Data and code from: Early developmental decline in HSP expression affects subsequent response to transient heat exposure

Understanding physiological responses to short-term changes in temperature
is of growing interest, considering the rising frequency and severity of
transient temperatures such as heat waves. During the embryonic
development of egg-laying vertebrates, inducible physiological responses
to transient heat are likely critical to short-term survival but may also
be energetically costly or disruptive to development. Inducible heat-shock
proteins (HSPs) are conserved molecular chaperones that act to safeguard
cellular protein homeostasis during transient stress. However, experiments
in ectotherms have shown that overexpression of HSPs can increase
embryonic mortality and reduce later thermotolerance. Yet, few studies
have explored natural developmental patterns of HSP expression and heat
inducibility in embryos of egg-laying ectothermic vertebrates. Using the
red-eared slider turtle (Trachemys scripta), we characterized the response
of five HSP genes in embryonic trunks following repeated 3-d transient
heat wave exposures. Interestingly, we found that the expression of most
HSPs naturally declined during early development and that warm
temperatures amplified this decline, while also accelerating developmental
rate. Only in a few instances did we observe induction of certain HSP
genes during heat wave exposures, though this depended on the thermal
history of the embryo. Specifically, induction of these genes during a
particular heat wave was reduced in embryos that had already experienced
two recent prior exposures relative to those experiencing it for the first
or second time, suggesting repeated heat exposures can attenuate
subsequent responses. The observed changes in HSP expression and
inducibility may relate to an individual’s need to balance thermotolerance
alongside extensive cellular differentiation and proliferation during
early development. The effects of incubation temperature on these changes
could also have important implications for how turtle embryos deal with
subsequent heat stress and may be similarly present in other ectothermic
vertebrates. Our study demonstrates the importance of considering
ontogenetic changes in physiological responses to temperature even across
embryonic development.