Identification of mRNAs that are up-regulated after fertilization in the murine zygote by suppression subtractive hybridization

Cloning of Porcine Pituitary Tumor Transforming Gene 1 and Its Expression in Porcine Oocytes and Embryos

The maternal-to-embryonic transition (MET) is a complex process that occurs during early mammalian embryogenesis and is characterized by activation of the zygotic genome, initiation of embryonic transcription, and replacement of maternal mRNA with embryonic mRNA. The objective of this study was to reveal the temporal expression and localization patterns of PTTG1 during early porcine embryonic development and to establish a relationship between PTTG1 and the MET. To achieve this goal, reverse transcription-polymerase chain reaction (RT-PCR) was performed to clone porcine PTTG1. Subsequently, germinal vesicle (GV)- and metaphase II (MII)-stage oocytes, zygotes, 2-, 4-, and 8-cell-stage embryos, morulas, and blastocysts were produced in vitro and their gene expression was analyzed. The results revealed that the coding sequence of porcine PTTG1 is 609-bp in length and that it encodes a 202-aa polypeptide. Using qRT-PCR, PTTG1 mRNA expression was observed to be maintained at high levels in GV- and MII-stage oocytes. The transcript levels in oocytes were also significantly higher than those in embryos from the zygote to blastocyst stages. Immunohistochemical analyses revealed that porcine PTTG1 was primarily localized to the cytoplasm and partially localized to the nucleus. Furthermore, the PTTG1 protein levels in MII-stage oocytes and zygotes were significantly higher than those in embryos from the 2-cell to blastocyst stage. After fertilization, the level of this protein began to decrease gradually until the blastocyst stage. The results of our study suggest that porcine PTTG1 is a new candidate maternal effect gene (MEG) that may participate in the processes of oocyte maturation and zygotic genome activation during porcine embryogenesis.

Developmental expression of ACRV1 in humans and mice

To identify the developmental expression of the ACRV1 gene in humans and mice, testes cDNA samples were collected at different post-natal days (days 4, 9, 18, 35, 54, and 6 months) from Balb/c mice and were hybridised to the mouse whole genome 430 2.0 Array (Affymetrix Inc.) chip. The characteristics of ACRV1 were analysed using various cellular and molecular biotechnologies. The results showed that the expression of mouse ACRV1 was not detected in mouse testes on days 4, 9, and 18 but was present on days 35, 54, and 6 months. Using RT-PCR analysis of mouse ACRV1, we determined that mouse ACRV1 was expressed specifically in the mouse testis, and its expression began at days 35. Western blot analysis demonstrated that human ACRV1 was primarily expressed in human testes, and immunofluorescent and immunohistochemistry staining showed that human ACRV1 protein was predominantly located in round and elongated spermatids in human testes, indicating that ACRV1 may play an important role in mammalian spermatogenesis and may be a target of a contraceptive vaccine.

Protamine-1 represents a sperm specific gene transcript: a study in Callithrix jacchus and Bos taurus

Spermatozoa are transcriptionally inactive cells, but contain acetylated histones, normally a characteristic of transcriptionally active cells. Acetylgroups are thought to represent epigenetic marks that are transmitted to the oocyte and are involved in starting gene expression in the zygote and in regulating gene expression during early embryogenesis. We performed reverse transcription polymerase chain reaction (RT-PCR) in the common marmoset monkey (Callithrix jacchus) and in bovine spermatozoa, oocytes, zygotes, two- and four-cell embryos to evaluate the presence of specific transcripts known to play a role during fertilisation and early embryo development, namely protamine-1 (PRM1), protamine-2 (PRM2), histone H1 (H1), histone H3 (H3), histone H4 (H4), cAMP-responsive element modulator (CREM), DNA methyltransferase-1 (DNMT1), TATA box-binding protein (TBP). All transcripts tested were present in spermatozoa of the common marmoset, while bull spermatozoa lack PRM2. Marmoset oocytes exhibited transcripts for H1, H3, H4 and TBP, whereas bovine oocytes revealed H1, H3, H4, CREM, DNMT and TBP mRNAs. In zygotes, we amplified H1, H4, TBP (marmoset) and PRM1, H1, H3, H4, CREM, DNMT1 and TBP (bovine). Two-cell embryos showed PCR products for H1, H3 and TBP in the marmoset. In the bovine, all transcripts could be observed except PRM2. In four-cell embryos, PCR signals were obtained for PRM1, H1, H3, H4 and TBP in the marmoset. In the bovine, all transcripts were detected except PRM2. Our data suggest that, in both C. jacchus and Bos taurus, PRM1 transcripts are delivered by the spermatozoon to the oocyte.

