Modulation of gene expression in the preimplantation mouse embryo by TGF-alpha and TGF-beta

Structural and functional analysis of transforming growth factor beta regulator 1 (TBRG1) in the red swamp crayfish Procambarus clarkii: The initial insight into TBRG1's role in invertebrate immunity

The transforming growth factor beta regulator 1 (TBRG1) is a growth inhibitory protein that acts as a tumor suppressor in human cancers, gaining its name for the transcriptional regulation by TGF-β. While extensive research has been conducted on the tumor-related function of TBRG1 in mammals, its significance in invertebrates remains largely unexplored. In this study, a homolog of TBRG1 was first structurally and functionally analyzed in the red swamp crayfish Procambarus clarkii. The full-length cDNA sequence was 2143 base pairs (bp) with a 1305 bp open reading frame (ORF) encoding a deduced protein of 434 amino acids (aa). The changes of PcTBRG1 transcripts upon immune challenges indicated its involvement in innate immunity. After knocking down PcTBRG1, the decline of bacteria clearance capacity revealed the participation of PcTBRG1 in the immune response. Furthermore, the downregulation of AMPs' expression after the cotreatment of RNAi and bacteria challenge suggested that PcTBRG1 might participate in innate immunity through regulating AMPs' expression. These results provided initial insight into the immune-related function of TBRG1 in invertebrates.

A combination of growth factors and cytokines alter preimplantation mouse embryo development, foetal development and gene expression profiles

Within the maternal tract, the preimplantation embryo is exposed to an array of growth factors (GFs) and cytokines, most of which are absent from culture media used in clinical IVF. Whilst the addition of individual GFs and cytokines to embryo culture media can improve preimplantation mouse embryo development, there is a lack of evidence on the combined synergistic effects of GFs and cytokines on embryo development and further foetal growth. Therefore, in this study, the effect of a combined group of GFs and cytokines on mouse preimplantation embryo development and subsequent foetal development and gene expression profiles was investigated. Supplementation of embryo culture media with an optimised combination of GFs and cytokines (0.05 ng/ml vascular endothelial GF, 1 ng/ml platelet-derived GF, 0.13 ng/ml insulin-like GF 1, 0.026 ng/ml insulin-like GF 2 and 1 ng/ml granulocyte colony-stimulating factor) had no effect on embryo morphokinetics but significantly increased trophectoderm cell number (P = 0.0002) and total cell number (P = 0.024). Treatment with this combination of GFs and cytokines also significantly increased blastocyst outgrowth area (P < 0.05) and, following embryo transfer, increased foetal weight (P = 0.027), crown-rump length (P = 0.017) and overall morphological development (P = 0.027). RNA-seq analysis of in vitro derived foetuses identified concurrent alterations to the transcriptional profiles of liver and placental tissues compared with those developed in vivo, with greater changes observed in the GF and cytokine treated group. Together these data highlight the importance of balancing the actions of such factors for the regulation of normal development and emphasise the need for further studies investigating this prior to clinical implementation.

Characterization of transforming growth factor beta regulator 1-like and association between its expression levels and growth of the giant tiger shrimp Penaeus monodon

Molecular markers that allow selection of juveniles and broodstock with improved growth performances are useful for the shrimp industry. Here, the full-length cDNA of transforming growth factor beta regulator 1-like (PmTbrg1-l) in the giant tiger shrimp Penaeus monodon was determined. It was 1184 bp in length and contained an open reading frame (ORF) of 975 bp corresponding to a deduced polypeptide of 324 amino acids. Successful RNA interference (RNAi) carried out using juveniles injected with PmTbrg1-l dsRNA revealed reduced levels of PmTbrg1-l and myostatin (PmMstm) in hemocytes when compared to shrimp injected with saline solution and GFP dsRNA (P < .05). Associations between single-strand conformational polymorphism (SSCP) patterns or single nucleotide polymorphism (SNP) patterns and growth-related parameters (average body weight and total length) were examined. Juveniles with pattern III (corresponding to A/A₉₁₈; N = 37) showed a trend for greater average body weight and total length than those with patterns II (G/G₉₁₈; N = 42) and IV (A/G₉₁₈; N = 75). The expression level of PmTbrg1-l in the hepatopancreas of females was significantly higher than that in males (P < .05) in two sample sets of three-month-old domesticated juveniles (N = 59 and 50; P < .05). Moreover, its expression level in large-size juveniles was significantly higher than that in medium-size and small-size juveniles in both groups of samples (P < .05). Results indicated that PmTbrg1-l is functionally related with growth of P. monodon.

