Murine Preimplantation Embryos Research Articles

Selecting Normalizers for MicroRNA RT-qPCR Expression Analysis in Murine Preimplantation Embryos and the Associated Conditioned Culture Media

Normalizing RT-qPCR miRNA datasets that encompass numerous preimplantation embryo stages requires the identification of miRNAs that may be used as stable reference genes. A need has also arisen for the normalization of the accompanying conditioned culture media as extracellular miRNAs may serve as biomarkers of embryo developmental competence. Here, we evaluate the stability of six commonly used miRNA normalization candidates, as well as small nuclear U6, using five different means of evaluation (BestKeeper, NormFinder, geNorm, the comparative Delta Ct method and RefFinder comprehensive analysis) to assess their stability throughout murine preimplantation embryo development from the oocyte to the late blastocyst stages, both in whole embryos and the associated conditioned culture media. In descending order of effectiveness, miR-16, miR-191 and miR-106 were identified as the most stable individual reference miRNAs for developing whole CD1 murine preimplantation embryos, while miR-16, miR-106 and miR-103 were ideal for the conditioned culture media. Notably, the widely used U6 reference was among the least appropriate for normalizing both whole embryo and conditioned media miRNA datasets. Incorporating multiple reference miRNAs into the normalization basis via a geometric mean was deemed beneficial, and combinations of each set of stable miRNAs are further recommended, pending validation on a per experiment basis.

SENESCENCE DURING IN VITRO EMBRYO DEVELOPMENT IN A MURINE MODEL

The objective of this study seeks to examine markers of senescence and the effect of environmental stressors on murine preimplantation embryos to develop a model to determine whether environmental stress can induce biomarkers of cellular senescence in the developing cells.

Lima1 mediates the pluripotency control of membrane dynamics and cellular metabolism

Lima1 is an extensively studied prognostic marker of malignancy and is also considered to be a tumour suppressor, but its role in a developmental context of non-transformed cells is poorly understood. Here, we characterise the expression pattern and examined the function of Lima1 in mouse embryos and pluripotent stem cell lines. We identify that Lima1 expression is controlled by the naïve pluripotency circuit and is required for the suppression of membrane blebbing, as well as for proper mitochondrial energetics in embryonic stem cells. Moreover, forcing Lima1 expression enables primed mouse and human pluripotent stem cells to be incorporated into murine pre-implantation embryos. Thus, Lima1 is a key effector molecule that mediates the pluripotency control of membrane dynamics and cellular metabolism.

RRNA biogenesis regulates mouse 2C-like state by 3D structure reorganization of peri-nucleolar heterochromatin

The nucleolus is the organelle for ribosome biogenesis and sensing various types of stress. However, its role in regulating stem cell fate remains unclear. Here, we present evidence that nucleolar stress induced by interfering rRNA biogenesis can drive the 2-cell stage embryo-like (2C-like) program and induce an expanded 2C-like cell population in mouse embryonic stem (mES) cells. Mechanistically, nucleolar integrity maintains normal liquid-liquid phase separation (LLPS) of the nucleolus and the formation of peri-nucleolar heterochromatin (PNH). Upon defects in rRNA biogenesis, the natural state of nucleolus LLPS is disrupted, causing dissociation of the NCL/TRIM28 complex from PNH and changes in epigenetic state and reorganization of the 3D structure of PNH, which leads to release of Dux, a 2C program transcription factor, from PNH to activate a 2C-like program. Correspondingly, embryos with rRNA biogenesis defect are unable to develop from 2-cell (2C) to 4-cell embryos, with delayed repression of 2C/ERV genes and a transcriptome skewed toward earlier cleavage embryo signatures. Our results highlight that rRNA-mediated nucleolar integrity and 3D structure reshaping of the PNH compartment regulates the fate transition of mES cells to 2C-like cells, and that rRNA biogenesis is a critical regulator during the 2-cell to 4-cell transition of murine pre-implantation embryo development.

A Comparative Analysis of Hippo Signaling Pathway Components during Murine and Bovine Early Mammalian Embryogenesis.

