ABSTRACT: Development of the embryonic head: Modelling the impact of WNT signalling activity on the differentiation of epiblast cells to neural progenitors [Dkk]
Project description:The impact of WNT signalling activity on the acquisition and restriction of lineage propensity of germ layer progenitors and the gene network activity for cell fate decision during the development of the embryonic head was modelled in the epiblast stem cells derived and maintained under different signalling conditions. Our findings showed that the modulation of WNT activity is critical for the specification of the anterior (head) tissue progenitors in the multipotent early epiblast and the repression of WNT activity enhances the ectoderm lineage potency of the epiblast cells and poises the activation of endogenous WNT activity that drives neurogenesis during head morphogenesis.
Project description:The modulation of WNT activity is critical for the specification of the anterior (head) tissue progenitors in the multipotent early epiblast and the repression of WNT activity enhances the ectoderm lineage potency of the epiblast cells and poises the activation of endogenous WNT activity that drives neurogenesis during head morphogenesis.
Project description:To define the sequence of events that lead to the generation of somatic motor neurons (MNs), we took advantage of ESCs, which can be directed to differentiate into spinal neural progenitors (NPs) in vitro (Gouti et al. 2014). This method relies on the exposure of ESCs, cultured as a monolayer, to a brief pulse of Wnt signalling prior to neural induction. Subsequently, removal of Wnt signalling and exposure to retinoic acid (RA) results in the generation of NPs. Exposure of these NPs to Shh signalling agonist SAG induces the expression of genes expressed in the ventral spinal cord and the induction of MNs.
Project description:The spinal cord is generated progressively as cells leave the caudal region of the elongating body axis such that the temporal steps of neural differentiation become spatially separated along the head to tail axis. At key stages, it is therefore possible to isolate near-adjacent cell populations from the same embryo in distinct differentiation states. Cells in the caudal lateral epiblast adjacent to the primitive streak (also known as the stem zone, SZ, in the chick) express both early neural and mesodermal genes. Other cells in the stem zone will gastrulate to form the paraxial mesoderm or remain in the epiblast cell sheet and become neural progenitors. These latter cells form a new region called the preneural tube (PNT), which is flanked by unsegmented presomitic mesoderm and represents an early neural progenitor state that can be induced by FGF signalling to revert back to a multi-potent SZ state. Rostral to this, the closed caudal neural tube (CNT) is flanked by somites and is an early site of co-expression of genes characteristic of neural progenitors, and of ventral patterning genes (Diez del Corral et al., 2003). The CNT contains the first few neurons and exposure to FGF cannot revert this tissue to a multi-potent SZ state (Diez del Corral et al., 2002). The transition from the PNT to the CNT thus involves commitment to a neural fate that this is regulated by a switch from FGF to retinoid signalling. More advanced neuroepithelium is then located in more rostral neural tube (RNT), in which neuronal differentiation is ongoing and dorsoventral pattern is refined. This experiment uses the Affymetrix GeneChip chicken genome microarray to compare the transcriptomes of microdissections of these spatially distinct cell populations from the elongating neural axis of HH stage 10 chick embryos. Dissections were carried out in L15 medium at 4°C and explants pooled in TRIzol reagent (Gibco) for RNA extraction. Notochord was removed by controlled trypsin digestion that aimed to keep the neural ventral midline. For the microarrays, at least five tissue samples for each region were pooled to make each of three biological replicates for each (n>15 for each region).
