Translational and post-translational modifications in meiosis of the mammalian oocyte

Hypoxia-targeted and spatial-selective tumor suppression by near infrared nanoantenna sensitized engineered bacteria

It is an active research area in the development of engineered bacteria to address the bottleneck issue of hypoxic tumors, which otherwisely possess resistance to chemotherapies, radiotherapies, and photodynamic therapies. Here we report a new method to ablate hypoxic tumors with NIR-nanoantenna sensitized engineered bacteria (NASEB) in a highly effective and dual selective manner. It features engineered E. coli MG1655 (EB) with coatings of lanthanide upconversion nanoparticles (UCNPs) as external antennas on bacterial surface (MG1655/HlyE-sfGFP@UCNP@PEG), enabling NIR laser-switchable generation/secretion of HlyE perforin to kill cancer cells. We have demonstrated that NASEB enrichment on hypoxic tumor sites via their innate chemotactic tendency, in assistance of localized NIR laser irradiation, can suppress tumors with improved efficacy and selectivity, thus minimizing potential side effects in cancer treatment. The NIR-responsive nanoantenna sensitized switching in engineering bacteria is distinct from the previous reports, promising conceptually new development of therapeutics against hypoxic tumors. STATEMENT OF SIGNIFICANCE: Tumor hypoxia exacerbates tumor progression, but also reduces the efficacy of conventional chemotherapies, radiotherapies, or photodynamic therapies. Here we develop near infrared Nano Antenna Sensitized Engineered Bacteria (NASEB) to treat hypoxic tumors. NASEB can accumulate and proliferate on hypoxic tumor sites via their innate chemotactic tendency. After receiving NIR laser signals, the upconversion nanoparticles on NASEB surface as antennas can transduce them to blue light for activation of HlyE perforin in the protein factory of EB. Our method features dual selectivity on the tumor sites, contributed by hypoxic tumor homing of anaerobic bacteria and spatial confinement through selective NIR laser irradiation. The concept of NASEB promises to address the challenges of tumor hypoxia for cancer therapies.

An electrophysiological characterization of naturally occurring tobacco alkaloids and their action on human α4β2 and α7 nicotinic acetylcholine receptors

Nicotinic acetylcholine receptor (nAChR) subtype-selective pharmacological profiles of tobacco alkaloids are essential for understanding the physiological effects of tobacco products. In this study, automated electrophysiology was used to functionally characterize the effects of distinct groups of tobacco alkaloids on human α4β2 and α7 nAChRs. We found that, in tobacco alkaloids, pyridine as a hydrogen bond acceptor and a basic nitrogen atom at a distance of 4-7 Å are pharmacophoric elements necessary for molecular recognition by α4β2 and α7 nAChRs with various degrees of selectivity, potency, and efficacy. While four alkaloids-nicotine, nornicotine, anabasine and R-anatabine-potently activated α4β2, they were also weak agonists of α7 nAChRs. Nicotine was the most potent agonist of α4β2, while anabasine elicited the highest activation of α7. None of the tobacco alkaloids enhanced nAChR activity elicited by the endogenous ligand acetylcholine; therefore, none was considered to be a positive allosteric modulator (PAM) of either α4β2 or α7 nAChRs. In contrast, we identified tobacco alkaloids, such as the tryptophan metabolite 6-hydroxykynurenic acid, that decreased the activity of both α4β2 and α7 nAChRs. Our study identified a class of alkaloids with positive and negative effects against human α4β2 and α7 nAChRs. It also revealed human α4β2 to be the principal receptor for sensing the most abundant alkaloids in tobacco leaves.

Dynamic expression of Epac and Rap1 in mouse oocytes and preimplantation embryos

Cyclic adenosine monophosphate (cAMP) is an important secondary messenger that has long been recognized to control the initiation of meiosis through the activation of protein kinase A (PKA) in mammalian oocytes. However, PKA is not the only target for cAMP. Recent studies on cAMP-dependent and PKA-independent pathways suggest that Ras-related protein-1 (Rap1) is activated through its cAMP-responsive guanine exchange factors (cAMP-GEFs), which comprises the involvement of exchange proteins directly activated by cAMP (Epac) in various cellular processes. The aim of the present study was to investigate the possible implication of a cAMP/Epac/Rap1 pathway in mouse oocytes and embryos. Reverse transcription polymerase chain reaction and immunohistochemistry assays demonstrated the expression of Epac and Rap1 in oocytes and embryos at different stages. Immunofluorescene demonstrated that Epac and Rap1 had different dynamic subcellular localizations and expression patterns in oocytes and embryos at different stages. It was therefore indicated that Epac and Rap1 may have multiple and specific functions during oocyte maturation and embryonic development.