Myst2/Kat7 histone acetyltransferase interaction proteomics reveals tumour-suppressor Niam as a novel binding partner in embryonic stem cells

MYST histone acetyltransferases have crucial functions in transcription, replication and DNA repair and are hence implicated in development and cancer. Here we characterise Myst2/Kat7/Hbo1 protein interactions in mouse embryonic stem cells by affinity purification coupled to mass spectrometry. This study confirms that in embryonic stem cells Myst2 is part of H3 and H4 histone acetylation complexes similar to those described in somatic cells. We identify a novel Myst2-associated protein, the tumour suppressor protein Niam (Nuclear Interactor of ARF and Mdm2). Human NIAM is involved in chromosome segregation, p53 regulation and cell proliferation in somatic cells, but its role in embryonic stem cells is unknown. We describe the first Niam embryonic stem cell interactome, which includes proteins with roles in DNA replication and repair, transcription, splicing and ribosome biogenesis. Many of Myst2 and Niam binding partners are required for correct embryonic development, implicating Myst2 and Niam in the cooperative regulation of this process and suggesting a novel role for Niam in embryonic biology. The data provides a useful resource for exploring Myst2 and Niam essential cellular functions and should contribute to deeper understanding of organism early development and survival as well as cancer. Data are available via ProteomeXchange with identifier PXD005987.

Pre- and Peri-/Post-Compaction Follistatin Treatment Increases In Vitro Production of Cattle Embryos

Our previous studies demonstrated that maternal (oocyte derived) follistatin (FST) expression is positively associated with bovine oocyte competence and exogenous follistatin treatment during the pre-compaction period of development (d 1–3 post insemination) is stimulatory to bovine early embryogenesis in vitro [blastocyst rates and cell numbers/allocation to trophectoderm (TE)]. In the present study, bovine embryos were treated with exogenous follistatin during d 1–3, d 4–7 and d 1–7 post insemination to test the hypothesis that embryotropic effects of exogenous follistatin are specific to the pre-compaction period (d 1–3) of early embryogenesis. Follistatin treatment during d 4–7 (peri-/post-compaction period) of embryo culture increased proportion of embryos reaching blastocyst and expanded blastocyst stage and total cell numbers compared to controls, but blastocyst rates and total cell numbers were lower than observed following d 1–3 (pre-compaction) follistatin treatment. Follistatin supplementation during d 1–7 of embryo culture increased development to blastocyst and expanded blastocyst stages and blastocyst total cell numbers compared to d 1–3 and d 4–7 follistatin treatment and untreated controls. A similar increase in blastocyst CDX2 mRNA and protein (TE cell marker) was observed in response to d 1–3, d 4–7 and d 1–7 follistatin treatment. However, an elevation in blastocyst BMP4 protein (TE cell regulator) was observed in response to d 1–3 and d 1–7, but not d 4–7 (peri-/post-compaction) follistatin treatment. In summary, our study revealed the potential utility of follistatin treatment for increasing the success rate of in vitro embryo production in cattle. Such results also expand our understanding of the embryotropic actions of follistatin and demonstrate that follistatin actions on blastocyst development and cell allocation to the TE layer are not specific to the pre-compaction period.

Evaluation of Mouse Oocyte In Vitro Maturation Developmental Competency in Dynamic Culture Systems by Design and Construction of A Lab on A Chip Device and Its Comparison with Conventional Culture System

Objective

In conventional assisted reproductive technology (ART), oocytes are cultured in static microdrops within Petri dishes that contain vast amounts of media. However, the in vivo environment is dynamic. This study assesses in vitro oocyte maturation through the use of a new microfluidic device. We evaluate oocyte fertilization to the blastocyct stage and their glutathione (GSH) contents in each experimental group.

