Stage-specific expressed sequence tags obtained during preimplantation bovine development by differential display RT-PCR and suppression subtractive hybridization

Early embryo-maternal communication in the oviduct: A review

An intact embryo-maternal communication is critical for the establishment of a successful pregnancy. To date, a huge number of studies have been performed describing the complex process of embryo-maternal signaling within the uterus. However, recent studies indicate that the early embryo communicates with the oviductal cells shortly after fertilizationand that this is important for the successful establishment of pregnancy. Only if the early embryo is capable to signal the mother within a precise timeframe and to garner a response, will the embryo be able to survive and reach the uterus. This review will give an overview of all the experimental designs which have investigated embryo-maternal interaction in the oviduct. In addition to that, it will provide a comprehensive analysis of the findings to date elucidating the morphological and molecular changes in the oviduct which are induced by the presence of the early embryo highlighting how the tubal responses affect embryo development and survival.

Altrenogest affects expression of galectin-3 and fibroblast growth factor 9 in the reproductive tract of sows

A synthetic progestin altrenogest (ALT) is used to synchronize the estrus cycle of swine for fixed-time artificial insemination (AI) and has been shown to improve follicular development and reproductive performances in post-weaning sows. However, the effects of ALT treatment on reproductive tracts, including the ovaries, oviducts and uterus have not been yet clarified. In this study, we examined the expression of genes involved in endometrial responses in ALT-treated sows. ALT did not significantly alter luteinizing hormone (LH), follicle-stimulating hormone (FSH) and estradiol profiles in blood compared to untreated control. Quantitative RT-polymerase chain reaction (qRT-PCR) analysis showed that the expression of genes encoding galectin-3 (LGALS3) and fibroblast growth factor 9 (FGF9) was upregulated in the reproductive tracts of ALT-treated sows, including the ovaries, oviducts and uteri. Moreover, ALT treatment induced the expression of FGF9 and galectin-3 proteins, and promoted their localization to the luminal epithelium of the oviducts and uterus. Our findings suggest that the enhancement of reproductive performance shown by ALT-treated sows is associated with the upregulation of galectin-3 and FGF9, which are essential for endometrial receptivity, successful implantation, and pregnancy.

Use of two new formulations as bovine embryo manipulation solution

This study aimed to evaluate the effect of two Embryo Manipulation Solutions (EMS and EMS supplemented) in maintenance of the viability of embryos, initially using structures derived from mice (first phase). Next, the efficiency of these solutions in routines of bovine embryo transfer was evaluated (second stage). Mice embryos were used in the stages of early blastocyst, and compact morula grades I and II. These embryos were initially randomly distributed and maintained for four hours in three solutions: Modified phosphate buffered saline (PBS; Control); EMS (treatment 1), and EMS supplemented (treatment 2). Subsequently, they were cultured in TCM 199 medium and evaluated in terms of total number of cells, morphometric characteristics, ultra structural aspects, detection of cell apoptosis, and quantification of Hsp70.3 gene expression. In the second phase, these same solutions were tested in the transfer of quality I and II bovine embryos (excellent and good). These embryos were transferred fresh to 58 recipients. The results showed that the total number of cells in embryos expanded blastocyst (ExB), the number of apoptotic cells, the cell, nuclear, nucleolar diameter and the nucleus/nucleolus ratio was similar among the treatments. The pregnancy rate shown on second phase was also similar. However, the EMS supplemented expressed more Hsp70.3 than EMS. The expression of Hsp70.3 was also greater for embryos in EMS than that of EMS supplemented. The McII embryos, EMS and EMS supplemented samples also expressed more Hsp70.3 compared to control embryos. In conclusion, the tested solutions can be used in routine embryo transfer techniques, replacing modified PBS solution as an effective media in maintaining embryo viability.

