Thermolability of mouse oocytes is due to the lack of expression and/or inducibility of Hsp70

Regulation of germline proteostasis by HSF1 and insulin/IGF-1 signaling

Protein homeostasis (proteostasis) is essential for cellular function and organismal health and requires the concerted actions of protein synthesis, folding, transport, and turnover. In sexually reproducing organisms, the immortal germline lineage passes genetic information across generations. Accumulating evidence indicates the importance of proteome integrity for germ cells as genome stability. As gametogenesis involves very active protein synthesis and is highly energy-demanding, it has unique requirements for proteostasis regulation and is sensitive to stress and nutrient availability. The heat shock factor 1 (HSF1), a key transcriptional regulator of cellular response to cytosolic and nuclear protein misfolding has evolutionarily conserved roles in germline development. Similarly, insulin/insulin-like growth factor-1 (IGF-1) signaling, a major nutrient-sensing pathway, impacts many aspects of gametogenesis. Here, we focus on HSF1 and IIS to review insights into their roles in germline proteostasis and discuss the implications on gamete quality control during stress and aging.

Improvement of in vitro-produced bovine embryo treated with coagulansin-A under heat-stressed condition

Heat stress has large effects on reproduction including conception rate in cattle. In this study, we examined the effects of coagulansin-A (coa-A), a steroidal lactone, on acquired thermo tolerance during in vitro production of bovine embryos. Oocytes were incubated in in vitro maturation (IVM) media with or without coa-A at two different temperatures, 40.5˚C and 42˚C, for 20 h. The treatment of coa-A significantly improved blastocyst development only at 40.5˚C (P < 0.05). Interestingly, immunofluorescence analysis demonstrated that coa-A induced heat shock protein 70 (HSP70) and phosphatidylinositol-3-kinase (PI3K), but significantly attenuated nuclear factor kappa B (NF-κB) and cyclooxygenase-2 (COX2). To determine the expression patterns of related genes at the transcription level, qRT-PCR was performed. Expression of HSP70 and PI3K was elevated, whereas expression of NF-κB, COX2 and inducible nitric oxide synthase (iNOS) was significantly (P < 0.05) downregulated in the coa-A-treated group compared with the control group. Moreover, pro-apoptotic genes were downregulated, and antiapoptic genes were upregulated in the coa-A group. We also counted the total cell number and apoptotic nuclei at the blastocyst and found that more cell numbers (143.1 ± 1.5) and less apoptotic damages (6.4 ± 0.5) in the coa-A treatment group comparing to control group (131.4 ± 2.0 and 10.8 ± 0.5), indicating the enhanced embryo quality. In conclusion, our results demonstrate that the coa-A not only improved the blastocyst development in vitro but also increased their resistance to heat stress condition through induction of HSP70/PI3K.

Coagulansin-A has beneficial effects on the development of bovine embryos in vitro via HSP70 induction

Treatment with the steroidal lactone, coagulansin-A, improves bovine oocyte maturation and embryo development in vitro by inducing heat shock protein 70 (HSP70), which reduces the levels of reactive oxygen species (ROS), DNA damage and inflammation.

Coagulansin-A (withanolide) is the steroidal lactone obtained from Withania coagulans which belong to Solanaceae family. The present study investigated the effects of coagulansin-A on bovine oocyte maturation and embryo development in vitro. All these oocytes were aspirated from the ovaries obtained from Korean Hanwoo cows at a local abattoir. To determine whether coagulansin-A has beneficial effects on bovine oocyte maturation in vitro, 355 oocytes per group (control and treated) in seven replicates were subjected with different concentrations (1, 2.5, 5, 7.5 and 10 μM) of coagulansin-A. The coagulansin-A was added in the in vitro maturation (IVM) media followed by in vitro fertilization (IVF) and then in vitro culture (IVC). Only treatment with 5 μM coagulansin-A remarkably (P<0.05) improved embryos development (Day 8 blastocyst) having 27.30 and 40.01% for control and coagulansin-A treated groups respectively. Treatment with 5 μM coagulansin-A significantly induced activation of heat shock protein 70 (HSP70) (P<0.05). Immunofluorescence analysis revealed that 5 μM coagulansin-A treatment also significantly inhibited oxidative stress and inflammation during bovine embryo development in vitro by decreasing 8-oxoguanosine (8-OxoG) (P<0.05) and nuclear factor-κB (NF-κB) (P<0.05). The expressions of HSP70 and NF-κB were also conformed through real-time PCR (RT-PCR). Additionally, the terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) assay confirmed that coagulansin-A treatment significantly improved the embryo quality and reduced bovine embryo DNA damage (P<0.05). The present study provides new information regarding the mechanisms by which coagulansin-A promotes bovine embryo development in vitro.