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

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

Serglycin proteoglycan deletion in mouse platelets: physiological effects and their implications for platelet contributions to thrombosis, inflammation, atherosclerosis, and metastasis

Serglycin is found in all nucleated hematopoietic cells and platelets, blood vessels, various reproductive and developmental tissues, and in chondrocytes. The serglycin knockout mouse has demonstrated that this proteoglycan is required for proper generation and function of secretory granules in several hematopoietic cells. The effects on platelets are profound, and include diminishing platelet aggregation responses and formation of platelet thrombi. This chapter will review cell-specific aspects of serglycin structure, its gene regulation, cell and tissue localization, and the effects of serglycin deletion on hematopoietic cell granule structure and function. The effects of serglycin knockout on platelets are described and discussed in detail. Rationales for further investigations into the contribution of serglycin to the known roles of platelets in thrombosis, inflammation, atherosclerosis, and tumor metastasis are presented.

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.

Gene expression during minor genome activation in preimplantation bovine development

The main goal of this study was to identify mRNA transcripts whose content increases during bovine minor embryonic genome activation. We compared the gene expression profile of the bovine 4-cell-stage embryo and MII oocyte using the technique of suppression subtractive hybridization. Differentially expressed amplicons were subcloned, and 60 of them were sequenced. The resulting DNA sequences were compared with GenBank databases using BLAST search. The expression of five differentially expressed genes with an apparent function in cell cycle progression, chromatin remodeling, and splicing or translation initiation was further characterized by a real-time RT-PCR. Centromere protein F, 350/400ka (CENPF), and splicing factor arginine/serine-rich 3 (SRFS3) show an increase in mRNA content during the 2- to 4-cell and late 8-cell stages. For the high mobility group nucleosomal binding domain 2 (HMGN2), the level of mRNA increases in 2- to 4-cell and morula embryos. The transcription of splicing factor SRFS3 is alpha-amanitin sensitive both during 4-cell and late 8-cell stages. The transcription of CENPF and HMGN2 is alpha-amanitin sensitive only at late 8-cell stage and morula, respectively. SRFS3 represents the first described gene with an important function in preimplantation development, which is also expressed during bovine minor genome activation, and it is alpha-amanitin sensitive during this period. All described genes can play an important role in the preimplantation development of bovine embryos.

Zygotic gene activation and maternal factors in mammals

Zygotic gene activation (ZGA) is the first event of gene expression after fertilization. Following fertilization, ZGA occurs within a short time interval depending on the animal species. Until ZGA, maternal proteins and transcripts stored in oocytes control embryonic development, indicating the importance of maternal factors for development. Somatic cell cloning also proves the potential of oocyte to reprogram the differentiated cell nuclei to embryonic nuclei. Recent studies show that the epigenetic modifications of nuclei play important roles in controlling gene expression during ZGA. However, the mechanisms that control ZGA remain largely unknown. This review will cover the current understanding of ZGA. Specifically, it will focus on the maternal factors that control gene expression during early embryogenesis.

Identification of zygotic genes expressed at the midblastula transition in zebrafish

Early development of the embryo is directed by maternal gene products and characterised by limited zygotic gene activity, cell division synchrony and no cell motility in several vertebrates including fish and frogs. At the midblastula transition (MBT), zygotic transcription is grossly activated, cells become motile and cell divisions become asynchronous. The aim of this study was to identify genes whose expression is up-regulated at the MBT in zebrafish. Suppression subtractive hybridisation (SSH) was employed to isolate 48 unique cDNAs, 28 of which show significant similarity to known genes and 20 represent novel cDNAs. Twenty one of these genes, with potential roles in transcriptional regulation, cell cycle control, and embryonic patterning showed increased expression at the MBT. Our results demonstrate the value of SSH as a tool to clone novel, zygotic, developmentally regulated genes that may be important in the progression of the MBT and embryonic patterning.

