Characteristic genome rearrangements accompany experimental
evolution.
Maitreya J. Dunham (1), Hassan Badrane (2), Patrick O. Brown (3),
R. Frank Rosenzweig (4), David Botstein (1)
(1) Department of Genetics, Stanford Univ. Medical School, 300 Pasteur
Dr., Stanford, CA 94305-5120, USA;
(2) University of Florida College of Medicine;
(3) HHMI, Biochemistry Department, Stanford University Medical School;
(4) University of Montana
Paquin, Adams, and Rosenzweig followed the evolution of eight
independent cultures of S. cerevisiae diploids for hundreds of
generations in glucose-limited chemostats. Ferea et al. (1999) reported
changes in global gene expression in three of these strains consistent
with a shift from reliance on fermentation to respiration. Here we
describe chromosomal rearrangements that occurred during the evolution
of six of the eight cultures, by the technique of Comparative Genomic
Hybridization on DNA microarrays. As with the gene expression results,
the genome rearrangements are surprisingly consistent. Three evolved
strains contain amplifications of regions of chromosome 4 that include
multiple high affinity hexose transporters; one of these is limited to
HXT6 and HXT7, as described previously by Brown et al.
(1998). Three strains contain nested deletions on chromosome 15.
Finally, and most strikingly, three strains have a deletion on
chromosome 14 that begins near CIT1, which encodes the first
enzyme in the tricarboxylic acid cycle. Other amplification and deletion
events were also observed. Most, if not all, of these rearrangements
occur in the immediate vicinity of sequences related to transposons. Two
of the breakpoints near CIT1 have been cloned and found to be
fused to a complete transposon, even though the wildtype sequence is
only a transposon end. The similarity of these events to those regularly
observed in other systems, especially cancer progression, will be
noted.
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