The time required for successful blastocyst formation varies among multiple species. The formation of a blastocyst is governed by numerous molecular cell signaling pathways, such as the Hippo signaling pathway. The Hippo signaling pathway is initiated by increased cell–cell contact and via apical polarity proteins (AMOT, PARD6, and NF2) during the period of preimplantation embryogenesis. Cell–cell contact and cell polarity activate (phosphorylates) the core cascade components of the pathway (mammalian sterile twenty like 1 and 2 (MST1/2) and large tumor suppressor 1 and 2 (LATS1/2)), which in turn phosphorylate the downstream effectors of the pathway (YAP1/TAZ). The Hippo pathway remains inactive with YAP1 (Yes Associated protein 1) present inside the nucleus in the trophectoderm (TE) cells (polar blastomeres) of the mouse blastocyst. In the inner cell mass (ICM) cells (apolar blastomeres), the pathway is activated with p-YAP1 present in the cytoplasm. On the contrary, during bovine embryogenesis, p-YAP1 is exclusively present in the nucleus in both TE and ICM cells. Contrary to mouse embryos, transcription co activator with PDZ-binding motif (TAZ) (also known as WWTR1) is also predominantly present in the cytoplasm in all the blastomeres during bovine embryogenesis. This review outlines the major differences in the localization and function of Hippo signaling pathway components of murine and bovine preimplantation embryos, suggesting significant differences in the regulation of this pathway in between the two species. The variance observed in the Hippo signaling pathway between murine and bovine embryos confirms that both of these early embryonic models are quite distinct. Moreover, based on the similarity of the Hippo signaling pathway between bovine and human early embryo development, bovine embryos could be an alternate model for understanding the regulation of the Hippo signaling pathway in human embryos.

Localization of plasminogen activator inhibitor type 1 and 2 in preimplantation mouse development in vitro

Plasminogen activator inhibitor type 1 (PAI-1) and type 2 (PAI-2) are the major endogenous inhibitors of fibrinolysis, or thrombolysis, as it is effective in blocking the conversion of plasminogen to plasmin. In mammalian embryos, both PAI-1 and PAI-2 proteins are expressed in the trophoblasts during and after implantation, suggesting their critical roles in implantation and placentation during pregnancy. However, it remains unclear how both proteins localize in the early stage embryos before implantation. In this study, 2 cell stage embryos were flushed from the oviducts and cultured to specified stages in medium at 37 ̊C in a 5% CO2 incubator. Embryos were fixed and double immunostained with anti-PAI-1 and anti- PAI-2 antibody. We determined the critical expression and localization patterns of PAI-1 and PAI-2 proteins in murine preimplantation embryos at 2 cell, 8 cell, morula and blastocyst stages by using confocal laser scanning microscope. We found that PAI-1 and PAI-2 constantly express in the embryos during preimplantation development, and these proteins localize in both the cytoplasm and the nucleus of each blastomere regardless of their developmental stage. Our results suggest that PAI-1 and PAI-2 proteins may play roles in early embryonic development before implantation.

GENOME EDITING OF A HUMAN EMBRYO – COULD CORRECTION REPLACE SCREENING?

Genome editing (CRISPR-Cas9 or Base Editing) is a revolutionary tool which allows DNA or RNA to be altered at directed loci in the genome with ease and efficiency. The technology, which is derived from and mimics the immune system of bacteria, offers unprecedented ability to alter, correct or insert genes into a genome. The technology has been adopted globally in the research setting and offers limitless potential for personalised medicine; indeed, somatic cell therapies are already benefiting from this technology. The advances in genome editing coupled with assisted reproductive technologies and genomics lend themselves to germline therapy and the correction of genetic disorders in embryos. Could correction replace screening? In order for this to reach the clinic, significant and rigorous testing must be carried out ensure that edits are controllable, reproducible and that mosaicism is avoided. Our research focuses on the delivery of components of CRISPR, assessing the accuracy of edits and measuring mosaicism in edited murine preimplantation embryos.

