Cytoplasmic changes in relation to nuclear maturation and early embryo developmental potential of porcine oocytes: effects of gonadotropins, cumulus cells, follicular size, and protein synthesis inhibition

The Impact of Centrosome Pathologies on Ovarian Cancer Development and Progression with a Focus on Centrosomes as Therapeutic Target

The impact of centrosome abnormalities on cancer cell proliferation has been recognized as early as 1914 (Boveri, Zur Frage der Entstehung maligner Tumoren. Jena: G. Fisher, 1914), but vigorous research on molecular levels has only recently started when it became fully apparent that centrosomes can be targeted for new cancer therapies. While best known for their microtubule-organizing capabilities as MTOC (microtubule organizing center) in interphase and mitosis, centrosomes are now further well known for a variety of different functions, some of which are related to microtubule organization and consequential activities such as cell division, migration, maintenance of cell shape, and vesicle transport powered by motor proteins, while other functions include essential roles in cell cycle regulation, metabolic activities, signal transduction, proteolytic activity, and several others that are now heavily being investigated for their role in diseases and disorders (reviewed in Schatten and Sun, Histochem Cell Biol 150:303-325, 2018; Schatten, Adv Anat Embryol Cell Biol 235:43-50, 2022a; Schatten, Adv Anat Embryol Cell Biol 235:17-35, 2022b).Cancer cell centrosomes differ from centrosomes in noncancer cells in displaying specific abnormalities that include phosphorylation abnormalities, overexpression of specific centrosomal proteins, abnormalities in centriole and centrosome duplication, formation of multipolar spindles that play a role in aneuploidy and genomic instability, and several others that are highlighted in the present review on ovarian cancer. Ovarian cancer cell centrosomes, like those in other cancers, display complex abnormalities that in part are based on the heterogeneity of cells in the cancer tissues resulting from different etiologies of individual cancer cells that will be discussed in more detail in this chapter.Because of the critical role of centrosomes in cancer cell proliferation, several lines of research are being pursued to target centrosomes for therapeutic intervention to inhibit abnormal cancer cell proliferation and control tumor progression. Specific centrosome abnormalities observed in ovarian cancer will be addressed in this chapter with a focus on targeting such aberrations for ovarian cancer-specific therapies.

The developmental potential of mature oocytes derived from rescue in vitro maturation

OBJECTIVE

To examine the developmental competence of immature oocytes in stimulated cycles, that matured after rescue in vitro maturation (IVM) compared with their sibling in vivo matured oocytes.

DESIGN

Retrospective cohort study.

SETTING

IVF clinic.

PATIENTS

A total of 182 patients underwent 200 controlled ovarian stimulation cycles with intracytoplasmic sperm injection cycles in which immature oocytes were retrieved and at least one mature oocyte was obtained through rescue IVM.

INTERVENTION

In vitro culture of immature germinal vesicle (GV) and metaphase I (MI) oocytes, retrieved in stimulated cycles.

MAIN OUTCOME MEASURES

Fertilization rate, cleavage rate, blastulation rate, ploidy of embryos evaluated using preimplantation genetic testing for aneuploidy, morphokinetic parameters and pregnancy outcomes.

RESULTS

In total, 2,288 oocytes were retrieved from 200 cycles. After denudation, 1,056 of the oocytes (46% ± 16%) were classified as metaphase II (MII). A total of 333/375 (89%) of MI oocytes and 292/540 (54%) of GV oocytes matured overnight and underwent intracytoplasmic sperm injection. The fertilization rates of matured oocytes from MI rescue IVM (R-MI) and from GV rescue IVM (R-GV) were comparable with those of their sibling MII oocytes (71% vs. 66%; 66% vs. 63%, respectively). Early cleavage rates (80% ± 35% vs. 92% ± 20%; 80% ± 42% vs. 95% ± 28%, respectively) and blastulation rates (32 ± 40% vs. 62 ± 33%; 24 ± 37% vs. 60 ± 35%, respectively) were significantly decreased in rescue IVM matured oocytes (R-oocytes)-derived zygotes, but the blastocyst (BL) euploidy rate and "good quality" BL rate were comparable with those of MII sibling-derived embryos. In addition, rescue IVM embryos showed significantly higher levels of multinucleation at the 2- and 4-cell stages, as well as higher rates of zygote direct cleavage from one to 3 to 4 cells. Overall, 21 transfers of rescue IVM embryos resulted in 3 healthy live births.

