Expression of the major heat shock protein (hsp 70) family during early mouse embryo development

Endometrial receptivity and embryo implantation in carnivores-commonalities and differences with other mammalian species

Endometrial receptivity and embryo implantation processes are a major point of pregnancy failure in many mammalian species, including humans. Although reproductive biology in many carnivore species remains enigmatic, the few that have been studied so far are invaluable comparative models. The goals of this review are to (1) summarize current data on the mechanisms involved in uterine receptivity and embryo implantation in carnivores, including commonalities and differences with other mammalian species and (2) identify research priorities to better understand a key phenomenon in a critical group of mammals. Besides unique reproductive traits in some carnivores (induced vs. spontaneous ovulation in cats, ovulation at the germinal vesicle stage in dogs), preimplantation embryo development is comparable with other orders. However, the timing of implantation varies, especially in species having an embryonic diapause. Mechanisms involved in endometrial receptivity and decidualization still remain to be fully understood, but specific markers have already been identified. Importantly, the use of endogenous hormones to control the ovarian activity may impact endometrial receptivity and subsequent embryo implantation. Next, research efforts should take advantage of advanced technologies to further study embryo implantation in carnivores and to provide more relevant models to reproductive medicine or for the conservation of rare and endangered species.

Thermal-treatment protocol to induce thermotolerance in bovine embryos

Artificial reproduction in dairy cattle is challenged by summer temperatures in tropical environments. We describe a treatment based on mild temperature increases to induce thermotolerance and improve the embryo's performance under heat stress conditions. A protocol was established to induce upregulation of heat shock protein A (HSPA, formerly known as HSP70) but not impair embryonic development. Thermal treatment (TT) had no effect on morula/blastocyst rate or blastocyst quality (cell number and apoptosis). Heat shock given one day after TT revealed higher (P=0.00) survival rates in TT blastocysts compared with Control. Treated embryos were transferred to recipients and no detrimental effects were observed regarding pregnancy rates, length, fetal growth or calf weight. Our results demonstrated that the established TT protocol could induce a thermal response by the embryo and is safe for further development.

Embryo-maternal communication in dogs: Immune system related factors

In the bitch, establishment of pregnancy is believed to be mainly initiated by the free-floating embryo in the uterus that is under progesterone influence. As in other species, the active participation of the embryo is no longer questioned. Secretory products are transported to the embryo-maternal interface and contribute to extra-cellular matrix (ECM) degradation, a change in the intrauterine immune milieu towards a reduction of immune cells and a change in lymphocyte subsets, cell differentiation, angiogenesis, and the balance between proliferation and apoptosis. For cell-to-cell communication between embryo and maternal tissue, biomolecules inclusive microRNAs might be transported and exchanged via extracellular vesicles (EVs) as in other species. Maternal acceptance of the fetal allograft is vital for the establishment of pregnancy. Findings so far indicate that the embryo avoids attacks from the maternal system via passive and active mechanisms. One hypothesis is that expression or suppression of surface molecules help the canine embryo to hide from the maternal immune system on one side and to actively destroy cytotoxic immune cells on the other side; there are further clues that the canine embryo blocks activation of intrauterine leukocytes. Intracellular repair mechanisms via heat shock proteins (HSP) are candidates under investigation. The presence and function of immunomodulatory intrauterine cells like Treg cells and their interaction with the embryo have been intensely studied in other species but remains to be investigated in the canine preimplantation uterus.

Genome-wide identification and characterization of heat shock protein family 70 provides insight into its divergent functions on immune response and development of Paralichthys olivaceus

Flatfish undergo extreme morphological development and settle to a benthic in the adult stage, and are likely to be more susceptible to environmental stress. Heat shock proteins 70 (hsp70) are involved in embryonic development and stress response in metazoan animals. However, the evolutionary history and functions of hsp70 in flatfish are poorly understood. Here, we identified 15 hsp70 genes in the genome of Japanese flounder (Paralichthys olivaceus), a flatfish endemic to northwestern Pacific Ocean. Gene structure and motifs of the Japanese flounder hsp70 were conserved, and there were few structure variants compared to other fish species. We constructed a maximum likelihood tree to understand the evolutionary relationship of the hsp70 genes among surveyed fish. Selection pressure analysis suggested that four genes, hspa4l, hspa9, hspa13, and hyou1, showed signs of positive selection. We then extracted transcriptome data on the Japanese flounder with Edwardsiella tarda to induce stress, and found that hspa9, hspa12b, hspa4l, hspa13, and hyou1 were highly expressed, likely to protect cells from stress. Interestingly, expression patterns of hsp70 genes were divergent in different developmental stages of the Japanese flounder. We found that at least one hsp70 gene was always highly expressed at various stages of embryonic development of the Japanese flounder, thereby indicating that hsp70 genes were constitutively expressed in the Japanese flounder. Our findings provide basic and useful resources to better understand hsp70 genes in flatfish.

Hyaluronan and hyaluronidase, which is better for embryo development?

