Accumulation of the proteolytic marker peptide ubiquitin in the trophoblast of mammalian blastocysts

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.

Differential control of retrovirus silencing in embryonic cells by proteasomal regulation of the ZFP809 retroviral repressor

Replication of the murine leukemia viruses is strongly suppressed in mouse embryonic stem (ES) cells. Proviral DNAs are formed normally but are then silenced by a large complex bound to DNA by the ES cell-specific zinc-finger protein ZFP809. We show here that ZFP809 expression is not regulated by transcription but rather by protein turnover: ZFP809 protein is stable in embryonic cells but highly unstable in differentiated cells. The protein is heavily modified by the accumulation of polyubiquitin chains in differentiated cells and stabilized by the proteasome inhibitor MG132. A short sequence of amino acids at the C terminus of ZFP809, including a single lysine residue (K391), is required for the rapid turnover of the protein. The silencing cofactor TRIM28 was found to promote the degradation of ZFP809 in differentiated cells. These findings suggest that the stem cell state is established not only by an unusual transcriptional profile but also by unusual regulation of protein levels through the proteasomal degradation pathway.

Proteomic profile of maternal-aged blastocoel fluid suggests a novel role for ubiquitin system in blastocyst quality

PURPOSE

The etiology of maternal aging, a common cause of female factor infertility and a rate-limiting step in vitro fertilization (IVF) success, remains still unclear. Proteomic changes responsible for the impaired successful pregnancy outcome after IVF with aged blastocysts have not been yet evaluated. The objective of this prospective study was to employ proteomic techniques and bioinformatic tools to enlight differences at the protein level in blastocoel fluid of aged and younger woman.

METHODS

Protein composition of human blastocoel fluid isolated by micromanipulation from 46 blastocysts of women aged <37 years (group A) and 29 of women aged ≥37 years (group B) have been identified by a shotgun proteomic approach based on high-resolution nano-liquid chromatography electrospray-ionization-tandem mass spectrometry (nLC-ESI-MS/MS) using label free for the relative quantification of their expression levels.

RESULTS

The proteomic analysis leads to the identification and quantification of 148 proteins; 132 and 116 proteins were identified in groups A and B, respectively. Interestingly, the identified proteins are mainly involved in processes aimed at fine tuning embryo implantation and development. Among the 100 proteins commonly expressed in both groups, 17 proteins are upregulated and 44 downregulated in group B compared to group A. Overall, the analysis identified 33 proteins, which were increased or present only in B while 76 were decreased in B or present only in A.

CONCLUSIONS

Data revealed that maternal aging mainly affects blastocyst survival and implantation through unbalancing the equilibrium of the ubiquitin system known to play a crucial role in fine-tuning several aspects required to ensure successful pregnancy outcome.

SNaPP: Simplified Nanoproteomics Platform for Reproducible Global Proteomic Analysis of Nanogram Protein Quantities

Global proteomic analyses of complex protein samples in nanogram quantities require a fastidious approach to achieve in-depth protein coverage and quantitative reproducibility. Biological samples are often severely mass limited and can preclude the application of more robust bulk sample processing workflows. In this study, we present a system that minimizes sample handling by using online immobilized trypsin digestion and solid phase extraction to create a simple, sensitive, robust, and reproducible platform for the analysis of nanogram-size proteomic samples. To demonstrate the effectiveness of our simplified nanoproteomics platform, we used the system to analyze preimplantation blastocysts collected on day 4 of pregnancy by flushing the uterine horns with saline. For each of our three sample groups, blastocysts were pooled from three mice resulting in 22, 22, and 25 blastocysts, respectively. The resulting proteomic data provide novel insight into mouse blastocyst protein expression on day 4 of normal pregnancy because we characterized 348 proteins that were identified in at least two sample groups, including 59 enzymes and blastocyst specific proteins (eg, zona pellucida proteins). This technology represents an important advance in which future studies could perform global proteomic analyses of blastocysts obtained from an individual mouse, thereby enabling researchers to investigate interindividual variation as well as increase the statistical power without increasing animal numbers. This approach is also easily adaptable to other mass-limited sample types.

