Molecular mechanisms of canalization: Hsp90 and beyond.

The Hsp90 chaperone machine facilitates the maturation of a diverse set of 'client' proteins. Many of these Hsp90 clients are essential nodes in signal transduction pathways and regulatory circuits,accounting for the important role Hsp90 plays in organismal development and responses to the environment. Recent findings suggest a broader impact of the chaperone on phenotype: fully functional Hsp90 canalizes wild-type phenotypes by suppressing underlying genetic and epigenetic variation. This variation can be expressed upon challenging the Hsp90 machinery by environmental stress, genetic or pharmaceutical targeting of Hsp90. The existence of Hsp90-buffered genetic and epigenetic variation together with plausible release mechanisms has wide-ranging implication for phenotype and possibly evolutionary processes. Here,we discuss the role of Hsp90 in canalization and organismal plasticity,and highlight important questions for future experimental inquiry.