The mammalian centrosome and its functional significance

The distribution and possible role of ERK8 in mouse oocyte meiotic maturation and early embryo cleavage

It is well known that extracellular signal-regulated kinase 8 (ERK8) plays pivotal roles in various mitotic events. But its physiological roles in oocyte meiotic maturation remain unclear. In this study, we found that although no specific ERK8 signal was detected in oocyte at the germinal vesicle stage, ERK8 began to migrate to the periphery of chromosomes shortly after germinal vesicle breakdown. At prometaphase I, metaphase I (MI), anaphase I, telophase I, and metaphase II (MII) stages, ERK8 was stably detected at the spindles. By taxol treatment, we clarified that the ERK8 signal was stained on the spindle fibers as well as microtubule asters in MI and MII oocytes. In fertilized eggs, the ERK8 signal was not observed in the two pronuclei stages. At prometaphase, metaphase, and anaphase of the first mitosis, ERK8 was detected on the mitotic spindle. ERK8 knock down by antibody microinjection and specific siRNA caused abnormal spindles, failed chromosome congression, and decreased first polar body extrusion. Taken together, our results suggest that ERK8 plays an important role in spindle organization during mouse oocyte meiotic maturation and early embryo cleavage.

WHAMM is required for meiotic spindle migration and asymmetric cytokinesis in mouse oocytes

WASP homolog associated with actin, membranes and microtubules (WHAMM) is a newly discovered nucleation-promoting factor that links actin and microtubule cytoskeleton and regulates transport from the endoplasmic reticulum to the Golgi apparatus. However, knowledge of WHAMM is limited to interphase somatic cells. In this study, we examined its localization and function in mouse oocytes during meiosis. Immunostaining showed that in the germinal vesicle (GV) stage, there was no WHAMM signal; after meiosis resumption, WHAMM was associated with the spindle at prometaphase I (Pro MI), metaphase I (MI), telophase I (TI) and metaphase II (MII) stages. Nocodazole and taxol treatments showed that WHAMM was localized around the MI spindle. Depletion of WHAMM by microinjection of specific short interfering (si)RNA into the oocyte cytoplasm resulted in failure of spindle migration, disruption of asymmetric cytokinesis and a decrease in the first polar body extrusion rate during meiotic maturation. Moreover, actin cap formation was also disrupted after WHAMM depletion, confirming the failure of spindle migration. Taken together, our data suggest that WHAMM is required for peripheral spindle migration and asymmetric cytokinesis during mouse oocyte maturation.

Centrosome aberrations associated with cellular senescence and p53 localization at supernumerary centrosomes

Centrosome overduplication or amplification has been observed in many human cancers and in premalignant tissue, but the mechanisms leading to such centrosome aberrations are not fully understood. We previously showed that abnormal mitotic cells with supernumerary centrosomes increase with replicative senescence in human fibroblasts, especially in a polyploid subpopulation. This study examines localization of p53 protein at centrosomes in mitotic cells, which is often observed in association with DNA damage response, to investigate a possible association between p53 localization and numerical centrosome aberrations induced by cellular senescence. Cultures at later passages or the 4th day after exposure to H(2)O(2) showed increased frequencies of mitotic cells with supernumerary centrosomes, especially in a polyploid subpopulation. Immunohistochemical analysis frequently showed p53-positive foci in mitotic cells, and some were localized at centrosomes. The number of p53-positive foci in mitotic cells and its localization to centrosomes increased with replicative and premature senescence. Supernumerary centrosomes showed higher frequencies of p53 localization compared to normally duplicated centrosomes. Centrosome-associated p53 protein was phosphorylated at Ser15. These data suggest a possible association between localization of p53 protein and numerical centrosome aberrations in replicatively or prematurely senescent cells.