The effect of light exposure on the cleavage rate and implantation capacity of preimplantation murine embryos

During assisted reproduction the embryos are subjected to light. We investigated the relationship between light exposure and the developmental- and implantation capacity of mouse embryos. In vitro cultured embryos were exposed to white or red filtered light, then transferred to the uteri of pseudo-pregnant females. The mice were sacrificed on day 8.5 and implantation sites were counted. The number of nucleic acid containing (PI+) extracellular vesicles (EVs) in culture media of light-exposed and control embryos, as well as, the effect of the EVs on IL-10 production of CD8+ spleen cells was determined by flow cytometry. DNA fragmentation in control and light exposed embryos was detected in a TUNEL assay. The effect of light on the expression of apoptosis-related molecules was assessed in an apoptosis array.Light exposure significantly reduced the implantation capacity of the embryos. The harmful effect was related to the wavelength, rather than to the brightness of the light. Culture media of light exposed groups contained significantly higher number of PI + EVs than those of the control embryos, and failed to induce IL-10 production of spleen cells. The number of nuclei with fragmented DNA, was significantly higher in embryos treated with white light, than in the other two groups.In conclusion exposure to white light impairs the implantation potential of in vitro cultured mouse embryos. These effects are partly corrected by using a red filter. Since there is no information on the light sensitivity of human embryos, embryo manipulation during IVF and ICSI should be performed with caution.

Haemoglobin expression in in vivo murine preimplantation embryos suggests a role in oxygen-regulated gene expression

Haemoglobin expression is not restricted to erythroid cells. We investigated the gene expression of the haemoglobin subunits haemoglobin, alpha adult chain 1 (Hba-a1) and haemoglobin, beta (Hbb), 2,3-bisphosphoglycerate mutase (Bpgm) and the oxygen-regulated genes BCL2/adenovirus E1B interacting protein 3 (Bnip3), solute carrier family 2 (facilitated glucose transporter), member 1 (Slc2a1) and N-myc downstream regulated gene 1 (Ndrg1) in the murine preimplantation embryo, comparing invivo to invitro gene expression. Relatively high levels of Hba-a1 and Hbb were expressed invivo from the 2-cell to blastocyst stage; in contrast, little or no expression occurred invitro. We hypothesised that the presence of haemoglobin invivo creates a low oxygen environment to induce oxygen-regulated gene expression, supported by high expression of Slc2a1 and Ndrg1 in invivo relative to invitro embryos. In addition, analysis of an invitro-derived human embryo gene expression public dataset revealed low expression of haemoglobin subunit alpha (HBA) and HBB, and high expression of BPGM. To explore whether there was a developmental stage-specific effect of haemoglobin, we added exogenous haemoglobin either up to the 4-cell stage or throughout development to the blastocyst stage, but observed no difference in blastocyst rate or the inner cell mass to trophectoderm cell ratio. We conclude that haemoglobin in the invivo preimplantation embryo raises an interesting premise of potential mechanisms for oxygen regulation, which may influence oxygen-regulated gene expression.

The effect of light exposure on the cleavage rate and implantation capacity of preimplantation murine embryos

The effect of light exposure on the cleavage rate and implantation capacity of preimplantation murine embryos

Effects of Nicotine and Tocotrienol-Rich Fraction Supplementation on Cytoskeletal Structures of Murine Pre-Implantation Embryos.

BackgroundCytoskeletal structures, in particular actin and tubulin, provide a fundamental framework in all cells, including embryos. The objective of this study was to evaluate the effects of nicotine, which is a source of oxidative stress, and subsequent supplementation with Tocotrienol-rich fraction (TRF) on actin and tubulin of 2- and 8-cell murine embryos.Material/MethodsThirty female Balb/C mice were divided into 4 groups: Group 1 received: subcutaneous (sc) injection of 0.9% NaCl; Group 2 received sc injection of 3.0 nicotine mg/kg bw/day; Group 3 received 3.0 sc injection of nicotine mg/kg bw/day +60 mg/kg bw/day TRF; and Group 4 received 60 sc injection of TRF mg/kg bw/day for 7 consecutive days. The animals were superovulated with 5 IU PMSG followed by 5 IU hCG 48 h later. Animals were cohabited with fertile males overnight and euthanized through cervical dislocation at 24 h post coitum. Embryos at the 2- and 8-cell stages were harvested, fixed, and stained to visualize actin and tubulin distributions by using CLSM.ResultsResults showed that at 2-cell stage, actin intensities were significantly reduced in the nicotine group compared to that of the control group (p<0.001). In Group 3, the intensity of actin significantly increased compared to that of the nicotine group (p<0.001). At 8-cell stage, actin intensity of the nicotine group was significantly lower than that of the control group (p<0.001). The intensities of actin in Group 3 were increased compared to that of nicotine treatment alone (p<0.001). The same trend was seen in tubulin at 2- and 8-cell stages. Interestingly, both actin and tubulin structures in the TRF-treated groups were enhanced compared to the control.ConclusionsThis study suggests that TRF prevents the deleterious effects of nicotine on the cytoskeletal structures of 2- and 8-cell stages of pre-implantation mice embryos in vitro.

