Maternal housekeeping proteins translated during bovine oocyte maturation and early embryo development

Fetal Ovarian Reserve: the Dynamic Changes in Ubiquitin C-Terminal Hydrolase L1

The regulation of protein turnover by the unique deubiquitinating enzyme ubiquitin C-terminal hydrolase L1 (UCHL1) is only seen in oocytes, spermatogonia, and neurons. Our objective was to investigate variation in expression of UCHL1 across fetal maturation of oocytes that result in lifelong ovarian reserve. We performed a retrospective cohort study of 25 fetal autopsy specimens from 21 to 36 weeks. This was an IRB-approved protocol with parental permission for use of tissues for research purposes. Tissues were stained for expression of the oocyte-specific protein UCHL1, and expression levels were evaluated using quantitative immunofluorescence across gestational ages after correction for the area and background absorbance. Corrected total cell fluorescence (CTCF) for expression of UCHL1 within human oocytes was compared across fetal gestational ages and oocyte size. Trends were analyzed using a locally weighted scatterplot smoothing algorithm. Local expression of UCHL1 increases in oocytes across ovarian development reaching a plateau at 27 weeks with the maintenance of elevated levels through 36 weeks gestational age. This maturation trend is also evidenced by the increase in protein expression as oocyte area increases (r = 0.5530, p ≤ 0.001) with the largest rise occurring as oocytes are enveloped into primordial follicles. The increase in expression as oocytes transition from oogonia into oocytes in primordial follicles and beyond may be part of the preparation of both oocytes and the surrounding somatic cells for the long-term maintenance of the ovarian reserve.

Proteomic analysis identifies potential markers in small white and small yellow follicle development in chickens

Extensive knowledge of follicular development is imperative for improving egg production in chickens. The functional role of follicles to produce oocytes (eggs) is well recognised; however, specific markers associated with follicle development have been poorly explored. Therefore, a tandem mass tag based proteomic technique was used to identify the status of the proteome of small white follicles (1-4mm) and small yellow follicles (6-8mm). Analysis of differentially expressed proteins (DEP, Fold Change>1.2, P -value<0.05) demonstrated a total of 92 proteins (n =92), of which 35 (n =35) were upregulated and 57 were downregulated. DEP were further used for gene ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes pathways. The GO analysis found that DEP were mainly associated with the RNA metabolic process, cellular component organisation, peptide biosynthetic process and protein folding, thereby suggesting a key role in the follicle development process. Kyoto Encyclopedia of Genes and Genomes enrichment pathway analysis of the DEP substantiated the findings of GO analysis and described that DEP are involved in regulation of the cytoskeleton, carbon metabolism and amino acid biosynthesis. The validation of proteomic data through real-time quantitative polymerase chain reaction suggested HSPA8, HSPA2, SOD1 and FKPB3 as potential markers of small white and small yellow follicle development. This study demonstrates an understanding of proteome dynamics and represents the most comprehensive information on the entire Guangxi Ma chicken follicular proteome.

DNA Methylation Profiles Suggest Intergenerational Transfer of Maternal Effects

The view of maternal effects (nongenetic maternal environmental influence on offspring phenotype) has changed from one of distracting complications in evolutionary genetics to an important evolutionary mechanism for improving offspring fitness. Recent studies have shown that maternal effects act as an adaptive mechanism to prepare offspring for stressful environments. Although research into the magnitude of maternal effects is abundant, the molecular mechanisms of maternal influences on offspring phenotypic variation are not fully understood. Despite recent work identifying DNA methylation as a potential mechanism of nongenetic inheritance, currently proposed links between DNA methylation and parental effects are indirect and primarily involve genomic imprinting. We combined a factorial breeding design and gene-targeted sequencing methods to assess inheritance of methylation during early life stages at 14 genes involved in growth, development, metabolism, stress response, and immune function of Chinook salmon (Oncorhynchus tshawytscha). We found little evidence for additive or nonadditive genetic effects acting on methylation levels during early development; however, we detected significant maternal effects. Consistent with conventional maternal effect data, maternal effects on methylation declined through development and were replaced with nonadditive effects when offspring began exogenous feeding. We mapped methylation at individual CpG sites across the selected candidate genes to test for variation in site-specific methylation profiles and found significant maternal effects at selected CpG sites that also declined with development stage. While intergenerational inheritance of methylated DNA is controversial, we show that CpG-specific methylation may function as an underlying molecular mechanism for maternal effects, with important implications for offspring fitness.

The neglected part of early embryonic development: maternal protein degradation

The degradation of maternally provided molecules is a very important process during early embryogenesis. However, the vast majority of studies deals with mRNA degradation and protein degradation is only a very little explored process yet. The aim of this article was to summarize current knowledge about the protein degradation during embryogenesis of mammals. In addition to resuming of known data concerning mammalian embryogenesis, we tried to fill the gaps in knowledge by comparison with facts known about protein degradation in early embryos of non-mammalian species. Maternal protein degradation seems to be driven by very strict rules in terms of specificity and timing. The degradation of some maternal proteins is certainly necessary for the normal course of embryonic genome activation (EGA) and several concrete proteins that need to be degraded before major EGA have been already found. Nevertheless, the most important period seems to take place even before preimplantation development-during oocyte maturation. The defects arisen during this period seems to be later irreparable.