Fertilization studies and assisted fertilization in mammals: their development and future

Studies of mammalian fertilization progressed very slowly in the beginning because of difficulties in obtaining a large quantity of fully mature eggs at one time. With progression of techniques to collect and handle eggs and spermatozoa, research in mammalian fertilization advanced rapidly. Today, far more papers are published on mammalian gametes and fertilization than those of all other animals combined. The development of assisted fertilization and related technologies revolutionized basic research as well as human reproductive medicine and animal husbandry. Reproduction is fundamental to human and animal lives. The author lists a few subjects of his personal interest for further development of basic and applied research of gametes and fertilization. Each reader will probably have more exciting subjects of future investigation.

New insights into subcomplex assembly and modifications of centrosomal proteins

This review provides a brief overview of the recent work on centrosome proteomics, protein complex identification and functional characterization with an emphasis on the literature of the last three years. Proteomics, genetic screens and comparative genomics studies in different model organisms have almost exhaustively identified the molecular components of the centrosome. However, much knowledge is still missing on the protein-protein interactions, protein modifications and molecular changes the centrosome undergoes throughout the cell cycle and development. The dynamic nature of this large multi-protein complex is reflected in the variety of annotated subcellular locations and biological processes of its proposed components. Some centrosomal proteins and complexes have been studied intensively in different organisms and provided detailed insight into centrosome functions. For example, the molecular, structural and functional characterization of the γ-Tubulin ring complex (γ-TuRC) and the the discovery of the Augmin/HAUS complex has advanced our understanding of microtubule (MT) capture, nucleation and organization. Surprising findings revealed new functions and localizations of proteins that were previously regarded as bona fide centriolar or centrosome components, e.g. at the kinetochore or in the nuclear pore complex regulating MT plus end capture or mRNA processing. Many centrosome components undergo posttranslational modifications such as phosphorylation, SUMOylation and ubiquitylation that are critical in modulating centrosome function and biology. A wealth of information has recently become available driven by new developments in technologies such as mass spectrometry, light and electron microscopy providing more detailed molecular and structural definition of the centrosome and particular roles of proteins throughout the cell cycle and development.

Subcellular localization of regulator of G protein signaling RGS7 complex in neurons and transfected cells

The R7 family of regulators of G protein signaling (RGS) is involved in many functions of the nervous system. This family includes RGS6, RGS7, RGS9, and RGS11 gene products and is defined by the presence of the characteristic first found in Disheveled, Egl-10, Pleckstrin (DEP), DEP helical extension (DHEX), Gγ-like, and RGS domains. Herein, we examined the subcellular localization of RGS7, the most broadly expressed R7 member. Our immunofluorescence studies of retinal and dorsal root ganglion neurons showed that RGS7 concentrated at the plasma membrane of cell bodies, in structures resembling lamellipodia or filopodia along the processes, and at the dendritic tips. At the plasma membrane of dorsal root ganglia neurons, RGS7 co-localized with its known binding partners R7 RGS binding protein (R7BP), Gαo, and Gαq. More than 50% of total RGS7-specific immunofluorescence was present in the cytoplasm, primarily within numerous small puncta that did not co-localize with R7BP. No specific RGS7 or R7BP immunoreactivity was detected in the nuclei. In transfected cell lines, ectopic RGS7 had both diffuse cytosolic and punctate localization patterns. RGS7 also localized in centrosomes. Structure-function analysis showed that the punctate localization was mediated by the DEP/DHEX domains, and centrosomal localization was dependent on the DHEX domain.

Cep70 promotes microtubule assembly in vitro by increasing microtubule elongation

Microtubules are dynamic cytoskeletal polymers present in all eukaryotic cells. In animal cells, they are organized by the centrosome, the major microtubule-organizing center. Many centrosomal proteins act coordinately to modulate microtubule assembly and organization. Our previous work has shown that Cep70, a novel centrosomal protein regulates microtubule assembly and organization in mammalian cells. However, the molecular details remain to be investigated. In this study, we investigated the molecular mechanism of how Cep70 regulates microtubule assembly using purified proteins. Our data showed that Cep70 increased the microtubule length without affecting the microtubule number in the purified system. These results demonstrate that Cep70 could directly regulate microtubule assembly by promoting microtubule elongation instead of microtubule nucleation.

