Biology subjects

Campas, O.

Publications and source records attributed to Campas, O..

13 recordsLinked to original sources

bioRxiv2025

Tissue surface mechanics constrains proliferation-driven forces to guide mammalian body axis elongation

Mammalian embryos undergo complex morphogenetic changes after implantation in the uterus. The elongation of the body along a head-to-tail axis is a pivotal event, as it lays the foundation of the body plan. While genetic and biochemical aspects of mammalian body elongation have been uncovered, the physical mechanism of axial morphogenesis remains unknown, largely due to the inaccessibility of the implanted embryo to physical measurements and manipulations in utero. Gastruloids, a stem-cell-based embryo model of mammalian axial morphogenesis, lift such limitations. Combining live imaging, direct mechanical measurements, and chemical and mechanical perturbations, here we show that axis elongation in mouse and human gastruloids is guided by a posterior actin cap at the tissue surface that constrains the expansive forces of cell proliferation. Measurements of mechanical stresses using oil microdroplets, as well as inhibition of cell proliferation and myosin activity, show that the forces driving elongation arise from cell proliferation, and not from convergent extension movements. We find that isotropic tissue expansion is redirected into posterior elongation by the formation of a supracellular actin cap at the posterior tissue surface that restricts lateral tissue expansion. Finally, we show that posterior elongation in mouse embryos displays the key features of the physical elongation mechanism reported for mouse and human gastruloids. These findings reveal that mammalian body axis elongation, including human, occurs via a different physical mechanism from other vertebrate species.

biophysics↗

bioRxiv2025

Species-specific basal fluidization shapes early forebrain development

The human forebrain exhibits an expanded surface area compared with other great apes. Despite progress in dissecting species-specific gene expression programs and cell lineages, the tissue-level physical mechanisms underlying human-specific neurodevelopment remain unclear. Here, by quantifying tissue dynamics and mechanics using oil microdroplets in cerebral organoids from humans, gorillas, chimpanzees, and mice, we uncover a transient tissue fluidization occurring exclusively in the basal region of human neuroepithelia. Enhanced droplet motility and frequent cell rearrangements reveal this basal fluidization, which gradually diminishes at the onset of neurogenesis in humans. By contrast, such basal fluidization is not detected in non-human neuroepithelia examined here. Mechanistically, basal fluidization is driven by basal nuclear fluctuations and facilitated by expanded intercellular spaces. Increasing N-cadherin expression in human neuroepithelia to gorilla levels suppresses both nuclear fluctuations and basal fluidization. Integrating simulations of neuroepithelial dynamics with experimental data, we further find that nuclear fluctuations underlying basal fluidization promote the insertion of newly divided nuclei into the basal side to support tangential surface expansion, a hallmark of human forebrain development.

developmental biology↗

bioRxiv2025

SpinePy enables automated 3D spatiotemporal quantification of multicellular in vitro systems

Organoids and stem-cell-based embryo models such as gastruloids are powerful systems to quantitatively study morphogenesis and patterning. This requires 3D analysis in reference frames that emerge dynamically over development, but are less stereotypical than in vivo. Meaningful statistical comparison and interpretation of biological and physical quantities in space and time -- such as signaling activity, gene expression or cell flows -- depend on proper quantification in these internal and dynamic coordinate systems, especially in in vitro systems that naturally exhibit larger variation. Here, we present a computational framework, packaged as a modular Python toolkit termed SpinePy, that identifies the emergent primary body axis ("spine") of individual gastruloids and constructs a local, dynamic coordinate system aligned to their morphology. SpinePy enables 3D quantification relative to evolving axes and statistical comparisons of morphodynamics, patterning, and densities across structures with varying geometries. We validate and benchmark SpinePy using both synthetic and experimental gastruloid data, providing practical insights into method performance. Using this framework, we generate 3D patterning maps from gastruloids formed with different initial cell numbers (N0). This reveals distinct patterning classes that are better explained by gastruloid volumes than by N0. While demonstrated in gastruloids, SpinePy is broadly applicable to any multicellular system where analysis relative to evolving internal axes is needed, advancing quantitative and comparative spatial biology.

developmental biology↗

bioRxiv2024

Morphodynamics of tip growing cells

Pollen tubes, root hairs and fungal hyphae elongate by adding material at their tips. The region in the immediate vicinity of the tip is dynamically pliable and allows for the addition of new wall material even as it flows in response to the turgor that drives it. Any imbalance between the rate of material addition and its consequent flow will cause a tip growing cell to either burst because its wall thins or stop growing because its wall thickens. We use an experimentally-inspired feedback law that couples vesicle exocytosis to wall mechanics via the local strain rate to construct a minimal theory for the dynamics of tip growing cells. Our theory characterizes the parameter regime where stable steady tip growth is possible in terms of two dimensionless parameters: a scaled turgor pressure, and a ratio of length scales describing gradients of wall extensibility and vesicle composition near the tip. Our analysis also explains the experimentally observed shape response of tip growing cells observed when external turgor is dynamically varied. All together our formalism provides a general framework for the coupled dynamics of internal vesicular transport and wall mechanics in tip-growing cells.