Proteomic Analysis of Fetal Ovary Reveals That Ovarian Developmental Potential Is Greater in Meishan Pigs than in Yorkshire Pigs

Time-dependent expression of functional proteins in fetal ovaries is important to understand the developmental process of the ovary. This study was carried out to enhance our understanding of the developmental process of porcine fetal ovaries and to better address the differences in fetal ovary development of local and foreign pigs. The objective of the present study is to test the expression of key proteins that regulate the growth and development of fetal ovaries in Meishan and Yorkshire porcine breeds by using proteomics technology. Six Meishan and 6 Yorkshire pregnant gilts were used in this experiment. Fetal ovaries were obtained from Yorkshire and Meishan gilts on days 55 and 90 of the gestation period. Using 2D-DIGE (two dimensional-difference in gel electrophoresis) analysis, the results showed that there are about 1551 and 1400 proteins in gilt fetal ovaries on days 55 and 90, respectively of the gestation. Using MALDI TOF-TOF MS analysis, 27 differentially expressed proteins were identified in the fetal ovaries of the 2 breeds on day 55 of gestation, and a total of 18 proteins were identified on day 90 of gestation. These differentially expressed proteins were involved in the regulation of biological processes (cell death, stress response, cytoskeletal proteins) and molecular functions (enzyme regulator activity). We also found that alpha-1-antitrypsin, actin, vimentin, and PP2A proteins promote the formation of primordial follicles in the ovaries of Yorkshire pigs on day 55 of gestation while low expression heat shock proteins and high expression alpha-fetoproteins (AFP) may promote Meishan fetal ovarian follicular development on day 90 of gestation. These findings provide a deeper understanding of how reduced expression of heat shock proteins and increased expression of AFP can significantly reduce the risk of reproductive disease in obese Meishan sows. Our study also shows how these proteins can increase the ovulation rate and may be responsible for the low reproductive efficiency reported in other obese breeds. The ovarian developmental potential was found to be greater in Meishan pigs than in Yorkshire pigs.

Osmotic stress induced by sodium chloride, sucrose or trehalose improves cryotolerance and developmental competence of porcine oocytes

Exposure of porcine oocytes to increased concentrations of NaCl prior to manipulation has been reported not only to increase cryotolerance after vitrification, but also to improve developmental competence after somatic cell nuclear transfer (SCNT). In the present study we compared the effects of NaCl with those of concentrated solutions of two non-permeable osmotic agents, namely sucrose and trehalose, on the cryotolerance and developmental competence of porcine oocytes. In Experiment 1, porcine in vitro-matured cumulus–oocyte complexes (COCs; n = 1200) were exposed to 588 mOsmol NaCl, sucrose or trehalose solutions for 1 h, allowed to recover for a further 1 h, vitrified, warmed and subjected to parthenogenetic activation. Both Day 2 (where Day 0 is the day of activation) cleavage and Day 7 blastocyst rates were significantly increased after NaCl, sucrose and trehalose osmotic treatments compared with untreated controls (cleavage: 46 ± 5%, 44 ± 7%, 45 ± 4% and 26 ± 6%, respectively; expanded blastocyst rate: 6 ± 1%, 6 ± 2%, 7 ± 2% and 1 ± 1%, respectively). In Experiment 2, COCs (n = 2000) were treated with 588 mOsmol NaCl, sucrose or trehalose, then used as recipients for SCNT (Day 0). Cleavage rates on Day 1 did not differ between the NaCl-, sucrose-, trehalose-treated and the untreated control groups (92 ± 3%, 95 ± 3%, 92 ± 2% and 94 ± 2%, respectively), but blastocyst rates on Day 6 were higher in all treated groups compared with control (64 ± 2%, 69 ± 5%, 65 ± 3% and 47 ± 4%, respectively). Cell numbers of Day 6 blastocysts were higher in the control and NaCl-treated groups compared with the sucrose- and trehalose-treated groups. In conclusion, treatment of porcine oocytes with osmotic stress improved developmental competence after vitrification combined with parthenogenetic activation, as well as after SCNT.

Expression of heat shock protein70 in pig oocytes: Heat shock response during oocyte growth

The heat shock response of growing and fully-grown pig oocytes was analyzed in vitro by determining heat shock protein70 (HSP70) synthesis under both normal conditions (39 degrees C; 0 and 6h) and after heat shock (43 degrees C; 1, 4 and 6h). The expression of HSP70 in oocytes was detected by immunoblotting analysis. Growing oocytes measuring 80-99 microm synthesized a high number of HSP70 without heat shock effect, and these were capable of increasing the synthesis of HSP70 after heat shock to a maximum after 1h. Growing oocytes measuring 100-115 microm also synthesized HSP70 without heat shock and after it, but the HSP70 synthesis was not statistically changed by increasing duration of heat shock. In fully-grown oocytes, great amounts of HSP70 were found without heat shock treatment, and the contents of HSP70 significantly decreased after heat shock. These results indicate that growing oocytes are able to synthesize HSP70 after heat shock. This ability declines at the end of the growth period, and fully-grown oocytes are unable to induce HSP70 synthesis after heat shock. HSP70 is synthesized and stored during oocyte growth. The high HSP70 synthesis in non-heat-treated growing oocytes and a great amount of HSP70 in fully-grown oocytes support the hypothesis that HSP70 is important for oocyte growth and maturation.

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.

