HEAT-INDUCED ALTERATIONS IN EMBRYONIC CYTOSKELETAL AND STRESS PROTEINS PRECEDE SOMITE MALFORMATIONS IN RAT EMBRYOS

Previous work from this laboratory has demonstrated that heat exposure on gestation day 10 (GD10) resulted in disrupted somite development 2 4 hr after exposure and subsequent thoracic skeletal malformations in neonates. The purpose of the present study was to examine the effects of in vitro heat shock on de novo protein synthesis and on cytoskeleta l protein levels in developing rat embryos. Explanted GD10 embryos wer e exposed to temperatures of 42-42.5 degrees C for 15 min. At various times postexposure (0-27 hr), embryos were labeled with S-35-methionin e and processed for sodium dodecyl sulfate-polyacrylamide gel electrop horesis (SDS-PAGE) separation. Transient enhanced de novo synthesis of 70- and 90-kD proteins was observed 1-8 hr after exposure. The 70-kD protein was identified as a eukaryotic stress protein and the presence of this protein was detected between 2 and 27 hr posttreatment. Weste rn blot analysis was used to detect quantitative changes in total acti n (microfilaments), tubulin (microtubules), and vimentin (intermediate filaments). Immediately following exposure, a reduction of total vime ntin to minimal detectable levels was observed in heat-treated embryos . Levels of total vimentin remained depressed for more than 2 hr and g radually returned to control levels 4-8 hr postexposure. No change in total actin or tubulin was detected in treated embryos. The data demon strate that heat-induced alterations in proteins comprising intermedia te filaments occur concomitantly with the induction of stress proteins and precede aberrant somite morphology. These alterations in embryoni c proteins may help elucidate the mechanism(s) by which skeletal malfo rmations are produced. (C) 1996 Wiley-Liss, Inc.