Cell lineage-specific signaling of insulin and insulin-like growth factor I in rabbit blastocysts

Time-aligned hourglass gastrulation models in rabbit and mouse

The hourglass model describes the convergence of species within the same phylum to a similar body plan during development; however, the molecular mechanisms underlying this phenomenon in mammals remain poorly described. Here, we compare rabbit and mouse time-resolved differentiation trajectories to revisit this model at single-cell resolution. We modeled gastrulation dynamics using hundreds of embryos sampled between gestation days 6.0 and 8.5 and compared the species using a framework for time-resolved single-cell differentiation-flows analysis. We find convergence toward similar cell-state compositions at E7.5, supported by the quantitatively conserved expression of 76 transcription factors, despite divergence in surrounding trophoblast and hypoblast signaling. However, we observed noticeable changes in specification timing of some lineages and divergence of primordial germ cell programs, which in the rabbit do not activate mesoderm genes. Comparative analysis of temporal differentiation models provides a basis for studying the evolution of gastrulation dynamics across mammals.

Effects of fetal bovine serum on trophectoderm and primitive endoderm cell allocation of in vitro-produced bovine embryos

Supplementing embryonic culture medium with fetal bovine serum (FBS) renders this medium undefined. Glucose and growth factors present in FBS may affect the results of cell differentiation studies. This study tested the hypothesis that FBS supplementation during in vitro culture (IVC) alters cell differentiation in early bovine embryo development. Bovine embryos were produced in vitro and randomly distributed into three experimental groups at 90 h post insemination (90 hpi): the KSOM-FBS group, which consisted of a 5% (v/v) FBS supplementation; the KSOM33 group, with the renewal of 33% of medium volume; and the KSOM-Zero group, without FBS supplementation nor renewal of the culture medium. The results showed that the blastocyst rate (blastocyst/oocytes) at 210 hpi in the KSOM-FBS group was higher than in the KSOM-Zero group but not different from the KSOM33 group. There were no significant changes in metabolism-related aspects, such as fluorescence intensities of CellROX Green and MitoTracker Red or reduced nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD+). Immunofluorescence analysis of CDX2 revealed that the lack of FBS or medium supplementation reduced the number of trophectoderm (TE) cells and total cells. Immunofluorescence analysis revealed a reduction of SOX17-positive cell numbers after FBS supplementation compared with the KSOM33 group. Therefore, we concluded that FBS absence reduced blastocyst rates; however, no reduction occurred when there was a 33% volume renewal of the medium at 90 hpi. We also concluded that FBS supplementation altered TE and primitive endoderm cell allocation during early bovine embryo development.

Identification of the Inner Cell Mass and the Trophectoderm Responses after an In Vitro Exposure to Glucose and Insulin during the Preimplantation Period in the Rabbit Embryo

The prevalence of metabolic diseases is increasing, leading to more women entering pregnancy with alterations in the glucose-insulin axis. The aim of this work was to investigate the effect of a hyperglycemic and/or hyperinsulinemic environment on the development of the preimplantation embryo. In rabbit embryos developed in vitro in the presence of high insulin (HI), high glucose (HG), or both (HGI), we determined the transcriptomes of the inner cell mass (ICM) and the trophectoderm (TE). HI induced 10 differentially expressed genes (DEG) in ICM and 1 in TE. HG ICM exhibited 41 DEGs involved in oxidative phosphorylation (OXPHOS) and cell number regulation. In HG ICM, proliferation was decreased (p < 0.01) and apoptosis increased (p < 0.001). HG TE displayed 132 DEG linked to mTOR signaling and regulation of cell number. In HG TE, proliferation was increased (p < 0.001) and apoptosis decreased (p < 0.001). HGI ICM presented 39 DEG involved in OXPHOS and no differences in proliferation and apoptosis. HGI TE showed 16 DEG linked to OXPHOS and cell number regulation and exhibited increased proliferation (p < 0.001). Exposure to HG and HGI during preimplantation development results in common and specific ICM and TE responses that could compromise the development of the future individual and placenta.

Insulin-like growth factor system components expressed at the conceptus-maternal interface during the establishment of equine pregnancy

In many species, the insulin-like growth factors (IGF1 and IGF2), their receptors and IGF binding proteins play important roles in preparing the endometrium for implantation, and regulating conceptus growth and development. To determine whether the IGF system may contribute to conceptus-maternal interaction during equine pre-implantation development, we evaluated mRNA expression for IGF system components in conceptuses, and endometrium recovered from pregnant and cycling mares, on days 7, 14, 21 and 28 after ovulation. We also investigated expression of IGF1, IGF2 and their receptors 6 and 11 days after transfer of day 8 embryos to synchronous (day 8) or asynchronous (day 3) recipient mares. Expression of IGF1 and IGF2, IGF1R, IGF2R, INSR and IGFBPs 1, 2, 4 and 5 was evident in endometrium and conceptus membranes during days 7–28. Endometrial IGF2, INSR, IGFBP1 and IGFBP2 expression increased between days 7 and 28 of pregnancy. In conceptus membranes, expression of all IGF system components increased with developmental stage. Immunohistochemistry revealed strong expression of IGF1, IGF2 and IGF1R in both endometrium and conceptus membranes, whereas INSR was highly expressed in endometrium but barely detectable in the conceptus. Finally, a negatively asynchronous uterine environment retarded IGF1, IGF2 and INSR expression in the conceptus, whereas in the endometrium only INSR expression was altered by asynchrony. The presence of IGFs, their receptors and IGFBPs in the endometrium and conceptus during early equine pregnancy, and down-regulation in the conceptus following asynchronous embryo transfer, suggest a role in conceptus-maternal communication during the preparation for implantation.

