Inducible 70 kDa heat shock proteins protect embryos from teratogen-induced exencephaly: Analysis using Hspa1a/a1b knockout mice.
BACKGROUND
It is well known that a variety of teratogens induce neural tube defects in animals; however, less is known about proteins that play a role in protecting embryos from teratogen-induced neural tube defects. Previously, our laboratory has shown that embryos overexpressing the 70-Da heat shock proteins (HSPs) Hspa1a and Hspa1b were partially protected from the deleterious effects of exposure to hyperthermia in vitro.


METHODS
In the present studies, we have used a transgenic mouse in which both of the stress-inducible HSPs Hspa1a and Hspa1b were deleted by homologous recombination. Time-mated Hspa1a/a1b(-/-) (KO) and wildtype (WT) mice were exposed to hyperthermia in vivo on gestational day 8.5.


RESULTS
Results show that 52% of the gestational day 15 fetuses from KO litters were exencephalic, whereas only 20% of WT fetuses were affected. In addition, 6% of treated KO fetuses also exhibited eye defects (microphthalmia and anopthalmia), defects not observed in WT fetuses exposed to hyperthermia. Lysotracker red staining and caspase-3 enzyme activity were examined within 10 hours after exposure to hyperthermia, and significantly greater levels of apoptosis and enzyme activity were observed in the KO embryos compared with WT embryos.


CONCLUSIONS
These results show that embryos lacking the Hspa1a and Hspa1b genes are significantly more sensitive to hyperthermia-induced neural tube and eye defects, and this increased sensitivity is correlated with increased amounts of apoptosis. Thus, these results also suggest that Hspa1a and Hspa1b play an important role in protecting embryos from hyperthermia-induced congenital defects, possibly by reducing hyperthermia-induced apoptosis.
Barrier
Marianne
M
Birth Defects Research Laboratory, Division of Genetics and Development, Department of Pediatrics, University of Washington, Seattle, Washington, USA. barrier.marianne@epa.gov
Dix
David J
DJ
Mirkes
Philip E
PE
D000818:Animals; D004195:Disease Models, Animal; D047108:Embryonic Development / Q000187:drug effects; D005124:Eye Abnormalities / Q000139:chemically induced / Q000196:embryology / Q000517:prevention & control; D005260:Female; D005334:Fever / Q000196:embryology*; D018507:Gene Expression Regulation, Developmental; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D018869:Heat-Shock Response; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009436:Neural Tube Defects / Q000196:embryology / Q000209:etiology / Q000517:prevention & control*; D011247:Pregnancy; D013723:Teratogens / Q000633:toxicity*
D018840:HSP70 Heat-Shock Proteins; D013723:Teratogens; C081884:heat-shock protein 70.1