Year: 2026
Type: preprint
Abstract: ABSTRACT The proper positioning of microtubule (MT) asters is essential to regulate division positioning and multi-cellular morphogenesis, yet the mechanisms regulating this process remain poorly understood. Using sea urchin zygotes as a model, we combined high-resolution imaging, perturbation assays, and 3D modeling to investigate the nature of forces driving sperm aster centration after fertilization. We show that centering asters are highly anisotropic, featuring long microtubules extending at the aster front that may engage with organelles in bulk cytoplasm to generate pulling forces. While vesicular compartments, like acidic organelles, mitochondria or yolk, contributed minimally, we found that the endoplasmic reticulum (ER) undergoes a massive compaction around the centering aster and drags cytosol to produce a reactive centering force on the aster. Perturbing ER organization by cytoplasmic stratification or Atlastin-mediated fragmentation disrupted aster centration. A two-fluid model suggests that the frictional interaction between the compacting ER and cytosol fluid is sufficient to recapitulate key features of aster centration. These findings identify the ER as an important cytoplasmic anchor for MT force exertion in bulk cytoplasm, to guide aster centering motion and influence early embryonic division geometries. More broadly, our results highlight the role of cytoplasmic architecture in shaping the mechanics of organelle positioning during development.
Institutions: Centre National de la Recherche Scientifique, Université Paris Cité, Institut Jacques Monod, Université Paris Sciences et Lettres, Sorbonne Université, Physique des Cellules et Cancers, Institut Curie, Institut Pasteur, Biologie du Développement et Cellules Souches, Inserm, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Université Paris-Saclay, CEA Paris-Saclay - Etablissement de Fontenay-aux-roses, Stabilité Génétique, Cellules Souches et Radiations, Institut de génétique et de développement de Rennes, Université de Rennes, Cibles Thérapeutiques et conception de médicaments
Language: English
Subfield: Cell Biology
Domain: Life Sciences
Open Access status: green
Funders: Biogen, Infrastructures en Biologie Santé et Agronomie, Agence Nationale de la Recherche, Fondation pour la Recherche Médicale, Conseil Régional, Île-de-France, Fondation ARC pour la Recherche sur le Cancer, Ligue Contre le Cancer, Centre National de la Recherche Scientifique, Fondation Bettencourt Schueller
OpenAlex ID: W7223572741