Allocation of Gamma-Tubulin Between Oocyte Cortex and Meiotic Spindle Influences Asymmetric Cytokinesis in the Mouse Oocyte1

Use of confocal microscopy and intracytoplasmic sperm injection (ICSI) to assess viability of equine oocytes from young and old mares after vitrification

BACKGROUND

The impact of vitrification on oocyte developmental competence as a function of donor age remains an important issue in assisted reproductive technologies (ARTs).

METHODS

Equine germinal vesicle (GV) or metaphase II (M(II) oocytes were vitrified using the Cryotop® method. Spindle organization and chromosome alignment were evaluated from confocal imaging data sets of in vivo (IVO) or in vitro (IVM) matured oocytes subjected to vitrification or not. Intracytoplasmic sperm injection (ICSI) from the same groups was used to assess developmental potential.

RESULTS

An increase in chromosome misalignment was observed in spindles from older mares when compared to those of younger mares (P < 0.05). When MII oocytes subjected to vitrification were examined following warming, there was no difference in the percentage of oocytes displaying chromosome misalignment. Next, GV oocytes, collected from the ovaries of younger and older mares, were compared between fresh IVM and IVM following vitrification and warming. For nonvitrified samples, an age difference was again noted for spindle organization and chromosome alignment, with a higher (P < 0.05) percentage of normal bipolar meiotic spindles with aligned chromosomes observed in nonvitrified oocytes from young versus older mares. Vitrification led to a reduction of spindle length (P < 0.05) for oocytes from old mares, whether vitrified at GV or MII stages, whereas this effect was not observed in oocytes from young mares except those vitrified at GV and subjected to IVM. Oocyte developmental potential after vitrification was evaluated after ICSI of vitrified and warmed MII or GV oocytes from young mares. From 25 MII oocytes, 18 oocytes were injected with sperm, and six blastocysts were produced, which, upon transfer to mares' uteri, resulted in four pregnancies. Immature (GV) oocytes collected from live mares were also vitrified, warmed, and matured in vitro before ICSI. In this group, nonvitrified, control, and vitrified oocytes did not differ (P > 0.05) with respect to the incidence of maturation to MII, cleavage after ICSI, or blastocyst development.

CONCLUSION

These findings demonstrate an effect of maternal age in an equine model at the level of meiotic spindle integrity and chromosome positioning that is influenced by both the meiotic stage at which oocytes are vitrified and whether meiotic maturation occurred in vivo or in vitro.

Rocking the Boat: The Decisive Roles of Rho Kinases During Oocyte, Blastocyst, and Stem Cell Development

The rho-associated coiled-coil-containing proteins (ROCKs or rho kinase) are effectors of the small rho-GTPase rhoA, which acts as a signaling molecule to regulate a variety of cellular processes, including cell proliferation, adhesion, polarity, cytokinesis, and survival. Owing to the multifunctionality of these kinases, an increasing number of studies focus on understanding the pleiotropic effects of the ROCK signaling pathway in the coordination and control of growth (proliferation, initiation, and progression), development (morphology and differentiation), and survival in many cell types. There is growing evidence that ROCKs actively phosphorylate several actin-binding proteins and intermediate filament proteins during oocyte cytokinesis, the preimplantation embryos as well as the stem cell development and differentiation. In this review, we focus on the participation of ROCK proteins in oocyte maturation, blastocyst formation, and stem cell development with a special focus on the selective targeting of ROCK isoforms, ROCK1, and ROCK2. The selective switching of cell fate through ROCK inhibition would provide a novel paradigm for in vitro oocyte maturation, experimental embryology, and clinical applications.

Cilostamide and forskolin maintain gap junction function of incubated dog follicles

Disruption of the communication between the oocyte and granulosa cells is one of the major causes of poor development of in vitro grown ovarian follicles and oocytes. The present study investigated the effect of two cAMP modulators, cilostamide and forskolin, on in vitro growth of isolated dog secondary follicles and enclosed oocytes, communication between the gamete and surrounding granulosa cells, expression of GJA1 and GDF9, as well as cAMP level. Secondary follicles were incubated with cilostamide or forskolin alone or a combination of 20 μM cilostamide +1 μM forskolin, and the diameter of the incubated follicles and enclosed oocytes assessed every 72 h. Gap junction activity, GJA1 and GDF9 expression and cAMP level were assessed on Days 6 and 12 and transzonal projection (TZP) density was evaluated on Day 12. Neither cilostamide nor forskolin alone enhanced in vitro growth of dog follicles and the enclosed oocytes (P > 0.05). However, these two cAMP modulators dose dependently sustained gap junction activity and stimulated cAMP production compared with the non-supplemented control. Cilostamide at the high dosage (20 μM) also upregulated GJA1 expression. The combination of cilostamide and forskolin supported oocyte growth during the first 9 days and upregulated GJA1 and GDF9 expression at Day 12 of in vitro culture. This combination treatment also sustained gap junction activity, cAMP production, and increased TZP function (calcein intensity: TZP density ratio). The findings indicated that a combination of cilostamide and forskolin supported growth and survival of oocytes enclosed within cultured follicles by sustaining cAMP production and gap junction activity.

Activin promotes growth and antral cavity expansion in the dog ovarian follicle

Understanding regulators of folliculogenesis remains limited in the domestic dog (Canis familiaris), which challenges our ability to develop in vitro follicle culture systems for canid genome rescue efforts. Here, we investigated the influence of activin on dog follicle development and survival, oocyte quality, and FSH receptor expression in culture. Preantral (150 - ≤230 μm diameter), early antral (231 - ≤330 μm), and antral (>330-550 μm) stage follicles were encapsulated in a fibrin-alginate hydrogel with 0, 100, or 200 ng/ml rhActivin plus 0, 0.1, 1, or 10 μg/ml FSH for 12 or 21 d of in vitro culture. All follicle groups increased in diameter (P < 0.05) with activin acting synergistically with FSH to improve (P < 0.05) growth and antral cavity expansion (to >630 μm) in early antral and antral cohorts. This complementary effect was not linked to changes in FSHR mRNA expression (P > 0.05). Although not influencing (P > 0.05) follicle survival or transzonal projection (TZP) density in shorter term 12 d culture, activin in the presence of 1 ng/ml FSH maintained TZP density from the 12-21 d interval. Activin also increased oocyte diameter and improved nuclear integrity compared to un-supplemented controls. These results indicate that activin acts synergistically with FSH to promote growth and antral cavity expansion of the dog follicle in vitro, information useful to formulating an effective culture microenvironment for this species.