Heat shock induces apoptosis related gene expression and apoptosis in porcine parthenotes developing in vitro

Successful in vitro development of embryos is dependent upon maintenance of cellular function in the embryonic microenvironment. However, the molecular aspects involved in the thermoprotection of embryos, against heat and cold stress it is not clear. The aim of this study was to determine the effects of heat and cold shock on the viability and development of porcine diploid parthenotes developing in vitro. Exposure of two-cell stage embryos to 41 degrees C did not affect further cleavage. However, prolonged heat shock, greater than 12h, reduced the percentage of blastocysts that developed from two-cell stage parthenotes, as well as the total number of nuclei in the blastocysts that formed. Furthermore, the degree of apoptosis was increased (P<0.05) in these blastocyst stage parthenotes. In contrast, exposure of two-cell parthenotes to cold (30 degrees C) for 24h did not affect the cleavage rates, development to blastocyst, nor the total cell numbers per blastocyst. Real time PCR revealed that quantitative expression of the Bcl-xL gene was not different, but amounts of HSP 70.2, Bak, and Caspase 3mRNA were significantly increased in the heat shocked embryos, as compared with untreated controls. These results suggest that porcine embryos are more tolerant to cold shock than to heat shock. Heat stress seems to induce apoptosis related gene expression in porcine parthenotes developing in vitro, which results in diminished parthenote viability.

Induced thermotolerance in bovine two-cell embryos and the role of heat shock protein 70 in embryonic development

Induced thermotolerance is a phenomenon whereby exposure to a mild heat shock can induce heat shock proteins (HSP) and other cellular changes to make cells more resistant to a subsequent, more severe heat shock. Given that the 2-cell bovine embryo is very sensitive to heat shock, but can also produce HSP70 in response to elevated temperature, experiments were conducted to test whether 2-cell embryos could be made to undergo induced thermotolerance. Another objective was to test the role of the heat-inducible form of heat shock protein 70 (HSP70i) in development and sensitivity of bovine embryos to heat shock. To test for induced thermotolerance, 2-cell bovine embryos were first exposed to a mild heat shock (40 degrees C for 1 hr, or 41 degrees C or 42 degrees C for 80 min), allowed to recover at 38.5 degrees C and 5% (v/v) CO2 for 2 hr, and then exposed to a severe heat shock (41 degrees C for 4.5, 6, or 12 hr). Regardless of the conditions, previous exposure to mild heat shock did not reduce the deleterious effect of heat shock on development of embryos to the blastocyst stage. The role of HSP70i in embryonic development was tested in two experiments by culturing embryos with a monoclonal antibody to the inducible form of HSP70. At both 38.5 degrees C and 41 degrees C, the proportion of 2-cell embryos that developed to blastocyst was reduced (P < 0.05) by addition of anti-HSP70i to the culture medium. In contrast, sensitivity to heat shock was not generally increased by addition of antibody. In conclusion, bovine 2-cell embryos appear incapable of induced thermotolerance. Lack of capacity for induced thermotolerance could explain in part the increased sensitivity of 2-cell embryos to heat shock as compared to embryos at later stages of development. Results also implicate a role for HSP70i in normal development of bovine embryos.

Differential induction of Hsp70-encoding genes in human hematopoietic cells

The rapid transcriptional activation of heat shock genes in response to stress is crucial for the cellular survival and the development of thermotolerance. Although heat shock response is a widespread phenomenon, certain cells exhibit a diminished induction of heat shock gene expression upon stress stimuli. Here we have analyzed the development of thermotolerance and induction of distinct Hsp70 encoding genes in three cell lines representing different hematopoietic cell types. We show that in response to heat shock, cell survival and induction of thermotolerance are impaired in Raji and HL60 cells, as compared with K562 cells. Accordingly, transcriptional induction of the hsp70 gene is diminished in Raji and HL60 cells. This appears to be due to inability of transcription factors, including HSF1 to bind to the hsp70.1 promoter in vivo. Consistent with the genomic footprint, analysis of hsp70.1 mRNA expression using a specific 3'-untranslated region probe reveals that induction of the hsp70.1 gene upon heat shock is completely abolished in Raji and HL60 cells. The suppression of the hsp70.1 promoter is not caused by impaired function of HSF1, since HSF1 is equally activated in all cell types and occupies another heat-inducible promoter, hsp90 alpha. Furthermore, among distinct inducible hsp70 genes, suppression seems to be specific for the hsp70.1 gene, since heat shock results in induction of hsp70.2 and hsp70B' mRNA expression in all cell lines. Taken together, our results demonstrate that distinct Hsp70-encoding genes contribute to the heat shock response in a cell type-dependent manner.