Effects of galectin-3 inhibition on endometrial cell cycle and adhesion

Galectin-3 (gal-3) and its ligands have been implicated in cell transformation and cancer metastasis. Gal-3 protein has been found in uterine epithelial cells adjacent to implanting blastocysts in different cell types. In order to investigate the role of gal-3 in the establishment of human endometrial receptivity, the expression of gal-3 in human endometrial cell line RL95-2 was silenced by RNA interference technology using gal-3 specific small RNA. The expression of gal-3 was detected by the reverse transcriptase-polymerase chain reaction and Western blot analysis. After the suppression of gal-3, cell cycle changes and the expression of integrin β1 were detected by flow cytometry. The adhesive ability of RL95-2 cells was analyzed by the adhesion test. Gal-3 siRNA transfection efficiency reached 70%-90%. The expression of gal-3 mRNA and protein in RL95-2 cells was strongly inhibited by 70%-90% after RNA interference. Inhibition of gal-3 expression decreased S-phase but increased G1 phase cells. Integrin β1 expression was down-regulated, and the adhesive ability of RL95-2 cells to fibronectin (FN) was significantly reduced. Gal-3 may be involved in the establishment of endometrial receptivity by regulating the proliferation and adhesion of endometrial cells. The influence on adhesion may be related with the integrin modulation.

Identification of mouse 8-cell embryo stage-specific genes by Digital Differential Display

Preimplantation development is critical for successful implantation and pregnancy. In the mouse preimplantation embryo, the first event of morphological and cellular differentiation is established during polarization and compaction at the 8-cell stage. The considerable cell surface and cytoplasmic changes and formation of different populations of cells at the 8-cell stage are fundamentally important for the development of all organisms. To determine genes that are specifically expressed at this crucial stage of embryo development and also to shed light on the different mechanisms that could be of importance during embryo development, we investigated mouse 8-cell and 4-cell embryo stage-specific genes using Digital Differential Display (DDD). The 8-cell stage-specific genes were sorted according to their ontology data from the Database for Annotation, Visualization and Integrated Discovery (DAVID), which outlines possible roles for the genes expressed at the 8-cell stage. This study highlights how online tools can be used to identify genes involved in embryo development. Identification of the 8-cell embryo stage-specific genes would open new opportunities for understanding molecular networks during the mid-preimplantation gene activation. Using bioinformatic tools, such as Digital Differential Display and DAVID, it will be possible to identify genes expressed at the 8-cell stage that are likely to be involved in mammalian preimplantation embryo development. Our results may provide a new foundation for molecular control at the onset of embryonic development in mammals, and should be of interest to the scientific community.

Gamete/embryo – oviduct interactions: implications onin vitroculture

Fertilization and development of mouse embryos occur in the oviduct. Accumulating data suggested that embryo-maternal communication exists in the preimplantation period, with the female reproductive tract providing the optimal microenvironment conducive to the development of embryos. Signals produced from the developing embryos not only affect their own transport in the oviduct, but the physiology and gene expression patterns of the oviduct. As a step towards understanding the action of embryos on oviductal physiology, both genomics and proteomics approaches are being used to unveil the underlying mechanism of embryo-maternal interaction at the preimplantation stage. Results from recent studies allow us to better understand the roles and the use of oviductal secretory proteins or factors that affect embryo development in vivo and in vitro. It has been shown that in vitro culture alters gene expression of the cultured embryos and may predispose the embryo to certain disease. Therefore, the interaction between gamete/embryo and oviduct in vitro and in vivo, and the long-term effects of embryo culture on foetal development warrant further investigation.

Unveiling the bovine embryo transcriptome during the maternal-to-embryonic transition

Bovine early embryos are transcriptionally inactive and subsist through the initial developmental stages by the consumption of the maternal supplies provided by the oocyte until its own genome activation. In bovine, the activation of transcription occurs during the 8- to 16-cell stages and is associated with a phase called the maternal-to-embryonic transition (MET) where maternal mRNA are replaced by embryonic ones. Although the importance of the MET is well accepted, since its inhibition blocks embryonic development, very little is known about the transcripts expressed at this crucial step in embryogenesis. In this study, we generated and characterized a cDNA library enriched in embryonic transcripts expressed at the MET in bovine. Suppression subtractive hybridization followed by microarray hybridization was used to isolate more than 300 different transcripts overexpressed in untreated late eight-cell embryos compared with those treated with the transcriptional inhibitor, alpha-amanitin. Validation by quantitative RT-PCR of 15 genes from this library revealed that they had remarkable consistency with the microarray data. The transcripts isolated in this cDNA library have an interesting composition in terms of molecular functions; the majority is involved in gene transcription, RNA processing, or protein biosynthesis, and some are potentially involved in the maintenance of pluripotency observed in embryos. This collection of genes associated with the MET is a novel and potent tool that will be helpful in the understanding of particular events such as the reprogramming of somatic cells by nuclear transfer or for the improvement of embryonic culture conditions.