Materials and Methods

In this experimental study, we established a dynamic culture condition. Immature oocytes were harvested from ovaries of Naval Medical Research Institute (NMRI) mice. Oocytes were randomly placed in static (passive) and dynamic (active) in vitro maturation (IVM) culture medium for 24 hours. In vitro matured oocytes underwent fertilization, after which we placed the pronucleus (PN) stage embryos in microdrops and followed their developmental stages to blastocyst formation after 3 days. GSH content of the in vitro matured oocytes was assessed by monochlorobimane (MCB) staining.

Results

We observed significantly higher percentages of mature metaphase II oocytes (MII) in the passive and active dynamic culture systems (DCS) compared to the static group (P<0.01). There were significantly less mean numbers of germinal vesicle (GV) and degenerated oocytes in the passive and active dynamic groups compared to the static group (P<0.01). Fertilization and blastocyst formation rate in the dynamic systems were statistically significant compared to the static cultures (P<0.01). There was significantly higher GSH content in dynamically matured oocytes compared to statically matured oocytes (P<0.01).

Conclusion

Dynamic culture for in vitro oocyte maturation improves their developmental competency in comparison with static culture conditions.

NIAM-deficient mice are predisposed to the development of proliferative lesions including B-cell lymphomas

Nuclear Interactor of ARF and Mdm2 (NIAM, gene designation Tbrg1) is a largely unstudied inhibitor of cell proliferation that helps maintain chromosomal stability. It is a novel activator of the ARF-Mdm2-Tip60-p53 tumor suppressor pathway as well as other undefined pathways important for genome maintenance. To examine its predicted role as a tumor suppressor, we generated NIAM mutant (NIAM^m/m) mice homozygous for a β-galactosidase expressing gene-trap cassette in the endogenous gene. The mutant mice expressed significantly lower levels of NIAM protein in tissues compared to wild-type animals. Fifty percent of aged NIAM deficient mice (14 to 21 months) developed proliferative lesions, including a uterine hemangioma, pulmonary papillary adenoma, and a Harderian gland adenoma. No age-matched wild-type or NIAM^+/m heterozygous animals developed lesions. In the spleen, NIAM^m/m mice had prominent white pulp expansion which correlated with enhanced increased reactive lymphoid hyperplasia and evidence of systemic inflammation. Notably, 17% of NIAM mutant mice had splenic white pulp features indicating early B-cell lymphoma. This correlated with selective expansion of marginal zone B cells in the spleens of younger, tumor-free NIAM-deficient mice. Unexpectedly, basal p53 expression and activity was largely unaffected by NIAM loss in isolated splenic B cells. In sum, NIAM down-regulation in vivo results in a significant predisposition to developing benign tumors or early stage cancers. These mice represent an outstanding platform for dissecting NIAM's role in tumorigenesis and various anti-cancer pathways, including p53 signaling.

The structure of the FYR domain of transforming growth factor beta regulator 1

Many chromatin-associated proteins contain two sequence motifs rich in phenylalanine/tyrosine residues of unknown function. These so-called FYRN and FYRC motifs are also found in transforming growth factor beta regulator 1 (TBRG1)/nuclear interactor of ARF and MDM2 (NIAM), a growth inhibitory protein that also plays a role in maintaining chromosomal stability. We have solved the structure of a fragment of TBRG1, which encompasses both of these motifs. The FYRN and FYRC regions each form part of a single folded module (the FYR domain), which adopts a novel α + β fold. Proteins such as the histone H3K4 methyltransferases trithorax and mixed lineage leukemia (MLL), in which the FYRN and FYRC regions are separated by hundreds of amino acids, are expected to contain FYR domains with a large insertion between two of the strands of the β-sheet.

Dynamic microfunnel culture enhances mouse embryo development and pregnancy rates

BACKGROUND

Despite advances in in vitro manipulation of preimplantation embryos, there is still a reduction in the quality of embryos produced leading to lower pregnancy rates compared with embryos produced in vivo. We hypothesized that a dynamic microfunnel embryo culture system would enhance outcomes by better mimicking the fluid-mechanical and biochemical stimulation embryos experience in vivo from ciliary currents and oviductal contractions.