Biomechanics and mechanical signaling in the ovary: a systematic review

PURPOSE

Mammalian oogenesis and folliculogenesis share a dynamic connection that is critical for gamete development. For maintenance of quiescence or follicular activation, follicles must respond to soluble signals (growth factors and hormones) and physical stresses, including mechanical forces and osmotic shifts. Likewise, mechanical processes are involved in cortical tension and cell polarity in oocytes. Our objective was to examine the contribution and influence of biomechanical signaling in female mammalian gametogenesis.

METHODS

We performed a systematic review to assess and summarize the effects of mechanical signaling and mechanotransduction in oocyte maturation and folliculogenesis and to explore possible clinical applications. The review identified 2568 publications of which 122 met the inclusion criteria.

RESULTS

The integration of mechanical and cell signaling pathways in gametogenesis is complex. Follicular activation or quiescence are influenced by mechanical signaling through the Hippo and Akt pathways involving the yes-associated protein (YAP), transcriptional coactivator with PDZ-binding motif (TAZ), phosphatase and tensin homolog deleted from chromosome 10 (PTEN) gene, the mammalian target of rapamycin (mTOR), and forkhead box O3 (FOXO3) gene.

CONCLUSIONS

There is overwhelming evidence that mechanical signaling plays a crucial role in development of the ovary, follicle, and oocyte throughout gametogenesis. Emerging data suggest the complexities of mechanotransduction and the biomechanics of oocytes and follicles are integral to understanding of primary ovarian insufficiency, ovarian aging, polycystic ovary syndrome, and applications of fertility preservation.

Initial characterisation of adult human ovarian cell populations isolated by DDX4 expression and aldehyde dehydrogenase activity

The existence of a population of putative stem cells with germline developmental potential (oogonial stem cells: OSCs) in the adult mammalian ovary has been marked by controversy over isolation methodology and potential for in-vitro transformation, particularly where cell sorting has been based on expression of DEAD box polypeptide 4 (DDX4). This study describes a refined tissue dissociation/fluorescence-activated cell sorting (FACS) protocol for the ovaries of adult women which results in increased cell viability and yield of putative OSCs. A FACS technique incorporating dual-detection of DDX4 with aldehyde dehydrogenase 1 (ALDH1) demonstrates the existence of two sub-populations of small DDX4-positive cells (approx. 7 µm diameter) with ALDH1 activity, distinguished by expression of differentially spliced DDX4 transcripts and of DAZL, a major regulator of germ cell differentiation. These may indicate stages of differentiation from a progenitor population and provide a likely explanation for the expression disparities reported previously. These findings provide a robust basis for the further characterisation of these cells, and exploration of their potential physiological roles and therapeutic application.

Use of Confocal Microscopy to Evaluate Equine Zygote Development After Sperm Injection of Oocytes Matured In Vivo or In Vitro

Confocal microscopy was used to image stages of equine zygote development, at timed intervals, after intracytoplasmic sperm injection (ICSI) of oocytes that were matured in vivo or in vitro. After fixation for 4, 6, 8, 12, or 16 h after ICSI, zygotes were incubated with α/β tubulin antibodies and human anticentromere antibody (CREST/ACA), washed, incubated in secondary antibodies, conjugated to either Alexa 488 or Alexa 647, and incubated with 561-Phalloidin and Hoechst 33258. An Olympus IX81 spinning disk confocal microscope was used for imaging. Data were analyzed using χ 2 and Fisher's exact tests. Minor differences in developmental phases were observed for oocytes matured in vivo or in vitro. Oocytes formed pronuclei earlier when matured in vivo (67% at 6 h and 80% at 8 h) than in vitro (13% at 6 and 8 h); 80% of oocytes matured in vitro formed pronuclei by 12 h. More (p=0.04) zygotes had atypical phenotypes, indicative of a failure of normal zygote development, when oocyte maturation occurred in vitro versus in vivo (30 and 11%, respectively). Some potential zygotes from oocytes matured in vivo had normal phenotypes, although development appeared to be delayed or arrested. Confocal microscopy provided a feasible method to assess equine zygote development using limited samples.

The lipid peroxidation product 4-hydroxynonenal contributes to oxidative stress-mediated deterioration of the ageing oocyte

An increase in intraovarian reactive oxygen species (ROS) has long been implicated in the decline in oocyte quality associated with maternal ageing. Oxidative stress (OS)-induced lipid peroxidation and the consequent generation of highly electrophilic aldehydes, such as 4-hydroxynonenal (4-HNE), represents a potential mechanism by which ROS can inflict damage in the ageing oocyte. In this study, we have established that aged oocytes are vulnerable to damage by 4-HNE resulting from increased cytosolic ROS production within the oocyte itself. Further, we demonstrated that the age-related induction of OS can be recapitulated by exposure of germinal vesicle (GV) oocytes to exogenous H₂O₂. Such treatments stimulated an increase in 4-HNE generation, which remained elevated during in vitro oocyte maturation to metaphase II. Additionally, exposure of GV oocytes to either H₂O₂ or 4-HNE resulted in decreased meiotic completion, increased spindle abnormalities, chromosome misalignments and aneuploidy. In seeking to account for these data, we revealed that proteins essential for oocyte health and meiotic development, namely α-, β-, and γ-tubulin are vulnerable to adduction via 4-HNE. Importantly, 4-HNE-tubulin adduction, as well as increased aneuploidy rates, were resolved by co-treatment with the antioxidant penicillamine, demonstrating a possible therapeutic mechanism to improve oocyte quality in older females.

Cytoskeletal alterations associated with donor age and culture interval for equine oocytes and potential zygotes that failed to cleave after intracytoplasmic sperm injection

Intracytoplasmic sperm injection (ICSI) is an established method to fertilise equine oocytes, but not all oocytes cleave after ICSI. The aims of the present study were to examine cytoskeleton patterns in oocytes after aging in vitro for 0, 24 or 48h (Experiment 1) and in potential zygotes that failed to cleave after ICSI of oocytes from donors of different ages (Experiment 2). Cytoplasmic multiasters were observed after oocyte aging for 48h (P<0.01). A similar increase in multiasters was observed with an increased interval after ICSI for young mares (9-13 years) but not old (20-25 years) mares. Actin vesicles were observed more frequently in sperm-injected oocytes from old than young mares. In the present study, multiasters appeared to be associated with cell aging, whereas actin vesicles were associated with aging of the oocyte donor.

