Nodal signaling makes growing up stressful
Summary by Katherine Rogers: Autorino, C., Khoromskaia, D., Harari, L., Floris, E., Booth, H., Pallares-Cartes, C., Petrasiunaite, V., Dorrity, M., Corominas-Murtra, B., Hadjivasiliou, Z., and Petridou, N. (2025). A closed feedback between tissue phase transitions and morphogen gradients drives patterning dynamics. bioRxiv. 10.1101/2025.06.06.658228
Image credit: Wikimedia Commons (Jacob Pruitt)
During embryogenesis, signaling molecules like Nodal establish the diverse cell fates needed to build a healthy animal by activating different developmental programs. Simultaneously, tissue mechanical properties change in space and time as the embryo shapes itself into a three-dimensional multicellular organism. In a recent preprint, Autorino et al. [1] demonstrated a surprising feedback relationship in zebrafish between Nodal signaling and tissue mechanics. They found evidence that Nodal signaling causes tissue stiffening, thereby blocking Nodal ligand from spreading further through the embryo. This appears to ensure that Nodal-mediated developmental programs are activated precisely when and where they are needed for healthy development.
As Nodal ligand diffuses through the extracellular space, it interacts with receptors studding cell surfaces, leading to signaling activation via nuclear translocation of the transcriptional effector Smad2. To measure Nodal signaling in live embryos, Autorino et al. used a GFP-tagged Smad2 [2]. Interestingly, Nodal activity correlated with stiffer tissue (mesendoderm) in wild type embryos, inferred using rigidity percolation theory [3,4]. Further, mutants lacking Nodal activity had floppier tissue, whereas mutants with excess Nodal activity had more rigid tissues, suggesting that Nodal signaling increases stiffness.
Conversely, tissue rigidity affected Nodal signaling itself. The authors experimentally decreased rigidity using two strategies: Opto-zGrad [5,6] to optogenetically degrade a cell-adhesion protein, and a loss-of-function mutation in wnt11, a cell adhesion-promoting Nodal target gene. Both manipulations increased Nodal’s signaling range. Strikingly, when rigidity was restored in wnt11 mutants using an optogenetic Opto-RhoGEF [7] tool to increase cell contractility, the Nodal signaling range shrunk back to normal. These results suggest a negative feedback strategy whereby Nodal signaling stiffens tissues, somehow restricting its own signaling range.
How might tissue rigidity restrict Nodal signaling? Nodal ligand must wend its way through the tortuous extracellular space to activate signaling over a distance. The authors found that GFP-tagged Nodal ligand [8] was able to move farther in floppier tissue (wnt11 mutants) than in wild type—and that re-stiffening floppy tissue using Opto-RhoGEF shrunk Nodal-GFP’s range back to normal. Tissue stiffening may therefore “close the extracellular highways” by which Nodal ligand spreads, explaining how stiffening shortens Nodal’s range. In future work it could be revealing to perform FRAP to directly measure the diffusivity of Nodal-GFP in tissues with experimentally altered rigidity.
The interplay between Nodal signaling and tissue mechanics may also have a role ensuring the accurate deployment of developmental programs. Using single-cell RNA-sequencing, the authors uncovered dysregulation of multiple Nodal target genes in floppy embryos (wnt11 mutants), as well as downregulation of the secreted Nodal inhibitor Lefty. They suggest that these changes stem from alterations in the spatial distribution of Nodal signaling caused by the absence of signaling/stiffness feedback. Future spatial transcriptomics experiments could be a useful test of this idea.
Together, this work uncovers a remarkable negative feedback mechanism in which Nodal signaling increases tissue rigidity, preventing further spreading of Nodal ligand and ensuring its activity is restricted to the appropriate domain. This link between signaling and tissue mechanics may help explain how the complex processes of cell fate specification and morphogenesis are coordinated.
References
1. Autorino, C., Khoromskaia, D., Harari, L., Floris, E., Booth, H., Pallares-Cartes, C., Petrasiunaite, V., Dorrity, M., Corominas-Murtra, B., Hadjivasiliou, Z., and Petridou, N. (2025). A closed feedback between tissue phase transitions and morphogen gradients drives patterning dynamics. bioRxiv. 10.1101/2025.06.06.658228.
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