Our aim was to examine size-specific effects of Hyaluronan (HA) on preimplantation embryo development. We investigated the effects of Hyalovet (HA, 500-750 kDa; the size produced by HA synthase-3, which is abundant in the oviduct), or HA treated with Hyaluronidase-2 (Hyal2; also expressed in the oviduct that breaks down HA into 20 kDa fragments). In experiment 1 (in vivo), oviducts of synchronized and superovulated ewes (n = 20) were surgically exposed on Day 2 post-mating, ligated, and infused with either Hyalovet, Hyalovet + Hyal2, Hyal2, or PBS (control). Ewes were killed 5 days later for recovery of embryos and oviductal epithelial cells (OEC). Blastocyst rates were significantly higher in Hyal2 and Hyalovet + Hyal2 oviducts. Hyaluronidase-2 infusion resulted in higher blastocyst cell numbers and hatching rates. This was associated with increased HSP70 expression in OEC. In contrast, Hyalovet resulted in the lowest development to blastocyst stage and lowest hatching rates, and decreased IGF2 and IGFBP2 expression in OEC. IGF1 and IL1α expression were not affected. In experiment 2, to rule out indirect effects of oviductal factors, ovine embryos were produced and cultured with the same treatments in vitro from Day 2 to 8. Hyaluronidase-2, but not Hyalovet, enhanced blastocyst formation and reduced inner cell mass apoptosis. Hyalovet inhibited hatching. In conclusion, the presence of large-size HA (500-750 kDa) in the vicinity of developing embryos appears to disturb the oviductal environment and embryo development in vivo and in vitro. In contrast, we show evidence that breakdown of HA into smaller fragments is required to maximize embryo development and blastocyst quality.

Molecular characterization and expression analysis of hsp60 gene homologue of sheep blowfly, Lucilia cuprina

The 60kDa heat shock protein (Hsp60) or chaperonin is one among the highly conserved families of heat shock proteins, known to be involved in variety of cellular activities, including protein folding, thermal protection, etc. In this study we sequence characterized hsp60 gene homologue of Lucilia cuprina, isolated and cloned from the genomic library as well as by genomic PCR, followed by RACE- PCR. The L. cuprina hsp60 gene/protein expression pattern was analyzed in various tissues, either at normal temperature (25±1°C) or after exposure to heat stress (42°C). The analysis of nucleotide sequence of Lchsp60 gene revealed absence of intron and the nuclear localizing signal (NLS). The deduced amino acid sequence showed presence of unique conserved sequences, such as those for mitochondrial localization, ATP binding, etc. Unlike Drosophila, Lucilia showed presence of only one isoform, i.e., hsp60A. Phylogenetic analysis of hsp60 gene homologues from different species revealed Lchsp60 to have >88.36% homology with D. melanogaster, 76.86% with L. sericata, 58.31% with mice, 57.99% with rat, and 57.72% with human. Expression analysis using Real Time PCR and fluorescence imaging showed significant enhancement in the expression level of Lchsp60 upon heat stress in a tissue specific manner, indicating its likely role in thermo-tolerance as well as in normal cellular activities.

HSFs and regulation of Hsp70.1 (Hspa1b) in oocytes and preimplantation embryos: new insights brought by transgenic and knockout mouse models

Gene encoding heat shock protein (Hsps) are induced following a thermal stress thanks to the activation of heat shock transcription factor (HSF) which interacts with heat shock elements (HSE) located within the sequence of Hsp promoters. This cellular and protective response (heat shock response (HSR)) is well known and evolutionarily conserved. Nevertheless, HSR does not function in all the cells produced during the life of a multicellular organism, e.g., early mouse embryos. Taking advantage of mouse transgenic and knockout models, we investigated the roles of trans (HSF 1 and 2) and cis (HSE) regulatory elements in the control of Hsp70.1 (Hspa1b) through several developmental steps from oocytes to blastocysts. Our studies confirm that, even in absence of any stress, HSF1 regulates Hsp70.1 in oocytes and early embryos. Our data emphasize the role of maternal and paternal HSFs in the developmentally regulated expression of Hsp70.1 observed when the zygotic genome activation occurs. Furthermore, in this unstressed developmental condition, affinity and binding to HSEs might be more permissive than in the stress response. Finally, submitting blastocyst to different stress conditions, we show that HSF2 is differentially required for Hsp expression and cell survival. Taken together, our findings indicate that the role of heat shock trans and cis regulatory elements evolve along the successive steps of early embryonic development.

General features of certain RNA populations from gametes and cumulus cells

Results described herein provide insight regarding certain features of gamete RNA and how they compare to cumulus cell RNA. In particular, 28S/18S rRNA ratio and size distribution of RNA molecules differed in total RNA from oocytes versus surrounding cumulus cells. Specifically, oocyte total RNA had a lower rRNA ratio and an increased abundance of smaller RNA sizes compared to RNA from surrounding cumulus. Extensive efforts demonstrated that observed differences were repeatable whether oocyte maturation occurred in vitro or in vivo, and were similar between the nuclear stages examined. Features of oocyte RNA were conserved across six mammalian species, yet differed from surrounding cumulus. Profiles of sperm RNA were also examined but had no discernible ribosomal RNA peaks and were conserved across four mammalian species. Because the oocyte and spermatozoon are highly specialized cells representing unique molecular entities required for proper embryo development, dissimilarities described herein likely represent real gamete versus cumulus RNA differences.

Cellular accumulation of heat shock protein (Hsp) 72i in fetuses of trained rats

Forty-five Sprague-Dawley rats (60-80 days old) were randomly placed into one of three groups: sedentary pregnant control (PC); prepregnancy trained animals that exercised throughout pregnancy (PR); and nonpregnant trained animals (NPR). Each exercising animal ran at approximately 60-70% aerobic capacity (VO2max) for 1 hour/day up to and including day 18 of gestation (term = 21 days). On day 20 of gestation, fetuses were excised from each pregnant animal and scrutinized for gross abnormalities. In 3 randomly chosen fetuses from each litter, brain, heart, kidney, hind limb, and placental tissues were removed to assess the accumulation of the inducible isoform of the 70-kilodalton heat shock protein (Hsp 72i). No significant differences were detected between fetal hearts, hind limbs, or placental tissues of PC or PR groups. No Hsp 72i signal could be detected in fetal kidney or brain tissues from either pregnant group. Results indicate that maternal core temperature did not reach the threshold that would induce either gross fetal abnormalities or a fetal heat shock protein response. However, fetal and placental growth was reduced by the exercise protocol.