The adverse outcome pathway (AOP) for chemical binding to tubulin in oocytes leading to aneuploid offspring

The Organisation for Economic Co-operation and Development (OECD) has launched the Adverse Outcome Pathway (AOP) Programme to advance knowledge of pathways of toxicity and improve the use of mechanistic information in risk assessment. An AOP links a molecular initiating event (MIE) to an adverse outcome (AO) through intermediate key events (KE). Here, we present the scientific evidence in support of an AOP whereby chemicals that bind to tubulin cause microtubule depolymerization resulting in spindle disorganization followed by altered chromosome alignment and segregation and the generation of aneuploidy in female germ cells, ultimately leading to aneuploidy in the offspring. Aneuploidy, an abnormal number of chromosomes that is not an exact multiple of the haploid number, is a well-known cause of human disease and represents a major cause of infertility, pregnancy failure, and serious genetic disorders in the offspring. Among chemicals that induce aneuploidy in female germ cells, a large majority impairs microtubule dynamics and spindle function. Colchicine, a prototypical chemical that binds to tubulin and causes microtubule depolymerization, is used here to illustrate the AOP. This AOP is specific to female germ cells exposed during the periovulation period. Although the majority of the data come from rodent studies, the available evidence suggests that the MIE and KEs are conserved across species and would occur in human oocytes. The development of AOPs related to mutagenicity in germ cells is expected to aid the identification of potential hazards to germ cell genomic integrity and support regulatory efforts to protect population health.

Caenorhabditis elegans Aurora A kinase is required for the formation of spindle microtubules in female meiosis

Female meiotic spindles are organized in the absence of centrosomes. Caenorhabditis elegans Aurora A (AIR-1) is dispensable for the initial assembly of meiotic microtubules within the oocyte nuclei, but its kinase activity is continuously required for the stabilization of meiotic spindle microtubules after germinal vesicle breakdown.

In many animals, female meiotic spindles are assembled in the absence of centrosomes, the major microtubule (MT)-organizing centers. How MTs are formed and organized into meiotic spindles is poorly understood. Here we report that, in Caenorhabditis elegans, Aurora A kinase/AIR-1 is required for the formation of spindle microtubules during female meiosis. When AIR-1 was depleted or its kinase activity was inhibited in C. elegans oocytes, although MTs were formed around chromosomes at germinal vesicle breakdown (GVBD), they were decreased during meiotic prometaphase and failed to form a bipolar spindle, and chromosomes were not separated into two masses. Whereas AIR-1 protein was detected on and around meiotic spindles, its kinase-active form was concentrated on chromosomes at prometaphase and on interchromosomal MTs during late anaphase and telophase. We also found that AIR-1 is involved in the assembly of short, dynamic MTs in the meiotic cytoplasm, and these short MTs were actively incorporated into meiotic spindles. Collectively our results suggest that, after GVBD, the kinase activity of AIR-1 is continuously required for the assembly and/or stabilization of female meiotic spindle MTs.

Pre-implantation developmental potential from in vivo and in vitro matured mouse oocytes: a cytoskeletal perspective on oocyte quality

Purpose

In the present study, fertilization and developmental potential of mouse oocytes matured in different conditions were tested. The efficiency of in vitro fertilization (IVF), pre-implantation development and some important aspects of cytokinesis during early cleavages are discussed.

Methods

In vivo matured (IVO), in vitro matured (IVM) and roscovitine-treated (IVM-Rosco) mouse oocytes were subjected to IVF under identical conditions. Three replicates per group were analyzed. Fertilization was identified by the presence of two pronuclei at 6–8 h post-fertilization. Evaluation of pre-implantation embryonic development was done daily from day 2 to day 5 and embryos were processed for analyses of chromatin, nuclear lamina, microtubules and centrosomal proteins by conventional and confocal fluorescence microscopy.

Results

Both IVM groups displayed lower fertilization rates when compared to in vivo controls. While IVO-derived embryos exhibit efficient and synchronous progression to the blastocyst stage, both IVM-derived embryos exhibit a delay in embryonic progression, and a lower blastocyst rate. Interestingly, IVM-Rosco M-II oocytes exhibited more blastomere symmetries and higher number of cells at the blastocyst stage than the IVM group with the most notable influence being on the centrosome-microtubule complex of blastomeres.

Conclusion

Our study strongly indicates that when compared to spontaneously in vitro matured oocytes, treatment with roscovitine may partially enhance developmental competence by maintaining coordination between nuclear and cytoplasmic events. Further evidence is given of cytoskeletal biomarkers that can be identified during in vitro oocyte maturation conditions.

Depletion of pericentrin in mouse oocytes disrupts microtubule organizing center function and meiotic spindle organization

Accurate chromosome segregation is dependent on the formation and stability of the microtubule spindle apparatus. Meiotic spindle assembly in oocytes differs from the process used during mitosis, and is regulated by unique microtubule organizing centers (MTOCs) that lack centrioles. To gain insight into the molecular composition and function of acentriolar MTOCs in mouse oocytes, we assessed the role of a key MTOC-associated protein, pericentrin (PCNT). In somatic cells, pericentrin functions as a scaffold that binds specific proteins at MTOCs, including γ-tubulin, which is necessary for microtubule nucleation. Pericentrin is expressed in oocytes, but the conservation of its function is not known. Pericentrin localizes specifically to MTOCs during prophase-I arrest in mouse oocytes recovered from pre-ovulatory ovarian follicles, and remains associated with MTOCs at spindle poles during metaphase-I and -II. To test function, specific siRNAs were used to knock down Pcnt transcripts in mouse oocytes. Efficient protein depletion was confirmed by Western blot as well as immunofluorescence analysis. Notably, meiotic spindle structure and chromosome alignment were disrupted in Pcnt-depleted oocytes. Disorganized spindle structures with reduced microtubule density and misaligned chromosomes were observed in the majority of these oocytes (∼ 70%). In addition, γ-tubulin localization to MTOCs was significantly reduced and microtubule regrowth, following cold treatment, was delayed in Pcnt-depleted oocytes. Thus, pericentrin is a key functional component of the unique acentriolar MTOCs of mouse oocytes, and plays an important role in regulating meiotic spindle assembly and/or stability.

Alginate encapsulation supports the growth and differentiation of human primordial follicles within ovarian cortical tissue

PURPOSE

In vitro follicle growth (IVFG) is an investigational fertility preservation technique in which immature follicles are grown in culture to produce mature eggs that can ultimately be fertilized. Although progress has been made in growing primate primary and secondary follicles in vitro, it has been a relatively greater challenge to isolate and culture primordial follicles. The purpose of this study was to develop methods to grow human primordial follicles in vitro using alginate hydrogels.

METHODS

We obtained human ovarian tissue for research purposes through the National Physicians Cooperative from nationwide sites and used it to test two methods for culturing primordial follicles. First, primordial follicles were isolated from the ovarian cortex and encapsulated in alginate hydrogels. Second, 1 mm × 1 mm pieces of 500 μm-thick human ovarian cortex containing primordial follicles were encapsulated in alginate hydrogels, and survival and follicle development within the tissue was assessed for up to 6 weeks.

