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

Apicobasal RNA asymmetries regulate cell fate in the early mouse embryo

The spatial sorting of RNA transcripts is fundamental for the refinement of gene expression to distinct subcellular regions. Although, in non-mammalian early embryogenesis, differential RNA localisation presages cell fate determination, in mammals it remains unclear. Here, we uncover apical-to-basal RNA asymmetries in outer blastomeres of 16-cell stage mouse preimplantation embryos. Basally directed RNA transport is facilitated in a microtubule- and lysosome-mediated manner. Yet, despite an increased accumulation of RNA transcripts in basal regions, higher translation activity occurs at the more dispersed apical RNA foci, demonstrated by spatial heterogeneities in RNA subtypes, RNA-organelle interactions and translation events. During the transition to the 32-cell stage, the biased inheritance of RNA transcripts, coupled with differential translation capacity, regulates cell fate allocation of trophectoderm and cells destined to form the pluripotent inner cell mass. Our study identifies a paradigm for the spatiotemporal regulation of post-transcriptional gene expression governing mammalian preimplantation embryogenesis and cell fate.

Heat shock proteins exhibit distinct spatiotemporal expression patterns in the domestic cat (Felis catus) ovary during the oestrous cycle

Heat shock proteins (HSP) are significant regulators of cell proliferation, differentiation and apoptosis. HSP participate in ovarian physiology through proliferative and apoptotic mechanisms and the modulation of sex steroid receptor functions. We investigated whether the expression and localisation patterns of HSP in the domestic cat ovary vary with the oestrous cycle stage. Immunohistochemical analysis revealed cell type-specific localisation patterns of HSPD1/HSP60, HSPA/HSP70, HSPC/HSP90 and HSPH/HSP105 in several ovarian cells of the domestic cat, including oocytes, follicular (granulosa and theca cells) and luteal cells, stromal and thecal interstitial cells, stromal cells, and vascular endothelial and smooth muscle cells during the anoestrous, follicular and luteal phases of the oestrous cycle. Western blot results showed that the expression of three HSP (HSPD1/HSP60, HSPA/HSP70 and HSPH/HSP105) varied with the oestrous cycle stage. While the maximal expression of HSPD1/HSP60 and HSPH/HSP105 occurred during the luteal phase, the expression of HSPA/HSP70 was minimal. The expressions of HSPA/HSP70 and HSPH/HSP105 were low during the follicular phase compared to the anoestrous phase. In conclusion, the alterations that occur in the expression of HSP in the domestic cat ovary during the different stages of the oestrous cycle imply that these proteins participate in the regulation of ovarian function under different physiological conditions.

Melatonin Restores the Developmental Competence of Heat Stressed Porcine Oocytes, and Alters the Expression of Genes Related to Oocyte Maturation

Simple Summary

Melatonin improves the quality and in vitro maturation (IVM) of oocytes under heat stress. Melatonin treatment counteracts the adverse effects induced by heat stress (HS), such as the poor survival rate and maturation rate, distribution of α-tubulin and F-actin, expression of NRF2 and GDF9 mRNA. However, HS and melatonin have similar effects on increasing expression of HSP70 and NRF2 mRNA. Furthermore, HS inhibits expression of GDF9 mRNA.

Abstract

Melatonin enhances the quality and in vitro maturation (IVM) of oocytes under heat stress (HS), but the mechanism of melatonin in reducing HS injury on oocytes is not fully understood. In this study, porcine cumulus-oocyte complexes (COCs) were randomly divided into three groups. The COCs of the control group were cultured at 38.5 °C for 42 h, and the COCs of the HS group were cultured at 41.5 °C for 4 h, and then transferred into 38.5 °C for 38 h. The COCs of the HS + melatonin group were cultured with 10⁻⁹ M melatonin under the same conditions as the HS group. The survival rate, maturation rate, distribution of α-tubulin and F-actin of the oocytes were assessed. In addition, the expression profiles for genes related to the oocyte maturation, including heat shock protein 70 (HSP70), nuclear factor erythroid 2-related factor 2 (NRF2), cyclin-dependent kinase 1 (CDK1), growth differentiation factor 9 (GDF9) were analyzed by real-time quantitative PCR. The results showed that HS decreased the survival rate and maturation rate, distribution of α-tubulin and F-actin, but melatonin treatment could partly counteract these adverse effects. In addition, HS increased expression of HSP70 and NRF2 mRNA, and melatonin treatment had a similar effect on HSP70 expression, but had a contrary effect on NRF2 expression. Furthermore, HS inhibited expression of CDK1 and GDF9 mRNA, but melatonin treatment could weaken the effect on GDF9 expression induced by HS. In summary, melatonin treatment could attenuate the unfavorable effects induced by HS to enhance developmental competence of porcine oocytes during IVM.

Heat shock protein 90α couples with the MAPK-signaling pathway to determine meiotic maturation of porcine oocytes

Heat shock protein 90 (Hsp90) functions as a molecular chaperone in its interaction with clients to influence multiple cellular and physiological processes. However, our current understanding on Hsp90's relationship with mammalian oocyte maturation is still very limited. Here, we aimed to investigate Hsp90's effect on pig oocyte meiotic maturation. Endogenous Hsp90α was constantly expressed at both mRNA and protein levels in porcine maturing oocytes. Addition of 2 µM 17-allylamino-17-demethoxygeldanamycin (17-AAG), the Hsp90 inhibitor, to in vitro mature cumulus-oocyte complexes (COC) significantly decreased Hsp90α protein level (P < 0.05), delayed germinal vesicle breakdown (GVBD) (P < 0.05), and impeded the first polar body (PB1) extrusion (P < 0.01) of porcine oocytes. 2 µM 17-AAG treatment during in vitro maturation also decreased the subsequent development competence as indicated by the lower cleavage (P < 0.001) and higher fragmentation (P < 0.001) rates of parthenotes, whereas no effects on the percentage and average cell number of blastocysts were found. Immunodepletion of Hsp90α by antibody microinjection into porcine oocytes at germinal vesicle and metaphase II stages induced similar defects of meiotic maturation and parthenote development, to that resulted from 2 µM inhibitor 17-AAG. For oocytes treated by 2 µM 17-AAG, the cytoplasm and membrane actin levels were weakened (P < 0.01), and the spindle assembly was disturbed (P < 0.05), due to decreased p-ERK1/2 level (P < 0.05). However, the mitochondrial function and early apoptosis were not affected, as demonstrated by rhodamine 123 staining and Annexin V assays. Our findings indicate that Hsp90α can couple with mitogen-activated protein kinase to regulate cytoskeletal structure and orchestrate meiotic maturation of porcine oocytes.

Improved development by melatonin treatment after vitrification of mouse metaphase II oocytes

The study was aimed to investigate the effect of melatonin on the development potential of mouse MII oocytes after cryopreservation. Mouse MII oocytes were subjected first to vitrification/warming and 2 h of in vitro culture (phase 1), then to parthenogenetic activation (PA) followed by in vitro culture of parthenogenetic embryos (phase 2). Different concentrations of melatonin (0, 10^-9, 10^-6 mol/L) were added to the medium during either phase 1, phase 2 or both phases. The fresh oocytes were used as control. When melatonin was used during both phases, 10^-9 mol/L melatonin-treated group showed similar rates of cleavage and 4-cell embryo development compared with control, which were significantly higher than those of melatonin-free group, while the rates in either 10^-6 mol/L melatonin-treated or melatonin-free groups were significantly lower than that in control. When 10^-9 mol/L melatonin was added during either phase 1 or phase 2, both cleavage and 4-cell embryo development rates of either group were significantly lower than those of control. After oocyte vitrification/warming and PA, the ROS levels increased significantly and maternal-to-zygotic transition (MZT) related genes (Dcp1a, Dcp2, Hspa1a, Eif1ax, Pou5f1, Sox2) expression were disorganized. However, after 10^-9 mol/L melatonin supplementation, the ROS levels decreased significantly compared with melatonin-free group, and the gene expressions were almost recovered to normal level of control group. These results demonstrated that 10^-9 mol/L melatonin supplementation could increase the developmental potential of vitrified-warmed mouse MII oocytes, which may result from ROS scavenging activities and recovery of normal levels of the expressions of MZT-related genes.

