Biomedical subjects

N Ovsenek

Publications and source records attributed to N Ovsenek.

21 records · Page 2Linked to original sources

PubMed1987

Decay of the oocyte-type heat shock response of Xenopus laevis.

Xenopus oocytes have a complex heat shock response. During transition of the oocyte into fertilized egg, the heat shock response undergoes several qualitative and quantitative changes culminating in its complete extinction. Heat shock induces oocytes to synthesize four heat shock proteins (hsps): 83, 76, 70, and 57. After ovulation, two additional proteins (hsps 22 and 16) are inducible. The heat shock response of spawned eggs can be modified by changing the ionic configuration of the external medium and by adding pyruvate and oxaloacetate to the media. Since Xenopus eggs do not synthesize mRNA, these modifications to the external medium apparently alter the utilization of preexisting messenger RNAs in protein synthesis. Artificial activation terminates inducibility of hsps 76, 57, and 16 and diminishes the hsp 70 response. Two new heat shock proteins-66 and 48-are also inducible in artificially activated eggs. Fertilization, on the other hand, terminates the heat shock response; no hsps can be induced. However, hsp 70 appears to be made constitutively in fertilized eggs. RNA blot analyses reveal that oogenic hsp 70 messenger RNA is retained in eggs and early embryos. This messenger is apparently used for heat-induced synthesis of hsp 70 before fertilization and for constitutive synthesis of hsp 70 in zygotes.

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PubMed1987

Examination of heat shock protein mRNA accumulation in early Xenopus laevis embryos.

Elevation of the incubation temperature of Xenopus laevis neurulae from 22 to 33-35 degrees C induced the accumulation of heat shock protein (hsp) 70 mRNA (2.7 kilobases (kb)) and a putative hsp 87 mRNA (3.2 kb). While constitutive levels of both hsp mRNAs were detectable in unfertilized eggs and cleavage-stage embryos, heat-induced accumulation was not observed until after the mid-blastula stage. Exposure of Xenopus laevis embryos to other stressors, such as sodium arsenite or ethanol, also induced a developmental stage-dependent accumulation of hsp 70 mRNA. To characterize the effect of temperature on hsp 70 mRNA induction, neurulae were exposed to a range of temperatures (27-37 degrees C) for 1 h. Heat-induced hsp 70 mRNA accumulation was first detectable at 27 degrees C, with relatively greater levels at 30-35 degrees C and lower levels at 37 degrees C. A more complex effect of temperature on hsp 70 mRNA accumulation was observed in a series of time course experiments. While continuous exposure of neurulae to heat shock (27-35 degrees C) induced a transient accumulation of hsp 70 mRNA, the temporal pattern of hsp 70 mRNA accumulation was temperature dependent. Exposure of embryos to 33-35 degrees C induced maximum relative levels of hsp 70 mRNA within 1-1.5 h, while at 30 and 27 degrees C peak hsp 70 mRNA accumulation occurred at 3 and 12 h, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMedDate not supplied

Examination of the DNA sequence-specific binding properties of heat shock transcription factor in Xenopus laevis embryos.

The binding of heat shock transcription factor (HSF) to the heat shock element (HSE) is necessary for transcriptional activation of eukaryotic heat shock protein (HSP) genes. The properties of Xenopus embryo HSF were examined by DNA mobility shift analysis employing a synthetic oligonucleotide corresponding to the proximal HSE in the promoter of the Xenopus HSP70B gene. Heat shock induced activation of HSF binding in Xenopus neurulae was not affected by an inhibition of protein synthesis, indicating that the mode of activation may be posttranslational. Also, while HSF binding was activated in control Drosophila cell extracts by in vitro heat shock or other chemical treatments, HSF binding in Xenopus embryo or somatic cell extract was not. Thus, the activation of Xenopus HSE-HSF binding may occur via a different mechanism compared with Drosophila. Furthermore, we determined that the native size of heat-induced HSF in pre- and post-midblastula stage Xenopus embryos is approximately 530 kilodaltons (kDa), which corresponds to a hexamer made up of 88 kDa monomers. Finally, the slower accumulation of HSP70 mRNA to peak levels found at lower heat shock temperatures was not correlated with HSE-HSF binding activity.

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