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Author: Milton, C. C.; Huynh, B.; Batterham, P.;
Rutherford, S. L.; Hoffmann, A. A.
Year: 2003
Title: Quantitative trait symmetry independent of
Hsp90 buffering: Distinct modes of genetic canalization and developmental
stability
Journal: Proceedings of the National
Academy of Sciences of the United States of America
Volume: 100
Pages: 13396-13401
Date: Nov
Abstract: The Hsp90 chaperone buffers development
against a wide range of morphological changes in many organisms and in Drosophila masks the effects of hidden genetic
variation. Theory predicts that genetic and nongenetic buffering will share
common mechanisms. For example, it is argued that Hsp90 genetic buffering
evolved solely as a by-product of environmental buffering, and that Hsp90
should mask morphological deviations from any source. To test this idea, we
examined the effect of Hsp90 on purely nongenetic variation in phenotype,
measured as differences between the left and right sides of several bilaterally
symmetrical bristle and wing traits in individual flies. Consistent with
previous reports, Hsp90 buffered the expression of rare morphogenic variants
specific to particular genetic backgrounds. However, neither trait-by-trait nor
global asymmetry was affected in outbred flies treated with an Hsp90 inhibitor
or across a series of inbred genetic backgrounds from a wild population tested
in isogenic F-1 heterozygotes carrying either (t) a dominant negative Hsp90
allele on a mutant 3rd chromosome or (it) a null P-insertion mutation, which
was introgressed into the control genetic background on all chromosomes. By
contrast, Hsp90-regulated trait means and significant effects of sex,
temperature, and genetic background on trait symmetry were clearly detected. We
conclude that, by maintaining the function of signaling proteins, Hsp90 masks
variation affecting target pathways and traits in populations independent of
purely nongenetic sources of variation, refuting the idea that a single
Hsp90-dependent process generally controls genetic canalization and developmental
stability.
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