METHODS AND RESULTS

Mouse embryos were cultured in microdrop-static control, microfunnel-static control or microfunnel-dynamic conditions with microfluidics. All groups tested had greater than 90% total blastocyst development from zygotes after 96 h culture. Blastocyst developmental stage was significantly enhanced (P < 0.01) under dynamic microfunnel culture conditions as evidenced by an increased percentage of hatching or hatched blastocysts (Microdrop-control 31%; Microfunnel-control 23%; Microfunnel-pulsatile 71%) and significantly higher (P < 0.01) average number of cells per blastocyst (Microdrop-control 67 +/- 3; Microfunnel-control 60 +/- 3; Microfunnel-pulsatile 109 +/- 5). Blastocyst cell numbers in dynamic microfunnel cultures (109 +/- 5) more closely matched numbers obtained from in vivo grown blastocysts (144 +/- 9). Importantly, dynamic microfunnel culture significantly improved embryo implantation and ongoing pregnancy rates over static culture to levels approaching that of in utero derived preimplantation embryos.

CONCLUSIONS

The improved pregnancy outcomes along with the simple and user-friendly design of the microfluidic/microfunnel system has potential to alleviate many inefficiencies in embryo production for biomedical research, genetic gain in domestic species and assisted reproductive technologies in humans.

Effect of medium conditioned with rat hepatoma BRL cells on '2-cell block' of random-bred mouse embryos cultured in vitro

The phenomenon of developmental arrest at the 2-cell stage of zygotes obtained from certain mouse strains during in vitro culture is known as the 2-cell block. The effect of conditioned medium (CM) with rat hepatoma BRL cells on the 2-cell block of CD-1 mouse zygotes was investigated in comparison with that of CM with rat hepatoma Reuber H-35 cells. In control medium with EDTA, 75.4% of 2-cell embryos developed to the 4- to 8-cell stages. In the same conditions, the BRL Mr <10000 fraction inhibited the development of 2-cell embryos to the 4- to 8-cell stages (57.7%), although the inhibition by this fraction was weaker than by the Reuber Mr <10000 fraction (19.8%). As a result of reversed-phase column chromatography, a 2-cell stage specific inhibitor of the cleavage of mouse embryos (Fr.B-25), which separated into the Mr <10000 fraction of the Reuber CM, was detected at a low level in the BRL Mr <10000 fraction. On the other hand, the Mr >10000 fraction of BRL CM accelerated the development of the embryos (90.3%). This beneficial effect was also evident even in the absence of EDTA. RT-PCR analysis revealed that mRNAs encoding the beta-A or beta-B subunit of activins (Mr ~29000), which are well characterized cytokines that act as releasers of the 2-cell block, were expressed in BRL cells. These results indicate that BRL cells synthesize Fr.B-25 at low levels, and that activins contained in the BRL CM probably contributed to overcoming the 2-cell block of CD-1 zygotes cultured in vitro.

TGFα and EGFR in ovine preimplantation embryos and effects on development

The present study aimed to assess location and relative amounts of transforming growth factor alpha (TGFalpha) and its receptor (EGFR) in ovine oocytes and preimplantation embryos by using immunohistochemical technique that was graded on a relative scale of 0-3, with 0 representing absence of staining, and 3 exhibiting prominent staining, and to evaluate the effects of TGFalpha/EGF on in vitro development of preimplantation embryos by adding different concentrations of EGF and TGFalpha to culture medium. The results showed that EGFR was abundant in cell plasma membranes in immature and mature oocytes, cumulus cells of immature cumulus-oocyte complexes (COC), fertilized oocytes and at different stages of embryo development. However, the relative amounts in inner cell mass (ICM) (1+) was less than that in trophectoderm (TE) cells (2+) at the blastocysts stage. The staining pattern for TGFalpha was a similar to EGFR. However, the staining for TGFalpha slightly increased in the fertilized oocytes (1-2+) as compared to immature and mature oocytes (1+). TGFalpha was mainly detected in the cytoplasm close to the membrane in both ICM and trophectoderm (TE) cells. The developmental rate of 8-cell stage embryos cultured with 5 ng/ml TGFalpha was increased as compared to other treatments (P<0.05). There was no significant difference in the rate of development of blastocysts cultured with 5 ng/ml TGFalpha, 20 ng/ml EGF, 20 ng/ml EGF+5 ng/ml TGFalpha or the control treatment (P>0.05). In addition, there was no significant difference in the number of cells in blastocyst stage as compared with different treatments (P>0.05). However, TGFalpha alone enhanced cell survival rated (P<0.01) and reduced apoptosis. We concluded that TGFalpha can improve development of ovine preimplantation embryos at the 8-cell and blastocyst stages in vitro.

