. To our knowledge, this is the first report of gene expression profiling by this technology in the mammalian female germ cell. Our results demonstrate that cDNA array screening is a suitable method for analyzing the transcription pattern in oocytes. About 300 identified genes were reproducibly shown to be expressed in the bovine oocyte, the largest profile available so far in this model. The relative abundance of most messenger RNAs appeared stable during IVM. However, 70 transcripts underwent a significant differential regulation (by a factor of at least two). Their potential role in the context of oocyte maturation is discussed. Together they constitute a molecular signature of the degree of oocyte cytoplasmic maturation achieved in vitro.

Messenger RNA stockpile of cyclin B, insulin-like growth factor I, insulin-like growth factor II, insulin-like growth factor receptor Ib, and p53 in the rainbow trout oocyte in relation with developmental competence

In the present study, correlations between the oocyte messenger RNA (mRNA) stockpile of Cyclin B, insulin-like growth factor I (IGF-I), insulin-like growth factor (IGF-II), insulin-like growth factor receptor Ib (IGFR Ib), and p53 transcripts and the developmental competence of the oocyte were studied. For this purpose, post-ovulatory ageing was used as a tool to generate oocytes of varying developmental competence. Mature female rainbow trout were held at 12 degrees C and periodically checked for ovulation. Oocytes were collected from each female at ovulation and 5, 14, 21 days later. For each collected egg batch, the abundance of several mRNAs in the oocyte was analyzed by real-time PCR and embryo development was monitored after fertilization. Egg quality was estimated not only through embryonic survival but also by studying the occurrence of specific morphological abnormalities. The present study showed that oocyte post-ovulatory ageing was associated with variations of the relative abundance of several studied transcripts within the oocyte. In addition, the abundance of specific mRNAs could be correlated with either the embryonic survival or the occurrence of malformations. Thus, the abundance of IGFR Ib and Cyclin B transcripts in the oocyte was correlated with the occurrence of morphological abnormalities observed at yolk-sac resorption (negatively for IGFR Ib and positively for Cyclin B), while the maternal stockpile of IGF-I, IGF-II, and IGFR Ib mRNAs was positively correlated with embryonic survival.

Quantification of housekeeping transcript levels during the development of bovine preimplantation embryos

In mammals, the study of gene expression in the preimplantation embryo has been difficult because the standard procedures used to quantify mRNA generally require large amounts of starting material. The development of protocols using different quantitative strategies generally involving the polymerase chain reaction (PCR) has provided new tools for exploration of gene expression in preimplantation embryos. However, the use of an internal standard, often referred as a housekeeping gene, is essential to normalize the mRNA levels. RNA levels of eight housekeeping genes were quantified using real time PCR throughout the preimplantation period of the bovine embryo to find the most suitable gene to be used as standard. Histone H2a was the best internal standard because the transcript levels were constant across the preimplantation period. Linear amplification of antisense RNA using the T7 promotor for in vitro transcription of the entire RNA pool was evaluated as a suitable way to preamplify the starting material prior to quantification and was effective in providing accurate RNA abundance profiles throughout the preimplantation period. However, the amplification appears to be template dependent because the amplification factors were higher for some genes.

Cyclooxygenase-2 and prostaglandin E(2)(PGE(2)) receptor messenger RNAs are affected by bovine oocyte maturation time and cumulus-oocyte complex quality, and PGE(2) induces moderate expansion of the bovine cumulus in vitro