Comparative Proteomic Analysis of Mature and Immature Oocytes of the Swamp Buffalo (Bubalus bubalis)

Maternal protein components change markedly during mammalian oogenesis. Many of these proteins have yet to be characterized and verified. In this study, a proteomics approach was used to evaluate changes in proteins during oogenesis in the Swamp Buffalo (Bubalus bubalis). Proteins from 500 immature oocytes and 500 in vitro matured oocytes were subjected to two-dimensional electrophoresis, and more than 400 spots were detected. Image analysis indicated that 17 proteins were differentially expressed between the two groups. Eight proteins were identified by mass spectrometry. In mature oocytes, three proteins were down-regulated: major vault protein (MVP), N-acetyllactosaminide β-1,6-N-acetylglucosaminyl-transferase (GCNT-2), and gem-associated protein (GEMIN)8, whereas five other proteins, heat shock protein (HSP)60, Ras-responsive element-binding protein 1 (RREB-1), heat shock cognate 71 kDa protein (HSC71), hemoglobin subunit α (HBA), and BMP-2-inducible protein kinase (BMP-2K), were up-regulated. The expression profiles of HSP60 and GEMIN8 were further verified by Western blotting. The changes in HSP60 protein expression demonstrate the increasing need for mitochondrial protein importation to facilitate macromolecular assembly during oocyte maturation. The down-regulation of GEMIN8 production implies that RNA splicing is impaired in mature oocytes.

Gel-based and gel-free identification of proteins and phosphopeptides during egg-to-larva transition in polychaete Neanthes arenaceodentata

The polychaete Neanthes arenaceodentata- is cosmopolitan in distribution-, has been used as a laboratory test animal. Life history of this species has several unique features; the female dies after spawning and the male incubates the fertilized eggs through the 21-segmented stage. The larvae leave the tube and commence feeding. Changes in protein abundance and phosphorylation were examined during early development of N. arenaceodentata. A gel-based approach and gel-free enrichment of phosphopeptides coupled with mass spectrometry were used to identify proteins and phosphopeptides in fertilized ova and larval stages. Patterns of proteins and phosphoproteins changed from fertilized ova to larval stages. Twelve proteins occurred in phosphorylated form and nine as stage specific proteins. Cytoskeletal proteins have exhibited differential phosphorylation from ova to larval stages; whereas, other proteins exhibited stage-specific phosphorylation patterns. Ten phosphopeptides were identified that showed phosphorylation sites on serine or threonine residues. Sixty percent of the identified proteins were related to structural reorganization and others with protein synthesis, stress response and attachment. The abundance and distribution of two cytoskeleton proteins were examined further by 2-DE Western blot analysis. This is the first report on changes in protein expression and phosphorylation sites at Thr/Ser in early development of N. arenaceodentata. The 2-DE proteome maps and identified phosphoproteins contributes toward understanding the state of fertilized ova and early larval stages and serves as a basis for further studies on proteomics changes under different developmental conditions in this and other polychaete species.

HSP70 mediates dissociation and reassociation of the 26S proteasome during adaptation to oxidative stress

We report an entirely new role for the HSP70 chaperone in dissociating 26S proteasome complexes (into free 20S proteasomes and bound 19S regulators), preserving 19S regulators, and reconstituting 26S proteasomes in the first 1-3h after mild oxidative stress. These responses, coupled with direct 20S proteasome activation by poly(ADP ribose) polymerase in the nucleus and by PA28αβ in the cytoplasm, instantly provide cells with increased capacity to degrade oxidatively damaged proteins and to survive the initial effects of stress exposure. Subsequent adaptive (hormetic) processes (3-24h after stress exposure), mediated by several signal transduction pathways and involving increased transcription/translation of 20S proteasomes, immunoproteasomes, and PA28αβ, abrogate the need for 26S proteasome dissociation. During this adaptive period, HSP70 releases its bound 19S regulators, 26S proteasomes are reconstituted, and ATP-stimulated proteolysis is restored. The 26S proteasome-dependent, and ATP-stimulated, turnover of ubiquitinylated proteins is essential for normal cell metabolism, and its restoration is required for successful stress adaptation.

Use of proteomics to identify highly abundant maternal factors that drive the egg-to-embryo transition

As IVF becomes an increasingly popular method for human reproduction, it is more critical than ever to understand the unique molecular composition of the mammalian oocyte. DNA microarray studies have successfully provided valuable information regarding the identity and dynamics of factors at the transcriptional level. However, the oocyte transcribes and stores a large amount of material that plays no obvious role in oogenesis, but instead is required to regulate embryogenesis. Therefore, an accurate picture of the functional state of the oocyte requires both transcriptional profiling and proteomics. Here, we summarize our previous studies of the oocyte proteome, and present new panels of oocyte proteins that we recently identified in screens of metaphase II-arrested mouse oocytes. Importantly, our studies indicate that several abundant oocyte proteins are not, as one might predict, ubiquitous housekeeping proteins, but instead are unique to the oocyte. Furthermore, mouse studies indicate that a number of these factors arise from maternal effect genes (MEGs). One of the identified MEG proteins, peptidylarginine deiminase 6, localizes to and is required for the formation of a poorly characterized, highly abundant cytoplasmic structure: the oocyte cytoplasmic lattices. Additionally, a number of other MEG-derived abundant proteins identified in our proteomic screens have been found by others to localize to another unique oocyte feature: the subcortical maternal complex. Based on these observations, we put forth the hypothesis that the mammalian oocyte contains several unique storage structures, which we have named maternal effect structures, that facilitate the oocyte-to-embryo transition.

5-AZA-2'-deoxycytidine (5-AZA-CdR) leads to down-regulation of Dnmt1o and gene expression in preimplantation mouse embryos

5-AZA-2'-deoxycytidine (5-AZA-CdR) is a demethylating, teratogenic agent and a mutagen, which causes defects in the developing mouse and rat after implantation. Our previous data indicated that 5-AZA-CdR (0.2 and 1.0 muM) inhibited the development of mouse preimplantation embryos. Pronuclear embryos exposed to 5-AZA-CdR at the pronuclear stage were unable to form 8-cell embryos, while 2-cell-stage embryos exposed to 5-AZA-CdR only developed into uncompacted 8-cell-stage embryos. And there was no formation of blastocysts when 4-cell embryos cultured in 5-AZA-CdR. In our present study, we detected Dnmt1o protein and some developmental gene expression in order to find the reasons for the developmental arrest. Dnmt1o could not traffic to 8-cell nuclei as control when embryos were exposed to 5-AZA-CdR. Dnmt1o was in cytoplasm at 2-cell and 4-cell stages before and after treated with 5-AZA-CdR. Gene expression changes were also detected in this research. Our data indicated that connexin 31 (Cx31), connexin 43 (Cx43), connexin 45 (Cx45), E-cadherin (Cdh1) and beta-catenin (Ctnnb1) were all downregulated by 5-AZA-CdR. Cx31, Cx43 and Cx45 are members of connexins family, which have a central role in gap junctions. Cdh1 and Ctnnb1 are necessary for the foundation of tight junctions. Therefore, developmental arrest induced by 5-AZA-CdR may be caused by the failure of Dnmt1o cytoplasmic-nuclear traffic and the down-regulation of developmental gene expression. Normal compaction and blastocoel cavitation need Dnmt1o traffic to 8-cell nuclei and the right gene expression, especially the correlative genes in gap junctions and tight junctions.

