A novel role for glycogen synthase kinase-3 in Xenopus development: maintenance of oocyte cell cycle arrest by a beta-catenin-independent mechanism

Function of glycogen synthase kinase3 in embryogenesis of Dermanyssus gallinae

In the life cycle of Dermanyssus gallinae, the embryo is a developmental stage that does not require blood meals, but needs glucose to produce adenosine triphosphate (ATP) through glycolysis or oxidative phosphorylation, providing energy for embryonic development. Glycogen synthase kinase 3 (GSK3), belonging to the serine/threonine kinase family, is a key enzyme involved in glycogen metabolism in many eukaryotes, but not be described in D. gallinae. The present study was conducted to explore the role of Dg-GSK3 in the embryogenesis of D. gallinae. The results of qPCR showed that Dg-GSK3 mRNA was expressed in different development stages of D. gallinae embryos. RNA interference (RNAi) was performed on the female mites and eggs by immersion, and it was found that lowering GSK3 expression level could significantly decrease the female egg laying rate and egg hatching rate (P < 0.05). Some eggs became shrunken and shriveled in appearance. The fecundity of female D. gallinae obtained from the rDg-GSK3-immunized group of chickens (2.56 ± 0.35 eggs per mite, P < 0.0001) decreased significantly from that of the control group (3.49 ± 0.35). The oviposition rate of rDg-GSK3-immunized group (75.94 ± 7.28 %, P = 0.0003）was significantly lower that of the control group (89.69 ± 2.63 %). In conclusion, Dg-GSK3 is a crucial gene during the embryogenesis of D. gallinae, which can affect both the female fecundity and the egg hatching, which help us understand the function of GSK3 gene in the embryogenesis of mites.

Effects of different concentrations of Chir98014 as an activator of Wnt/beta-catenin signaling pathway on oocyte in-vitro maturation and subsequent embryonic development in Sanjabi ewes

The present study was conducted to investigate the effects of the activator factor of the WNT pathway, chir98014, leading to the in vitro sheep oocyte maturation medium, on the cumulus cell development, different nuclear maturation stages and the following process of embryonic development. Experiments included (a) addition of different concentrations (0, 0.1, 0.5, 1 µm) of chir98014 to the maturation medium and evaluation of the cumulus cell expansion, (b) addition of different concentrations of chir98014 to the maturation medium and investigation of different nuclear maturation stages, (c) addition of different concentrations of chir98014 to the maturation medium and examination of the subsequent embryonic maturation process and (d) addition of different concentrations of chir98014 to the embryonic development culture medium (the first 48 hr) and investigation of the subsequent embryonic development process. The extracted data were analysed using the SPSS software, considering the significance level of p < .05 and making the mean comparisons. The results showed that the addition of the 0.1 µM concentration of chir98014 to the maturation medium had no significant effects on the oocyte maturation and embryo development post-fertilization but it enhanced the Cumulus-oocyte complexes (COCs) expansion. In the fourth experiment, the low concentration of chir98014 in the embryo culture media improved the embryo development process, whereas the high one had a detrimental effect on it, as compared to the control group. Thus, the presence of the lower concentrations of this compound in the embryonic culture medium had favourable effects on the development of embryos.

IGF-1 treatment during in vitro maturation improves developmental potential of ovine oocytes through the regulation of PI3K/Akt and apoptosis signaling

This study aimed to assess the effect of the insulin-like grow factor 1 (IGF-1) treatment during in vitro maturation on the gene expression and developmental ability of ovine oocytes. Ovine cumulus-oocyte complexes (COC) were matured in vitro without (control) or with the supplementation of IGF-1 (100 ng/ml) and then subjected to in vitro fertilization and culture. The rate of oocyte maturation and embryo development was recorded and expression of the selected genes (involved in the PI3K/Akt and apoptosis signaling) was assessed in the matured oocytes. The IGF-1 treatment significantly (p < .05) improved the oocyte maturation rate (%) as compared to the control (81.5 ± 2.40 vs. 73.6 ± 0.94). Similarly, as compared to the control, the IGF-1 treatment significantly (p < .05) improved the rate (%) of cleavage (54.7 ± 1.58 vs. 67.2 ± 3.65) and the formation of 4-8 cell embryos (30.7 ± 2.89 vs. 44.1 ± 4.01) and morula (20.7 ± 2.08 vs. 32.8 ± 2.78). The IGF-1 treatment significantly (p < .05) upregulated the expression of IGF1R, PI3KR1, AKT1 and BCL2 and downregulated the expression of GSK3β, FOXO3 and CASP9 in the matured oocytes. In conclusion, the IGF-1 treatment significantly improved the developmental competence of ovine oocytes through the regulation of the PI3K/Akt and apoptosis signaling.

