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This is a very cool experiment but I'm still not seeing the connection to epigenetics. This experiment shows the importance of Hsp90 to proper cell function. By properly “buffering” mutations that would otherwise cause a misfunction it allows variation to accumulate. When they knock out Hsp90 all sorts of weird stuff happens because all these “silent” mutations speak up. If some of these mutations are actually beneficial they can be acted upon by evolution through natural selection. Where does epigenetics come in?

Hsp90 as a capacitor for morphological evolution
Suzanne L. Rutherford1,2 & Susan Lindquist1

Howard Hughes Medical Institute, University of Chicago, 5841 South Maryland Avenue MC1028, Chicago, Illinois 60637, USA
Present address: Developmental Biology Center, University of California at Irvine, 4205 Biological Science II, Irvine, California 92697-2275, USA.
Correspondence to: Correspondence and requests for materials should be addressed to S.L.

Top of pageAbstractThe heat-shock protein Hsp90 supports diverse but specific signal transducers and lies at the interface of several developmental pathways. We report here that when Drosophila Hsp90 is mutant or pharmacologically impaired, phenotypic variation affecting nearly any adult structure is produced, with specific variants depending on the genetic background and occurring both in laboratory strains and in wild populations. Multiple, previously silent, genetic determinants produced these variants and, when enriched by selection, they rapidly became independent of the Hsp90 mutation. Therefore, widespread variation affecting morphogenic pathways exists in nature, but is usually silent; Hsp90 buffers this variation, allowing it to accumulate under neutral conditions. When Hsp90 buffering is compromised, for example by temperature, cryptic variants are expressed and selection can lead to the continued expression of these traits, even when Hsp90 function is restored. This provides a plausible mechanism for promoting evolutionary change in otherwise entrenched developmental processes.

Where does epigenetics come in? I notice the source left off the quote marks around the epigenetics part. From your source....

THE THREE MAIN TYPES OF EPIGENETIC INFORMATION
Cytosine DNA methylation is a covalent modification of DNA, in which a methyl group is transferred from S-adenosylmethionine to the C-5 position of cytosine by a family of cytosine (DNA-5)-methyltransferases. DNA methylation occurs almost exclusively at CpG nucleotides and has an important contributing role in the regulation of gene expression and the silencing of repeat elements in the genome.

Genomic imprinting is parent-of-origin-specific allele silencing, or relative silencing of one parental allele compared with the other parental allele. It is maintained, in part, by differentially methylated regions within or near imprinted genes, and it is normally reprogrammed in the germline.

Histone modifications—including acetylation, methylation and phosphorylation—are important in transcriptional regulation and many are stably maintained during cell division, although the mechanism for this epigenetic inheritance is not yet well understood. Proteins that mediate these modifications are often associated within the same complexes as those that regulate DNA methylation.