Spatiotemporal dynamics of OCT4 protein localization during preimplantation development in mice.

Spatiotemporal expression of transcription factors is crucial for genomic reprogramming. Pou5f1 (Oct4) is an essential transcription factor for reprogramming. A recent study reported that OCT4A, which is crucial for establishment and maintenance of pluripotent cells, is expressed in oocytes, but maternal OCT4A is dispensable for totipotency induction. Whereas another study reported that OCT4B, which is not related to pluripotency, is predominantly expressed instead of OCT4A during early preimplantation phases in mice. To determine the expression states of OCT4 in murine preimplantation embryos, we conducted in-depth expression and functional analyses. We found that pluripotency-related OCT4 mainly localizes to the cytoplasm in early preimplantation phases, with no major nuclear localization until the 8–16-cell stage despite high expression in both oocytes and early embryos. RNA-sequencing analysis using oocytes and early preimplantation embryos could not identify the splice variants creating alternative forms of OCT4 protein. Forced expression of OCT4 in zygotes by the injection of polyadenylated mRNA clearly showed nuclear localization of OCT4 protein around 3–5-fold greater than physiological levels and impaired developmental competency in a dose-dependent manner. Embryos with modest overexpression of OCT4 could develop to the 16-cell stage; however, more than 50% of the embryos were arrested at this stage, similar to the results for OCT4 depletion. In contrast, extensive overexpression of OCT4 resulted in complete arrest at the 2-cell stage accompanied by downregulation of zygotically activated genes and repetitive elements related to the totipotent state. These results demonstrated that OCT4 protein localization was spatiotemporally altered during preimplantation development, and strict control of Oct4 protein levels was essential for proper totipotential reprogramming.

Lower total cell numbers in mouse preimplantation embryos cultured in human assisted reproductive technique (ART) media are not induced by apoptosis

A common feature of assisted reproductive techniques such as IVF or intracytoplasmic sperm injection is the IVC of oocytes or preimplantation embryos in artificial culture media. The IVC conditions are selected to mimic the environment of the female genital tract. We have shown that murine preimplantation embryos respond to different culture media with changes in developmental rates, cellular lineage composition, and gene expression patterns. In this study, we explored whether apoptosis is responsible for cell loss in mouse preimplantation embryos after exposure to different human culture media. We examined total embryonic cell count as well as the pattern of protein expression for caspase-9 (intrinsic pathway), caspase-8 (extrinsic pathway), and the executioner caspase-3 via immunohistochemical staining. Total cell counts decline in embryos cultured either in innovative sequential medium 1 and Blast Assist (Origio) or human tubal fluid and MultiBlast (Irvine Scientific) when compared to KSOM(aa). Few cells were caspase-9 and -3 positive in all experimental groups. Staining for caspase-8 was almost undetectable. We conclude that embryonic cell loss is not associated with higher rates of intrinsic apoptotic cell loss. Our results suggest that the culture medium–dependent decline in total cell count and the developmental restriction in embryos cultured in innovative sequential medium 1/Blast Assist and human tubal fluid/MultiBlast are related to processes affecting cell proliferation.

Effect of DNase treatment on RNA extraction from preimplantation murine embryos.