CONCLUSIONS

For patients with a low maturation rate and/or low numbers of mature oocytes at retrieval, rescue IVM may contribute more competent oocytes and additional viable BLs for transfer from the same stimulation cycle, maximizing the chances for pregnancy and live birth.

In vitro growth culture in a medium with reduced sodium chloride improves maturation and developmental competence of pig oocytes derived from small antral follicles

The objective of this study was to evaluate the effects of reducing the sodium chloride content in in vitro growth (IVG) medium to 61.6 mM on in vitro maturation (IVM) and embryonic development of pig oocytes derived from small antral follicles (SAF) less than 3 mm in diameter. SAF oocytes were cultured for 2 days to induce IVG in alpha-minimal essential medium with 108 mM NaCl (αMEM-108) or porcine zygote medium (PZM) containing 61.6 mM (PZM-61.6) or 108 mM (PZM-108) NaCl. These media were further supplemented with 1 mM dibutyryl cyclic adenosine monophosphate (dbcAMP) and 10% (v/v) fetal bovine serum. After IVG culture, oocytes were matured for 44 h in our standard IVM medium. The IVG culture in PZM-61.6 significantly increased nuclear maturation (88.0 ± 2.2%) of SAF oocytes compared to that in PZM-108 (77.3 ± 3.9%) or αMEM-108 (75.9 ± 3.8%). After parthenogenesis (PA), the proportions of blastocysts, based on the number of metaphase II (MII) oocytes, induced for PA were not different among IVG oocytes cultured in PZM-61.6 (50.2 ± 3.0%), PZM-108 (46.8 ± 2.9%), or αMEM-108 (45.6 ± 2.9%). The IVM oocytes derived from IVG in PZM-61.6 showed increased perivitelline space (PVS) (12.1 ± 0.6 μm) and intra-oocyte glutathione (GSH) content (1.19 ± 0.04 pixels/oocyte) compared to PVS (8.0 ± 0.5 and 7.4 ± 0.4 μm) and GSH (1.03 ± 0.04 and 1.00 ± 0.04 pixels/oocyte) of oocytes derived from PZM-108 and αMEM-108, respectively. The IVG culture in PZM-61.6 stimulated meiotic resumption after IVG and faster nuclear progression after IVM than that in αMEM-108. After somatic cell nuclear transfer (SCNT), the blastocyst formation of SAF oocytes grown in PZM-61.6 (17.8 ± 3.3%) was higher than that of oocytes grown in PZM-108 (7.5 ± 2.7%) but not different from that of oocytes in αMEM-108 (11.4 ± 3.4%). Regardless of the different osmotic pressures, nuclear maturation was significantly increased by IVG culture in PZM with reduced NaCl (86.8 ± 2.3 and 84.9 ± 4.2% in PZM-61.6 and PZM-61.6 with sorbitol, respectively) than in PZM-108 (70.5 ± 3.4%). Blastocyst formation was not affected by the differences in NaCl content and osmotic pressure of the IVG medium, whereas the mean number of cells in blastocysts was significantly higher following IVG culture in PZM-61.6 than in the other groups. In conclusion, the results demonstrate that, following SCNT in pigs, IVG culture of SAF oocytes in a medium with a reduced NaCl concentration stimulates oocyte maturation and improves subsequent embryonic development.