Heat shock proteins Hsp70-1 and Hsp70-3 Are necessary and sufficient to prevent arsenite-induced dysmorphology in mouse embryos

Heat Shock Proteins (HSPs) represent a variety of protein families that are induced by stressors such as heat and toxicants, and the induction of HSPs in the organogenesis stage rodent embryo is well established. It has been proposed that thermotolerance and chemotolerance result from expression of the HSPs. However, whether these proteins function to prevent dysmorphogenesis and which family members serve this function are unknown. Therefore, we evaluated the specific ability of stress-inducible Hsp70-1 and Hsp70-3 to prevent arsenite-induced dysmorphology in the cultured mouse embryo using gain- and loss-of-function models. Loss of HSP function was accomplished by injecting antisense oligonucleotides directed against hsp70-1 and hsp 70-3 mRNAs into the amniotic cavity of cultured Day 9 mouse embryos. Suppression of hsp70-1 and hsp70-3 expression resulted in an up to six-fold increase in the incidence of arsenite-induced neural tube defects. Gain of HSP function was accomplished by microinjecting a transgene with a constitutive promotor driving expression of the hsp70-1 coding region, and resulted in a decreased incidence of arsenite-induced neural tube defects. These results indicate that Hsp70-1 and Hsp70-3 are both necessary and sufficient for preventing arsenite-induced dysmorphology in early-somite staged mouse embryos. Mol. Reprod. Dev. 59:285-293, 2001.

Responsiveness of early embryos to environmental insults: potential protective roles of HSP70 and glutathione

Early embryos are not as passive as previously thought. In the bovine, embryos as early as the 2-cell stage can respond to environmental insults at both the cellular and molecular level by altering expression of specific genes and synthesis of proteins. Moreover, sex related differences exist in how early embryos respond to otherwise hostile environments. As aggressive as early embryos may be to tolerate environment insults, the majority will fail to continue in development. Reduced developmental potential of embryos exposed to elevated temperatures is likely due to direct effects on the early embryo. However, as embryos proceed in development they acquire the ability to better withstand environmental insults. Developmental acquisition of tolerance to environmental stress may be contingent upon acquisition of protective biochemical mechanisms or simply due to increased cell numbers. Correlative evidence has suggested a potential role of heat shock protein 70 and glutathione for protection of embryos in face of elevated temperature. Of these two possibilities, HSP70 appears least likely to play a significant role in developmental acquisition of thermotolerance. Bovine embryos as early as the 2-cell stage, are able to mount a heat shock response; a developmental stage that is most sensitive to elevated temperatures. A more likely candidate for conferring increased resistance of early embryos to elevated temperature is glutathione.

HSP70 expression is increased during the day in a diurnal animal, the golden-mantled ground squirrel Spermophilus lateralis

Heat shock protein 70 (HSP70) gene expression was studied in a seasonal hibernator, the diurnal ground squirrel, Spermophilus lateralis. RNA transcripts of 2.7 and 2.9 kb hybridizing to an HSP70 cDNA were expressed in both brain and peripheral tissues of pre-hibernation euthermic animals; higher levels of expression were observed during the day than during nighttime samples. A decline in the expression of both transcripts occurred in all tissues examined during hibernation that remained low throughout the hibernation season, including the interbout euthermic periods and regardless of time of day. Quantitative comparisons showed pre-hibernation nighttime HSP70 expression to be as low as that observed during hibernation, despite the drastic increase in metabolic state and nearly 30 degrees C difference in body temperature. In contrast to HSP70, some mRNAs, such as beta-actin and HSP60, remained relatively constant, while others, such as glyceraldehyde 3-phosphate dehydrogenase, increased in specific tissues during the hibernation season. These results indicate that the expression of a highly conserved gene involved in protection from cellular stress, HSP70, can vary with an animal's arousal state.

Thermotolerance of IVM-derived bovine oocytes and embryos after short-term heat shock

A series of experiments were designed to study the effect of elevated temperatures on developmental competence of bovine oocytes and embryos produced in vitro. In experiment 1, the effect of heat shock (HS) by a mild elevated temperature (40.5 degrees C) for 0, 30, or 60 min on the viability of in vitro matured (IVM) oocytes was tested following in vitro fertilization (IVF) and culture. No significant difference was observed between the control (39 degrees C) and the heat-treated groups in cleavage, blastocyst formation, or hatching (P > 0.05). In experiment 2, when the HS temperature was increased to 41.5 degrees C, neither the cleavage rate nor blastocyst development was affected by treatment. However, the rate of blastocyst hatching appeared lower in the HS groups (13% in control group vs. 3.9% and 5.6% in 30 min and 60 min, respectively; P < 0.05). When IVM oocytes were treated at 43 degrees C prior to IVF (experiment 3), no difference was detected in blastocyst and expanded blastocyst development following heat treatment for 0, 15, or 30 min, but heat treatment of oocytes for 45 or 60 min significantly reduced blastocyst and expanded blastocyst formation (P < 0.05). In experiment 4, the thermotolerance of day 3 and day 4 bovine IVF embryos were compared. When embryos were pre-treated with a mild elevated temperature (40.5 degrees C) for 1 hr, and then with a higher temperature (43 degrees C) for 1 hr, no improvement in thermotolerance of the embryos was observed as compared to those treated at 43 degrees C alone. However, a higher thermotolerance was observed in day 4 than day 3 embryos. In conclusion, treatment at 43 degrees C, but not 40.5 degrees C or 41.5 degrees C significantly reduced oocyte developmental competence. An increase in thermotolerance was observed from day 3 to day 4 of in vitro embryonic development, which corresponds to the maternal to zygotic transition of gene expression in bovine embryos.

