Stress-induced heat shock protein gene expression is developmentally r
egulated during early embryogenesis of the frog, Xenopus laevis. For e
xample, a number of heat shock protein genes, such as hsp70, hsp90, an
d ubiquitin are not heat-inducible until after the midblastula stage o
f embryogenesis. Furthermore, the family of small heat shock protein g
enes, hsp30, are differentially expressed after the midblastula stage
as well as being regulated at the level of mRNA stability. Many of the
se stress proteins are also synthesized constitutively during oogenesi
s and embryogenesis during which they may act as molecular chaperones
as well as being involved in sequestering proteins in an inactive stat
e until required by the developing embryo. Furthermore the induction o
f these stress protein genes has been correlated with enhanced thermor
esistance. During stressful conditions heat shock proteins probably pr
event aggregation or misfolding of damaged proteins within the embryo.