Adenovirus-mediated Aurora A shRNA driven by stathmin promoter suppressed tumor growth and enhanced paclitaxel chemotherapy sensitivity in human breast carcinoma cells

Aurora A has multiple key functions in tumor initiation and progression and is overexpressed in many cancers. Several ongoing clinical trials are assessing the unique therapeutic potential of Aurora-based targeted therapy, but several severe adverse events such as hematopoietic toxicity have been observed in the early-phase clinical trials because Aurora A is also involved in normal cells proliferation process. The strategy to develop tumor-specific inhibition of this target may be an alteration for the treatment of Aurora A overexpression tumors. In this study, we developed a novel tumor-specific RNA interference adenovirus system targeting Aurora A by using stathmin promoter and investigated the effects of it on the proliferation, apoptosis and chemotherapy sensitivity in human breast carcinoma cells both in vitro and in vivo. The results showed that treatment of human breast carcinoma cells (SK-BR-3 and MDA-MB-231) by Aurora A short hairpin RNA (shRNA) driven by stathmin gene promoter not only inhibited the cells proliferation, but also enhanced the chemosensitivity to paclitaxel via downregulation of Aurora A mRNA and protein expression, which further decreased the phosphatidylinositol 3 kinase/Akt and p-BRCA1 protein expression. Furthermore, there were no obvious phenotypes changes observed in normally differentiated epithelial cells of MCF210. Therefore, stathmin promoter-driving Aurora A shRNA adenoviral system may have potential use, with targeted tumor gene silencing effect and as adjuvant tumor-specific therapy method, in the treatment of human breast carcinomas.

The Sperm Centrosome: Its Role and Significance in Nature and Human Assisted Reproduction

In humans and other non-rodent mammalian species, the sperm's centriole-centrosome complex is an essential component for successful fertilization and serves as template for all centrioles during subsequent cell divisions, embryo development, divisions of most adult somatic cells, as well as in primary cilia formation and functions. Dysfunctions of this complex can be causes for infertility, developmental disorders, and play a role in various adulthood diseases. While assisted reproductive technology (ART) has been able to overcome sperm motility dysfunctions by employing intracytoplasmic sperm injection (ICSI), we currently do not yet have therapies to overcome dysfunctions of the centriole-centrosome complex although several lines of investigations have addressed the causes for centriole-centrosome dysfunctions and implications for sperm aster formation and union of the parental genomes. The present review highlights the importance of the centriole-centrosome complex and its significance for fertilization and embryo development.

The biology and evolution of polyspermy: insights from cellular and functional studies of sperm and centrosomal behavior in the fertilized egg

Recent studies of centrosome biogenesis, microtubule dynamics, and their management point to their role in mediating conditions such as aging and cancer. Centrosome dysfunction is also a hallmark of pathological polyspermy. Polyspermy occurs when the oocyte is penetrated by more than one sperm and can be pathological because an excess of centrosomes compromises development. However, in some taxa, multiple sperm enter the egg with no apparent adverse effect on zygote viability. Thus, some taxa can manage excess centrosomes and represent cases of non-pathological polyspermy. While these two forms of polyspermy have long been known, we argue that there is limited understanding of the proximate and ultimate processes that underlie this taxonomic variation in the outcome of polyspermy and that studying this variation could help uncover the control and role(s) of centrosomes during fertilization in particular, but also mitosis in general. To encourage such studies we: 1) describe taxonomic differences in the outcome of polyspermy, 2) discuss mechanistic aspects of reproductive biology that may contribute to the different consequences of polyspermy, and 3) outline the potential selective events that could lead to the evolution of variation in polyspermy outcomes. We suggest that novel insights into centrosome biology may occur by cooperative studies between reproductive and evolutionary biologists focusing on the mechanisms generating variation in the fitness consequences of polyspermy, and in the taxonomic distribution of all these events. The consequent discoveries of these studies may lead to informative insights into cancer and aging along with other centrosome-related diseases and syndromes.