RESULTS

We found that human ovarian tissue could be kept at 4 °C for up to 24 h while still maintaining follicle viability. Primordial follicles isolated from ovarian tissue did not survive culture. However, encapsulation and culture of ovarian cortical pieces supported the survival, differentiation, and growth of primordial and primary follicles. Within several weeks of culture, many of the ovarian tissue pieces had formed a defined surface epithelium and contained growing preantral and antral follicles.

CONCLUSIONS

The early stages of in vitro human follicle development require the support of the native ovarian cortex.

Bioengineering the ovarian follicle microenvironment

Chemo- and radiation therapies used to treat cancer can have the unintended effect of making patients infertile. Clinically established fertility preservation methods, such as egg and embryo cryopreservation, are not applicable to all patients, which has motivated the development of strategies that involve ovarian tissue removal and cryopreservation before the first sterilizing treatment. To restore fertility at a later date, the early-stage follicles present in the tissue must be matured to produce functional oocytes, a process that is not possible using existing cell culture technologies. This review describes the application of tissue engineering principles to promote ovarian follicle maturation and produce mature oocytes through either in vitro culture or transplantation. The design principles for these engineered systems are presented, along with identification of emerging opportunities in reproductive biology.

TFIIB co-localizes and interacts with α-tubulin during oocyte meiosis in the mouse and depletion of TFIIB causes arrest of subsequent embryo development

TFIIB (transcription factor IIB) is a transcription factor that provides a bridge between promoter-bound TFIID and RNA polymerase II, and it is a target of various transcriptional activator proteins that stimulate the pre-initiation complex assembly. The localization and/or attachment matrix of TFIIB in the cytoplast is not well understood. This study focuses on the function of TFIIB and its interrelationship with α-tubulins in a mouse model. During oocyte maturation TFIIB distributes throughout the entire nucleus of the germinal vesicle (GV). After progression to GV breakdown (GVBD), TFIIB and α-tubulin co-localize and accumulate in the vicinity of the condensed chromosomes. During the MII stage, the TFIIB signals are more concentrated at the equatorial plate and the kinetochores. Colcemid treatment of oocytes disrupts the microtubule (MT) system, although the TFIIB signals are still present with the altered MT state. Injection of oocytes with TFIIB antibodies and siRNAs causes abnormal spindle formation and irregular chromosome alignment. These findings suggest that TFIIB dissociates from the condensed chromatids and then tightly binds to microtubules from GVBD to the MII phase. The assembly and disassembly of TFIIB may very well be associated with and driven by microtubules. TFIIB maintains its contact with the α-tubulins and its co-localization forms a unique distribution pattern. Depletion of Tf2b in oocytes results in a significant decrease in TFIIB expression, although polar body extrusion does not appear to be affected. Knockdown of Tf2b dramatically affects subsequent embryo development with more than 85% of the embryos arrested at the 2-cell stage. These arrested embryos still maintain apparently normal morphology for at least 96h without any obvious degeneration. Analysis of the effects of TFIIB in somatic cells by co-transfection of BiFC plasmids pHA-Tf2b and pFlag-Tuba1α further confirms a direct interaction between TFIIB and α-tubulins.

The road to maturation: somatic cell interaction and self-organization of the mammalian oocyte

Mammalian oocytes go through a long and complex developmental process while acquiring the competencies that are required for fertilization and embryogenesis. Recent advances in molecular genetics and quantitative live imaging reveal new insights into the molecular basis of the communication between the oocyte and ovarian somatic cells as well as the dynamic cytoskeleton-based events that drive each step along the pathway to maturity. Whereas self-organization of microtubules and motor proteins direct meiotic spindle assembly for achieving genome reduction, actin filaments are instrumental for spindle positioning and the establishment of oocyte polarity needed for extrusion of polar bodies. Meiotic chromatin provides key instructive signals while being 'chauffeured' by both cytoskeletal systems.

Fusicoccanes: diterpenes with surprising biological functions

Fusicoccin is the best-studied member of a class of diterpenes sharing a 5-8-5 ring structure, called fusicoccanes. Fusicoccin was and still is a 'tool in plant physiology', targeting the main engine of plasma membrane transport, the P-type H(+)-ATPase, assisted by members of the 14-3-3 family. The key position of 14-3-3 proteins in cell biology, combined with a broader specificity of other fusicoccanes as shown by crystallography studies, make fusicoccanes a versatile tool in plant and animal biology. In this review, we examine recent evidence that fusicoccanes act on animal cells, describe the discovery of the fungal biosynthetic pathway and emphasize that lower (liverworts) and higher plants produce fusicoccanes with intriguing biological activities.

Polarity and asymmetry during mouse oogenesis and oocyte maturation

Cell polarity and asymmetry play a fundamental role in embryo development. The unequal segregation of determinants, cues, and activities is the major event in the differentiation of cell fate and function in all multicellular organisms. In oocytes, polarity and asymmetry in the distribution of different molecules are prerequisites for the progression and proper outcome of embryonic development. The mouse oocyte, like the oocytes of other mammals, seems to apply a less stringent strategy of polarization than other vertebrates. The mouse embryo undergoes a regulative type of development, which permits the full rectification of development even if the embryo loses up to half of its cells or its size is experimentally doubled during the early stages of embryogenesis. Such pliability is strongly related to the proper oocyte polarization before fertilization. Thus, the molecular mechanisms leading to the development and maintenance of oocyte polarity must be included in any fundamental understanding of the principles of embryo development. In this chapter, we provide an overview of current knowledge regarding the development and maintenance of polarity and asymmetry in the distribution of organelles and molecules in the mouse oocyte. Curiously, the mouse oocyte becomes polarized at least twice during ontogenesis; the question of how this phenomenon is achieved and what role it might play is addressed in this chapter.

The spatial and mechanical challenges of female meiosis

Recent work shows that cytokinesis and other cellular morphogenesis events are tuned by an interplay among biochemical signals, cell shape, and cellular mechanics. In cytokinesis, this includes cross-talk between the cortical cytoskeleton and the mitotic spindle in coordination with cell cycle control, resulting in characteristic changes in cellular morphology and mechanics through metaphase and cytokinesis. The changes in cellular mechanics affect not just overall cell shape, but also mitotic spindle morphology and function. This review will address how these principles apply to oocytes undergoing the asymmetric cell divisions of meiosis I and II. The biochemical signals that regulate cell cycle timing during meiotic maturation and egg activation are crucial for temporal control of meiosis. Spatial control of the meiotic divisions is also important, ensuring that the chromosomes are segregated evenly and that meiotic division is clearly asymmetric, yielding two daughter cells - oocyte and polar body - with enormous volume differences. In contrast to mitotic cells, the oocyte does not undergo overt changes in cell shape with its progression through meiosis, but instead maintains a relatively round morphology with the exception of very localized changes at the time of polar body emission. Placement of the metaphase-I and -II spindles at the oocyte periphery is clearly important for normal polar body emission, although this is likely not the only control element. Here, consideration is given to how cellular mechanics could contribute to successful mammalian female meiosis, ultimately affecting egg quality and competence to form a healthy embryo.

