Project description:Morphogen signalling forms an activity gradient and instructs cell identities in a signalling strength-dependent manner to pattern developing tissues. However, developing tissues also undergo dynamic morphogenesis, which may produce cells with unfit morphogen signalling and consequent noisy morphogen gradient. Here we show that a cell competition-related system corrects such noisy morphogen gradients. Zebrafish imaging analyses of the Wnt/β-catenin signalling gradient, which acts as a morphogen to establish embryonic anterior-posterior patterning, revealed that unfit cells with abnormal Wnt/β-catenin activity spontaneously appear and produce noise in the gradient. Communication between unfit and neighbouring fit cells via cadherin proteins stimulates apoptosis of the unfit cells by activating Smad signalling and reactive oxygen species production. This unfit cell elimination is required for proper Wnt/β-catenin gradient formation and consequent anterior-posterior patterning. Because this gradient controls patterning not only in the embryo but also in adult tissues, this system may support tissue robustness and disease prevention.
Project description:Morphogen signalling forms an activity gradient and instructs cell identities in a signalling strength-dependent manner to pattern developing tissues. However, developing tissues also undergo dynamic morphogenesis, which may produce cells with unfit morphogen signalling and consequent noisy morphogen gradient. Here we show that a cell competition-related system corrects such noisy morphogen gradients. Zebrafish imaging analyses of the Wnt/β-catenin signalling gradient, which acts as a morphogen to establish embryonic anterior-posterior patterning, revealed that unfit cells with abnormal Wnt/β-catenin activity spontaneously appear and produce noise in the gradient. Communication between unfit and neighbouring fit cells via cadherin proteins stimulates apoptosis of the unfit cells by activating Smad signalling and reactive oxygen species production. This unfit cell elimination is required for proper Wnt/β-catenin gradient formation and consequent anterior-posterior patterning. Because this gradient controls patterning not only in the embryo but also in adult tissues, this system may support tissue robustness and disease prevention.
Project description:Positional patterning during human brain development is orchestrated through highly coordinated interplays of locally produced inductive signals. While animal models have elucidated general signaling pathways during early neurodevelopment, individual morphogens' effects underlying the proper human brain regionalization remain unclear. Current technologies are limited in generating stable, well-confined gradients in neural organoids for robust regionalization. Here, we report a Matrigel-free passive diffusion-based morphogen gradient generator (PdMG) that reliably established a steep exogenous spatial morphogen gradient in human neural organoids. We further established dorsal-ventral forebrain, rostral-caudal fore-midbrain-like, and rostral-caudal fore-hindbrain-like patterning by applying Sonic hedgehog/ WNT-inhibitor, WNT, and retinoic acid gradients, respectively. Spatial transcriptomics analysis revealed robust regionalization in early-stage patterned organoids, as well as active neurogenesis and GABAergic interneuron migrations in late-stage patterned organoids. Together, this study provides a framework for modeling the spatial-temporal morphogen dynamics that regulate key cell fate specifications and axis formations using patterned neural organoid models.
Project description:It has now become clear that the process of fate specification during early embryogenesis is mediated by a handful of key signaling pathways. However, how the temporal and spatial integration of these signals plays out to give rise to self-organization of tissues remains obscure. Here we use artificial human gastruloids and quantitative single-cell analysis to dissect the temporal integration of two key pathways WNT and ACTIVIN that along with BMP control gastrulation and primitive streak patterning in model systems. We showed that ACTIVIN elicits a transient signaling response, as well as a transient induction of differentiation. However, unlike BMP and WNT, ACTIVIN cannot induce stable primitive streak formation and mesodermal patterning. Pre-exposure to WNT switches the response of cells to ACTIVIN whereby it becomes a concentration dependent morphogen. This provides evidence for WNT signaling memory that occurs at the transcriptional level and not as a modifier of ACTIVIN signaling dynamics.
Project description:The phenomenon of embryonic scaling, the ability of embryos to regulate their structure in proportion to size, is a fascinating yet underexplored area of study. First described in sea urchin embryos by Hans Driesch, this phenomenon is now recognized as a striking example of how living organisms use non-equilibrium self-organization to generate pattern-determining morphogen gradients that scale with embryo size. Although specific molecular mechanisms for scaling morphogens gradients have been described in some cases, a general approach for the targeted identification such mechanism had not been elaborated until recently. In search of a solution, we hypothesized the obligatory participation in the scaling mechanisms of special genes, which we named scalers, with their expression being sensitive to the size of the embryo and their protein products regulating the scale of morphogen gradients. As proof of principle, we recently identified scalers by detecting differentially expressing genes in wild-type and half-size Xenopus laevis gastrula embryos. We also described a novel mechanism by which one of the identified scalers, the gene encoding metalloproteinase 3 (Mmp3), modulates gradients of the morphogenic protein Bmp and its antagonists Chordin and Noggin1/2 based on Xenopus laevis embryo size. To test the universality of the scalers hypothesis, we now applied our method of identifying scalers that adjust Bmp/Chordin gradients to the size of the sea urchin embryo, Strongylocentrotus droebachiensis. Our results show that at least two members of the gene cluster encoding astacin proteinases of the Span family, namely bp10 and Span, exhibit properties characteristic of scalers in the embryos of this species. Notably, their expression increases in half-size embryos, and their protein products specifically digest Chordin. Additionally, we found that the loss of function of bp10 and span lead to contraction of the ventral domain of the Bmp signaling nuclear effector, pSmad1/5. These findings not only validate the scalers hypothesis but also uncover a novel mechanism by which Span proteinases fine-tune Chordin and Bmp morphogen gradients in sea urchins, offering promising avenues for future research into scaling mechanisms across biological systems.