The significant role of centrosomes in stem cell division and differentiation

The role of centrosomes in stem cell division has recently been highlighted and further ascribes important functions to centrosomes in stem cell maintenance, cellular differentiation, and development. Advanced cell and molecular studies coupled with immunofluorescence, electron microscopy, and live cell imaging of specific centrosome proteins have contributed greatly to our knowledge of centrosome composition, structure, and dynamics and have uncovered new insights into mechanisms of centrosome functions in asymmetric cell division. The establishment of asymmetry and differential positioning of mother and daughter centrosomes during stem cell mitosis is important for allowing one cell to maintain stem cell characteristics while the sibling cell undergoes differentiation. Another key role for centrosomes has been revealed in primary cilia of embryonic stem cells that play significant roles in cellular signaling and are therefore critically important for stem cell decisions. Studies of signaling through primary cilia may contribute important information that may aid in the production of specific cells that are suitable for tissue repair and regeneration in the field of regenerative medicine.

Systems biomechanics of centrosome positioning: A conserved complexity

Positioning of centrosomes within cells determines the directionality of cell division, as well as directionality of cellular activities in the interphase. This brief review focuses on similarities (and differences) of centrosome positioning during early divisions in the Caenorhabditis embryo and during the interaction of T lymphocytes with other cells in the course of immune response. In the study of the two phenomena, a synergy of experimentation and numerical mechanical analysis has recently been achieved. The picture that emerges from these studies is one in which simple physical forces under the constraints of the basic cell structure lead to complex, "life-like" mechanical behavior. This behavior includes instability of equilibria, irreversibility of structural transitions and multidimensional, multiperiodic oscillations. This new picture of cell mechanics may form an interesting paradigm for future research.

Cellular and molecular mechanisms of various types of oocyte aging

It is well established that age-related decline of a woman's fertility is related to the poor developmental potential of her gametes. The age-associated decline in female fertility is largely attributable to the oocyte aging caused by ovarian aging. Age-associated oocyte aging results in a decrease in oocyte quality. In contrast to ovarian aging, there is a concept of postovulatory oocyte aging. Postovulatory aging of oocytes, not being fertilized for a prolonged time after ovulation, is known to significantly affect the development of oocytes. Both categories of oocyte aging have similar phenotypes of reproductive failure. However, the mechanisms of the decline in oocyte quality are not necessarily equivalent. An age-dependent increase in aneuploidy is a key determinant of oocyte quality. The reduced expression of molecules regulating cell cycle control during meiosis might be involved in the age-dependent increase in aneuploidy. The mechanism of age-associated oocyte aging might be involved in mitochondrial dysfunction, whose etiologies are still unknown. Alternatively, the mechanism of postovulatory oocyte aging might be involved in reactive oxygen species-induced mitochondrial injury pathways followed by abnormal intracellular Ca²⁺ regulation of the endoplasmic reticulum. We suggest that future research into the mechanism of oocyte aging will be necessary to develop a method to rescue the poor developmental potential of aged oocytes.

Human embryonic stem cells suffer from centrosomal amplification

Propagation of human embryonic stem cells (hESCs) in culture tends to alter karyotype, potentially limiting the prospective use of these cells in patients. The chromosomal instability of some malignancies is considered to be driven, at least in part, by centrosomal overamplification, perturbing balanced chromosome segregation. Here, we report, for the first time, that very high percentage of cultured hESCs has supernumerary centrosomes during mitosis. Supernumerary centrosomes were strictly associated with an undifferentiated hESC state and progressively disappeared on prolonged propagation in culture. Improved attachment to culture substratum and inhibition of CDK2 and Aurora A (key regulators of centrosomal metabolism) diminished the frequency of multicentrosomal mitoses. Thus, both attenuated cell attachment and deregulation of machinery controlling centrosome number contribute to centrosomal overamplification in hESCs. Linking the excessive number of centrosomes in mitoses to the ploidy indicated that both overduplication within a single cell cycle and mitotic failure contributed to generation of numerical centrosomal abnormalities in hESCs. Collectively, our data indicate that supernumerary centrosomes are a significant risk factor for chromosome instability in cultured hESCs and should be evaluated when new culture conditions are being implemented.

