From oogenesis through gastrulation: developmental regulation of apoptosis

[Lack of GAGA protein in Trl mutants causes massive cell death in Drosophila spermatogenesis and oogenesis]

Белок дрозофилы GAGA (GAF) является фактором эпигенетической регуляции транскрипции большой группы генов с широким разнообразием клеточных функций. GAF кодируется геном Trithorax-like (Trl), который экспрессируется в различных органах и тканях на всех стадиях онтогенеза дрозофилы. Мутации этого гена вызывают множественные нарушения развития. В предыдущих работах мы показали, что этот белок необходим для развития половой системы как самцов, так и самок дрозофилы. Снижение экспрессии гена Trl приводило ко множественным нарушениям спермато- и оогенеза. Одно из значительных нарушений было связано с массовой деградацией и потерей клеток зародышевого пути, что позволило предположить, что этот белок вовлечен в регуляцию клеточной гибели. В представленной работе мы провели более детальное цитологическое исследование, чтобы определить, какой тип гибели клеток зародышевого пути характерен для Trl-мутантов, и происходят ли нарушения или изменения этого процесса по сравнению с нормой. Полученные результаты показали, что недостаток белка GAF вызывает массовую гибель клеток зародышевого пути как у самок, так и самцов дрозофилы, но проявляется эта гибель в зависимости от пола по-разному. У самок, мутантных по гену Trl, фенотипически этот процесс не отличается от нормы и в гибнущих яйцевых камерах выявлены признаки апоптоза и аутофагии клеток зародышевого пути. У самцов, мутантных по гену Trl, в отличие от самок, не обнаружены признаки апоптоза. У самцов мутации Trl индуцируют массовую гибель клеток через аутофагию, что не характерно для сперматогенеза дрозофилы и не описано ранее ни в норме, ни у мутаций по другим генам. Таким образом, недостаток GAF у мутантов Trl приводит к усилению апоптотической и аутофагической гибели клеток зародышевого пути. Эктопическая клеточная гибель и атрофия зародышевой линии, вероятно, связаны с нарушением экспрессии генов-мишеней GAGAфактора, среди которых есть гены, регулирующие как апоптоз, так и аутофагию.

Loss of Drosophila E3 Ubiquitin Ligase Hyd Promotes Extra Mitosis in Germline Cysts and Massive Cell Death During Oogenesis

The Drosophila hyperplastic disc (hyd) gene is the ortholog of mammalian tumor suppressor EDD, which is implicated in a wide variety of cellular processes, and its regulation is impaired in various tumors. It is a member of the highly conserved HECT family of E3 ubiquitin ligases, which directly attach ubiquitin to targeted substrates. In early works, it was shown that Drosophila Hyd may be a tumor suppressor because it is involved in the control of imaginal-disc cell proliferation and growth. In this study, we demonstrated that Hyd is also important for the regulation of female germ cell proliferation and that its depletion leads to additional germline cell mitoses. Furthermore, we revealed a previously unknown Hyd function associated with the maintenance of germ cells' viability. A reduction in hyd expression by either mutations or RNA interference resulted in large-scale germ cell death at different stages of oogenesis. Thus, the analysis of phenotypes arising from the hyd deficiency points to Hyd's role in the regulation of germline metabolic processes during oogenesis.

Fluoride impairs ovary development by affecting oogenesis and inducing oxidative stress and apoptosis in female zebrafish (Danio rerio)

Previous studies have shown that waterborne fluoride exposure has adverse effects on the reproductive system of zebrafish. However, the underlying toxic mechanisms were still not clear. In the present study, female zebrafish were exposed to different concentrations of 0.787 (Control), 18.599, 36.832 mg/L of fluoride for 30 d and 60 d, and the effects of different doses of fluoride on ovary development, reproductive hormones, oogenesis, ROS content, antioxidant levels, and the expression of apoptosis-related genes and proteins in the ovaries of female zebrafish were analyzed. The results showed that ovarian weight and GSI were significantly decreased, FSH, LH and VTG levels were significantly reduced, the transcriptional profiles of oogenesis-related genes (tgfβ1, bmp15, gdf9, mprα, mprβ, ptg2β) were remarkably altered, ROS levels was notably increased, the SOD, CAT, GPx activities and GSH content as well as their mRNA expressions were significantly decreased, MDA content was remarkably increased, the expressions of apoptosis-related genes and proteins (caspase3, caspase8, caspase9, Fas-L, Cytochrome C, Bax and Bcl-2) were significantly changed, the ratio of Bax/Bcl-2 protein levels were notably increased. Taken together, this study demonstrated that fluoride exposure significantly affected ovarian development, decreased the reproductive hormones, affected oogenesis, induced oxidative stress, caused apoptosis through both extrinsic and intrinsic pathways in ovary of zebrafish. Indicating that oogenesis, oxidative stress, and apoptosis were responsible for the impairment of ovarian development.