Transcriptomic and proteomic analyses of ovarian follicles reveal the role of VLDLR in chicken follicle selection

Background

Follicle selection in chickens refers to the process of selecting one follicle from a group of small yellow follicles (SY, 6–8 mm in diameter) for development into 12–15 mm hierarchical follicles (usually F6 follicles), which is an important process affecting laying performance in the poultry industry. Although transcriptomic analysis of chicken ovarian follicles has been reported, integrated analysis of chicken follicles for selection by using both transcriptomic and proteomic approaches is still rarely performed. In this study, we compared the proteomes and transcriptomes of SY and F6 follicles in laying hens and identified several genes involved in chicken follicle selection.

Results

Transcriptomic analysis revealed 855 differentially expressed genes (DEGs) between SY follicles and F6 follicles in laying hens, among which 202 were upregulated and 653 were downregulated. Proteomic analysis revealed 259 differentially expressed proteins (DEPs), including 175 upregulated and 84 downregulated proteins. Among the identified DEGs and DEPs, changes in the expression of seven genes, including VLDLR1, WIF1, NGFR, AMH, BMP15, GDF6 and MMP13, and nine proteins, including VLDLR, VTG1, VTG3, PSCA, APOB, APOV1, F10, ZP2 and ZP3L2, were validated. Further analysis indicated that the mRNA level of chicken VLDLR was higher in F6 follicles than in SY follicles and was also higher in granulosa cells (GCs) than in thecal cells (TCs), and it was stimulated by FSH in GCs.

Conclusions

By comparing the proteomes and transcriptomes of SY and F6 follicles in laying hens, we identified several differentially expressed proteins/genes that might play certain roles in chicken follicle selection. These data may contribute to the identification of functional genes and proteins involved in chicken follicle selection.

Review: Sperm-oocyte interactions and their implications for bull fertility, with emphasis on the ubiquitin-proteasome system

Fertilization is an intricate cascade of events that irreversibly alter the participating male and female gamete and ultimately lead to the union of paternal and maternal genomes in the zygote. Fertilization starts with sperm capacitation within the oviductal sperm reservoir, followed by gamete recognition, sperm-zona pellucida interactions and sperm-oolemma adhesion and fusion, followed by sperm incorporation, oocyte activation, pronuclear development and embryo cleavage. At fertilization, bull spermatozoon loses its acrosome and plasma membrane components and contributes chromosomes, centriole, perinuclear theca proteins and regulatory RNAs to the zygote. While also incorporated in oocyte cytoplasm, structures of the sperm tail, including mitochondrial sheath, axoneme, fibrous sheath and outer dense fibers are degraded and recycled. The ability of some of these sperm contributed components to give rise to functional zygotic structures and properly induce embryonic development may vary between bulls, bearing on their reproductive performance, and on the fitness, health, fertility and production traits of their offspring. Proper functioning, recycling and remodeling of gamete structures at fertilization is aided by the ubiquitin-proteasome system (UPS), the universal substrate-specific protein recycling pathway present in bovine and other mammalian oocytes and spermatozoa. This review is focused on the aspects of UPS relevant to bovine fertilization and bull fertility.

Use of focused ultrasonication in activity-based profiling of deubiquitinating enzymes in tissue

To develop a reproducible tissue lysis method that retains enzyme function for activity-based protein profiling, we compared four different methods to obtain protein extracts from bovine lung tissue: focused ultrasonication, standard sonication, mortar & pestle method, and homogenization combined with standard sonication. Focused ultrasonication and mortar & pestle methods were sufficiently effective for activity-based profiling of deubiquitinases in tissue, and focused ultrasonication also had the fastest processing time. We used focused-ultrasonicator for subsequent activity-based proteomic analysis of deubiquitinases to test the compatibility of this method in sample preparation for activity-based chemical proteomics.

Proteomic profiling of eggs from a hybrid abalone and its parental lines: Haliotis discus hannai Ino and Haliotis gigantea

Proteomic analysis was performed on the eggs of hybrid abalone and their corresponding parental lines. A total of 915 ± 19 stained protein spots were detected from Haliotis discus hannai♀ × H. discus hannai♂ (DD), 935 ± 16 from H. gigantea♀ × H. gigantea♂ (GG) and 923 ± 13 from H. gigantea♀ × H. discus hannai♂ (GD). The spots from DD and GD were clustered together. The distance between DD and GG was maximal by hierarchical cluster analysis. A total of 112 protein gel spots were identified; of these, 59 were abalone proteins. The proteins were involved in major biological processes including energy metabolism, proliferation, apoptosis, signal transduction, immunity, lipid metabolism, electron carrier proteins, protein biosynthesis and decomposition, and cytoskeletal structure. Three of 20 differential expression protein spots involved in energy metabolism exhibited as upregulated in GD, 13 spots exhibited additivity, and four spots exhibited as downregulated in the offspring. Eleven protein spots were expressed at the highest level in DD. The proteins involved in stress responses included superoxide dismutase, peroxiredoxin 6, thioredoxin peroxidase and glutathione-S-transferase. Two of seven differential expression protein spots involved in response to stress exhibited as upregulated in GD, three exhibited additivity, and two exhibited as downregulated. These results might suggest that proteomic approaches are suitable for the analysis of hybrids and the functional prediction of abalone hybridization.