SUMO-1 plays crucial roles for spindle organization, chromosome congression, and chromosome segregation during mouse oocyte meiotic maturation

Small ubiquitin-related modifier-1 (SUMO-1)-dependent modifications of many target proteins are involved in a range of intracellular processes. Previous studies reported the localization of SUMO-1 during oocyte meiosis, and that overexpression of Sentrin/SUMO-specific protease 2 (SENP2), a de-SUMOylation protease, altered SUMO-modified proteins, and caused defects in metaphase-II spindle organization. In this study, we detailed the consequences of SUMO-1-mediated SUMOylation by either inhibition of SUMO-1 or UBC9 with a specific antibody or their depletion by specific siRNA microinjection. Inhibition or depletion of SUMO-1 or UBC9 in germinal vesicle (GV)-stage oocytes decreased the rates of germinal vesicle breakdown and first polar body (PB1) extrusion; caused defective spindle organization and misaligned chromosomes; and led to aneuploidy in matured oocytes. Stage-specific antibody injections suggested that SUMO-1 functions before anaphase I during PB1 extrusion. Further experiments indicated that the localization of γ-tubulin was disordered after SUMO-1 inhibition, and that SUMO-1 depletion disrupted kinetochore-microtubule attachment at metaphase I. Moreover, SUMO-1 inhibition resulted in less-condensed chromosomes, altered localization of REC8 and securin, and reduced BUBR1 accumulation at the centromere. On the other hand, overexpression of SUMO-1 in GV-stage oocytes had no significant effect on oocyte maturation. In conclusion, our results implied that SUMO-1 plays crucial roles during oocyte meiotic maturation, specifically involving spindle assembly and chromosome behavior, by regulating kinetochore-microtubule attachment and the localization of γ-tubulin, BUBR1, REC8, and securin.

Comparative biology of cAMP-induced germinal vesicle breakdown in marine invertebrate oocytes

During maturation, oocytes must undergo a process of nuclear disassembly, or "germinal vesicle breakdown" (GVBD), that is regulated by signaling pathways involving cyclic AMP (cAMP). In vertebrate and starfish oocytes, cAMP elevation typically prevents GVBD. Alternatively, increased concentrations of intra-oocytic cAMP trigger, rather than inhibit, GVBD in several groups of marine invertebrates. To integrate what is known about the stimulation of GVBD by intra-oocytic cAMP, this article reviews published data for ascidian, bivalve, brittle star, jellyfish, and nemertean oocytes. The bulk of the review concentrates on the three most intensively analyzed groups known to display cAMP-induced GVBD-nemerteans, ascidians, and jellyfish. In addition, this synopsis also presents some previously unpublished findings regarding the stimulatory effects of intra-oocytic cAMP on GVBD in jellyfish and the annelid worm Pseudopotamilla occelata. Finally, factors that may account for the currently known distribution of cAMP-induced GVBD across animal groups are discussed.

Gene expression profile of rat ovarian tissue following xenotransplantation into immune-deficient mice

Immune-compromised mice have been used as gonadal tissue recipients to develop gametes of various mammalian species. The aim of this research was to determine gene expression differences between fresh and frozen–thawed rat xenotransplanted (XT) ovaries as well the gene expression differences between XT and sexually mature rat ovaries that were non-transplanted (NT). Ovaries from sexually immature female rats were transplanted under the kidney capsule of ovariectomized athymic nude mice either fresh or after freezing. The XT ovaries were collected ∼10–12 weeks after xenografting for microarray analysis. The NT ovaries were collected from sexually mature rats. Gene expression was very similar between fresh and cryopreserved XT ovaries: 125 genes were twofold up- or downregulated, but level of regulation was not statistically significant. Overall patterns of gene expression between XT and NT ovaries were very different indicated by the absence of diagonal relationship between XT and NT ovary gene expression. More than 3000 genes were significantly (P<0.01) up- or downregulated between XT and NT ovaries. Genes involved in metabolic processes, lipid metabolism, and growth were downregulated in XT ovaries, whereas genes involved in immune and inflammatory response were upregulated in XT ovaries. The results showed that ovarian tissue xenografting significantly alters genes responsible for ovarian metabolism and function and leads to an upregulation of genes responsible for graft rejection.