Molecular cloning and transcriptional and functional analysis of glycogen synthase kinase-3β in Haemaphysalis longicornis (Acari, Ixodidae)

Glycogen synthase kinase 3 (GSK-3), which belongs to the serine/threonine kinase family, regulates glycogen metabolism, Wnt signaling, hormonal regulation, and embryonic development in many eukaryotes. Here, we cloned a complete open reading frame (ORF) of glycogen synthase kinase 3β (GSK-3β) from Haemaphysalis longicornis and characterized its transcriptional and functional status. The ORF of GSK-3β possesses 1242 nucleotides encoding a mature protein of 413 amino acid residues. GSK-3β nucleotide and protein sequences are highly conserved among different vertebrate and invertebrate animals, with identity between 47.8–100% and 63.2–88.7%, respectively. Sequence comparison showed one signature domain between the residues of 51 and 335 amino acids, which was identified as a protein kinase (serine/threonine). RT-PCR showed GSK-3β mRNA present in all developmental stages of H. longicornis. Interestingly, a higher transcript level was observed in nymph and 7-day-old eggs compared with others by real-time PCR, indicating a role of GSK-3β in the early stages of life. The functional status of GSK-3β was characterized by RNA interference (RNAi) and caused significant (p < 0.05) reduction in feeding and reproduction, as well as an abnormality in eggs and hatching. Taken together, our results suggest that GSK-3β may be an important candidate for a multiple antigen vaccine for controlling the tick population.

Phosphorylation Dynamics Dominate the Regulated Proteome during Early Xenopus Development

The earliest stages of animal development are largely controlled by changes in protein phosphorylation mediated by signaling pathways and cyclin-dependent kinases. In order to decipher these complex networks and to discover new aspects of regulation by this post-translational modification, we undertook an analysis of the X. laevis phosphoproteome at seven developmental stages beginning with stage VI oocytes and ending with two-cell embryos. Concurrent measurement of the proteome and phosphoproteome enabled measurement of phosphosite occupancy as a function of developmental stage. We observed little change in protein expression levels during this period. We detected the expected phosphorylation of MAP kinases, translational regulatory proteins, and subunits of APC/C that validate the accuracy of our measurements. We find that more than half the identified proteins possess multiple sites of phosphorylation that are often clustered, where kinases work together in a hierarchical manner to create stretches of phosphorylated residues, which may be a means to amplify signals or stabilize a particular protein conformation. Conversely, other proteins have opposing sites of phosphorylation that seemingly reflect distinct changes in activity during this developmental timeline.

Morphological analysis of CDC2 and glycogen synthase kinase 3β phosphorylation as markers of g2 → m transition in glioma

G2 → M transition is a strategic target for glioma chemotherapy. Key players in G2 → M transition include CDC2 and glycogen synthase kinase 3β (GSK3β), which are highly regulated by posttranslational phosphorylation. This report is a morphological analysis of CDC2 and GSK3β phosphorylation using immunohistochemistry in gliomas with different biological properties. GBM showed a 2.8-fold and 5.6-fold increase in number of cells positive for pThr161CDC2 and a 4.2- and 6.9-fold increase in number of cells positive for pTyr15CDC2 relative to oligodendroglioma and ependymoma, respectively. Elevated labeling for inhibited phospho-CDC2 (pTyr15CDC) correlates with elevated levels of phosphorylated glycogen synthase kinase 3β (GSK3β). 71% of the GBM cases showed intermediate to high intensity staining for pSer9SGK3β 53% of oligodendroglioma, and 73% of ependymoma showed low intensity staining. CDC2 gene amplification correlates with increased survival in glioblastoma multiforme (GBM) and astrocytoma WHO grades II-III, but not in oligodendroglioma WHO grades II-III.