The nuclear mitotic apparatus (NuMA) protein: localization and dynamics in human oocytes, fertilization and early embryos

The oocyte's meiotic spindle is a dynamic structure that relies on microtubule organization and regulation by centrosomes. Disorganization of centrosomal proteins, including the nuclear mitotic apparatus (NuMA) protein and the molecular motor complex dynein/dynactin, can lead to chromosomal instability and developmental abnormalities. The present study reports the distribution and function of these proteins in human oocytes, zygotes and early embryos. A total of 239 oocytes, 90 zygotes and discarded embryos were fixed and analyzed with confocal microscopy for NuMA and dynactin distribution together with microtubules and chromatin. Microtubule-associated dynein-dependent transport functions were explored by inhibiting phosphatase and ATPase activity with sodium-orthovanadate (SOV). At germinal vesicle (GV) stages, NuMA was dispersed across the nucleoplasm. After GV breaks down, NuMA became cytoplasmic before localizing at the spindle poles in metaphase I and II oocytes. Aberrant NuMA localization patterns were found during oocyte in vitro maturation. After fertilization, normal and abnormal pronuclear stage zygotes and embryos displayed translocation of NuMA to interphase nuclei. SOV treatment for up to 2 h induced lower maturation rates with chromosomal scattering and ectopic localization of NuMA. Accurate distribution of NuMA is important for oocyte maturation, zygote and embryo development in humans. Proper assembly of NuMA is likely necessary for bipolar spindle organization and human oocyte developmental competence.

CSPP is a ciliary protein interacting with Nephrocystin 8 and required for cilia formation

We described previously the cell cycle- and microtubule-related functions of two splice isoforms of the centrosome spindle pole-associated protein (CSPP and CSPP-L). Here, we show that endogenous CSPP isoforms not only localize to centrosomes and the midbody in cycling cells but also extend to the cilia axoneme in postmitotic resting cells. They are required for ciliogenesis in hTERT-RPE1 cells in vitro and are expressed in ciliated renal, retinal, and respiratory cells in vivo. We report that CSPP isoforms require their common C-terminal domain to interact with Nephrocystin 8 (NPHP8/RPGRIP1L) and to form a ternary complex with NPHP8 and NPHP4. We find CSPP-L to be required for the efficient localization of NPHP8 but not NPHP4 to the basal body. The ciliogenesis defect in hTERT-RPE1 cells is, however, not mediated through loss of NPHP8. Similar to the effects of ectopical expression of CSPP-L, cilia length increased in NPHP8-depleted cells. Our results thus suggest that CSPP proteins may be involved in further cytoskeletal organization of the basal body and its primary cilium. To conclude, we have identified a novel, nonmitotic function of CSPP proteins placing them into a ciliary protein network crucial for normal renal and retinal tissue architecture and physiology.

A new organellar complex in rat sympathetic neurons

Membranous compartments of neurons such as axons, dendrites and modified primary cilia are defining features of neuronal phenotype. This is unlike organelles deep to the plasma membrane, which are for the most part generic and not related directly to morphological, neurochemical or functional specializations. However, here we use multi-label immunohistochemistry combined with confocal and electron microscopy to identify a very large (∼6 microns in diameter), entirely intracellular neuronal organelle which occurs singly in a ubiquitous but neurochemically distinct and morphologically simple subset of sympathetic ganglion neurons. Although usually toroidal, it also occurs as twists or rods depending on its intracellular position: tori are most often perinuclear whereas rods are often found in axons. These ‘loukoumasomes’ (doughnut-like bodies) bind a monoclonal antibody raised against beta-III-tubulin (SDL.3D10), although their inability to bind other beta-III-tubulin monoclonal antibodies indicate that the responsible antigen is not known. Position-morphology relationships within neurons and their expression of non-muscle heavy chain myosin suggest a dynamic structure. They associate with nematosomes, enigmatic nucleolus-like organelles present in many neural and non-neural tissues, which we now show to be composed of filamentous actin. Loukoumasomes also separately interact with mother centrioles forming the basal body of primary cilia. They express gamma tubulin, a microtubule nucleator which localizes to non-neuronal centrosomes, and cenexin, a mother centriole-associated protein required for ciliogenesis. These data reveal a hitherto undescribed organelle, and depict it as an intracellular transport machine, shuttling material between the primary cilium, the nematosome, and the axon.