Developmental dynamics of cloned Mexican bighorn sheep embryos using morphological quality standards

The developmental dynamics of cloned Mexican bighorn sheep (Ovis canadensis mexicana) embryos were evaluated based on morphological quality standards. Categories determined by standards were correlated with the embryonic development stage, number of nuclei and viability. The results showed no differences in the blastocyst rate between the experimental (cloned Mexican bighorn sheep embryos) and control (parthenogenetic domestic sheep embryos) groups (p > .05), while type IV fragmentation was higher in clones (p < .05). The standards allowed for the identification of embryos that divided at least once or fragmented after 24 hr of culture. The highest percentage of morulae appeared at 96 hr, the final stages of development: nonsegmented, blocked, fragmented and blastocysts appeared at 192 hr. Embryonic quality decreased over time, making 96 hr the ideal time point to predict the final morphological quality of embryos. Nuclear staining of the morulae and blastocysts showed that higher embryo quality was associated with a higher percentage of normal and viable blastomeres. The evaluated criteria allowed for descriptions of the dynamics, stage and quality of cloned Mexican bighorn sheep embryos with a high degree of reliability. In addition, developmental anomalies, including fragmentation, multinucleation and blocking, were identified.

The maternal control in the embryonic development of zebrafish

The maternal control directing the very first hours of life is of pivotal importance for ensuring proper development to the growing embryo. Thanks to the finely regulated inheritance of maternal factors including mRNAs and proteins produced during oogenesis and stored into the mature oocyte, the embryo is sustained throughout the so-called maternal-to-zygotic transition, a period in development characterized by a species-specific length in time, during which critical biological changes regarding cell cycle and zygotic transcriptional activation occur. In order not to provoke any kind of persistent damage, the process must be delicately balanced. Surprisingly, our knowledge as to the possible effects of beneficial bacteria regarding the modulation of the quality and/or quantity of both maternally-supplied and zygotically-transcribed mRNAs, is very limited. To date, only one group has investigated the consequences of the parentally-supplied Lactobacillus rhamnosus on the storage of mRNAs into mature oocytes, leading to an altered maternal control process in the F1 generation. Particular attention was called on the monitoring of several biomarkers involved in autophagy, apoptosis and axis patterning, while data on miRNA generation and pluripotency maintenance are herein presented for the first time, and can assist in laying the ground for further investigations in this field. In this review, the reader is supplied with the current knowledge on the above-mentioned biological process, first by drawing the general background and then by emphasizing the most important findings that have highlighted their focal role in normal animal development.

Autophagy is required for sea urchin oogenesis and early development

Autophagy is a major intracellular pathway for the degradation and recycling of cytosolic components. Emerging evidence has demonstrated its crucial role during the embryo development of invertebrates and vertebrates. We recently demonstrated a massive activation of autophagy in Paracentrotus lividus embryos under cadmium stress conditions, and the existence of a temporal relationship between induced autophagy and apoptosis. Although there have been numerous studies on the role of autophagy in the development of different organisms, information on the autophagic process during oogenesis or at the start of development in marine invertebrates is very limited. Here we report our recent data on the occurrence of autophagy at these key phases of development. In order to investigate autophagy trends we performed in vivo assays to detect autophagolysomes, as well as in situ analysis with anti-LC3 antibody to detect autophagosomes before the fusion with lysosomes. From data generated through confocal laser scanning microscopy and quantification of autophagic signals we have drawn several unequivocal conclusions. The results showed a copious and rising number of autophagic organelles that had specific localization. Interestingly the increase in autophagy that occurred just after fertilization has been proved to be crucial for correct initiation of the developmental programme: irreversible developmental delays and morphologic anomalies were induced by short autophagic inhibition. This work focused on the sea urchin model system and corroborates evidence on the need for self-digestion during development, enriching the knowledge on autophagy, a biological mechanism belonging to evolutionarily different organisms.

