Title

The spatial and temporal regulation of morphogenesis in the budding yeast Saccharomyces cerevisiae

Date of Award

5-2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Advisor(s)

Scott E. Erdman

Keywords

Morphogenesis, Cell polarity, Paxillin, Calcium

Subject Categories

Cell and Developmental Biology | Molecular Biology

Abstract

Contributing to a number of cellular responses including fibroblast motility and axonal guidance, morphogenesis, more commonly referred to as polarized growth, is fundamental to many aspects of cell and developmental biology. An important goal for understanding the mechanisms of polarized growth is to determine the full complement of polarity proteins functioning in the establishment and maintenance of polarized growth sites as well as their dynamics of assembly and disassembly. To elucidate these mechanisms, we employed the model eukaryote budding yeast or Saccharomyces cerevisiae . Given that S. cerevisiae exhibits polarized growth in at least two facets of its life cycle: vegetative growth (or budding) and mating, we focused our investigations on the roles of two genes, PXL1 and FIG1 , with putative functions during these aspects of polarized growth in budding yeast.

Sequence analysis of Pxl1p, or Paxillin-like protein 1, revealed the presence of two C-terminal LIM domains that bear homology to those of the mammalian scaffolding protein paxillin. In higher eukaryotes, paxillin is targeted to polarized growth sites via its LIM domains where it has been shown to function in the assembly and maintenance of polarization sites through its associations with various signaling and actin cytoskeletal organization components. Similar to paxillin, localization of Pxl1p to polarized growth sites is dependent on the function of its individual LIM domains. At these sites, Pxl1p participates in such polarized growth events as budding and mating projection formation, possibly as a modulator of Rho GTPase signaling. These findings demonstrate an evolutionarily conserved role for LIM domain proteins as mediators of cell signaling and cytoskeletal organization during polarized growth.

The discovery of FIG1 , or F actor- i nduced g ene 1 , in a screen for pheromone-regulated genes suggested Fig1p functions exclusively at the time of mating. In this collaborative study, Fig1p has been shown to act as a novel component or regulator of the calcium influx system LACS. Our studies demonstrate LACS activities function cooperatively with those of HACS to positively regulate cell fusion via the influx of calcium ions at the time of mating, providing the first direct evidence for calcium signals in promoting cell-cell fusion during yeast mating.

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