The signal pathway of gonadotrophins-induced mammalian oocyte meiotic resumption

Fully grown mammalian oocytes are arrested at the first meiotic prophase until a surge of gonadotrophin at the mid-cycle. The actions of gonadotrophins, follicle stimulating hormone (FSH) and luteinizing hormone (LH), on oocyte meiotic resumption are believed to be mediated in large part through increasing the production of cyclic adenosine 3',5'-monophosphate and subsequent activation of mitogen-activated protein kinase (MAPK) in its surrounding cumulus granulosa cells. Recent findings indicate that gonadotrophins-induced epidermal growth factor-like growth factors, meiosis activating sterol and gonadal steroid hormones, possibly via protein kinase A II and protein kinase C pathways, are involved in the activation of MAPK. Another second messenger cyclic guanosine 3',5'-monophosphate induced by nitric oxide or natriuretic peptides system mediates the function of gonadotrophins during oocyte meiotic resumption. FSH and LH induced pathways may either directly overlap or each hormone may utilize redundant pathways in oocyte maturation. A detailed appreciation of different FSH and LH-activated signaling pathways in mammalian oocytes will be needed in understanding their actions in follicular development and oocyte maturation.

CDC25B acts as a potential target of PRKACA in fertilized mouse eggs

Protein kinase A (PRKACA) has been documented as a pivotal regulator in meiosis and mitosis arrest. Although our previous work has established that PRKACA regulates cell cycle progression of mouse fertilized eggs by inhibiting M-phase promoting factor (MPF), little is known about the intermediate factor between PRKACA and MPF in the mitotic cell cycle. In this study, we investigated the role of the PRKACA/CDC25B pathway on the early development of mouse fertilized eggs. Overexpression of unphosphorylatable CDC25B mutant (Cdc25b-S321A or Cdc25b-S229A/S321A) rapidly caused G2-phase eggs to enter mitosis. Microinjection of either Cdc25b-WT or Cdc25b-S229A mRNA also promoted G2/M transition, but much less efficiently than Cdc25b-S321A and Cdc25b-S229A/S321A. Moreover, mouse fertilized eggs overrode the G2 arrest by microinjection of either Cdc25b-S321A or Cdc25b-S229A/S321A mRNA, which efficiently resulted in MPF activation by directly dephosphorylating CDC2A-Tyr15, despite culture under conditions that maintained exogenous dibutyryl cAMP. Using a highly specific antibody against phospho-Ser321 of CDC25B in Western blotting, we showed that CDC25B-Ser321 was phosphorylated at the G1 and S phases, whereas Ser321 was dephosphorylated at the G2 and M phases in vivo. Our findings identify CDC25B as a potential target of PRKACA and show that PRKACA regulates G2/M transition by phosphorylating CDC25B-Ser321 but not CDC25B-Ser229 on the first mitotic division of mouse fertilized eggs.

An active protein kinase A (PKA) is involved in meiotic arrest of rat growing oocytes

Reinitiation of meiosis in meiotically competent, fully grown mammalian oocytes is governed by a fall in intraoocyte cAMP concentrations and the subsequent inactivation of protein kinase A (PKA). A similar reduction in intraoocyte cAMP concentrations in growing, meiotically incompetent rat oocytes not leading to resumption of meiosis, questions the involvement of PKA in the regulation of meiosis at this early stage of oocyte development. We examined the possibility of whether PKA activity maintains growing oocytes in meiotic arrest and further explored the mode of activation of PKA under conditions of relatively low cAMP concentrations. Our experiment demonstrated that inactivation of PKA stimulates growing rat oocytes to resume meiosis, and elevates the activity of their maturation-promoting factor (MPF). We also found that the expressions of type I and type II regulatory subunits (RI and RII) of PKA are higher in growing and fully grown oocytes, respectively. In addition, we revealed that the common 1:1 ratio between the regulatory (R) and catalytic (C) subunits of PKA is apparently not abrogated and, in accordance PKA activity in growing oocyte-cell extract is fully dependent on cAMP. Finally, we identified in growing oocytes, the A kinase anchoring protein (AKAP) 140, which was previously depicted in fully grown oocytes. We conclude that an active PKA prevents growing oocytes from resuming meiosis. Our findings further suggest that relatively high abundance of the PKAI isoform and/or its subcellular compartmentalization, through interaction with AKAP140, could possibly account for the high basal PKA activity at relatively low intraoocyte cAMP concentrations.