Glycogen synthase kinase 3B in bovine oocytes and granulosa cells: possible involvement in meiosis during in vitro maturation

Glycogen synthase kinase 3 (GSK3) regulates cellular metabolism and cell cycle via different signalling pathways. In response to insulin and growth factors GSK3 is serine-phosphorylated and inactivated. We analysed GSK3B expression and activation in bovine cumulus cells (CC) and oocytes at different meiotic stagesin vitroin parallel with MAP kinases ERK (MAPK3/MAPK1) and p38 (MAPK14). GSK3B localised to cytoplasm in granulosa cells and in oocytes throughout folliculogenesis. In mature metaphase-II (MII) oocytes, GSK3B was concentrated to the region of midzone between the oocyte and the first polar body, as well as active phospho-Thr Aurora A kinase (AURKA). Duringin vitromaturation (IVM), in oocytes, phospho-Ser9-GSK3B level increased as well as phospho-MAPK3/MAPK1, while phospho-MAPK14 decreased. In CC, phospho-MAPK14 increased upon germinal vesicle breakdown (GVBD)/metaphase-I (MI) and then decreased during transition to MII. Administration of inhibitors of GSK3 activity (lithium chloride or 2′Z,3′E -6-bromoindirubin-3′-oxime) rapidly increased phospho-Ser9-GSK3B, and led to transient decrease of phospho-MAPK3/MAPK1 and to durable enhancing of phospho-MAPK14 in granulosa primary cell culture. GSK3 inhibitors during IVM diminished cumulus expansion and delayed meiotic progression. In cumulus, phospho-MAPK14 level was significantly higher in the presence of inhibitors, comparing with control, through the time of MI/MII transition. In oocytes, phospho-GSK3B was increased and phospho-MAPK3/MAPK1 was decreased before GVBD and oocytes were mainly arrested at MI. Therefore, GSK3B might regulate oocyte meiosis, notably MI/MII transition being the part of MAPK3/1 and MAPK14 pathways in oocytes and CC. GSK3B might be also involved in the local activation of AURKA that controls this transition.

Tuning the activation threshold of a kinase network by nested feedback loops

Determining proper responsiveness to incoming signals is fundamental to all biological systems. We demonstrate that intracellular signaling nodes can tune a signaling network's response threshold away from the basal median effective concentration established by ligand-receptor interactions. Focusing on the bistable kinase network that governs progesterone-induced meiotic entry in Xenopus oocytes, we characterized glycogen synthase kinase-3beta (GSK-3beta) as a dampener of progesterone responsiveness. GSK-3beta engages the meiotic kinase network through a double-negative feedback loop; this specific feedback architecture raises the progesterone threshold in correspondence with the strength of double-negative signaling. We also identified a marker of nutritional status, l-leucine, which lowers the progesterone threshold, indicating that oocytes integrate additional signals into their cell-fate decisions by modulating progesterone responsiveness.

Expression and activity of glycogen synthase kinase during vitellogenesis and embryogenesis of Rhipicephalus (Boophilus) microplus

Glycogen synthase kinase 3 (GSK-3) is classically described as a key enzyme involved in glycogen metabolism in mammals. GSK-3 belongs to a highly conserved family of serine/threonine protein kinases, whose members are involved in hormonal regulation, nuclear signaling, and cell fate determination in higher eukaryotes. We have cloned and characterized the RmGSK-3 gene from Rhipicephalus (Boophilus) microplus tick embryos. DNA and protein sequence analysis depicted high similarity to the corresponding enzyme, from both vertebrate and invertebrate animals. In addition, the mRNA transcription profile identified during embryogenesis was analyzed. We observed that the RmGSK-3 mRNA rapidly decreases from the 1st to 3rd day of development, and increases from the 3rd to 15th day. After the 15th day of development, we observed a near 50% reduction in RmGSK-3 mRNA transcription in comparison to the 1st day. We detected the GSK-3beta isoform in egg homogenates throughout embryogenesis using Western blot analysis. RmGSK-3 mRNA was present in fat body, midgut and ovary from partially and fully engorged adult female ticks. The highest mRNA level was observed in ovaries from both developmental stages and in first-day eggs. Furthermore, RmGSK-3 activity correlated with glycogen content variation. Finally, kinase activity in egg homogenates was inhibited by the specific inhibitor, SB-216763. These data suggest that RmGSK-3beta may be involved in glycogen metabolism regulation during R. microplus embryogenesis.