Porcine follicular fluid derived from > 8 mm sized follicles improves oocyte maturation and embryo development during in vitro maturation of pigs

The aim of the present study was to investigate the effects of porcine follicular fluid (pFF) from large-sized (LFF; >8 mm in diameter) and medium-sized (MFF; 3-6 mm in diameter) follicles on the maturation and developmental competence of porcine oocytes. Cumulus-oocyte complexes (COCs) were collected from follicles 3-6 mm in diameter. The collected COCs were incubated for 22 h with LFF or MFF (in vitro maturation (IVM)-I stage) and were incubated subsequently for 22 h with LFF or MFF (IVM-II stage). Cumulus expansion was confirmed after the IVM-I stage and nuclear maturation was evaluated after the IVM-II stage. Intracellular glutathione (GSH) and reactive oxygen species (ROS) levels were measured and embryonic development was evaluated. Relative cumulus expansion and GSH levels were higher in the LFF group compared with in the MFF group after the IVM-I stage (P < 0.05). After the IVM-II stage, the numbers of oocytes in metaphase-II were increased in the LFF group and GSH content was higher in all of the LFF treatment groups compared with in the MFF treatment groups during both IVM stages (P < 0.05). ROS levels were reduced by LFF treatment regardless of IVM stage (P < 0.05). Blastocyst formation and the total numbers of cells in blastocysts were increased in all LFF treatment groups compared with the control group (P < 0.05). These results suggested that pFF from large follicles at the IVM stage could improve nucleic and cytoplasmic maturation status and further embryonic development through reducing ROS levels and enhancing responsiveness to gonadotropins.

Cortical Granule Distribution and Expression Pattern of Genes Regulating Cellular Component Size, Morphogenesis, and Potential to Differentiation are Related to Oocyte Developmental Competence and Maturational Capacity In Vivo and In Vitro

Polyspermia is an adverse phenomenon during mammalian fertilization when more than one sperm fuses with a single oocyte. The egg cell is prepared to prevent polyspermia by, among other ways, producing cortical granules (CGs), which are specialized intracellular structures containing enzymes that aim to harden the zona pellucida and block the fusion of subsequent sperm. This work focused on exploring the expression profile of genes that may be associated with cortical reactions, and evaluated the distribution of CGs in immature oocytes and the peripheral density of CGs in mature oocytes. Oocytes were isolated and then processed for in vitro maturation (IVM). Transcriptomic analysis of genes belonging to five ontological groups has been conducted. Six genes showed increased expression after IVM (ARHGEF2, MAP1B, CXCL12, FN1, DAB2, and SOX9), while the majority of genes decreased expression after IVM. Using CG distribution analysis in immature oocytes, movement towards the cortical zone of the oocyte during meiotic competence acquisition was observed. CGs peripheral density decreased with the rise in meiotic competence during the IVM process. The current results reveal important new insights into the in vitro maturation of oocytes. Our results may serve as a basis for further studies to investigate the cortical reaction of oocytes.

Potential of Auraptene in Improvement of Oocyte Maturation, Fertilization Rate, and Inflammation in Polycystic Ovary Syndrome Mouse Model

Polycystic ovary with poor-quality oocytes has remained problematic in polycystic ovary syndrome (PCOS) patients. It is well documented that the inflammation and production of reactive oxygen species (ROS) in PCOS ovaries are significantly higher than normal voluntaries. In this study, we hypothesized that auraptene (AUR), as a coumarin derivative with anti-inflammatory properties, may be effective in improvement of oocyte maturation and fertilization rate in PCOS patients. For this purpose, PCOS model was induced in NMRI mice and confirmed by ovarian histopathology observations and hormonal assays. PCOS-induced mice were administrated with AUR (PCOS-AUR) and metformin (PCOS-MET), and their effects on inflammation, apoptosis rate, oocyte maturation, and in vitro fertilization capacity were determined and compared with those normal and PCOS animals treated with sesame oil (PCOS-sesame oil) and no treatment (PCOS). Treatment with AUR and MET decreased the inflammation and apoptosis rates in PCOS mice compared with PCOS animals with no treatment. PCOS-AUR and PCOS-MET oocytes also showed higher intracellular glutathione and lower ROS concentrations compared with PCOS mice, indicating improved oocyte maturation rate. PCOS-AUR and PCOS-MET groups showed higher percentages of expansion rate and MII stage oocytes, and lower rate of abnormal oocytes compared with PCOS with no treatment. The rate of fertilization in the oocytes isolated from PCOS-AUR and PCOS-MET groups was higher than PCOS-sesame oil and PCOS groups. Our findings suggest that AUR can be considered as a potential candidate for improvement of oocyte maturation and fertilization capacity in PCOS patients, comparable to MET.

