Development: Hippo Signalling Turns the Embryo Inside Out

Expression profiles of oviductal mRNAs and lncRNAs in the follicular phase and luteal phase of sheep (Ovis aries) with 2 fecundity gene (FecB) genotypes

FecB (also known as BMPR1B) is a crucial gene in sheep reproduction, which has a mutation (A746G) that was found to increase the ovulation rate and litter size. The FecB mutation is associated with reproductive endocrinology, such mutation can control external estrous characteristics and affect follicle-stimulating hormone during the estrous cycle. Previous researches showed that the FecB mutation can regulate the transcriptomic profiles in the reproductive-related tissues including hypothalamus, pituitary, and ovary during the estrous cycle of small-tailed Han (STH) sheep. However, little research has been reported on the correlation between FecB mutation and the estrous cycle in STH sheep oviduct. To investigate the coding and noncoding transcriptomic profiles involved in the estrous cycle and FecB in the sheep oviduct, RNA sequencing was performed to analyze the transcriptomic profiles of mRNAs and long noncoding RNAs (lncRNAs) in the oviduct during the estrous cycle of STH sheep with mutant (FecBBB) and wild-type (FecB++) genotypes. In total, 21,863 lncRNAs and 43,674 mRNAs were screened, the results showed that mRNAs had significantly higher expression levels than the lncRNAs, and the expression levels of these screened transcripts were lower in the follicular phase than they were in the luteal phase. Among them, the oviductal glycoprotein gene (OVGP1) had the highest expression level. In the comparison between the follicular and luteal phases, 57 differentially expressed (DE) lncRNAs and 637 DE mRNAs were detected, including FSTL5 mRNA and LNC_016628 lncRNA. In the comparison between the FecBBB and FecB++ genotypes, 26 DE lncRNAs and 421 DE mRNAs were detected, including EEF1D mRNA and LNC_006270 lncRNA. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes functional enrichment analysis indicated that the DE mRNAs were enriched mainly in terms related to reproduction such as the tight junction, SAGA complex, ATP-binding cassette, nestin, and Hippo signaling pathway. The interaction network between DE lncRNAs and DE mRNAs indicated that LNC_018420 may be the key regulator in sheep oviduct. Together, our results can provide novel insights into the oviductal transcriptomic function against a FecB mutation background in sheep reproduction.

Differential regulation of Hippo signaling pathway components between 8-cell and blastocyst stages of bovine preimplantation embryogenesis

The Hippo signaling pathway is an important regulator of lineage segregation (trophectoderm and inner cell mass) during blastocyst formation in the mouse embryos. However, the role and regulation of Hippo signaling pathway components during bovine embryonic development is not completely understood. This study was thus designed to interpret the roles of Hippo cell signaling pathway components using two different yet specific chemical inhibitors (Cerivastatin and XMU-MP-1). A significant decrease in the blastocyst rates were observed on treatment with Cerivastatin and XMU-MP-1 inhibitors for the treatment groups, in comparison to the control groups. At the 8-cell stage, a significant decrease was observed in the gene expression and nuclear protein localization of YAP1 (Yes Associated Protein 1) and pYAP1 components of Hippo signaling pathway. However, no such effect of Cerivastatin treatment was observed on the localization of TAZ at this cell stage. On the contrary, during bovine blastocyst formation a significant decrease in the gene expression and nuclear localization of both YAP1 and TAZ suggest differences in the regulation of these components at 8-cell and blastocyst stages of embryonic development. Furthermore, XMU-MP-1 mediated chemical inhibition of Mst1 at the blastocyst stage also suggests differences in the regulation of Yap1 and Taz components of Hippo signaling pathway. Overall, this study indicates novel differences in the regulation of Hippo signaling transcript levels and protein localization between the 8-cell and blastocyst stages of bovine preimplantation embryonic development.

The aryl hydrocarbon receptor promotes differentiation during mouse preimplantational embryo development

Mammalian embryogenesis is a complex process controlled by transcription factors that regulate the balance between pluripotency and differentiation. Transcription factor aryl hydrocarbon receptor (AhR) regulates OCT4/POU5F1 and NANOG, both essential controllers of pluripotency, stemness and early embryo development. Molecular mechanisms controlling OCT4/POU5F1 and NANOG during embryogenesis remain unidentified. We show that AhR regulates pluripotency factors and maintains the metabolic activity required for proper embryo differentiation. AhR-lacking embryos (AhR^−/−) showed a pluripotent phenotype characterized by a delayed expression of trophectoderm differentiation markers. Accordingly, central pluripotency factors OCT4/POU5F1 and NANOG were overexpressed in AhR^−/− embryos at initial developmental stages. An altered intracellular localization of these factors was observed in the absence of AhR and, importantly, Oct4 had an opposite expression pattern with respect to AhR from the two-cell stage to blastocyst, suggesting a negative regulation of OCT4/POU5F by AhR. We propose that AhR is a regulator of pluripotency and differentiation in early mouse embryogenesis.