Project description:Correct neural progenitor fate determination requires the coordination of extrinsic fate determinant signals with intrinsic responses. Post-translational modifications dynamically alter protein function and so are ideally situated to regulate development. Here we show that the deubiquitylaying enzyme, Usp9x modulates both intrinsic and extrinsic regulators of mouse neural progenitors. Nestin-cre mediated deletion of Usp9x from neural progenitors results in a transient disruption of cell adhesion and apical-basal polarity as well as the premature differentiation of intermediate neural progenitors. Ablation of Usp9x also significantly increased β-catenin protein levels, especially S33/S37/T41 phospho-β-catenin, and Wnt signalling. Usp9x was found to be part of the β-catenin destruction complex and loss of Usp9x affects destruction complex composition. Notch signalling was also increased in Usp9x ablated neural progenitors, coinciding with decreased Itch and Numb, and increased Notch intracellular domain protein levels. Usp9x co-localized and immunopreciptiated with Numb from neural progenitors suggesting it is required for Numb stabilisation. These data suggest Usp9x plays a role in coordinating intrinsic responses to extrinsic signals during neural development.
Project description:During gastrulation, epiblast cells are pluripotent and their fate is thought to be constrained principally by their position. Cell fate is progressively restricted by localised signalling cues from areas including the primitive streak (PS). However, it is unknown whether this restriction accompanies, at the single cell level, a reduction in potency. Investigation of these early transition events in vitro is possible via the use of Epiblast Stem Cells (EpiSCs), self-renewing pluripotent cell lines equivalent to the postimplantation epiblast. Strikingly, EpiSCs express various early lineage-specific markers in self-renewing conditions. However, it is unknown whether cells that express these markers are pluripotent, spontaneously differentiated, or biased towards specific lineages. Here we show that EpiSC are inherently heterogeneous and contain two major and mutually exclusive subpopulations with PS and neural characteristics respectively. Using differentiation assays and embryo grafting we demonstrate that PS-like EpiSCs are biased towards mesoderm and endoderm differentiation but they still retain their pluripotent character. The acquisition of a PS character by undifferentiated EpiSC is mediated by paracrine Wnt signalling. Elevation of Wnt activity promotes further restriction into PS-associated cell fates which occurs via the generation of distinct clonal mesendodermal and neuromesodermal precursors. Collectively, our data suggest that primed pluripotency encompasses a range of reversible lineage-biased states reflecting the birth of pioneer lineage precursors from a pool of uncommitted EpiSCs similar to the earliest cell fate restriction events taking place in the gastrula-stage epiblast. Total RNA obtained (3 biological replicates) from flow sorted dsRed2+, dsRed2-, and +CHIRON treated for 48h cells was isolated and labelled/amplified using the IlluminaM-BM-. TotalPrepM-bM-^DM-" RNA Amplification Kit (Life Technologies)
Project description:Human development relies on the correct replication, maintenance and segregation of our genetic blueprints. How these processes are monitored across embryonic lineages, and why genomic mosaicism varies during development remain unknown. Using pluripotent stem cells, we identify that several patterning signals –including WNT, BMP and FGF– converge into the modulation of DNA replication stress and damage during S-phase, which in turn controls chromosome segregation fidelity in mitosis. We show that the WNT and BMP signals protect from excessive origin firing, DNA damage and chromosome missegregation derived from stalled forks in pluripotency. Cell signalling control of chromosome segregation declines during lineage specification into the three germ layers, but re-emerges in neural progenitors. In particular, we find that the neurogenic factor FGF2 induces DNA replication stress-mediated chromosome missegregation during the onset of neurogenesis, which could provide a rationale for the elevated chromosomal mosaicism of the developing brain. Our results highlight roles for morphogens and cellular identity in genome maintenance that contribute to somatic mosaicism during mammalian development.
Project description:In this study, we used chemically-defined media to induce the in vitro differentiation of mouse embryonic stem cells (ESCs) towards eye field fates. Inhibition of Wnt/ß-Catenin signalling was sufficient to drive ESCs to telencephalic, but not retinal fates. Instead, retinal progenitors could be generated from competent differentiating mouse and human ESCs by the activation of Activin/Nodal signaling within a narrow temporal window corresponding to the emergence of primitive anterior neural progenitors. Our results reveal insights into the mechanisms of eye field specification and open new avenues towards the generation of retinal progenitors for translational medicine.