A novel nuclear interactor of ARF and MDM2 (NIAM) that maintains chromosomal stability

The ARF tumor suppressor signals through p53 and other poorly defined anti-proliferative pathways to block carcinogenesis. In a search for new regulators of ARF signaling, we discovered a novel nuclear protein that we named NIAM (nuclear interactor of ARF and MDM2) for its ability to bind both ARF and the p53 antagonist MDM2. NIAM protein is normally expressed at low to undetectable levels in cells because of, at least in part, MDM2-mediated ubiquitination and proteasomal degradation. When reintroduced into cells, NIAM activated p53, caused a G1 phase cell cycle arrest, and collaborated with ARF in an additive fashion to suppress proliferation. Notably, NIAM retains growth inhibitory activity in cells lacking ARF and/or p53, and knockdown experiments revealed that it is not essential for ARF-mediated growth inhibition. Thus, NIAM and ARF act in separate anti-proliferative pathways that intersect mechanistically and suppress growth more effectively when jointly activated. Intriguingly, silencing of NIAM accelerated chromosomal instability, and microarray analyses showed reduced NIAM mRNA expression in numerous primary human tumors. This study identifies a novel protein with tumor suppressor-like behaviors and functional links to ARF-MDM2-p53 signaling.

Apoptosis in mammalian preimplantation embryos: regulation by survival factors

The formation of a developmentally competent mammalian blastocyst requires the transition from a unicellular state, the fertilized zygote, to a differentiated multicellular structure. In common with other developing organisms, generation of the required cell population involves the processes of cell division, differentiation and cell death, all of which can be regulated by peptide growth factors. Cell death in the preimplantation embryo occurs by apoptosis and, by analogy with other systems, may serve to eliminate unwanted cells during the critical developmental transitions that take place during this period. Cells may be eliminated because they are abnormal or possess defects, including damaged DNA or chromosomal abnormalities. At the early cleavage stages, apoptosis may be associated with activation of the embryonic genome and may contribute to the blastomere fragmentation commonly observed in human IVF embryos. The major wave of apoptosis occurs in a number of species in the inner cell mass of the blastocyst, as identified using nuclear labelling including terminal transferase-mediated dUTP nick end labelling (TUNEL) and fluorescence and confocal microscopy. Apoptosis may protect the integrity and cellular composition of the inner cell mass, by eliminating damaged cells or possibly those with an inappropriate phenotype. Preimplantation embryos express genes involved in the regulation and execution of apoptosis and their cells can undergo this default pathway in the absence of exogenous survival signals. Evidence is now accumulating from several species that apoptosis in the embryo is regulated by soluble peptide growth factors acting as survival factors in an autocrine or paracrine manner. To date, these include transforming growth factor alpha and members of the insulin-like growth factor family. Apoptosis may also be affected by environmental factors, including culture conditions and the composition of media. The regulation of apoptosis in the preimplantation embryo is likely to be of critical importance for both embryo viability and for later development, since the cells of the inner cell mass give rise to the fetus and carry the germ line.

Temporal effect of human oviductal cell and its derived embryotrophic factors on mouse embryo development

Mouse embryos at different stages of development were cocultured with human oviduct cells or cultured in the presence of oviduct-derived embryotrophic factor-1, -2, and -3 (ETF-1, -2, and -3) for various amounts of time within the preimplantation period. Cocultures that included the period from 48 to 72 h post-hCG stimulated cell division and increased the cell numbers in the inner cell mass (ICM) of the exposed blastocyst. Exposure of embryos to oviductal cells from 96 to 120 h post-hCG increased the cell number in the trophectoderm (TE), blastocyst size, hatching rate, attachment, and in vitro spreading of the blastocyst. ETF-1 and ETF-2 affected embryos between 48 and 72 h post-hCG by increasing the number of cells in the ICM. In contrast, ETF-3 had a more profound effect on embryos that were exposed from 96 to 120 h post-hCG, where it mostly affected the development of TE cells, leading to higher hatching rate. Human oviductal cells improved mouse embryo development partly by the production of high molecular weight embryotrophic factors. These factors had differential effects on mouse embryo development.

