Periodic Reporting for period 4 - MorphoNotch (Multi-scale analysis of the interplay between cell morphology and cell-cell signaling)
Période du rapport: 2020-12-01 au 2022-05-31
Signaling, genetic regulatory circuits, and tissue morphology are inherently coupled to each other during embryonic development. Although changes in cellular and tissue morphology are commonly treated as a downstream consequence of cell fate decision processes, there are multiple examples where morphological changes occur concurrently with the differentiation processes. This suggests that a feedback between cell morphology and regulatory processes can play an important role in coordinating tissue development. Currently, however, we lack the experimental, theoretical, and conceptual tools to understand this interplay between cell morphology, signaling, and regulatory circuits. In particular, we need to understand (1) how intercellular signaling depends on the cellular morphology and on the properties of the boundary between cells, and (2) how intercellular signaling, genetic circuits, and cell mechanics integrate to generate robust differentiation patterns.
In this project we combined quantitative in-vitro and in-vivo experiments with mathematical modeling to address these questions in the context of Notch signaling and Notch mediated patterning, typically used for coordinating differentiation between neighboring cells during development. Our goals were to elucidate how the geometry and the molecular composition of the boundary between cells affect signaling. At the tissue level, we aimed at understanding how the interplay between cell morphology, cell mechanics, and Notch signaling gives rise to robust patterning in the mammalian inner ear. This research provided the conceptual framework and methodologies required for a systems level understanding of development that interconnects cell morphology, cell mechanics, and regulatory circuits.
The grant produced several important scientific papers that highlighted the following conclusions:
(1) Notch signaling depends on the contact area between cells. This dependence can be important for cell fate decisions
(2) The precise pattern of sensory hair cells in the inner is achieved through mechanical forces that drive cellular rearrangements.
(3) Feedback between Notch mediated patterning and mechanically driven morphological changes drive precise hair cell patterning.
(4) Notch signaling is involved in the spatiotemporal coordination of neural stem cells in adult zebrafish brain.
In the long run, the insights and knowledge obtained in this project are expected to have implications on basic understanding of a variety of developmental processes as well as on the potential development of regenerative approaches to hearing loss.
In this project we combined quantitative in-vitro and in-vivo experiments with mathematical modeling to address these questions in the context of Notch signaling and Notch mediated patterning, typically used for coordinating differentiation between neighboring cells during development. Our goals were to elucidate how the geometry and the molecular composition of the boundary between cells affect signaling. At the tissue level, we aimed at understanding how the interplay between cell morphology, cell mechanics, and Notch signaling gives rise to robust patterning in the mammalian inner ear. This research provided the conceptual framework and methodologies required for a systems level understanding of development that interconnects cell morphology, cell mechanics, and regulatory circuits.
The grant produced several important scientific papers that highlighted the following conclusions:
(1) Notch signaling depends on the contact area between cells. This dependence can be important for cell fate decisions
(2) The precise pattern of sensory hair cells in the inner is achieved through mechanical forces that drive cellular rearrangements.
(3) Feedback between Notch mediated patterning and mechanically driven morphological changes drive precise hair cell patterning.
(4) Notch signaling is involved in the spatiotemporal coordination of neural stem cells in adult zebrafish brain.
In the long run, the insights and knowledge obtained in this project are expected to have implications on basic understanding of a variety of developmental processes as well as on the potential development of regenerative approaches to hearing loss.
The main results in the project are the following:
1) We have shown for the first time that Notch signaling is proportional to contact area between cells for contact diameters ranging between 1-40μm. We have used mathematical modeling to show that dependence of signaling on contact area can bias cell fate decisions in a lateral inhibition process. We found that differentiation of hair cells and supporting cells in the chick inner ear is consistent with model and shows correlation between cells fate and cell geometry (i.e smaller cells are more likely to adopt hair cell fate). These results highlight the role of the interplay between cell morphology and cell-cell signaling during development. Results were published in Shaya et. al., Developmental Cell, 2017.
2) In collaboration with the lab Laure Bally-Cuif at the Pasteur Institute in Paris, we combined live imaging of adult zebrafish brain (performed by the Bally Cuif lab) with mathematical modelling to show how the spatiotemporal distribution of neural stem cells and neuron is affected by Notch signalling. In particular, we developed a new type of lateral inhibition model which captures the homeostatic distributions of neural stem cells. The model combines lateral inhibition with a 2D vertex model that tracks the lineage of stem cells as they are activated, divide, and differentiate. These results were published in Dray et al., Cell Stem Cell, 2021.
3) We have shown that the transition from disordered to ordered checkerboard-like pattern of hair cells and supporting cells in the mammalian hearing organ, the organ of Corti, is based on mechanical forces rather than signaling events. Using time-lapse imaging of mouse cochlear explants, we showed that hair cells rearrange gradually into a precise checkerboard-like pattern through a tissue-wide shear motion that coordinates intercalation and delamination events. Using mechanical models of the tissue that combine Notch mediated lateral inhibition, we showed that global shear and local repulsion forces on hair cells are sufficient to drive the transition from disordered to ordered cellular pattern. The findings in this work suggest that mechanical forces drive precise hair cell patterning in a process strikingly analogous to the process of shear-induced crystallization in polymer and granular physics. This breakthrough work highlights the role of mechanical forces in driving precise developmental patterning processes. This work was published in: Cohen et al., Nature Communications, 2020.