Heat-shock proteins, molecular chaperones, and the stress response: evolutionary and ecological physiology

Molecular chaperones, including the heat-shock proteins (Hsps), are a ubiquitous feature of cells in which these proteins cope with stress-induced denaturation of other proteins. Hsps have received the most attention in model organisms undergoing experimental stress in the laboratory, and the function of Hsps at the molecular and cellular level is becoming well understood in this context. A complementary focus is now emerging on the Hsps of both model and nonmodel organisms undergoing stress in nature, on the roles of Hsps in the stress physiology of whole multicellular eukaryotes and the tissues and organs they comprise, and on the ecological and evolutionary correlates of variation in Hsps and the genes that encode them. This focus discloses that (a) expression of Hsps can occur in nature, (b) all species have hsp genes but they vary in the patterns of their expression, (c) Hsp expression can be correlated with resistance to stress, and (d) species' thresholds for Hsp expression are correlated with levels of stress that they naturally undergo. These conclusions are now well established and may require little additional confirmation; many significant questions remain unanswered concerning both the mechanisms of Hsp-mediated stress tolerance at the organismal level and the evolutionary mechanisms that have diversified the hsp genes.

Heat shock protein 70 (Hsp70) protects postimplantation murine embryos from the embryolethal effects of hyperthermia

Previous work has shown that there is a positive correlation between the induction of Hsp70 and its transient nuclear localization and the acquisition and loss of induced thermotolerance in postimplantation rat embryos. To determine whether Hsp70 is sufficient to induce thermotolerance in postimplantation mammalian embryos, we used a transgenic mouse in which the normally strictly inducible Hsp70 is constitutively expressed in the embryo under the control of a beta-actin promoter. Day 8.0 mouse embryos heterozygous for the Hsp70 transgene were not protected from the embryotoxic effects of hyperthermia (43 degrees C); however, homozygous embryos, expressing approximately twice as much Hsp70 as heterozygous embryos, were partially protected (increased embryo viability) from the embryolethal effects of hyperthermia. Although the viability of transgenic embryos was significantly increased compared with that of nontransgenic embryos, this protection did not extend to embryo growth and development. To determine whether the failure to achieve a more robust protection was related to the expression of insufficient Hsp70 in transgenic embryos, we undertook experiments to determine whether the level of Hsp70 correlated with the level of thermotolerance induced by various lengths of a 41 degrees C heat shock. A 41 degrees C, 5-minute heat shock failed to induce Hsp70 or thermotolerance, a 41 degrees C, 15-minute heat shock induced Hsp70 and a significant level of thermotolerance, while a 41 degrees C, 60-minute heat shock induced an even higher level of Hsp70 as well as a higher level of thermotolerance. Quantitation of Hsp70 levels indicated that thermotolerance was associated with levels of Hsp70 of 820 pg/microg embryo protein or greater. Subsequent quantitation of the amount of Hsp70 expressed in homozygous transgenic embryos indicated a level of 577 pg/microg embryo protein, that is, a level below that associated with induced thermotolerance. Overall, results presented indicate that Hsp70 does play a direct role in the induction of thermotolerance in postimplantation mouse embryos; however, the level of thermotolerance is dependent on the level of Hsp70 expressed.

Heat conditioning induces heat shock proteins in broiler chickens and turkey poults

Peripheral leukocyte heat shock proteins (HSP: HSP90, HSP70, and HSP23) from broiler chickens and turkey poults were induced by in vitro and in vivo high temperature exposure. Heat conditioning, via a daily 1 h exposure to 41 C, enhanced in vitro HSP expression in leukocytes from chickens heat-conditioned for 1 to 2 wk, and a similar response was found in turkey poults with 3 wk of heat conditioning causing the greatest HSP expression. In vivo heat exposure trials caused maximization of HSP expression after 1 wk of daily heat conditioning exposures in broilers, but no additional enhancement was seen in chickens heat conditioned for 2 wk. Enhancement in HSP expression was evident for periods up to 4 wk after termination of the daily heat conditioning episodes.

Response of preimplantation murine embryos to heat shock as modified by developmental stage and glutathione status

Objectives were to characterize developmental changes in response to heat shock in the preimplantation mouse embryo and to evaluate whether ability to synthesize glutathione is important for thermal resistance in mouse embryos. Heat shock (41 degrees C for 1 or 2 h) was most effective at disrupting development to the blastocyst stage when applied to embryos at the 2-cell stage that were delayed in development. Effects of heat shock on ability of embryos to undergo hatching were similar for 2-cell, 4-cell, and morula stage embryos. The phenomenon of induced thermotolerance, for which exposure to a mild heat shock increases resistance to a more severe heat shock, depended upon stage of development and whether embryos developed in vitro or in vivo. In particular, induced thermotolerance was observed for morulae derived from development in vivo but not for 2-cell embryos or morulae that developed in culture. Administration of buthionine sulfoximine to inhibit glutathione synthesis did not increase thermal sensitivity of 2-cell embryos or morulae but did reduce subsequent development of 2-cell embryos at both 37 degrees and 41 degrees C. In summary, changes in the ability of 2-cell through morula stages to continue to develop following a single heat shock were generally minimal. However, 2-cell embryos delayed in development had reduced thermal resistance, and therefore, maternal heat stress may be more likely to cause mortality of embryos that are already compromised in development. There were also developmental changes in the capacity of embryos to undergo induced thermotolerance. Glutathione synthesis was important for development of embryos but inhibition of glutathione synthesis did not make embryos more susceptible to heat shock.

