Detection of mRNAs coding for translationally regulated heat-shock proteins in non-heat-shocked thymic lymphocytes

In vitro thermal stress induces apoptosis and reduces development of porcine parthenotes

The precise physiological causes that result in reduced development of oocytes after heat shock (HS) are not clear. In this study, apoptosis, heat shock protein70 (hsp70), and in vitro development of porcine oocytes were evaluated after HS. Porcine cumulus-oocyte complexes (COCs) were subjected to in vitro maturation for 42 h. The matured oocytes were then heated at 41.5 degrees C for 0 h (control, C0h), 1 h (HS1h), 2 h (HS2h), or 4 h (HS4h). An additional group of oocytes was cultured for 4 h without HS (control, C4h). In Experiment 1, expression of hsp70 was detected by Western-blotting and no difference between controls and HS groups was observed. In Experiment 2, apoptosis of matured oocytes after HS was examined by Annexin V-FITC and TUNEL. No significant TUNEL-positive signals were detected in the heated oocytes compared to the controls, but the intensity of Annexin V-FITC labeling among different groups increased with length of HS and in vitro culture (P<0.05). Oocytes were parthenogenetically activated by an electric pulse plus 6-DMAP (Experiment 3). Mean (+/-S.E.M.) embryonic development in HS2h (cleavage: 42+/-29%; blastocyst: 11+/-10%) and HS4h (cleavage: 36+/-28%; blastocyst: 11+/-8%) were decreased when compared to those in C0h (cleavage: 63+/-12%; blastocyst: 24+/-14%) and C4h (cleavage: 66+/-8%; blastocyst: 21+/-11%). Numbers of blastocysts with TUNEL-positive signals were similar among groups, but the signals increased before the eight-cell stage in HS groups (P<0.05). In conclusion, developmental competence of matured pig oocytes was compromised after heat shock, but it was not closely associated with the expression of oocyte hsp70. However, there may be a link between apoptosis and developmental competence of porcine oocytes.

Transcriptional control of development, protein synthesis, and heat-induced heat shock protein 70 synthesis in 2-cell bovine embryos

Experiments were performed to evaluate the role of transcription in early development of bovine embryos. Two transcription inhibitors-5, 6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) and actinomycin D-were used to test whether 1) the inhibitors alter the rate of early embryonic development and protein synthesis, 2) heat shock increases the steady-state amounts of mRNA for the inducible form of heat shock protein 70 (HSP70) in embryos, and 3) this latter effect is blocked by transcription inhibitors. Addition of either DRB or actinomycin D to culture medium beginning 8 h postinsemination (hpi) reduced the proportion of oocytes that had undergone cleavage by 32-34 hpi. Both transcription inhibitors also reduced the proportion of cleaved embryos that reached the 4-cell stage by 32-34 hpi. Incorporation of (35)S-labeled amino acids into de novo synthesized protein by bovine 2-cell embryos was lower for embryos cultured with DRB. Using reverse transcription-polymerase chain reaction, HSP70 mRNA in 2- and 4-cell embryos was increased by exposure to 42 degrees C. Both inhibitors reduced amounts of HSP70 mRNA at 42 degrees C. Results indicate that bovine embryos can undergo transcription in response to heat shock as early as the 2-cell stage. Moreover, the observations that transcription inhibitors reduce rates of cleavage and early development point out the importance of transcription for development from the earliest period of embryonic life.

Lamin B is a prompt heat shock protein

The cellular response to hyperthermia involves the increased synthesis of heat shock proteins (HSPs) within several hours after treatment. In addition, a subset of proteins has been shown to be increased immediately after heating. These "prompt" HSPs are predominantly found in the nuclear matrix-intermediate filament fraction and are not present or detectable in unheated cells. Since the nuclear matrix has been suggested to be a target for heat-induced cell killing, prompt HSPs may play a prominent role in the heat shock response. Using Western blotting and flow cytometry, we found that an increase in the synthesis of lamin B, one of the major proteins of the nuclear lamina, is induced during heating at 45.5 degrees C but not during heating at 42 degrees C. Since it is an abundant protein which is constitutively expressed in mammalian cells, lamin B appears to be a unique member of the prompt HSP family. The kinetics of induction of lamin B during 45.5 degrees C heating did not correlate with the dose-dependent reduction in cell survival. While increased levels of lamin B during 45.5 degrees C heating do not appear to confer a survival advantage directly, a possible role for lamin B in cellular recovery after heat shock cannot be discounted.