Characterization of SCF-Complex during Bovine Preimplantation Development

The degradation of maternal proteins is one of the most important events during early development, and it is presumed to be essential for embryonic genome activation (EGA), but the precise mechanism is still not known. It is thought that a large proportion of the degradation of maternal proteins is mediated by the ubiquitin-proteolytic system. In this study we focused on the expression of the Skp1-Cullin1-F-box (SCF) complex, a modular RING-type E3 ubiquitin-ligase, during bovine preimplantation development. The complex consists of three invariable components—Cul1, Skp1, Rbx1 and F-box protein, which determines the substrate specificity. The protein level and mRNA expression of all three invariable members were determined. Cul1 and Skp1 mRNA synthesis was activated at early embryonic stages, at the 4c and early 8c stage, respectively, which suggests that these transcripts are necessary for preparing the embryo for EGA. CUL1 protein level increased from MII to the morula stage, with a significant difference between MII and L8c, and between MII and the morula. The CUL1 protein was localized primarily to nuclei and to a lesser extent to the cytoplasm, with a lower signal in the inner cell mass (ICM) compared to the trophectoderm (TE) at the blastocyst stage. The level of SKP1 protein significantly increased from MII oocytes to 4c embryos, but then significantly decreased again. The localization of the SKP1 protein was analysed throughout the cell and similarly to CUL1 at the blastocyst stage, the staining was less intensive in the ICM. There were no statistical differences in RBX1 protein level and localization. The active SCF-complex, which is determined by the interaction of Cul1 and Skp1, was found throughout the whole embryo during preimplantation development, but there was a difference at the blastocyst stage, which exhibits a much stronger signal in the TE than in the ICM. These results suggest that all these genes could play an important role during preimplantation development. This paper reveals comprehensive expression profile, the basic but important knowledge necessary for further studying.

Embryo implantation failure and other reproductive defects in Ube2q1-deficient female mice

The ubiquitination process is indispensable for proteome regulation. Three classes of ubiquitin (Ub)-related proteins can be distinguished: E1, E2 and E3. Proteins from the E2 class are responsible for the transfer of Ubls from E1 to the target protein. For this activity, interaction with class E3 ligases is usually required. Ub-conjugating enzyme E2Q 1 (UBE2Q1) belongs to the E2 class of Ub-related enzymes and is demonstrated to be involved in the regulation of membrane B4GALT1 protein. Here, we demonstrate that human UBE2Q1 and mouse Ube2q1 are widely expressed and highly conserved genes. To elucidate the function of UBE2Q1 protein, we generated knockout mouse model. No overt phenotype was detected in UBE2Q1-deficient males, but in mutant females, pleiotropic reproductive defects were observed including altered oestrus cycle, abnormal sexual behaviour and reduced offspring care. Moreover, in the uterus of mutant females, significantly increased embryonic lethality and decreased implantation capacity of homozygous mutant embryos were noticed. We found that Ube2q1 is not expressed in the uterus of non-pregnant females but its expression is up-regulated during pregnancy. Taken together, Ube2q1 is involved in different aspects of female fertility.

Essential role of the CUL4B ubiquitin ligase in extra-embryonic tissue development during mouse embryogenesis

Mutations of the CUL4B ubiquitin ligase gene are causally linked to syndromic X-linked mental retardation (XLMR). However, the pathogenic role of CUL4B mutations in neuronal and developmental defects is not understood. We have generated mice with targeted disruption of Cul4b, and observed embryonic lethality with pronounced growth inhibition and increased apoptosis in extra-embryonic tissues. Cul4b, but not its paralog Cul4a, is expressed at high levels in extra-embryonic tissues post implantation. Silencing of CUL4B expression in an extra-embryonic cell line resulted in the robust accumulation of the CUL4 substrate p21(Cip1/WAF) and G2/M cell cycle arrest, which could be partially rescued by silencing of p21(Cip1/WAF). Epiblast-specific deletion of Cul4b prevented embryonic lethality and gave rise to viable Cul4b null mice. Therefore, while dispensable in the embryo proper, Cul4b performs an essential developmental role in the extra-embryonic tissues. Our study offers a strategy to generate viable Cul4b-deficient mice to model the potential neuronal and behavioral deficiencies of human CUL4B XLMR patients.

