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John McCusker

Associate Professor
Molecular Genetics and Microbiology
Research Interest: 
Genetics
Research Summary: 
Chronological life span and quantitative genetics in yeast.
Research Description: 

Chronological life span
Starvation is used to study an important aspect of aging - chronological life span (CLS). In principle, starvation for any one of the 20 amino acids, which presumably results in the accumulation of the cognate uncharged tRNA(s), Gcn2p activation and inhibition of translation initiation, might be expected to elicit the same stress response and to have the same effect on CLS. However, in carefully designed experiments in S. cerevisiae that avoid toxic amino acid biosynthetic intermediates and satisfy any secondary auxotrophic requirements, we find that amino acid starvation CLS is more complex and far more interesting. Rather than starvation for each amino acid having ~ the same effect on CLS, we find that amino acid starvation CLS is amino acid-specific, varying across a > 1,000´ range. Thus, there are amino acid-specific starvation CLS responses that are likely relevant to other stresses and, as with general control, are likely evolutionarily conserved.

Quantitative genetics in S. cerevisiae
S. cerevisiae is a model eukaryote, an excellent model for quantitative genetics and an emerging opportunistic pathogen. In addition to some population genetics, the pathogenesis aspect of this area of this research is two-fold – analysis of the quantitative traits of growth/survival in serum (originally, growth/survival in mice) and high temperature growth in vitro. The non-pathogenesis aspect of this area of research looks at a variety of seemingly unrelated quantitative traits, such as high temperature growth, mitochondrial genome maintenance, sporulation, cycloheximide resistance, etc.

One key to our analysis of quantitative traits is that we are oligonucleotide tagging all of the segregants, which greatly reduces labor costs and facilitates phenotyping. In combination with genotyping all of the segregants, this will create the quantitative genetic analog of the S. cerevisiae deletion collection, which will greatly facilitate quantitative genetic analysis. We have genotyped and oligonucleotide tagged 480 segregants of EM93 and > 600 segregants of YJM145/S288c. We are currently genotyping > 600 tagged segregants of RM11/S288c. We will genotype and tag > 600 segregants of YJM145/RM11. Tagging these segregants allows us to phenotype in parallel, which greatly cuts phenotyping costs and improves phenotyping data quality. Genotyping these segregants allows us to move from association mapping to the much more effective QTL mapping. The combination of genotyping and tagging such large numbers of segregants and adding oligonucleotide tags to each of these segregants dramatically improves our ability to map QTLs and then identify the relevant QTGs.

Publications: 
Sequential elimination of major-effect contributors identifies additional quantitative trait loci conditioning high-temperature growth in yeast.
Sinha H, David L, Pascon RC, Clauder-Münster S, Krishnakumar S, Nguyen M, Shi G, Dean J, Davis RW, Oefner PJ, McCusker JH, Steinmetz LM.
Genetics. 2008. 180:1661-70.

Complex genetic interactions in a quantitative trait locus.
Sinha H, Nicholson BP, Steinmetz LM, McCusker JH.
PLoS Genet. 2006. 2:e13.

Dissecting the architecture of a quantitative trait locus in yeast.
Steinmetz LM, Sinha H, Richards DR, Spiegelman JI, Oefner PJ, McCusker JH, Davis RW.
Nature. 2002. 416:326-30.

Microsatellite analysis of genetic diversity among clinical and nonclinical Saccharomyces cerevisiae isolates suggests heterozygote advantage in clinical environments.
Muller LA, McCusker JH.
Mol Ecol. 2009. 18:2779-86.

Fungal homoserine kinase (thr1Delta) mutants are attenuated in virulence and die rapidly upon threonine starvation and serum incubation.
Kingsbury JM, McCusker JH.
Eukaryot Cell. 2010. 9:729-37.