Early Onset of Heat-Shock Response in Mouse Embryos Revealed by Quantification of Stress-Induciblehsp70iRNA

Heat shock response is fully established in mouse embryos at the blastocyst stage, but it is unclear when this response first arises during development. To shed light on this question, we used a single-tube method to quantify mRNA levels of the heat shock protein genes hsp70.1 and hsp70.3 ( hsp70i) in individual cleavage-stage embryos that had or had not been heat-shocked. While untreated, healthy embryos contained very low copy numbers of hsp70i RNA, heat shock rapidly induced the synthesis of hundreds of hsp70i transcripts per blastomere at both the 4-cell and the 8-cell stages. In addition, we performed hsp70i measurements in embryos that had not been heat-shocked but had been very slow in developing. Quantification of hsp70i RNA and genomic DNA copy numbers in these slow-growing embryos demonstrated the presence of two distinct populations. Some of the embryos contained considerable levels of hsp70i RNA, a finding consistent with the hypothesis of endogenous metabolic stress accompanied by cell cycle arrest and delayed development. Other slow-growing embryos contained no hsp70i RNA and fewer than expected hsp70i gene copies, suggesting the possibility of ongoing apoptosis. In conclusion, this study demonstrates that mouse embryos can activate hsp70i expression in response to sub-lethal levels of stress as early as at the 4-cell stage. Our results also indicate that quantification of hsp70i DNA and RNA copy numbers may provide a diagnostic tool for embryonic health.

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.

Stress response in mesoangioblast stem cells

Stem cells are presumed to survive various stresses, since they are recruited to areas of tissue damage and regeneration, where inflammatory cytokines and cytotoxic cells may result in severe cell injury. We explored the ability of mesoangioblasts to respond to different cell stresses such as heat, heavy metals and osmotic stress, by analyzing heat shock protein (HSP)70 synthesis as a stress indicator. We found that the A6 mesoangioblast stem cells constitutively synthesize HSP70 in a heat shock transcription factor (HSF)-independent way. However, A6 respond to heat shock and cadmium treatment by synthesizing HSP70 over the constitutive expression and this synthesis is HSF1 dependent. The exposure of A6 to copper or to a hypertonic medium does neither induce HSP70 synthesis nor activation of HSF1, while a constitutive binding of constitutive heat shock element binding factor was found. Together, these data suggest that mesoangioblasts constitutively express HSP70 as an 'a priori' activation mechanism, while they maintain the ability to respond to stress stimuli.

Mercury, cadmium, and arsenite enhance heat shock protein synthesis in chick embryos prior to embryotoxicity

BACKGROUND

Cells respond to adverse environmental stimuli by enhancing the expression of specific genes, the products of which include a suite of proteins known as heat shock proteins (hsps), a response often attributed to cellular protection.

METHODS

In this study, we characterized alterations in hsp expression in chick embryos (Hamburger-Hamilton stage 17, 72 h) exposed in ovo to arsenite (As), mercury (Hg), and cadmium (Cd), known developmental toxicants. Embryos were incubated for 2 h following exposure to 3, 10, 30, or 100 nmol metal, or for 2, 4, 12, or 24 h following treatment with 10 nmol metal.

RESULTS

An enhanced de novo synthesis of 24-, 70-, and 90-kD, 70- and 90-kD, and 70-kD proteins was observed with As, Hg, and Cd treatments, respectively. These responses were transient; apparent rates of protein synthesis were maximal 2-4 h after exposure and returned to control rates by 24 h. Actinomycin D experiments demonstrated that arsenite-induced expression of these proteins is transcriptionally regulated. Immunoblotting experiments identified the 24-, 70-, and 90-kD proteins as the heat shock proteins hsp24, hsp70, and hsp90, respectively. Exposure duration-related abnormalities were noted in the neural tube with all metals and in the ganglia and somites with Cd and As. Retina, allantois, and limb defects were specific to Cd-treated embryos, and branchial arch defects were specific to As-treated embryos.

CONCLUSIONS

The data support metal-induced developmental abnormalities, which are preceded by synthesis of stress proteins.

Genomic cloning of the Hsc71 gene in the hermaphroditic teleost Rivulus marmoratus and analysis of its expression in skeletal muscle: identification of a novel muscle-preferred regulatory element

To further our understanding of the role of stress proteins in development as well as in adaptation of fish to adverse environmental conditions, we undertook molecular analyses of stress protein encoding genes from the hermaphroditic teleost Rivulus marmoratus. We isolated a genomic clone containing the Hsc71 gene (rm-hsc71m) and its upstream sequences. rm-Hsc71m is not induced by external stress, but is enriched in a tissue-specific manner during early development. In adult, the strongest expression appeared in skeletal muscle, whereas lower expression was seen in the gill, eye and brain. To understand the regulatory basis of high muscle expression of rm-hsc71m, transfection of R.marmoratus muscle tissue was performed using 5' deletion fragments containing the rm-hsc71m promoter driving EGFP expression. An upstream region from -2.7 to -1.9 kb was identified as a muscle-specific regulatory region. Within this region, we identified at least three sites with the novel sequence TGTnACA interacting with a fish muscle factor having an M(r) of 32 000. Our data indicate that rm-hsc71m expression in skeletal muscle is controlled by a muscle-specific regulatory element containing this novel motif.

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.

Lead: male-mediated effects on reproduction and development in the rat

The present study was designed to determine the effect of relatively low levels of lead acetate (25 and 250 ppm) exposure on fertility and offspring viability in male Sprague-Dawley rats. Protein synthesis in 2-cell embryos was monitored by [35S] methionine labeling and two-dimensional SDS gel electrophoresis. Fertility was reduced in males with blood lead levels in the range 27-60 microg/dL. Lead was found to affect initial genomic expression in embryos fathered by male rats with blood lead levels as low as 15-23 microg/dL. Dose-dependent increases were seen in an unidentified set of proteins with a relative molecular weight of approximately 70 kDa (Mr). These results indicate that male-mediated effects of lead may be observed in the 2-cell embryo. The alteration observed in embryonic gene expression with paternal lead exposure may be useful for studying the role of the paternal contribution to the activation of the embryonic genome and protein synthesis in the early embryo.