The Fanconi anemia/BRCA gene network in zebrafish: embryonic expression and comparative genomics

Fanconi anemia (FA) is a genetic disease resulting in bone marrow failure, high cancer risks, and infertility, and developmental anomalies including microphthalmia, microcephaly, hypoplastic radius and thumb. Here we present cDNA sequences, genetic mapping, and genomic analyses for the four previously undescribed zebrafish FA genes (fanci, fancj, fancm, and fancn), and show that they reverted to single copy after the teleost genome duplication. We tested the hypothesis that FA genes are expressed during embryonic development in tissues that are disrupted in human patients by investigating fanc gene expression patterns. We found fanc gene maternal message, which can provide Fanc proteins to repair DNA damage encountered in rapid cleavage divisions. Zygotic expression was broad but especially strong in eyes, central nervous system and hematopoietic tissues. In the pectoral fin bud at hatching, fanc genes were expressed specifically in the apical ectodermal ridge, a signaling center for fin/limb development that may be relevant to the radius/thumb anomaly of FA patients. Hatching embryos expressed fanc genes strongly in the oral epithelium, a site of squamous cell carcinomas in FA patients. Larval and adult zebrafish expressed fanc genes in proliferative regions of the brain, which may be related to microcephaly in FA. Mature ovaries and testes expressed fanc genes in specific stages of oocyte and spermatocyte development, which may be related to DNA repair during homologous recombination in meiosis and to infertility in human patients. The intestine strongly expressed some fanc genes specifically in proliferative zones. Our results show that zebrafish has a complete complement of fanc genes in single copy and that these genes are expressed in zebrafish embryos and adults in proliferative tissues that are often affected in FA patients. These results support the notion that zebrafish offers an attractive experimental system to help unravel mechanisms relevant not only to FA, but also to breast cancer, given the involvement of fancj (brip1), fancn (palb2) and fancd1 (brca2) in both conditions.

Transcriptional modulation of the pre-implantation embryo-specific Rnf35 gene by the Y-box protein NF-Y/CBF

Maternal-to-zygotic transition of a fertilized egg and the subsequent pre-implantation development of the embryo involve zygotic genome activation and reprogramming of gene expression. The goal of the present study is to establish a model suitable for the characterization of transcriptional modulation of mammalian pre-implantation development. Rnf35 is a mouse RING-finger protein gene that is temporally transcribed in the early embryo, but is permanently silenced before the blastocyst stage of development. We first show that the Chinese-hamster ovary-K1 cells are unique in supporting Rnf35 promoter activities in transient transfection assays. Using the permissive Chinese-hamster ovary-K1 cell line, we show that Rnf35 transcription is driven by an Inr (initiator) core promoter element in the absence of a TATA box; the Inr promoter function is confirmed by direct microinjection of mouse one-cell embryos. This is the first demonstration of the involvement of an Inr core promoter element in transcription in pre-implantation development. We show that the Rnf35 promoter is regulated by three obligatory Y-box (CCAAT-box) elements: two Y boxes (Y(I) and Y(II)) located at -81 are coupled in a palindrome and act synergistically in contributing to Rnf35 transcription; the third Y box (Y(III)) is situated at -13, just upstream of the Inr element, and may be an integral part of the Inr function. Electrophoretic mobility-shift assays and competition experiments further reveal that the Y(I) box is bound by the ubiquitous NF-Y (nuclear factor-Y)/CBF (CCAAT-binding factor) and that Y(II) is targeted by an unidentified protein(s) that acts synergistically with the NF-Y. We suggest that the NF-Y, targeting at a Y-box sequence, may function as an important activator in transcriptional regulation of the Rnf35 gene in the pre-implantation embryo.

Negative transcriptional modulation and silencing of the bi-exonic Rnf35 gene in the preimplantation embryo. Binding of the CCAAT-displacement protein/Cux to the untranslated exon 1 sequence

Previous works have indicated promiscuous transcription from the zygotic genome immediately after fertilization. The mouse Rnf35 gene is bi-exonic in structure and is transcribed in the preimplantation embryo until it is permanently silenced at the blastocyst stage of development. We have previously shown that Rnf35 transcription is positively regulated by the nuclear factor Y. Using the uniquely permissive Chinese hamster ovary-K1 cell line in transient transfection assays, we demonstrate in this work that the Rnf35 promoter was negatively modulated by a cis-cognate repressor element, designated as the downstream exon 1 repressor, or DER, residing between +72 and +95 in the untranslated exon 1 of the Rnf35 gene. Simultaneous mutagenesis of the two half-sections, DER1 and DER2, of the DER sequence was required for derepression suggesting participation of multiple proteins in the DER-dependent transcriptional repression. Electrophoretic mobility shift assays demonstrated that the 3'-half of DER (DER2) was targeted by the repressor CCAAT-displacement protein (CDP)/Cux. Chromatin immunoprecipitation experiments further demonstrated in vivo CDP-DER association in the blastocyst and the 8.5 day embryo. Furthermore, the DER-dependent repression was partially relieved in vivo in co-transfection with an antisense CDP construct. Transcription of the Cdp gene was shown to first occur between the eight-cell and the blastocyst stages, correlating and possibly explaining the onset of Rnf35 silencing at the blastocyst stage. Taken together, our results suggest that the evolutionarily acquired exon 1 of Rnf35, and possibly exon 1 of other similarly structured bi-exonic early embryonic genes, contributes to transcriptional modulation and silencing in the developing mouse embryo.

Effect of paternal heat stress on the development in vitro of preimplantation embryos in the mouse

This study was conducted to investigate the effects of paternal heat stress on the development in vitro of preimplantation embryos in the mouse. Female C57/CBA mice were superovulated using eCG/hCG and mated either to an untreated (control) male mouse or to one that had been exposed for 24 h to an ambient temperature of 36 +/- 0.1 degrees C and 62 +/- 0.4% relative humidity, between 3 and 42 days previously. Putative zygotes were collected from the oviducts of mated mice, 25-28 h after hCG injection, and cultured in vitro. Embryo development was evaluated at 24-h intervals for up to 120 h. Paternal heat stress significantly reduced the proportion of embryos that developed normally during 24-120 h of in vitro culture, when zygotes were sired by males which had been heat stressed between 7 and 35 days prior to mating. Maximum impairment to development (including nondevelopment, abnormal and dying/dead embryos) occurred in those embryos sired by males at days 14 and 21 after heating. Embryo development returned to control levels by day 42 after heat stress. Furthermore, whilst all stages of embryo development were affected by paternal heat stress, the proportion of embryos at the two-cell stage appeared to be most severely affected. Four-cell to morula stages and the morula to blastocyst stage also demonstrated impairment at days 14, 21, 28 and 35 after heating. These results demonstrate that a single episode of paternal heat stress significantly reduces the development of preimplantation embryos, and this is not recovered until day 42 after heating. The present results also support previous work demonstrating that sperm from the epididymis as well as germ cells in the testis are susceptible to damage by heat stress, with both spermatids and spermatocytes being the most vulnerable.

Isolation of nascent messenger RNA from mouse preimplantation embryos

The expression of the zygotic genome starts at the late one-cell stage in mouse embryos, and its regulation changes dynamically until the late two-cell stage. To understand this process, it is important to accumulate the profiles of the genes transcribed at any given instant at each stage of development. However, because large amounts of maternal mRNA accumulate in embryos to sustain early development, it is difficult to determine the profile of newly synthesized mRNA just after gene activation. To overcome this difficulty, we established a novel method of isolating nascent mRNA from the large pool of preexisting mRNA. Briefly, the procedure was as follows. Embryos were electrically permeabilized and loaded with 5-bromouridine-5'-triphosphate (BrUTP). Nascent mRNA with incorporated BrU was isolated by immunoprecipitation with an antibody recognizing BrU. The cDNA was synthesized from the isolated mRNA, and its abundance was evaluated using semiquantitative real-time PCR. Using this method, we examined the amounts of newly synthesized eIF-1A, MuERV-L, and cyclin-A2 transcripts in two-cell mouse embryos and compared them with the quantities of these transcripts present in the total mRNA pool. The amount of each transcript in the nascent mRNA fraction and in the total mRNA pool changed differently over time, demonstrating that this method can be used to obtain profiles of genes transcribed during development.