Expression of cyclooxygenase-2 (COX-2) and prostaglandin E(2) (PGE(2)) receptor 2 (EP2) are necessary for rodent cumulus expansion in vivo. Prostaglandin E(2) receptor 3 (EP3) has been detected in bovine preovulatory follicles and corpora lutea. The current experiments examined the effect of PGE(2) on bovine cumulus expansion in vitro and expression of COX-2, EP1, EP2, EP3, and EP4 mRNAs in bovine cumulus-oocyte complexes (COCs) at 0, 6, 12, 18, and 24 h time points during maturation in vitro. Concentrations of PGE(2) above 50 ng/ml resulted in moderate cumulus expansion of bovine COCs, but expansion did not occur in the absence of serum. COX-2 mRNA expression increased in bovine COCs at 6 h and 12 h of maturation, then decreased. EP2 mRNA was detectable by reverse transcription-polymerase chain reaction at all time points. EP3 mRNA expression increased in COCs from 0 to 6 h and remained at this higher level through the culture period. Very low levels of EP4 mRNA expression were detectable, but EP1 was not detected in bovine COCs. Because EP receptor mRNAs and COX-2 mRNA are expressed in bovine COCs, there exists the potential for a prostaglandin autocrine/paracrine regulatory pathway during oocyte maturation. Differential expression of the EP3 mRNA among varying COC classes indicates that this gene product may be a useful marker of oocyte competence. Although the PGE(2) pathway is involved in cumulus expansion, serum factors are required to mediate PGE(2)-induced expansion.

Effects of culture system and protein supplementation on mRNA expression in pre-implantation bovine embryos

Assisted reproduction technologies have made great progress during the last 15 years in most mammalian species, including humans. Growing evidence indicates that bovine pre-implantation development is a superior model for investigating early human development than the mouse. The purpose of this study was to investigate the effects of two basic culture systems [tissue culture medium (TCM) with 5% CO(2) in air or synthetic oviduct fluid (SOF) with 7% O(2), 88% N(2,) 5% CO(2)] and various protein supplements (serum, bovine serum albumin or polyvinyl alcohol) on the relative abundance of a set of developmentally important gene transcripts in bovine morulae and blastocysts and to compare the results with those for their in-vivo-derived counterparts. The basic culture system including the basic medium composition and oxygen tension had profound effects on the amounts of specific transcripts in bovine embryos, whereas the 'protein source' had only weak effects. Significant differences (P < or = 0.05) in the relative abundance of specific gene transcripts were detected between in-vivo and in-vitro-derived embryos, especially at the morula stage. More differences were found between embryos produced in the TCM system and in-vivo-derived embryos than between SOF-generated embryos and their in-vivo counterparts. No differences were found in the relative abundance of gene transcripts in embryos generated under chemically defined conditions in the two different laboratories. It is concluded that the SOF system provides an environment in which pre-implantation development of bovine embryos is more similar to that occurring in vivo than in the TCM system.

Factors controlling the loss of immunoreactive somatic histone H1 from blastomere nuclei in oocyte cytoplasm: a potential marker of nuclear reprogramming

Nuclei of differentiated cells can acquire totipotency following transfer into the cytoplasm of oocytes. While the molecular basis of this nuclear reprogramming remains unknown, the developmental potential of nuclear-transfer embryos is influenced by the cell-cycle stage of both donor and recipient. As somatic H1 becomes immunologically undetectable on bovine embryonic nuclei following transfer into ooplasm and reappears during development of the reconstructed embryo, suggesting that it may act as a marker of nuclear reprogramming, we investigated the link between cell-cycle state and depletion of immunoreactive H1 following nuclear transplantation. Blastomere nuclei at M-, G1-, or G2-phase were introduced into ooplasts at metaphase II, telophase II, or interphase, and the reconstructed embryos were processed for immunofluorescent detection of somatic histone H1. Immunoreactivity was lost more quickly from donor nuclei at metaphase than at G1 or G2. Regardless of the stage of the donor nucleus, immunoreactivity was lost most rapidly when the recipient cytoplast was at metaphase and most slowly when the recipient was at interphase. When the recipient oocyte was not enucleated, however, immunoreactive H1 remained in the donor nucleus. The phosphorylation inhibitors 6-DMAP, roscovitine, and H89 inhibited the depletion of immunoreactive H1 from G2, but not G1, donor nuclei. In addition, immunoreactive H1 was depleted from mouse blastomere nuclei following transfer into bovine oocytes. Finally, expression of the developmentally regulated gene, eIF-1A, but not of Gapdh, was extinguished in metaphase recipients but not in interphase recipients. These results indicate that evolutionarily conserved cell-cycle-regulated activities, nuclear elements, and phosphorylation-linked events participate in the depletion of immunoreactive histone H1 from blastomere nuclei transferred in oocyte cytoplasm and that this is linked to changes in gene expression in the transferred nucleus.