Inhibition of hsp70-1 and hsp70-3 expression disrupts preimplantation embryogenesis and heightens embryo sensitivity to arsenic

Mouse 70-kDa heat shock proteins Hsp70-1 and Hsp70-3 (Hsp70-1/3) are stress-inducible protein chaperones thought to protect embryonic cells and tissues from the effects of a wide range of environmental exposures. Hsp70-1/3 are expressed constitutively, and at times are stress-inducible during various stages of preimplantation embryogenesis. In order to elucidate the functions of constitutive and stress-inducible Hsp70 expression in mouse preimplantation embryos, the consequences of inhibiting expression with antisense oligonucleotides complementary to the mRNAs of hsp70-1 and hsp70-3 (A070-1/3) were evaluated. Transfection of preimplantation embryos (four-cell stage) with 2.5 microM A070-1/3 had no effect on in vitro blastocoel formation. However, transfection with 5 or 10 microM A070-1/3 reduced in vitro blastocyst development to 30% and 0%, respectively (approximately 90% control embryos developed to blastocyst). Thus constitutive expression of Hsp70-1/3 appears significant to preimplantation embryogenesis. Limiting expression of Hsp70-1/3 with 5 microM A070-1/3 also heightened embryo sensitivity to arsenic, resulting in less than 5% in vitro development to blastocyst in the presence of the subtoxic dose of 0.4 microM sodium arsenite. Whether the combined effect of A070-1/3 and arsenic is due to blocking inducible expression of the Hsp70s, or due to further reducing the amount of constitutively expressed Hsp70s available to the embryo is not known at this time. However, these results clearly indicate that some minimal amount of Hsp70-1 and/or Hsp70-3 is required for preimplantation embryogenesis, and that increasing the demand for Hsp70s by arsenic exposure heightens this requirement.

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.

Developmental activation of an episomic hsp70 gene promoter in two-cell mouse embryos by transcription factor Sp1

To investigate the control of zygotic genome expression in two-cell mouse embryos, we studied transcription factors required for transient expression of microinjected DNA constructs driven by the promoter of one of the earliest genes activated after fertilization in this system, the heat shock gene hsp70. Cis-acting elements required for hsp70 activation were first investigated by mutational analysis. Mutation of the TATA box and a proximal GC box strongly inhibited construct expression, while that of a CCAAT box had no effect. Transcription factors binding the wild-type hsp70 promoter were then titrated in vivo by coinjecting the construct with double-stranded oligodeoxyribonucleotides containing definite consensus sequences. Wild-type GC box oligonucleotides strongly inhibited construct expression, while those containing mutated GC boxes, wild-type CCAAT boxes, and heat shock elements had no effects. Finally, construct expression was challenged by coinjecting antibodies to specific transcription factors. Antibodies to factor Sp1 depressed construct expression in a dose-dependent manner, while those to Sp2, HSF1 and HSF2 were ineffective. These results pinpoint the Sp1 transcription factor as an absolute requirement for activation of the hsp70 gene promoter in two-cell mouse embryos, and make this factor a candidate for a major regulator of the onset of murine zygotic genome expression.

Evidence for the involvement of mouse heat shock factor 1 in the atypical expression of the HSP70.1 heat shock gene during mouse zygotic genome activation

The mouse HSP70.1 gene, which codes for a heat shock protein (hsp70), is highly transcribed at the onset of zygotic genome activation (ZGA). This expression, which occurs in the absence of stress, is then repressed. It has been claimed that this gene does not exhibit a stress response until the blastocyst stage. The promoter of HSP70.1 contains four heat shock element (HSE) boxes which are the binding sites of heat shock transcription factors (HSF). We have been studying the presence and localization of the mouse HSFs, mHSF1 and mHSF2, at different stages of embryo development. We show that mHSF1 is already present at the one-cell stage and concentrated in the nucleus. Moreover, by mutagenizing HSE sequences and performing competition experiments (in transgenic embryos with the HSP70.1 promoter inserted before a reporter gene), we show that, in contrast with previous findings, HSE boxes are involved in this spontaneous activation. Therefore, we suggest that HSF1 and HSE are important in this transient expression at the two-cell stage and that the absence of typical inducibility at this early stage of development results mainly from the high level of spontaneous transcription of this gene during the ZGA.

Developmental and afterload stress regulation of heat shock proteins in the ovine myocardium

Heat shock proteins (hsps) are produced in the myocardium in response to stresses such as ischemia, hyperthermia, and increased afterload. The role of these stress proteins in the developing myocardium is unknown. Expression of the inducible (hsp 72) and cognate (hsc 73) hsps was determined in the immature ovine myocardium during the perinatal transition, and their role in subsequent myocardial growth was examined. hsp synthesis was also studied during acute afterload stress in newborns by aortic banding to a gradient of 50 torr for 4 h. Expression of the inducible (hsp 72) isoform is developmentally regulated in both right and left ventricles: low levels in the fetus, increasing throughout development, and peaking in the 14-25-d newborn and adult. The cognate (hsc 73) isoform remains unchanged during development in the left ventricle but decreases with age in the right ventricle. The inducible (hsp 72) isoform is also developmentally regulated in the lung, increasing postnatally to a peak in the 14-25-d-old and adult sheep. Finally, newborn myocardium demonstrated a rapid increase in hsp expression in response to afterload stress, similar to that seen in the adult.

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.

