In my research proposal I had planned to use the experimental evolution approach to evolve multicellular forms in the filasterean Capsaspora owczarzaki. The experimental procedure did not change, the used specie was however ex-changed to the Ichthyosporean Sphaeroforma arctica. This change was mainly due, to the incapacity to select for C. owczarzaki aggregate as they float rather than sediment. Moreover, the growth medium of C. owczarzaki is highly rich in nutrient and thus very susceptible to contamination, which is extremely troublesome during long-term selection.
To summarize, the project yielded 1 peer-reviewed and published manuscript as well as a second publication in preparation. Here i will briefly summarize the different projects and the main outcome.
- Cell-cycle and Cellularization regulation in S. arctica :
Prior to the Marie-curie fund, I've been involved in a project published in Current Biology in which we characterise with Andrej Ondracka the cell cycle of Sphaeroforma arctica and discover that nuclear division cycles are under the control of a timer which is a unique feature among unicellular organisms. We further showed that the timer mechanisms is decoupled from cell size regulation. Such discovery show interesting cell biological similarities between insect early embryo and Ichthyosporean development. This was the stepping stone for my Marie-Curie project in which we analyzed the cellularization of S. arctica. Indeed, we further investigated the cell-cycle of Sphaeroforma arctica using Microscopy, RNAseq and chemical inhibition. Our results show that Sphaeroforma arctica undergoes a sophisticated cell division process also known as cellularization. This process allows the multi-nucleated coenocyte to undergo division to generate hundreds of uninucleated newborn cells. This process involved coordinated plasma membrane invaginations relying on an extensive actomyosin network. We also show that an intermediary stage of cellularization represents a self-organized, clonally-generated, polarized layer of cells resembling the animal epithelium. We further show that this cell stage is associated with distinct gene expression of cell adhesion proteins including catenins and integrins, both known as major regulators of cell-cell and cell-matrix adhesion in animals. This work has been published in eLife and featured in another eLife paper written by Prof. Mukund Thathai.
Finally, although not yet published, I've obtained Sphaeroforma arctica mutants using experimental evolutions. These mutants show distinct clonal multicellularity and are and will be further investigated to better understand how they acquired these novel traits.
In other projects , I've been involved in better characterising the cell cycle of C. owczarzaki and the dynamics of microtubule cytoskeleton during this cycle. I also been involved in characterising the role of actin-dependent filopodia in establishing integral-mediated adhesion in C. owczarzaki. Both projects will soon be published.