The adenosine salvage pathway as an alternative to mitochondrial production of ATP in maturing mammalian oocytes

Although the oocyte is the largest cell in the body and an unavoidable phase in life, its physiology is still poorly understood, and other cell types provide little insight into its unique nature. Even basic cellular functions in the oocyte such as energy metabolism are not yet fully understood. It is known that the mitochondria of the female gamete exhibit an immature form characterized by limited energy production from glucose and oxidative phosphorylation. We show that the bovine oocyte uses alternative means to maintain ATP production during maturation, namely, the adenosine salvage pathway. Meiosis resumption is triggered by destruction of cyclic AMP by phosphodiesterases producing adenosine monophosphate that is converted into ATP by adenylate kinases and creatine kinases. Inhibition of these enzymes decreased ATP production, and addition of their substrates restored ATP production in denuded oocytes. Addition of phosphocreatine to the oocyte maturation medium influenced the phenotype of the resulting blastocysts. We propose a model in which adenylate kinases and creatine kinases act as drivers of ATP production from added AMP during oocyte maturation.

Deubiquitinating enzymes in oocyte maturation, fertilization and preimplantation embryo development

Post-translational modifications of cellular proteins by ubiquitin and ubiquitin-like protein modifiers are important regulatory events involved in diverse aspects of gamete and embryo physiology including oocyte maturation, fertilization and development of embryos to term. Deubiquitinating enzymes (DUBs) regulate proteolysis by reversing ubiquitination, which targets proteins to the 26S proteasome. The ubiquitin C-terminal hydrolases (UCHs) comprise are DUBs that play a role in the removal of multi-ubiquitin chains. We review here the roles of UCHs in oocytes maturation, fertilization and development in mouse, bovine, porcine and rhesus monkeys. Oocyte UCHs contributes to fertilization and embryogenesis by regulating the physiology of the oocyte and blastomere cortex as well as oocyte spindle. Lack of UCHs in embryos reduces fertilization, while mutant embryos fail to undergo compaction and blastocyst formation. In addition to advancing our understanding of reproductive process, research on the role of deubiquitinating enzymes will allow us to better understand and treat human infertility, and to optimize reproductive performance in agriculturally important livestock species.

Rapidly cleaving bovine two-cell embryos have better developmental potential and a distinctive mRNA pattern

Mammalian embryos that rapidly reach the two-cell stage in culture have a higher probability of becoming viable blastocysts. Our goal was to separate two-cell bovine embryos based on their zygotic cleavage timing, and to assess their global mRNA levels. Following in vitro fertilization, all embryos that cleaved by 29.5 hpi (early) were cultured separately from those that divided at 46 hpi (late). The blastocyst rates were 46.1 ± 3.7% and 6.1 ± 3.4% for early- and late-cleavers, respectively (P < 0.01). Seven replicates of selected two-cell embryos were collected at each time point for microarray characterization (n = 4) and quantitative reverse-transcriptase PCR (n = 3); the rest were left in culture for blastocyst evaluation. A total of 774 and 594 probes were preferentially present in early- and late-cleaving embryos, respectively (fold change ± 1.5, P < 0.05), with important contrasts related to cell cycle, gene expression, RNA processing, and protein degradation functions. A total of 12 transcripts were assessed by quantitative PCR, of which ATM, ATR, CTNNB1, MSH6, MRE11A, PCNA, APC, CENPE, and GRB2 were in agreement with the hybridization results. Since most of these molecules are directly or indirectly associated with cell-cycle regulation, DNA damage response, and transcription control, our results strongly suggest key roles for those biological functions in mammalian preimplantation development.

Proteomic evidence of a paedomorphic evolutionary process within a marine snail species: a strategy for adapting to extreme ecological conditions?

The exposed and sheltered ecotypes of the marine snail Littorina saxatilis from European rocky shores are considered a key model system to study adaptation and ecological speciation. Previous studies showed that two ecotypes (RB and SU) of this species in NW Spain have adapted differently to different shore levels and microhabitats. In order to understand how this divergent adaptive process has been accomplished, we followed a quantitative proteomic approach to investigate the proteome variation in a number of different biological factors, that is, ecotype, ontogeny and their interactions. This approach allowed testing the hypothesis that one of the ecotypes has evolved by paedomorphosis, and also whether or not the molecular mechanisms related to ecotype differentiation are set up in early developmental stages. Additionally, the identification of some candidate proteins using mass spectrometry provides some functional insights into these evolutionary processes. Results from this study provided evidence of higher ontogenetic differentiation at proteome level in the RB (metamorphic) than in SU (paedomorphic) ecotype that point to the possibility of juvenile stage retention in this latter ecotype. The level of protein expression (proteome) differences between ecotypes maintained nearly constant from late embryonic stages to adulthood, although some proteins involved in these changes considerably differed in embryonic compared to other ontogenetic stages. Paedomorphosis may be the evolutionary response of the SU ecotype of solving the trade-off during sexually immaturity that is caused by the evolution of small size arising from adaptation to the wave-exposed habitat. Some potential candidate genes of adaptation related to energetic metabolism have been identified, providing a promising baseline for future functional analyses.