Parental exposure to natural mixtures of persistent organic pollutants (POP) induced changes in transcription of apoptosis-related genes in offspring zebrafish embryos

Apoptosis is an integral element of development that may also be initiated by environmental contaminants. The aim of the present study was to assess potential changes in the regulation of apoptotic genes in zebrafish embryos following parental exposure to two natural mixtures of persistent organic pollutants (POP). The mixture from Lake Mjøsa contained exceptionally high concentrations of polybrominated diphenyl ethers (PBDE), as well as relatively high levels of polychlorinated biphenyls (PCB) and dichlorodiphenyltrichloroethane (DDT). The mixture from Lake Losna contained background concentrations of POP. Genes involved in the apoptotic machinery were screened for their expression profile at four time points during embryonic development. Thirteen and 15 genes involved in apoptosis were found to be significantly upregulated in the high-exposure and background exposure groups, respectively, compared with controls. Modulation of apoptotic genes was restricted only to the first time point, which corresponds with the blastula stage. Although there were substantial differences in POP concentrations between mixtures, genes underlying the apoptosis process showed almost similar responses to the two mixtures. In both exposure groups the main executors of apoptosis p53, casp 2, casp 6, cassp 8, and BAX displayed upregulation compared to controls, suggesting that these POP induce apoptosis via a p53-dependent mechanism. Upregulation of genes that play a critical role in apoptosis suggests that disturbance of normal apoptotic signaling during gametogenesis and embryogenesis may be one of the central mechanisms involved in adverse reproductive effects produced by POP in zebrafish.

Enhanced UV-B radiation during pupal stage reduce body mass and fat content, while increasing deformities, mortality and cell death in female adults of solitary bee Osmia bicornis

The effects of enhanced UV-B radiation on the oogenesis and morpho-anatomical characteristics of the European solitary red mason bee Osmia bicornis L. (Hymenoptera: Megachilidae) were tested under laboratory conditions. Cocooned females in the pupal stage were exposed directly to different doses (0, 9.24, 12.32, and 24.64 kJ/m(2) /d) of artificial UV-B. Our experiments revealed that enhanced UV-B radiation can reduce body mass and fat body content, cause deformities and increase mortality. Following UV exposure at all 3 different doses, the body mass of bees was all significantly reduced compared to the control, with the highest UV dose causing the largest reduction. Similarly, following UV-B radiation, in treated groups the fat body index decreased and the fat body index was the lowest in the group receiving the highest dose of UV radiation. Mortality and morphological deformities, between untreated and exposed females varied considerably and increased with the dose of UV-B radiation. Morphological deformities were mainly manifested in the wings and mouthparts, and occurred more frequently with an increased dose of UV. Cell death was quantified by the Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay (DNA fragmentation) during early stages of oogenesis of O. bicornis females. The bees, after UV-B exposure exhibited more germarium cells with fragmented DNA. The TUNEL test indicated that in germarium, low doses of UV-B poorly induced the cell death during early development. However, exposure to moderate UV-B dose increased programmed cell death. In females treated with the highest dose of UV-B the vast majority of germarium cells were TUNEL-positive.

Subtractive phage display technology identifies zebrafish marcksb that is required for gastrulation

In the present study, we used a phage display technique to screen differentially expressed proteins from zebrafish post-gastrula embryos. With a subtractive screening approach, 6 types of single-chain Fv fragments (scFvs) were screened out from an scFv antibody phage display library by biopanning against zebrafish embryonic homogenate. Four scFv fragments (scFv1, scFv3, scFv4 and scFv6) showed significantly stronger binding to the tailbud embryos than to the 30%-epiboly embryos. A T7 phage display cDNA library was constructed from zebrafish tailbud embryos and used to identify the antigens potentially recognized by scFv1, which showed the highest frequency and strongest binding against the tailbud embryos. We acquired 4 candidate epitopes using scFv1 and the corresponding genes showed significantly higher expression levels at tailbud stage than at 30%-epiboly. The most potent epitope of scFv1 was the clone scFv1-2, which showed strong homology to zebrafish myristoylated alanine-rich C-kinase substrate b (Marcksb). Western blot analysis confirmed the high expression of marcksb in the post-gastrula embryos, and the endogenous expression of Marcksb was interfered by injection of scFv1. Zebrafish marcksb showed dynamic expression patterns during embryonic development. Knockdown of marcksb strongly affected gastrulation movements. Moreover, we revealed that zebrafish marcksb is required for cell membrane protrusion and F-actin alignment. Thus, our study uncovered 4 types of scFvs binding to zebrafish post-gastrula embryos, and the epitope of scFv1 was found to be required for normal gastrulation of zebrafish. To our knowledge, this was the first attempt to combine phage display technique with the embryonic and developmental study of vertebrates, and we were able to identify zebrafish marcksb that was required for gastrulation.