The quality of RNA is crucial when performing microarray experiments. This is particularly important when dealing with preimplantation embryos, from which a minimum yield of RNA of good quality can be produced. We report the optimization of several RNA extraction methods applied to preimplantation embryos at different stages of development. The quality of the samples was confirmed using a microarray and reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) analysis. A total of 30 cultured two-cell stage embryos of ICR mice were pooled at the 8-cell, morula, and blastocyst stages. The embryos were divided into two groups comprising DNase-treated and non-DNase-treated RNA samples. Total RNA was extracted using a Pico Pure RNA Isolation Kit following the manufacturer protocol, with some modifications. Lysed samples were bound to a silica-based filter, treated with deoxyribonuclease I (DNase I), and washed several times before elution. RNA concentration and integrity were evaluated using an Agilent 2100 Bioanalyzer and an RNA 6000 Pico Assay kit. Although concentrations of non-DNase-treated RNAs were higher than DNase-treated RNA, DNase-treated RNA gave a higher RNA integrity number compared with non-DNase-treated RNA. Inclusion of DNase treatment in the RNA extraction procedure gave the best quality RNA samples from preimplantation embryos, as validated by microarray and RT-qPCR quality control.

UDP-glucuronosyltransferase 1a enzymes are present and active in the mouse blastocyst.

The UDP-glucuronosyltransferase (UGT) enzymes are critical for regulating nutrients, hormones, and endobiotics, as well as for detoxifying xenobiotics. Human and murine fetuses are known to express glucuronidation enzymes, but there are currently no data prior to implantation. Here we addressed this gap in knowledge and tested whether Ugt enzymes are already present in preimplantation-stage embryos. Blastocysts were obtained after in vitro fertilization with gametes from B6D2F1 hybrid mice and from embryo culture. Protein expression and localization were determined using pan-specific UGT1A and UGT2B, as well as anti-human isoform-specific antibodies. Immunofluorescence analysis showed that blastocysts expressed Ugt1a globally, in the cytoplasm and nuclei of all of the cells. Western blots demonstrated the presence of Ugt1a6 but not Ugt1a1, Ugt1a3, Ugt1a4, or Ugt1a9. The Ugt2b proteins were not detected by either assay. The level of Ugt activity in murine blastocysts was comparable with that of the adult human liver (per milligram of protein), but the activity of β-glucuronidase, an Ugt-partnering enzyme responsible for substrate regeneration, was lower. Altogether, these data confirm that Ugt1a proteins are present and active in preimplantation murine embryos and point to a potential role for these proteins in implantation and early embryonic and fetal development.

Calcitonin Promotes Mouse Pre‐implantation Development: Involvement of Calcium Mobilization and P38 Mitogen‐Activated Protein Kinase Activation

The study was designed to examine the effects of calcitonin (CT) on the development of murine pre-implantation embryos and possible molecular mechanisms involved in the process. In the present study, the 2-cell embryos were treated with different concentration of CT in vitro for the indicated time and the results demonstrated that CT promoted the development of the pre-implantation embryos in a dosage-dependent manner by increasing the intracellular Ca(2+) level. Furthermore, the present study showed that CT significantly increased the expression of phospho-P38MAPK (Mitogen-Activated Protein Kinase) of the pre-implantation embryos by Western blots and pre-treatment of specific P38MAPK inhibitor significantly reduced the promotion effects of CT on the embryonic development in vitro culture. Moreover, the results of intrauterine horn injection showed that the average number of embryos implanted in CT-antibody or specific P38 MAPK inhibitor-treated uterus was significantly lower than that of the corresponding control, respectively. And the observation of tissue specimen suggested that some embryos were degenerated in CT-antibody or specific P38 MAPK inhibitor-treated uterus, and adipose vacuoles were present in the decidual cells. In conclusion, CT promoted the development of pre-implantation embryos and the intracellular Ca(2+) -dependent P38MAPK signal molecule was involved in the process.

Cytoskeletal alterations in different developmental stages of in vivo cryopreserved preimplantation murine embryos.