Molecular/cellular biology of the heat stress response and its role in agent-induced teratogenesis

Available data indicate that heat shock proteins act as chaperones under non-stress conditions by assisting in: (1) the folding of newly synthesized proteins, (2) the intracellular translocation of proteins, and (3) the function of other proteins. As we gain additional information concerning cellular physiology, we may find that heat shock proteins play a key role in many additional cellular functions. When cells experience thermal or chemical stress, heat shock proteins take on a new role, conserved from bacteria to humans, of protecting cells from the detrimental effects of stress. This latter role takes on added significance for the embryo in which the developmental program must be read linearly, with little opportunity to cycle backward to complete a missed segment of the program. Although circumstantial evidence clearly implicates heat shock proteins in protecting embryos from thermal stress, definitive evidence is still lacking. The challenge for the future is to obtain such definitive data. Ideally, such information will lead to new therapeutic paradigms that will afford protection to the human embryo/fetus exposed to thermal/chemical stress.

Ontogeny of temperature-regulated heat shock protein 70 synthesis in preimplantation bovine embryos

Development of the preimplantation embryo is very susceptible to disruption by heat shock. As embryos proceed through development, they acquire resistance to heat shock, perhaps because they become transcriptionally active and can respond to environmental changes by undergoing transcriptionally-regulated cellular adaptation. Objectives were to determine the ontogeny of heat shock protein 70 (HSP70) synthesis in preimplantation bovine embryos and to ascertain whether heat-induced increases in HSP70 in embryos are caused by environmental alterations in gene expression. Exposure of bovine embryos to heat shock induced synthesis of a 68 kDa form of HSP70 called HSP68 as early as the two-cell stage of development. Induction of HSP68 was alpha-amanitin independent at the two-cell stage but was blocked by alpha-amanitin as early as the early four-cell stage. Therefore, heat-induced synthesis of HSP68 is regulated at the level of transcription at a time before the major round of embryonic genome activation is considered to occur. Two other constitutive HSP70 molecules were identified called heat shock cognates (HSC) 71 and 70; both proteins were synthesized during all stages of development from the two-cell to hatched blastocyst stages. However, heat-induced synthesis of HSC71 and HSC70 was not evident until the expanded blastocyst stage. In conclusion, environmental signals can activate gene expression before the major round of embryonic genome activation occurs in bovine embryos. Moreover, differences in thermal sensitivity of early embryos to heat shock is not caused by an inability to synthesize HSP70, suggesting that other mechanisms are involved in developmental acquisition of thermotolerance.

Differential responses of bovine oocytes and preimplantation embryos to heat shock

The authors sought to determine whether developmental differences in the magnitude of embryonic mortality caused by heat stress in vivo are caused by changes in resistance of embryos to elevated temperature. In this regard, responses of oocytes, two-cell embryos, four-to eight-cell embryos, and compacted morulae to heat shock were compared. An additional goal was to define further the role of cumulus cells and glutathione in thermoprotection of oocytes. In experiment 1, heat shock (41 degrees C for 12 hr) decreased the number of embryos developing to the blastocyst stage for two-cell (26% vs. 0%) and four- to eight-cell (25% vs. 10%) embryos but did not affect morulae (37% vs. 42%). In experiment 2, exposure of two-cell embryos to 41 degrees C for 12 hr reduced the number of four- to eight-cell embryos present 24 hr after the end of heat shock (88% vs. 62%). In experiment 3, heat shock reduced the number of two-cell embryos developing to blastocyst (49% vs. 8%) but did not affect subsequent development of oocytes when heat shock occurred during the first 12 hr of maturation (46% vs. 41% development to blastocyst); membrane integrity was not altered. In experiment 4, oocytes were cultured with an inhibitor of glutathione synthesis, DL-buthionine-[S,R]-sulfoximine (BSO), for 24 hr and exposed to 41 degrees C for the first 12 hr of maturation. Percentages of blastocysts were 35% (39 degrees C), 18% (41 degrees C), 17% (39 degrees C + BSO), and 11% (41 degrees C + BSO). For experiment 5, oocytes were either denuded or left with cumulus intact and were then radiolabeled with [35S]methionine and [35S]cysteine at 39 degrees C or 41 degrees C for 12 hr. Exposure of oocytes to 41 degrees C for 12 hr reduced overall synthesis of 35S-labeled TCA-precipitable intracellular proteins (18,160 vs. 14,594 dpm/oocyte), whereas presence of cumulus increased synthesis (9,509 vs. 23,246). Analysis by two-dimensional SDS PAGE and fluorography revealed that heat shock protein 68 (HSP68) and two other putative heat shock proteins, P71 and P70, were synthesized by all oocytes regardless of treatment. Heat shock did not alter the synthesis of HSP68 or P71 but decreased amounts of newly synthesized P70. Cumulus cells increased synthesis of P71 and P70. Results indicate there is a biphasic change in resistance to elevations in temperature as oocytes mature, become fertilized, and develop. Resistance declines from the oocyte to the two-cell stage and then increases. Evidence suggests a role for cumulus cells in increasing HSP70 molecules and protein synthesis. Data also indicate a role for glutathione in oocyte function.

