Biology subjects

Kardos, R.

Publications and source records attributed to Kardos, R..

3 recordsLinked to original sources

bioRxiv2023

BMP-dependent patterning of ectoderm tissue material properties modulates lateral mesendoderm cell migration during early zebrafish gastrulation

Cell migration is a fundamental process during embryonic development. Most studies on cell migration in vivo have focussed on the migration of cells using the extracellular matrix (ECM) as their substrate for migration. In contrast, much less is known about how cells migrate on other cells, as found in early embryos when the ECM has not yet formed. Here, we show that lateral mesendoderm (LME) cells in the early zebrafish gastrula use the overlying ectoderm as their substrate for migration. We show that the lateral ectoderm is permissive for the animal pole-directed migration of LME cells, while the ectoderm at the animal pole of the gastrula halts animal pole-directed LME migration. These differences in the permissive properties of the ectoderm for LME migration are due to the lateral ectoderm being more cohesive and viscous than the animal ectoderm. Consistently, tuning cell contractility in lateral and animal ectoderm via modulation of the actomyosin cytoskeleton is sufficient to change their permissiveness for LME migration. Finally, we found that BMP signalling is critical for reducing animal ectoderm cohesion and, thus, its capacity to halt LME migration towards the animal pole. Collectively, these findings identify a critical role of ectoderm tissue cohesion and viscosity in guiding LME migration during zebrafish gastrulation.

developmental biology↗

bioRxiv2022

Yolk granule fusion and microtubule aster formation regulate cortical granule translocation and exocytosis in zebrafish oocytes

Dynamic reorganization of the cytoplasm is key to many core cellular processes, such as cell division, cell migration and cell polarization. Cytoskeletal rearrangements are thought to constitute the main drivers of cytoplasmic flows and reorganization. In contrast, remarkably little is known about how dynamic changes in size and shape of cell organelles affect large-scale cytoplasmic organization. Here, we show that within the maturing zebrafish oocyte, the surface localization of exocytosis-competent cortical granules upon germinal vesicle breakdown is achieved by the combined activities of yolk granule fusion and microtubule aster formation and translocation. We find that cortical granules are moved towards the oocyte surface through radially-outward cytoplasmic flows induced by yolk granules fusing within the oocyte center in response to GV breakdown. We further show that vesicles decorated with the small Rab GTPase Rab11, a master regulator of vesicular trafficking and exocytosis, accumulate together with cortical granules at the oocyte surface. This accumulation is achieved by Rab11-positive vesicles being transported by acentrosomal microtubule asters, the formation of which is induced by the release of CyclinB/Cdk1 upon GV breakdown, and which display a net movement towards the oocyte surface by preferentially binding to the oocyte actin cortex. We finally demonstrate that the decoration of cortical granules by Rab11 at the oocyte surface is needed for cortical granule release and subsequent chorion elevation, a process central in oocyte activation. Collectively, these findings unravel a yet unrecognized role of organelle fusion, functioning together with cytoskeletal rearrangements, in determining cytoplasmic organization during oocyte maturation.

developmental biology↗

bioRxiv2022

Morphogen gradient orchestrates pattern-preserving tissue morphogenesis via motility-driven (un)jamming

Embryo development requires both biochemical signalling generating patterns of cell fates and active mechanical forces driving tissue shape changes. Yet, how these fundamental processes are coordinated in space and time, and, especially, how tissue patterning is preserved despite the complex cellular flows occurring during morphogenesis, remains poorly understood. Here, we show that a Nodal/TGF-{beta} morphogen gradient orchestrates pattern-preserving mesendoderm internalization movements during zebrafish gastrulation by triggering a motility-driven (un)jamming transition. We find that graded Nodal signalling, in addition to its highly conserved role in mesendoderm patterning, mechanically subdivides the tissue into a small fraction of highly protrusive leader cells able to locally unjam and thus autonomously internalize, and less protrusive followers, which remain jammed and need to be pulled inwards by the leaders. Using minimal particle-based simulations and experimental perturbations, we further show that this binary mechanical switch, when combined with Nodal-dependent preferential adhesion coupling leaders to followers, is critical for triggering collective and orderly mesendoderm internalization, thus preserving tissue patterning. This provides a simple, yet quantitative, theoretical framework for how a morphogen-encoded (un)jamming transition can bidirectionally couple tissue mechanics with patterning during complex three-dimensional morphogenesis.

developmental biology↗