Comparative proteomic analysis of proteins involved in oocyte meiotic maturation in mice

After birth, oocytes stay at the diplotene stage in prophase of meiosis I. Meiosis resumes about 1 day before ovulation, and arrests in metaphase II (MII) after ovulation. The mature, MII oocytes are then ready for fertilization and to provide materials for early embryonic development. Proteomic characterization of oocytes can help identify proteins that are important for female meiotic maturation and early embryonic development. In this study, we compared the proteomic profiles between the germinal vesicle and MII mouse oocytes by two-dimensional electrophoresis; 95 differentially expressed protein spots corresponding to 63 proteins were identified. Many of these proteins are known to be essential for oocyte meiosis and early embryonic development, such as adenylosuccinate synthetase, nucleoplasmin-2, and protein-arginine deiminase type-6. Of the 12 proteins that were identified and are highly expressed in oocytes, a novel protein, E330034G19Rik, was found to be oocyte-specific. According to analysis by bioinformatics, it may regulate chromosome segregation during meiosis or cleavage. An in-depth study of these proteins will help us better understand the mechanisms of oocyte meiotic maturation, fertilization, and early embryogenesis. It will also help us understand the mechanisms of diseases that stem from abnormal oocyte maturation, such as polycystic ovary syndrome and premature ovary failure.

Essential role of maternal UCHL1 and UCHL3 in fertilization and preimplantation embryo development

Post-translational protein modification by ubiquitination, a signal for lysosomal or proteasomal proteolysis, can be regulated and reversed by deubiquitinating enzymes (DUBs). This study examined the roles of UCHL1 and UCHL3, two members of ubiquitin C-terminal hydrolase (UCH) family of DUBs, in murine fertilization and preimplantation development. Before fertilization, these proteins were associated with the oocyte cortex (UCHL1) and meiotic spindle (UCHL3). Intracytoplasmic injection of the general UCH-family inhibitor ubiquitin-aldehyde (UBAL) or antibodies against UCHL3 into mature metaphase II oocytes blocked fertilization by reducing sperm penetration of the zona pellucida and incorporation into the ooplasm, suggesting a role for cortical UCHL1 in sperm incorporation. Both UBAL and antibodies against UCHL1 injected at the onset of oocyte maturation (germinal vesicle stage) reduced the fertilizing ability of oocytes. The subfertile Uchl1(gad-/-) mutant mice showed an intriguing pattern of switched UCH localization, with UCHL3 replacing UCHL1 in the oocyte cortex. While fertilization defects were not observed, the embryos from homozygous Uchl1(gad-/-) mutant females failed to undergo morula compaction and did not form blastocysts in vivo, indicating a maternal effect related to UCHL1 deficiency. We conclude that the activity of oocyte UCHs contributes to fertilization and embryogenesis by regulating the physiology of the oocyte and blastomere cortex.

Effects of ubiquitin C-terminal hydrolase L1 deficiency on mouse ova

Maternal proteins are rapidly degraded by the ubiquitin-proteasome system during oocyte maturation in mice. Ubiquitin C-terminal hydrolase L1 (UCHL1) is highly and specifically expressed in mouse ova and is involved in the polyspermy block. However, the role of UCHL1 in the underlying mechanism of polyspermy block is poorly understood. To address this issue, we performed a comprehensive proteomic analysis to identify maternal proteins that were relevant to the role of UCHL1 in mouse ova using UCHL1-deficient gad. Furthermore, we assessed morphological features in gad mouse ova using transmission electron microscopy. NACHT, LRR, and PYD domain-containing (NALP) family proteins and endoplasmic reticulum (ER) chaperones were identified by proteomic analysis. We also found that the 'maternal antigen that embryos require' (NLRP5 (MATER)) protein level increased significantly in gad mouse ova compared with that in wild-type mice. In an ultrastructural study, gad mouse ova contained less ER in the cortex than in wild-type mice. These results provide new insights into the role of UCHL1 in the mechanism of polyspermy block in mouse ova.

