Using embryological data from 14 mammalian orders, the hypothesis is presented that in placental mammals, epiblast cavitation and polar trophoblast loss are alternative developmental solutions to ...shield the central epiblast from extraembryonic signalling. It is argued that such reciprocal signalling between the edge of the epiblast and the adjoining polar trophoblast or edge of the mural trophoblast or with the amniotic ectoderm is necessary for the induction of gastrulation. This article is part of the theme issue 'Extraembryonic tissues: exploring concepts, definitions and functions across the animal kingdom'.
This review describes in detail the morphological, cytoskeletal and gene expression events leading to the gene regulatory network bifurcation point of trophoblast and inner cell mass cells in a ...variety of mammalian preimplantation embryos. The interrelated processes of compaction and polarity establishment are discussed in terms of how they affect YAP/WWTR activity and the location and fate of cells. Comparisons between mouse, human, cattle, pig and rabbit embryos suggest a conserved role for YAP/WWTR signalling in trophoblast induction in eutherian animals though the mechanisms for, and timing of, YAP/WWTR activation differs among species. Downstream targets show further differences, with the trophoblast marker GATA3 being a direct target in all examined mammals, while CDX2-positive and SOX2-negative regulation varies.
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•Onset of compaction relative to polarisation varies among mammalian embryos.•De novo polarisation in embryos transits from apical domain to apical ring stage.•Restriction of nuclear YAP correlates to apical ring stage and trophoblast specification.•Hippo/Lats signals regulate YAP activity in mammalian embryos but not exclusively.•Variations in YAP/TEAD regulation of trophoblast lineage factors CDX2 and GATA3.
A detailed morphological staging system for cattle embryos at stages following blastocyst hatching and preceding gastrulation is presented here together with spatiotemporal mapping of gene expression ...for BMP4, BRACHYURY, CERBERUS1 (CER1), CRIPTO, EOMESODERMIN, FURIN and NODAL. Five stages are defined based on distinct developmental events. The first of these is the differentiation of the visceral hypoblast underlying the epiblast, from the parietal hypoblast underlying the mural trophoblast. The second concerns the formation of an asymmetrically positioned, morphologically recognisable region within the visceral hypoblast that is marked by the presence of CER1 and absence of BMP4 expression. We have termed this the anterior visceral hypoblast or AVH. Intra-epiblast cavity formation and the disappearance of the polar trophoblast overlying the epiblast (Rauber's layer) have been mapped in relation to AVH formation. The third chronological event involves the transition of the epiblast into the embryonic ectoderm with concomitant onset of posterior NODAL, EOMES and BRACHYURY expression. Lastly, gastrulation commences as the posterior medial embryonic ectoderm layer thickens to form the primitive streak and cells ingress between the embryonic ectoderm and hypoblast. At this stage a novel domain of CER1 expression is seen whereas the AVH disappears. Comparison with the mouse reveals that while gene expression patterns at the onset of gastrulation are well conserved, asymmetry establishment, which relies on extraembryonic tissues such as the hypoblast and trophoblast, has diverged in terms of both gene expression and morphology.
The growth of viable cattle embryos in culture to stages beyond the hatching blastocyst is of interest to developmental biologists wishing to understand developmental events beyond the first lineage ...decision, as well as for commercial applications, because a lengthening of the culturing time allows more time for diagnostic tests on biopsies, whereas extended survival can be used as a better assay system for monitoring developmental potential. We here report on a novel extended culture medium for embryo growth until embryonic day (Day) 12. We used a non-invasive morphological characterisation system that scored viability, inner cell mass (ICM) grade, hatching and embryo and ICM diameter. The basal medium was based on published uterine fluid concentrations of amino acids, carbohydrates and electrolytes. Addition of fetal bovine serum was necessary and the additive ITSX greatly improved culture success. We tested the inclusion of a seven-growth factor cocktail consisting of Activin A, Artemin, BMP4, EGF, FGF4, GM-CSF/CSF2 and LIF, as well as omission of individual components of the cocktail. In the context of the growth factor cocktail, Artemin and BMP4 provided the greatest benefit, while FGF omission had more positive than negative effects on embryo characteristics. Lastly, replacement of ITSX by B27-additive led to the most successful culture of embryos, in all media permutations.
•Development of a new basal culture medium allowing extended in vitro cattle embryo growth.•Addition of a cocktail of seven growth factors improved embryo viability and ICM quality.•Artemin and BMP4 are most beneficial for embryo size and viability and ICM quality.•B27 supplementation to basal culture medium is highly beneficial and superior to ITSX.
Steering Handbook Harrer, Manfred; Pfeffer, Peter
2016, 20160625, 2016-07-06
eBook
This edited volume presents basic principles as well as advanced concepts of the computational modeling of steering systems. Moreover, the book includes the components and functionalities of modern ...steering system, which are presented comprehensively and in a practical way. The book is written by more than 15 leading experts from the automotive industry and its components suppliers. The target audience primarily comprises practicing engineers, developers, researchers as well as graduate students who want to specialize in this field.