Monoamine oxidases in development

Monoamine oxidases (MAOs) are flavoproteins of the outer mitochondrial membrane that catalyze the oxidative deamination of biogenic and xenobiotic amines. In mammals there are two isoforms (MAO-A and MAO-B) that can be distinguished on the basis of their substrate specificity and their sensitivity towards specific inhibitors. Both isoforms are expressed in most tissues, but their expression in the central nervous system and their ability to metabolize monoaminergic neurotransmitters have focused MAO research on the functionality of the mature brain. MAO activities have been related to neurodegenerative diseases as well as to neurological and psychiatric disorders. More recently evidence has been accumulating indicating that MAO isoforms are expressed not only in adult mammals, but also before birth, and that defective MAO expression induces developmental abnormalities in particular of the brain. This review is aimed at summarizing and critically evaluating the new findings on the developmental functions of MAO isoforms during embryogenesis.

The apoptotic regulator Nrz controls cytoskeletal dynamics via the regulation of Ca2+ trafficking in the zebrafish blastula

Bcl-2 family members are key regulators of apoptosis. Their involvement in other cellular processes has been so far overlooked. We have studied the role of the Bcl-2 homolog Nrz in the developing zebrafish. Nrz was found to be localized to the yolk syncytial layer, a region containing numerous mitochondria and ER membranes. Nrz knockdown resulted in developmental arrest before gastrulation, due to free Ca(2+) increase in the yolk cell, activating myosin light chain kinase, which led to premature contraction of actin-myosin cables in the margin and separation of the blastomeres from the yolk cell. In the yolk syncytial layer, Nrz appears to prevent the release of Ca(2+) from the endoplasmic reticulum by directly interacting with the IP3R1 Ca(2+) channel. Thus, the Bcl-2 family may participate in early development, not only by controlling apoptosis but also by acting on cytoskeletal dynamics and cell movements via Ca(2+) fluxes inside the embryo.

Normal levels of p27 are necessary for somite segmentation and determining pronephric organ size

The Xenopus laevis cyclin dependent kinase inhibitor p27(Xic1) has been shown to be involved in exit from the cell cycle and differentiation of cells into a quiescent state in the nervous system, muscle tissue, heart and retina. We show that p27(Xic1) is expressed in the developing kidney in the nephrostomal regions. Using overexpression and morpholino oligonucleotide (MO) knock-down approaches we show normal levels of p27(Xic1) regulate pronephros organ size by regulating cell cycle exit. Knock-down of p27(Xic1) expression using a MO prevented myogenesis, as previously reported; an effect that subsequently inhibits pronephrogenesis. Furthermore, we show that normal levels of p27(Xic1) are required for somite segmentation also through its cell cycle control function. Finally, we provide evidence to suggest correct paraxial mesoderm segmentation is not necessary for pronephric induction in the intermediate mesoderm. These results indicate novel developmental roles for p27(Xic1), and reveal its differentiation function is not universally utilised in all developing tissues.

Apoptosis: Focus on sea urchin development

It has been proposed that the apoptosis is an essential requirement for the evolution of all animals, in fact the apoptotic program is highly conserved from nematodes to mammals. Throughout development, apoptosis is employed by multicellular organisms to eliminate damaged or unnecessary cells. Here, we will discuss both developmental programmed cell death (PCD) under normal conditions and stress induced apoptosis, in sea urchin embryos. Sea urchin represent an excellent model system for studying embryogenesis and cellular processes involved in metamorphosis. PCD plays an essential role in sculpting and remodelling the embryos and larvae undergoing metamorphosis. Moreover, this marine organism directly interacts with its environment, and is susceptible to effects of several aquatic contaminants. Apoptosis can be adopted as a defence mechanism against any environmental chemical, physical and mechanical stress, for removing irreversibly damaged cells. This review, while not comprehensive in its reporting, aims to provide an overview of current knowledge on mechanisms to regulate physiological and the induced apoptotic program in sea urchin embryos.

The genetics and cell biology of Wolbachia-host interactions

Wolbachia are gram-negative bacteria that are widespread in nature, carried by the majority of insect species as well as some mites, crustaceans, and filarial nematodes. Wolbachia can range from parasitic to symbiotic, depending upon the interaction with the host species. The success of Wolbachia is attributed to efficient maternal transmission and manipulations of host reproduction that favor infected females, such as sperm-egg cytoplasmic incompatibility (CI). Much remains unknown about the mechanistic basis for Wolbachia-host interactions. Here we summarize the current understanding of Wolbachia interaction with insect hosts, with a focus on Drosophila. The areas of discussion include Wolbachia transmission in oogenesis, Wolbachia distribution in spermatogenesis, induction and rescue of the CI phenotype, Wolbachia genomics, and Wolbachia-membrane interactions.