4) Most recently, we combined live imaging of mouse inner ear explants with hybrid mechano-regulatory models to elucidate the mechanisms underlying the formation of a single row of inner hair cells (IHC). We identify three processes that contribute to the formation of a single IHC row. First, we identify a new morphological transition, termed ‘hopping intercalation’, that allows nascent IHC to physically ‘hop’ under the apical plane into their final position. Second, we show that nascent IHC that express low levels of Atoh1 delaminate. Finally, we use laser ablation to show that differential adhesion between different cell types contributes to straightening of the IHC row. Our experimental results and modeling thus support a mechanism for precise patterning based on coordination between Notch mediated differentiation and mechanically driven organization that is likely relevant for many developmental processes. This work is currently in review. A preprint of the manuscript can be found in: https://www.biorxiv.org/content/10.1101/2022.01.24.477468v3
1) We have shown for the first time that Notch signaling is proportional to contact area between cells for contact diameters ranging between 1-40μm. We have used mathematical modeling to show that dependence of signaling on contact area can bias cell fate decisions in a lateral inhibition process. We found that differentiation of hair cells and supporting cells in the chick inner ear is consistent with model and shows correlation between cells fate and cell geometry (i.e smaller cells are more likely to adopt hair cell fate). These results highlight the role of the interplay between cell morphology and cell-cell signaling during development. Results were published in Shaya et. al., Developmental Cell, 2017.
2) In collaboration with the lab Laure Bally-Cuif at the Pasteur Institute in Paris, we combined live imaging of adult zebrafish brain (performed by the Bally Cuif lab) with mathematical modelling to show how the spatiotemporal distribution of neural stem cells and neuron is affected by Notch signalling. In particular, we developed a new type of lateral inhibition model which captures the homeostatic distributions of neural stem cells. The model combines lateral inhibition with a 2D vertex model that tracks the lineage of stem cells as they are activated, divide, and differentiate. These results were published in Dray et al., Cell Stem Cell, 2021.
3) We have shown that the transition from disordered to ordered checkerboard-like pattern of hair cells and supporting cells in the mammalian hearing organ, the organ of Corti, is based on mechanical forces rather than signaling events. Using time-lapse imaging of mouse cochlear explants, we showed that hair cells rearrange gradually into a precise checkerboard-like pattern through a tissue-wide shear motion that coordinates intercalation and delamination events. Using mechanical models of the tissue that combine Notch mediated lateral inhibition, we showed that global shear and local repulsion forces on hair cells are sufficient to drive the transition from disordered to ordered cellular pattern. The findings in this work suggest that mechanical forces drive precise hair cell patterning in a process strikingly analogous to the process of shear-induced crystallization in polymer and granular physics. This breakthrough work highlights the role of mechanical forces in driving precise developmental patterning processes. This work was published in: Cohen et al., Nature Communications, 2020.
4) Most recently, we combined live imaging of mouse inner ear explants with hybrid mechano-regulatory models to elucidate the mechanisms underlying the formation of a single row of inner hair cells (IHC). We identify three processes that contribute to the formation of a single IHC row. First, we identify a new morphological transition, termed ‘hopping intercalation’, that allows nascent IHC to physically ‘hop’ under the apical plane into their final position. Second, we show that nascent IHC that express low levels of Atoh1 delaminate. Finally, we use laser ablation to show that differential adhesion between different cell types contributes to straightening of the IHC row. Our experimental results and modeling thus support a mechanism for precise patterning based on coordination between Notch mediated differentiation and mechanically driven organization that is likely relevant for many developmental processes. This work is currently in review. A preprint of the manuscript can be found in: https://www.biorxiv.org/content/10.1101/2022.01.24.477468v3
Significant progress beyond the state of the art include:
1. We have shown for the first time that Notch signaling depends on the contact area and that this dependence can influence cell fate decisions.
2. We have elucidated the role of mechanical forces in generating precise alternating patterns in the inner ear. In particular, we revealed unexpected processes underlying inner ear development including the presence of shear forces acting on hair cells, and a new morphological transition termed ‘hopping intercalation’ used by hair cells to move into their right position.
3. We have shown that neural stem cell activation is not random, but is spatiotemporally coordinated by Notch signaling.
4. We have developed a new modelling platform that takes into account both signaling mediated differentiation and mechanical driven reorganization. This platform can be generalized for many developmental processes.
1. We have shown for the first time that Notch signaling depends on the contact area and that this dependence can influence cell fate decisions.
2. We have elucidated the role of mechanical forces in generating precise alternating patterns in the inner ear. In particular, we revealed unexpected processes underlying inner ear development including the presence of shear forces acting on hair cells, and a new morphological transition termed ‘hopping intercalation’ used by hair cells to move into their right position.
3. We have shown that neural stem cell activation is not random, but is spatiotemporally coordinated by Notch signaling.
4. We have developed a new modelling platform that takes into account both signaling mediated differentiation and mechanical driven reorganization. This platform can be generalized for many developmental processes.