Regulation of histone H3 lysine 9 methylation in oocytes and early pre-implantation embryos

Epigenetic modifications of the genome, such as covalent modification of histone residues, ensure appropriate gene activation during pre-implantation development, and are probably involved in the asymmetric reprogramming of the parental genomes after fertilization. We investigated the methylation patterns of histone H3 at lysine 9 (H3/K9), and the regulatory mechanism involved in the asymmetric remodeling of parental genomes during early preimplantation development in mice. Immunocytochemistry with an antibody that specifically recognizes methylated H3/K9 showed a very weak or absent methylation signal in the male pronucleus, whereas a distinct methylation signal was detected in the female pronucleus. This asymmetric H3/K9 methylation pattern in the different parental genomes persisted until the two-cell stage. However, de novo methylation of H3/K9 occurred and the asymmetry was lost during the four-cell stage. The unmethylated male pronucleus underwent de novo methylation when it was transferred into enucleated GV- or MII-stage oocytes, which suggests that histone H3 methylase is active before fertilization, but not afterwards, and that the asymmetric methylation pattern is generated by this change in methylase activity in the cytoplasm after fertilization. Thus, histone H3 is methylated only in the maternal chromosomes, which are present in the oocytes before fertilization, and is not methylated in the paternal chromosomes, which are absent. The maintenance of asymmetric H3/K9 methylation patterns in early embryos is an active process that depends on protein synthesis and zygotic transcription, as de novo methylation in the male pronucleus occurred when either protein synthesis or gene expression was inhibited by cycloheximide orα-amanitin, respectively. In addition, corresponding de novo methylation of H3/K9 and DNA occurred when the male pronucleus was transferred to an enucleated GV oocyte. Our results suggest that H3/K9 methylation is an epigenetic marker of parental genome origin during early preimplantation development.

The primate embryo gene expression resource: a novel resource to facilitate rapid analysis of gene expression patterns in non-human primate oocytes and preimplantation stage embryos

Detailed molecular studies of preimplantation stage development in a suitable nonhuman primate model organism have been inhibited due to the cost and scarcity of embryos. To circumvent these limitations, we have created a new resource for the research community, designated as the Primate Embryo Gene Expression Resource (PREGER). The PREGER sample collection currently contains over 160 informative samples of oocytes, obtained from various sized antral follicles, and embryos obtained through a variety of different protocols. The PREGER makes it possible to undertake quantitative gene-expression studies in rhesus monkey oocytes and embryos through simple and cost-effective hybridization-based methods. The PREGER also makes available other molecular tools to facilitate nonhuman primate embryology. We used PREGER here to compare the temporal expression patterns of five housekeeping mRNAs and three transcription factor mRNAs between mouse and rhesus monkey. We observed noticeable differences in temporal expression patterns between species for some mRNAs, but clear similarities for others. Our results also provide new information related to genome activation and the effects of embryo culture conditions on gene expression in primate embryos. These results provide one illustration of how the PREGER can be employed to obtain novel insight into primate embryogenesis.

Serp-1, a viral anti-inflammatory serpin, regulates cellular serine proteinase and serpin responses to vascular injury

Complex DNA viruses have tapped into cellular serpin responses that act as key regulatory steps in coagulation and inflammatory cascades. Serp-1 is one such viral serpin that effectively protects virus-infected tissues from host inflammatory responses. When given as purified protein, Serp-1 markedly inhibits vascular monocyte invasion and plaque growth in animal models. We have investigated mechanisms of viral serpin inhibition of vascular inflammatory responses. In vascular injury models, Serp-1 altered early cellular plasminogen activator (tissue plasminogen activator), inhibitor (PAI-1), and receptor (urokinase-type plasminogen activator) expression (p < 0.01). Serp-1, but not a reactive center loop mutant, up-regulated PAI-1 serpin expression in human endothelial cells. Treatment of endothelial cells with antibody to urokinase-type plasminogen activator and vitronectin blocked Serp-1-induced changes. Significantly, Serp-1 blocked intimal hyperplasia (p < 0.0001) after aortic allograft transplant (p < 0.0001) in PAI-1-deficient mice. Serp-1 also blocked plaque growth after aortic isograft transplant and after wire-induced injury (p < 0.05) in PAI-1-deficient mice indicating that increase in PAI-1 expression is not required for Serp-1 to block vasculopathy development. Serp-1 did not inhibit plaque growth in uPAR-deficient mice after aortic allograft transplant. We conclude that the poxviral serpin, Serp-1, attenuates vascular inflammatory responses to injury through a pathway mediated by native uPA receptors and vitronectin.

Chromatin configuration and transcriptional control in human and mouse oocytes

In vitro maturation of human oocytes at the germinal vesicle (GV) stage could offer an alternative in several cases of female infertility. It however rests on a better knowledge of the quality of human oocyte. Using fluorescence imaging of DNA and of the transcription sites, combined with electron microscopy, we show that human oocytes follow size-dependent changes in chromatin configuration, transcription sites distribution and nuclear ultrastructure that follow those observed in mouse GV oocytes. We thus analyzed in mouse GV oocytes the phosphorylation dependence of the transcriptional activity. We show by Western blot that, while active GV oocytes have approximately the same proportion of hypo- and hyperphosphorylated forms of the RNA polymerase II (RNAP II), the hyperphosphorylated form is almost absent from inactive oocytes. We also show that (1) RNAP II-dependent transcription is much less sensitive to various kinase inhibitors in mouse oocytes than in somatic cells or mouse one-cell embryos, although the phosphorylation equilibrium of RNAP II was largely shifted towards the hypo-phosphorylated form upon treatment with these inhibitors (2) RNAP I is completely insensitive to kinase inhibitors in GV oocytes.

Oolemmal proteomics--identification of highly abundant heat shock proteins and molecular chaperones in the mature mouse egg and their localization on the plasma membrane

BACKGROUND

The mature mouse egg contains the full complement of maternal proteins required for fertilization, the transition to zygotic transcription, and the beginning stages of embryogenesis. Many of these proteins remain to be characterized, therefore in this study we have identified highly abundant egg proteins using a proteomic approach and found that several of these proteins also appear to localize to the egg surface. Characterization of such molecules will provide important insight into the cellular events of fertilization and early development.

METHODS

In order to identify some of the more abundant egg proteins, whole egg extracts were resolved on coomassie-stained two-dimensional (2D) PAGE gels. Several highly abundant protein spots were cored and microsequenced by tandem mass spectrometry (TMS), and determined to be molecular chaperone proteins. Concurrent experiments were performed to identify oolemmal proteins using 2D avidin blotting. Proteins spots that appeared to be surface labeled by biotinylation were correlated with the initial coomassie-stained reference gel. Surprisingly, some of the surface labelled proteins corresponded to those abundant chaperone proteins previously identified. To confirm whether these molecules are accumulating at the oolemmal surface in eggs, we performed immunofluoresence on live, zona-free eggs using antibodies to HSP70, HSP90, GRP94, GRP78, calreticulin and calnexin.

RESULTS

The putative surface-labeled proteins identified by biotinylation included the molecular chaperones HSP70 (MW 70 KDa, pI 5.5), HSP90a (MW 85 KDa, pI 4.9), GRP94 (MW 92 KDa, pI 4.7), GRP78 (MW 72 KDa, pI 5.0), Oxygen regulated protein 150 (ORP150; MW 111 KDa, pI 5.1), Calreticulin (MW 48 KDa, pI 4.3), Calnexin (MW 65 KDa, pI 4.5), and Protein disulfide isomerase (PDI; MW 57 KDa, pI 4.8). Immunofluoresence results showed that antibodies to HSP90, GRP94, GRP78 and calreticulin were reactive with oolemmal proteins. We were unable to confirm surface localization of HSP70 or calnexin by this method.

CONCLUSIONS

We report here the identification of nine highly abundant molecular chaperones in the mouse egg proteome. In addition, we present preliminary data suggesting that these molecules localize to the oolemma of the mature mouse egg.

Dynamic Changes in the Expression of Protein Tyrosine Phosphatases During Preimplantation Mouse Development: Semi-Quantification by Real-Time PCR

Protein tyrosine phosphatase (PTP) expression was examined in preimplantation mouse embryos. We previously reported that SHP-2, LAR, PTPT9, SHP-1, and mRPTPB were expressed in preimplantation mouse embryos. Here, we examined changes in the expression levels of these PTPs during preimplantation development. cDNA was obtained by reverse transcription of embryo mRNA, amplified with 10 PCR cycles, and then subjected to real-time fluorescence-monitored PCR. Experiments with an mRNA dilution series revealed that the data obtained matched the quantities of mRNA used. The measurements obtained with real-time fluorescence-monitored PCR showed that the expression of each PTP mRNA changed dynamically, and that each had a different expression pattern. This suggests that PTPs are involved in the regulation of growth and differentiation during preimplantation development.

