Does the External Environment of Cells, in Addition to their Genetic Programs, Play a Role in the Localization of their Division Sites ?

Abstract

Oriented cell division and establishment of cell polarity are central to development of many organisms [Drubin & Nelson 96]. Yeast cells exhibit defined patterns of oriented cell divisions by choosing a specific bud site on their cell cortex. The current understanding is that the site for bud formation is determined genetically, depending on cell type [Ni & Snyder 01, Aronov et al 07]. In haploid cells, bud sites are adjacent to the previous bud neck site: This is the axial pattern. In diploid cells, mother cells select bud sites either adjacent to their previous daughter cells or on their opposite end, whereas daughter cells always choose a bud site directed away from their mother: This is the bipolar pattern. It is believed that cells respond to cortical cues that mark positions on the cell cortex to establish these cell type-specific budding patterns. Recruitment of proteins to the presumptive bud site is thought to direct the cytoskeleton and secretory apparatus toward the bud site, thereby restricting new growth to the bud.Might the external environment play an additional role in the localization of bud sites, such as confinement via some mechanical and/or chemical sensing? To address this question, we perform image analysis of budding yeast cells in a two-dimensional micro-fluidic chamber, allowing for a controlled growth environment over multiple cell cycles [Charvin et al 08].