Sperm proteasome and fertilization

The omnipresent ubiquitin–proteasome system (UPS) is an ATP-dependent enzymatic machinery that targets substrate proteins for degradation by the 26S proteasome by tagging them with an isopeptide chain composed of covalently linked molecules of ubiquitin, a small chaperone protein. The current knowledge of UPS involvement in the process of sperm penetration through vitelline coat (VC) during human and animal fertilization is reviewed in this study, with attention also being given to sperm capacitation and acrosome reaction/exocytosis. In ascidians, spermatozoa release ubiquitin-activating and conjugating enzymes, proteasomes, and unconjugated ubiquitin to first ubiquitinate and then degrade the sperm receptor on the VC; in echinoderms and mammals, the VC (zona pellucida/ZP in mammals) is ubiquitinated during oogenesis and the sperm receptor degraded during fertilization. Various proteasomal subunits and associated enzymes have been detected in spermatozoa and localized to sperm acrosome and other sperm structures. By using specific fluorometric substrates, proteasome-specific proteolytic and deubiquitinating activities can be measured in live, intact spermatozoa and in sperm protein extracts. The requirement of proteasomal proteolysis during fertilization has been documented by the application of various proteasome-specific inhibitors and antibodies. A similar effect was achieved by depletion of sperm-surface ATP. Degradation of VC/ZP-associated sperm receptor proteins by sperm-borne proteasomes has been demonstrated in ascidians and sea urchins. On the applied side, polyspermy has been ameliorated by modulating sperm-associated deubiquitinating enzymes. Diagnostic and therapeutic applications could emerge in human reproductive medicine. Altogether, the studies on sperm proteasome indicate that animal fertilization is controlled in part by a unique, gamete associated, extracellular UPS.

Method to isolate polyribosomal mRNA from scarce samples such as mammalian oocytes and early embryos

Background

Although the transcriptome of minute quantities of cells can be profiled using nucleic acid amplification techniques, it remains difficult to distinguish between active and stored messenger RNA. Transcript storage occurs at specific stages of gametogenesis and is particularly important in oogenesis as stored maternal mRNA is used to sustain de novo protein synthesis during the early developmental stages until the embryonic genome gets activated. In many cases, stored mRNA can be several times more abundant than mRNA ready for translation. In order to identify active mRNA in bovine oocytes, we sought to develop a method of isolating very small amounts of polyribosome mRNA.

Results

The proposed method is based on mixing the extracted oocyte cytoplasm with a preparation of polyribosomes obtained from a non-homologous source (Drosophila) and using sucrose density gradient ultracentrifugation to separate the polyribosomes. It involves cross-linking the non-homologous polyribosomes and neutralizing the cross-linking agent. Using this method, we show that certain stages of oocyte maturation coincide with changes in the abundance of polyribosomal mRNA but not total RNA or poly(A). We also show that the abundance of selected sequences matched changes in the corresponding protein levels.

Conclusions

We report here the successful use of a method to profile mRNA present in the polyribosomal fraction obtained from as little as 75 mammalian oocytes. Polyribosomal mRNA fractionation thus provides a new tool for studying gametogenesis and early development with better representation of the underlying physiological status.

Dynamic proteome signatures in gametes, embryos and their maternal environment

Comprehensive molecular analysis at the level of proteins represents a technically demanding, but indispensable, task since several post-transcriptional regulation mechanisms disable a valid prediction of quantitative protein expression profiles from transcriptome analysis. In crucial steps of gamete and early embryo development, de novo transcription is silenced, meaning that almost all macromolecular events take place at the level of proteins. In this review, we describe selected examples of dynamic proteome signatures addressing capacitation of spermatozoa, in vitro maturation of oocytes, effect of oestrous cycle on oviduct epithelial cells and embryo-induced alterations to the maternal environment. We also present details of the experimental strategies applied and the experiments performed to verify quantitative proteomic data. Far from being comprehensive, examples were selected to cover several mammalian species as well as the most powerful proteomic techniques currently applied. To enable non-experts in the field of proteomics to appraise published proteomic data, our examples are preceded by a customised description of quantitative proteomic methods, covering 2D difference gel electrophoresis (2D-DIGE), nano-liquid chromatography combined with tandem mass spectrometry, and label-free as well as stable-isotope labelling strategies for mass spectrometry-based quantifications.

Proteome profiling of early seed development in Cunninghamia lanceolata (Lamb.) Hook

Knowledge of the proteome of the early gymnosperm embryo could provide important information for optimizing plant cloning procedures and for establishing platforms for research into plant development/regulation and in vitro transgenic studies. Compared with angiosperms, it is more difficult to induce somatic embryogenesis in gymnosperms; success in this endeavour could be increased, however, if proteomic information was available on the complex, dynamic, and multistage processes of gymnosperm embryogenesis in vivo. A proteomic analysis of Chinese fir seeds in six developmental stages was carried out during early embryogenesis. Proteins were extracted from seeds dissected from immature cones and separated by two-dimensional difference gel electrophoresis. Analysis with DeCyder 6.5 software revealed 136 spots that differed in kinetics of appearance. Analysis by liquid chromatography coupled to tandem mass spectrometry and MALDI-TOF mass spectrometry identified proteins represented by 71 of the spots. Functional annotation of these seed proteins revealed their involvement in programmed cell death and chromatin modification, indicating that the proteins may play a central role in determining the number of zygotic embryos generated and controlling embryo patterning and shape remodelling. The analysis also revealed other proteins involved in carbon metabolism, methionine metabolism, energy production, protein storage, synthesis and stabilization, disease/defence, the cytoskeleton, and embryo development. The comprehensive protein expression profiles generated by our study provide new insights into the complex developmental processes in the seeds of the Chinese fir.