Gamma-tubulin is required for bipolar spindle assembly and for proper kinetochore microtubule attachments during prometaphase I in Drosophila oocytes

In many animal species the meiosis I spindle in oocytes is anastral and lacks centrosomes. Previous studies of Drosophila oocytes failed to detect the native form of the germline-specific γ-tubulin (γTub37C) in meiosis I spindles, and genetic studies have yielded conflicting data regarding the role of γTub37C in the formation of bipolar spindles at meiosis I. Our examination of living and fixed oocytes carrying either a null allele or strong missense mutation in the γtub37C gene demonstrates a role for γTub37C in the positioning of the oocyte nucleus during late prophase, as well as in the formation and maintenance of bipolar spindles in Drosophila oocytes. Prometaphase I spindles in γtub37C mutant oocytes showed wide, non-tapered spindle poles and disrupted positioning. Additionally, chromosomes failed to align properly on the spindle and showed morphological defects. The kinetochores failed to properly co-orient and often lacked proper attachments to the microtubule bundles, suggesting that γTub37C is required to stabilize kinetochore microtubule attachments in anastral spindles. Although spindle bipolarity was sometimes achieved by metaphase I in both γtub37C mutants, the resulting chromosome masses displayed highly disrupted chromosome alignment. Therefore, our data conclusively demonstrate a role for γTub37C in both the formation of the anastral meiosis I spindle and in the proper attachment of kinetochore microtubules. Finally, multispectral imaging demonstrates the presences of native γTub37C along the length of wild-type meiosis I spindles.

Proper chromosome segregation during cell division is essential. Missegregation of mitotic chromosomes leads to cell death or cancer, and chromosome missegregation during meiosis leads to miscarriage and birth defects. Cells utilize a bipolar microtubule-based structure known as the meiotic or mitotic spindle to segregate chromosomes. Because proper bipolar spindle formation is critically important for chromosome segregation, cells have many redundant mechanisms to ensure that this structure is properly formed. In most animal cells, centrosomes containing γ-tubulin protein complexes help organize and shape the bipolar spindle. Since meiosis I spindles in oocytes lack centrosomes, the mechanisms by which a meiotic bipolar spindle is assembled are not fully understood. In Drosophila oocytes it was not clear whether γ-tubulin played a role in bipolar spindle assembly or if it was even present on the meiotic spindle. We demonstrate that γ-tubulin plays vital roles in bipolar spindle formation and maintenance, as well as in aligning the chromosomes on the oocyte spindle. Additionally, we show that γ-tubulin is present on the bipolar spindle in Drosophila oocytes. More importantly, we demonstrate that γ-tubulin plays a critical role in the formation of the kinetochore microtubules that are required to properly orient chromosomes on the meiotic spindle.

Simulated microgravity compromises mouse oocyte maturation by disrupting meiotic spindle organization and inducing cytoplasmic blebbing

In the present study, we discovered that mouse oocyte maturation was inhibited by simulated microgravity via disturbing spindle organization. We cultured mouse oocytes under microgravity condition simulated by NASA's rotary cell culture system, examined the maturation rate and observed the spindle morphology (organization of cytoskeleton) during the mouse oocytes meiotic maturation. While the rate of germinal vesicle breakdown did not differ between 1 g gravity and simulated microgravity, rate of oocyte maturation decreased significantly in simulated microgravity. The rate of maturation was 8.94% in simulated microgravity and was 73.0% in 1 g gravity. The results show that the maturation of mouse oocytes in vitro was inhibited by the simulated microgravity. The spindle morphology observation shows that the microtubules and chromosomes can not form a complete spindle during oocyte meiotic maturation under simulated microgravity. And the disorder of γ-tubulin may partially result in disorganization of microtubules under simulated microgravity. These observations suggest that the meiotic spindle organization is gravity dependent. Although the spindle organization was disrupted by simulated microgravity, the function and organization of microfilaments were not pronouncedly affected by simulated microgravity. And we found that simulated microgravity induced oocytes cytoplasmic blebbing via an unknown mechanism. Transmission electron microscope detection showed that the components of the blebs were identified with the cytoplasm. Collectively, these results indicated that the simulated microgravity inhibits mouse oocyte maturation via disturbing spindle organization and inducing cytoplasmic blebbing.

John JC. Interspecies somatic cell nuclear transfer is dependent on compatible mitochondrial DNA and reprogramming factors

Interspecies somatic cell nuclear transfer (iSCNT) involves the transfer of a nucleus or cell from one species into the cytoplasm of an enucleated oocyte from another. Once activated, reconstructed oocytes can be cultured in vitro to blastocyst, the final stage of preimplantation development. However, they often arrest during the early stages of preimplantation development; fail to reprogramme the somatic nucleus; and eliminate the accompanying donor cell's mitochondrial DNA (mtDNA) in favour of the recipient oocyte's genetically more divergent population. This last point has consequences for the production of ATP by the electron transfer chain, which is encoded by nuclear and mtDNA. Using a murine-porcine interspecies model, we investigated the importance of nuclear-cytoplasmic compatibility on successful development. Initially, we transferred murine fetal fibroblasts into enucleated porcine oocytes, which resulted in extremely low blastocyst rates (0.48%); and failure to replicate nuclear DNA and express Oct-4, the key marker of reprogramming. Using allele specific-PCR, we detected peak levels of murine mtDNA at 0.14±0.055% of total mtDNA at the 2-cell embryo stage and then at ever-decreasing levels to the blastocyst stage (<0.001%). Furthermore, these embryos had an overall mtDNA profile similar to porcine embryos. We then depleted porcine oocytes of their mtDNA using 10 µM 2′,3′-dideoxycytidine and transferred murine somatic cells along with murine embryonic stem cell extract, which expressed key pluripotent genes associated with reprogramming and contained mitochondria, into these oocytes. Blastocyst rates increased significantly (3.38%) compared to embryos generated from non-supplemented oocytes (P<0.01). They also had significantly more murine mtDNA at the 2-cell stage than the non-supplemented embryos, which was maintained throughout early preimplantation development. At later stages, these embryos possessed 49.99±2.97% murine mtDNA. They also exhibited an mtDNA profile similar to murine preimplantation embryos. Overall, these data demonstrate that the addition of species compatible mtDNA and reprogramming factors improves developmental outcomes for iSCNT embryos.