The maternal legacy to the embryo: cytoplasmic components and their effects on early development

RNA molecules and proteins are accumulated in the oocyte cytoplasm during its growth phase and are used to sustain the early phases of embryonic development before embryo DNA transcription begins. This makes the oocyte a very special cell, quite different from somatic cells where RNA and proteins usually undergo a rapid turnover. To enable the storage and timely use of such stored molecules, various mechanisms are effective in the oocyte and are gradually being elucidated. Our understanding of such mechanisms is important for constantly improving therapy for human and animal reproductive disorders as well as for understanding the process of nuclear reprogramming during cloning procedure or stem cell generation. This review focuses on the various aspects of these regulatory processes in an attempt to give an overview of the present knowledge on post-transcriptional and post-translational mechanisms taking place during oocyte maturation and early development. Mechanisms such as cytoplasmic regulation of the poly(A) tail, RNA localization and protein phosphorylation are described in some detail. Because most data are available from lower species these are presented together with appropriate reference to the mammalian oocyte when data are known, or when important differences have been described.

Subtractive hybridization used to identify mRNA associated with the maturation of bovine oocytes

The main objective of this project is to identify mRNA associated with oocyte maturation and embryonic developmental competency. The knowledge of genes and their accumulated mRNA is essential to better understand the mechanisms involved in the oocyte maturation and the survival of the in vitro produced embryo. We used bovine slaughterhouse-recovered ovaries and collected the oocytes from two follicle size categories: <2 mm and 3-5 mm. The mRNA content of oocytes from follicles 3-5 mm where considered to be more competent when compared to the content of oocytes from follicles <2 mm. In this report we compare two different technical approaches both involving PCR to compare the mRNA pools of the oocytes. In the first approach we performed the differential display (DDRT) technique to amplify and display side by side the cDNAs of groups of 10 denuded oocytes. From this approach, we isolated 28 different bands. After analysis, three of those bands had strong homology with known genes. In the second approach pools of 50 denuded oocytes were submitted to suppressive subtraction hybridization (SSH). We identified several known genes like cyclin B1, splicing factor ccl.4, cytochrome c oxidase, and mineralocorticoid receptor while numerous other clones remain unidentified. The cyclin B1 clone was used as a probe to evaluate its follicular size specificity on virtual Northern blot. The PCR basis of these techniques allows comparison of mRNA from tissues of low abundance such as oocytes. In this study the SSH resulted in longer clones than DDRT and showed high specificity.

High-throughput single-strand conformation polymorphism analysis by capillary electrophoresis

Mutation detection plays a great role in genetic and medical research and clinical diagnosis of inherited diseases and particular cancers. Single-strand conformation polymorphism (SSCP) analysis is one of the most popular methods for detection of mutations. Recently, automated capillary electrophoresis (CE) systems have been used in SSCP analysis instead of conventional slab gel electrophoresis. SSCP analysis in combination with CE is a rapid, simple, sensitive and high-throughput mutation screening tool, and has been successfully applied for mutation detection involving human tumor suppressor genes, oncogenes and disease-causing genes. The new technique has a great potential for mutation screening of large numbers of samples in clinical diagnosis. This review discusses basic issues about the methodology of SSCP analysis based on CE and summarizes several key applications.

Impact of bovine oocyte maturation media on oocyte transcript levels, blastocyst development, cell number, and apoptosis

The objectives were 1) to investigate the effects of oocyte maturation in serum-free and amino acid-supplemented defined media on oocyte transcript levels, blastocyst cell number, and apoptosis; 2) to investigate the influence of oocyte maturation culture atmosphere on blastocyst development, total cell number, and apoptosis; and 3) to examine the influence of epidermal growth factor (EGF) during oocyte maturation on blastocyst cell number and apoptosis. The results demonstrate that blastocysts derived from in vitro maturation, fertilization, and embryo culture protocols undergo apoptosis but that apoptotic levels are not greatly influenced by the oocyte maturation environment. Amino acid supplementation of oocyte maturation media was associated with enhanced developmental frequencies, increased blastocyst cell number, and elevated oocyte maternal mRNA levels. Oocyte maturation with supplemented synthetic oviduct fluid medium (cSOFMaa) resulted in blastocyst cell numbers comparable to those observed with Tissue Culture Medium 199 + newborn calf serum. Blastocyst development was reduced following oocyte maturation under a 5% CO(2), 7% O(2), 88% N(2) culture atmosphere. EGF supplementation of oocyte maturation medium resulted in a concentration-dependent increase in blastocyst development but did not influence blastocyst total cell number or apoptosis. Our findings indicate that cSOFMaa medium is an effective base medium for bovine oocyte maturation.