The influence of growth factors on the development of preimplantation mammalian embryos

The development of the preimplantation mammalian embryo from a fertilized egg to a blastocyst capable of implanting in the uterus is a complex process. Cell division must be carefully programmed. The embryonic genome must be activated at the appropriate stage of development, and the pattern of gene expression must be carefully coordinated for the initiation of the correct program of differentiation. Cell fates must be chosen to establish specific cell types such as the inner cell mass and the trophectoderm, which give rise to the embryo proper and the placenta, respectively. This review summarizes recent findings concerning the influence of growth factors on the development of preimplantation mammalian embryos. Maternal factors secreted into the lumen of the female reproductive tract as well as substances synthesized by the developing embryo itself help to regulate this process. Studies of embryos in culture and investigations using homologous recombination to create embryos and animals null for specific genes have enabled the identification of several growth factors that appear essential for preimplantation mammalian embryo development. Some of the factors are required maternal factors; others are embryo-derived autocrine and paracrine factors. Studies using molecular biology are beginning to identify differences in the patterns of genes expressed by naturally derived embryos and those developing in culture. The knowledge gained from studies on growth factors, media, embryonic development, and gene expression should help improve culture conditions for embryos and will provide for safer outcomes from assisted reproductive procedures in human and animal clinics.

The developmental competence of mammalian oocytes: a convenient but biologically fuzzy concept

Oocyte developmental competence is often used to qualify in vitro procedures for embryo production. It supposedly accounts for the oocyte's ability to develop into a normal, viable and fertile offspring after fertilization, but for practical reasons it often characterizes the ability of such oocytes to develop to the blastocyst stage in vitro. Molecular tools compatible with the analysis of very small amounts of material have resulted in research aimed at designing molecular criteria to define this competence. However we feel that such research strategies easily lead to misunderstanding of the regulative processes that drive embryo development. Artificially induced blastocyst stage is a poor predictor of oocyte developmental competence. However preimplantation stages also appear to be sensitive to environmental conditions that can induce long-lasting detrimental effects. Larger scale analysis now made available by a functional genomics approach provides a more accurate understanding of the complex regulative networks that sustain the molecular mechanisms responsible for normal development. We propose that the concept of developmental competence should be used more cautiously and also should refer more explicitly to the experimental context it intends to enlighten.

Onset of zygotic transcription and maternal transcript legacy in the rabbit embryo

Onset of zygotic transcription is progressive from the one-cell stage onward in the rabbit embryo. Maternal transcripts remain fairly stable until the 8-16 cell stage when major transcriptional activation of the zygotic genome takes place. To understand the mechanisms of the maternal-to-zygotic transition in the genetic information governing development, we asked whether a progressive synthesis of zygotic transcripts takes over the maternal molecules, or whether the synthesis of zygotic transcripts is very abrupt and independent of the persistence of the maternal counterparts. To answer this question, we set up mRNA differential display experiments comparing the mRNA content of rabbit embryos at different stages during the preimplantation period. We isolated eight zygotic transcripts whose synthesis is abruptly turned on at the 8-16 cell stage. These transcripts are involved in general cellular metabolism and their maternal counterparts are still present up to the four-cell and even the 8-16 cell stage. This identification of early zygotic transcripts suggests that global long range modifications of chromatin structure result in a rapid increase in transcription rates during the major transcriptional activation of the zygotic genome.