Protein kinase Akt2/PKBβ is involved in blastomere proliferation of preimplantation mouse embryos

Activation of Akt/Protein Kinase B (PKB) by phosphatidylinositol-3-kinase (PI3K) controls several cellular functions largely studied in mammalian cells, including preimplantation embryos. We previously showed that early mouse embryos inherit active Akt from oocytes and that the intracellular localization of this enzyme at the two-cell stage depends on the T-cell leukemia/lymphoma 1 oncogenic protein, Tcl1. We have now investigated whether Akt isoforms, namely Akt1, Akt2 and Akt3, exert a specific role in blastomere proliferation during preimplantation embryo development. We show that, in contrast to other Akt family members, Akt2 enters male and female pronuclei of mouse preimplantation embryos at the late one-cell stage and thereafter maintains a nuclear localization during later embryo cleavage stages. Depleting one-cell embryos of single Akt family members by microinjecting Akt isoform-specific antibodies into wild-type zygotes, we observed that: (a) Akt2 is necessary for normal embryo progression through cleavage stages; and (b) the specific nuclear targeting of Akt2 in two-cell embryos depends on Tcl1. Our results indicate that preimplantation mouse embryos have a peculiar regulation of blastomere proliferation based on the activity of the Akt/PKB family member Akt2, which is mediated by the oncogenic protein Tcl1. Both Akt2 and Tcl1 are essential for early blastomere proliferation and embryo development.

Trophoblastic microRNAs are downregulated in a diabetic pregnancy through an inhibition of Drosha

MicroRNAs are promising biological markers for prenatal diagnosis. They regulate placental development and are present in maternal plasma. Maternal metabolic diseases are major risk factors for placental deterioration. We analysed the influence of a maternal insulin-dependent diabetes mellitus on microRNA expression in maternal plasma and in blastocysts employing an in vivo rabbit diabetic pregnancy model and an in vitro embryo culture in hyperglycaemic and hypoinsulinaemic medium. Maternal diabetes led to a marked downregulation of Dicer protein in embryoblast cells and Drosha protein in trophoblast cells. MiR-27b, miR-141 and miR-191 were decreased in trophoblast cells and in maternal plasma of diabetic rabbits. In vitro studies indicate, that maternal hyperglycaemia and hypoinsulinaemia partially contribute to the downregulation of trophoblastic microRNAs. As the altered microRNA expression was detectable in maternal plasma, too, the plasma microRNA signature could serve as an early biological marker for the prediction of trophoblast function during a diabetic pregnancy.

Building Principles for Constructing a Mammalian Blastocyst Embryo

The self-organisation of a fertilised egg to form a blastocyst structure, which consists of three distinct cell lineages (trophoblast, epiblast and hypoblast) arranged around an off-centre cavity, is unique to mammals. While the starting point (the zygote) and endpoint (the blastocyst) are similar in all mammals, the intervening events have diverged. This review examines and compares the descriptive and functional data surrounding embryonic gene activation, symmetry-breaking, first and second lineage establishment, and fate commitment in a wide range of mammalian orders. The exquisite detail known from mouse embryogenesis, embryonic stem cell studies and the wealth of recent single cell transcriptomic experiments are used to highlight the building principles underlying early mammalian embryonic development.

Iloprost supports early development of in vitro-produced porcine embryos through activation of the phosphatidylinositol 3-kinase/AKT signalling pathway

Despite evidence of the presence of prostaglandin (PG) I₂ in mammalian oviducts, its role in early development of in vitro-produced (IVP) embryos is largely unknown. Thus, in the present study we examined the effects of iloprost, a PGI₂ analogue, on the in vitro developmental competence of early porcine embryos and the underlying mechanism(s). To examine the effects of iloprost on the development rate of IVF embryos, iloprost was added to the in vitro culture (IVC) medium and cultured for 6 days. Supplementation of the IVC medium with iloprost significantly improved developmental parameters, such as blastocyst formation rate, the trophectoderm:inner cell mass ratio and cell survival in IVF and parthenogenetically activated (PA) embryos. In addition, post-blastulation development into the expanded blastocyst stage was improved in iloprost-treated groups compared with controls. Interestingly, the phosphatidylinositol 3-kinase (PI3K)/AKT signalling pathway was significantly activated by iloprost supplementation in a concentration-dependent manner (10-1000nM), and the beneficial effects of iloprost on the early development of porcine IVF and PA embryos was completely ablated by treatment with 2.5μM wortmannin, a PI3K/AKT signalling inhibitor. Importantly, expression of the PI3K/AKT signalling pathway was significantly reduced in somatic cell nuclear transfer (SCNT) compared with IVF embryos, and iloprost supported the early development of SCNT embryos, as was the case for IVF and PA embryos, suggesting a consistent effect of iloprost on the IVC of IVP porcine embryos. Together, these results indicate that iloprost can be a useful IVC supplement for production of IVP early porcine embryos with high developmental competence.

Overexpression of Hepatocyte Growth Factor mRNA Induced by Gene Transfer Attenuates Neointimal Hyperplasia After Balloon Injury

Hepatic growth factor (HGF) has been widely used in studies on arterial remodeling after injury, and results turn out to be inconsistent. The changes of endogenous HGF expression after injury also remain controversial. This study clarified the role of exogenous human HGF (hHGF) gene transfer in neointimal hyperplasia and investigated the associated alterations of endogenous HGF and c-Met expressions under endothelial denudation with or without hHGF gene transfer using a balloon-injured rabbit aorta model. Sixty-one rabbits were randomly divided into normal controls, endothelial injury, endothelial injury with hHGF, or the control vector gene transfer groups. On weeks 1, 2, 4, and 8 after injury, neointimal hyperplasia and endothelialization were evaluated by the ratio of neointimal area to medial area (N/M ratio), CD31-positive staining, α-smooth muscle actin, and endothelial nitric oxide synthase expressions using histological analysis, immunohistochemistry staining, or real-time quantitative reverse transcriptase polymerase chain reaction. Endogenous rabbit HGF (rHGF) and c-Met expressions were detected with immunohistochemistry staining and quantitative reverse transcriptase polymerase chain reaction. It was found that expressions of endogeneous rHGF and c-Met in endothelial injury upregulated with peak levels on week 2 or week 4 after injury (p < 0.01). On week 1 after hHGF transfer, neointimal hyperplasia was significantly inhibited (p < 0.001), with decreased α-smooth muscle actin expression (p < 0.05) and improved endothelial cells regeneration and function (p < 0.01). More remarkable overexpression of endogenous rHGF and c-Met mRNAs were detected, and lowered positive staining of rHGF and c-Met was shown in the neointima (p < 0.05). These results demonstrated hHGF gene transfer induced further overexpression of endogenous rHGF and c-Met mRNAs but lowered immunoreactivities of rHGF and c-Met in the neointima, thus leading to significant attenuation of neointimal hyperplasia.

