Though cells of diverse origins exhibit varied shapes, mechanisms of cell polarization are conserved. Conceptually, intrinsic or extracellular polarization cues inform the localization of cortical landmarks. These landmarks recruit the core polarization machinery at appropriate location. In turn, the polarization machinery engages effectors and signaling pathways to transduce this spatial information into productive cell organization.

To probe the mechanisms of cell polarization, we use a simple unicellular model, the eukaryotic fission yeast Schizosaccharomyces pombe. This haploid yeast exhibits a very regular rod shape: it grows by polarized extension at cell extremities and divides by middle fission at a defined cell size. Our work investigates several broad topics.

Cdc42 and the core cell polarization machinery: We aim to define the composition and mechanisms of the core polarization machinery. One important factor is the small Rho-family GTPase Cdc42, which drives the organization of the actin cytoskeleton and of secretion at cell poles. We also investigate the organization of actin cables, tracks for vesicular traffic.

Microtubules – intrinsic cues for cell polarization: In proliferating cells, microtubules align along cell length and transport polarization landmarks to cell poles. We investigate how these landmarks recruit the polarization machinery to drive bipolar cell growth.

Cell polarization and cell fusion during sexual differentiation: During sexual differentiation, cells respond to pheromone and grow towards a mating partner. This culminates in the fusion between the two cells to produce a diploid zygote. We study the process by which cells engage in this distinct polarization program to choose a mate. We also investigate the spatial organization of the cell-cell fusion machinery.

Coordination of cell growth with division: Cells reproducibly divide at constant cell size. The mechanisms of cell size homeostasis remain very elusive. We focus on how geometric cues, provided through concentration gradients of a kinase from the cell extremities, contribute to defining an appropriate division size.