Analysis of the budding yeast pH 4-7 proteome in meiosis

Meiosis, the developmental programme generating haploid gametes from diploid precursors, requires two cell divisions and many innovations. In budding yeast, a large number of genes are expressed exclusively during meiosis while others are repressed compared to vegetative growth. Microarray analysis has shown that gene expression during meiosis is highly regulated, and has been used to classify yeast genes according to meiotic temporal expression pattern. In this study, we have begun to investigate the kinetics of meiotic protein expression using a proteomics approach. 2-D DIGE was used to characterise the temporal protein expression patterns of the budding yeast pH 4-7 proteome in meiosis. More than 1400 meiotic protein spots were visualised and at least 63 spots were temporally regulated during meiosis in a statistically significant manner. Gel spots with significant expression changes were excised and 26 unique proteins were identified using LC-MS/MS. The identified proteins could be classified into functional categories and the genes encoding a number of these were previously shown to be involved in yeast sporulation and meiosis. This data set was used to assemble the first differential 2-D PAGE map of budding yeast meiosis, which can be accessed through a web server. This work represents one of the first quantitative proteomic analyses of meiosis in yeast and will provide a valuable resource for future investigations.

Role of ubiquitin C-terminal hydrolase-L1 in antipolyspermy defense of mammalian oocytes

The ubiquitin-proteasome system regulates many cellular processes through rapid proteasomal degradation of ubiquitin-tagged proteins. Ubiquitin C-terminal hydrolase-L1 (UCHL1) is one of the most abundant proteins in mammalian oocytes. It has weak hydrolytic activity as a monomer and acts as a ubiquitin ligase in its dimeric or oligomeric form. Recently published data show that insufficiency in UCHL1 activity coincides with polyspermic fertilization; however, the mechanism by which UCHL1 contributes to this process remains unclear. Using UCHL1-specific inhibitors, we induced a high rate of polyspermy in bovine zygotes after in vitro fertilization. We also detected decreased levels in the monomeric ubiquitin and polyubiquitin pool. The presence of UCHL1 inhibitors in maturation medium enhanced formation of presumptive UCHL1 oligomers and subsequently increased abundance of K63-linked polyubiquitin chains in oocytes. We analyzed the dynamics of cortical granules (CGs) in UCHL1-inhibited oocytes; both migration of CGs toward the cortex during oocyte maturation and fertilization-induced extrusion of CGs were impaired. These alterations in CG dynamics coincided with high polyspermy incidence in in vitro-produced UCHL1-inhibited zygotes. These data indicate that antipolyspermy defense in bovine oocytes may rely on UCHL1-controlled functioning of CGs.

Proteomic analysis of parthenogenetic and in vitro fertilized porcine embryos

Proteomic data from embryos are essential for the completion of whole proteome catalog due to embryo-specific expression of certain proteins. In this study, using reverse phase LC-MS/MS combined with 1-D SDS-PAGE, we identified 1625 mammalian and 735 Sus scrofa proteins from porcine zygotes that included both cytosolic and membranous proteins. We also found that the global protein profiles of parthenogenetically activated (PA) and in vitro fertilized (IVF) zygotes were similar but differences in expression of individual proteins were also evident. These differences were not due to culture conditions, polyspermy or non-activation of oocytes, as the same culture method was used in both groups, the frequency of polyspermy was 24.3+/-3.0% and the rates of oocyte activation did not differ (p>0.05) between PA and IVF embryos. Consistent with proteomic data, fluorescent Hoechst 33 342 staining and terminal deoxynucleotidyl transferase dUTP nick end labeling assay also revealed that PA embryos were of poor quality as they contained less cells per blastocyst and were more predisposed to apoptosis (p<0.05), although their in vitro development rates were similar. To our knowledge, this is the first report on global peptide sequencing and quantification of protein in PA and IVF embryos by LC-MS/MS that may be useful as a reference map for future studies.

Highly sensitive saturation labeling reveals changes in abundance of cell cycle-associated proteins and redox enzyme variants during oocyte maturation in vitro

Oocyte maturation is a complex process and a critical issue in assisted reproduction techniques (ART) in humans and other mammals. We used a sensitive 2-D DIGE saturation labeling approach including an internal pooled standard for quantitative proteome profiling of immature versus in vitro matured bovine oocytes in six independent samples. The study comprised 48 2D gel images representing 24 DIGE experiments. From 250 ng sample analyzed per gel, quantitative analysis revealed an average of 2244 spots in pH 4-7 images and 1291 spots in pH 6-9 images. Thirty-eight spots with different intensities were detected in total. Spots of a preparative gel from 2200 oocytes were identified by nano-LC-MS/MS analysis. The ten spots which could be unambiguously identified include the Ca2+-binding protein translationally controlled tumor protein, enzymes of the Krebs and pentose phosphate cycles, clusterin, 14-3-3 epsilon, elongation factor-1 gamma, and redox enzymes such as polymorphic forms of GST Mu 5 and peroxiredoxin-3. The cellular distribution of two proteins was determined by confocal laser scanning microscopy. The interesting protein candidates identified by this study may help to improve the in vitro maturation process in order to increase the rate of successful in vitro fertilization and other ART in cattle and other mammals.