Effects of gonadotrophins and insulin on glucose uptake in the porcine cumulus-oocyte complex during IVM

The combination of gonadotrophins (LH and FSH) and insulin is frequently used in porcine oocyte IVM, but the individual effects of gonadotrophins and insulin have not been completely studied. The aim of this study was to investigate the mechanisms involved in glucose metabolism in the swine cumulus-oocyte complex (COC), analysing the effects of gonadotrophins (10IUmL-1 LH+10IUmL-1 FSH) and 0.4μUmL-1 insulin, during 44h of IVM, on glucose transport and consumption, as well as on nuclear maturation and sperm penetration. We evaluated the effects of gonadotrophins and insulin separately or in combination on glucose consumption, membrane permeability to the glucose fluorescent analogue 6-(N -(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-6-deoxyglucose (6-NBDG), the presence of GLUT-4 and oocyte maturation rates, after 44h of IVM. Nuclear maturation percentages increased significantly following the addition of gonadotrophins alone or in combination with insulin to the culture medium (P P P <0.0001). Although gonadotrophins and insulin increased GLUT-4 expression, neither modified 6-NBDG incorporation. In conclusion, gonadotrophins and insulin had different effects during IVM; although gonadotrophins increased maturation rates and glucose consumption, they had no effect on glucose transport, and insulin improved sperm penetration without affecting the parameters related to glucose utilisation. Therefore, glucose metabolism is likely to be primarily regulated by its consumption in metabolic pathways rather than by changes in membrane permeability.

Thymoquinone reduces intracytoplasmic oxidative stress and improves epigenetic modification in polycystic ovary syndrome mice oocytes, during in-vitro maturation

Although in-vitro maturation (IVM) of oocytes has been presented as an alternative treatment to traditional stimulated in-vitro fertilization, the culture condition can be improved by natural antioxidants. Thus, we investigated the protective effect of Thymoquinone (TQ) during IVM in the polycystic ovary syndrome (PCOS) mice model. The induction of PCOS was made by dehydroepiandrosterone via subcutaneous injection, in prepubertal female B6D2F1-mice. After 21 days later, germinal vesicle (GV)-stage-oocytes were extracted and incubated in IVM media containing 0, 1.0, 10.0, and 100.0 μM of TQ. To assess fertilization and blastulation rates, after 22-24 hr, the treated oocytes were fertilized in-vitro with epididymal spermatozoa. Some other oocytes were evaluated for maturation, epigenetic, and oxidative stress markers. Similarly, the mRNA expression of epigenetic enzymes genes (Dnmt1 and Hdac1), three maternally derived genes (Mapk, CyclinB, and Cdk1) and apoptosis-related genes (Bax and Bcl2) were assessed. Our results showed that the maturation, fertilization, and blastulation rates were significantly higher in the 10.0 μM TQ-treated group compared with the untreated group and likewise with in-vivo matured oocytes. The Bax expression was reduced in 10.0 μM TQ matured oocytes, but Bcl2, Dnmt1, Hdac1, Cdk1, and Mapk were upregulated in this group compared to other groups. Furthermore, dimethylation of histone-3 at lysine-9 (H3K9m2) and DNA methylation were significantly increased whereas H4K12 acetylation (H4K12ac) was decreased in the 10.0 μM TQ-treated group in comparison with control and in-vivo matured oocytes. Therefore, our results are suggesting that 10.0 μM TQ may enhance the developmental competence of PCOS oocytes via the modulation of oxidative stress and epigenetic alterations.