Possible involvement of phosphatidylinositol 3-kinase, but not protein kinase B or glycogen synthase kinase 3beta, in progesterone-induced oocyte maturation in the Japanese brown frog, Rana japonica

It is known that amphibian oocytes undergo maturation through the formation and activation of maturation-promoting factor (MPF) in response to stimulation by the maturation-inducing hormone progesterone; however, the signal transduction pathway that links the hormonal stimulation on the oocyte surface to the activation of MPF in the oocyte cytoplasm remains a mystery. The aim of this study was to investigate whether the signal transduction mediated by phosphatidylinositol 3-kinase (PI3K), protein kinase B (PKB), and glycogen synthase kinase 3beta (GSK3beta) is involved in progesterone-induced oocyte maturation in the Japanese brown frog, Rana japonica. Inhibitors of PI3K, wortmannin and LY294002, inhibited progesterone-stimulated germinal vesicle breakdown (GVBD) only when the oocytes were treated at the initial phase of maturation, suggesting that PI3K is involved in the progesterone-induced maturation of Rana oocytes. However, we also obtained results suggesting that PKB and GSK3beta are not involved in Rana oocyte maturation. A constitutively active PKB expressed in the oocytes failed to induce GVBD in the absence of progesterone despite its high level of kinase activity. A Myc-tagged PKB expressed in the oocytes (used to monitor endogenous PKB activity) was not activated in the process of progesterone-induced oocyte maturation. Overexpression of GSK3beta, which is reported to retard the progress of Xenopus oocyte maturation, had no effect on Rana oocyte maturation. On the basis of these results, we propose that PI3K is involved in the initiation of Rana oocyte maturation, but that neither PKB nor GSK3beta is a component of the PI3K signal transduction pathway.

Swedish amyloid precursor protein mutation increases cell cycle-related proteins in vitro and in vivo

Reactivation of the cell cycle, including DNA replication, might play a major role in Alzheimer's disease. In this study, we report that the expressions of Swedish double mutation of amyloid precursor protein (Swe-APP) or of the APP intracellular domain (AICD) into nerve growth factor (NGF)-differentiated PC12 cells or rat primary cortical neurons increased mRNA and protein levels of cyclin D1 and cyclin B1. Treatment with lithium chloride (a glycogen synthase kinase-3beta inhibitor) down-regulated cyclin B1 induced by Swe-APP expression but up-regulated cyclin D1 expression induced by Swe-APP, suggesting that glycogen synthase kinase-3beta activity is involved in these expression changes of cyclins D1 and B1. Swe-APP, which is a prevailing cause of familial Alzheimer's disease, is well known to increase amyloid beta peptide production both in vitro and in vivo, but the underlying molecular means whereby it leads to the pathogenesis of AD remains unknown. The finding that cyclin D1 and B1 expressions were up-regulated by Swe-APP in in vitro cultured cells was substantiated in the brain tissues of Tg2576 mice, which harbor the Swe-APP mutation. These results suggest that some disturbances in cell cycle regulation may be involved in Swe-APP or AICD-induced neurodegeneration and that these contribute to the pathogenesis of AD.

Insulin signaling in mouse oocytes

Continuous exposure of follicles/oocytes to elevated levels of insulin compromises embryonic developmental competence, although the underlying cellular mechanisms are unknown. The objectives of the present study were to determine whether mouse oocytes have insulin receptors and a functional insulin signaling cascade, and whether insulin exposure during oocyte growth or maturation influences meiotic progression and chromatin remodeling. Immunoblot and immunocytochemical analyses of germinal vesicle-intact (GVI) oocytes demonstrated the presence of insulin receptor-beta. Insulin receptor expression in oocytes was increased by gonadotropin stimulation, and remained elevated throughout meiotic maturation. Fully grown GVI oocytes contained 3-phosphoinositide-dependent protein kinase-1 (PDPK1), thymoma viral proto-oncogene 1 (AKT1), and glycogen synthase kinase 3 (GSK3). In vitro maturation of GVI oocytes in 5 microg/ml insulin had no influence on meiotic progression or the incidence of normal metaphase II (MII) chromosome condensation. Treatment of oocytes during maturation had no effect on GSK3A/B protein expression or phosphorylation of S21/9. However, the culturing of preantral follicles for 10 days with 5 microg/ml insulin increased the phosphorylation of oocyte GSK3B, indicating GSK3 inactivation. The rates of development to metaphase I (MI) were similar for oocytes obtained from insulin-treated follicles and controls, whereas the incidence of abnormal MI chromatin condensation was significantly higher in oocytes obtained from follicles cultured with insulin compared to those cultured without insulin. These results demonstrate that oocytes contain a functional insulin signaling pathway, and that insulin exposure during oocyte growth results in chromatin remodeling aberrations. These findings begin to elucidate the mechanisms by which chronic elevated insulin influences oocyte meiosis, chromatin remodeling, and embryonic developmental competence.