A distinct H2A.X isoform is enriched in Xenopus laevis eggs and early embryos and is phosphorylated in the absence of a checkpoint

Histone H2A.X is an H2A variant present in multicellular organisms that is specifically phosphorylated on the serine in the C-terminal consensus sequence, canonically "SQEY," in response to DNA damage. We have recently shown the significance of phosphorylation of the penultimate tyrosine for maintenance and processing of the DNA damage response in mammalian cells. Here, we report the identification of distinct H2A.X variants in the eggs and early embryos of the frog Xenopus laevis that contain a C-terminal SQEF, among other changes; we have denoted these proteins as "H2A.X-F." H2A.X-F is present only in late-staged oocytes, eggs, and premidblastula transition embryos and is not present in somatic cells. Similar unannotated isoforms were identified in other rapidly developing aquatic species, such as Xenopus tropicalis, goldfish, and zebrafish, and in Arabidopsis and chickpea. Furthermore, we demonstrate by mass spectrometry and phospho-specific antibodies that H2A.X-F is phosphorylated in the absence of exogenous DNA damage, in both actively dividing, unperturbed embryos and cell-free egg extract in the absence and presence of DNA damage and S-phase checkpoint conditions. We propose that this isoform may be involved in modulating the cellular response to the rapid early cell cycles in externally developing species.

Journey to the grave: signaling events regulating removal of apoptotic cells

Programmed cell death is critical both for organ formation during development and during adult life, when billions of cells must be removed every day. The culmination of the apoptotic process is the specific recognition and engulfment of the apoptotic cell by a phagocyte. A number of recent studies have revealed a series of evolutionarily conserved proteins that link corpse recognition to membrane movement, facilitating the internalization of the target and its subsequent degradation. Two potential signaling modules have been identified: one involving the CED-12/ELMO and CED-5/Dock180 proteins, which function as a bipartite guanine nucleotide exchange factor (GEF) for Rac1, and a second involving CED-1/LRP1 (a potential engulfment receptor) and the adaptor protein CED-6/GULP. Recognition of the apoptotic cell modulates cytokine secretion by the phagocyte, resulting in an anti-inflammatory state distinct from that induced by necrotic cells. The recent molecular delineation of the phagocytic process and the identification of novel signaling proteins involved in engulfment have provided an exciting new platform for future studies into this biologically important process.

Overexpression of repulsive guidance molecule (RGM) a induces cell death through Neogenin in early vertebrate development

Repulsive guidance molecule (RGM) a is a glycosylphosphatidylinositol (GPI)-anchored plasma membrane protein that has been implicated in chemorepulsive axon guidance. Although RGMa binds the transmembrane receptor Neogenin, the developmental events controlled by the RGMa-Neogenin interactions in vivo remain largely unknown. We have cloned full-length RGMa from Xenopus borealis for the first time and identified two homologous genes referred to as RGMa1 and RGMa2. Here we show RGMa1 overexpression at 2-cell-stage resulted in cell death, which lead to an early embryonic lethal phenotype of the embryos. Time-lapse photomicroscopy revealed that embryos began to show initial morphological defects from approximately 5 h post-fertilization (hpf) which was then followed by extensive blastomere cell death at approximately 11 hpf. This phenotype was rescued by simultaneous knock down of RGMa using translation blocking anti-sense morpholinos. Knock down of the RGMa1 receptor Neogenin in RGMa1 overexpressing embryos was also able to rescue the phenotype. Together these results indicated that RGMa1 was signalling through Neogenin to induce cell death in the early embryo. While previous studies have suggested that Neogenin is a dependence receptor that induces cell death in the absence of RGM, we have instead shown that Neogenin-RGM interactions induce cell death in the early embryo. The roles of RGMa1 and Neogenin appear to be context specific so that their co-ordinated and regulated expressions are essential for normal development of the vertebrate embryo.

The Drosophila nucleoporin gene nup154 is required for correct microfilament dynamics and cell death during oogenesis

The Drosophila nucleoporin gene nup154 is required in both male and female germline for successful gametogenesis. Mutant flies lack differentiated sperm and lay abnormal eggs. We demonstrated that the egg phenotype was associated with specific alterations of the actin cytoskeleton at different stages of oogenesis. Actually, mutant egg chambers displayed an abnormal organization of both subcortical microfilaments and cytoplasmic actin bundles, that led to defective nurse cell dumping. TUNEL analysis also showed that the dumpless phenotype was associated with delayed apoptosis. The nup154 gene product was localized by conventional immunofluorescence microscopy to the nuclear envelope in a distinct punctuate pattern, characteristic of nuclear pore complex components. TEM analysis revealed that the protein was mainly distributed along filamentous structures that extended radially on the nuclear side of the pore, suggesting that Nup154 could be an integral component of the basket filaments associated with the nuclear pore complexes. We propose that Nup154 is necessary for correct nuclear pore complex functions and that the proper regulation of the actin cytoskeleton dynamics strongly relies upon nuclear pore integrity.