Blastocyst elongation, trophoblastic differentiation, and embryonic pattern formation

The molecular basis of ungulate and non-rodent conceptus elongation and gastrulation remains poorly understood; however, use of state-of-the-art genomic technologies is beginning to elucidate the mechanisms regulating these complicated processes. For instance, transcriptome analysis of elongating porcine concepti indicates that protein synthesis and trafficking, cell growth and proliferation, and cellular morphology are major regulated processes. Furthermore, potential autocrine roles of estrogen and interleukin-1-β in regulating porcine conceptus growth and remodeling and metabolism have become evident. The importance of estrogen in pig is emphasized by the altered expression of essential steroidogenic and trophoblast factors in lagging ovoid concepti. In ruminants, the characteristic mononucleate trophoblast cells differentiate into a second lineage important for implantation, the binucleate trophoblast, and transcriptome profiling of bovine concepti has revealed a gene cluster associated with rapid trophoblast proliferation and differentiation. Gene cluster analysis has also provided evidence of correlated spatiotemporal expression and emphasized the significance of the bovine trophoblast cell lineage and the regulatory mechanism of trophoblast function. As a part of the gastrulation process in the mammalian conceptus, specification of the germ layers and hence definitive body axes occur in advance of primitive streak formation. Processing of the transforming growth factor-β-signaling molecules nodal and BMP4 by specific proteases is emerging as a decisive step in the initial patterning of the pre-gastrulation embryo. The topography of expression of these and other secreted molecules with reference to embryonic and extraembryonic tissues determines their local interaction potential. Their ensuing signaling leads to the specification of axial epiblast and hypoblast compartments through cellular migration and differentiation and, in particular, the specification of the early germ layer tissues in the epiblast via gene expression characteristic of endoderm and mesoderm precursor cells.

Identification and expression analysis of genes associated with bovine blastocyst formation

BACKGROUND

Normal preimplantation embryo development encompasses a series of events including first cleavage division, activation of the embryonic genome, compaction and blastocyst formation. First lineage differentiation starts at the blastocyst stage with the formation of the trophectoderm and the inner cell mass. The main objective of this study was the detection, identification and expression analysis of genes associated with blastocyst formation in order to help us better understand this process. This information could lead to improvements of in vitro embryo production procedures.

RESULTS

A subtractive cDNA library was constructed enriched for transcripts preferentially expressed at the blastocyst stage compared to the 2-cell and 8-cell stage. Sequence information was obtained for 65 randomly selected clones. The RNA expression levels of 12 candidate genes were determined throughout 3 stages of preimplantation embryo development (2-cell, 8-cell and blastocyst) and compared with the RNA expression levels of in vivo "golden standard" embryos using real-time PCR. The RNA expression profiles of 9 (75%) transcripts (KRT18, FN1, MYL6, ATP1B3, FTH1, HINT1, SLC25A5, ATP6V0B, RPL10) were in agreement with the subtractive cDNA cloning approach, whereas for the remaining 3 (25%) (ACTN1, COPE, EEF1A1) the RNA expression level was equal or even higher at the earlier developmental stages compared to the blastocyst stage. Moreover, significant differences in RNA expression levels were observed between in vitro and in vivo produced embryos. By immunofluorescent labelling, the protein expression of KRT18, FN1 and MYL6 was determined throughout bovine preimplantation embryo development and showed the same pattern as the RNA expression analyses.

CONCLUSION

By subtractive cDNA cloning, candidate genes involved in blastocyst formation were identified. For several candidate genes, important differences in gene expression were observed between in vivo and in vitro produced embryos, reflecting the influence of the in vitro culture system on the embryonic gene expression. Both RNA and protein expression analysis demonstrated that KRT18, FN1 and MYL6 are differentially expressed during preimplantation embryo development and those genes can be considered as markers for bovine blastocyst formation.

