Regionally specific levels and patterns of keratin 8 expression in the mouse embryo visceral endoderm emerge upon anterior-posterior axis determination.

The mechanical properties of the different germ layers of the early mammalian embryo are likely to be critical for morphogenesis. Cytoskeleton components (actin and myosin, microtubules, intermediate filaments) are major determinants of epithelial plasticity and resilience to stress. Here, we take advantage of a mouse reporter for Keratin 8 to record the pattern of the keratin intermediate filaments network in the first epithelia of the developing mouse embryo.

NANOG initiates epiblast fate through the coordination of pluripotency genes expression.

The epiblast is the source of all mammalian embryonic tissues and of pluripotent embryonic stem cells. It differentiates alongside the primitive endoderm in a "salt and pepper" pattern from inner cell mass (ICM) progenitors during the preimplantation stages through the activity of NANOG, GATA6 and the FGF pathway. When and how epiblast lineage specification is initiated is still unclear.

Hair Growth Activity of Three Plants of the Polynesian Cosmetopoeia and Their Regulatory Effect on Dermal Papilla Cells.

Hair loss is becoming increasingly prevalent as dietary and living habits change. The search for natural products to limit hair loss has led to tapping into traditional cosmetic knowledge. We studied three plants of the Polynesian cosmetopoeia, , and , to determine their ability to promote hair growth.

Ex Vivo Culture for Preimplantation Mouse Embryo to Analyze Pluripotency.

A couple of days after fertilization of a mouse oocyte by a sperm, two sequential cell differentiation events segregate pluripotent cells that can be identified by the presence of specific markers. Early mammalian embryos are relatively easy to recover as they are not yet implanted in the uterus matrix. Several decades of experimentation have enabled to find appropriate media to culture them, and therefore provide an excellent way to test different experimental setups such as the use of signaling inhibitors.

Netrin-1 promotes naive pluripotency through Neo1 and Unc5b co-regulation of Wnt and MAPK signalling.

In mouse embryonic stem cells (mESCs), chemical blockade of Gsk3α/β and Mek1/2 (2i) instructs a self-renewing ground state whose endogenous inducers are unknown. Here we show that the axon guidance cue Netrin-1 promotes naive pluripotency by triggering profound signalling, transcriptomic and epigenetic changes in mESCs. Furthermore, we demonstrate that Netrin-1 can substitute for blockade of Gsk3α/β and Mek1/2 to sustain self-renewal of mESCs in combination with leukaemia inhibitory factor and regulates the formation of the mouse pluripotent blastocyst.

Regulation of the ERK signalling pathway in the developing mouse blastocyst.

Activation of the ERK signalling pathway is essential for the differentiation of the inner cell mass (ICM) during mouse preimplantation development. We show here that ERK phosphorylation occurs in ICM precursor cells, in differentiated primitive endoderm (PrE) cells as well as in the mature, formative state epiblast (Epi). We further show that DUSP4 and ETV5, factors often involved in negative-feedback loops of the FGF pathway, are differently regulated.

Computational models for the dynamics of early mouse embryogenesis.

Early embryonic development, from the zygote to the blastocyst, is a paradigm of a dynamic, self-organised process. It involves gene expression, mechanical interactions between cells, cell division and inter- and intracellular signalling. Imaging and transcriptomic data have significantly improved our understanding of early embryogenesis in mammals.

Primitive Endoderm Differentiation: From Specification to Epithelialization.

At the time of implantation, the mouse blastocyst has developed three cell lineages: the epiblast (Epi), the primitive endoderm (PrE), and the trophectoderm (TE). The PrE and TE are extraembryonic tissues but their interactions with the Epi are critical to sustain embryonic growth, as well as to pattern the embryo. We review here the cellular and molecular events that lead to the production of PrE and Epi lineages and discuss the different hypotheses that are proposed for the induction of these cell types.

A multiscale model of early cell lineage specification including cell division.

Embryonic development is a self-organised process during which cells divide, interact, change fate according to a complex gene regulatory network and organise themselves in a three-dimensional space. Here, we model this complex dynamic phenomenon in the context of the acquisition of epiblast and primitive endoderm identities within the inner cell mass of the preimplantation embryo in the mouse. The multiscale model describes cell division and interactions between cells, as well as biochemical reactions inside each individual cell and in the extracellular matrix.

Cripto is essential to capture mouse epiblast stem cell and human embryonic stem cell pluripotency.

Known molecular determinants of developmental plasticity are mainly transcription factors, while the extrinsic regulation of this process has been largely unexplored. Here we identify Cripto as one of the earliest epiblast markers and a key extracellular determinant of the naive and primed pluripotent states. We demonstrate that Cripto sustains mouse embryonic stem cell (ESC) self-renewal by modulating Wnt/β-catenin, whereas it maintains mouse epiblast stem cell (EpiSC) and human ESC pluripotency through Nodal/Smad2.

Lineage specification in the mouse preimplantation embryo.

During mouse preimplantation embryo development, totipotent blastomeres generate the first three cell lineages of the embryo: trophectoderm, epiblast and primitive endoderm. In recent years, studies have shown that this process appears to be regulated by differences in cell-cell interactions, gene expression and the microenvironment of individual cells, rather than the active partitioning of maternal determinants. Precisely how these differences first emerge and how they dictate subsequent molecular and cellular behaviours are key questions in the field.

Cell Fate Specification Based on Tristability in the Inner Cell Mass of Mouse Blastocysts.

During development, interactions between transcription factors control the specification of different cell fates. The regulatory networks of genetic interactions often exhibit multiple stable steady states; such multistability provides a common dynamical basis for differentiation. During early murine embryogenesis, cells from the inner cell mass (ICM) can be specified in epiblast (Epi) or primitive endoderm (PrE).

