Introduction

The heat shock proteins (Hsps) are a group of highly conserved proteins that have major physiological roles in protein homeostasis [1, 2]. In most cell types, 1–2% of total proteins consist of heat shock proteins even prior to stress, which suggests important roles for these proteins in the biology and physiology of the unstressed cell. These roles particularly concern regulating the folding and unfolding of other proteins. The term ‘heat shock proteins’ was coined because these proteins were first identified on the basis of their increased synthesis following exposure to elevated temperatures [3]. Subsequently, it has been clearly shown that they can be induced following a variety of stressful stimuli. Some heat shock proteins, such as Hsp90 (each heat shock protein is named according to its mass in kilodaltons – see Chapter 1 for more details), are detectable at significant levels in unstressed cells and increase in abundance following a suitable stimulus, whereas others such as Hsp70 exist in both constitutively expressed and inducible forms [4, 5].

The dual role of heat shock proteins in both normal and stressed cells evidently requires the existence of complex regulatory processes which ensure that the correct expression pattern is produced. Indeed, such processes must be operative at the very earliest stages of embryonic development, since the genes encoding Hsp70 and Hsp90 are amongst the first embryonic genes to be transcribed [6, 7].