Maternally derived transcripts: identification and characterisation during oocyte maturation and early cleavage

The identification and characterisation of differentially regulated genes in oocytes and early embryos are required to understand the mechanisms involved in maturation, fertilisation, early cleavage and even long-term development. Several methods, including reverse transcription-polymerase chain reaction-based suppression subtractive hybridisation, differential display and cDNA microarray, have been applied to identify maternally derived genes in mammalian oocytes. However, conventional gene-knockout experiments to determine specific gene functions are labour intensive and inefficient. Recent developments include the use of RNA interference techniques to establish specific gene functions in mammalian oocytes and early embryos. Regulation of the poly(A) tail length is a major factor in controlling the activities of maternal transcripts in mammals. Further studies are required to clarify the mechanisms by which expression levels of maternally derived transcripts are regulated. In the present review, we focus on the identification and functions of the differentially expressed transcripts during oocyte maturation, fertilisation and early cleavage.

Transcript profiles of some developmentally important genes detected in bovine oocytes and in vitro-produced blastocysts using RNA amplification and cDNA microarrays

To study the mRNA transcript profiles of some potential candidate developmental genes during bovine oocyte and blastocyst stages, RNA amplification procedures, cDNA microarray of 82 target genes spotted onto glass slide and real-time polymerase chain reaction (PCR) were used. Messenger RNAs were isolated from in vitro-produced bovine matured oocytes and blastocysts. Using equal amounts of input mRNAs but different cycles of amplifications, cDNAs were produced and served as template for RNA amplification by the in vitro transcriptions. After amplification, the RNA yields transcribed from cDNAs of different cycles were evaluated both by hybridization on the cDNA microarrays and by using real-time PCR techniques. The analyses indicated best results from lower amplification cycle templates with consistent signals at hybridization. Generally, the RNA yield was directly proportional to the amplification cycle but inversely related with signal consistency at repeated hybridizations. Using the protocols established, equal amounts of amplified RNA from matured oocytes and blastocysts were hybridized to the array. Analyses of replicated hybridizations indicated that 35 transcripts were differentially expressed. Most of these were not described in previous bovine embryo studies. Independent analyses of 23 transcripts with real-time PCR and unamplified RNA confirmed the results of 22 genes. Moreover, the functional analyses showed various roles related to development. Hence, it is possible to conclude that the genes identified here are potential candidates for characterizing developmental competence, and that the methods established can be used for large-scale gene expression analysis with more comprehensive arrays.

The Effect of Nitric Oxide Inhibition and Temporal Expression Patterns of the mRNA and Protein Products of Nitric Oxide Synthase Genes During In Vitro Development of Bovine Pre-implantation Embryos

This study was conducted to determine the effect of Nitric oxide (NO) inhibition in bovine in vitro development and expression analysis of the three Nitric oxide synthase (NOS) isoforms: endothelial (eNOS), neuronal (nNOS) and inducible (iNOS), mRNA and protein in bovine oocytes and embryos. Selective inhibitor of NOS, N-omega-nitro-l-arginine methyl ester (l-NAME) was applied at different doses (0, 0.1, 1 and 10 mm) in maturation (experiment 1A), culture medium (experiment 1B) and in both maturation and culture media (experiment 1C). No significant differences were observed in cleavage and blastocyst rates when oocytes were matured in the presence of l-NAME as long as the inhibitor was omitted during fertilization and culture. However, significantly lower blastocyst rates were observed when l-NAME was present at higher level (10 mm) in culture medium alone and in both maturation and culture media. In experiment 2, mRNA isolated from triplicate pools of oocytes and embryos (n = 15-20) was subjected to quantitative real time reverse transcription polymerase chain reaction to investigate the expression of eNOS, iNOS and nNOS mRNA in normal IVP bovine oocytes and embryos. While eNOS and iNOS transcripts were detected at higher level in oocytes (immature and mature), two-cell and four-cell stage embryos, the nNOS was detected only in immature oocyte, two-cell and morula stages. In experiment 3, eNOS and iNOS protein expression analysis was performed in IVP oocytes and embryos and both proteins were detected in the cytoplasm and the nuclei (weak) of oocytes and embryos. These data provide the first evidence for the role of NO production and the presence of mRNA and protein products of NOS isoforms during bovine embryogenesis.