plant biology↗

bioRxiv2022

In situ quantification of osmotic pressure within living embryonic tissues

Mechanics is known to play a fundamental role in many cellular and developmental processes. Beyond active forces and material properties, osmotic pressure is believed to control essential cell and tissue characteristics. However, it remains very challenging to perform in situ and in vivo measurements of osmotic pressure. Here we introduce doubleemulsion droplet sensors that enable local measurements of osmotic pressure intra- and extra-cellularly within 3D multicellular systems, including living tissues. After generating and calibrating the sensors, we measured the osmotic pressure in blastomeres of early zebrafish embryos as well as in the interstitial fluid between the cells of the blastula by monitoring the size of droplets previously inserted in the embryo. Our results show a balance between intracellular and interstitial osmotic pressures, with values of approximately 0.7 MPa, but a large pressure imbalance between the inside and outside of the embryo. The ability to measure osmotic pressure in 3D multicellular systems (developing embryos, organoids, etc.) will help understand its role in fundamental biological processes.

biophysics↗

bioRxiv2022

A nuclear jamming transition in vertebrate organogenesis

Jamming of cell collectives and associated rigidity transitions have been shown to play a key role in tissue dynamics, structure and morphogenesis. In cellular jamming, the physical state of the tissue is controlled by cellular density and the mechanics of cell-cell contacts. A potential contribution of subcellular organelles to the emergent tissue mechanics and architecture, as well as in the control of rigidity transitions, has not been explored. Here we show the existence of a nuclear jamming transition in which jamming of nuclei constrains cell movements beyond cellular jamming, with physical interactions between nuclei controlling the emergent physical properties and architecture of the tissue. We develop a computational framework and show that nuclear volume fraction and nuclear anisotropy are key parameters to understand the emergent tissue physical state. Analysis of tissue architecture during eye and brain development in zebrafish shows that these tissues undergo a nuclear jamming transition as they form, with increasing nuclear packing leading to more ordered cellular arrangements, reminiscent of the crystalline cellular packings in the functional adult eye. Our results reveal a novel rigidity transition associated with nuclear jamming, and highlight an important role for the nucleus in the control of emergent tissue mechanics and architecture.

biophysics↗

bioRxiv2021

Stress-driven tissue fluidization physically segments vertebrate somites

The precise and robust formation of embryonic structures is essential for the function of the organism. During somitogenesis, genetic traveling waves in the presomitic mesoderm orchestrate somite formation and the segmentation of the vertebrate body axis. While key molecular and genetic aspects of this process are known, the mechanical events required to robustly define sharp somite boundaries and physically segment the presomitic mesoderm remain unclear. Here we show that both mechanical noise in the tissue and somite boundary tension are optimized to define sharp somite boundaries and robustly segment the body axis. We find that a large, actomyosin-driven increase in boundary tension progressively straightens the nascent somite-somite boundary. While noise is typically believed to be detrimental to robustness, our results show how mechanical noise in the tissue, introduced by active tension fluctuations at cell contacts, is necessary to fully straighten somite boundaries and minimize variation across individuals. Chemical and optogenetic perturbations of both boundary tension and mechanical noise in the surrounding tissue show that zebrafish embryos optimally tune these quantities to the values necessary to ensure maximal somite boundary straightness. Altogether, these results reveal the physical mechanism of somite formation in zebrafish and uncover how optimal mechanical noise helps robustly shape embryonic structures.

biophysics↗

bioRxiv2021

STRESS, an automated geometrical characterization of deformable particles for in vivo measurements of cell and tissue mechanical stresses