Protein expression profile of the mouse metaphase-II oocyte

The mature oocyte contains the full complement of maternal proteins required for fertilization, the transition to zygotic transcription, and the beginning stages of embryogenesis. Many of these proteins have yet to be characterized. In this study, two-dimensional electrophoresis (2-DE) of mouse metaphase-II (MII) oocyte proteins, stained with silver staining or Pro-Q Diamond dye, was performed to describe the proteome and phosphoproteome of the mouse oocyte derived from ICR mice. A total of 869 selected protein spots, corresponding to 380 unique proteins, were identified successfully by mass spectrometry, in which 90 protein spots representing 53 unique proteins have been stained with Pro-Q Diamond, indicating that they are in phosphorylated forms. All identified proteins were bioinformatically annotated in detail and compared with the embryonic stem cell (ESC) proteome. A proteome reference database for the mouse oocyte was established from the protein data generated in this study, which can be accessed over the Internet ( http://reprod.njmu.edu.cn/2d). This database is the most detailed mouse oocyte proteomic database to date. It should be valuable in expanding our knowledge of the regulation of signaling in oogenesis, fertilization, and embryo development, while revealing potential mechanisms for epigenetic reprogramming.

Genetic variation underlying protein expression in eggs of the marine mussel Mytilus edulis

Study of the genetic basis of gene expression variation is central to attempts to understand the causes of evolutionary change. Although there are many transcriptomics studies estimating genetic variance and heritability in model organisms such as humans there is a lack of equivalent proteomics studies. In the present study, the heritability underlying egg protein expression was estimated in the marine mussel Mytilus. We believe this to be the first such measurement of genetic variation for gene expression in eggs of any organism. The study of eggs is important in evolutionary theory and life history analysis because maternal effects might have profound effects on the rate of evolution of offspring traits. Evidence is presented that the egg proteome varies significantly between individual females and that heritability of protein expression in mussel eggs is moderate to high suggesting abundant genetic variation on which natural selection might act. The study of the mussel egg proteome is also important because of the unusual system of mitochondrial DNA inheritance in mussels whereby different mitochondrial genomes are transmitted independently through female and male lineages (doubly uniparental inheritance). It is likely that the mechanism underlying this system involves the interaction of specific egg factors with sperm mitochondria following fertilization, and its elucidation might be advanced by study of the proteome in females having different progeny sex ratios. Putative identifications are presented here for egg proteins using MS/MS in Mytilus lines differing in sex ratio. Ontology terms relating to stress response and protein folding occur more frequently for proteins showing large expression differences between the lines. The distribution of ontology terms in mussel eggs was compared with those for previous mussel proteomics studies (using other tissues) and with mammal eggs. Significant differences were observed between mussel eggs and mussel tissues but not between the two types of eggs.

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

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

The quiet embryo hypothesis: molecular characteristics favoring viability

It has been proposed that the viability of early mammalian embryos is associated with a metabolism that is "quiet" rather than "active" (Leese HJ, 2002:BioEssays 24:845-849). The data on which this hypothesis was based were largely drawn from measurements on the depletion and appearance of amino acids from the culture medium. Data on the de novo synthesis of protein in in vivo- and in vitro-derived bovine embryos, as determined from the flux of radiolabeled methionine, have provided further support of the hypothesis and are interpreted to provide a new set of testable propositions that could illuminate the molecular basis of the quiet metabolism phenotype. The propositions are based on the premise that the extent of DNA damage, and the RNA and protein content of the immature oocyte, are key factors in determining whether the zygote progresses to the blastocyst stage. We propose that stochastic events and environmental stresses determine whether the condition of the genome, transcriptome, and proteome of the zygote will support development. Several molecular components are identified that may determine the viability of a zygote, and we speculate that the cellular response to unfavorable events or excessive DNA damage may be the premature activation of the embryonic genome and of apoptosis.

Proteomic analysis of porcine oocytes during in vitro maturation reveals essential role for the ubiquitin C-terminal hydrolase-L1

In this study, we performed proteomic analysis of porcine oocytes duringin vitromaturation. Comparison of oocytes at the initial and final stages of meiotic division characterized candidate proteins that were differentially synthesized duringin vitromaturation. While the biosynthesis of many of these proteins was significantly decreased, we found four proteins with increased biosynthetic rate, which are supposed to play an essential role in meiosis. Among them, the ubiquitin C-terminal hydrolase-L1 (UCH-L1) was identified by mass spectrometry. To study the regulatory role of UCH-L1 in the process of meiosis in pig model, we used a specific inhibitor of this enzyme, marked C30, belonging to the class of isatinO-acyl oximes. When germinal vesicle (GV) stage cumulus-enclosed oocytes were treated with C30, GV breakdown was inhibited after 28 h of culture, and most of the oocytes were arrested at the first meiosis after 44 h. The block of metaphase I–anaphase transition was not completely reversible. In addition, the inhibition of UCH-L1 resulted in elevated histone H1 kinase activity, corresponding to cyclin–dependent kinase(CDK1)–cyclin B1 complex, and a low level of monoubiquitin. These results supported the hypothesis that UCH-L1 might play a role in metaphase I–anaphase transition by regulating ubiquitin-dependent proteasome mechanisms. In summary, a proteomic approach coupled with protein verification study revealed an essential role of UCH-L1 in the completion of the first meiosis and its transition to anaphase.

