Periodic Reporting for period 1 - COORDINATION (Coordination of mouse embryogenesis in space and time at implantation)
Periodo di rendicontazione: 2023-03-01 al 2025-08-31
Self-organisation is a key feature of living systems and entails complex interplay between multiple inputs across various spatio-temporal scales. Using pre-implantation mouse embryos as a model system, our studies revealed a principle of regulative development, in which feedback between cell fate, polarity and mechanics ensures robust control of embryo shape and pattern. However, as embryos implant into the uterus, this self-organisation mechanism needs to be integrated in the context of surrounding tissues. In this project, we aim to understand how developmental mechanisms are coordinated across cells and tissues in space and time, using peri-implantation mouse embryos as a model system. Upon implantation, the mouse embryo undergoes a key transition in morphogenesis, cell cycle and growth, and exhibits a remarkable capacity for embryo size regulation. We developed ex vivo 3D culture and light-sheet microscopy to recapitulate morphogenesis and embryo-uterus interactions, and analyse changes in cell shape, fate, polarity and mechanics. Using these methods, we will 1) mechanistically understand the transformation from the blastocyst to the egg cylinder as embryonic-extraembryonic and uterine tissues interact. We will use embryo size control as a paradigm to 2) study how embryo size is sensed and feeds back to regulate the temporal progression of development. At the cellular level, we will characterize cell growth dynamics that underlies embryo growth control, and identify what triggers the transition from cleavage to proliferative cell cycle at mammalian mid-blastula transition. Finally, we will 3) investigate the role of embryo-uterus interactions in embryo morphogenesis and positioning within the uterus.
Overall, we made an excellent progress in projects addressing three major aims. This resulted in publication of 4 research papers (Fabrèges et al. 2024 Science; Moghe et al. 2025 Nat Cell Biol; Ichikawa et al. 2025 bioRxiv; Guruciaga et al. 2024 arXiv).
The first study (Fabrèges et al. 2024 Science) demonstrated a key role of cell division timing variability in embryonic patterning, hence revealing the coordination between the temporal progression of cell cycle and the spatial cell allocation. To this end, we built a morphomap of embryogenesis in mouse, rabbit and monkey embryos, which revealed that although cell divisions desynchronise passively, 8-cell embryos display robust 3D morphogenesis. Using topological analysis and genetic perturbations in mouse, we showed that embryos progressively change their cellular connectivity to a preferred topology, which can be predicted by a physical model where noise and actomyosin-contractility facilitate topological transitions lowering surface energy. This favours compact embryo packing at the 8- and 16-cell stages and promotes higher number of inner cells. Synchronised division reduced embryo packing and generated more mis-allocated cells and fewer inner-cell-mass cells.
The second study (Moghe et al. 2025 Nat Cell Biol) revealed that coupling of spatio-temporal developmental parameters ensures patterning robustness. This study investigated how precision in patterning is achieved despite the inherent developmental variability, using mouse blastocysts in which salt-and-pepper epiblast (EPI) and primitive endoderm (PrE) cells pattern the inner cell mass. Measuring cell fate and dynamics, we found that PrE cells form apical polarity-dependent protrusions required for migration towards the fluid cavity surface, where they are trapped due to decreased surface tension. Concomitantly, PrE cells deposit an extracellular matrix gradient, breaking the tissue-level symmetry and collectively guiding their own migration. Tissue size perturbations of mouse embryos and their comparison with monkey and human blastocysts further demonstrate that the fixed proportion of PrE/EPI cells is optimal with respect to tissue size and geometry and, despite variability, ensures patterning robustness.
Finally, in the studies under peer-review (Ichikawa et al. 2025 bioRxiv; Guruciaga et al. 2024 arXiv), we showed in experiments and theory that tissue-tissue boundaries guide EPI cell alignment and central lumen positioning, presenting a mechanism and functional significance of EPI tissue patterning in spatial contexts.
The first study (Fabrèges et al. 2024 Science) demonstrated a key role of cell division timing variability in embryonic patterning, hence revealing the coordination between the temporal progression of cell cycle and the spatial cell allocation. To this end, we built a morphomap of embryogenesis in mouse, rabbit and monkey embryos, which revealed that although cell divisions desynchronise passively, 8-cell embryos display robust 3D morphogenesis. Using topological analysis and genetic perturbations in mouse, we showed that embryos progressively change their cellular connectivity to a preferred topology, which can be predicted by a physical model where noise and actomyosin-contractility facilitate topological transitions lowering surface energy. This favours compact embryo packing at the 8- and 16-cell stages and promotes higher number of inner cells. Synchronised division reduced embryo packing and generated more mis-allocated cells and fewer inner-cell-mass cells.
The second study (Moghe et al. 2025 Nat Cell Biol) revealed that coupling of spatio-temporal developmental parameters ensures patterning robustness. This study investigated how precision in patterning is achieved despite the inherent developmental variability, using mouse blastocysts in which salt-and-pepper epiblast (EPI) and primitive endoderm (PrE) cells pattern the inner cell mass. Measuring cell fate and dynamics, we found that PrE cells form apical polarity-dependent protrusions required for migration towards the fluid cavity surface, where they are trapped due to decreased surface tension. Concomitantly, PrE cells deposit an extracellular matrix gradient, breaking the tissue-level symmetry and collectively guiding their own migration. Tissue size perturbations of mouse embryos and their comparison with monkey and human blastocysts further demonstrate that the fixed proportion of PrE/EPI cells is optimal with respect to tissue size and geometry and, despite variability, ensures patterning robustness.
Finally, in the studies under peer-review (Ichikawa et al. 2025 bioRxiv; Guruciaga et al. 2024 arXiv), we showed in experiments and theory that tissue-tissue boundaries guide EPI cell alignment and central lumen positioning, presenting a mechanism and functional significance of EPI tissue patterning in spatial contexts.
As part of Aim 3, we established a new interdisciplinary collaboration with an industry partner (Lukas Krainer, Prospective Instruments LK OG, Austria) to build the intravital microscopy, extensively tested each microscope component to identify and observe the embryo-uterus interaction, and optimized and finalized its design. The mammalian implantation process is largely enigmatic, and the dynamic embryo-uterus interaction and its underlying mechanisms are poorly understood. This new intravital microscopy will provide a fresh window and potentially transform the research of early mammalian development.