Primitive endoderm differentiation: from specification to epithelium formation.

In amniotes, primitive endoderm (PrE) plays important roles not only for nutrient support but also as an inductive tissue required for embryo patterning. PrE is an epithelial monolayer that is visible shortly before embryo implantation and is one of the first three cell lineages produced by the embryo. We review here the molecular mechanisms that have been uncovered during the past 10 years on PrE and epiblast cell lineage specification within the inner cell mass of the blastocyst and on their subsequent steps of differentiation.

Assessment of cell lineages and cell death in blastocysts by immunostaining.

During the last decade it has been shown that most mammalian blastocysts consisted of three cell lineages. Immunofluorescence with multiple antibodies enables to identify each cell type allowing an easy detection of eventual defects. It is complementary to RT-PCR experiments as this technique allows to look at cell position and to analyze and count the proportions between the different cell types.

Gata6, Nanog and Erk signaling control cell fate in the inner cell mass through a tristable regulatory network.

During blastocyst formation, inner cell mass (ICM) cells differentiate into either epiblast (Epi) or primitive endoderm (PrE) cells, labeled by Nanog and Gata6, respectively, and organized in a salt-and-pepper pattern. Previous work in the mouse has shown that, in absence of Nanog, all ICM cells adopt a PrE identity. Moreover, the activation or the blockade of the Fgf/RTK pathway biases cell fate specification towards either PrE or Epi, respectively.

A close look at the mammalian blastocyst: epiblast and primitive endoderm formation.

During early development, the mammalian embryo undergoes a series of profound changes that lead to the formation of two extraembryonic tissues--the trophectoderm and the primitive endoderm. These tissues encapsulate the pluripotent epiblast at the time of implantation. The current model proposes that the formation of these lineages results from two consecutive binary cell fate decisions.

Fluorescent mRNA labeling through cytoplasmic FISH.

RNA in situ hybridization (ISH) has been widely used in cell and developmental biology research to study gene expression. Classical ISH protocols use colorimetric staining approaches, such as the assay with nitro blue tetrazolium/5-bromo-4-chloro-3-indolyl-phosphate (NBT/BCIP), which do not allow the implementation of multiple probe analyses and do not enable investigators to achieve cellular resolution. Here we describe a protocol to determine the presence of target cytoplasmic RNA via cytoplasmic fluorescence ISH (cFISH), an approach that renders possible the visualization of specific RNA strands from the whole tissue down to the cell.

Bmi1 facilitates primitive endoderm formation by stabilizing Gata6 during early mouse development.

The transcription factors Nanog and Gata6 are critical to specify the epiblast versus primitive endoderm (PrE) lineages. However, little is known about the mechanisms that regulate the protein stability and activity of these factors in the developing embryo. Here we uncover an early developmental function for the Polycomb group member Bmi1 in supporting PrE lineage formation through Gata6 protein stabilization.

Primitive endoderm differentiates via a three-step mechanism involving Nanog and RTK signaling.

During preimplantation mouse development, the inner cell mass (ICM) differentiates into two cell lineages--the epiblast and the primitive endoderm (PrE)--whose precursors are identifiable by reciprocal expression of Nanog and Gata6, respectively. PrE formation depends on Nanog by a non-cell-autonomous mechanism. To decipher early cell- and non-cell-autonomous effects, we performed a mosaic knockdown of Nanog and found that this is sufficient to induce a PrE fate cell autonomously.

The RNA-binding protein Unr prevents mouse embryonic stem cells differentiation toward the primitive endoderm lineage.

The maintenance of embryonic stem cells (ESCs) pluripotency depends on key transcription factors, chromatin remodeling proteins, and microRNAs. The roles of RNA-binding proteins are however poorly understood. We report that the cytoplasmic RNA-binding protein Unr prevents the differentiation of ESCs into primitive endoderm (PrE).

[Early embryogenesis in mammals: stem cells and first commitment steps].

In mammals, embryonic and extraembryonic cell lineages segregate during the first steps of cell differentiation in the preimplantation embryo. Indeed, mammal embryos contain very low energy stocks and thus get ready for implantation very early to be able to absorb nutrients from the mother, first through the yolk sac and then through the placenta. These first steps involve classical genetic and morphogenetic processes as well as specific mechanisms of early embryo development such as epigenetic reprogramming and maintenance of pluripotent cells.

Dynamic expression of Lrp2 pathway members reveals progressive epithelial differentiation of primitive endoderm in mouse blastocyst.

Mesenchyme to epithelium transitions are crucial to embryonic development. The early mouse embryo offers an excellent model to study epithelium formation as during the first three days of development two epithelia are formed, the trophectoderm (TE) and the primitive endoderm (PrE). We have previously shown that PrE cells are determined within the blastocyst ICM long before epithelium formation.

Disruption of early proximodistal patterning and AVE formation in Apc mutants.

In the postimplantation mouse embryo, axial patterning begins with the restriction of expression of a set of genes to the distal visceral endoderm (DVE). This proximodistal (PD) axis is subsequently transformed into an anteroposterior axis as the VE migrates anteriorly to form the anterior visceral endoderm (AVE). Both Nodal and Wnt signaling pathways are involved in these events.

Early lineage segregation between epiblast and primitive endoderm in mouse blastocysts through the Grb2-MAPK pathway.

It has been thought that early inner cell mass (ICM) is a homogeneous population and that cell position in the ICM leads to the formation of two lineages, epiblast (EPI) and primitive endoderm (PE), by E4.5. Here, however, we show that the ICM at E3.