Exogenous growth factors do not affect the development of individually cultured murine embryos

PURPOSE

The objective of this study was to evaluate the effects of multiple growth factors on the development of individually cultured murine embryos.

METHODS

Embryos produced by in vitro fertilization using in vitro (IVM) or in vivo (IVO) matured oocytes from three strains of mice (CF1, Swiss Webster, B6D2F1) were cultured individually (10 μl) in the absence (control) or presence of growth factors (paf, epidermal growth factor [EGF], insulin-like growth factor 1 [IGF-1], and granulocyte-macrophage colony-stimulating factor [GM-CSF]). Blastocyst formation, hatching, and blastocyst cell numbers (trophectoderm, inner cell mass, and total) were evaluated on days 4 and 5 of culture. Post-hatching development of CF1 IVO embryos was also evaluated in vitro and in vivo.

RESULTS

The presence of growth factors did not improve the proportion of embryos forming blastocysts or initiating hatching for any of the types of embryos tested. The only significant (P < 0.05) effect of growth factors was a decrease in the proportion of embryos that formed blastocysts by day 5 in CF1 IVM embryos. The presence of growth factors also did not affect blastocyst cell numbers. For CF1 IVO embryos, the presence of growth factors during culture did not affect the proportion of embryos that attached to fibronectin-coated dishes, the size of the resulting outgrowths, or in vivo development following transfer.

CONCLUSION

Combinations of paf, EGF, GM-CSF, and IGF-1 did not improve development of murine embryos cultured individually in a sequential medium containing a defined protein source.

Hydrogen prevents corneal endothelial damage in phacoemulsification cataract surgery

In phacoemulsification, ultrasound induces hydroxyl radical (·OH) formation, damaging corneal endothelium. Whether H2 can prevent such oxidative damage in phacoemulsification was examined by in vitro and in vivo studies. H2 was dissolved in a commercial irrigating solution. The effects of H2 against ·OH generation were first confirmed in vitro by electron-spin resonance (ESR) and hydroxyphenyl fluorescein (HPF). ESR showed a significantly decreased signal magnitude, and fluorescence intensity by oxidized HPF was significantly less in the H2-dissolved solution. The effects of H2 in phacoemulsification were evaluated in rabbits, comparing H2-dissolved and control solutions. Five hours after the procedure, the whole cornea was excised and subjected to image analysis for corneal edema, real-time semiquantitative PCR (qPCR) for heme oxygenase (HO)-1, catalase (CAT), superoxide dismutase 1 (SOD1), and SOD2 mRNA, and immunohistochemistry. Corneal edema was significantly less and the increases in anti-oxidative HO-1, CAT and SOD2 mRNA expressions were significantly suppressed in the H2 group. In addition, corneal endothelial cell expressions of two oxidative stress markers, 4-HNE and 8-OHdG, were significantly lower in the H2 group. In conclusion, H2 dissolved in the ocular irrigating solution protected corneal endothelial cells from phacoemulsification-induced oxidative stress and damage.

Autocrine embryotropins revisited: how do embryos communicate with each other in vitro when cultured in groups?

In the absence of the maternal genital tract, preimplantation embryos can develop in vitro in culture medium where all communication with the oviduct or uterus is absent. In several mammalian species, it has been observed that embryos cultured in groups thrive better than those cultured singly. Here we argue that group-cultured embryos are able to promote their own development in vitro by the production of autocrine embryotropins that putatively serve as a communication tool. The concept of effective communication implies an origin, a signalling agent, and finally a recipient that is able to decode the message. We illustrate this concept by demonstrating that preimplantation embryos are able to secrete autocrine factors in several ways, including active secretion, passive outflow, or as messengers bound to a molecular vehicle or transported within extracellular vesicles. Likewise, we broaden the traditional view that inter-embryo communication is dictated mainly by growth factors, by discussing a wide range of other biochemical messengers including proteins, lipids, neurotransmitters, saccharides, and microRNAs, all of which can be exchanged among embryos cultured in a group. Finally, we describe how different classes of messenger molecules are decoded by the embryo and influence embryo development by triggering different pathways. When autocrine embryotropins such as insulin-like growth factor-I (IGF-I) or platelet activating factor (PAF) bind to their appropriate receptor, the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) pathway will be activated which is important for embryo survival. On the other hand, the mitogen-activated protein kinase (MAPK) pathway is activated when compounds such as hyaluronic acid and serotonin bind to their respective receptors, thereby acting as growth factors. By activating the peroxisome-proliferator-activated receptor family (PPAR) pathway, lipophilic autocrine factors such as prostaglandins or fatty acids have both survival and anti-apoptotic functions. In conclusion, considering different types of messenger molecules simultaneously will be crucial to understanding more comprehensively how embryos communicate with each other in group-culture systems. This approach will assist in the development of novel media for single-embryo culture.

Maternal Diabetes Leads to Adaptation in Embryonic Amino Acid Metabolism during Early Pregnancy

During pregnancy an adequate amino acid supply is essential for embryo development and fetal growth. We have studied amino acid composition and branched chain amino acid (BCAA) metabolism at day 6 p.c. in diabetic rabbits and blastocysts. In the plasma of diabetic rabbits the concentrations of 12 amino acids were altered in comparison to the controls. Notably, the concentrations of the BCAA leucine, isoleucine and valine were approximately three-fold higher in diabetic rabbits than in the control. In the cavity fluid of blastocysts from diabetic rabbits BCAA concentrations were twice as high as those from controls, indicating a close link between maternal diabetes and embryonic BCAA metabolism. The expression of BCAA oxidizing enzymes and BCAA transporter was analysed in maternal tissues and in blastocysts. The RNA amounts of three oxidizing enzymes, i.e. branched chain aminotransferase 2 (Bcat2), branched chain ketoacid dehydrogenase (Bckdha) and dehydrolipoyl dehydrogenase (Dld), were markedly increased in maternal adipose tissue and decreased in liver and skeletal muscle of diabetic rabbits than in those of controls. Blastocysts of diabetic rabbits revealed a higher Bcat2 mRNA and protein abundance in comparison to control blastocysts. The expression of BCAA transporter LAT1 and LAT2 were unaltered in endometrium of diabetic and healthy rabbits, whereas LAT2 transcripts were increased in blastocysts of diabetic rabbits. In correlation to high embryonic BCAA levels the phosphorylation amount of the nutrient sensor mammalian target of rapamycin (mTOR) was enhanced in blastocysts caused by maternal diabetes. These results demonstrate a direct impact of maternal diabetes on BCAA concentrations and degradation in mammalian blastocysts with influence on embryonic mTOR signalling.

