Functional differentiation of quiescent and non-quiescent cells in yeast stationary-phase cultures

Characterization of differentiated quiescent and non-quiescent cells in yeast stationary-phase cultures.

Anthony D. Aragon*, Angelina L. Rodriguez*, Osorio Meirelles^†, Sushmita Roy^‡, George S. Davidson^§, Phillip H. Tapia*, Chris Allen^¶, Ray Joe*, Don Benn*, and Margaret Werner-Washburne*

Departments of *Biology, ^†Math and Statistics, ^‡Computer Science, University of New Mexico, Albuquerque, NM 87131; ^§Sandia National Laboratories, Albuquerque NM 87185, and ^¶Department of Cytometry, University of New Mexico Health Sciences Center, Albuquerque NM 87131

Abstract

Cells in glucose-limited Saccharomyces cerevisiae cultures differentiate into quiescent (Q) and non-quiescent (NQ) fractions before entering stationary phase. To understand this differentiation, Q and NQ cells from 101 deletion-mutant strains were tested for viability and reproductive capacity. Eleven mutants that affected one or both phenotypes in Q or NQ fractions were identified. NQ fractions exhibit a high level of petite colonies and 9 mutants affecting this phenotype were identified. Microarray analysis revealed over 1300 mRNAs distinguished Q from NQ fractions. Q cell-specific mRNAs encode proteins involved in membrane maintenance, oxidative stress response, and signal transduction. NQ-cell mRNAs, consistent with apoptosis in these cells, encode proteins involved in Ty-element transposition and DNA recombination. More than 2000 protease-labile mRNAs were identified only in Q cells, consistent with these cells being physiologically poised to respond to environmental changes. Our results indicate that Q and NQ cells differentiate significantly, with Q cells providing genomic stability and NQ cells providing nutrients to Q cells as well as a regular source of genetic diversity through mutation and transposition. These studies are relevant to chronological aging, cell-cycle, and genome-evolution and provide insight into complex responses that even simple organisms have to starvation.