Expression of the HSP 70.1 gene, a landmark of early zygotic activity in the mouse embryo, is restricted to the first burst of transcription

Activation of the mouse embryonic genome at the 2-cell stage is characterized by the synthesis of several alpha-amanitin-sensitive polypeptides, some of which belong to the multigenic hsp 70 family. In the present work we show that a member of this family, the HSP 70.1 gene, is highly transcribed at the onset of zygotic genome activation. Transcription of this gene began as early as the 1-cell stage. Expression of the gene continued through the early 2-cell stage but was repressed before the completion of the second round of DNA replication. During this period we observed that the level of transcription was modulated by in vitro culture conditions. The coincidence of repression of HSP70.1 transcription with the second round of DNA replication was not found for other transcription-dependent polypeptides synthesized at the 2-cell stage.

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.

Activity of a microinjected inducible murine hsp68 gene promoter depends on plasmid configuration and the presence of heat shock elements in mouse dictyate oocytes but not in two-cell embryos

After fertilization in the mouse, the zygotic genome is activated in two-cell embryos by the spontaneous expression, among other genes, of the major inducible heat shock gene, hsp68, in the absence of heat-inducibility of heat shock genes. To obtain information on this phenomenon, we have probed one- and two-cell embryo's ability to express microinjected reporter DNA constructs, containing the Escherichia coli lacZ gene driven by promoters from early SV40 genes, the human beta-actin gene, and the normal or HSE-deleted mouse hsp68 gene. Activity of these promoters was also tested in mouse granulosa cells and dictyate oocytes, as a function of circular/linear construct configuration and occurrence of heat shock. The hsp68 promoter was heat-inducible in both granulosa cells and oocytes. Its heat activation required the presence of HSEs and, in the oocytes, of construct linear configuration. In the embryos however, this promoter was expressed independently of the presence of HSEs and of construct configuration, and its activity was not affected by heat shock. When constructs with early SV40 and beta-actin promoters were injected into one-cell embryos, they appeared to be inactivated with the first embryonic cleavage, in agreement with previous observations [Wiekowski et al., 1992]. By contrast, both normal and HSE-deleted hsp68 promoters maintained their activity through the first cleavage, providing the first evidence of a gene escaping such transcriptional repression. Present results confirm previous findings on hsp68 expression during early mouse development, and suggest that this activation is mediated by a factor(s) other than HSF.

Molecular cloning of a novel mRNA sequence expressed in cleavage stage mouse embryos

In an approach to study genes transcribed during early mouse development, a cDNA library was constructed from poly(A) RNA isolated from the 8-cell morula. The cDNA library was differentially screened with labelled cDNA probes synthesized on poly(A) RNA isolated from the 8-cell morula or unfertilized eggs. Six clones which increased in abundance in the 8-cell morula were selected and further analyzed. Sequencing analyses showed that some of these clones corresponded to RNA transcripts from B1 and B2 repetitive sequences, as well as mRNA for cytochrome C oxidase I and NADH dehydrogenase III derived from the mitochondrial genome. One clone was not identical to any known sequences. The unidentified sequence (MO25) was found at low levels in the unfertilized egg, but increased at the 2-cell stage. The predicted amino acid sequence revealed that the MO25 gene may encode a Ca2+ binding protein.

Gene expression in pre-implantation mammalian embryos

The pre-implantation mammalian embryo is initially under the control of maternal informational macromolecules that are accumulated during oogenesis. Subsequently, the genetic program of development becomes dependent upon new transcription derived from activation of the embryonic genome. Several embryonic transcripts including those that encode growth factors, cell junction components and plasma membrane ion transporters are required for normal progression of the embryo to the blastocyst stage. The pattern of genes expressed and the overall program of development is subject to the influences of genomic imprinting as well as external influences encountered by the embryo within the maternal reproductive tract.

Regulation of hsp70 mRNA levels during oocyte maturation and zygotic gene activation in the mouse

Protein phosphorylation catalyzed by the cAMP-dependent protein kinase is implicated in transcriptional activation of the embryonic genome in the two-cell mouse embryo, while heat shock protein (hsp70) has been identified as one of the first products of zygotic gene activation. Using reverse transcription-polymerase chain reaction we have analyzed relative changes in the amount of hsp70 mRNA during oocyte maturation and early embryogenesis. We report that the amount of hsp70 mRNA decreases after germinal vesicle breakdown, while inhibiting germinal vesicle breakdown inhibits this maturation-associated decrease. The amount of hsp70 mRNA increases between the one- and two-cell stages. This increase is inhibited by either alpha-amanitin or the cAMP-dependent protein kinase inhibitor H-8; the same concentration of H-7, which is a more potent inhibitor of protein kinase C, has little inhibitory effect on this increase in the relative amount of hsp70 mRNA. Last, addition of cycloheximide to one-cell embryos late in G2 inhibits neither cleavage to the two-cell stage nor the increase in the relative amount of hsp70 mRNA. These results strengthen the previous proposal that protein phosphorylation is involved in zygotic gene activation in the two-cell mouse embryo.

Stage-specific expression of a family of proteins that are major products of zygotic gene activation in the mouse embryo

Transcriptional activation of the embryonic genome occurs during the two-cell stage in the mouse embryo and is marked by the synthesis of a set of alpha-amanitin-sensitive proteins of Mr 73,000, 70,000, and 68,000. We have characterized these three proteins by two-dimensional gel electrophoresis of [35S]methionine radiolabeled two-cell embryos. Their isoelectric points range from 6.2 to 6.8 and their synthesis, which can constitute 5-10% of total protein synthesis, is restricted to the two-cell stage. These proteins are not heat shock proteins that have previously been reported as major products of transcriptional activation. Peptide mapping by limited proteolysis indicates that these three proteins are highly related to one another and the results of pulse-chase experiments indicate that they are likely to be degraded by the eight-cell stage. These proteins are nuclear-associated and insoluble in 2% Triton X-100/0.3 M KCl. Although these proteins share some features with somatic lamins--they exhibit solubility properties similar to somatic lamins--they do not cross-react with polyclonal antibodies to either lamins A/C or B, nor do they comigrate with somatic lamins on two-dimensional gels. Additional evidence that these proteins are not lamins is that although treatment of two-cell embryos with okadaic acid, which is an inhibitor of protein phosphatases 1 and 2A, results in precocious nuclear envelope breakdown, the proteins remain insoluble in 2% Triton X-100/0.3 M KCl.