Vitrification alters rabbit foetal placenta at transcriptomic and proteomic level

Although numerous studies have demonstrated that cryopreservation alters gene expression, less is known about those embryos that implanted successfully and continued in gestation. To raise the question of the neutrality of this technique, we examine the effects of vitrification through gestation in rabbit before and after the implantation. We monitored the distribution of losses of 569 vitrified morulae, observing that embryos which reach the last pre-implantatory stage are able to implant. However, we found that not all implanted embryos had the ability to continue with their gestation. The results reveal that vitrification decreased foetus and maternal placenta weights at mid-gestation, but led to a higher offspring birth weight. A novel finding is that while no differences in gene expression were detected in pre-implantatory embryos at day 6, vitrification affects a gene and protein expression in the placenta at day 14. Our results for first time reveal strong evidence of modifications in implanted embryos subjected to vitrification, suggesting that the crucial step that vitrified embryos must overcome is the placenta formation. On the basis of these findings, our work leaves the question open as to whether the effects we observed that cause vitrification during foetal development could give rise to some type of physiological or metabolic alteration in adulthood.

Oviductal and endometrial mRNA expression of implantation candidate biomarkers during early pregnancy in rabbit

Prenatal losses are a complex problem. Pregnancy requires orchestrated communication between the embryo and the uterus that includes secretions from the embryo to signal pregnancy recognition and secretion and remodelling from the uterine epithelium. Most of these losses are characterized by asynchronization between embryo and uterus. To better understand possible causes, an analysis was conducted of gene expression of a set of transcripts related to maternal recognition and establishment of rabbit pregnancy (uteroglobin,SCGB1A1; integrin α1,ITGA1; interferon-γ,IFNG; vascular endothelial growth factor,VEGF) in oviduct and uterine tissue at 16, 72 or 144 h post-ovulation and insemination. In the oviduct tissue, a significant decrease in the level ofSCGB1A1mRNA expression was observed from 144 h post-ovulation. In the case ofITGA1, the transcript abundance was initially lower, but mRNA expression increased significantly at 72 and 144 h post-ovulation. ForIFNG, a huge decrease was observed from 16 to 72 h post-ovulation. Finally, no significant differences were observed in theVEGFtranscript. For the endometrium, the results showed a significant decline in the level ofSCGB1A1mRNA expression from 16 to 144 h post-ovulation induction. The highest levels ofITGA1transcript were detected at 144 h, followed by the 16 h group and lower at 72 h post-ovulation. ForIFNGthere were no significant differences among post-ovulation induction times. Finally, it was possible to observe thatVEGFmRNA abundance was present at low levels at 16 h post-ovulation and remained low at 72 h, but increased at 144 h. The functional significance of these observations may provide new insights into the maternal role in prenatal losses.

cAMP-responsive element binding protein: a vital link in embryonic hormonal adaptation

The transcription factor cAMP responsive element-binding protein (CREB) and activating transcription factors (ATFs) are downstream components of the insulin/IGF cascade, playing crucial roles in maintaining cell viability and embryo survival. One of the CREB target genes is adiponectin, which acts synergistically with insulin. We have studied the CREB-ATF-adiponectin network in rabbit preimplantation development in vivo and in vitro. From the blastocyst stage onwards, CREB and ATF1, ATF3, and ATF4 are present with increasing expression for CREB, ATF1, and ATF3 during gastrulation and with a dominant expression in the embryoblast (EB). In vitro stimulation with insulin and IGF-I reduced CREB and ATF1 transcripts by approximately 50%, whereas CREB phosphorylation was increased. Activation of CREB was accompanied by subsequent reduction in adiponectin and adiponectin receptor (adipoR)1 expression. Under in vivo conditions of diabetes type 1, maternal adiponectin levels were up-regulated in serum and endometrium. Embryonic CREB expression was altered in a cell lineage-specific pattern. Although in EB cells CREB localization did not change, it was translocated from the nucleus into the cytosol in trophoblast (TB) cells. In TB, adiponectin expression was increased (diabetic 427.8 ± 59.3 pg/mL vs normoinsulinaemic 143.9 ± 26.5 pg/mL), whereas it was no longer measureable in the EB. Analysis of embryonic adipoRs showed an increased expression of adipoR1 and no changes in adipoR2 transcription. We conclude that the transcription factors CREB and ATFs vitally participate in embryo-maternal cross talk before implantation in a cell lineage-specific manner. Embryonic CREB/ATFs act as insulin/IGF sensors. Lack of insulin is compensated by a CREB-mediated adiponectin expression, which may maintain glucose uptake in blastocysts grown in diabetic mothers.

