Heat shock factor 2-like activity in mouse blastocysts.

The expression of heat shock genes is induced in all living cells by a series of proteotoxic treatments. Heat shock genes are also activated spontaneously during different phases of embryonic development. HSP89 alpha and HSC70 are expressed at a high level in the mouse blastocyst. A family of factors, called HSFs, are able to bind to the promoters of heat shock genes on upstream conserved elements (HSEs). HSF1 is unable to bind to HSE sequences in absence of stress. It is activated after a stress by post-translational modifications and conformational change. HSF2 shows common structural domains with HSF1; however, it is active at normal temperatures. Recently we showed the presence of an abundant HSE-binding activity in nonshocked blastocysts. We demonstrate here by using polyclonal antibodies that HSF2 is the major constituent of this constitutive HSE-binding activity. HSF2 might be involved in the control of heat shock gene expression during early mammalian embryogenesis.