Biology subjects

Laussu, J.

Publications and source records attributed to Laussu, J..

4 recordsLinked to original sources

bioRxiv2025

Automated cell naming reveals reproducible and variable features of ascidian embryogenesis

Ascidians develop with highly reproducible cell lineages, making them ideal models for quantitative comparisons of morphogenesis between individuals and species. Yet, identifying corresponding cells across embryos has so far relied on slow, manual annotation following the Conklin nomenclature, which limits scalability and consistency. We present an automated framework that assigns cell identities in three-dimensional time-lapse reconstructions of ascidian embryos by transferring names from a reference set of manually curated embryos. The process operates in two steps: an initiation phase, which globally aligns early embryos to establish initial correspondences, and a propagation phase, which propagates names through time and cell divisions by comparing the pattern of contacts each cell forms with its neighbors. Applied to eight wild-type Phallusia mammillata and one Ascidiella aspersa embryo, the pipeline assigns consistent names up to stages containing about 700 cells, corrects inconsistencies in earlier datasets, and extends Conklins rules to internal tissues beyond gastrulation. Using this unified reference, we quantify natural variability in division timing and orientation, confirming the global robustness and revealing local variability of ascidian morphogenesis. The same framework also demonstrates its use to quantitatively phenotype experimentally perturbed embryos, such as those with inhibited ERK signaling. This work provides both a validated collection of coherently named ascidian embryos and open-source tools for automated cell identification and phenotypic comparison, establishing a foundation for systematic, quantitative, and evolutionary analyses of animal development.

developmental biology↗

bioRxiv2024

Unveiling mechanical interactions between cell division and extracellular matrix in human colonic epithelium organoids: A 4D study using DVC

Cell division is a major event in tissue homeostasis, enabling renewal and regeneration. Stem cells, in particular, play an important role in this homeostasis, thanks to their ability to perform symmetric or asymmetric cell divisions. To study cell division, the human colon epithelium represents a model of choice due to its rapid renewal and therefore high proliferative potential. Currently, studying the live mechanical interactions between the epithelium and its matrix in vivo is challenging due to the lack of suitable methods. 3D human colon organoids seeded in Matrigel(R) are good models for this purpose as, from isolated stem cells, they recapitulate the tissue architecture organization and properties. This culture set-up also allows to study the matrix displacements around the organoid. Here, we studied the impact of cell division within the colonic epithelium on the extracellular matrix. We performed and validated an original experimental and analytical process with a 3D time-lapse confocal microscopy to follow cell mitosis and matrix movements on which we performed Digital Volume Correlation. We showed that these two different types of cell division impact the matrix differently with the asymmetric divisions causing a mainly uniaxial displacement, whereas symmetric ones involved a multiaxial and more important one.

cell biology↗

bioRxiv2019

Multiscale mechanical model for cell division orientation in developing biological systems

Developing biological structures are highly complex systems, within which shape dynamics at different places is tightly coordinated. One key process at play during development is the regulation of cell division orientation. In this work, through a reformulation of cell division in terms of its energetic cost, we propose that oriented cell division is one mechanism by which cells can read and react to mechanical forces propagating in a tissue even in the absence of interphase cellular elongation in the direction of these forces. This view reproduces standard geometric division long-axis rules as a special case of a more general behaviour, in which systematic deviations from these rules can emerge. We show that states of anisotropic tension in multicellular systems can be the cause of these deviations, as often experimentally found in living tissues. Our results provide a unifying view on the different intracellular mechanisms at play in orienting cell division: they are processes which minimize energy loss, reflecting a trade-off between local and long-range mechanical signals. The consequences of this competition are explored in simulated tissues and confirmed in vivo during both the development of the pupal epithelium of dorsal thorax in D. melanogaster and the epidermal morphogenesis of ascidian embryos. Author summaryIn this work we reformulate the process of cell division orientation in development as a mechanical-energy optimization. We show that classical rules for division orientation naturally emerge when a cell minimizes the work performed against its local environment. Moreover, when multicellular stress profiles are taken into account, observed systematic violations of these rules are explained in correlation with states of anisotropic tension within the tissue. We confirm our findings experimentally on developing systems imaged with cellular resolution. Our results provide a new paradigm to understand cell division in multicellular contexts and contribute to building a physical view of biological phenomena.

biophysics↗

bioRxiv2017

Contact-dependent cell communications drive morphological invariance during ascidian embryogenesis

Canalization of developmental processes ensures the reproducibility and robustness of embryogenesis within each species. In its extreme form, found in ascidians, early embryonic cell lineages are invariant between embryos within and between species, despite rapid genomic divergence. To resolve this paradox, we used live light-sheet imaging to quantify individual cell behaviors in digitalized embryos and explore the forces that canalize their development. This quantitative approach revealed that individual cell geometries and cell contacts are strongly constrained, and that these constraints are tightly linked to the control of fate specification by local cell inductions. While in vertebrates ligand concentration usually controls cell inductions, we found that this role is fulfilled in ascidians by the area of contacts between signaling and responding cells. We propose that the duality between geometric and genetic control of inductions contributes to the counterintuitive inverse correlation between geometric and genetic variability during embryogenesis.

developmental biology↗