Thyroid hormone supplementation improves bovine embryo development in vitro

BACKGROUND

Early embryo development (EED) forms the basis of assisted reproductive technologies (ARTs), which are used to treat human infertility and to propagate other mammalian species. Thyroid hormones (THs) play an important role in the post-implantation development of the embryo in mammals; however, the effects of THs on pre-attachment embryos are not known. Currently utilized in-vitro embryo production media are devoid of THs and hence our main objective was to examine whether THs affected EED in a bovine model.

METHODS

To determine if THs are present at the site of fertilization and EED in cattle, we evaluated the presence of the hormones in oviductal and uterine horn tissues. To assess the outcome of free TH supplementation (50 ng/ml of each hormone: triiodothyronine-T3 and thyroxin-T4), embryos were followed through standard and TH-supplemented in-vitro procedures, and evaluated for the cleavage rates, blastocyst formation rate and hatching rates. Embryo quality was assessed using TUNEL assay and post-cryopreservation survival was also evaluated.

RESULTS

Although TH levels in in-vitro culture media were found to be approximately 60% of the administered doses, the TH-treated embryos exhibited significant increases in blastocyst formation and hatching rates (P < 0.05). Embryo quality was significantly improved in the treated groups as demonstrated by greater total cell counts and reduced proportions of apoptotic cells (P < 0.05). Finally, TH supplementation was associated with improved post-cryopreservation viability, defined by blastocyst re-expansion and hatching rates after frozen embryos had been thawed and cultured (P < 0.05).

CONCLUSIONS

These findings not only provide a way of optimizing ART efficiency, but also further our understanding of how THs influence embryonic development in mammals.

Cadmium-induced activation of stress signaling pathways, disruption of ubiquitin-dependent protein degradation and apoptosis in primary rat Sertoli cell-gonocyte cocultures

Cadmium (Cd) is a ubiquitous environmental pollutant that has been associated with male reproductive toxicity in both humans and animal models. The underlying mechanism of this response, however, is still uncharacterized. To address this issue, we employed a recently developed and optimized three-dimensional primary Sertoli cell-gonocyte coculture system and examined the time- and dose-dependent effects of Cd on morphological alterations, cell viability, activation of stress signaling pathway proteins, and the disruption of the ubiquitin proteasome system (UPS). Our results demonstrated that Cd exposure lead to time- and dose-dependent morphological changes that are associated with the induction of apoptosis. In response to Cd, we also saw a disruption of the UPS as evaluated through the accumulation of high-molecular weight polyubiquitinated proteins (HMW-polyUb) as well as alterations in proteasome activity. Robust activation of cellular stress response, measured through the increased phosphorylation of stress-activated protein kinase/c-jun N-terminal kinase and p38, paralleled the accumulation of HMW-polyUb. In addition, p53, a key regulatory protein, was upregulated and underwent increased ubiquitination in response to Cd. To further characterize the role of the UPS in Cd cellular response, we compared the above changes with two classic proteasomal inhibitors, lactacystin, and MG132. The stress response and the accumulation of HWM-polyUb induced by Cd were consistent with the response seen with MG132 but not with lactacystin. In addition, Cd treatment resulted in a dose- and time-dependent effect on proteasome activity, but the overall Cd-induced proteasomal inhibition was unique as compared to MG132 and lactacystin. Taken together, our studies further characterize Cd-induced in vitro testicular toxicity and highlight the potential role of the UPS in this response.