Modulation of O-GlcNAc glycosylation during Xenopus oocyte maturation

O-linked N-acetylglucosamine (O-GlcNAc) glycosylation is a post-translational modification, which is believed antagonises phosphorylation. We have studied the O-GlcNAc level during Xenopus oocyte meiotic resumption, taking advantage of the high synchrony of this model which is dependent upon a burst of phosphorylation. Stimulation of immature stage VI oocytes using progesterone was followed by a 4.51 +/- 0.32 fold increase in the GlcNAc content, concomitantly to an increase in phosphorylation, notably on two cytoplasmic proteins of 66 and 97 kDa. The increase of O-GlcNAc for the 97 kDa protein, which we identified as beta-catenin was partly related to its accumulation during maturation, as was demonstrated by the use of the protein synthesis inhibitor--cycloheximide. Microinjection of free GlcNAc, which inhibits O-glycosylated proteins-lectins interactions, delayed the progesterone-induced maturation without affecting the O-GlcNAc content. Our results suggest that O-GlcNAc glycosylation could regulate protein-protein interactions required for the cell cycle kinetic.

Proteasome inhibition and Tau proteolysis: an unexpected regulation

Increasing evidence suggests that an inhibition of the proteasome, as demonstrated in Parkinson's disease, might be involved in Alzheimer's disease. In this disease and other Tauopathies, Tau proteins are hyperphosphorylated and aggregated within degenerating neurons. In this state, Tau is also ubiquitinated, suggesting that the proteasome might be involved in Tau proteolysis. Thus, to investigate if proteasome inhibition leads to accumulation, hyperphosphorylation and aggregation of Tau, we used neuroblastoma cells overexpressing Tau proteins. Surprisingly, we showed that the inhibition of the proteasome led to a bidirectional degradation of Tau. Following this result, the cellular mechanisms that may degrade Tau were investigated.

Progesterone and insulin stimulation of CPEB-dependent polyadenylation is regulated by Aurora A and glycogen synthase kinase-3

Progesterone stimulation of Xenopus oocyte maturation requires the cytoplasmic polyadenylation-induced translation of mos and cyclin B mRNAs. One cis element that drives polyadenylation is the CPE, which is bound by the protein CPEB. Polyadenylation is stimulated by Aurora A (Eg2)-catalyzed CPEB serine 174 phosphorylation, which occurs soon after oocytes are exposed to progesterone. Here, we show that insulin also stimulates Aurora A-catalyzed CPEB S174 phosphorylation, cytoplasmic polyadenylation, translation, and oocyte maturation. However, these insulin-induced events are uniquely controlled by PI3 kinase and PKC-zeta, which act upstream of Aurora A. The intersection of the progesterone and insulin signaling pathways occurs at glycogen synthase kinase 3 (GSK-3), which regulates the activity of Aurora A. GSK-3 and Aurora A interact in vivo, and overexpressed GSK-3 inhibits Aurora A-catalyzed CPEB phosphorylation. In vitro, GSK-3 phosphorylates Aurora A on S290/291, the result of which is an autophosphorylation of serine 349. GSK-3 phosphorylated Aurora A, or Aurora A proteins with S290/291D or S349D mutations, have reduced or no capacity to phosphorylate CPEB. Conversely, Aurora A proteins with S290/291A or S349A mutations are constitutively active. These results suggest that the progesterone and insulin stimulate maturation by inhibiting GSK-3, which allows Aurora A activation and CPEB-mediated translation.