Secondary follicle growth and oocyte maturation during encapsulated three-dimensional culture in rhesus monkeys: effects of gonadotrophins, oxygen and fetuin

BACKGROUND

An alginate-based matrix supports the three-dimensional (3D) architecture of non-human primate follicles and, in the presence of FSH, permits the in vitro development of pre-antral follicles to the small antral stage, including the production of ovarian steroids and paracrine factors. The current study investigated the ability of gonadotrophins, fetuin and oxygen (O₂) to improve primate follicle growth and oocyte maturation in vitro.

METHODS

Macaque secondary follicles were isolated from the early follicular phase ovaries, encapsulated in a sodium alginate matrix and cultured individually for 40 days in supplemented medium. The effects of recombinant human (rh) FSH (15, 3 and 0.3 ng/ml for high, medium and low FSH, respectively), bovine fetuin (1 or 0 mg/ml) and O₂ (5 or 20% v/v) were examined. Half of the follicles in each culture condition received rhLH on Day 30-40. Follicles that reached antral stage were treated with rh chorionic gonadotrophin for 34 h to initiate oocyte meiotic maturation. Media were analyzed for ovarian steroids and anti-müllerian hormone (AMH).

RESULTS

Improved culture conditions supported non-human primate, secondary follicle growth to the antral stage and, for the first time, promoted oocyte maturation to the MII stage. In the presence of fetuin at 5% O₂, follicles had the highest survival rate if cultured with high or medium FSH, whereas follicles grew to larger diameters at Week 5 in low FSH. Oocyte health and maturation were promoted under 5% O₂. High FSH stimulated steroid production by growing follicles, and steroidogenesis by follicles cultured with low FSH was promoted by LH. AMH biosynthesis was elevated with high compared with low FSH and for longer under 5% O₂ than under 20% O₂.

CONCLUSIONS

This encapsulated 3D culture model permits further studies on the endocrine and local factors that influence primate follicle growth and oocyte maturation, with relevance to enhancing fertility preservation options in women.

Evaluation of maturation competence of metaphase II oocytes in mice based on the distance between pericentriolar materials of meiotic spindle: distance of PCM during oocyte maturation

PURPOSE

To ascertain whether metaphase II (MII) spindle shape influences oocyte competence, we examined the meiotic spindle organization in in vivo ovulated (IVO) oocytes and in spontaneously matured or follicle stimulating hormone (FSH)-induced oocytes.

METHODS

FSH-induced oocytes matured in Waymouth's MB752/1 or human tubal fluid (HTF) media and oocytes matured spontaneously in the basal medium were obtained, and spindles were detected by immunofluorescence. To evaluate the fertilization-associated differences in spindle morphology, we performed in vitro fertilization and analysed integrin mRNA expression.

RESULTS

The distance between the pericentriolar materials (PCMs) in oocytes matured under all conditions was initially more, but it reduced gradually and increased again thereafter. Therefore, oocytes exhibiting a reduction in the distance between PCMs had the highest development rate to blastocyst in each condition.

CONCLUSION

These results indicate that the 'maturation competence' of MII oocytes can be evaluated on the basis of the distance between PCMs.

Demecolcine- and nocodazole-induced enucleation in mouse and goat oocytes for the preparation of recipient cytoplasts in somatic cell nuclear transfer procedures

Treatment of pre-activated oocytes with demecolcine (DEM) has been shown to induce the extrusion of all oocyte chromosomes within the second polar body (PB2). However, induced enucleation (IE) rates are generally low and the competence of these cytoplasts to support embryonic development following somatic cell nuclear transfer (SCNT) is impaired. Here, we explored whether short treatments with DEM or another antimitotic, nocodazole (NOC), improve IE efficiency, and determined the most appropriate timing for nuclear transfer in the cytoplasts produced. We show, for the first time, that IE can be accomplished in mouse and goat oocytes using NOC and that short treatments with DEM or NOC result in similar IE rates, which proved to be strain- and species-specific. Because enucleation induced by both antimitotic drugs is reversible, the IE protocol was combined with the mechanical aspiration of PB2s to increase permanent enucleation rates in mouse oocytes. None of the cloned mouse embryos produced from the resultant cytoplasts developed to the blastocyst stage. However, when they were reconstructed prior to the activation and antimitotic treatment, their in vitro embryonic development was similar to that of cloned embryos produced from mechanically-enucleated oocytes.

p38α MAPK is a MTOC-associated protein regulating spindle assembly, spindle length and accurate chromosome segregation during mouse oocyte meiotic maturation

P38αMAPK (p38α) is usually activated in response to various stresses and plays a role in the inhibition of cell proliferation and tumor progression, but little is known about its roles in meiotic spindle assembly. In this study, we characterized the dynamic localization of p38α and explored its function in mouse oocyte meiotic maturation. P38α specifically colocalized with γ-tubulin and Plk1 at the center of MTOCs and spindle poles. Depletion of p38α by specific morpholino injection resulted in severely defective spindles and misaligned chromosomes probably via MK2 dephosphorylation. Notably, depletion of p38α led to significant spindle pole defects, spindle elongation, non-tethered kinetochore microtubules and increased microtubule tension. The disruption of spindle stability was coupled with decreased γ-tubulin and Plk1 at MTOCs. Overexpression of Eg5, a conserved motor protein, also caused spindle elongation and its morpholino injection almost completely rescued spindle elongation caused by p38α depletion. In addition, p38α-depletion decreased BubR1 and interfered with spindle assembly checkpoint (SAC), which resulted in aneuploid oocytes. Together, these data indicate that p38α is an important component of MTOCs, which regulates spindle assembly and spindle length, as well as stabilizes the spindle and spindle poles. Perturbed SAC and abnormal microtubule tension may be responsible for the misaligned chromosomes and high aneuploidy in p38α-depleted mouse oocytes.