Quantitative analysis of gene expression in preimplantation mouse embryos using green fluorescent protein reporter

We have developed a method to monitor noninvasively, quantitatively, and in real-time transcription in living preimplantation mouse embryos by measuring expression of a short half-life form of enhanced green fluorescent protein (EGFP) following microinjection of a plasmid-borne EGFP reporter gene. A standard curve was established by injecting known amounts of recombinant green fluorescent protein, and transcriptional activity was then determined by interpolating the amount of fluorescence in the DNA-injected embryos. This approach permitted multiple measurements in single embryos with no significant detrimental effect on embryonic development as long as light exposure was brief (<30 sec) and no more than two measurements were made each day. This method should facilitate analysis of the regulation of gene expression in preimplantation embryos; in particular, during the maternal-to-zygotic transition, and in other species in which limited numbers of embryos are available.

Programmed cell death in the neurulating embryo is prevented by the chaperone heat shock cognate 70

Neuronal cell death is a genuine developmental process, with precise regulation and defined roles. In striking contrast, characterization of cell death that occurs at early stages of neural development is very limited. We previously showed that embryonic proinsulin increases the level of the chaperone heat shock cognate 70 (Hsc70) and reduces the incidence of apoptosis in the neurulating chick embryo [de la Rosa, et al. (1998), Proc. Natl. Acad. Sci. USA, 95, 9950]. We now demonstrate that Hsc70 is directly involved in cell survival during neurulation, as specific downregulation of endogenous Hsc70 by antisense oligodeoxynucleotide interference provoked an increase in apoptosis both in vitro and in ovo. In parallel, activation of caspase-3 was increased after hsc70 antisense oligodeoxynucleotide treatment. Dead cells were located mostly in the developing nervous system, distributed in areas where the incidence of cell death was high. These areas coincided both in vivo and under different death-inducing conditions, including antisense interference and growth factor deprivation. Hsc70 immunostaining was strong in at least some areas of high cell death. Apoptotic cells within these areas presented undetectable Hsc70 levels, however, suggesting that this protein acts as an intrinsic protector of neuroepithelial and neural precursor cells.

Trophectoderm-specific expression of the X-linked Bex1/Rex3 gene in preimplantation stage mouse embryos

The Bex1/Rex3 gene was recently identified as an X-linked gene that is differentially expressed between parthenogenetic and normal fertilized, preimplantation stage mouse embryos. The Bex1/Rex3 gene appears to be expressed preferentially from the maternal X chromosome in blastocysts, but from either X chromosome in later stage embryonic tissues and adult tissues. To investigate whether differential expression of the Bex1/Rex3 gene between normal and parthenogenetic blastocyst stage embryos reflects genomic imprinting at the Bex1/Rex3 locus itself, or instead is the result of preferential inactivation of the paternal X chromosome or differences in timing of cellular differentiation, we examined in detail the expression pattern of the Bex1/Rex3 mRNA in normal preimplantation stage embryos, and compared its expression between androgenetic, gynogenetic, and normal fertilized embryos. Expression data reveal that the Bex1/Rex3 gene is initially transcribed at the 2-cell stage, transiently induced at the 8-cell stage, and then increases in expression again at the blastocyst stage. Very little expression is observed in isolated inner cell masses, indicating selective expression in the trophectoderm. Comparisons of Bex1/Rex3 mRNA expression between male and female androgenetic and control embryos and gynogenetic embros failed to reveal any significant difference in expression between the different classes of embryos at the 8-cell stage, or the expanding blastocyst stage (121 hr post-hCG). At the late blastocyst stage (141 hr post-hCG), expression was significantly lower in XY control embryos as compared with XX controls. Bex1/Rex3 mRNA expression did not differ between XX and XY androgenones at the blastocyst stage or between gynogenones and XX control embryos. Thus, the Bex1/Rex3 gene does not appear to be regulated directly by genomic imprinting during the preimplantation period, just as it is not regulated by imprinting at later stages. Apparent differences in gene expression may arise through the effects of trophectoderm-specific expression coupled with differences in timing of trophectoderm differentiation between the different classes of embryos and effects of preferential paternal X chromosome inactivation (XCI).

Role of protein synthesis in the development of a transcriptionally permissive state in one-cell stage mouse embryos

The time of onset of gene transcription in the mouse embryo is temporally regulated. A prominent feature of this regulation is a change during the one-cell stage from a transcriptionally nonpermissive state to a transcriptionally permissive state. During the early one-cell stage, the cytoplasm is either inadequate or suppressive for nuclear gene transcription, but by the late one-cell stage, the cytoplasm acquires the ability to support gene transcription either in endogenous nuclei or exogenous nuclei introduced microsurgically. We have investigated the role of protein synthesis in this cytoplasmic transition. Nuclei from two-cell stage embryos treated with alpha-amanitin were used to evaluate the transcriptional permissiveness of late one-cell stage cytoplasm, as indicated by the production of transcripts from four genes that are specifically transcribed at elevated rates during the two-cell stage. Two of these genes were transcribed following nuclear transfer to late one-cell stage cytoplasm, and two were not transcribed. Treatment of the recipient cytoplasm with cycloheximide to inhibit protein synthesis from the early to the late one-cell stage inhibited the transcription of the two genes that were transcribed in the untreated, late one-cell stage recipients. These results indicate that acquisition of the transcriptionally permissive state during the one-cell stage is facilitated by protein synthesis, and that the transcriptional permissiveness in the late one-cell stage cytoplasm is limited to certain genes.

DNA damaging agents increase gadd153 (CHOP-10) messenger RNA levels in bovine preimplantation embryos cultured in vitro

DNA damage and other forms of stress are believed to be important factors in reducing the efficiency of in vitro embryo transfer techniques in farm animals. The expression of mRNAs from stress-responsive genes such as gadd153 (CHOP-10, ddit3) may provide a means of assessing the quality of embryos produced in vitro. Treatment of bovine granulosa cell cultures with the DNA-damaging agents, methyl methane-sulphonate (MMS) or sodium arsenite, induced the expression of an mRNA, which hybridized with the hamster gadd153 cDNA. Part of the corresponding bovine cDNA was amplified by nested polymerase chain reaction (PCR), cloned, and sequenced. Using a sensitive reverse transcriptase-PCR assay we have investigated the expression of gadd153 and beta-actin in blastocyst-stage bovine embryos treated with MMS or sodium arsenite. Both agents produced an increase in the ratio of gadd153 mRNA relative to beta-actin. These results show that there are changes in gene expression in blastocyst-stage bovine embryos in response to genotoxic stress, suggesting that an increase in gadd153 mRNA is a useful marker of DNA damage and metabolic stress in preimplantation embryos.

Selective reduction of dormant maternal mRNAs in mouse oocytes by RNA interference

Specific mRNA degradation mediated by double-stranded RNA (dsRNA), which is termed RNA interference (RNAi), is a useful tool with which to study gene function in several systems. We report here that in mouse oocytes, RNAi provides a suitable and robust approach to study the function of dormant maternal mRNAs. Mos (originally known as c-mos) and tissue plasminogen activator (tPA, Plat) mRNAs are dormant maternal mRNAs that are recruited during oocyte maturation; translation of Mos mRNA results in the activation of MAP kinase. dsRNA directed towards Mos or Plat mRNAs in mouse oocytes effectively results in the specific reduction of the targeted mRNA in both a time- and concentration-dependent manner. Moreover, dsRNA is more potent than either sense or antisense RNAs. Targeting the Mos mRNA results in inhibiting the appearance of MAP kinase activity and can result in parthenogenetic activation. Mos dsRNA, therefore, faithfully phenocopies the Mos null mutant. Targeting the Plat mRNA with Plat dsRNA results in inhibiting production of tPA activity. Finally, effective reduction of the Mos and Plat mRNA is observed with stoichiometric amounts of Mos and Plat dsRNA, respectively.