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AhR regulates pluripotency factors OCT4 and NANOG during early embryo differentiation

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AhR lacking embryos (AhR^−/−) show a pluripotent phenotype

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Pluripotent phenotype of AhR^−/− embryos show enhanced glycolytic metabolism

Characterisation of the Hippo signalling pathway during bovine preimplantation embryo development

Blastocyst formation is an important milestone during preimplantation embryo development. During murine preimplantation embryogenesis, the Hippo signalling pathway is known to play a significant role in lineage segregation and henceforth the formation of blastocysts. However, the role of this cell signalling pathway during bovine embryogenesis remains unknown. Thus, the aim of the present study was to characterise the Hippo signalling pathway during bovine preimplantation embryo development. mRNA transcripts of Hippo signalling pathway constituents (i.e. crumbs cell polarity complex component 3 (CRB3), mammalian sterile 20-like 1 (MST1), mammalian sterile 20-like 2 (MST2), Yes associated protein 1 (YAP1), transcriptional coactivator with PDZ-binding motif (TAZ)) were observed during all stages of bovine preimplantation embryo development. To evaluate the localisation of Hippo pathway components, bovine embryos at timed stages of development were stained using specific antibodies and observed under a laser confocal microscope. Although MST1/2 proteins were in the cytoplasm during various stages of bovine embryonic development, TAZ and phosphorylated (p-) YAP were detected in the nucleus during the blastocyst stages. Localisation of TAZ and p-YAP proteins was distinct in the bovine compared with mouse model, suggesting that the Hippo signalling pathway is regulated differently in early bovine embryos.

Time of first polar body extrusion affects the developmental competence of equine oocytes after intracytoplasmic sperm injection

Assisted reproduction techniques (ARTs) have become widespread in the equine breeding industry. In particular, the combination of oocyte recovery from live mares followed by IVM and intracytoplasmic sperm injection (ICSI) has increased markedly among the ARTs used with valuable or low-fertility animals. There is currently no consensus among research groups regarding the optimal oocyte maturation period to produce high-quality embryos. In this study, we report the maturation dynamics of equine oocytes at different time points, from 20 to 40h (Experiment 1). In addition, in Experiment 2, equine ICSI blastocysts were produced from oocytes that exhibited early (up to 24h) or late (28-30h) extrusion of the first polar body (PB). Blastocyst rates and diameter were recorded and embryo quality was assessed by analysing the number of apoptotic cells and Yes-associated protein 1 (YAP1) expression. By 20h of IVM, 42% of oocytes were mature, and the remaining oocytes matured within the next 17h of IVM. Although no differences were found in cell apoptosis or the number of YAP1-positive cells between groups exhibiting early and late PB extrusion, embryos from the early group (Group I) exhibited an improved total cell number and blastocyst rate compared to embryos from the late group (Group II) (18.60% vs 10.17% respectively).

Effect of Maternal Age on Hippo Pathway Related Gene Expressions and Protein Localization Pattern in Human Embryos

Objective

The Hippo pathway plays an important role in embryo development, and separation of trophectoderm (TE) and inner cell mass (ICM) cell lines. Therefore, this study investigated effect of maternal age on activity of Hippo pathway in human embryos.

Materials and Methods

In this experimental study, the developed up embryos to the blastocyst stage and the embryos whose growth stopped at the morula stage were collected from women aged 20-30 years old (young group, 94 embryos) and >37 years (old group, 89 embryos). Expression of OCT4, SOX2, CDX2, GATA3, YAP genes and the relevant proteins, in the both groups were evaluated using respectively quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and immunofluorescence methods.

Results

There was no significant difference in the expression level of OCT4, SOX2, CDX2, GATA3 and YAP genes in blastocyst and morula stages, between the two groups. However, SOX2 and CDX2 gene expressions in morula stage embryos of the old group was statistically lower than that of the young group (P=0.007 and P=0.008, respectively). Additionally, in the embryos collected from women with >37 years of age, at the blastocyst stage, phospho-YAP (p-YAP) protein was found to be accumulated in the TE, but it was almost disappeared from the ICM. Additionally, in the old group, contrary to the expectation, YAP protein was expressed in the ICM, rather than TE.

Conclusion

The results of this study showed that YAP and P-YAP among the Hippo signalling pathway may be altered by increasing age.