Inhibition of FGF receptor signalling in Xenopus oocytes: differential effect of Grb7, Grb10 and Grb14

The role of Grb7 adapters, Grb7, Grb10, and Grb14, was investigated in Xenopus oocytes expressing fibroblast growth factor receptors (FGFR). FGF-induced maturation of FGFR-expressing oocytes was blocked by previous injection of Grb7 or Grb14, but not Grb10. This effect correlated with Grb7/14 binding to the receptor, and inhibition of the Ras-dependent pathway. Interestingly, the phosphorylated insulin receptor interacting region (PIR) and Src 2 homology domains (SH2) of Grb7 and Grb14 were differently implicated in the inhibition of FGFR signalling. This study provided further evidence for specificity of the biological action of the Grb7 adapters on receptor tyrosine kinase signalling.

Evidence for a role of glycogen synthase kinase-3 beta in rodent spermatogenesis

Glycogen synthase kinase-3 beta (GSK-3 beta) regulates cell metabolism, cell cycle, and cell fate through the phosphorylation of a diverse array of substrates. Herein, we provide evidence that supports a role for GSK-3 in mammalian meiosis and spermatogenesis. Immunostaining of testis sections showed that while GSK-3 alpha was ubiquitous in the seminiferous tubules, GSK-3 beta was expressed in premeiotic type B spermatogonia, in both meiotic preleptotene and leptotene spermatocytes, as well as in Sertoli cells in both the mouse and rat. Thus, GSK-3 beta is expressed in germ cells entering meiosis. In addition, intense immunoreactivity was detected in rat step 6 though 11 spermatids. In situ hybridization (ISH) in rat testis confirmed the immunostaining pattern in leptotene and spermatids and showed a GSK-3 beta messenger RNA (mRNA) signal in some pachytene spermatocytes. The restricted pattern of expression suggests cell-specific regulation of Gsk-3 beta mRNA. To determine whether GSK-3 is required for meiosis entry, rat stage VIIa seminiferous tubule segments were cultured with selective small-molecule GSK-3 inhibitors. These compounds markedly and dose-dependently suppressed meiotic synthesis (S)-phase DNA. Since a yeast GSK-3 homolog, Rim11p (regulator of inducer of meiosis), is pivotal to meiosis entry, we tested whether GSK-3 beta complements Rim11p function in meiosis. Rim11p phosphorylates transcription factors Ume6p (unscheduled meiotic gene expression) and Ime1p (inducer of meiosis) to induce meiosis entry. Overexpression of murine GSK-3 beta in a rim11 mutant yeast failed to rescue the sporulation defect. Our finding that GSK-3 beta interacted only with Ume6p but not with IME1 in a yeast 2-hybrid assay suggests that noncomplementation reflects partial divergence in substrate specificity. This work provides the basis for future studies of GSK-3 beta signaling in mammalian meiosis and spermatogenesis.

DIF-1, an anti-tumor substance found in Dictyostelium discoideum, inhibits progesterone-induced oocyte maturation in Xenopus laevis

Differentiation-inducing factor-1 (DIF-1; 1-(3,5-dichloro-2,6-dihydroxy-4-methoxyphenyl)hexan-1-one) is a putative morphogen that induces stalk-cell formation in the cellular slime mold Dictyostelium discoideum. DIF-1 has previously been shown to suppress cell growth in mammalian cells. In this study, we examined the effects of DIF-1 on the progesterone-induced germinal vesicle breakdown in Xenopus laevis, which is thought to be mediated by a decrease in intracellular cAMP and the subsequent activation of mitogen-activated protein kinase (MAPK) and maturation-promoting factor, a complex of cdc2 and cyclin B, which regulates germinal vesicle breakdown. DIF-1 at 10-40 microM inhibited progesterone-induced germinal vesicle breakdown in de-folliculated oocytes in a dose-dependent manner. Progesterone-induced cdc2 activation, MAPK activation, and c-Mos accumulation were inhibited by DIF-1. Furthermore, DIF-1 was found to inhibit the progesterone-induced cAMP decrease in the oocytes. These results indicate that DIF-1 inhibits progesterone-induced germinal vesicle breakdown possibly by blocking the progesterone-induced decrease in [cAMP](i) and the subsequent events in Xenopus oocytes.