Effects of X chromosome number and parental origin on X-linked gene expression in preimplantation mouse embryos

Diploid androgenetic mouse embryos, possessing two sets of paternally inherited chromosomes, and control fertilized embryos were used to examine the relative effects of X chromosome number and parental chromosome origin on androgenone viability and X-linked gene expression. A significant difference in efficiency of blastocyst formation was observed between XX and XY androgenones in some experiments, but this difference was not uniformly observed. Significant effects of both X chromosome number and parental origin on X-linked gene expression were observed. Male and female control embryos expressed the XIST: RNA initially. This expression was followed by a preferential reduction in XIST: RNA abundance in male embryos, indicating that dosage compensation for the X chromosome may normally require the downregulation of XIST: RNA expression in male embryos, in conjunction with the production of stable XIST: transcripts in female embryos. By the late blastocyst stage, XX control embryos expressed significantly more XIST: RNA than did XY embryos. Unlike their normal counterparts, XX androgenones did not express significantly more XIST: RNA than did XY androgenones at the late blastocyst stage. Androgenones exhibited severe repression of the Pgk1 gene, but during development to the late blastocyst stage Pgk1 mRNA expression increased in XX androgenones and decreased in XY androgenones. Thus, the initial repression of the Pgk1 gene in XX androgenones was lost as the XIST: RNA declined in abundance, and this loss was correlated with a failure of XX androgenones to express significantly more XIST: RNA than did XY androgenones. These results indicate that androgenones may lack a factor that is expressed from the maternal genome and required for dosage compensation in preimplantation embryos. The results also indicate that early dosage compensation in preimplantation embryos may normally be reversible, thus providing flexibility to meet different developmental requirements of the embryonic and extraembryonic lineages.

Molecular characterization of a heat shock cognate cDNA of zebrafish, hsc70, and developmental expression of the corresponding transcripts

To elucidate the potential role of the hsp70 gene family in developmental processes in vertebrates, we chose to study the expression of one of these genes in zebrafish. A zebrafish gastrula cDNA library was screened with a Pleurodeles waltl hsp70 cDNA probe. A 2.3-kb cDNA was thus isolated and sequenced. The predicted amino acid sequence contained an open reading frame encoding for a 649-amino acid polypeptide. Sequence analysis showed strong homology with hsp70-related gene sequences in other species; in particular, the strongest homology was found with the cognate members of this family. Tests of heat inducibility revealed that transcripts were expressed at normal temperature, but the level of transcript expression increased after heat shock. Moreover, experiments of the neosynthesis of total proteins in heat shock conditions and corresponding immunoblotting assays showed that 24-h-stage embryos are able to respond to heat shock. The quantity of 70 kDa proteins, recognized by a specific antibody of the HSP/C70 protein family, is expressed in control condition and increased significantly after heat shock. Furthermore, Northern blot analysis of transcript expression showed that the corresponding mRNAs were detected throughout embryonic development in the absence of any heat shock. Our clone, named hsc70, thus corresponded to a cognate member of the hsp70 gene family, expressed under normal conditions during development, but also heat inducible. The spatio-temporal pattern of transcripts during development was determined by in situ hybridization on wholemount embryos at different stages. As a maternal RNA, hsc70 mRNA was uniformly present in the embryo, up to the end of gastrulation. Later, a tissue-specific enrichment of hsc70 transcripts was detected in the central nervous system (CNS) and in a fraction of the somites. These results suggest that the hsc70 gene may be involved in developmental differentiation events.

Translation of maternal messenger ribonucleic acids encoding transcription factors during genome activation in early mouse embryos

Embryonic genome activation (EGA) in mice is sensitive to treatment with cycloheximide, indicating that protein synthesis plays an important role in mediating EGA. We hypothesized that regulated maternal mRNA recruitment may control the time of EGA by controlling the time of appearance of certain transcription factors (TFs). We also hypothesized that synthesis of other TFs may contribute to EGA independently of controlling the timing of EGA. To test these hypotheses, we used sucrose density gradient fractionation coupled to a quantitative reverse transcription-polymerase chain reaction method to compare polysomal mRNA abundances of specific TF mRNAs between metaphase II oocytes, 1-cell-stage embryos, and 2-cell-stage embryos. We observed a 2-cell-stage-specific increase in polysomal abundance of mouse TEA DNA binding domain 2 (mTEAD-2) mRNA, coincident with the first appearance of mTEAD activity in the early embryo. The mRNAs encoding Sp1, TATA binding protein, and cyclic AMP response element binding protein did not undergo translational recruitment, but exhibited differences in polysomal abundance. We also observed a continuous, high proportion in the polysomal fraction for the mRNA encoding ribosomal protein L23 mRNA, which contrasted with the patterns observed for other maternal transcripts. These observations are consistent with the hypothesis that regulated recruitment of maternal TF mRNAs may control the time of activation of some genes during EGA, and that continuous synthesis of other TFs, like Sp1, may facilitate EGA.

Modulation of mouse preimplantation embryo development by acrogranin (epithelin/granulin precursor)

Preimplantation mammalian embryos in culture secrete autocrine growth factors into the surrounding medium that, in turn, stimulate the development of the embryos. The full complement of these factors is unknown. Since one hallmark of embryo development is the formation of an epithelium, the trophectoderm, we tested the hypothesis that one such embryo-derived growth factor is acrogranin (epithelin/granulin precursor), a factor that possesses growth-regulatory activities principally toward epithelial cells. We found that acrogranin mRNA was expressed in preimplantation mouse embryos with the transcript levels rising to their highest point in blastocysts, coincident with the appearance of the trophectoderm. Indirect immunofluorescence confocal microscopy of preimplantation mouse embryos at different developmental stages revealed that acrogranin immunostaining was most concentrated in the trophectoderm of blastocysts. Immunoblotting and immunoprecipitation experiments demonstrated that the embryos secreted acrogranin into the surrounding medium. To determine how altering the levels of acrogranin in the culture medium surrounding the embryos might affect embryonic growth and development, acrogranin protein levels in the culture medium were decreased with a function-blocking antibody or increased by adding the purified acrogranin to the medium. In both a concentration-dependent and a reversible manner, affinity-purified anti-acrogranin antibody significantly inhibited the development of eight-cell embryos to the blastocyst stage compared to controls (no added immunoglobulin or nonspecific IgG). Furthermore, embryo cell numbers were significantly decreased in the presence of the highest concentrations of acrogranin antibody compared to control embryos. Exogenous acrogranin added to cultures of eight-cell embryos accelerated the time for the onset of cavitation, as well as stimulating the rate of blastocoel expansion and increasing the number of trophectoderm cells compared to controls. These results indicate that acrogranin can regulate the appearance of the epithelium in the developing mouse blastocyst, the growth of the trophectoderm, and/or the function of the embryonic epithelium.

Upregulation of CHOP-10 (gadd153) expression in the mouse blastocyst as a response to stress

CHOP-10 (also known as gadd153 or Ddit3) is one of the genes overexpressed by mammalian cells exposed to cytotoxic agents or to nutrient stress. The response of this gene to stress was studied in the mouse blastocyst and in F9 embryonal carcinoma cells. When mouse blastocysts were exposed to the alkylating agent MMS, the metabolic inhibitor sodium arsenite or an inhibitor of protein glycosylation tunicamycin, levels of the CHOP-10 mRNA were increased by two- to threefold relative to the mRNA for beta-actin. There was no increase in gene expression when blastocysts were treated with the inhibitor of nucleotide synthesis PALA. These results show that the response of CHOP-10 is dependent on the type of stress applied to the embryo. When F9 embryonal carcinoma cells were treated with MMS or sodium arsenite, CHOP-10 expression was induced by fourfold within 4 hr of treatment. The induction following tunicamycin treatment was slower requiring at least 24 hr. The response to tunicamycin was greater in cells treated with retinoic acid to induce differentiation. The results suggest that there is a link between the extent of glycoprotein synthesis and the sensitivity of CHOP-10 to tunicamycin. The inhibitor PALA did not change CHOP-10 expression in the presence or absence of retinoic acid. In F9 cells an increase in the expression of CHOP-10 was followed by cell death due to apoptosis. The overexpression of CHOP-10 may be a marker for one of the pathways that lead to apoptosis in the blastocyst. These results suggest that there is more than one control system regulating growth arrest in the blastocyst and the fetal outcome may differ depending on the type of stress encountered in culture.