Discovery of pluripotency-associated microRNAs in rabbit preimplantation embryos and embryonic stem-like cells

MicroRNAs (miRNAs) are small non-coding RNAs that regulate multiple biological processes. Increasing experimental evidence implies an important regulatory role of miRNAs during embryonic development and in embryonic stem (ES) cell biology. In the current study, we have described and analyzed the expression profile of pluripotency-associated miRNAs in rabbit embryos and ES-like cells. The rabbit specific ocu-miR-302 and ocu-miR-290 clusters, and three homologs of the human C19MC cluster (ocu-miR-512, ocu-miR-520e, and ocu-miR-498) were identified in rabbit preimplantation embryos and ES-like cells. The ocu-miR-302 cluster was highly similar to its human homolog, while ocu-miR-290 revealed a low level of evolutionary conservation with its mouse homologous cluster. The expression of the ocu-miR-302 cluster began at the 3.5 days post-coitum early blastocyst stage and they stayed highly expressed in rabbit ES-like cells. In contrast, a high expression level of the ocu-miR-290 cluster was detected during preimplantation embryonic development, but a low level of expression was found in rabbit ES-like cells. Differential expression of the ocu-miR-302 cluster and ocu-miR-512 miRNA was detected in rabbit trophoblast and embryoblast. We also found that Lefty has two potential target sites in its 3′UTR for ocu-miR-302a and its expression level increased upon ocu-miR-302a inhibition. We suggest that the expression of the ocu-miR-302 cluster is characteristic of the rabbit ES-like cell, while the ocu-miR-290 cluster may play a crucial role during early embryonic development. This study presents the first identification, to our knowledge, of pluripotency-associated miRNAs in rabbit preimplantation embryos and ES-like cells, which can open up new avenues to investigate the regulatory function of ocu-miRNAs in embryonic development and stem cell biology.

Insulin growth factor adjustment in preimplantation rabbit blastocysts and uterine tissues in response to maternal type 1 diabetes

Insulin-like growth factors (IGFs) are well-known regulators of embryonic growth and differentiation. IGF function is closely related to insulin action. IGFs are available to the preimplantation embryo through maternal blood (endocrine action), uterine secretions (paracrine action) and by the embryo itself (autocrine action). In rabbit blastocysts, embryonic IGF1 and IGF2 are specifically strong in the embryoblast (ICM). Signalling of IGFs and insulin in blastocysts follows the classical pathway with Erk1/2 and Akt kinase activation. The aim of this study was to analyse signalling of IGFs in experimental insulin dependent diabetes (exp IDD) in pregnancy, employing a diabetic rabbit model with uterine hypoinsulinemia and hyperglycaemia. Exp IDD was induced in female rabbits by alloxan treatment prior to mating. At 6 days p.c., the maternal and embryonic IGFs were quantified by RT-PCR and ELISA. In pregnant females, hepatic IGF1 expression and IGF1 serum levels were decreased while IGF1 and IGF2 were increased in endometrium. In blastocysts, IGF1 RNA and protein was approx. 7.5-fold and 2-fold higher, respectively, than in controls from normoglycemic females. In cultured control blastocysts supplemented with IGF1 or insulin in vitro for 1 or 12 h, IGF1 and insulin receptors as well as IGF1 and IGF2 were downregulated. In cultured T1D blastocysts activation of Akt and Erk1/2 was impaired with lower amounts of total Akt and Erk1/2 protein and a reduced phosphorylation capacity after IGF1 supplementation. Our data show that the IGF axis is severely altered in embryo-maternal interactions in exp IDD pregnancy. Both, the endometrium and the blastocyst produce more IGF1 and IGF2. The increased endogenous IGF1 and IGF2 expression by the blastocyst compensates for the loss of systemic insulin and IGF. However, this counterbalance does not fill the gap of the reduced insulin/IGF sensitivity, leading to a developmental delay of blastocysts in exp IDD pregnancy.

Rabbit as a reproductive model for human health

The renaissance of the laboratory rabbit as a reproductive model for human health is closely related to the growing evidence of periconceptional metabolic programming and its determining effects on offspring and adult health. Advantages of rabbit reproduction are the exact timing of fertilization and pregnancy stages, high cell numbers and yield in blastocysts, relatively late implantation at a time when gastrulation is already proceeding, detailed morphologic and molecular knowledge on gastrulation stages, and a hemochorial placenta structured similarly to the human placenta. To understand, for example, the mechanisms of periconceptional programming and its effects on metabolic health in adulthood, these advantages help to elucidate even subtle changes in metabolism and development during the pre- and peri-implantation period and during gastrulation in individual embryos. Gastrulation represents a central turning point in ontogenesis in which a limited number of cells program the development of the three germ layers and, hence, the embryo proper. Newly developed transgenic and molecular tools offer promising chances for further scientific progress to be attained with this reproductive model species.

Survival signaling in the preimplantation embryo

The autopoietic development of the preimplantation embryo may in part be explained by the actions of autocrine tropic ligands. The net effect of these mediators is to support the survival of cells within the early embryo. In the mouse, the actions of autocrine ligands are required by the 2-cell stage of development, and they can act in concert with paracrine mediators present within the reproductive tract. These mediators act via 1-o-phosphatidylinositol-3-kinase signaling which has the dual effects of activating calcium/calmodulin-dependent kinase/CREB transcription factor and AKT (protein kinase B)/MDM2 mediated survival pathways. The activated CREB drives transcription of prosurvival effectors, including the proto-oncogenes c-Fos and Bcl2. The AKT induces the phosphorylation and activation of MDM2 which causes the ubiquitination and resultant degradation of P53 resulting in the latency of P53 action. Tropic signals provide coordinated mechanisms for maintaining the survival of the cells of the early embryo. Disturbance of survival signaling has the net effect of reducing the number of cells populating the early embryo, due in part to the P53-mediated reduction in the pluripotent inner cell mass stem cell population within the embryo. The resultant embryos have a markedly reduced capacity for development beyond the implantation stage and those that do implant tend to be anembryonic.

Metabolism of the preimplantation embryo: 40 years on

This review considers how our understanding of preimplantation embryo metabolism has progressed since the pioneering work on this topic in the late 1960s and early 1970s. Research has been stimulated by a desire to understand how metabolic events contribute to the development of the zygote into the blastocyst, the need for biomarkers of embryo health with which to improve the success of assisted conception technologies, and latterly by the ‘Developmental Origins of Health and Disease’ (DOHaD) concept. However, arguably, progress has not been as great as it might have been due to methodological difficulties in working with tiny amounts of tissue and the low priority assigned to fundamental research on fertility and infertility, with developments driven more by technical than scientific advances. Nevertheless, considerable progress has been made in defining the roles of the traditional nutrients: pyruvate, glucose, lactate, and amino acids; originally considered as energy sources and biosynthetic precursors, but now recognized as having multiple, overlapping functions. Other nutrients; notably lipids, are beginning to attract the attention they deserve. The pivotal role of mitochondria in early embryo development and the DOHaD concept, and in providing a cellular focus for metabolic events is now recognized. Some unifying ideas are discussed; namely ‘stress–response models’ and the ‘quiet embryo hypothesis’; the latter aiming to relate the metabolism of individual preimplantation embryos to their subsequent viability. The review concludes by updating the state of knowledge of preimplantation embryo metabolism in the early 1970s and listing some future research questions.