Project description:Understanding how transcription factors regulate organized cellular diversity in developing tissues remains a major challenge due to their pleiotropic functions. We addressed this by monitoring and genetically modulating the activity of PAX3 and PAX7 during the specification of neural progenitor pools in the embryonic spinal cord. Using mouse models, we show that the balance between the transcriptional activating and repressing functions of these factors is modulated along the dorsoventral axis and is instructive to the patterning of spinal progenitor pools. By combining loss-of-function experiments with functional genomics in spinal organoids, we demonstrate that PAX-mediated repression and activation rely on distinct cis-regulatory genomic modules. This enables both the coexistence of their dual activity in dorsal cell progenitors and the specific control of two major differentiation programs. PAX promotes H3K27me3 deposition at silencers to repress ventral identities, while at enhancers, they act as pioneer factors, opening and activating cis-regulatory modules to specify dorsal-most identities. Finally, we show that this pioneer activity is restricted to cells exposed to BMP morphogens, ensuring spatial specificity. These findings reveal how PAX proteins, modulated by morphogen gradients, orchestrate neuronal diversity in the spinal cord, providing a robust framework for neural subtype specification.
Project description:This is the simple model without diffusion described in th epublication
Sharp developmental thresholds defined through bistability by antagonistic gradients of retinoic acid and FGF signaling.
Goldbeter A, Gonze D, Pourquié O. Dev Dyn. 2007 Jun;236(6):1495-508. PMID:
17497689, doi:10.1016/j.jtbi.2008.01.006
Abstract:
The establishment of thresholds along morphogen gradients in the embryo is poorly understood. Using mathematical modeling, we show that mutually inhibitory gradients can generate and position sharp morphogen thresholds in the embryonic space. Taking vertebrate segmentation as a paradigm, we demonstrate that the antagonistic gradients of retinoic acid (RA) and Fibroblast Growth Factor (FGF) along the presomitic mesoderm (PSM) may lead to the coexistence of two stable steady states. Here, we propose that this bistability is associated with abrupt switches in the levels of FGF and RA signaling, which permit the synchronized activation of segmentation genes, such as mesp2, in successive cohorts of PSM cells in response to the segmentation clock, thereby defining the future segments. Bistability resulting from mutual inhibition of RA and FGF provides a molecular mechanism for the all-or-none transitions assumed in the "clock and wavefront" somitogenesis model. Given that mutually antagonistic signaling gradients are common in development, such bistable switches could represent an important principle underlying embryonic patterning.
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To cite BioModels Database, please use: Li C, Donizelli M, Rodriguez N, Dharuri H, Endler L, Chelliah V, Li L, He E, Henry A, Stefan MI, Snoep JL, Hucka M, Le Novère N, Laibe C (2010) BioModels Database: An enhanced, curated and annotated resource for published quantitative kinetic models. BMC Syst Biol., 4:92.
Project description:In this study, we have investigated the molecular basis of Shh signalling during development of the secondary palate and how CNCC patterning and fate is influenced by the Shh signalling network. Using a gain-of-function mouse model to activate Smoothened (R26SmoM2) signalling in the palatal mesenchyme (Osr2-IresCre), we demonstrate ectopic Hh-Smo signalling results in fully penetrant cleft palate, disrupted oral-nasal patterning and defective palatine bone formation. We show that a series of Fox transcription factors, including the novel direct target Foxl1, function downstream of Hh signalling in the secondary palate. Furthermore, we demonstrate that Wnt/BMP antagonists, in particular Sostdc1, are positively regulated by Hh signalling, concomitant with down-regulation of key regulators of osteogenesis and BMP signalling effectors. Microarray analysis was performed on excised palatal shelves from Osr2-IresCre+/- (wild-type) and Osr2-IresCre;Smo+/M2 (mutant) embryos at embryonic day (E)13.5. Osr2-IresCre (PMID:17941042) and R26SmoM2 (PMID:15107405) mice have been described previously.
Project description:Purpose: Characterization of cell types in wild-type and TCTN2 KO human neural tube organoids (hNTOs). Methods: Wild-type and TCTN2 KO hNTOs were harvested at day11. Libraries were prepared using Single Cell 3′Library & gel Bead kit v3.1 (10x Genomics, Cat# PN-1000121) according to the manufacturer’s protocol for 10000 cells recovery. Results: 13 neural progenitor cells were detected in wild-type hNTOs, and TCTN2 deficiency led to reduction of ventral progenitors cells. Conclusions: A well-organized nueral tube organoid was constructed by applying BMP and SHH morphogen gradients.
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.