Cortical mechanics and meiosis II completion in mammalian oocytes are mediated by myosin-II and Ezrin-Radixin-Moesin (ERM) proteins

Cell division is inherently mechanical, with cell mechanics being a critical determinant governing the cell shape changes that accompany progression through the cell cycle. The mechanical properties of symmetrically dividing mitotic cells have been well characterized, whereas the contribution of cellular mechanics to the strikingly asymmetric divisions of female meiosis is very poorly understood. Progression of the mammalian oocyte through meiosis involves remodeling of the cortex and proper orientation of the meiotic spindle, and thus we hypothesized that cortical tension and stiffness would change through meiotic maturation and fertilization to facilitate and/or direct cellular remodeling. This work shows that tension in mouse oocytes drops about sixfold during meiotic maturation from prophase I to metaphase II and then increases ∼1.6-fold upon fertilization. The metaphase II egg is polarized, with tension differing ∼2.5-fold between the cortex over the meiotic spindle and the opposite cortex, suggesting that meiotic maturation is accompanied by assembly of a cortical domain with stiffer mechanics as part of the process to achieve asymmetric cytokinesis. We further demonstrate that actin, myosin-II, and the ERM (Ezrin/Radixin/Moesin) family of proteins are enriched in complementary cortical domains and mediate cellular mechanics in mammalian eggs. Manipulation of actin, myosin-II, and ERM function alters tension levels and also is associated with dramatic spindle abnormalities with completion of meiosis II after fertilization. Thus, myosin-II and ERM proteins modulate mechanical properties in oocytes, contributing to cell polarity and to completion of meiosis.

Zinc availability regulates exit from meiosis in maturing mammalian oocytes

Cellular metal ion fluxes are known in the case of alkali and alkaline earth metals but not well documented for transition metals. Here, we describe major changes in the zinc physiology of the mammalian oocyte as it matures and initiates embryonic development. Single-cell elemental analysis of mouse oocytes by synchrotron-based x-ray fluorescence microscopy (XFM) revealed a 50% increase in total zinc content within the 12-14 hour period of meiotic maturation. Perturbation of zinc homeostasis with a cell-permeable small molecule chelator blocked meiotic progression past telophase I. Zinc supplementation rescued this phenotype when administered prior to this meiotic block. However, following telophase arrest, zinc triggered parthenogenesis, suggesting that exit from this meiotic step is tightly regulated by the availability of a zinc-dependent signal. These results implicate the zinc bolus acquired during meiotic maturation as an important part of the maternal legacy to the embryo.

Cumulus-oocyte complexes from small antral follicles during the early follicular phase of menstrual cycles in rhesus monkeys yield oocytes that reinitiate meiosis and fertilize in vitro

The stage at which follicle-enclosed cumulus-oocyte complexes achieve developmental competence in primates is unknown. Therefore, studies were designed to characterize the ability of oocytes in small antral follicles present during the menstrual cycle to spontaneously resume meiosis, fertilize, and support early embryo development. Ovaries were removed from adult rhesus monkeys (n = 12) during the early follicular phase (Days 3-4) of spontaneous cycles. Small antral follicles were divided into five groups according to their diameter; group I: <0.5 mm; group II: 0.5-0.99 mm; group III: 1.0-1.49 mm; group IV: 1.5-1.99 mm; and group V: 2.0-2.5 mm. The cumulus-oocyte complex from healthy small antral follicles (devoid of dark oocytes or granulosa cells) were extracted (n = 199) and cultured for 48 h under different conditions: in TALP (tyrode, albumin, lactate, pyruvate) medium alone, SAGE medium alone, or plus gonadotropins. At 48 h, oocyte meiotic status and diameter were measured after treatment of cumulus-oocyte complexes with hyaluronidase. Cumulus-oocyte complexes derived from follicles of 0.5- to 2-mm diameter contain oocytes that typically reinitiate meiosis in the absence or presence of gonadotropins and fertilize via in vitro fertilization or intracytoplasmic sperm injection. Moreover, the inseminated oocytes can reach the morula stage but arrest. Thus, the ability of these oocytes to complete maturation, as monitored from subsequent embryonic development after fertilization, is suboptimal. Further studies on primate IVM of oocytes from SAFs are warranted in order for them to be considered as an additional, novel source of gametes for fertility preservation in cancer patients.

Noninvasive index of cryorecovery and growth potential for human follicles in vitro

Cryopreservation of oocytes and embryos is commonly used to preserve fertility. However, women undergoing cancer treatment may not have the time or may not be good candidates for these options. Ovarian cortical tissue cryopreservation and subsequent tissue transplant has been proven successful yet inefficient in preserving larger secondary follicles, and is not recommended as a fertility preservation option for women with certain cancers. We evaluated cryopreservation of individual follicles as an alternative option in rodents, nonhuman primates, and human primates. Under optimal conditions, cryopreserved mouse secondary follicles were able to reestablish granulosa cell-oocyte interactions, which are essential for subsequent follicle growth. Individual secondary follicles survived cryopreservation, were able to be cultured in a three-dimensional alginate hydrogel matrix to the antral stage, and the enclosed oocytes were competent for fertilization. Using a vital imaging technique (pol-scope) employed in many fertility centers, we were able to bioassay the thawed, cultured follicles for the presence of transzonal connections between the somatic and germ cells. Perturbations in these linkages were shown to be reversed when follicles were cryopreserved under optimal freezing conditions. We applied the optimized cryopreservation protocol to isolated rhesus monkey and human secondary follicles, and using the birefringent bioassay, we were able to show good correlation between early follicle growth and healthy somatic cell-oocyte connections. Our results suggest that ovarian follicles can be cryopreserved, thawed, and analyzed noninvasively, making follicle preservation an additional option for young cancer patients.

Activin promotes follicular integrity and oogenesis in cultured pre-antral bovine follicles

The aim of this study was to determine the individual and combined effect of activin and follicle stimulating hormone (FSH) on somatic and germ cell development in cultured pre-antral follicles. Pre-antral bovine follicles (mean diameter 157 +/- 3, range 132-199 microm) were cultured for 8 days in serum-free medium in the presence of either 100 ng/ml of recombinant human activin A (rhAct A), 100 ng/ml rhAct A combined with a high (100 ng/ml) or low (50 ng/ml) concentration of recombinant FSH (rFSH) or 50 ng/ml rFSH alone. Intrafollicular connexin 43 expression and actin-based cell adhesion were assessed on Day 2 and 4 of culture. Steroidogenesis was evaluated after Day 4 and 8. Follicles exposed to 100 ng/ml activin maintained expression of connexin 43 at the follicular periphery. In the presence of activin, with or without 100 ng/ml or 50 ng/ml FSH, follicles were steroidogenic undergoing significant growth (P < 0.01), granulosa cell proliferation (P < 0.01) and antral cavity formation (P < 0.05) compared with cultured controls. Maximum oocyte growth occurred in the presence of 100 ng/ml activin alone with a significant percentage of these oocytes maintaining normal morphology over controls (P < 0.05). These results are consistent with a role for activin in maintaining oocyte granulosa cell interactions due to increased peripheral granulosa cell adhesion to the basement membrane and retention of adhesion at the surface of the zona pellucida. Thus, the polarized expression of cell contact interactions promoted by activin supports ongoing folliculogenesis.