On the emerging role of rabbit as human disease model and the instrumental role of novel transgenic tools

The laboratory rabbit (Oryctolagus cuniculus) is widely used as a model for human diseases, because of its size, which permits non-lethal monitoring of physiological changes and similar disease characteristics. Novel transgenic tools such as, the zinc finger nuclease method and the sleeping beauty transposon mediated or BAC transgenesis were recently adapted to the laboratory rabbit and opened new opportunities in precise tissue and developmental stage specific gene expression/silencing, coupled with increased transgenic efficiencies. Many facets of human development and diseases cannot be investigated in rodents. This is especially true for early prenatal development, its long-lasting effects on health and complex disorders, and some economically important diseases such as atherosclerosis or cardiovascular diseases. The first transgenic rabbits models of arrhythmogenesis mimic human cardiac diseases much better than transgenic mice and hereby underline the importance of non-mouse models. Another emerging field is epigenetic reprogramming and pathogenic mechanisms in diabetic pregnancy, where rabbit models are indispensable. Beyond that rabbit is used for decades as major source of polyclonal antibodies and recently in monoclonal antibody production. Alteration of its genome to increase the efficiency and value of the antibodies by humanization of the immunoglobulin genes, or by increasing the expression of a special receptor (Fc receptor) that augments humoral immune response is a current demand.

Gastrulation in rabbit blastocysts depends on insulin and insulin-like-growth-factor 1

Insulin and insulin-like-growth-factor 1 (IGF1) are components of the uterine secretions. As potent growth factors they influence early embryo development. The underlying molecular mechanisms are largely unknown. Here we report on the effects of insulin and IGF1 on early gastrulation in rabbit blastocysts. We have studied blastocysts grown in vivo in metabolically healthy rabbits, in rabbits with type 1 diabetes and in vitro in the presence or absence of insulin or IGF1. Embryonic disc morphology and expression of Brachyury, Wnt3a and Wnt4 were analysed by qPCR and IHC. Pre-gastrulated blastocysts (stage 0/1) cultured with insulin or IGF1 showed a significantly higher capacity to form the posterior mesoderm and primitive streak (stage 2 and 3) than blastocysts cultured without growth factors. In gastrulating blastocysts the levels of the mesoderm-specific transcription factor Brachyury and the Wnt signalling molecules Wnt3a and Wnt4 showed a stage-specific expression pattern with Brachyury transcripts increasing from stage 0/1 to 3. Wnt4 protein was found spread over the whole embryoblast. Insulin induced Wnt3a, Wnt4 and Brachyury expression in a temporal- and stage-specific pattern. Only blastocysts cultured with insulin reached the Wnt3a, Wnt4 and Brachyury expression levels of stage 2 in vivo blastocysts, indicating that insulin is required for Wnt3a, Wnt4 and Brachyury expression during gastrulation. Insulin-induced Wnt3a and Wnt4 expression preceded Brachyury. Wnt3a-induced expression could be depleted by MEK1 inhibition (PD98059). Involvement of insulin in embryonic Wnt3a expression was further shown in vivo with Wnt3a expression being notably down regulated in stage 2 blastocysts from rabbits with type 1 diabetes. Blastocysts grown in diabetic rabbits are retarded in development, a finding which supports our current results that insulin is highly likely required for early mesoderm formation in rabbit blastocysts by inducing a distinct spatiotemporal expression profile of Wnt3a, Wnt4 and Brachyury.

effect of embryonic genotype on reference gene selection for RT-qPCR normalization

To obtain more reliable results with biological significance, it requires data normalization using an appropriate internal control gene. In rabbits, there are classic stable reference genes that have been identified for normalization in oocytes and pre-implantation stage embryos. However, effects of embryonic genotype on reference gene selection have not been elucidated. The aim of this study was to test (i) the stability of mRNA transcription level for histone (H2afz) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) genes in rabbit blastocysts from two lines selected by different criteria (litter size and post-weaning daily weight gain) and (ii) its influence on biological significance examined by means of a set of embryonic transcripts, such as POU5F1 (Oct-4), epidermal growth factor receptor (erbB3), transforming growth factor-beta2, vascular endothelial growth factor and gamma interferon (Ifn-gamma). The geNorm, NormFinder and BestKeeper programs showed similar results, pointing out that H2afz and GAPDH were the most stable reference genes in rabbits selected on litter size at weaning. Moreover, our study revealed that embryonic genotype affected target gene expression when a single reference gene was used to analyse mRNA expression in blastocysts. Results showed that GAPDH gene is better than H2afz for gene expression studies of both embryo genotypes. A normalization factor derived from H2afz and GAPDH is likely to be appropriate when RT-qPCR was performed in rabbit embryos with different genotypes.

mRNA expression in rabbit blastocyst and endometrial tissue of candidate gene involved in gestational losses

Gestation is a complex process that involves different growth factors, cytokines and adhesion proteins related with embryo development, cellular differentiation and proliferation, embryo-endometrium interaction, angiogenesis, maternal-embryonic recognition and growth development of placenta and embryos. In this study, we examine pre-implantational (at 6 days of gestation) and gestational (at 12 days and total from ovulation to birth) losses in two rabbit lines selected by different criteria (post-weaning daily gain and litter size) and the pattern of a set of candidate transcripts, at 6 days of gestation, related with embryo development and implantation process, such as Oct-4, epidermal growth factor receptor 3 (erbB3), Transforming Growth Factor β2, Vascular Endothelial Growth Factor and Interferon γ and related with insulin-like growth factors signalling as insulin growth factors I and II and their receptors in rabbit blastocysts and endometrial tissue. Similar pre-implantational losses were obtained in both lines. However, the gestational losses of the line selected by post-weaning daily gain clearly mirrored an increase in losses by 50% at 12 days and at birth (22.4 vs 9.5 and 50.2 vs 25.4, respectively, between line selected by post-weaning daily gain and line selected by litter size). In blastocysts and endometrial tissue at 6 days of gestation qRT-PCR assays indicated that the mean insulin-like growth factor (IGF)-IIR mRNA expression was down-regulated in line selected by post-weaning daily gain. Dysregulation of the IGF-IIR could be potential reasons for induced gestational losses. We conclude that IGF-IIR gene expression in blastocyst and endometrial tissue at 6th day of gestation tends to decline in line selected by post-weaning daily gain. The functional significance related with gestational losses is uncertain.