From cellular mechanotransduction to the formation of embryonic tissues and organs, mechanics has been shown to play an important role in the control of cell behavior and embryonic development. Most of our existing knowledge of how mechanics affects cell behavior comes from in vitro studies, mainly because measuring cell and tissue mechanics in 3D multicellular systems, and especially in vivo, remains challenging. Oil microdroplet sensors, and more recently gel microbeads, use surface deformations to directly quantify mechanical stresses within developing tissues, in vivo and in situ, as well as in 3D in vitro systems like organoids or multicellular spheroids. However, an automated analysis software able to quantify the spatiotemporal evolution of stresses and their characteristics from particle deformations is lacking. Here we develop STRESS (Surface Topography Reconstruction for Evaluation of Spatiotemporal Stresses), an analysis software to quantify the geometry of deformable particles of spherical topology, such as microdroplets or gel microbeads, that enables the automatic quantification of the temporal evolution of stresses in the system and the spatiotemporal features of stress inhomogeneities in the tissue. As a test case, we apply these new code to measure the temporal evolution of mechanical stresses using oil microdroplets in developing zebrafish tissues. Starting from a 3D timelapse of a droplet, the software automatically calculates the statistics of local anisotropic stresses, decouples the deformation modes associated with tissue- and cell-scale stresses, obtains their spatial features on the droplet surface and analyzes their spatiotemporal variations using spatial and temporal stress autocorrelations. The automated nature of the analysis will help users obtain quantitative information about mechanical stresses in a wide range of 3D multicellular systems, from developing embryos or tissue explants to organoids. Author summaryThe measurement of mechanical stresses in 3D multicellular systems, such as living tissues, has been very challenging because of a lack in technologies for this purpose. Novel microdroplet techniques enable direct, quantitative in situ measurements of mechanical stresses in these systems. However, computational tools to obtain mechanical stresses from 3D images of microdroplets in an automated and accurate manner are lacking. Here we develop STRESS, an automated analysis software to analyze the spatiotemporal characteristics of mechanical stresses from microdroplet deformations in a wide range of systems, from living embryonic tissues and tissue explants to organoids and multicellular spheroids.

biophysics↗

bioRxiv2021

Mechanics of the cellular microenvironment as perceived by cells in vivo

Tissue morphogenesis and repair, as well as organ homeostasis, require cells to constantly monitor their 3D microenvironment and adapt their behaviors in response to local biochemical and mechanical cues1-6. In vitro studies have shown that substrate stiffness and stress relaxation are important mechanical parameters in the control of cell proliferation and differentiation, stem cell maintenance, cell migration 7-11, as well as tumor progression and metastasis12,13. Yet, the mechanical parameters of the microenvironment that cells perceive in vivo, within 3D tissues, remain unknown. In complex materials with strain- and time-dependent material properties, the perceived mechanical parameters depend both on the strain and timescales at which the material is mechanically probed14. Here, we quantify in vivo and in situ the mechanics of the cellular microenvironment that cells probe during vertebrate presomitic mesoderm (PSM) specification. By analyzing the magnitude and dynamics of endogenous, cell-generated strains, we show that individual cells preferentially probe the stiffness associated with deformations of the supracellular, foam-like tissue architecture. We reveal how stress relaxation leads to a perceived microenvironment stiffness that decreases over time, with cells probing the softest regime. While stress relaxation timescales are spatially uniform in the tissue, most mechanical parameters, including those probed by cells, vary along the anteroposterior axis, as mesodermal progenitors commit to different lineages. Understanding the mechanical parameters that cells probe in their native 3D environment is important for quantitative studies of mechanosensation in vivo2-4,6,15 and can help design scaffolds for tissue engineering applications16-18.

biophysics↗

bioRxiv2020

Mechanical control of tissue shape and morphogenetic flows during vertebrate body axis elongation

Shaping embryonic tissues into their functional morphologies requires cells to control the physical state of the tissue in space and time. While regional variations in cellular forces or cell proliferation have been typically assumed to be the main physical factors controlling tissue morphogenesis, recent experiments have revealed that spatial variations in the tissue physical (fluid/solid) state play a key role in shaping embryonic tissues. Here we theoretically study how the regional control of fluid and solid tissue states guides morphogenetic flows to shape the extending vertebrate body axis. Our results show that both the existence of a fluid-to-solid tissue transition along the anteroposterior axis and the tissue surface tension determine the shape of the tissue and its ability to elongate unidirectionally, with large tissue tensions preventing unidirectional elongation and promoting blob-like tissue expansions. We predict both the tissue morphogenetic flows and stresses that enable unidirectional axis elongation. Our results show the existence of a sharp transition in the structure of morphogenetic flows, from a flow with no vortices to a flow with two counter-rotating vortices, caused by a transition in the number and location of topological defects in the flow field. Finally, comparing the theoretical predictions to quantitative measurements of both tissue flows and shape during zebrafish body axis elongation, we show that the observed morphogenetic events can be explained by the mere existence of a fluid-to-solid tissue transition along the anteroposterior axis. These results highlight the role of spatiotemporally-controlled fluid-to-solid transitions in the tissue state as a physical mechanism of embryonic morphogenesis.