Ultrastructure of preimplantation genetic diagnosis-derived human blastocysts grown in a coculture system after vitrification

OBJECTIVE

To evaluate ultrastructural features of preimplantation genetic diagnosis (PGD) blastocysts before and after vitrification.

DESIGN

Descriptive study of both vitrified and fresh hatching blastocysts.

SETTING

PGD program at the Instituto Universitario, Instituto Valenciano de Infertilidad.

PATIENT(S)

Patients undergoing PGD donated their abnormal embryos for research (n = 26).

INTERVENTION(S)

Biopsied embryos were cultured in the presence of human endometrial cells until day 6. Sixteen blastocysts were vitrified. A total of 11 high-scored hatching blastocysts, 6 warmed and 5 fresh, were fixed for ultrastructure.

MAIN OUTCOME MEASURE(S)

The cytoskeleton structure, type of intercellular junctions, and basic intracellular organelles in trophoectoderm cells and the inner cell mass were analyzed.

RESULT(S)

Ten of 16 blastocysts (62%) survived the warming process. Six of these showed no signs of cell degeneration and light microscopy revealed similar ultrastructural characteristics to those of controls. However, in trophoectoderm cells from both fresh and cryopreserved blastocysts, a reduced number of tight junctions and the presence of degradation bodies were detected.

CONCLUSION(S)

The particular ultrastructural features observed in PGD-derived blastocysts could be related to embryo manipulation and culture conditions. Vitrification does not seem to alter blastocysts, as those that survive hatching do not display detectable cellular alterations when observed through electron microscopy.

MATER protein expression and intracellular localization throughout folliculogenesis and preimplantation embryo development in the bovine

Background

Mater (Maternal Antigen that Embryos Require), also known as Nalp5 (NACHT, leucine rich repeat and PYD containing 5), is an oocyte-specific maternal effect gene required for early embryonic development beyond the two-cell stage in mouse. We previously characterized the bovine orthologue MATER as an oocyte marker gene in cattle, and this gene was recently assigned to a QTL region for reproductive traits.

Results

Here we have analyzed gene expression during folliculogenesis and preimplantation embryo development. In situ hybridization and immunohistochemistry on bovine ovarian section revealed that both the transcript and protein are restricted to the oocyte from primary follicles onwards, and accumulate in the oocyte cytoplasm during follicle growth. In immature oocytes, cytoplasmic, and more precisely cytosolic localization of MATER was confirmed by immunohistochemistry coupled with confocal microscopy and immunogold electron microscopy. By real-time PCR, MATER messenger RNA was observed to decrease strongly during maturation, and progressively during the embryo cleavage stages; it was hardly detected in morulae and blastocysts. The protein persisted after fertilization up until the blastocyst stage, and was mostly degraded after hatching. A similar predominantly cytoplasmic localization was observed in blastomeres from embryos up to 8-cells, with an apparent concentration near the nuclear membrane.

Conclusion

Altogether, these expression patterns are consistent with bovine MATER protein being an oocyte specific maternal effect factor as in mouse.

Blastocysts don't go it alone. Extrinsic signals fine-tune the intrinsic developmental program of trophoblast cells

The preimplantation embryo floats freely within the oviduct and is capable of developing into a blastocyst independently of the maternal reproductive tract. While establishment of the trophoblast lineage is dependent on expression of developmental regulatory genes, further differentiation leading to blastocyst implantation in the uterus requires external cues emanating from the microenvironment. Recent studies suggest that trophoblast differentiation requires intracellular signaling initiated by uterine-derived growth factors and integrin-binding components of the extracellular matrix. The progression of trophoblast development from the early blastocyst stage through the onset of implantation appears to be largely independent of new gene expression. Instead, extrinsic signals direct the sequential trafficking of cell surface receptors to orchestrate the developmental program that initiates blastocyst implantation. The dependence on external cues could coordinate embryonic activities with the developing uterine endometrium. Biochemical events that regulate trophoblast adhesion to fibronectin are presented to illustrate a developmental strategy employed by the peri-implantation blastocyst.