Regulation of the expression of proto-oncogenes by autocrine embryotropins in the early mouse embryo

Autocrine embryotropins act as survival signals for the preimplantation embryo. In this study we examined the role of Paf in the transcription of the key proto-oncogenes Bcl2 and Fos. Transcripts were detected in oocytes and some cohorts of zygotes but not in cohorts of 2-cell, 8-cell, and blastocyst stage embryos. Immunolocalization of BCL2 and FOS showed little staining in oocytes and zygotes but increased staining in the embryo from the 2-cell to blastocyst stage. Paf (37 nM) treatment of 2-cell embryos caused an alpha-amanitin (26 μM)-sensitive increase in Bcl2 and Fos transcripts 20 min after treatment that subsided by 40 min. This increase was blocked by inhibition of calcium (by BAPTA-AM) or phosphatidylinositol-3-kinase signaling (by LY294002). Paf challenge also caused increased staining of BCL2 and FOS. Increased staining of FOS required new protein synthesis that had a half-life of 2-4 h after Paf challenge. Only a small proportion (∼12%) of individual 2-cell embryos collected from the reproductive tract had detectable Bcl2 and Fos. This dichotomous pattern of transcript expression is consistent with the known periodic actions of Paf (which has a periodicity of ∼90 min) and the relatively short half-life of the resulting transcripts. A BCL2 antagonist (HA14-1) caused a dose-dependent decrease in the capacity of cultured zygotes to develop to morphological blastocysts, which was partially reversed by the simultaneous addition of Paf to medium. The results show that Paf induces periodic transient transcriptions of key proto-oncogenes that result in the persistent presence of the resulting proteins in the preimplantation phase of development.

Increased apoptosis in bovine blastocysts exposed to high levels of IGF1 is not associated with downregulation of the IGF1 receptor

The hypothesis that high concentrations of IGF1 can impair embryo development was investigated in a bovine in vitro model to reflect conditions in polycystic ovary syndrome (PCOS) patients. Embryos were either cultured in the absence or presence of a physiological (100 ng/ml) or supraphysiological (1000 ng/ml) IGF1 concentration. Cell allocation, apoptosis, transcript and protein expression of selected genes involved in apoptosis, glucose metabolism and the IGF system were analysed. Supraphysiological IGF1 concentration did not improve blastocyst formation over controls, but induced higher levels of apoptosis, decreased TP53 protein expression in the trophectoderm and increased the number of cells in the inner cell mass (ICM). The increase in ICM cells corresponded with an increase in IGF1 receptor (IGF1R) protein in the ICM. A small, but significant, percentage of blastocysts displayed a hypertrophic ICM, not observed in controls and virtually absent in embryos treated with physiological concentrations of IGF1. Physiological IGF1 concentrations increased total IGF1R protein expression and upregulated IGFBP3 transcripts leading to an increase in blastocyst formation with no effects on cell number or apoptosis. In conclusion, the results support the hypothesis of detrimental effects of supraphysiological IGF1 concentrations on early pregnancy. However, our results do not support the premise that increased apoptosis associated with high levels of IGF1 is mediated via downregulation of the IGF1R as previously found in preimplantation mouse embryos. This in vitro system with the bovine preimplantation embryo reflects critical features of fertility in PCOS patients and could thus serve as a useful model for in-depth mechanistic studies.

Maternal diabetes impairs gastrulation and insulin and IGF-I receptor expression in rabbit blastocysts

Women with type 1 diabetes are subfertile. Diabetes negatively affects pregnancy by causing early miscarriage and poor prenatal outcomes. In this study we examine consequences of maternal type 1 diabetes on early embryo development, metabolic gene expression, and the pattern of insulin receptor (IR) and IGF-I receptor (IGF-IR) distribution in rabbit blastocysts. In female rabbits, type 1 diabetes was induced by alloxan treatment. Six-day-old blastocysts were recovered and assessed for receptor distribution and metabolic gene expression. In vitro culture of blastocysts was performed in medium containing 1 mm, 10 mm, or 25 mm glucose, simulating normo- and hyperglycemic developmental condition in vitro. The fertility rate of the diabetic rabbits clearly mirrored subfertility with a drop in blastocyst numbers by 40% (13.3 blastocysts in diabetic vs. 21.9 in control females). In blastocysts onset and progression of gastrulation was delayed and expression of IR and IGF-IR and their metabolic target genes (hexokinase, phosphoenolpyruvate carboxykinase), both in vivo and in vitro, was down-regulated. The amount of apoptotic cells in the embryonic disc was increased, correlating closely with the reduced transcription of the bcl-x(L) gene. Blastocyst development is clearly impaired by type 1 diabetes during early pregnancy. Insulin-stimulated metabolic genes and IR and IGF-IR are down-regulated, resulting in reduced insulin and IGF sensitivity and a delay in development. Dysregulation of the IGF system and embryonic glucose metabolism are potential reasons for diabetogenous subfertility and embryopathies and start as soon as during the first days of life.