Developmental regulation of heat-shock response in mouse oogenesis: identification of differentially responsive oocyte classes during Graafian follicle development

The response to heat (hs response) of dictyate mouse oocytes at various differentiation stages was analyzed in vitro, by determining patterns of oocyte heat-shock (hs) gene expression and heat-shock protein (HSP) synthesis, under both normal conditions and after an hs. Growing oocytes constitutively synthesized HSP89 and HSC70, and, in contrast to preovulatory oocytes which do not display an hs response, displayed a heat-elicited, transcription-dependent synthesis of two HSP68 isoforms, but not of other inducible HSPs. To determine the developmental schedule of hs response disappearance during oogenesis, fully grown oocytes from Graafian follicles were morphologically sorted into three discrete classes related to the follicle development, namely, loosely associated with granulosa cells (LA oocytes, from small Graafian follicles), intermediately associated with granulosa cells (IA oocytes, from medium-sized Graafian follicles), and cumulus-associated (CA oocytes, from mature follicles). LA oocytes displayed an hs response qualitatively similar to, but smaller in extent than, that of growing oocytes, and were able to resume and complete spontaneous meiotic maturation in vitro at a high rate after hs. We conclude that hs response of mouse dictyate oocytes is maximal during growth period, significantly declines with acquisition of full oocyte size and antrum formation within the follicle, and is finally shut off with oocyte/follicle terminal differentiation.

Diminished phosphorylation of a heat shock protein (HSP 27) in infant acute lymphoblastic leukemia

We have previously reported lack of expression of a polypeptide designated L3 in infant acute lymphoblastic leukemia (ALL). Expression of L3 occurred predominantly in older children with pre-B ALL. We have recently reported the expression during B cell ontogeny of two other polypeptides, designated L2 and L4 with a similar Mr as L3, which were identified as phosphorylated and non-phosphorylated forms respectively of the low Mr heat shock protein. hsp27. In this study we have characterized L3 and identified it as another phosphorylated form of hsp27. The two phosphorylated forms appear to be differentially expressed in acute leukemia. L3 levels in infants who expressed hsp27 isoforms L2 and L4 were significantly diminished compared to levels in older children with an equivalent amount of hsp27. We conclude that leukemic cells in infant ALL exhibit a unique pattern of phosphorylation of hsp27 expressed at a pre-B cell stage of differentiation.

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

Eukaryotic and prokaryotic cells have been shown to respond to physical and chemical stress by the induction of proteins called heat shock proteins. Heat shock protein 70 (Hsp70), is the most ubiquitous of these proteins. Although heat shock proteins are generally thought to protect cells from physiologically stressful stimuli, it cannot be assumed that this is so, because several cases exist in which thermotolerance is acquired without the production of heat shock proteins, and in several other cases the hyperproduction of these heat shock proteins does not produce thermotolerance. In this study we show that unfertilized mouse oocytes are sensitive to elevated temperatures, and that the synthesis of Hsp70 cannot be induced in these oocytes. Furthermore, our data demonstrate that the expression of Hsp70 in mouse oocytes is sufficient for the acquisition of thermotolerance. Mouse oocytes were injected with mRNA for Hsp70, and the viability of these oocytes was determined after heating. The number of viable oocytes was significantly higher in the group injected with Hsp70 mRNA and then heated compared with oocytes injected with Hsp70 antisense mRNA and sham-injected controls treated in an identical manner. No significant differences in the number of viable oocytes were found between the group that had been injected with Hsp70 mRNA, heated, and then allowed to recover for 3 hr and the group maintained at 37 degrees C throughout.(ABSTRACT TRUNCATED AT 250 WORDS)

Embryonic resistance to chemical and physical factors: manifestation, mechanism, role in reproduction and in adaptation to ecology

Chemical and physical factors may adversely affect embryonic development. As an example of chemical factors, the effects of diabetic metabolic factors on embryonic development in mammals was reviewed. The existence of a stage-dependent reaction of embryos was found. At preimplantation stages diabetic metabolic factors are embryotoxic and lethal, and the blastocysts reacted by an "all-or-none" response. Early somite embryos showed a higher resistance to the effects of diabetic metabolic factors resulting in various types of malformations. Both groups of embryos showed a very high sensitivity to the effects of combined diabetic metabolic factors. Congenital defects in term foetuses were lower than those observed during middle phases of pregnancy because some of the severely malformed embryos resorb during gestation. The effects of temperature on embryonic development were presented as an example of physical influences. In man, hyperthermia in pregnancy seems to correlate with defects in the development of the nervous and skeletal systems. In domestic animals, changes in environmental temperature correlated with depressions of reproduction rate. In laboratory animals, hyperthermia caused the development of congenital malformations. Stage-dependent as well as genetic differences in embryonic susceptibility to hyperthermia were found. Critical periods in sensitivity of embryos to hyperthermic influences were also observed. It has been shown that, in spite of similar external manifestations of the reaction of embryos to effects of diabetes and hyperthermia, the mechanism of these reactions was different. High resistance of early reptile and bird embryos to influences of temperature was considered as an example of morphofunctional adaptations in early embryogenesis of vertebrates to their development in terrestrial conditions.