Ubiquitin proteasome pathway gene expression varies in rhesus monkey oocytes and embryos of different developmental potential

Protein degradation via the ubiquitin-proteasome pathway (UPP) plays a key role in diverse aspects of cell physiology and development. In the early embryo, the UPP may play an important role in the transition from maternal to embryonic control of development. Disruptions in the UPP could thus compromise embryo developmental potential. Additionally, species-specific requirements may dictate diverse patterns of regulation of the UPP components. To investigate the expression of UPP components in a nonhuman primate embryo model, to compare expression between a primate and nonprimate species, and to determine whether disruption of this pathway may contribute to reduced developmental potential, we examined the expression of >50 mRNAs encoding UPP components in rhesus monkey oocytes and embryos. We compared this expression between the rhesus monkey and mouse embryo and between rhesus monkey oocytes and embryos of high, intermediate, and low developmental potential. We report here the temporal patterns of UPP gene expression in oocytes and during preimplantation development, including striking differences between the rhesus monkey and mouse. We also report significant differences in UPP gene expression correlating with oocyte and embryo developmental competence and associated with altered regulation of maternally inherited mRNAs encoding these proteins.

Ubiquitin C-terminal hydrolase-activity is involved in sperm acrosomal function and anti-polyspermy defense during porcine fertilization

The 26S proteasome, which is a multi-subunit protease with specificity for substrate proteins that are postranslationally modified by ubiquitination, has been implicated in acrosomal function and sperm-zona pellucida (ZP) penetration during mammalian fertilization. Ubiquitin C-terminal hydrolases (UCHs) are responsible for the removal of polyubiquitin chains during substrate priming for proteasomal proteolysis. The inhibition of deubiquitination increases the rate of proteasomal proteolysis. Consequently, we have hypothesized that inhibition of sperm acrosome-borne UCHs increases the rate of sperm-ZP penetration and polyspermy during porcine in vitro fertilization (IVF). Ubiquitin aldehyde (UA), which is a specific nonpermeating UCH inhibitor, significantly (P < 0.05) increased polyspermy during porcine IVF and reduced (P < 0.05) UCH enzymatic activity measured in motile boar spermatozoa using a specific fluorometric UCH substrate, ubiquitin-AMC. Antibodies against two closely related UCHs, UCHL1 and UCHL3, detected these UCHs in the oocyte cortex and on the sperm acrosome, respectively, and increased the rate of polyspermy during IVF, consistent with the UA-induced polyspermy surge. In the oocyte, UCHL3 was primarily associated with the meiotic spindle. Sperm-borne UCHL3 was localized to the acrosomal surface and coimmunoprecipitated with a peripheral acrosomal membrane protein, spermadhesin AQN1. Recombinant UCHs, UCHL3, and isopeptidase T reduced polyspermy when added to the fertilization medium. UCHL1 was detected in the oocyte cortex but not on the sperm surface, and was partially degraded 6-8 h after fertilization. Enucleated oocyte-somatic cell electrofusion caused polarized redistribution of cortical UCHL1. We conclude that sperm-acrosomal UCHs are involved in sperm-ZP interactions and antipolyspermy defense. Modulation of UCH activity could facilitate the management of polyspermy during IVF and provide insights into male infertility.

Genetics and genomics to improve fertility in high producing dairy cows

Improving dairy cow fertility by means of genetic selection is likely to become increasingly important, since it is now well established that declining fertility cannot only be arrested by improved management. Profit margins per kg milk produced are decreasing, therefore farmers need to reduce cost and increase herd size. This restricts the labor input per cow and the disposable cost of getting a cow pregnant, whilst at the same time hormone treatments have become less acceptable. This makes it unlikely that additional management interventions will maintain fertility at acceptable levels in the near future. Genetic improvement seems the obvious solution. Effective selection tools are available in most Western countries using traditional breeding value estimation procedures. Also, in addition to gene assisted selection using individual genes or QTL, high throughput Single Nucleotide Polymorphism (SNP) technology allows genetic improvement of fertility based on information from the whole genome (tens of thousands SNP per animal), i.e. genomic selection. Simulation studies have shown that genomic selection improves the accuracy of selecting juvenile animals compared with traditional breeding methods and compared with selection using information from a few genes or QTL only. Research in the areas genomics and proteomics promise to make genetic selection even more effective. The genomic and proteomics technologies combined with the bioinformatics tools that support the interpretation of gene functioning and protein expression facilitate an exciting starting point for the development of new management strategies and tools for the improvement of reproductive performance.