Characteristics of 292 Testis-Specific Genes in Human

To explore their genomic and functional characteristics, 292 human testis-specific genes were obtained from a UniGene library and a full-scale analysis was made. Various bioinformatics tools were applied to analyze the gene ontology and chromosome location, and the expression profiles of eight selected candidates from the 292 genes were analyzed using RT-PCR for 12 adult human tissues. The results showed that of the total 292 genes, 153 were known (114 assigned genes and 39 named genes), and 139 were unknown. Of the 114 assigned genes, 63 were labeled to molecular function, 28 to cellular component, 23 to biological process. All 292 genes are distributed on human chromosomes at different gene density, lower gene density appears on chromosomes 21 (R=0.22), X (R=0.33), 14 (R=0.39), 10 (R=0.61), 8 (R=0.63), and 18 (R=0.67) and higher density on chromosomes 19 (R=3.65), 20 (R=1.83), 16 (R=1.74), and 17 (R=1.64). The expression profile of the eight selected genes in the 12 human tissues showed that five candidate genes: Hs.443729, Hs.115366, Hs.558087, Hs.534501, and Hs.132104 were expressed exclusively in human testis; Hs.132310, Hs.443299 were expressed highly in testis and also expressed weakly in human heart; Hs.160370 was expressed in human testis, ovary, uterus, and not expressed in other tissues. Our study can be a basis for characterization of the function of human testis-specific genes during male mammalian spermatogenesis.

Identification and characteristics of a novel testis-specific gene, Tsc21, in mice and human

Testis-specific genes are essential for spermatogenesis in mammalian male reproduction. We have identified a novel gene, Tsc21, exclusively expressed in mice and human testes from the results of the Affymetrix Genechip analysis in the six developmental stages of testis of postnatal Balb/C mice. The full cDNA length of Tsc21 was 810 bp, with a 543 bp open reading frame encoding a 180 amino acids protein with a predicted molecular weight of 21.040 kDa. A Blast search in the mouse genome database localized the Tsc21 gene to mice chromosome 6C3. Multiple amino acid sequence alignment of human, mouse, and rat homologous genes showed that mice Tsc21 protein was highly homologous with the human Tsc21 gene (70%) and rat Tsc21 gene (86%). The results of reverse transcriptase-polymerase chain reaction analysis showed that the mice Tsc21 is exclusively expressed in the testis and epididymis of mice, and its expression is only detected after the mice is 35 days old. Human Tsc21 is also exclusively expressed in testis of human. Considering the expression profile Tsc21 in mice and human, we propose that Tsc21 may play a role during mammalian male spermatogenesis. Our study should be a basis for function characterization of the Tsc21 gene, leading to the elucidation of the molecular events underlying mammalian male reproduction.

The influence of follicle size, FSH-enriched maturation medium, and early cleavage on bovine oocyte maternal mRNA levels

Transcription is arrested in the bovine oocyte within the first few hours of in vitro maturation, thus the stored maternal mRNAs accumulated in the oocyte are essential to sustain development until the Maternal-Zygotic Transition. In vivo matured oocytes have superior blastocyst formation rates than in vitro matured oocytes, suggesting that the mRNA content of these oocytes is of higher quality. To determine which transcripts may be associated with developmental competence, a Suppressive Subtractive Hybridization was performed between oocytes collected by ovariectomy at 6 hr post-LH surge and oocytes from slaughterhouse collected after 6 hr of maturation, resulting in a library enriched in these functionally important mRNAs. The clones were spotted onto a cDNA microarray and transcripts potentially associated with developmental competence were hybridized onto these slides. Hybridizations were performed with transcripts up-regulated in oocytes cultured for 6 hr in the presence or absence of rFSH in vitro, and secondly with transcripts up regulated in early-cleaving embryos versus those at the one-cell stage at 36 hr postfertilization. From these hybridizations, 13 candidates were selected. Their functional association with embryonic competence was validated by measuring their relative transcript levels by quantitative real-time PCR in eight different conditions: oocytes cultured with or without rFSH, early--versus late-cleaving embryos, and oocytes from different follicle sizes (1-3, 3-5, 5-8, and >8 mm of diameter). The gene candidates CCNB2, PTTG1, H2A, CKS1, PSMB2, SKIIP, CDC5L, RGS16, and PRDX1 showed a significant quantitative association with competence compared to BMP15, GDF9, CCNB1, and STK6.

The human cumulus--oocyte complex gene-expression profile

BACKGROUND

The understanding of the mechanisms regulating human oocyte maturation is still rudimentary. We have identified transcripts differentially expressed between immature and mature oocytes and cumulus cells.

METHODS

Using oligonucleotide microarrays, genome-wide gene expression was studied in pooled immature and mature oocytes or cumulus cells from patients who underwent IVF.