HSP70 is essential to the neuroprotective effect of heat-shock

Many kinds of injuries induce 72 kDa heat-shock protein (HSP70) in the central nervous system. We investigated the role of HSP70 in promoting the survival of rat hippocampal neurons in primary culture. Heat-shock (42 degrees C for 30 min) significantly increased the number of surviving neurons independently of the initial density of plated cells, suggesting a direct effect on the neurons. Immunohistochemical detection revealed that HSP70 was expressed in virtually all cells six hours after the heat-shock and the immunostaining became stronger during the observation period of 72 h. HSP70 immunoreactivity was localized in the nucleus at 24 h after the heat-shock, but was diffused throughout the cytoplasm at 72 h. Addition of an antisense oligonucleotide to the medium significantly suppressed the neuroprotective effect of the heat-shock to control level, while a sense oligonucleotide had no effect. HSP70 immunoreactivity was completely abolished in the presence of the antisense oligonucleotide. These results indicate that HSP70 is essential for neuroprotection by heat-shock.

Microinjection of in vitro transcribed RNA and antisense oligonucleotides in mouse oocytes and early embryos to study the gain- and loss-of-function of genes

Mouse oocytes have proven useful in experiments aimed at studying gene function. They have been used to analyze the gain-of-function acquired after microinjection of RNA transcribed in vitro from specific gene constructs, and for establishing loss-of-function mutation obtained by injecting in vitro transcribed antisense RNA and/or synthetic oligonucleotides. This article presents protocols utilized in these studies. Specifically, the acquisition of mouse oocytes and/or embryos, the genesis of the necessary DNA and/or RNA to be used, and procedures for microinjection.

HSP70-2 is part of the synaptonemal complex in mouse and hamster spermatocytes

Mouse spermatogenic cells are known to express HSP70-2, a member of the HSP70 family of heat-shock proteins. The purpose of the present study was to characterize further the expression and localization of HSP70-2 in meiotic cells of mice and hamsters. After separating mouse spermatogenic cells into cytoplasmic and nuclear fractions, proteins were separated by two-dimensional gel electrophoresis and detected with HSP-specific antibodies. Of several HSP70 proteins identified in the cytoplasm, only HSC70 and HSP70-2 were also detected in the nucleus. Immunocytological analyses of spermatocyte prophase cells revealed that HSP70-2 was associated with the synaptonemal complex. Surface-spread synaptonemal complexes at pachytene and diplotene stages labeled distinctly with the antiserum to HSP70-2. Synaptonemal complexes from fetal mouse oocytes failed to show any evidence of HSP70-2. Reverse-transcriptase-polymerase chain reaction (RT-PCR) analyses of gene expression confirmed this sex specificity; Hsp70-2 mRNA was detected in mouse testes, but not ovaries. These findings are suggestive of a previously unsuspected sexual dimorphism in structure and/or function of the synaptonemal complex.

Regulation of heat shock protein 70 synthesis by heat shock in the preimplantation murine embryo

Induced thermotolerance in murine embryos occurs at the 8-cell stage when embryos are maintained in vitro but not until the blastocyst stage if development proceeds in vivo. Present results indicate that ability of embryos to undergo induced thermotolerance is not limited by heat shock protein 70 (HSP70) synthesis. Exposure of 8-cell embryos to 40 degrees C enhanced synthesis of 2 constitutive HSP70 proteins (HSC70 and HSC72) and induced another protein, HSP68; exposure of 43 degrees C was required to induce similar responses in expanded blastocysts. Unlike induced thermotolerance, increased synthesis of HSP70 molecules did not depend on whether embryos were cultured or developed in vivo. Thus, other biochemical mechanisms in addition to HSP70 confer thermotolerance in the preimplantation-stage murine embryo. The observation that the temperature threshold for induction of HSP70 synthesis increased from the 8-cell to the blastocyst stage is indicative of these other biochemical processes.