Identification of two related markers for common acute lymphoblastic leukemia as heat shock proteins

By direct analysis of the polypeptide constituents of leukemic cells, we have previously detected several polypeptides that are restricted in their expression to acute lymphoblastic leukemia (ALL). In this study, we provide evidence that two polypeptides designated L2 and L4 are structurally related and represent novel markers for common ALL. Partial amino acid sequence analysis did not uncover differences between L2 and L4. The sequences obtained correspond to a previously cloned human gene designated hsp 27 that is expressed, following heat shock treatment, in a variety of cells. 32Pi incorporation studies indicate that L4 is an unphosphorylated form and L2 is a phosphorylated form of hsp27. The two forms were inducible by heat shock in leukemic and nonleukemic lymphoid cells. Thus, in acute leukemia, the common ALL subtype is uniquely characterized by the constitutive expression of a polypeptide that represents a major cellular phosphoprotein.

Embryonic and maternal heat shock responses to a teratogenic hyperthermic insult

Exposing embryos to elevated temperatures both in vivo and in vitro has been shown to result in the production of offspring with severe congenital abnormalities. While a direct effect of heat cannot be excluded, recent interest has been focused on the possible role that the induction of the heat shock response may have in the etiology of the observed congenital defects. In the present study, mouse embryos from inbred strains known to differ in terms of their sensitivity to heat-induced exencephaly were treated in vivo and their heat shock response determined using SDS-PAGE electrophoretic techniques. Further, the embryonic responses were compared with a maternal cell type. We observed excellent agreement between the two test systems following exposure to a teratogenic hyperthermic insult. Both the embryonic and maternal cells underwent a reduction in total protein synthesis and an enhanced synthesis of four heat shock proteins migrating with the molecular weights of 68, 70, 97, and 110 kDa. The results failed to indicate any strong correlation between the heat shock response and enhanced genetic sensitivity to hyperthermia-induced neural tube defects.

Expression of heat shock proteins by isolated mouse spermatogenic cells

Proteins of the hsp70 family are abundant in mouse spermatogenic cells. These cells also synthesize relatively large amounts of a 70,000-molecular-weight protein (P70) that appears to be a cell-specific isoform of hsp70, the major heat-inducible protein (R.L. Allen, D.A. O'Brien, and E.M. Eddy, Mol. Cell. Biol. 8:828-832, 1988). In this study, proteins of unstressed and heat-stressed spermatogenic cells consisting of purified preparations of preleptotene, leptotene-zygotene, pachytene spermatocytes, and round spermatids were analyzed by two-dimensional polyacrylamide gel electrophoresis. Unstressed preleptotene and leptotene-zygotene spermatocytes contained little P70, whereas relatively large amounts of P70 were present in pachytene spermatocytes and round spermatids. Labeling studies showed that P70 was synthesized primarily in pachytene spermatocytes and that little synthesis occurred in round spermatids or in preleptotene and leptotene-zygotene stages of spermatogenesis. Synthesis of hsp70 was not detectable in unstressed cells but was induced in all stages of isolated germ cells following heat stress. These results indicate that P70 is expressed in a stage-specific manner during cell differentiation, whereas hsp70 is synthesized in response to stress in all populations of isolated spermatogenic cells examined.

Effect of age and busulphan treatment on the hsp70 gene-related transcript level in rat testes

Northern blot analysis was used to determine the expression pattern of a testis-specific, heat shock gene (hsp70)-related transcript (hst70 RNA) in rats during sexual maturation, following administration of busulphan and in aged rats with progressive tubular degeneration. The level of the hst70 RNA in testes of rats aged 4, 7, 12, 19, 21 or 24 months decreased gradually with age. In the atrophic testes of old rats with tubules depleted of germ cells, the hst70 transcript was undetectable. Transient arrest of spermatogenesis in rats aged 2 months following injection of a single dose of busulphan (10 mg/kg) resulted in a parallel but transient decrease in the transcript level to undetectable values, followed by its reappearance after resumption of spermatogenesis. The transcript was absent from testes containing tubules depleted of spermatocytes and spermatids and reappeared when a new generation of round spermatids repopulated the seminiferous tubules. Possible expression of the hst70 gene prior to the formation of early spermatids is discussed.

Elevated expression of proto-oncogenes accompany enhanced induction of heat-shock genes after exposure of rat embryos in utero to ionizing irradiation

We have recently found that the effects of exposing rat embryos in utero to teratogens capable of producing cardiac anomalies were expressed later as enhanced induction of heat-shock proteins (hsp70 family) when embryonic hearts were cultured in vitro. However, it remained to be determined whether heat-shock proteins are induced in vivo after exposure to teratogens. The heat-shock response in some mammalian systems is known to be accompanied by elevated expression of proto-oncogenes. Using gene-specific DNA probes, we examined the levels of the expression (transcription) of heat-shock protein genes and two nuclear proto-oncogenes, c-fos and c-myc, in the embryos removed from irradiated pregnant mother rats 4 or 5 days after the irradiation. We found that the levels of expression in vivo of the hsp70 and c-myc genes in the irradiated embryos increased by approximately twofold as compared with those in the control. The expression in vivo of the c-fos gene was not detected in either the irradiated or non-irradiated embryos. After 0.5-hr incubation in vitro of the embryos, however, the expression of the c-fos gene in the irradiated embryos was highly enhanced whereas the control showed no changes. Although the exact functions of these gene products still remain obscure, the enhanced expression of hsp70 gene(s) and the nuclear proto-oncogenes observed in the present study may reflect repair of intracellular damages and/or regeneration of tissue by compensatory cell proliferation, processes that may disturb the normal program of organogenesis.

