Björn Goldenbogen (HU)
01.01.2019 – 31.12.2020
Yeast mating is an easy accessible model system for cell to cell communication, with well known molecular components. Using experimental and theoretical methods we want to shed light on the less understood spatio-temporal dynamics of those components to find general principles of cell communications.
Saccharomyces cerevisiae, or bakers yeast, proliferates through asymmetric cell division (budding). In its haploid form yeast can additionally undergo mating, a process that occurs in time and space. In order to mate, two cells of opposing mating type (MATa / MATα) must grow towards each other and form a stable connection at the zone of contact and fuse their cytoplasm and their nuclei. The process requires constant and complex communication via pheromones small peptides, exclusively secreted by one mating type and sensed by the other. Although involved pheromone signaling pathway is one of the best studied signaling pathways, a temporally complete picture of the mating morphogenesis and including the requisite spatio-temporal cell-to-cell communication is still missing. In this project we addressed three related topics.
To understand the differences between vegetative and mating morphogenesis we used a combined theoretical and experimental approach. Considering pressure, mechanical cell wall properties, osmolyte concentration and water flux, we formulated three ODEs to model cell growth. Supported by measurements of single-cell growth trajectories and cell wall elasticity, the model showed that the volume of these asymmetrically dividing cells follows a sigmoidal curve and suggests that plastic properties are what distinguish mother and bud cell and thus allows the bud to expand. This is in contrast to the initial steps of mating morphogenesis, in which the elasticity controls the shape and the growth.
Unlike budding or shmooing cells, the shape of the zygotes renders the measurement of the cell wall elasticity by atomic force microscopy impossible. Therefore, we aimed to establish a new method for measuring local cell wall deformations using Fluorescence Lifetime Imaging and Fluoresce
nce Resonance Energy Transfer (FLIM-FRET). From the spatial strain profile we can infere the local Young’s modulus of the zygote cell wall. The approach bases on fluorophores embedded into the cell wall and their the varying density depending on the extend of the elastic expansion of the cell wall. Establishing of such a method is still ongonig research.
In our previous work we used biquadratic springs for the description of the elastic surface and implemented plastic expansion by elongation of the used triangular reference grid according to the local mechanical stress and the concentration of modeled signalling molecules. In close collaboration with the WIAS we are started to search for a alternative mathematical description of cell wall growth to reflect our new found insights.
T. Altenburg, B. Goldenbogen, J. Uhlendorf, and E. Klipp. Osmolyte homeostasis controls single-cell growth rate and maximum cell size of Saccharomyces cerevisiae. npj Systems Biology and Applications, 5(1):34, 2019.
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