Large-scale transcriptional analysis of bovine embryo biopsies in relation to pregnancy success after transfer to recipients

The purpose of this work is to address the relationship between transcriptional profile of embryos and the pregnancy success based on gene expression analysis of blastocyst biopsies taken prior to transfer to recipients. Biopsies (30-40% of the intact embryo) were taken from in vitro-produced day 7 blastocysts (n = 118), and 60-70% were transferred to recipients after reexpansion. Based on the success of pregnancy, biopsies were pooled in three groups (each 10 biopsies) namely: those resulting in no pregnancy (G1), resorbed embryos (G2), and those resulting in calf delivery (G3). Gene expression analysis of these groups was performed using home-made bovine preimplantation-specific cDNA array (219 clones) and BlueChip (with approximately 2,000 clones). Microarray data analysis results revealed a total of 52 and 58 genes were differentially regulated during comparison between G1 vs. G3 and G2 vs. G3. Biopsies resulted in calf delivery were enriched with genes necessary for implantation (COX2 and CDX2), carbohydrate metabolism (ALOX15), growth factor (BMP15), signal transduction (PLAU), and placenta-specific 8 (PLAC8). Biopsies from embryos resulting in resorption are enriched with transcripts involved protein phosphorylation (KRT8), plasma membrane (OCLN), and glucose metabolism (PGK1 and AKR1B1). Biopsies from embryos resulting in no pregnancy are enriched with transcripts involved inflammatory cytokines (TNF), protein amino acid binding (EEF1A1), transcription factors (MSX1, PTTG1), glucose metabolism (PGK1, AKR1B1), and CD9, which is an inhibitor of implantation. In conclusion, we generated direct candidates of blastocyst-specific genes which may play an important role in determining the fate of the embryo after transfer.

Cross-species hybridizations on a multi-species cDNA microarray to identify evolutionarily conserved genes expressed in oocytes

BACKGROUND

Comparative genomic analysis using cDNA microarray is a new approach and a useful tool to identify important genetic sequences or genes that are conserved throughout evolution. Identification of these conserved sequences will help elucidate important molecular mechanisms or pathways common to many species. For example, the stockpiled transcripts in the oocyte necessary for successful fertilization and early embryonic development still remain relatively unknown. The objective of this study was to identify genes expressed in oocytes and conserved in three evolutionarily distant species.

RESULTS

In this study we report the construction of a multi-species cDNA microarray containing 3,456 transcripts from three distinct oocyte-libraries from bovine, mouse and Xenopus laevis. Following the cross-species hybridizations, data analysis revealed that 1,541 positive hybridization signals were generated by oocytes of all three species, and 268 of these are preferentially expressed in the oocyte. Data reproducibility analyses comparing same-species to cross-species hybridization indicates that cross-species hybridizations are highly reproducible, thus increasing the confidence level in their specificity. A validation by RT-PCR using gene- and species-specific primers confirmed that cross-species hybridization allows the production of specific and reliable data. Finally, a second validation step through gene-specific microarray hybridizations further supported the validity of our cross-species microarray results. Results from these cross-species hybridizations on our multi-species cDNA microarray revealed that SMFN (Small fragment nuclease), Spin (Spindlin), and PRMT1 (Protein arginine methyltransferase 1) are transcripts present in oocytes and conserved in three evolutionarily distant species.

CONCLUSION

Cross-species hybridization using a multi-species cDNA microarray is a powerful tool for the discovery of genes involved in evolutionarily conserved molecular mechanisms. The present study identified conserved genes in the oocytes of three distant species that will help understand the unique role of maternal transcripts in early embryonic development.

