Worm Breeder's Gazette 15(1): 38 (October 1, 1997)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Department of Biology/Toxicology, Ashland University, Ashland, Ohio 44805
Induction of heat shock proteins in response to thermal stress
is a well-characterized phenomenon reported to occur in many organisms
including C. elegans (Heschl and Baillie, DNA 8: 233-43, 1989). Other
stressors, including chemical stressors, have also been shown to induce
these proteins (D. Jones et al., Toxicology 109: 119-27, 1996). We
have hypothesized that chemicals affecting energy metabolism will also
induce the heat shock response. As a test compound, we chose sodium
azide, an inhibitor of oxidative phosphorylation, that is also used as
a nematode anesthetic. We have found that exposure to low levels of
this chemical confers thermotolerance in the nematode.
To test our hypothesis, we developed the following protocol:
the wild type (N2) strain received a 1 hr pre-treatment with either
azide or 33oC. After a 4 hr recovery at 22oC, nematodes were heat
shocked at 37oC for 2 hrs. After heat shock, worms recovered again at
22oC for 4 hrs before the number of surviving worms was determined. A
4 hr recovery period was necessary because worms are not moving
immediately after the 37oC heat shock. Additionally, we have observed
that temperature fluctuation as little as 1.5oC can critically affect
the outcome. For example, temperatures rising to 38.5oC for 4 minutes
prove lethal to all worms. Azide concentrations of 5.0-20mM were
chosen based on preliminary studies which indicated that concentrations
>20mM were lethal. The control worms (receiving only the heat shock)
had a 0.08 survival probability while animals receiving the 33oC
pre-treatment had a 0.89 survival probability, illustrating the classic
heat shock response. At all concentrations, the sodium azide
pre-treated worms showed an increased survival probability when
compared to the control. 10mM (0.07%) sodium azide, corresponding to
the concentration typically used as an anesthetic, conferred maximal
(0.70) survival probability.
We are currently using Western Blots to test our hypothesis
that the molecular mechanism of the response to azide is the same as
the response to elevated temperatures. The hsps we are examining
include hsp90, 70, 60, and 16 (hsp16 antibody kindly provided by Peter
Candido).
We have also been searching for hsp mutants. Elizabeth Malone
and Jim Thomas reported at the worm meeting that daf-21 is really a
hsp90 mutation. We are currently testing their temperature sensitive
mutant (JT6130). Grown at the permissive temperature of 16oC, JT6130
survived heat shock after receiving pre-treatment with either azide or
33oC. However, these worms showed a reduction in survival probability
when compared to N2. At the restricted temperature of 25oC, the worms
pre-treated with either azide or 33oC did not survive the heat shock.
These results strongly suggest that hsp90 is an important part of the
worm's response to stress.
We are searching ACEDB, as well as the literature, for
information on mutants with defects in some aspect of energy
metabolism. Like daf-21 and hsp90, we suspect that mutations in energy
metabolism proteins may have already been identified by other names;
therefore, we welcome any additional information concerning mutants
that are thought to be involved in energy metabolism.