NEDD1 is crucial for meiotic spindle stability and accurate chromosome segregation in mammalian oocytes

Defects in meiotic spindle structure contribute to chromosome segregation errors leading to genomic instability in oocytes and embryos upon fertilization. In this study, we analyzed the mechanisms that control spindle microtubule nucleation and stability in mammalian oocytes, and identified NEDD1/GCP-WD as a key regulator. NEDD1 specifically co-localizes with gamma-tubulin and pericentrin at microtubule-organizing centers (MTOCs) in mouse oocytes arrested at prophase-I. During metaphase-I and metaphase-II, the protein remains associated with MTOCs, in a pericentrin dependent manner. Notably, knockdown of Nedd1 transcripts using specific siRNAs resulted in a high incidence (65-70%) of metaphase-I arrest. The arrested oocytes were characterized by disrupted meiotic spindle structure, reduced microtubule density and significant chromosome misalignment. Detection of MAD2 at kinetochores indicated an absence of stable chromosome-microtubule attachment as well as activation of the spindle assembly checkpoint (SAC). Importantly, the disruption of meiotic spindle stability was associated with decreased gamma-tubulin at MTOCs in NEDD1-depleted oocytes, as well as a high frequency of chromosome non-disjunction errors leading to aneuploidy (50%) in the oocytes that did progress to metaphase-II. This study demonstrates that NEDD1 is an essential component of acentriolar oocyte MTOCs, which functions in the regulation of meiotic spindle stability. Moreover, it underscores that disruption of spindle stability in oocytes can lead to chromosomes segregation errors that are not fully resolved by SAC.

Cumulus cell contact during oocyte maturation in mice regulates meiotic spindle positioning and enhances developmental competence

PURPOSE

To investigate the role of cumulus cell contact during oocyte maturation on meiotic spindle assembly and the acquisition of developmental competence.

METHODS

Cumulus oocyte complexes isolated from mouse ovaries subjected to in vitro or in vivo maturation were analyzed by confocal microscopy with respect to oocyte somatic cell contacts and for their ability to develop after parthenogenic activation during embryo culture.

RESULTS

Cell contact is maintained during maturation in vivo, predisposing oocytes to cortical meiotic spindle assembly and developmental competence acquisition. In contrast, oocytes matured in vitro lose cell contact coincident with central meiotic spindle assembly that results in cleavage delays upon egg activation and failure to form blastocysts. Experimental disruption of cell contact by the actin-depolymerizing agent latrunculin B results in the formation of enlarged meiotic spindles with dispersed chromosomes unlike the compact ordering of chromosomes observed on spindles formed after in vivo maturation, suggesting a link between cell contact and the acquisition of developmental competence.

CONCLUSIONS

Somatic cell contact optimizes oocyte quality during meiotic maturation by regulating the spatial organization and function of the meiotic spindle through actin-dependent mechanisms that enhance development.

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.

In vitro grown human ovarian follicles from cancer patients support oocyte growth

BACKGROUND

Young female adult and adolescent cancer patients facing life-preserving but fertility-threatening chemo- or radiation-therapy are increasingly seeking options to protect their reproductive potential. Ovarian tissue cryopreservation with transplantation is a promising technique to safeguard fertility in cancer patients. However, this method may risk re-introduction of the original cancer to the survivor of the disease. Thus, developing a method for in vitro growth of immature follicles may provide a method for fertility restoration in the future.

METHODS

Human secondary follicles were isolated from ovarian tissues obtained from cancer patients and grown in vitro within a bio-engineered culture system for 30 days.

RESULTS

Human ovarian follicles became steroidogenically active, and developed from the early secondary to antral stage in vitro. The follicles contained healthy, growing oocytes that were connected by transzonal projections between the somatic cells and oocyte.

CONCLUSIONS

Our data support the notion that human follicle development can be achieved in vitro in a bio-engineered culture system. More studies are required to investigate whether the fully sized oocytes obtained from in vitro grown follicle are competent to resume meiosis and be fertilized.

Functions of Fyn kinase in the completion of meiosis in mouse oocytes

Oocyte maturation invokes complex signaling pathways to achieve cytoplasmic and nuclear competencies for fertilization and development. The Src-family kinases FYN, YES and SRC are expressed in mammalian oocytes but their function during oocyte maturation remains an open question. Using chemical inhibitor, siRNA knockdown, and gene deletion strategies the function of Src-family kinases was evaluated in mouse oocytes during maturation under in vivo and in vitro conditions. Suppression of Src-family as a group with SKI606 greatly reduced meiotic cell cycle progression to metaphase-II. Knockdown of FYN kinase expression after injection of FYN siRNA resulted in an approximately 50% reduction in progression to metaphase-II similar to what was observed in oocytes isolated from FYN (-/-) mice matured in vitro. Meiotic cell cycle impairment due to a Fyn kinase deficiency was also evident during oocyte maturation in vivo since ovulated cumulus oocyte complexes collected from FYN (-/-) mice included immature metaphase-I oocytes (18%). Commonalities in meiotic spindle and chromosome alignment defects under these experimental conditions demonstrate a significant role for Fyn kinase activity in meiotic maturation.

Protein kinase C delta (PKCdelta) interacts with microtubule organizing center (MTOC)-associated proteins and participates in meiotic spindle organization

Defects in meiotic spindle structure can lead to chromosome segregation errors and genomic instability. In this study the potential role of protein kinase C delta (PKCdelta) on meiotic spindle organization was evaluated in mouse oocytes. PKCdelta was previously shown to be phosphorylated during meiotic maturation and concentrate on the meiotic spindle during metaphases I and II. Currently we show that when phosphorylated on Threonine 505 (pPKCdelta(Thr505)), within the activation loop of its C4 domain, PKCdelta expression was restricted to the meiotic spindle poles and a few specific cytoplasmic foci. In addition, pPKCdelta(Thr505) co-localized with two key microtubule organizing center (MTOC)-associated proteins, pericentrin and gamma-tubulin. An interaction between pPKCdelta(Thr505) and pericentrin as well as gamma-tubulin was confirmed by co-immunoprecipitation analysis using both fetal fibroblast cells and oocytes. Notably, targeted knockdown of PKCdelta expression in oocytes using short interfering RNAs effectively reduced pPKCdelta(Thr505) protein expression at MTOCs and leads to a significant (P < 0.05) disruption of meiotic spindle organization and chromosome alignment during MI and MII. Moreover, both gamma-tubulin and pericentrin expression at MTOCs were decreased in pPKCdelta(Thr505)-depleted oocytes. In sum, these results indicate that pPKCdelta(Thr505) interacts with MTOC-associated proteins and plays a role in meiotic spindle organization in mammalian oocytes.