Disruption of the dynamic sub-cellular localization of the Xenopus tumorhead protein causes embryonic lethality at the early gastrula transition

The Xenopus laevis tumorhead (TH) protein, a positive regulator of cell proliferation during embryogenesis, shuttles from the cell periphery into the nucleus during embryogenesis. In these studies, we performed a detailed analysis of TH's subcellular localization pattern to characterize its dynamic behavior. We found that TH exhibits distinct patterns of localization in different germ layers. At the blastula stage, TH is present in the apical cell periphery of prospective mesodermal and ectodermal cells. At the gastrula stage, TH is distributed throughout the entire cytoplasm of prospective mesodermal and ectodermal cells, whereas it shows nuclear localization in presumptive endodermal cells. TH moves into the nucleus of mesodermal and ectodermal cells during the neurula and early tailbud stages. To understand if TH is regulated by changes in its subcellular localization, we used a TH mutant containing signals for farnesylation and palmitoylation to tether the protein to the plasma membrane. Ubiquitous overexpression of this mutant causes embryonic lethality at the early gastrula transition. Further examination using TUNEL assays indicated that wild-type TH overexpression induces apoptosis during gastrulation, and that this effect is exacerbated by the overexpression of the membrane-bound TH mutant. Taken together, our results suggest that changes in the sub-cellular localization of the TH protein are important for its function because blocking the nuclear translocation of overexpressed TH increases apoptosis and causes embryos to die. Our data also suggest that TH plays a role outside the nucleus when it is present at the cell periphery.

p42MAPK-mediated phosphorylation of xEIAP/XLX in Xenopus cytostatic factor-arrested egg extracts

BACKGROUND

BIR family proteins are evolutionarily conserved anti-apoptotic molecules. One member of Xenopus BIR family proteins, xEIAP/XLX, is a weak apoptosis inhibitor and rapidly degraded in a cell-free apoptotic execution system derived from interphase egg extracts. However, unfertilized eggs are naturally arrested at the metaphase of meiosis II by the concerted activities of Mos-MEK-p42MAPK-p90Rsk kinase cascade (cytostatic factor pathway) and many mitotic kinases. Previous studies suggest that cytostatic factor-arrested egg extracts are more resistant to spontaneous apoptosis than interphase egg extracts in a p42MAPK-dependent manner. We tested whether xEIAP/XLX might be phosphorylated in cytostatic factor-arrested egg extracts, and also examined whether xEIAP/XLX could be functionally regulated by phosphorylation.

RESULTS

We found that p42MAPK was the major kinase phosphorylating xEIAP/XLX in cytostatic factor-arrested egg extracts, and three Ser residues (Ser 235/251/254) were identified as p42MAPK-mediated phosphorylation sites. We characterized the behaviors of various xEIAP/XLX mutants that could not be phosphorylated by p42MAPK. However, neither protein stability nor anti-apoptotic ability of xEIAP/XLX was significantly altered by the substitution of Ser with either Ala or Asp at these three sites.

CONCLUSION

xEIAP/XLX is physiologically phosphorylated by p42MAPK in Xenopus unfertilized eggs. However, this protein may not serve as an essential mediator of p42MAPK-dependent anti-apoptotic activity.

Checkpoint-apoptosis uncoupling in human and mouse embryonic stem cells: a source of karyotpic instability

Karyotypic abnormalities in cultured embryonic stem cells (ESCs), especially near-diploid aneuploidy, are potential obstacles to ESC use in regenerative medicine. Events causing chromosomal abnormalities in ESCs may be related to events in tumor cells causing chromosomal instability (CIN) in human disease. However, the underlying mechanisms are unknown. Using multiparametric permeabilized-cell flow cytometric analysis, we found that the mitotic-spindle checkpoint, which helps maintain chromosomal integrity during all cell divisions, functions in human and mouse ESCs, but does not initiate apoptosis as it does in somatic cells. This allows an unusual tolerance to polyploidy resulting from failed mitosis, which is common in rapidly proliferating cell populations and which is reduced to near-diploid aneuploidy, which is also common in human neoplastic disease. Checkpoint activation in ESC-derived early-differentiated cells results in robust apoptosis without polyploidy/aneuploidy similar to that in somatic cells. Thus, the spindle checkpoint is "uncoupled" from apoptosis in ESCs and is a likely source of karyotypic abnormalities. This natural behavior of ESCs to tolerate/survive varying degrees of ploidy change could complicate genome-reprogramming studies and stem-cell plasticity studies, but could also reveal clues about the mechanisms of CIN in human tumors.