Assessment by differential display-RT-PCR of mRNA transcript transitions and alpha-amanitin sensitivity during bovine preattachment development

The objectives of this study were to compare patterns of mRNA expression, investigate the onset of transcription, and isolate stage-specific and alpha-amanitin-sensitive mRNAs during early bovine development by differential-display-reverse transcription-polymerase chain reaction (DD-RT-PCR). Embryos representing a preattachment developmental series from the 1-cell to the expanded/hatched blastocyst stage were cultured in synthetic oviduct fluid medium + citrate and amino acids (cSOFMaa) with and without alpha-amanitin (100 microg/mL) for 4 and 12 hr. mRNA profiles were displayed by DD-RT-PCR using 5' primers A and N. Total conserved cDNA banding patterns varied according to embryo stage with cDNA band numbers declining during early cleavage stages compared to oocyte values and then increasing in total number from the 6-8-cell stage through to the blastocyst stage. A cDNA banding pattern was established at the 8-16-cell stage that was largely unchanged through to the blastocyst stage. These findings with respect to cDNA banding patterns were conserved between oligo primer sets and experimental replicates. alpha-Amanitin sensitivity was first detected at the 2-5-cell stage but became predominant following the 6-8-cell stage of development to eventually affect the appearance of up to 40% of all cDNA bands by the blastocyst stage. A 12 hr alpha-amanitin treatment was required to effectively block (3)H-uridine incorporation into mRNA in blastocyst stage embryos. Several stage-specific and alpha-amanitin-sensitive cDNAs were isolated and they will be a focus for future studies. In conclusion, DD-RT-PCR is an effective tool for contrasting gene expression patterns and isolating uncharacterized mRNA transcripts during bovine early development. Mol. Reprod. Dev. 55:152-163, 2000.

Alterations of expression of developmentally important genes in preimplantation bovine embryos by in vitro culture conditions: implications for subsequent development

Recent advances in molecular technology and in vitro production of bovine embryos have enabled studies of gene transcription in preimplantation embryos. On the basis of knowledge of the sequence of the selected gene, various modifications of Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) technology have been employed. Several lines of evidence in mouse and cattle indicate that expression patterns of genes from in vitro-produced embryos are not necessarily representative of those of in vivo embryos. An important gene that has been found to be expressed by in vivo-derived bovine blastocysts, but not in their in vitro-produced counterparts, is the Connexin43 gene that is crucial for maintenance of compaction. The bovine leukemia inhibitory factor (bLIF) and LIF-receptor-beta (LR-beta) genes were expressed by in vitro-produced embryos, but not in their in vivo counterparts. The heat shock protein gene 70.1 (Hsp 70.1) was upregulated by blastocysts produced in vitro compared to in vivo embryos, while the glucose transporter-1 mRNA (Glut-1) was downregulated by morulae produced in vitro as compared to in vivo-derived morulae. Furthermore, mRNA expression levels of a set of "marker genes" were shown to be affected by the presence or absence of serum in the culture medium. Most embryos grown under serum-free conditions had higher mRNA abundances than those cultured in serum-enriched medium. It is hypothesized that persistent alterations of the normal gene expression patterns may be responsible for the large offspring syndrome that is observed in approximately one third of the calves resulting from the transfer of in vitro-produced embryos. A primary candidate for such deviations may be an altered methylation pattern that can either lead to silencing or induction of a specific gene. Messenger RNA phenotyping of genes essential in early development provides a useful tool to assess the normality of the produced embryos and a tool to optimize in vitro culture conditions for bovine embryos.