Identification of specific mRNAs affected by treatments producing long-term facilitation in Aplysia

Neural correlates of long-term sensitization of defensive withdrawal reflexes in Aplysia occur in sensory neurons in the pleural ganglia and can be mimicked by exposure of these neurons to serotonin (5-HT). Studies using inhibitors indicate that transcription is necessary for production of long-term facilitation by 5-HT. Several mRNAs that change in response to 5-HT have been identified, but the molecular events responsible for long-term facilitation have not yet been fully described. To detect additional changes in mRNAs, we investigated the effects of 5-HT (1.5 hr) on levels of mRNA in pleural-pedal ganglia using in vitro translation. Four mRNAs were affected by 5-HT, three of which were identified as calmodulin (CaM), phosphoglycerate kinase (PGK), and a novel gene product (protein 3). Using RNase protection assays, we found that 5-HT increased all three mRNAs in the pleural sensory neurons. CaM and protein 3 mRNAs were also increased in the sensory neurons by sensitization training. Furthermore, stimulation of peripheral nerves of pleural-pedal ganglia, an in vitro analog of sensitization training, increased the incorporation of labeled amino acids into CaM, PGK, and protein 3. These results indicate that increases in CaM, PGK, and protein 3 are part of the early response of sensory neurons to stimuli that produce long-term facilitation, and that CaM and protein 3 could have a role in the generation of long-term sensitization.

Corticosteroid-induced proteins in brain

Cumulative exposure of hippocampal neurons to stress-like levels of corticosterone produces a negative spectrum of cellular alterations from ultrastructural changes to disruption of dendritic morphology and eventual degeneration. An experimental system which adapts itself to characterization of corticosteroid-induced proteins which mediate such effects is the hippocampal slice incubated in the presence of a radiolabeled amino acid following treatment of rats with corticosterone. The most consistently observed response to elevated corticosterone levels produced by exogenous injection is synthesis of a hippocampal cytosolic protein which has characteristics of glycerol phosphate dehydrogenase. Because synthesis of this protein is enhanced with a short latency as serum corticosterone levels are increased and terminated quickly upon re-establishment of basal conditions, it serves as a valid biological marker of the response of the hippocampus to short-term stress. In contrast, alterations in synthesis of other proteins following corticosterone treatment only become apparent under defined conditions or after chronic treatment. For example, steroid-inhibited synthesis of a hippocampal protein with an approximate molecular weight of 25,000 is only observed when slices are incubated at an elevated temperature. Such negative changes may represent loss of adaptive responses that protect the neuron from damage by cellular insults.

Heat-induced stabilization of the nuclear matrix: a morphological and biochemical analysis in murine erythroleukemia cells

Using mouse erythroleukemia cells we performed a comprehensive morphological and biochemical study of the nuclear matrix obtained after exposure of isolated nuclei to 37 degrees C or from cells heat shocked in vivo at 43 or 45 degrees C. At the ultrastructural level it was possible to see that in the absence of a 37 degrees C incubation of purified nuclei, the final matrix lacked well-defined nucleolar remnants but a peripheral lamina was clearly visible, as well as a sparse fibrogranular network which was located at the periphery of the structures. On the contrary, after a 37 degrees C nuclear incubation, very electron-dense nucleolar remnants were observed along with an abundant meshwork dispersed throughout the interior of the structures. When intact cells were heat shocked in vivo, electron-dense residual nucleoli were present only when isolated nuclei had been exposed to 37 degrees C in vitro, whereas without such an incubation, they were not as easily distinguishable and appeared less electron-dense. In the latter case the inner network was more evenly distributed. After purified nuclei were incubated at 37 degrees C for 45 min, the high salt and DNase I resistant fraction retained about 18% of the nuclear protein whereas if the heating was omitted protein recovery dropped to 6%. An increase in the recovery of intact structures in the matrix fraction was the main reason for the higher protein recovery. Heating nuclei in vitro further increased the amount of nuclear protein present in the matrix fraction even if intact cells had been heat shocked in vivo. No major qualitative differences were seen when the polypeptide pattern of the various types of nuclear matrices was analyzed on one-dimensional polyacrylamide gels and this finding was further supported by Western blot analysis with a monoclonal antibody to lamins A and C. These results show that heating mainly stabilizes the nucleolar remnants of the matrix and to a lesser extent the inner network, but the morphology of the final structures is different depending on whether the stabilization is performed in vivo or in vitro.

Characterization of a glucocorticoid-sensitive hippocampal protein

Increased synthesis of a rat hippocampal protein with an apparent molecular weight (Mr) of 35,000 Da occurs in response to elevation of serum corticosterone levels. Subcellular fractionation has localized this protein in the cytosol. Two-dimensional gel electrophoresis indicated that this protein has an isoelectric point (IEP) of 6.6. A similar protein in liver has a slightly higher Mr and an IEP of 6.8. Increased synthesis of one additional hippocampal protein with an Mr of 46,000 Da and an IEP of 6.2 and of two other liver proteins, one with an Mr of 53,000 Da and an IEP of 6.2 and the other with an Mr of 45,000 Da and a range of IEPs from 8.7 to 7.8, was also seen after injection of corticosterone into rats. One possible identity of the 35,000 Da protein is glycerol 3-phosphate dehydrogenase (GPDH), based upon the reported Mr and IEP of this enzyme. The 35,000 Da hippocampal protein co-eluted from a gel filtration column with GPDH activity. No alteration of hippocampal GPDH activity was seen in intact rats 4 or 24 h after injection of either corticosterone or the type II receptor-specific agonist RU 28362. However, daily administration of corticosterone to rats beginning 10 days after adrenalectomy returned hippocampal GPDH activity to normal values after 2-3 days. In contrast, synthesis of the 35,000 Da protein was maximally increased 4 h after a single injection of steroid and not elevated at later times.