Epidermal growth factor receptor and ligands in elongating bovine blastocysts

Preimplantation development depends on multiple interactions between mother and embryo. The Epidermal Growth Factor Receptor (EGF-R) and its ligands are potential components of the embryo-maternal cross-talk: Employing RT-PCR, in situ hybridization, and immunohistochemistry, we investigated on mRNA and protein level the expression of EGF-R, Epidermal Growth Factor (EGF), Transforming Growth Factor alpha (TGF-alpha), and Heparin-binding EGF-like Growth Factor (HB-EGF) in spherical and elongating bovine blastocysts between day 13 and day 16 of gestation, and in endometrium at day 13 of gestation. EGF-R mRNA and protein were detected in trophoblast and endoderm cells of all blastocyst stages that were studied, and in luminal and some glandular epithelial cells of the endometrium at day 13. EGF protein was detected in both blastocysts and endometrial epithelium. TGF-alpha transcripts and protein were present in blastocysts prior to and after elongation and in uterine glandular and luminal epithelium at day 13 of gestation. HB-EGF mRNA and protein was shown in the endoderm, and the protein also was detected immunohistochemically in about 45% of the blastocysts. This presence of the EGF receptor-ligand system in the endometrium and the preimplantation embryo at the time of blastocyst elongation suggests an important role for these growth factors during bovine preimplantation development.

Increased incidence of apoptosis in transforming growth factor alpha-deficient mouse blastocysts

We previously demonstrated that exogenous transforming growth factor alpha (TGFalpha) reduces the incidence of apoptosis in mouse blastocysts that develop in vitro but does not result in an increase in cell number or the incidence of development to the blastocyst stage. Thus, TGFalpha may function as a cell survival factor in the preimplantation mouse embryo. To extend these studies, we have now examined the development of TGFalpha-deficient preimplantation embryos in vitro and in vivo in TGFalpha-deficient mothers. We found that in both instances the incidence of apoptosis is dramatically increased in the TGFalpha-deficient blastocysts and that this increase is essentially restricted to the cells of the inner cell mass when the embryos develop in vivo but extends to the trophectoderm cells for embryos that develop in vitro. The absence of endogenous TGFalpha has little effect on the incidence of development to the blastocyst stage and cell number, cell lineage allocation, blastocoel volume, and the timing and incidence of hatching in these blastocysts, when compared to wild-type embryos. These results buttress our previous suggestion that TGFalpha functions as a cell survival factor in the preimplantation mouse embryo.

Ethanol-induced intracellular calcium mobilization rapidly alters gene expression in the mouse blastocyst

The induction of intracellular Ca2+ release in pre-implantation mouse embryos accelerates their subsequent rate of development in vitro through a calmodulin-dependent mechanism [Stachecki J.J., Armant D.R. Transient release of calcium from inositol 1,4,5-trisphosphate-specific stores regulates mouse pre-implantation development. Development 1996; 122: 2485-2496]. To examine the hypothesis that intracellular Ca2+ signaling alters embryonic gene expression, individual transcript levels were compared by mRNA differential display before and 1 h after intracellular Ca2+ mobilization with ethanol in mouse blastocysts. Ten up-regulated and four down-regulated genes were observed, representing 3.5% of approximately 400 transcripts that were resolved. After sequencing, most of the DNA fragments appeared to be novel; however, two amplicons that increased after Ca2+ mobilization were identified as arginase and ubiquitin conjugating enzyme (E2). The up-regulation of arginase mRNA (3.5-fold after 2 h) was confirmed by reverse transcription and the polymerase chain reaction using specific oligonucleotide primers derived from the deduced mouse embryo sequence. A corresponding 2.5-fold increase in arginase enzymatic activity peaked 9 h after ethanol exposure. Increased expression of arginase and other genes may mediate the onset of rapid cell proliferation and differentiation that is induced by Ca2+ signaling during pre-implantation development.

Identification of maternal transcripts that progressively disappear during the cleavage period of rabbit embryos

In order to characterize the changes that occur in the population of maternally inherited transcripts before the transition from maternal to zygotic control of embryonic development (MZT) in mammals, we used rabbit embryos where zygotic transcription becomes necessary only after the fourth cleavage division, during the second day that follows fertilization. In the present work we have associated mRNA differential display and an RT-PCR based-method that allows amplification of the whole population of messengers to identify and characterize maternal transcripts which are degraded throughout this early period of development. While there is no major degradation of the polyA RNA population before MZT we identify 4 transcripts which progressively disappear up until the 8-16 cell stage. We also show that the degradation of one of these maternal messengers is controlled by zygotic transcription, which is not the case for the three others. This messenger shows homology with the human FGF9 gene and is potentially a good candidate to address the question of the molecular control of maternal to zygotic transition in early mammalian embryogenesis.