The role of mitochondrial function in the oocyte and embryo

Mitochondria have long been known to be the powerhouses of the cell but they also contribute to redox and Ca2+ homeostasis, provide intermediary metabolites and store proapoptotic factors. Mitochondria have a unique behavior during development. They are maternally transmitted with little (if any) paternal contribution, and they originate from a restricted founder population, which is amplified during oogenesis. Then, having established the full complement of mitochondria in the fully grown oocyte, there is no further increase of the mitochondrial population during early development. The localization of mitochondria in the egg during maturation and their segregation to blastomeres in the cleaving embryo are strictly regulated. Gradients in the distribution of mitochondria present in the egg have the potential to give rise to blastomeres receiving different numbers of mitochondria. Such maternally inherited differences in mitochondrial distribution are thought to play roles in defining the long-term viability of the blastomere in some cases and embryonic axes and patterning in others. Mitochondria may also regulate development by a number of other means, including modulating Ca2+ signaling, and the production of ATP, reactive oxygen species, and intermediary metabolites. If the participation of mitochondria in the regulation of sperm-triggered Ca2+ oscillations is now well established, the role of other properties of mitochondrial function during development remain largely unexplored probably due to the difficulty of accessing the mitochondrial compartment in an embryo. Maintaining a functional complement of maternally derived mitochondria is vital for the early embryo. Mitochondrial dysfunction may not only compromise developmental processes but also trigger apoptosis in the embryo. This dual role for mitochondria (to maintain life or to commit to cell death) may well represent a quality control system in the early embryo that will determine whether the embryo proceeds further into development or is quickly eliminated.

Antioxidant metabolism of Xenopus laevis embryos during the first days of development

Reactive oxygen species (ROS) are formed and degraded in all aerobic organisms, but their role during embryonic development has not yet been well established. In this paper, we report the activities of various enzymes involved in antioxidant metabolism during the first 7 days of embryonic development of Xenopus laevis embryos. During the first two days of development, embryo antioxidant metabolism is based on catalase and superoxide dismutase activities. Later, the glutathione system is activated, and the activity of all the enzymes involved increases. The results presented in this study, together with previously reported data, support the hypothesis that antioxidant defences may include enzymes that are genetically regulated, while the other systems that appear to be environmentally modulated become relevant later in development, probably to protect embryos from environmental and toxic factors.

Cell death induced by GSM 900-MHz and DCS 1800-MHz mobile telephony radiation

In the present study, the TUNEL (Terminal deoxynucleotide transferase dUTP Nick End Labeling) assay--a well known technique widely used for detecting fragmented DNA in various types of cells--was used to detect cell death (DNA fragmentation) in a biological model, the early and mid stages of oogenesis of the insect Drosophila melanogaster. The flies were exposed in vivo to either GSM 900-MHz (Global System for Mobile telecommunications) or DCS 1800-MHz (Digital Cellular System) radiation from a common digital mobile phone, for few minutes per day during the first 6 days of their adult life. The exposure conditions were similar to those to which a mobile phone user is exposed, and were determined according to previous studies of ours [D.J. Panagopoulos, A. Karabarbounis, L.H. Margaritis, Effect of GSM 900-MHz mobile phone radiation on the reproductive capacity of D. melanogaster, Electromagn. Biol. Med. 23 (1) (2004) 29-43; D.J. Panagopoulos, N. Messini, A. Karabarbounis, A.L. Philippetis, L.H. Margaritis, Radio frequency electromagnetic radiation within "safety levels" alters the physiological function of insects, in: P. Kostarakis, P. Stavroulakis (Eds.), Proceedings of the Millennium International Workshop on Biological Effects of Electromagnetic Fields, Heraklion, Crete, Greece, October 17-20, 2000, pp. 169-175, ISBN: 960-86733-0-5; D.J. Panagopoulos, L.H. Margaritis, Effects of electromagnetic fields on the reproductive capacity of D. melanogaster, in: P. Stavroulakis (Ed.), Biological Effects of Electromagnetic Fields, Springer, 2003, pp. 545-578], which had shown a large decrease in the oviposition of the same insect caused by GSM radiation. Our present results suggest that the decrease in oviposition previously reported, is due to degeneration of large numbers of egg chambers after DNA fragmentation of their constituent cells, induced by both types of mobile telephony radiation. Induced cell death is recorded for the first time, in all types of cells constituting an egg chamber (follicle cells, nurse cells and the oocyte) and in all stages of the early and mid-oogenesis, from germarium to stage 10, during which programmed cell death does not physiologically occur. Germarium and stages 7-8 were found to be the most sensitive developmental stages also in response to electromagnetic stress induced by the GSM and DCS fields and, moreover, germarium was found to be even more sensitive than stages 7-8.