Identification of a novel male reproduction-related gene and its regulated expression patterns in the prawn, Macrobrachium rosenbergii

To identify male-specific genes that could be involved in male development, we screened a subtracted male reproductive tract library and isolated a novel gene named Mar-Mrr (M. rosenbergii male reproduction-related gene). The Mar-Mrr cDNA sequence consists of 683 nucleotides with a 333 nucleotide open reading frame, encoding putative 110 amino acids (11.7473 kDa) precursor protein and a signal peptide consisting of 24 amino acids. Significant developmentally dependent accumulation of the mRNA was observed in the male reproductive tract, specifically in epithelial cells of vas deferens and terminal ampullae.

Transcriptome analysis in blastocyst hatching by cDNA microarray*

BACKGROUND

Hatching is an important process for early embryo development, differentiation and implantation. However, little is known about its regulatory mechanisms. By integrating the technologies of RNA amplification and cDNA microarrays, it has become possible to study the gene expression profile at this critical stage.

METHODS

Pre-hatched and hatched ICR mouse embryos (25 blastocysts in each group were used in the triplicate experiments) were collected for RNA extraction, amplification, and microarray analysis (the mouse cDNA microarray, 6144 genes, including expressed sequence tags).

RESULTS

According to cDNA microarray data, we have identified 85 genes that were expressed at a higher level in hatched blastocyst than in pre-hatched blastocysts. In this study, 47 hatching-related candidate genes were verified via re-sequencing. Some of these genes have been selected and confirmed by real-time quantitative RT-PCR. These hatching-specific genes were also expressed at a lower level in the delayed growth embryos (morula or blastocyst without hatching at day 6 post hCG). These genes included: cell adhesion and migration molecules [E-cadherin, neuronal cell adhesion molecule (NCAM), lectin, galactose binding, soluble 7 (Lgals7), vanin 3 and biglycan], epigenetic regulators (Dnmt1, and SIN3 yeast homolog A), stress response regulators (heme oxygenase 1) and immunoresponse regulators [interleukin (IL)-2-inducible T-cell kinase, IL-4R, interferon-gamma receptor 2, and neurotrophin]. The immunostaining of E-cadherin and NCAM showed strong and specific localization in hatched blastocyst.

CONCLUSIONS

This work provides important information for studying the mechanisms of blastocyst hatching and implantation. These hatching-specific genes may have potential as new drug targets for controlling fertility.

Galectin fingerprinting in human endometrium and decidua during the menstrual cycle and in early gestation

The emerging functionality of the sugar code via cell surface glycans and endogenous lectins ascribes pertinent roles in cell physiology to the carbohydrate signals of cellular glycoconjugates. To initiate monitoring of endogenous lectins in human endometrium, we focused on a family of growth/adhesion-regulatory lectins, i.e. galectins. Comprehensive fingerprinting was performed on samples throughout the menstrual cycle and in decidua. The endometrium (n = 30) and decidua (n = 7) were collected from patients undergoing hysterectomy for benign reasons and from induced abortions. Measurements by RT-PCR and then by multiprobe RNase protection assay with total endometrial and decidual tissue and with epithelial cells, stromal cells and CD45-positive cell fractions (n = 16), isolated by the use of antibody-coated magnetic beads, revealed a predominant expression of galectins-1 and -3. Protein analysis was performed by immunocytochemistry with monoclonal and polyclonal antibodies (n = 40). Galectin-1 was localized mainly in stromal cells, whereas galectin-3 was predominantly found in epithelial cells. Expression of galectin-1 increased significantly in the late secretory phase endometrium and in the decidual tissue. Expression of galectin-3 increased significantly during the secretory phase of the menstrual cycle. Cycle-dependent expression of galectin-1 in stromal cells and galectin-3 in epithelial cells suggest these lectins to be involved in the regulation of different endometrial cellular functions.

Whole-genome approaches for large-scale gene identification and expression analysis in mammalian preimplantation embryos

The elucidation, unravelling and understanding of the molecular basis of transcriptional control during preimplantion development is of utmost importance if we are to intervene and eliminate or reduce abnormalities associated with growth, disease and infertility by applying assisted reproduction. Importantly, these studies should enhance our knowledge of basic reproductive biology and its application to regenerative medicine and livestock production. A major obstacle impeding progress in these areas is the ability to successfully generate molecular portraits of preimplantation embryos from their minute amounts of RNA. The present review describes the various approaches whereby classical embryology fuses with molecular biology, high-throughput genomics and systems biology to address and solve questions related to early development in mammals.