Expression of cell death regulatory genes and limited apoptosis induction in avian blastodermal cells

Apoptosis is a well-established cellular mechanism for selective cell deletion during development. However, little is known about the expression of an apoptotic pathway and its role in determining the relative sensitivity of the early, pre-gastrula, avian embryo to stress-induced cell death. We examined the sensitivity of avian blastodermal cells to engage in apoptosis upon exposure to etoposide, a topoisomerase II-inhibitor that rapidly and efficiently induces apoptosis in many cell types. We found that while the blastodermal cells are capable of engaging in apoptosis, they are highly resistant to such induction with respect to both concentration of drug required and length of exposure, even when compared to a tumor cell line with a known multi-drug resistant phenotype. Additionally, we assessed the expression of several candidate regulatory genes in blastodiscs from infertile eggs (i.e., maternal RNA transcripts), blastodermal cells immediately following oviposition, and various stages of early development up to gastrulation. This analysis revealed that several genes whose products have anti-apoptotic activity, including bcl-2, bcl-xL, hsp70, grp78 and the glutathione S-transferases, are expressed as early as the stage 1 embryo in the newly oviposited egg. These transcripts are also found in the infertile blastodisc, suggesting a role for maternally derived transcripts in the protection of the oocyte and zygote. Significantly, constitutive levels of hsp70 mRNA exceeded those of the other anti-apoptotic genes in the blastodermal cells. These results contribute to an emerging picture of stress resistance at the earliest stages of avian embryo development which involves multiple anti-apoptotic genes that act at different regulatory points in the apoptotic cascade.

Transient expression of a translation initiation factor is conservatively associated with embryonic gene activation in murine and bovine embryos

In the present study the abundance of mRNAs for eukaryotic translation initiation factors eIF-1A (formerly known as eIF-4C), -2alpha, -4A, -4E, and -5 was examined in in vivo-derived mouse embryos throughout preimplantation development using a semiquantitative reverse transcription-polymerase chain reaction assay. Although the mRNA profile for each gene is unique, only mRNA for eIF-1A transiently increases during embryonic gene activation (EGA) at the 2-cell stage, and this was confirmed by an independent hybridization-based assay. In in vitro-developed bovine embryos, mRNA for eIF-1A was transiently detected at the 8-cell stage, when the major activation of the genome occurs in this species. As in the mouse, detection in 8-cell bovine embryos was sensitive to the transcriptional inhibitor alpha-amanitin. It was also observed at the same time relative to cleavage in embryos cultured in defined medium under a reduced oxygen environment, and in medium supplemented with serum and somatic cells in 5% CO2 in air. Neither the chronology of early cleavage divisions nor the yield of bovine blastocysts differed in these culture media. Our results suggest that transient expression of eIF-1A in the mouse and cow is a conserved pattern of gene expression associated with EGA in mammals.

Heat shock proteins in retinal neurogenesis: identification of the PM1 antigen as the chick Hsc70 and its expression in comparison to that of other chaperones

While the role of heat shock proteins under experimental stress conditions is clearly characterized, their expression in unstressed cells and tissues and their functions in normal cell physiology, besides their chaperone action, remain largely undetermined. We report here the identification in chicken of the antigen recognized by the monoclonal antibody PM1 [Hernández-Sánchez et al. (1994) Eur. J. Neurosci., 6,1801-1810] as the noninducible chaperone heat-shock cognate 70 (Hsc70). Its identity was determined by partial peptide sequencing, immuno-crossreactivity and two-dimensional gel-electrophoresis. In addition, we examined its expression during chick embryo retinal neurogenesis. The early widespread Hsc70 immunostaining corresponding to most, if not all, of the neuroepithelial cells becomes restricted to a subpopulation of these cells in the peripheral retina as development proceeds. On the other hand, retinal ganglion cells, differentiating in the opposite central-to-peripheral gradient, retained Hsc70 immunostaining. Other molecular chaperones, the heat-shock proteins Hsp40, Hsp60 and Hsp90, did not seem to compensate the loss of Hsc70. They also showed decreasing immunostaining patterns as neurogenesis proceeds, although distinctive from that of Hsc70, whereas Hsp70 was not detected in the embryonic retina. This precise cellular and developmental regulation of Hsc70, a generally considered constitutive molecular chaperone, in unstressed embryos, together with the expression of other chaperones, provides new tools and a further insight on neural precursor heterogeneity, and suggests possible specific cellular roles of chaperone function during vertebrate neurogenesis.

Modulation of the chaperone heat shock cognate 70 by embryonic (pro)insulin correlates with prevention of apoptosis

Insights have emerged concerning insulin function during development, from the finding that apoptosis during chicken embryo neurulation is prevented by prepancreatic (pro)insulin. While characterizing the molecules involved in this survival effect of insulin, we found insulin-dependent regulation of the molecular chaperone heat shock cognate 70 kDa (Hsc70), whose cloning in chicken is reported here. This chaperone, generally considered constitutively expressed, showed regulation of its mRNA and protein levels in unstressed embryos during early development. More important, Hsc70 levels were found to depend on endogenous (pro)insulin, as shown by using antisense oligodeoxynucleotides against (pro)insulin mRNA in cultured neurulating embryos. Further, in the cultured embryos, apoptosis affected mainly cells with the lowest level of Hsc70, as shown by simultaneous Hsc70 immunostaining and terminal deoxynucleotidyltransferase-mediated UTP nick end labeling. These results argue in favor of Hsc70 involvement, modulated by embryonic (pro)insulin, in the prevention of apoptosis during early development and suggest a role for a molecular chaperone in normal embryogenesis.

Stage-specific expression and cellular localization of the heat shock factor 2 isoforms in the rat seminiferous epithelium

Heat shock transcription factors (HSFs) are generally known as regulators of cellular stress response. The mammalian HSF1 functions as a classical stress factor, whereas HSF2 is active during certain developmental processes, including embryogenesis and spermatogenesis. In the present study, we examined HSF2 expression at specific stages of the rat seminiferous epithelial cycle. We found that expression of the alternatively spliced HSF2-alpha and HSF2-beta isoforms is developmentally regulated in a stage-specific manner. Studies on cellular localization demonstrated that HSF2 is present in the nuclei of early pachytene spermatocytes at stages I-IV and in the nuclei of round spermatids at stages V-VIIab. In contrast a strong HSF2 immunoreactivity was detected in small distinct cytoplasmic regions from zygotene spermatocytes to maturation phase spermatids. Immunoelectron microscopic analysis revealed that these structures are mainly cytoplasmic bridges between germ cells. Our results on cellular localization of HSF2 and stage-specific expression of the HSF2 isoforms indicate that HSF2, in addition to its function as a nuclear transcription factor, may be involved in other cellular processes during spermatogenesis, possibly in the sharing process of gene products between the germ cells.

Analysis of variation in relative mRNA abundance for specific gene transcripts in single bovine oocytes and early embryos

Variation in the abundance of a specific gene transcript was assessed in single bovine oocytes and in vitro-derived blastocysts. Transcripts encoding the Na+,K(+)-ATPase alpha 1 subunit were detected by reverse-transcription polymerase chain reaction (RT-PCR) and quantified relative to an exogenously supplied rabbit alpha-globin mRNA using laser-induced fluorescence capillary electrophoresis (LIF-CE). The precision of this relative abundance (RA) calculation was predicted and shown to resolve 2-fold differences in transcript abundance between individual blastocysts and predicted in oocytes to resolve 3-fold differences. The RA of the alpha 1 subunit transcript differed by 2- to 3-fold among blastocysts, and 3- to 6-fold among oocytes. Comparison of a general population of oocytes with blastocysts revealed little overlap in RA values between the two groups, with a 8- to 14-fold increase in the mean RA for each group with development observed in two successive experiments (P < or = 0.05). In contrast, oocytes selected for their developmental competence on the basis of morphologic criteria exhibited only a 1.6- to 1.7-fold developmental increase when the assay was performed on cDNA generated from either embryo pools (n = 6 versus 6) or individuals (n = 7 versus 7), respectively. These results provide the first characterization of the degree of heterogeneity in the abundance of a specific mRNA transcript among individual mammalian oocytes and preimplantation embryos and demonstrate that transcript relative abundance can be correlated with bovine oocyte morphology.