Role of cAMP modulator supplementations during oocyte in vitro maturation in domestic animals

Cyclic adenosine monophosphate (cAMP) is an important molecule in signal transduction within the cell, functioning as a second cell messenger of gonadotrophin stimulation. The concentration of cAMP in cumulus-oocyte complexes (COCs) is known to be controlled through modulation of its synthesis by adenylyl cyclase (AC) and by degradation through the cyclic nucleotide phosphodiesterase (PDE) enzymes. One of the main obstacles for in vitro embryo production is the optimization of reproduction processes that occur in oocyte maturation. The function of cAMP is important in maintaining meiotic arrest in mammalian oocytes. When the oocyte is physically removed from the antral follicle for in vitro maturation (IVM), intra-oocyte cAMP concentrations decrease and spontaneous meiotic resumption begins, due to the depletion of inhibitory factors from the follicle. In many studies, relatively greater cAMP concentrations before IVM has been reported to improve oocyte competence, leading to subsequent benefits in embryonic development in different species. There, therefore, has been an increase in oocyte cAMP concentrations with several treatments and different approaches, such as invasive AC, stimulators of AC activity, PDE inhibitors, and cAMP analogs. The aim of this review is to comprehensively evaluate and provide data related to (i) the use of cAMP modulators during IVM and the effects on completion of meiosis and cytoplasmic reorganization, which are required for development of oocytes with the capacity to contribute to fertilization and subsequent embryonic development; and (ii) the main cAMP modulators and the effects when used in oocyte IVM.

In vitro maturation of collared peccary (Pecari tajacu) oocytes after different incubation times

ABSTRACT: Oocyte in vitro maturation (IVM) is the first step of the in vitro reproductive technologies that enables mature oocytes to be generated ex vivo and after used for embryo production. In this sense, the establishment of culture environment, as oocyte incubation time, is essential for the success of the IVM. Therefore, the study was carried out to investigate the relationship between the meiotic potential and the IVM times of collared peccary oocytes, wild mammals of great commercial and ecological interest. Thus, ovaries were collected of females derived from captivity and transported to the laboratory within 1 hour of slaughtering. The oocytes derived from follicles (3-6mm in diameter) were recovered by aspirated and sliced. Good quality oocytes (evenly granulated cytoplasm with a least one layer of surrounding cumulus cells) were selected and subjected to culture in TCM 199 supplemented with 10µg/mL FSH, 10% FBS and 100µM cysteamine at 38.5°C, 5% CO2 and maximum humidity for 24 or 48 hours. After the incubation period, the nuclear status, the presence of first polar body and the expansion of cumulus cells of oocytes were assessed. The data obtained were analyzed by Fisher exact test (P<0.05). A total of four sessions (2-3 females per session) were performed, resulting in eighteen aspirated and sliced ovaries with normal morphological characteristics. An oocyte recovery rate of about 83.1% (59/71) was obtained with 3.3 oocytes/ovary and 2.3 viable oocytes/ovary. After different incubation times, differences (P<0.05) were observed in 24 and 48 hours for expansion of the cumulus cells (38.1% vs. 100%), presence of first polar body (52.4% vs. 90.5%) and nuclear status in second metaphase (19.0% vs. 76.2%), respectively. In conclusion, 48 hours is suitable time for the in vitro maturation of oocytes derived from collared peccaries when compared to the time of 24 hours, according to the meiotic potential observed. Additional studies should be conducted to improve the quality of the oocyte culture environment, as medium composition, aiming to obtain viable mature oocytes for other in vitro biotechnologies.

Effects of embryo-derived exosomes on the development of bovine cloned embryos

The developmental competence of in vitro cultured (IVC) embryos is markedly lower than that of their in vivo counterparts, suggesting the need for optimization of IVC protocols. Embryo culture medium is routinely replaced three days after initial culture in bovine, however, whether this protocol is superior to continuous nonrenewal culture method under current conditions remains unclear. Using bovine somatic cell nuclear transfer (SCNT) embryos as the model, our results showed that compared with routine renewal treatment, nonrenewal culture system significantly improved blastocyst formation, blastocyst quality (increased total cell number, decreased stress and apoptosis, enhanced Oct-4 expression and ratio of ICM/TE), as well as following development to term. Existence and function of SCNT embryo-derived exosomes were then investigated to reveal the cause of impaired development induced by culture medium replacement. Exosomes were successfully isolated through differential centrifugation and identified by both electron microscopy and immunostaining against exosomal membrane marker CD9. Supplementation of extracted exosomes into freshly renewed medium significantly rescued not only blastocyst formation and quality (in vitro development), but also following growth to term (in vivo development). Notably, ratio of ICM/TE and calving rate were enhanced to a similar level as that in nonrenewal group. In conclusion, our results for the first time indicate that 1: bovine SCNT embryos can secrete exosomes into chemically defined culture medium during IVC; 2: secreted exosomes are essential for SCNT blastocyst formation, blastocyst quality, and following development to term; 3: removal of exosomes induced by culture medium replacement impairs SCNT embryo development, which can be avoided by nonrenewal culture procedure or markedly recovered by exosome supplementation.