Phospholipid transfer protein (PLTP) mRNA expression is stimulated by developing embryos in the oviduct

In mammal, fertilization and early preimplantation embryo development occurs in the oviduct. Evidence is accumulating that the oviductal epithelia secrete various biomolecules to the lumen during the secretory phase of the estrus cycle to enhance embryo development. This secretory activity of the oviduct is under the regulation of steroid hormones. Observations also suggested that the gametes and embryos modulate the physiology and gene-expressing pattern of the oviduct. However, the underlying molecular changes remain elusive. We hypothesize that the developing embryos interact with the surrounding environment and affect the gene expression patterns of the oviduct, thereby modulating the oviductal secretory activity conducive to the preimplantation embryo development. To test this hypothesis, suppression subtractive hybridization (SSH) was used to compare the gene expressions in mouse oviduct containing transferred in vitro cultured preimplantation embryos with that of oviduct containing oocytes during the preimplantation period. We reported here the identification and characterization of phospholipids transfer protein (PLTP), which is highly expressed in the embryo-containing oviduct and localized at the oviductal epithelium by in situ hybridization. PLTP contains signal peptide putative for secretory function. More importantly, PLTP mRNA increases in the oviductal epithelia of pregnant, but not pseudo-pregnant mice when assayed by real-time PCR. Taken together, our data suggested that PLTP may play important role(s) during in vivo preimplantation embryo development. This molecule would be a target to delineate the mechanisms and the roles of oviductal secretory proteins on early embryonic development.

Global gene expression analysis comparing bovine blastocysts flushed on day 7 or produced in vitro

In vitro produced (IVP) bovine embryos have darker cytoplasm, reduced buoyant density, fragile zonae pellucidae, chromosomal abnormalities, higher pregnancy failure rates, and altered gene expression compared to embryos produced in vivo. Characterization of early deviations in gene expression would enable us to better understand the biology of early embryo development and improve in vitro culture systems. Here we compared gene expression between Day 7 blastocysts generated in TCM199 with 5% FBS and Day 7 in vivo derived blastocysts and using suppression-subtractive hybridization (SSH). Pools of 25 embryos for both driver and tester were used in the RNA extraction process. The subtracted products were cloned and subjected to differential hybridization screening analysis. cDNAs were isolated, single-pass sequenced, and subjected to BLAST search. Of 32 in vivo ESTs (expressed sequence tags) that provided sequence information, 30 matched homologous sequences in GenBank. Of 32 in vitro ESTs, 22 provided specific matches while the remaining ten represented novel transcripts. Two in vivo ESTs, galectin-1 and fibronectin, and one in vitro EST, filamin A, were further characterized using real-time quantitative PCR. To further examine the reproducibility of the SSH data, three different pools of embryos with each pool containing ten embryos produced from each of the following production systems, namely, in vivo, IVP in TCM199 with 5% FBS and CR1aa with 5% FBS were used for real-time reverse transcription-polymerase chain reaction (RT-PCR) confirmation studies. Significant increases in the expression level of galectin-1 and fibronectin were observed in the in vivo derived blastocysts compared to blastocysts produced in TCM199 with 5% FBS and CR1aa cultures. No significant difference in filamin A expression was found between blastocysts produced in vivo and those derived from either of the in vitro production systems. We conclude that these techniques are useful to characterize the transcriptome of the early preattachment embryo and observed deviations in mRNA expression may partially explain the differences in quality between in vivo and IVP embryos.