Mitochondria in early development: linking the microenvironment, metabolism and the epigenome

Mitochondria, originally of bacterial origin, are highly dynamic organelles that have evolved a symbiotic relationship within eukaryotic cells. Mitochondria undergo dynamic, stage-specific restructuring and redistribution during oocyte maturation and preimplantation embryo development, necessary to support key developmental events. Mitochondria also fulfil a wide range of functions beyond ATP synthesis, including the production of intracellular reactive oxygen species and calcium regulation, and are active participants in the regulation of signal transduction pathways. Communication between not only mitochondria and the nucleus, but also with other organelles, is emerging as a critical function which regulates preimplantation development. Significantly, perturbations and deficits in mitochondrial function manifest not only as reduced quality and/or poor oocyte and embryo development but contribute to post-implantation failure, long-term cell function and adult disease. A growing body of evidence indicates that altered availability of metabolic co-factors modulate the activity of epigenetic modifiers, such that oocyte and embryo mitochondrial activity and dynamics have the capacity to establish long-lasting alterations to the epigenetic landscape. It is proposed that preimplantation embryo development may represent a sensitive window during which epigenetic regulation by mitochondria is likely to have significant short- and long-term effects on embryo, and offspring, health. Hence, mitochondrial integrity, communication and metabolism are critical links between the environment, the epigenome and the regulation of embryo development.

Identification of extracellular vesicles and characterization of miRNA expression profiles in human blastocoel fluid

In this study, for the first time, we demonstrated the presence of microRNAs and extracellular vesicles in human blastocoel fluid. The bioinformatic and comparative analyses identified the biological function of blastocoel fluid microRNAs and suggested a potential role inside the human blastocyst. We found 89 microRNAs, expressed at different levels, able to regulate critical signaling pathways controlling embryo development, such as pluripotency, cell reprogramming, epigenetic modifications, intercellular communication, cell adhesion and cell fate. Blastocoel fluid microRNAs reflect the miRNome of embryonic cells and their presence, associated with the discovery of extracellular vesicles, inside blastocoel fluid, strongly suggests their important role in mediating cell communication among blastocyst cells. Their characterization is important to better understand the earliest stages of embryogenesis and the complex circuits regulating pluripotency. Moreover, blastocoel fluid microRNA profiles could be influenced by blastocyst quality, therefore, microRNAs might be used to assess embryo potential in IVF cycles.

Transcriptional Regulation and Genes Involved in First Lineage Specification During Preimplantation Development

The successful development from a single-cell zygote into a complex multicellular organism requires precise coordination of multiple cell-fate decisions. The very first of these is lineage specification into the inner cell mass (ICM) and trophectoderm (TE) during mammalian preimplantation development. In mouse embryos, transcription factors (TFs) such as Oct4, Sox2, and Nanog are enriched in cells of ICM, which gives rise to the fetus and yolk sac. Conversely, TFs such as Cdx2 and Eomes become highly upregulated in TE, which contribute to the placenta. Here, we review the current understanding of key transcriptional control mechanisms and genes responsible for these distinct differences during the first cell lineage specification. In particular, we highlight recent insights gained through advances in genome manipulation, live imaging, single-cell transcriptomics, and loss-of-function studies.

Multiple phases in regulation of Nanog expression during pre-implantation development

Nanog is a key transcriptional factor for the maintenance of pluripotency of ES cells, iPS cells or cells in early mammalian embryos. The expression of Nanog is mainly localized to the epiblast in the late blastocyst. The Nanog gene expression pattern varies between embryos and between blastomeres during blastocyst formation. In this report, we traced the changes of Nanog expression in each cell in developing preimplantation mouse embryos through time-lapse observation of Nanog-GFP transgenic mouse embryos. The expression pattern of Nanog was classified into four phases depending on the developmental stage. Nanog expression started at very low levels during cleavage stages. It increased stochastically during the morula stage, but its expression level had no clear correlation with future cell fates. After the 32-cell stage, when embryos form the blastocyst cavity, Nanog expression was upregulated mainly in ICM cells while it was repressed in the future primitive endoderm lineage in an FGF signaling-dependent manner in the later stages. These results indicate that there are multiple phases in the transcriptional regulation of Nanog during blastocyst formation.

Emerging Role of the Hippo Signaling Pathway in Position Sensing and Lineage Specification in Mammalian Preimplantation Embryos

In preimplantation mouse embryos, the first lineage differentiation takes place in the 8- to 16-cell-stage embryo and results in formation of the trophectoderm (TE) and inner cell mass (ICM), which will give rise to the trophoblast of the placenta and the embryo proper, respectively. Although, it is widely accepted that positioning of a cell within the embryo influences lineage differentiation, the mechanism underlying differential lineage differentiation and how it involves cell position are largely unknown. Interestingly, novel cues from the Hippo pathway have been recently demonstrated in the preimplantation mouse embryo. Unlike the mechanisms reported from epithelium-cultured cells, the Hippo pathway was found to be responsible for translating positional information to lineage specification through a position-sensing mechanism. Disruption of Hippo pathway-component genes in early embryos results in failure of lineage specification and failure of postimplantation development. In this review, we discuss the unique role of the Hippo signaling pathway in early embryo development and its role in lineage specification. Understanding the activity and regulation of the Hippo pathway may offer new insights into other areas of developmental biology that evolve from understanding of this cell-fate specification in the early embryonic cell.