RESULTS

In addition to known genes, such as DAZL, BMP15 or GDF9, oocytes up-regulated 1514 genes. We show that PTTG3 and AURKC are respectively the securin and the Aurora kinase preferentially expressed during oocyte meiosis. Strikingly, oocytes overexpressed previously unreported growth factors such as TNFSF13/APRIL, FGF9, FGF14 and IL4 and transcription factors including OTX2, SOX15 and SOX30. Conversely, cumulus cells, in addition to known genes such as LHCGR or BMPR2, overexpressed cell-to-cell signalling genes including TNFSF11/RANKL, numerous complement components, semaphorins (SEMA3A, SEMA6A and SEMA6D) and CD genes such as CD200. We also identified 52 genes progressively increasing during oocyte maturation, including CDC25A and SOCS7.

CONCLUSION

The identification of genes that were up- and down-regulated during oocyte maturation greatly improves our understanding of oocyte biology and will provide new markers that signal viable and competent oocytes. Furthermore, genes found expressed in cumulus cells are potential markers of granulosa cell tumours.

Differential Expression of Alternatively Spliced Transcripts of HLA-G in Human Preimplantation Embryos and Inner Cell Masses

It has been reported that preimplantation human embryos secrete HLA-G, and the levels may be predictive of their ability to implant. However, it is not known which of the membrane-bound (HLA-G 1-4) and soluble (HLA-G 5-6) alternatively spliced forms are present, nor the developmental stage at which they appear. Therefore, we have investigated HLA-G mRNA isoform expression on single embryos at the two-, four-, six-, and eight-cell, morula, and blastocyst stages. The percentage of embryos expressing each HLA-G isoform mRNA increased with developmental stage, but contrary to expectation, HLA-G5 mRNA was not detected in single two- to eight-cell embryos and was only expressed by 20% of morulae and blastocysts. Similarly, soluble HLA-G6 mRNA was not detected until the blastocyst stage and then in only one-third of embryos. In contrast, labeling with MEM G/9 Ab (specific for HLA-G1 and -G5) was observed in 15 of 20 two- to eight-cell embryos and 5 of 5 blastocysts. This disparity between mRNA and protein may be due to HLA-G protein remaining from maternal oocyte stores produced before embryonic genome activation and brings into question the measurement of soluble HLA-G for clinical evaluation of embryo quality. Although HLA-G is expressed in the preimplantation embryo, later it is primarily expressed in the invasive trophoblast of the placenta rather than the fetus. Therefore, we have investigated whether down-regulation of HLA-G first occurs in the inner cell mass (precursor fetal cells) of the blastocyst and, in support of this concept, have shown the absence HLA-G1 and -G5 protein and mRNA.

SSH adequacy to preimplantation mammalian development: scarce specific transcripts cloning despite irregular normalisation

Background

SSH has emerged as a widely used technology to identify genes that are differentially regulated between two biological situations. Because it includes a normalisation step, it is used for preference to clone low abundance differentially expressed transcripts. It does not require previous sequence knowledge and may start from PCR amplified cDNAs. It is thus particularly well suited to biological situations where specific genes are expressed and tiny amounts of RNA are available. This is the case during early mammalian embryo development. In this field, few differentially expressed genes have been characterized from SSH libraries, but an overall assessment of the quality of SSH libraries is still required. Because we are interested in the more systematic establishment of SSH libraries from early embryos, we have developed a simple and reliable strategy based on reporter transcript follow-up to check SSH library quality and repeatability when starting with small amounts of RNA.

Results

Four independent subtracted libraries were constructed. They aimed to analyze key events in the preimplantation development of rabbit and bovine embryos. The performance of the SSH procedure was assessed through the large-scale screening of thousands of clones from each library for exogenous reporter transcripts mimicking either tester specific or tester/driver common transcripts. Our results show that abundant transcripts escape normalisation which is only efficient for rare and moderately abundant transcripts. Sequencing 1600 clones from one of the libraries confirmed and extended our results to endogenous transcripts and demonstrated that some very abundant transcripts common to tester and driver escaped subtraction. Nonetheless, the four libraries were greatly enriched in clones encoding for very rare (0.0005% of mRNAs) tester-specific transcripts.

Conclusion

The close agreement between our hybridization and sequencing results shows that the addition and follow-up of exogenous reporter transcripts provides an easy and reliable means to check SSH performance. Despite some cases of irregular normalisation and subtraction failure, we have shown that SSH repeatedly enriches the libraries in very rare, tester-specific transcripts, and can thus be considered as a powerful tool to investigate situations where small amounts of biological material are available, such as during early mammalian development.

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.