biophysics↗

bioRxiv2020

Embryonic Tissues as Active Foams

The physical state of embryonic tissues emerges from non-equilibrium, collective interactions among constituent cells. Cellular jamming, rigidity transitions and characteristics of glassy dynamics have all been observed in multicellular systems, but there is no unifying framework to describe all these behaviors. Here we develop a general computational framework that enables the description of embryonic tissue dynamics, accounting for the presence of extracellular spaces, complex cell shapes and tension fluctuations. In addition to previously reported rigidity transitions, we find a distinct rigidity transition governed by the magnitude of tension fluctuations. Our results indicate that tissues are maximally rigid at the structural transition between confluent and non-confluent states, with actively-generated tension fluctuations controlling stress relaxation and tissue fluidization. Comparing simulation results to experimental data, we show that tension fluctuations do control rigidity transitions in embryonic tissues, highlighting a key role of non-equilibrium tension dynamics in developmental processes.

biophysics↗

bioRxiv2020

Physical constraints on early blastomere packings

At very early embryonic stages, when embryos are composed of just a few cells, establishing the correct packing arrangements (contacts) between cells is essential for the proper development of the organism. As early as the 4-cell stage, the observed cellular packings in different species are distinct and, in many cases, differ from the equilibrium packings expected for simple adherent and deformable particles. It is unclear what are the specific roles that different physical parameters, such as the forces between blastomeres, their division times, orientation of cell division and embryonic confinement, play in the control of these packing configurations. Here we simulate the non-equilibrium dynamics of cells in early embryos and systematically study how these different parameters affect embryonic packings at the 4-cell stage. In the absence of embryo confinement, we find that cellular packings are not robust, with multiple packing configurations simultaneously possible and very sensitive to parameter changes. Our results indicate that the geometry of the embryo confinement determines the packing configurations at the 4-cell stage, removing degeneracy in the possible packing configurations and overriding division rules in most cases. Overall, these results indicate that physical confinement of the embryo is essential to robustly specify proper cellular arrangements at very early developmental stages. Author summaryAt the initial stages of embryogenesis, the precise arrangement of cells in the embryo is critical to ensure that each cell gets the right chemical and physical signals to guide the formation of the organism. Even when the embryo is made of only four cells, different species feature varying cellular arrangements: cells in mouse embryos arrange as a tetrahedron, in the nematode worm C. elegans cells make a diamond and in sea urchins cells arrange in a square configuration. How do cells in embryos of different species control their arrangements? Using computer simulations, we studied how cell divisions, physical contacts between cells and the confinement of the embryo by an eggshell affect the arrangements of cells when the embryos have only 4 cells. We find that the shape of the confining eggshell plays a key role in controlling the cell arrangements, removing unwanted arrangements and robustly specifying the proper contacts between cells. Our results highlight the important roles of embryonic confinement in establishing the proper cell-cell contacts as the embryo starts to develop.

biophysics↗

bioRxiv2020

Coordinating cell polarization and morphogenesis through mechanical feedback

Many cellular processes require cell polarization to be maintained as the cell changes shape, grows or moves. Without feedback mechanisms relaying information about cell shape to the polarity molecular machinery, the coordination between cell polarization and morphogenesis, movement or growth would not be possible. Here we theoretically and computationally study the role of a genetically-encoded mechanical feedback (in the Cell Wall Integrity Pathway) as a potential coordination mechanism between cell morphogenesis and polarity during budding yeast mating projection growth. We developed a coarse-grained continuum description of the coupled dynamics of cell polarization and morphogenesis as well as 3D stochastic simulations of the molecular polarization machinery in the evolving cell shape. Both theoretical approaches show that in the absence of mechanical feedback (or in the presence of weak feedback), cell polarity cannot be maintained at the projection tip during growth, with the polarization cap wandering off the projection tip, arresting morphogenesis. In contrast, for mechanical feedback strengths above a threshold, cells can robustly maintain cell polarization at the tip and simultaneously sustain mating projection growth. These results indicate that the mechanical feedback encoded in the Cell Wall Integrity pathway can provide important positional information to the molecular machinery in the cell, thereby enabling the coordination of cell polarization and morphogenesis. Author summaryCell migration, morphogenesis and secretion are among the vast number of cellular processes that require cells to define a preferred spatial direction to perform essential tasks. This is achieved by setting an intracellular molecular gradient that polarizes the cell. While the molecular players involved in cell polarization and some of the mechanisms that cells use to establish such molecular gradients are known, it remains unclear how cells maintain polarization as they dramatically change shape during morphogenesis, migration, etc. Here we identify a potential feedback control mechanism, encoded genetically in cells, that provides the molecular polarization machinery with the necessary information about cell geometry to maintain cell polarization during cell shape changes.

biophysics↗