Periodic Reporting for period 1 - REGCORD (Mechanisms of tissue size regulation in spinal cord development)
Okres sprawozdawczy: 2022-12-01 do 2025-05-31
Several decades ago, experiments in several mammalian species asked what will happen if early embryos lose some of their cells or have more cells than normal. These experiments have shown that mammalian embryos possess the remarkable ability to correct deviations from the normal size in early development – a phenomenon termed “restorative growth”. This observation implies that organs have intrinsic mechanisms that can sense deviations from tissue size and compensate to correct them. Although this has been observed a long time ago, the mechanisms are still unclear. The goal of this project is to identify the mechanisms by which developing organs measure and control their size. We focus on the developing spinal cord of mouse embryos to address this question, because this is an experimentally tractable system that allows combining quantitative measurements and precise manipulations. In this project, we will test two hypotheses. One is that restorative growth depends on biochemical signals, called morphogens, that spread through developing tissues, including the spinal cord. These signals are promising candidates because of their important roles in embryonic development, such as establishing the spatial organisation of cell types, as well as promoting organ growth. The second hypothesis is that tissue growth is regulated by changes in mechanical forces. These are not necessarily mutually exclusive mechanisms and could operate in parallel.
So far, our preliminary data indicate that restorative growth occurs in an organ-intrinsic manner, suggesting that systemic signals or signals between organs are not involved. Instead, our data indicate that morphogens play a role in restorative growth. We are currently dissecting the underlying mechanisms.
So far, our preliminary data indicate that restorative growth occurs in an organ-intrinsic manner, suggesting that systemic signals or signals between organs are not involved. Instead, our data indicate that morphogens play a role in restorative growth. We are currently dissecting the underlying mechanisms.
Our first step was to show that restorative growth occurs in an organ-instrinc manner and is independent from signals or forces coming from adjacent tissues. To do this we perturbed the size of the spinal cord specifically and showed that it is able to recover. To further validate this conclusion, we wanted to test if restorative growth can also occur in vitro in neural tube organoids. In order to do this, we established a new spinal cord organoid system. This system differs from previous systems, because it is simplified (a two-dimensional layer of cells, rather than a 3D structure), it is initialized in a geometrically controlled manner, which makes it reproducible and quantifiable, and grows over time, which allows us to study growth control quantitatively. We are currently using this system to further investigate restorative growth and the underlying mechanisms.
Our approach involves a combination of in vitro and in vivo assays. We are testing the roles of specific morphogen signaling pathways both in embryos, as well as in organoids. This work is still ongoing.
In addition, we developed new experimental approaches and computational tools to study the mechanical properties of the tissue. In particular, we used very sparse labelling of individual cells and tracked how the daughter cells are distributed in space in the developing spinal cord epithelium. These experiments showed that daughter cells were more spread at early developmental stages. We developed a computational cell based model of the tissue to analyze these data. Our analysis showed that the tissue material properties change over time. Importantly, the tools that we developed can now be applied in the context of restorative growth, to understand the role of mechanical properties in controlling tissue growth.
Our approach involves a combination of in vitro and in vivo assays. We are testing the roles of specific morphogen signaling pathways both in embryos, as well as in organoids. This work is still ongoing.
In addition, we developed new experimental approaches and computational tools to study the mechanical properties of the tissue. In particular, we used very sparse labelling of individual cells and tracked how the daughter cells are distributed in space in the developing spinal cord epithelium. These experiments showed that daughter cells were more spread at early developmental stages. We developed a computational cell based model of the tissue to analyze these data. Our analysis showed that the tissue material properties change over time. Importantly, the tools that we developed can now be applied in the context of restorative growth, to understand the role of mechanical properties in controlling tissue growth.
The results that we obtained so far have scientific impact that advances our current understanding of developmental mechanisms. We developed a new method for generating dorsal neural tube organoids that will be applicable to further studies of dorsal neural tube development, and in particular allows for quantitative studies of pattern formation and growth in vitro. Using this system, we obtained novel research results. We showed that the BMP signaling gradient has characteristic biphasic temporal dynamics and we uncovered the underlying mechanism. Our results generate also new questions that we, as well as others, are pursuing in follow up projects.
We also developed a computational model of the developing neural tube. This resource is freely available to the community. The research findings that stemmed from this are published in Nature Physics.
We also developed a computational model of the developing neural tube. This resource is freely available to the community. The research findings that stemmed from this are published in Nature Physics.