Correlation of human sperm centrosomal proteins with fertility

OBJECTIVE

The centrosome is the microtubule organizing center (MTOC) paternally inherited by the zygote during fertilization. As the centrosome is located in the midpiece of the sperm tail, we presume that oligoasthenozoospermic sperm samples should also have abnormal concentrations of centrosomal proteins. This study therefore aims to determine if there is any correlation between sperm centrosomal proteins, centrin, α and γ-tubulin, in sperm samples from normozoospermic and oligoasthenozoospermic men.

MATERIALS AND METHODS

Proteins were extracted from the normozoospermic and oligoasthenozoospermic sperm samples and analyzed by Western Blot and ELISA for centrin, α and γ-tubulin.

RESULTS

The levels of centrin, α and γ-tubulin are markedly lower in oligoasthenozoospermic sperm samples as compared to the normozoospermic sperm samples.

CONCLUSIONS

Lower centrosomal protein expression in sperm samples of oligoasthenozoospermic infertile males may be a possible cause for their reduced fertility status. Further studies on these proteins are warranted to design rational approaches for the diagnosis and treatment of male infertility.

Xenopus axin-related protein: a link between its centrosomal localization and function in the Wnt/beta-catenin pathway

The Wnt/beta-catenin signaling pathway regulates cell proliferation and cell fate determination in multiple systems. However, the subcellular localization of Wnt pathway components and the significance of this localization for the pathway regulation have not been extensively analyzed. Here we report that Xenopus Axin-related protein (XARP), a component of the beta-catenin destruction complex, is localized to the centrosome. This localization of XARP requires the presence of the DIX domain and an adjacent region. Since other components of the Wnt pathway have also been shown to associate with the centrosome, we tested a hypothesis that the beta-catenin destruction complex operates at the centrosome. However, XARP mutants with poor centrosomal localization revealed an enhanced rather than decreased ability to antagonize the Wnt/beta-catenin pathway. Our data are consistent with the idea that the inactivation of XARP at the centrosome is an important regulatory point in Wnt signaling.

The transcriptional repressor Kaiso localizes at the mitotic spindle and is a constituent of the pericentriolar material

Kaiso is a BTB/POZ zinc finger protein known as a transcriptional repressor. It was originally identified through its in vitro association with the Armadillo protein p120ctn. Subcellular localization of Kaiso in cell lines and in normal and cancerous human tissues revealed that its expression is not restricted to the nucleus. In the present study we monitored Kaiso's subcellular localization during the cell cycle and found the following: (1) during interphase, Kaiso is located not only in the nucleus, but also on microtubular structures, including the centrosome; (2) at metaphase, it is present at the centrosomes and on the spindle microtubules; (3) during telophase, it accumulates at the midbody. We found that Kaiso is a genuine PCM component that belongs to a pericentrin molecular complex. We analyzed the functions of different domains of Kaiso by visualizing the subcellular distribution of GFP-tagged Kaiso fragments throughout the cell cycle. Our results indicate that two domains are responsible for targeting Kaiso to the centrosomes and microtubules. The first domain, designated SA1 for spindle-associated domain 1, is located in the center of the Kaiso protein and localizes at the spindle microtubules and centrosomes; the second domain, SA2, is an evolutionarily conserved domain situated just before the zinc finger domain and might be responsible for localizing Kaiso towards the centrosomal region. Constructs containing both SA domains and Kaiso's aminoterminal BTB/POZ domain triggered the formation of abnormal centrosomes. We also observed that overexpression of longer or full-length Kaiso constructs led to mitotic cell arrest and frequent cell death. Knockdown of Kaiso accelerated cell proliferation. Our data reveal a new target for Kaiso at the centrosomes and spindle microtubules during mitosis. They also strongly imply that Kaiso's function as a transcriptional regulator might be linked to the control of the cell cycle and to cell proliferation in cancer.