BackgroundThis study aimed to investigate the effects of vitrification and slow freezing on actin, tubulin, and nuclei of in vivo preimplantation murine embryos at various developmental stages using a Confocal Laser Scanning Microscope (CLSM).Material/MethodsFifty female mice, aged 4–6 weeks, were used in this study. Animals were superovulated, cohabitated overnight, and sacrificed. Fallopian tubes were excised and flushed. Embryos at the 2-cell stage were collected and cultured to obtain 4- and 8-cell stages before being cryopreserved using vitrification and slow freezing. Fixed embryos were stained with fluorescence-labelled antibodies against actin and tubulin, as well as DAPI for staining the nucleus. Labelled embryos were scanned using CLSM and images were analyzed with Q-Win software V3.ResultsThe fluorescence intensity of both vitrified and slow-frozen embryos was significantly lower for tubulin, actin, and nucleus as compared to non-cryopreserved embryos (p<0.001). Intensities of tubulin, actin, and nucleus in each stage were also decreased in vitrified and slow-frozen groups as compared to non-cryopreserved embryos.ConclusionsCryopreservation of mouse embryos by slow freezing had a more detrimental effect on the actin, tubulin, and nucleus structure of the embryos compared to vitrification. Vitrification is therefore superior to slow freezing in terms of embryonic cryotolerance.

Non-intact zona improves development of murine preimplantation embryos transfected by an adenovirus vector

The present study explored whether embryos could be transfected by the adenovirus-vector if the zona pellucida (ZP) was not completely removed. An adenovirus vector with green fluorescent protein (pAdGFP) was used to transfect mouse non-intact zona zygotes (following partial removal of the ZP induced by pronase), zona-free and zona-intact embryos. Non-intact zona and zona-free embryos expressed GFP (confirmed with inverted fluorescence microscopy) after 48 h of culture. The transfection rate of non-intact zona group was up to 51% and the entire zona-free group was transfected. However, none of the zona-intact embryos was transfected. Regardless of whether non-intact zona embryos were transfected by pAd-GFP, their developmental rate (74.3 ± 2.4 and 69.2 ± 3.3% for non-transfected and transfected, respectively; mean ± SEM) was higher (P<0.05) than that of zona-free embryos without and with transfection (54.5 ± 4.3 and 46.7 ± 5.5%). Developmental potential of embryos was decreased for ZP-digestion (non-intact zona 71.8 ± 1.6%; zona-free 50.6 ± 2.2%, P<0.05) or pAd-GFP expression (nontransfected 64.4 ± 1.9%; transfected 56.0 ± 2.1%, P<0.05); therefore, ZP-digestion affected more intensely embryos development than pAd-GFP expression. In summary, non-intact zona murine embryos were readily transfected by the adenovirus-vector, and had much greater development potential than zona-free embryos. Although, the susceptibility of the ZP to digestion by pronase varied among embryos, on average, approximately 3.5 to 4.0 min of digestion resulted in partial removal of the ZP and promoted both transfection and satisfactory embryonic development. It is expected that this method could be used to increase the efficiency of generating transgenic animals.

CCN5 Expression in mammals. III. Early embryonic mouse development

CCN proteins play crucial roles in development, angiogenesis, cell motility, matrix turnover, proliferation, and other fundamental cell processes. Early embryonic lethality in CCN5 knockout and over-expressing mice led us to characterize CCN5 distribution in early development. Previous papers in this series showed that CCN5 is expressed widely in mice from E9.5 to adult; however, its distribution before E9.5 has not been studied. To fill this gap in our knowledge of CCN5 expression in mammals, RT-PCR was performed on preimplantation murine embryos: 1 cell, 2 cell, 4 cell, early morula, late morula, and blastocyst. CCN5 mRNA was not detected in 1, 2, or 4 cell embryos. It was first detected at the early morula stage and persisted to the preimplantation blastocyst stage. Immunohistochemical staining showed widespread CCN5 expression in post-implantation blastocysts (E4.5), E5.5, E6.5, and E7.5 stage embryos. Consistent with our previous study on E9.5 embryos, this expression was not limited to a particular germ layer or cell type. The widespread distribution of CCN5 in early embryos suggests a crucial role in development.

Age does not influence the effect of embryo fragmentation on successful blastocyst development

We evaluated the rate of blastocyst development in day 3 embryos with appropriate cellular division and investigated whether maternal age modified the effect of embryo fragmentation on blastulation. Our data showed a significant negative correlation between the degree of embryo fragmentation and rate of blastocyst development, but age did not exert an effect on the degree of fragmentation in embryos with appropriate cleaving status, nor did it modify the significant effect embryo fragmentation had on blastocyst formation.