Differential subcellular sequestration of proapoptotic and antiapoptotic proteins and colocalization of Bcl-xL with the germ plasm, inXenopus laevis oocytes

Apoptosis is an important element of normal embryonic development and gametogenesis in invertebrate and vertebrate species. Although the components of apoptotic machinery are present in Xenopus laevis fully grown stage VI oocytes and eggs, apoptosis in the developing Xenopus ovary is limited to the somatic cells with no indication of apoptosis in the germ cells. Considering the possibility that Xenopus previtellogenic oocytes might lack the components of the apoptotic pathway, we analyzed Xenopus Stage I oocytes for the presence of the proapoptotic factors Bax and tumor suppressor p53, and antiapoptotic factors Bcl-x(L) and mitochondrial heat shock protein 60 (Hsp60). We found that pro- and antiapoptotic proteins are present in Xenopus oocytes but, surprisingly, they are located in distinct subcellular compartments with proapoptotic proteins Bax and p53 being sequestered in the oocyte nucleus and antiapoptotic protein Bcl-x(L) sequestered in the cytoplasm and highly enriched in the METRO region of the mitochondrial cloud, where it colocalized with the germ plasm, and Hsp60 colocalizing with all mitochondria. The absence of apoptosis in Xenopus early oogenesis is maybe due to differential sequestration of pro- and antiapoptotic molecules.

XLX is an IAP family member regulated by phosphorylation during meiosis

The balance between proliferation and cell death is critical for embryonic development and adult tissue homeostasis. Within an individual cell, coordination of these pathways is aided by direct communication between cell cycle factors and molecules that regulate apoptosis. Here, we show that XLX, a Xenopus laevis inhibitor of apoptosis (IAP) family member, exhibits characteristics typical of an IAP, such as caspase inhibition and autoubiquitylation. However, unlike other IAPs described thus far, we found that XLX is phosphorylated during meiosis by protein kinases that belong to the MAPK and MPF pathways. Finally, we show that caspase-dependent cleavage of XLX is altered when XLX is phosphorylated. In addition to furthering our understanding of the post-translational regulation of an IAP, these findings reveal a novel link between cell cycle-regulated protein kinases and a component potentially involved in apoptosis.

Yaf2 inhibits caspase 8-mediated apoptosis and regulates cell survival during zebrafish embryogenesis

Rybp (DEDAF) is a member of the Rybp/Yaf2 protein family and has been shown to encode pro-apoptotic functions and to be essential for mouse embryogenesis. The related Yaf2 protein has not been studied extensively at the cellular or organismal levels. Here we describe zebrafish yaf2 (zyaf2) and show that it is widely expressed during early embryogenesis, with subsequent enrichment of transcripts in the anterior head region. Depletion of zYaf2 during embryogenesis using specific morpholinos activates a wide-spread program of apoptosis and causes developmental arrest before the one somite stage. Partial depletion of Yaf2, achieved by injecting lower dosages of morpholino, circumvents the early arrest but leads to CNS degeneration associated with excessive apoptosis. These phenotypes can be rescued by co-injection of human YAF2 mRNA with the morpholinos or by treatment with a pan-caspase inhibitor or a caspase 8-specific inhibitor. Finally, the observed activation of caspase 8 in the morphants is in accord with the ability of Yaf2 to inhibit caspase 8-mediated apoptosis in cultured cells. Our findings implicate Yaf2 as a survival factor during early zebrafish development and organogenesis. This may suggest that Yaf2 and Rybp can encode opposing functions in the regulation of apoptosis.

Programmed cell death in the germline

In many organisms, programmed cell death of germ cells is required for normal development. This often occurs through highly conserved events including the transfer of vital cellular material to the growing gametes following death of neighboring cells. Germline cell death also plays a role in such diverse processes as removal of abnormal or superfluous cells at certain checkpoints, establishment of caste differentiation, and individualization of gametes. This review focuses on the cell death events that occur during gametogenesis in both vertebrates and invertebrates. It also examines the signals and machinery that initiate and carry out these germ cell deaths.