Up-regulation and nuclear localization of beta-catenin in endometrial carcinoma in response to progesterone therapy

Ovarian hormones are considered to be capable of regulating expression of beta-catenins. A possible role of beta-catenin in alteration of cell morphology has been proposed, but little is known about beta-catenin expression during changes in the tumor morphology of endometrial carcinomas induced by progesterone therapy. To clarify changes in expression of beta-catenin and their relation to morphological alteration, expression of hormone receptors and several cell kinetic markers, sequential biopsy and hysterectomy specimens of 23 endometrial carcinoma and 6 complex hyperplasia with atypia (atypical hyperplasia) cases receiving progesterone therapy were investigated. In vitro assay was also conducted using two endometrial carcinoma cell lines (HEC265 and Ishikawa) expressing progesterone receptors (PRs). An increase of nuclear beta-catenin accumulation was evident during progesterone therapy in endometrial carcinomas and atypical hyperplasias. The nuclear labeling indices were significantly associated with gene mutations and alteration in morphological features in response to progesterone, independently of the status of Ki-67, p21WAF1 and p27Kip1, and hormone receptors. In HEC265 having a beta-catenin gene mutation (A32V), cytoplasmic beta-catenin levels were elevated by progesterone treatment, linked to down-regulation of PR expression, but such changes were relatively minor in Ishikawa without the gene alterations. These findings demonstrate a possible role of progesterone in regulation of beta-catenin expression in endometrial tumors. Moreover, nuclear beta-catenin accumulation, like gene abnormalities, is associated with the alteration of tumor morphology due to progesterone, indicating that beta-catenin may be a clinically useful marker of hormone therapeutic effects.

Modelling Alzheimer-specific abnormal Tau phosphorylation independently of GSK3beta and PKA kinase activities

In Alzheimer's disease, neurofibrillary degeneration results from the aggregation of abnormally phosphorylated Tau proteins into paired helical filaments. These Tau variants displayed specific epitopes that are immunoreactive with anti-phospho-Tau antibodies such as AT100. As shown in in vitro experiments, glycogen synthase kinase 3 beta (GSK3beta) and protein kinase A (PKA) may be key kinases in these phosphorylation events. In the present study, Tau was microinjected into Xenopus oocytes. Surprisingly, in this system, AT100 was generated without any GSK3beta and PKA contribution during the progesterone or insulin-induced maturation process. Our results demonstrate that a non-modified physiological process in a cell model can generate the most specific Alzheimer epitope of Tau pathology.

A constitutively active form of the protein kinase p90Rsk1 is sufficient to trigger the G2/M transition in Xenopus oocytes

The protein kinase p90(Rsk) has previously been implicated as a key target of the MAPK pathway during M phase of meiosis II in Xenopus oocytes. To determine whether Rsk is a mediator of MAPK for stimulation of the G(2)/M transition early in meiosis I, we sought to generate a form of Rsk that would be constitutively active in resting, G(2) phase oocytes. Initial studies revealed that an N-terminal truncation of 43 amino acids conferred enhanced specific activity on the enzyme in G(2) phase, and stability was highest if the C terminus was not truncated. The full-length enzyme is known to be activated by phosphorylation at five sites. Two of these sites and flanking residues were replaced with either aspartic or glutamic acid, and Tyr(699) was mutated to alanine. The resulting construct, termed fully activated (FA) Rsk, had constitutive activity in G(2) phase, with a specific activity equivalent to that of wild type Rsk in M phase. In eight independent experiments approximately 45% of oocytes expressing FA-Rsk underwent germinal vesicle breakdown (GVBD, the G(2)/M transition) in the absence of progesterone, and this effect could be observed even in the presence of the MAPK kinase inhibitor U0126. Moreover, the specific activity of FA-Rsk in vivo was unaffected by U0126. In oocytes that did not undergo GVBD with FA-Rsk expression, subsequent treatment with progesterone resulted in a very rapid rate of GVBD even in the presence of U0126 to inhibit the endogenous MAPK/Rsk pathway. These results indicate that Rsk is the mediator of MAPK effects for the G(2)/M transition in meiosis I and in a subpopulation of oocytes Rsk is sufficient to trigger the G(2)/M transition.

Regulation of the meiotic cell cycle in oocytes

The mitotic and meiotic cell cycle share many regulators, but there are also important differences between the two processes. The meiotic maturation of Xenopus oocytes has proved useful for understanding the regulation of Cdc2-cyclin-B, a key activator of G2/M progression. New insights have been made recently into the signalling mechanisms that induce G2-arrested oocytes to resume and complete the meiotic cell cycle.