Extending the knowledge in histochemistry and cell biology

Central to modern Histochemistry and Cell Biology stands the need for visualization of cellular and molecular processes. In the past several years, a variety of techniques has been achieved bridging traditional light microscopy, fluorescence microscopy and electron microscopy with powerful software-based post-processing and computer modeling. Researchers now have various tools available to investigate problems of interest from bird's- up to worm's-eye of view, focusing on tissues, cells, proteins or finally single molecules. Applications of new approaches in combination with well-established traditional techniques of mRNA, DNA or protein analysis have led to enlightening and prudent studies which have paved the way toward a better understanding of not only physiological but also pathological processes in the field of cell biology. This review is intended to summarize articles standing for the progress made in "histo-biochemical" techniques and their manifold applications.

Centrosome abnormalities during porcine oocyte aging

Centrosomes are critically important for maintaining meiotic spindle integrity in the meiosis II (MII) stage where oocytes are arrested in most mammalian species before fertilization takes place. In women of advanced ages or during in vitro fertilization (IVF) procedures, aneuploidy is frequently seen as a result of oocyte aging, which is strongly related to centrosome instability. Abnormal distribution of centrosomes and microtubules has been reported in aging human and mouse oocytes. This study reports the dynamic changes of centrosomes and the microtubule cytoskeleton in porcine oocytes during aging and treatment by caffeine to restore spindle integrity in aging oocytes. We tested the effects of caffeine on the MII spindle with focus on microtubules and on the centrosome proteins gamma-tubulin and NuMA (nuclear mitotic apparatus protein). The results revealed that in porcine oocytes aged for 48 hr., centrosomes were absent and spindles became abnormal and disorganized; however, caffeine could prevent these changes or restore centrosome integrity in the meiotic spindle poles and displayed similar MII spindles as those seen in fresh oocytes.

The functional significance of centrosomes in mammalian meiosis, fertilization, development, nuclear transfer, and stem cell differentiation

Centrosomes had been discovered in germ cells and germ cells continue to provide excellent but also challenging material in which to study complex centrosomal dynamics. The present review highlights the importance of centrosomes for meiotic spindle integrity and the susceptibility of meiotic spindle centrosomes to aging and drugs or toxic agents which may be associated with female infertility, aneuploidy, and developmental abnormalities. We discuss cell and molecular aspects of centrosomes during fertilization, a critical stage in which centrosomes play crucial roles in precisely organizing the sperm aster that allows apposition of male and female genomes followed by formation of the zygote aster that is important for the formation of the bipolar spindle apparatus during cell division. Development of an embryo involves sequential cell divisions in which centrosomes play a critical role in establishing asymmetry that allows differentiation of cells and targeted signal transductions for the developing embryo. Asymmetric centrosome dynamics are also critical for stem cell division to maintain one daughter cell as a stem cell while the other daughter cell undergoes centrosome growth in preparation for differentiation. This review also discusses the complex interactions of somatic cell centrosomes with the recipient oocyte in reconstructed (cloned) embryos in which centrosome remodeling is crucial to fulfill functions that are carried out by the zygote centrosome in fertilized eggs. We close our discussion with a look at centrosome dysfunctions and implications for male fertility and assisted reproduction.

Mitotic phosphatases: from entry guards to exit guides

While the importance of protein kinases for the spatial and temporal control of mitotic events has long been recognized, mitotic phosphatases have only recently come into the limelight. It is now well established that protein phosphatases counteract mitotic kinases, so contributing to the generation of switch-like responses at mitotic stage transitions. In addition, the timely dephosphorylation of mitotic phosphoproteins by tightly regulated phosphatases is required for the assembly and stability of the mitotic spindle, the initiation of anaphase, and exit from mitosis. Mitotic phosphatases also emerge as effectors of the DNA damage and spindle assembly checkpoints. These new findings show that protein phosphatases regulate every step of mitosis and provide novel insights into the dynamic and versatile nature of mitotic phosphoregulation.