Quantitative expression analysis of blastocyst-derived gene transcripts in preimplantation developmental stages of in vitro-produced bovine embryos using real-time polymerase chain reaction technology

The main objective of the present study was to analyse the quantitative expression pattern of genes from a subtracted blastocyst transcriptome throughout the preimplantation developmental stages of in vitro-produced bovine oocytes and embryos. For this purpose, Day 5 morula (M) cDNAs were subtracted from Day 7 blastocyst (B) cDNAs (B–M) and used to establish a B–M subtracted cDNA library, as reported previously. From the total generated clones, 19 were analysed quantitatively. The mRNA samples isolated from pools of immature oocytes (n = 150), mature oocytes (n = 150) and two-cell (n = 80), four-cell (n = 40), eight-cell (n = 20), morula (n = 6) and blastocyst (n = 3) embryos were reverse transcribed and subjected to real-time polymerase chain reaction (PCR) using sequence-specific primers and SYBR green as the DNA dye. A relative standard curve method was used to analyse the real-time data taking the morula stage as a calibrator. Applying suppression subtractive hybridisation (SSH), a total of 71 clones, which represent 33 different expressed sequence tags, were generated and available for analysis. Most transcripts were analysed for the first time in bovine embryogenesis. The real-time PCR has validated the results of SSH positively for 84% (16/19) of transcripts, whereas 16% (3/19) showed deviation in the expression pattern from the one seen during SSH. Several transcript-specific expression patterns were observed for genes that play decisive roles in bovine embryogenesis. In addition to identification, accurately quantifying the expression profiles of transcripts during development will pave the way towards understanding the molecular mechanisms of embryogenesis and their potential role in early embryo development. Most importantly, the present study has contributed to the enrichment of bovine embryo gene collection by generating new transcripts involved in bovine embryo development.

Embryogenomics of pre-implantation mammalian development: current status

Pre-implantation development is marked by many critical molecular events, including the maternal to zygotic transition and the first differentiation of cells. Understanding such events is important, for both basic reproductive biology and practical applications, including regenerative medicine and livestock production. Scarcity of materials has hampered the progress of the field, but systematic genomics approaches are beginning to be applied to the study of pre-implantation development, resulting in unprecedented amounts of data about the pre-implantation process. The first step in embryogenomics is to collect and sequence cDNAs (expressed sequence tags (ESTs)) for genes that are expressed and function in these early embryos. Mouse work is the most advanced, with 140111 ESTs derived from all stages of pre-implantation development currently available in the public sequence database. For other mammals, at present only approximately 1000 ESTs can be found in the public database, but efforts by several groups are generating cDNA libraries and ESTs. In the present review, the current status of the implementation of these investigative tools for mammalian pre-implantation embryos is discussed.

Identification and quantification of differentially expressed transcripts in in vitro-produced bovine preimplantation stage embryos

In this study, we used mRNA differential display reverse transcription polymerase chain reaction (DDRT-PCR) to analyze the mRNA expression patterns in in vitro-produced bovine 8-cell, 16-cell, morula, and blastocyst stage embryos and isolate differentially expressed amplicons. Moreover, we have used a fluorescence monitored real time quantitative PCR to quantify and analyze the expression patterns of the target differentially expressed transcripts through out the preimplantation stages from oocytes to blastocyst. For this, total RNA isolated from bovine 8-cell (n = 188), 16-cell (n = 94), morula (n = 35), and blastocyst (n = 15) were reverse transcribed and subjected to DDRT-PCR. Target differentially expressed transcripts were quantified by real time quantitative PCR. The cDNA banding pattern analysis revealed that large number of cDNA bands were conserved at 8-cell and blastocyst stage with a slight decrease at the morula stage. A total of 16 amplicons were cloned and sequenced. All expressed sequence tags (ESTs), except 1C19, showed sequence similarity with known genes or ESTs in GenBank. Sixty-two percent (10/16) of cDNA bands representing differentially expressed genes originated from 8-cell stage and the rest derived from the 16-cell, morula, or blastocyst stage. The quantitative PCR analysis has validated the expression patterns of 75% (12/16) of our transcripts to be in agreement with the results of DDRT-PCR. However, the quantitative PCR results of four transcripts showed a deviation from the pattern seen in DDRT-PCR. In conclusion, we have successfully applied mRNA DDRT-PCR to identify and isolate stage-specific expressed genes in bovine preimplantation embryos. In addition to validating the results of DDRT-PCR, quantitative real time PCR provides quantitative data on the expression of target genes.