Graft site and gonadotrophin stimulation influences the number and quality of oocytes from murine ovarian tissue grafts

Ovarian tissue cryopreservation and subsequent transplantation can restore fertility in cancer patients. This study used a mouse ovarian grafting model to investigate whether the graft site (bursal cavity, the kidney capsule or subcutaneous) influences the number, fertilization rate and developmental potential of oocytes recovered from grafts and whether using a standard gonadotrophin stimulation protocol would increase oocyte yield from the grafts. Mouse ovarian tissue was grafted into four week old mice and collected three weeks later. Graft recipients were treated either with or without exogenous gonadotrophin stimulation prior to graft collection. Grafted ovaries yielded oocytes that were either at the germinal vesicle (GV) stage or mature metaphase II (MII) stage at collection. These GV oocytes were matured beforein vitrofertilization (IVF), while the MII oocytes underwent IVF immediately. Oocytes collected from the oviducts of non-grafted superovulated mice of the same age served as controls. Two-cell embryos were transferred to pseudopregnant recipients and recovered at day 15 of gestation or left to go to term. Graft retrieval and the number of oocytes from each graft were lowest from the subcutaneous graft site. The number of two-cell embryos produced was significantly higher for oocytes from the grafts to the bursa as compared with the other sites. All graft sites gave rise to embryos with comparable implantation rates and developmental potential to fetuses and offspring following transfer. However, the oocytes from grafted ovaries had a significantly lower developmental potential when compared with the control group. Stimulation with exogenous gonadotrophins did not significantly increase oocyte yield from grafted ovaries but did enhance oocyte maturation and development. In conclusion, graft site affects the number and quality of oocytes produced from ovarian grafts.

Profiling of gender-specific gene expression for Trichostrongylus vitrinus (Nematoda: Strongylida) by microarray analysis of expressed sequence tag libraries constructed by suppressive-subtractive hybridisation

Gender-specific gene expression in Trichostrongylus vitrinus (order Strongylida) was investigated by constructing male- and female-specific gene archives using a suppressive-subtractive hybridisation approach, sequencing of expressed sequence tags from these archives, comparison with genes of Caenorhabditis elegans and other organisms, and expression profiling of a representative subset of 716 expressed sequence tags by microarray and macroarray analysis. Of these T. vitrinus expressed sequence tags, 391 had sequence homology to C. elegans genes. Of the remaining expressed sequence tags, 62 had homology to genes of other species of parasitic nematodes, and 263 expressed sequence tags had no significant homology. Expression profiling showed gender-specific expression for 561 of the 716 T. vitrinus expressed sequence tags. Male-specific protein kinases and protein phosphatases, major sperm proteins and enzymes involved in carbohydrate metabolism were abundant in the cDNA archive. Female-specific vitellogenins, heat-shock proteins and chaperonins were also highly represented. Genes involved in a number of cellular processes, such as ubiquitination and proteasome function, gene transcription, cell signalling, protein-protein interactions and chromatin assembly and function were also expressed in a gender-specific manner. The potential roles of these genes in gametogenesis, embryogenesis and reproduction in the parasitic nematode are discussed in relation to the known roles of their homologues in C. elegans.

Cyclic nucleotide phosphodiesterase 3A-deficient mice as a model of female infertility

Since cAMP blocks meiotic maturation of mammalian and amphibian oocytes in vitro and cyclic nucleotide phosphodiesterase 3A (PDE3A) is primarily responsible for oocyte cAMP hydrolysis, we generated PDE3A-deficient mice by homologous recombination. The Pde3a(-/-) females were viable and ovulated a normal number of oocytes but were completely infertile, because ovulated oocytes were arrested at the germinal vesicle stage and, therefore, could not be fertilized. Pde3a(-/-) oocytes lacked cAMP-specific PDE activity, contained increased cAMP levels, and failed to undergo spontaneous maturation in vitro (up to 48 hours). Meiotic maturation in Pde3a(-/-) oocytes was restored by inhibiting protein kinase A (PKA) with adenosine-3',5'-cyclic monophosphorothioate, Rp-isomer (Rp-cAMPS) or by injection of protein kinase inhibitor peptide (PKI) or mRNA coding for phosphatase CDC25, which confirms that increased cAMP-PKA signaling is responsible for the meiotic blockade. Pde3a(-/-) oocytes that underwent germinal vesicle breakdown showed activation of MPF and MAPK, completed the first meiotic division extruding a polar body, and became competent for fertilization by spermatozoa. We believe that these findings provide the first genetic evidence indicating that resumption of meiosis in vivo and in vitro requires PDE3A activity. Pde3a(-/-) mice represent an in vivo model where meiotic maturation and ovulation are dissociated, which underscores inhibition of oocyte maturation as a potential strategy for contraception.