Work Package 1.
In this project, we have completed most significant parts of aim1 and aim3, by publishing a first paper in J. Cell Biology: Tanimoto et al. 2016. We have also recently published a supportive method paper “Tanimoto and Minc, Methods Cell Biology 2017”, and a review article in J. Cell Science “Haupt and Minc, 2018”. In those papers we study the centration of sperm asters in sea urchin embryos. These MT asters grow and move to the exact center of the cell. This motion is ubiquitousto all animal’s embryos, and essential for embryogenesis and karyogamy. We find that asters move in a self-organized manner, by continuously probing the geometry of eggs to faithfully target the cell center. We also propose a model for how the speed of MT asters may be determined from the growth rates of MTs in the aster. This part of the work was performed by Hirokazu Tanimoto a post-doc hired on the project, and in collaboration with Akatsuki Kimura (NIG, Japan).
We are now completing aim2, by performing detailed tracking of vesicle movement associated with the centration of sperm asters. We could establish precise maps of vesicle centration, for differentent domembranes compartments (Endosomes, Lysososmes, ER etc..) . This analysis is being finished by Jeremy Sallé and Javad Najafi, and has been performed by Aurélien Guillou , an engineer hired on the project.
. A manuscript on those aspects is being finalized. In parallel, Héliciane Palenzuela a PhD student hired on the project finished an “in vitro reconstitution” of the forces exerted by vesicles moving on microtubules in bulk (Palenzuela et al. Curr Biol 2020). A review article was also published on these aspects (Xie and Minc, Front. Cell Biol, 2020)
Work Package 2.
For this part of the project, we have pioneered the use of in vivo magnetic tweezers, in which magnetic beads are attached to the center of MT asters, and serve to apply calibrated forces to moving asters inside cells. A first key publication on this part, was published in Nature Physics “Tanimoto,Sallé, Dodin and Minc, 2018”. In this paper, we use in vivo tweezers to compute forces associated with aster motion and positioning. A second manuscript (Sallé et al. J Cell Biol 2019) used of those magnetic beads and tweezers to control the position and orientation of cell division in embryos. This work is mainly led by Jeremy Sallé a post-doc working on the project, with the help of Jing Xie, Dmitry Ershov and Serge Dmitrieff, who have also been hired on the project. A final direction in the context of Jing Xie PhD thesis (initially funded by the ERC grant, and now through an individual fellowship from the Chinese council), is to use tweezers to systematically map forces throughout embryogenesis as cells become smaller and smaller and exhibit rich patterns of oriented divisions. A manuscript is being finalized for the year 2021. This last aspect shall allow to complete aim 2.
Work Package 3.
The first aim of the WP, is also partially completed, through the recent publication of a modelling paper in which we can model and predict the overall division patterns of different embryos: “Pierre et al. Developmental Cell, 2016”. This work was achieved by Anaëlle Pierre, a PhD student with an independent fellowship, and with the help of Jeremy Sallé, and in collaboration with Martin Wühr at Princeton University. Using those models, we made important predictions on the simple mechanical rules controlling the position and orientation of subsequent divisions during embryonic development.
Finally, Dmitry Ershov a post-doc hired on the project, recently improved the modelling framework, to create a simple open-access platform for predicting cell divisions in 3D, this work is, published as a book chapter in “Vertebrate Embryogenesis: Embryological, Cellular, and Genetic Methods, 2nd Edition (ed. F. Pelegri) in 2019”.