Effects of environmental pollutants on the reproduction and welfare of ruminants

Anthropogenic pollutants comprise a wide range of synthetic organic compounds and heavy metals, which are dispersed throughout the environment, usually at low concentrations. Exposure of ruminants, as for all other animals, is unavoidable and while the levels of exposure to most chemicals are usually too low to induce any physiological effects, combinations of pollutants can act additively or synergistically to perturb multiple physiological systems at all ages but particularly in the developing foetus. In sheep, organs affected by pollutant exposure include the ovary, testis, hypothalamus and pituitary gland and bone. Reported effects of exposure include changes in organ weight and gross structure, histology and gene and protein expression but these changes are not reflected in changes in reproductive performance under the conditions tested. These results illustrate the complexity of the effects of endocrine disrupting compounds on the reproductive axis, which make it difficult to extrapolate between, or even within, species. Effects of pollutant exposure on the thyroid gland, immune, cardiovascular and obesogenic systems have not been shown explicitly, in ruminants, but work on other species suggests that these systems can also be perturbed. It is concluded that exposure to a mixture of anthropogenic pollutants has significant effects on a wide variety of physiological systems, including the reproductive system. Although this physiological insult has not yet been shown to lead to a reduction in ruminant gross performance, there are already reports indicating that anthropogenic pollutant exposure can compromise several physiological systems and may pose a significant threat to both reproductive performance and welfare in the longer term. At present, many potential mechanisms of action for individual chemicals have been identified but knowledge of factors affecting the rate of tissue exposure and of the effects of combinations of chemicals on physiological systems is poor. Nevertheless, both are vital for the identification of risks to animal productivity and welfare.

Muscleblind-like 1 (Mbnl1) promotes insulin receptor exon 11 inclusion via binding to a downstream evolutionarily conserved intronic enhancer

The insulin receptor exists as two isoforms, IR-A and IR-B, which result from alternative splicing of exon 11 in the primary transcript. These two isoforms show a cell-specific distribution, and their relative proportions also vary during development, aging, and in different disease states. We have previously demonstrated that both intron 10 and the alternatively spliced exon 11 contain regulatory sequences that affect insulin receptor splicing both positively and negatively and that these sequences bind the serine/arginine-rich (SR) proteins SRp20 and SF2/ASF and the CELF protein CUG-BP1. In this study, we describe a new intronic splicing element within intron 11 that is highly conserved across species. Using minigenes carrying deletion mutations within intron 11, we demonstrated that this sequence functions as an intronic splicing enhancer. We subsequently used RNA affinity chromatography to identify Mbnl1 as a splicing factor that recognizes this enhancer. By ribonucleoprotein immunoprecipitation, we also established that Mbnl1 binds specifically to the INSR (insulin receptor gene) RNA. Overexpression or knockdown of Mbnl1 in hepatoma and embryonic kidney cells altered the levels of exon 11 inclusion. Finally, we showed that deletion of the intronic enhancer eliminates the ability of Mbnl1 to promote exon inclusion. Collectively, these findings demonstrate a role for Mbnl1 in controlling insulin receptor exon 11 inclusion via binding to a downstream intronic enhancer element.

Genes and signals regulating murine trophoblast cell development

A fundamental step in embryonic development is cell differentiation whereby highly specialised cell types are developed from a single undifferentiated, fertilised egg. One of the earliest lineages to form in the mammalian conceptus is the trophoblast, which contributes exclusively to the extraembryonic structures that form the placenta. Trophoblast giant cells (TGCs) in the rodent placenta form the outermost layer of the extraembryonic compartment, establish direct contact with maternal cells, and produce a number of pregnancy-specific cytokine hormones. Giant cells differentiate from proliferative trophoblasts as they exit the cell cycle and enter a genome-amplifying endocycle. Normal differentiation of secondary TGCs is a critical step toward the formation of the placenta and normal embryonic development. Trophoblast development is also of particular interest to the developmental biologist and immunobiologist, as these cells constitute the immediate cellular boundary between the embryonic and maternal tissues. Abnormalities in the development of secondary TGCs results in severe malfunction of the placenta. Herein we review new information that has been accumulated recently regarding the molecular and cellular regulation of trophoblast and placenta development. In particular, we discuss the molecular aspects of murine TGC differentiation. We also focus on the role of growth and transcription factors in TGC development.

Expression of glucose transporter isoforms and the insulin receptor during hamster preimplantation embryo development

During preimplantation development, embryos of many species are known to express up to five isoforms of the facilitative glucose transporter proteins (GLUT). Development of hamster blastocysts is inhibited by glucose. We therefore investigated GLUT isoform and insulin receptor (IR) expression in hamster preimplantation embryos cultured in glucose-free medium from the 8-cell stage onwards. We show that GLUT1, 3 and 8 mRNA are constitutively expressed from the 8-cell to the blastocyst stage. The IR is expressed from the morula stage onwards. Messenger RNA of the insulin-responsive GLUT4 was not detected at any stage. GLUT1 and 3 were localised by immunocytochemistry. GLUT1 was expressed in both embryoblast and trophoblast, in the latter, mainly in basal and lateral membranes directed towards the blastocoel and embryoblast. GLUT3 was exclusively localised in the apical membrane of trophoblast cells. We show that hamster preimplantation embryos express several GLUT isoforms thus closely resembling embryos of other mammalian species. Despite endogenous IR expression, the insulin-sensitive isoform GLUT4 was not expressed, indicating that the insulin-mediated glucose uptake known from classical insulin target cells may not be relevant for hamster blastocysts.

Phosphatidylinositol 3-kinase signaling in mammalian preimplantation embryo development

The development of the preimplantation mammalian embryo is an autopoietic process; once initiated development proceeds without an absolute requirement for external information or growth cues. This developmental autonomy is partly explained by the generation of autocrine trophic ligands that are released and act back on the embryo via specific receptors. Several embryotrophic ligands cause receptor-dependent activation of 1-o-phosphatidylinositol 3-kinase. This enzyme phosphorylates phosphatidylinositol-4,5-bisphosphate to form phosphatidylinositol-3,4,5-trisphosphate. Genetic or pharmacological ablation of this enzyme activity disrupts normal development of preimplantation embryos. Phosphatidylinositol-3,4,5-trisphosphate is a membrane lipid that acts as a docking site for a wide range of proteins possessing the pleckstrin homology (PH) domain. Such proteins are important regulators of cell survival, proliferation, and differentiation. RAC-alpha serine/threonine protein kinase is an important PH domain protein and its activity is required for normal preimplantation embryo development and survival. The activity of a range of PH domain proteins is also implicated in the normal development of the embryo. This review critically examines the evidence for the activation of 1-o-phosphatidylinositol 3-kinase in the generation of pleiotypic trophic response to embryotrophins in the autopoietic development of the preimplantation embryo.