In the scope of this research project, which is to develop a comprehensive model of the yeast pheromone response, we investigate the mutual communication between cells in cultures of mixed haploid yeast cells. During the mating process haploid S. cerevisiae cells need to sense the concentration gradient of pheromones, secreted by the cells of the opposite mating type. MATa cells export a-factor and are senstive for alpha factor, while MATalpha cells secrete alpha factor and are sensitive for a-factor. Since yeast cells are not capable of active movement neither to position themselves according to the gradient nor to close the distance to the pheromone secreting cell, all these processes are highly interlocked and precisely orchestrated. In this project we want to shed light on this cell to cell communication and understand its mutual character, by utilizing both theoretical and experimental approaches, such as bulk-surface partial differential equations and flow cytometry. Insides in this mutual communication will not only help to obtain a comprehensive picture of the model organism S. cerevisiae but can also serve as model for cell to cell communication in complex tissues.

Image from Goldenbogen et al., Open Biol (2016), CC BY 4.0 license

We investigate the cell shape dynamics of mating S. cerevisiae in time and space focusing on cell polarity and mechanical cell wall changes. During the mating process haploid S. cerevisiae cells need to sense the concentration gradient of pheromones, secreted by the cells of the opposite mating type. Since yeast cells are not capable of active movement neither to position themselves according to the gradient nor to close the distance to pheromone secreting cell. To facilitate cell-cell contact, yeast cells need to change their growing pattern from budding to directed growth. In our work we are focusing on this pheromone activated and controlled shape change and aim to unravel the contribution of subcellular structures such as the cell wall. We approach this question experimentally using different microscopy techniques such as atomic force microscopy and fluorescence microscopy. The experimental findings are complemented theoretically by using partial differential equations to model cell polarity as well as applying continuum mechanics to describe the shape change. Our aim is to develop a comprehensive model of the yeast pheromone response to gain a deeper understanding of eukaryotic signaling.

Female selection of sperm is often called the female cryptic choice. Our aim is to decrypt this mechanism, i.e. to optimize artificial insemination. Sperms travelling through the female genital tract can hardly become studied in vivo, especially in endangered species. Which number of sperms is essential for successful fertilization? This question becomes especially interesting, because sperm concentration in humans is constantly decreasing. Which sperm properties qualifies successful sperms? To which extend play chemo- and thermotaxis or the response of the female immune system a role? There are many mechanisms presumably playing a role in the female cryptic choice, but without modeling it is hard to test and quantify these mechanisms. We currently work on our first agent based model (ABM), which aims to describe sperm movement in a mathematical description of the bovine reproduction tract.

Yeast is a single cell fungus and as fungus its cellular integrity is protected by a cell wall, containing mostly glucan, protein and chitin. Hence, cellular growth or shape development has to be accompanied by alterations of the cell wall. In this project we investigate whether those alterations have an impact on the mechanical properties of the cell wall and what the implications on the shape dynamics could be. To study cell wall properties we perform localized nano-indentation experiments on living yeast cells using atomic force microscopy (AFM), as well as osmotically driven relaxation experiments using microfluidic devices. Based on the acquired mechanical cell wall properties and the principles of continuum mechanics we develop theoretical models for the growth of yeast cells.