Protein synthetic patterns in immature and mature human oocytes

A preliminary study of protein synthesis and amino acid transport in human oocytes was initiated. Qualitative patterns or protein synthesis were examined in individual oocytes cultured in medium containing radiolabeled methionine. The protein synthetic profile of immature oocytes, resolved by one-dimensional electrophoresis and fluorography, was observed to change markedly following germinal vesicle breakdown and oocyte maturation. No further differences in the one-dimensional protein synthetic patterns were observed in mature oocytes maintained in culture from 10 hours up to as long as 50 hours. The protein synthetic pattern of follicular cells was observed to be distinct from that of oocytes and was characterized by the predominant synthesis of a polypeptide with Mr = 44,000. Based on the specific activity of the methionine precursor, the absolute rate of synthesis was calculated to be about 50 pg protein/oocyte/hour. Total protein content was measured to be about 150 ng/egg. Competition of methionine uptake by leucine, efflux of radiolabeled methionine from preloaded oocytes into medium containing methionine and uptake of methionine in medium with low sodium ion concentration was observed. These findings are consistent with the presence of an L (leucine-preferring) system for neutral amino acid transport, similar to that in mouse and rabbit eggs. These studies provide basic data for further analysis of oocytes and perhaps preimplantation-stage embryos in the future.

Expression of a testis-specific hsp70 gene-related RNA in defined stages of rat seminiferous epithelium

Changes in the level of a testis-specific hsp70 gene-related transcript (hst70 RNA) and its cellular localization during the cycle of rat seminiferous epithelium have been investigated. Segments of seminiferous tubules at defined stages of the cycle were isolated in living condition by transillumination-assisted microdissection and the exact stages identified by phase-contrast microscopy of live cell squashes. The levels of the hst70 RNA were determined by Northern and slot blotting of whole cell lysates. High levels were found in stages XII-XIV and I to early VII of the cycle, and low levels were found in other stages, i.e., late VII (VIId) through VIII-XI of the cycle. The in situ hybridization revealed that the hst70 gene was activated in late pachytene primary spermatocytes during stage XII of the cycle, and that mRNA was then present in cells during differentiation through diakinesis, meiotic divisions, and early spermiogenesis (steps 1 through early 7). The activation of the gene coding for hst70 RNA shortly before meiotic divisions may indicate that the gene product is needed either during differentiation of late spermatocytes into spermatids or later during spermiogenesis, and that the mRNA may be stored in early spermatids.

Identification and sequence analysis of a new member of the mouse HSP70 gene family and characterization of its unique cellular and developmental pattern of expression in the male germ line

A unique member of the mouse HSP70 gene family has been isolated and characterized with respect to its DNA sequence organization and expression. The gene contains extensive similarity to a heat shock-inducible HSP70 gene within the coding region but diverges in both 3' and 5' nontranslated regions. The gene does not yield transcripts in response to heat shock in mouse L cells. Rather, the gene appears to be activated uniquely in the male germ line. Analysis of RNA from different developmental stages and from enriched populations of spermatogenic cells revealed that this gene is expressed during the prophase stage of meiosis. A transcript different in size from the major heat-inducible mouse transcripts is most abundant in meiotic prophase spermatocytes and decreases in abundance in postmeiotic stages of spermatogenesis. This pattern of expression is distinct from that observed for another member of this gene family, which was previously shown to be expressed abundantly in postmeiotic germ cells. These observations suggest that specific HSP70 gene family members play distinct roles in the differentiation of the germ cell lineage in mammals.

Expression of heat shock proteins by isolated mouse spermatogenic cells

Proteins of the hsp70 family are abundant in mouse spermatogenic cells. These cells also synthesize relatively large amounts of a 70,000-molecular-weight protein (P70) that appears to be a cell-specific isoform of hsp70, the major heat-inducible protein (R.L. Allen, D.A. O'Brien, and E.M. Eddy, Mol. Cell. Biol. 8:828-832, 1988). In this study, proteins of unstressed and heat-stressed spermatogenic cells consisting of purified preparations of preleptotene, leptotene-zygotene, pachytene spermatocytes, and round spermatids were analyzed by two-dimensional polyacrylamide gel electrophoresis. Unstressed preleptotene and leptotene-zygotene spermatocytes contained little P70, whereas relatively large amounts of P70 were present in pachytene spermatocytes and round spermatids. Labeling studies showed that P70 was synthesized primarily in pachytene spermatocytes and that little synthesis occurred in round spermatids or in preleptotene and leptotene-zygotene stages of spermatogenesis. Synthesis of hsp70 was not detectable in unstressed cells but was induced in all stages of isolated germ cells following heat stress. These results indicate that P70 is expressed in a stage-specific manner during cell differentiation, whereas hsp70 is synthesized in response to stress in all populations of isolated spermatogenic cells examined.

Identification and sequence analysis of a new member of the mouse HSP70 gene family and characterization of its unique cellular and developmental pattern of expression in the male germ line

A unique member of the mouse HSP70 gene family has been isolated and characterized with respect to its DNA sequence organization and expression. The gene contains extensive similarity to a heat shock-inducible HSP70 gene within the coding region but diverges in both 3' and 5' nontranslated regions. The gene does not yield transcripts in response to heat shock in mouse L cells. Rather, the gene appears to be activated uniquely in the male germ line. Analysis of RNA from different developmental stages and from enriched populations of spermatogenic cells revealed that this gene is expressed during the prophase stage of meiosis. A transcript different in size from the major heat-inducible mouse transcripts is most abundant in meiotic prophase spermatocytes and decreases in abundance in postmeiotic stages of spermatogenesis. This pattern of expression is distinct from that observed for another member of this gene family, which was previously shown to be expressed abundantly in postmeiotic germ cells. These observations suggest that specific HSP70 gene family members play distinct roles in the differentiation of the germ cell lineage in mammals.