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.
We have previously described an extended embryo culture system, based on uterine composition, growth factors and the cell culture additive B27, for growing cattle embryos in vitro beyond embryonic ...day 7. Here, extended in vitro embryos are compared to embryos developed in the uterus and are used to establish a developmental staging framework useful for understanding developmental events occurring until Day 10. Immunofluorescence or mRNA expression of the ICM/epiblast markers OCT4, SOX2 and NANOG, hypoblast markers GATA6, SOX17 and GATA4 and trophoblast genes CDX2, GATA3, ASCL2 and IFNT revealed the presence of four stages during this period that can be molecularly distinguished. These are expanded blastocyst, hatched blastocyst, hypoblast layering and early hypoblast migration. Interestingly NANOG and SOX17 show reciprocal expression at the expanded blastocyst stage, well before SOX2 and GATA6 expression refines to a similar so-called "salt and pepper" mutually exclusive expression in the ICM at the hatched blastocyst stage. GATA4 expression is only seen from stages when the hypoblast starts migrating around the blastocyst cavity. Intriguingly, trophoblast still expresses GATA6 and OCT4 in all cells during the expanded blastocyst phase, while SOX2 and SOX17 are seen in only some trophoblast cells. By the hypoblast-epiblast layering stage no trophoblast expression remains except for that of OCT4 protein, which starts waning in trophoblast once the hypoblast begins migrating. Lastly, it is shown that cultured embryos exhibit increased expression of the stress marker TP53 in the epiblast and hypoblast at late stages in comparison to embryos produced in the uterine environment.
The trophectoderm (TE) and inner cell mass (ICM) are committed and marked by reciprocal expression of Cdx2 and Oct4 in mouse late blastocysts. We find that the TE is not committed at equivalent ...stages in cattle, and that bovine Cdx2 is required later, for TE maintenance, but does not repress
Oct4 expression. A
mouse Oct4 (
mOct4) reporter, repressed in mouse TE, remained active in the cattle TE;
bovine Oct4 constructs were not repressed in the mouse TE.
mOct4 has acquired Tcfap2 binding sites mediating Cdx2-independent repression—cattle, humans, and rabbits do not contain these sites and maintain high
Oct4 levels in the TE. Our data suggest that the regulatory circuitry determining ICM/TE identity has been rewired in mice, to allow rapid TE differentiation and early blastocyst implantation. These findings thus emphasize ways in which mice may not be representative of the earliest stages of mammalian development and stem cell biology.
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► Late blastocyst cattle trophectoderm (TE) expresses Oct4 and is not yet committed ► Cdx2 is required for cattle TE maintenance but not for Oct4 repression ► The mouse Oct4 locus is also repressed via AP2 binding sites that are not conserved ► TE regulatory circuitry correlates with the timing of TE commitment and implantation
On the enigmatic disappearance of Rauber’s layer van Leeuwen, Jessica; Rawson, Pisana; Berg, Debra K. ...
Proceedings of the National Academy of Sciences - PNAS,
07/2020, Volume:
117, Issue:
28
Journal Article
Peer reviewed
Open access
The polar trophoblast overlays the epiblast in eutherian mammals and, depending on the species, has one of two different fates. It either remains a single-layered, thinning epithelium called ...“Rauber’s layer,” which soon disintegrates, or, alternatively, it keeps proliferating, contributing heavily to the population of differentiating, invasive trophoblast cells and, at least in mice, to the induction of gastrulation. While loss of the persistent polar trophoblast in mice leads to reduced induction of gastrulation, we show here that prevention of the loss of the polar trophoblast in cattle results in ectopic domains of the gastrulation marker, BRACHYURY. This phenotype, and increased epiblast proliferation, arose when Rauber’s layer was maintained for a day longer by countering apoptosis through BCL2 overexpression. This suggests that the disappearance of Rauber’s layer is a necessity, presumably to avoid excessive signaling interactions between this layer and the subjacent epiblast. We note that, in all species in which the polar trophoblast persists, including humans and mice, ectopic polar trophoblast signaling is prevented via epiblast cavitation which leads to the (pro)amniotic cavity, whose function is to distance the central epiblast from such signaling interactions.
Trophoblast development Pfeffer, Peter L; Pearton, David J
Reproduction
143, Issue:
3
Journal Article
Peer reviewed
Open access
This review summarises current knowledge about the specification, commitment and maintenance of the trophoblast lineage in mice and cattle. Results from gene expression studies, in vivo ...loss-of-function models and in vitro systems using trophoblast and embryonic stem cells have been assimilated into a model seeking to explain trophoblast ontogeny via gene regulatory networks. While trophoblast differentiation is quite distinct between cattle and mice, as would be expected from their different modes of implantation, recent studies have demonstrated that differences arise much earlier during trophoblast development.
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