Temporal patterns of embryonic gene expression and their dependence on oogenetic factors

Successful development of a fertilized egg beyond early cleavage divisions requires the de novo initiation and subsequent regulation of embryonic transcription. The egg provides the specialized environment within which the newly formed zygotic nucleus initiates its developmental program and as a result plays an obligatory role in its regulation. Although the precise timing of the onset of embryonic transcription in mammals varies during early cleavage divisions, several common elements exist. In the present essay we review the current literature on the timing and control of embryonic gene expression in mammals, and discuss recent findings from our laboratory on gene expression patterns in bovine embryos and their relation to other species, and zygotic gene activation (ZGA). Lastly, we discuss the putative role of maternally inherited factors in conferring developmental competence to the blastocyst stage, and a method to identify such factors present in oocytes as mRNA.

The growth arrest genes gas5, gas6, and CHOP-10 (gadd153) are expressed in the mouse preimplantation embryo

The gas and gadd family of genes, known collectively as the growth arrest genes, are associated with the negative control of mammalian cell growth. The steady-state levels of their mRNAs are increased by three to fivefold when exponentially multiplying cells are exposed to a variety of stresses including inadequate nutrition or the removal of serum. Reverse transcription-polymerase chain reaction (RT-PCR) has been used to analyze growth arrest gene expression in the preimplantation mouse embryo. The gas5, gas6, and CHOP-10 (gadd153, Ddit3) genes were expressed from the eight-cell stage onward. The gas2 and gas3 genes associated with apoptosis were not expressed. Embryos were cultured in kSOM medium and a semiquantitative RT-PCR method was used to measure the relative gene expression using beta-actin mRNA as a reference. The ratio of gas5 to beta-actin mRNA was high at the eight-cell stage and fell three to fivefold during development. The decline in the gas5:beta-actin ratio corresponded to the activation of true cell growth (cytokinesis). The gas6:beta-actin ratio was low at the eight-cell stage and increased by twofold as the blastocyst formed. CHOP-10 was expressed at a constant level throughout development. Embryos that had developed in vivo were compared with the equivalent blastocyst-stage embryos cultured in kSOM medium. There were no significant differences in the ratio of CHOP-10, gas5, or gas6 mRNAs relative to beta-actin. These results suggest that these genes are expressed as part of normal early embryonic development. The potential roles of the growth arrest genes are discussed.

Requirement for protein synthesis during embryonic genome activation in mice

Embryonic genome activation (EGA) occurs by the 2-cell stage in mouse embryos. To understand the molecular basis of EGA, it is important to determine whether EGA can be supported by maternally inherited factors or if it requires the synthesis of additional transcription factors. We used a quantitative reverse transcription-polymerase chain reaction (RT-PCR) method to test whether protein synthesis is required for the transcriptional activation of six housekeeping genes (U2afbp-rs, Hprt, Pdha1, Prps1, Odc, and Cox7c). Cycloheximide treatment reduced the expression of these mRNAs in 2-cell embryos to the same degree as alpha-amanitin treatment. Cycloheximide treatment did not reduce the expression of maternally inherited mRNAs, indicating that its effect is specific for transcription-dependent gene expression. These results contrast with earlier results reported for the Hsp70 gene. This difference may reflect differences in promoter requirements. We conclude that protein synthesis is required for the activation of most, if not all, housekeeping genes in the mouse embryo, and that the time of EGA may be controlled, in part, by the regulated recruitment of maternal mRNAs encoding key transcription factors.

Regulation of gene expression in the preimplantation mouse embryo: temporal and spatial patterns of expression of the transcription factor Sp1

Activation of the embryonic genome during preimplantation mouse development entails a dramatic reprogramming of the pattern of gene expression. The complement of transcription factors that are present in the early embryo and that must intrinsically be involved in this reprogramming is essentially uncharacterized. We and others have demonstrated that transcription factor Sp1 is present in the mouse oocyte and early cleavage stage preimplantation embryo. Due to Sp1's prominent role in regulating the expression of a vast array of genes that are involved in cell proliferation and differentiation, as well as in general housekeeping functions, we characterized the temporal and spatial patterns of Sp1 expression during preimplantation development. The relative abundance of Sp1 transcripts, as well as transcripts for the TATA box-binding protein TBP, decreases during oocyte maturation and reaches a minimum level in the two-cell stage, after which time the abundance of these transcripts increases progressively to the blastocyst stage. Immunoblotting experiments detect Sp1 species of Mr = 95,000 and 105,000 at all stages of preimplantation development. The amount of Sp1 increases about 8-fold during preimplantation development, and an alpha-amanitin-insensitive increase is observed between G1 and G2 of the one-cell embryo; this increase may reflect the mobilization of a maternal Sp1 transcript. Immunocytochemical experiments also reveal a similar increase in the amount of Sp1 during preimplantation; the nuclear concentration of Sp1 is greater in the trophectoderm cells than in the inner cell mass cells. Finally, gel-shift experiments document an increase during preimplantation development of a DNA-binding activity that is likely due to Sp1. These increases in the abundance of the Sp1 protein and an Sp1-like DNA-binding activity parallel increases in the rate of transcription that occur during preimplantation development.

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.

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.

Regulation of the acquisition of meiotic competence in the mouse: changes in the subcellular localization of cdc2, cyclin B1, cdc25C and wee1, and in the concentration of these proteins and their transcripts

During their development, mammalian oocytes acquire the ability to resume meiosis. We demonstrate that the concentration of p34cdc2 increases during the acquisition of meiotic competence, as determined by immunoblotting, whereas the concentration of cyclin B1 decreases. Laser-scanning confocal microscopy corroborated these changes and furthermore indicate that an increase occurs in the nuclear concentration of each protein. Results of immunoblotting experiments demonstrate that associated with the acquisition of meiotic competence is an increase in the concentration of cdc25C, an activator of p34cdc2/cyclin B kinase, and a decrease in wee1, an inhibitor of cdc2/cyclin B kinase. These changes were again corroborated by laser-scanning confocal microscopy, which also indicates that an increase in the nuclear concentration of wee1 occurs. The concentration of the transcripts encoding these proteins, however, is essentially similar in meiotically incompetent and competent oocytes. Thus, these changes in protein concentration that occur during oocyte development likely reflect changes in the translational efficiency of their mRNAs. Consistent with this is that the relative rate of synthesis of p34cdc2 in meiotically competent oocytes is approximately 3 times greater than that in meiotically incompetent oocytes, whereas the stability of newly synthesized p34cdc2 is essentially the same in each cell type.

Multiple members of the connexin gene family participate in preimplantation development of the mouse

The connexin gene family, of which there are at least 12 members in rodents, encodes the protein subunits intercellular membrane channels (gap junction channels). Because of the diverse structural and biophysical properties exhibited by the different connexins, it has been proposed that each may play a unique role in development or homeostasis. We have begun to test this hypothesis in the preimplantation mouse embryo in which de novo gap junction assembly is a developmentally regulated event. As a first step, we have used reverse transcription-polymerase chain reaction (RT-PCR) to determine the connexin mRNA phenotype of mouse blastocysts, and have identified transcripts of connexins 30.3, 31, 31.1, 40, 43, and 45. Quantitative measurements indicated that all six of these connexin genes are transcribed after fertilization. They can be divided into two groups with respect to the timing of mRNA accumulation: Cx31, Cx43, and Cx45 mRNAs accumulate continuously from the two- or four-cell stage, whereas Cx30.3, Cx31.1, and Cx40 mRNAs accumulate beginning in the eight-cell stage. All six mRNAs were found to co-sediment with polyribosomes from their time of first appearance, indicating that all six are translated. The expression of Cx31.1 and Cx40 was examined by confocal immunofluorescence microscopy; whereas both could be detected in compacting embryos, only Cx31.1 could be seen in punctate membrane foci indicative of gap junctions. Taken together with other results (published or submitted), our findings indicate that at least four connexins (Cx31, 31.1, 43 and 45) contribute to gap junctions in preimplantation development. The expression of multiple connexin genes during this early period of embryogenesis (when there are only two distinct cell types) raises questions about the functional significance of connexin diversity in this context.