The role of centrosomes in mammalian fertilization and its significance for ICSI

Centrosome integrity is critically important for successful fertilization and embryo development. In humans, the sperm contributes the dominant centrosomal material containing centrioles and centrosomal components onto which oocyte centrosomal proteins assemble after sperm incorporation to form the sperm aster that is essential for uniting sperm and oocyte pronuclei. Increasingly, dysfunctional sperm centrosomes have been identified as a factor for sperm-derived infertility and heterologous Intracytoplasmic Sperm Injection (ICSI) has been used to assess centrosome and sperm aster formation and clearly established a relationship between infertility and sperm centrosomal dysfunction. ICSI has been used successfully to provide novel treatment to overcome male factor infertility and it may open up new possibilities to correct specific sperm-related centrosome dysfunctions at molecular levels. New data indicate that it is now possible to replace dysfunctional centrosomes with functional donor sperm centrosomes which may provide new treatment for couples in which infertility is a result of centrosome-related sperm dysfunctions.

Impact of insemination technique, semen quality and oocyte cryopreservation on pronuclear morphology of zygotes derived from sibling oocytes

Pronuclear morphology seems to be an important predictive value of zygote development and integrity. In this study we want to evaluate the effect of insemination technique, male factor and oocyte cryopreservation on pronuclear morphology of zygotes derived from sibling oocytes in our Centre of Reproductive Medicine, Department of Obstetrics and Gynecology, Arcispedale S. Maria Nuova, Reggio Emilia, Italy. Subjects (n = 190) were submitted to IVF cycles with non-frozen and frozen sibling oocytes. Morphological evaluations were assessed using zygote pronuclear morphology (pronuclei, nucleoli and axis) in four groups: Group 1: 144 zygotes from 85 conventional IVF cycles with non-frozen oocytes; Group 2: 164 zygotes from 85 intracytoplasmic sperm injection (ICSI) cycles with Group 1 patients' sibling frozen oocytes; Group 3: 221 zygotes from 123 ICSI cycles with non-frozen oocytes; Group 4: 197 zygotes from 123 ICSI cycles with Group 3 patients' sibling frozen oocytes. No differences between Group 1 and Group 2 were seen. Group 3 was statistically different from Group 4 in relation to the nucleolar morphology. Oocyte cryopreservation procedure modified the nucleolar morphology of zygotes only in the presence of poor semen quality.

PAK signaling in oncogenesis

The p21-activated kinase (PAK) family of serine/threonine kinases is important in physiological processes including motility, survival, mitosis, transcription and translation. PAKs are evolutionally conserved and widely expressed in a variety of tissues and are often overexpressed in multiple cancer types. Depending on structural and functional similarities, the six members of PAK family are divided into two groups with three members in each group. Group I PAKs are activated by extracellular signals through GTPase-dependent and GTPase-independent mechanisms. In contrast, group II PAKs are constitutively active. Over the years, accumulating data from tissue culture models and human tumors has increased our understanding about the biology of PAK family members. In this review, we have summarized the complex regulation of PAK and its downstream diverse myriads of effectors, which in turn are responsible for the biological effects of PAK family of kinases in cancer cells.

State-of-the-art technologies, current opinions and developments, and novel findings: news from the field of histochemistry and cell biology

Investigations of cell and tissue structure and function using innovative methods and approaches have again yielded numerous exciting findings in recent months and have added important data to current knowledge, inspiring new ideas and hypotheses in various fields of modern life sciences. Topics and contents of comprehensive expert reviews covering different aspects in methodological advances, cell biology, tissue function and morphology, and novel findings reported in original papers are summarized in the present review.

The primary cilium coordinates signaling pathways in cell cycle control and migration during development and tissue repair

Cell cycle control and migration are critical processes during development and maintenance of tissue functions. Recently, primary cilia were shown to take part in coordination of the signaling pathways that control these cellular processes in human health and disease. In this review, we present an overview of the function of primary cilia and the centrosome in the signaling pathways that regulate cell cycle control and migration with focus on ciliary signaling via platelet-derived growth factor receptor alpha (PDGFRalpha). We also consider how the primary cilium and the centrosome interact with the extracellular matrix, coordinate Wnt signaling, and modulate cytoskeletal changes that impinge on both cell cycle control and cell migration.