Dorsal downregulation of GSK3beta by a non-Wnt-like mechanism is an early molecular consequence of cortical rotation in early Xenopus embryos

Cortical rotation and concomitant dorsal translocation of cytoplasmic determinants are the earliest events known to be necessary for dorsoventral patterning in Xenopus embryos. The earliest known molecular target is beta-catenin, which is essential for dorsal development and becomes dorsally enriched shortly after cortical rotation. In mammalian cells cytoplasmic accumulation of beta-catenin follows reduction of the specific activity of glycogen synthase kinase 3-beta (GSK3beta). In Xenopus embryos, exogenous GSK3beta) suppresses dorsal development as predicted and GSK3beta dominant negative (kinase dead) mutants cause ectopic axis formation. However, endogenous GSK3beta regulation is poorly characterized. Here we demonstrate two modes of GSK3beta regulation in Xenopus. Endogenous mechanisms cause depletion of GSK3beta protein on the dorsal side of the embryo. The timing, location and magnitude of the depletion correspond to those of endogenous beta-catenin accumulation. UV and D(2)O treatments that abolish and enhance dorsal character of the embryo, respectively, correspondingly abolish and enhance GSK3beta depletion. A candidate regulator of GSK3beta, GSK3-binding protein (GBP), known to be essential for axis formation, also induces depletion of GSK3beta. Depletion of GSK3beta is a previously undescribed mode of regulation of this signal transducer. The other mode of regulation is observed in response to Wnt and dishevelled expression. Neither Wnt nor dishevelled causes depletion but instead they reduce GSK3beta-specific activity. Thus, Wnt/Dsh and GBP appear to effect two biochemically distinct modes of GSK3beta regulation.

Regulation of Xenopus p21-activated kinase (X-PAK2) by Cdc42 and maturation-promoting factor controls Xenopus oocyte maturation

Signal transduction cascades involved in regulation of the cell cycle machinery are poorly understood. In the Xenopus oocyte model, meiotic maturation is triggered by MPF, a complex of p34(cdc2)-cyclin B, which is activated in response to a progesterone signal by largely unknown mechanisms. We have previously shown that the p21-activated kinase (PAK) family negatively regulates the MPF amplification loop. In this study, we identify the endogenous PAK2 as a key enzyme in this regulation and describe the pathways by which PAK2 is regulated. We show that the small GTPase Cdc42 is required for maintenance of active endogenous X-PAK2 in resting stage VI oocytes, whereas Rac1 is not involved in this regulation. During the process of maturation, X-PAK2 phosphorylation results in its inactivation and allows maturation to proceed to completion. Activation of mitogen-activated protein kinase and cyclin B-p34(cdc2) is coincident with X-PAK2 inactivation, and purified active MPF inhibits X-PAK2, demonstrating the existence of a new positive feedback loop. Our results confirm and extend the importance of p21-activated kinases in the control of the G(2)/M transition. We hypothesize that the X-PAK2/Cdc42 pathway could link p34(cdc2) activity to the major cytoskeleton rearrangements leading to spindle migration and anchorage to the animal pole cortex.

Dissociation of MAP kinase activation and MPF activation in hormone-stimulated maturation of Xenopus oocytes

MAP kinase activation occurs during meiotic maturation of oocytes from all animals, but the requirement for MAP kinase activation in reinitiation of meiosis appears to vary between different classes. In particular, it has become accepted that MAP kinase activation is necessary for progesterone-stimulated meiotic maturation of Xenopus oocytes, while this is clearly not the case in other systems. In this paper, we demonstrate that MAP kinase activation in Xenopus oocytes is an early response to progesterone and can be temporally dissociated from MPF activation. We show that MAP kinase activation can be suppressed by treatment with geldanamycin or by overexpression of the MAP kinase phosphatase Pyst1. A transient and low-level early activation of MAP kinase increases the efficiency of cell cycle activation later on, when MAP kinase activity is no longer essential. Many oocytes can still undergo reinitiation of meiosis in the absence of active MAP kinase. Suppression of MAP kinase activation does not affect the formation or activation of Cdc2-cyclin B complexes, but reduces the level of active Cdc2 kinase. We discuss these findings in the context of a universal mechanism for meiotic maturation in oocytes throughout the animal kingdom.