Induced thermotolerance during early development of murine and bovine embryos

During early development, elevated temperatures have deleterious effects on embryonic viability and development. The primary objective of the current study was to determine the ontogeny of induced thermotolerance during early murine embryonic development. Embryos were either retrieved from superovulated ICR female mice at the 2 cell and 4 cell stages and cultured thereafter or were retrieved from oviducts or uterine horns at the desired stage of development. Induction of thermotolerance was detected by evaluating viability and further development after embryos were exposed to homeothermic temperature (37 degrees C), mild heat shock (40 degrees C for 1 h), severe heat shock (42 degrees C for 1 h or 43 degrees C for 2 h), or mild heat shock followed by severe heat shock (to induce thermotolerance). Induction of thermotolerance was observed beginning at the 8 cell stage when embryos were developed in culture from the 2 cell to 4 cell stage. When embryos were developed in vivo (i.e., were retrieved from the reproductive tract at the desired stage of development), thermotolerance was not induced until the blastocyst stage of development. The induction of thermotolerance was dependent on serum supplementation since induction of thermotolerance was not observed when embryos were placed in medium without serum. Induced thermotolerance could also be demonstrated in bovine blastocysts. In conclusion, embryos acquire the ability to undergo thermotolerance as they progress through development. The timing of processes leading to acquisition of thermotolerance can, however, be hastened by exposure of embryos to in vitro conditions.

Developmental changes in embryonic resistance to adverse effects of maternal heat stress in cows

The objective of this study was to determine whether bovine embryos become more resistant to deleterious effects of maternal heat stress as early embryonic development progresses. Superovulated, lactating Holstein cows were bred by AI and assigned to be heat stressed on d 1, 3, 5, or 7 of pregnancy (d 0 = day of estrus) or not heat stressed (control). Embryos were retrieved from the uterus on d 8 and evaluated for viability and stage of development. Compared with embryos of control cows, embryos of cows receiving heat stress on d 1 had decreased viability and development. Maternal heat stress on other days had no detrimental effect on embryonic viability or stage of development. Bovine embryos become more resistant to adverse effects of maternal heat stress as pregnancy progresses; substantial resistance develops by d 3. This information may be useful in design of environmental modification systems that provide cooling at critical periods of gestation to enhance pregnancy rates during summer in hot climates.

Lack of concordance between heat shock proteins and the development of tolerance to teratogen-induced neural tube defects

The present study was undertaken to examine the role of heat shock response in the development of tolerance and cross-tolerance in an in vivo murine model of teratogen-induced neural tube defects. The experimental paradigm designed to address this question was to utilize inbred mouse strains that differed in their sensitivity to hyperthermia and valproic acid induced neural tube defects, subjecting the dams to subteratogenic pretreatments with either heat or valproic acid at two different timepoints during development prior to the administration of the teratogenic insult. A statistically significant reduction in the frequency of neural tube defects and/or embryolethality following a pretreatment in dams subsequently exposed to a teratogenic treatment was considered evidence for the induction of tolerance. This was observed in the SWV embryos exposed to the 38 degrees C pretreatment at 8:06 and to embryos exposed to either pretreatment temperature at 8:10 prior to a teratogenic heat shock at 8:12. In the LM/Bc embryos, only the 41 degrees C pretreatment at 8:06 induced thermotolerance. There was no evidence of tolerance induced in either mouse strain using valproic acid. On the other hand, cross-tolerance was clearly demonstrated in this study, with a low temperature (41 degrees C) pretreatment successfully protecting SWV fetuses from a subsequent teratogenic treatment with valproic acid, while valproic acid (200 mg/kg) was effective in reducing the risk of hyperthermia-induced neural tube defects in the LM/Bc fetuses. In all instances, tolerance was induced in the absence of significant induction of hsp synthesis. The lack of concordance between hsps and thermotolerance suggests that some other factor(s) is involved in conferring thermotolerance on developing murine embryos.

Genetic differences in heat-induced tolerance to cadmium in cultured mouse embryos are not correlated with changes in a 68-kD heat shock protein

Heat-induced cross-tolerance to cadmium was investigated in two inbred strains of mice, BALB/c and SWV, using a whole embryo culture system. Embryos were exposed to a pretreatment of 5 min at 43 degrees C and subsequently to an embryotoxic concentration of cadmium, 1.75 microM. The two types of embryos responded differently to the heat pretreatment, as cross-tolerance was induced in SWV but not in BALB/c mice. In SWV embryos, prior exposure to 43 degrees C for 5 min essentially eliminated the negative effects of cadmium on embryonic development and growth. However, in BALB/c embryos, no protection was observed. The variation in development of cross-tolerance in embryos from the two strains of mice was not correlated with differences in the induction of a 68-kD heat-shock protein (hsp68). There was a rapid increase in this protein in both strains after the initial heat exposure but not excess induction in the SWV strain that developed tolerance. The induction of hsp68 is therefore not sufficient to elicit cross-tolerance, and other mechanisms are likely to be important in the protective response of the embryo.

Heat Shock Proteins in Hypoxic-Ischemic Brain Injury: A Perspective

There is much to suggest that the induction of heat shock protein synthesis is an important response to injury and stress in the brain. The role of heat shock proteins in neurological disease has been approached from two points-of-view. First, the induction and synthesis of specific proteins after brain cell injury provide a window through which insight on the regulation of gene expression in pathological tissue can be obtained. These studies have broad implications for understanding pathophysiological mechanisms of disease. Second, putative cell protective effects of heat shock proteins in brain tissue provide insight into biochemical mechanisms of selective neuronal vulnerability. These studies have extremely important clinical implications since cell sensitivity to injury can seemingly be modified. The role of heat shock proteins in hypoxic-ischemic brain injury is discussed forthwith.