Bisphenol S negatively affects the meotic maturation of pig oocytes

Bisphenol A (BPA), a chemical component of plastics, is a widely distributed environmental pollutant and contaminant of water, air, and food that negatively impacts human health. Concerns regarding BPA have led to the use of BPA-free alternatives, one of which is bisphenol S (BPS). However, the effects of BPS are not well characterized, and its specific effects on reproduction and fertility remain unknown. It is therefore necessary to evaluate any effects of BPS on mammalian oocytes. The present study is the first to demonstrate the markedly negative effects of BPS on pig oocyte maturation in vitro, even at doses lower than those humans are exposed to in the environment. Our results demonstrate (1) an effect of BPS on the course of the meiotic cell cycle; (2) the failure of tubulin fibre formation, which controls proper chromosome movement; (3) changes in the supply of maternal mRNA; (4) changes in the protein amounts and distribution of oestrogen receptors α and β and of aromatase; and (5) disrupted cumulus cell expansion. Thus, these results confirm that BPS is an example of regrettable substitution because this substance exerts similar or even worse negative effects than those of the material it replaced.

Hampered cumulus expansion of porcine cumulus-oocyte complexes by excessive presence of alpha2 -macroglobulin is likely mediated via inhibition of zinc-dependent metalloproteases

In vitro maturation (IVM) in serum causes hampered expansion of porcine cumulus-oocyte complexes (COCs) due to excessive alpha₂ -macroglobulin (A2M). This study investigated two hypotheses that could explain the effect of A2M: (i) binding of epidermal growth factor (EGF) to A2M, followed by its decreased availability; and (ii) inhibition of zinc-dependent metalloproteases. Cumulus expansion was evaluated based on the diameter of the COCs, the proportion of COCs participating in a floating cloud and the proportion of COCs with loss of cumulus cells. The first hypothesis of decreased EGF availability was tested by increasing the EGF concentration (20 and 50 ng/mL vs. 10 ng/mL), but was not confirmed because cumulus expansion did not improve. To verify the second hypothesis of inhibited zinc-dependent metalloproteases, the effect of tissue inhibitor of metalloproteases-3 (TIMP-3) on cumulus expansion during IVM with and without A2M was investigated. To immuno-neutralize A2M, serum was pre-incubated with A2M antibodies. Impaired cumulus expansion because of TIMP-3 could only be observed during IVM in 10% of serum with A2M antibodies. No effect of TIMP-3 was observed in medium without A2M antibodies. These results indicate that A2M and TIMP-3 share a common target, a zinc-dependent metalloprotease. Future research is directed toward the identification of the protease involved.

Fibroblast growth factor 10 markedly improves in vitro maturation of porcine cumulus-oocyte complexes

Growth factors synthesized by ovarian somatic cells affect cumulus cell expansion and oocyte maturation in vitro. Fibroblast growth factor 10 (FGF10), for example, is a known regulator of mammalian cumulus-oocyte complex maturation. In this study, we investigated the effects of 0, 5, 10, 50, and 100 ng/mL FGF10 (5F, 10F, 50F, and 100F, respectively) on in vitro cumulus cell expansion, oocyte maturation, and embryo development. The percentage of fully expanded cumulus cells at the oocyte's metaphase-II (MII) stage was significantly higher in the 10F-treated group than in the control. Transcript abundance of the cumulus cell expansion-related gene encoding hyaluronian synthase 2 (HAS2) in cumulus cells at oocyte germinal vesicle breakdown (GVBD) was significantly higher in the 10F- and 50F-treated groups compared to untreated controls, whereas the mRNA abundance of the protease cathepsin B (CTSB) at the oocyte MII stage was remarkably decreased in the 10F-treated group. The percentage of oocytes with normal spindles was greater in the 10F- and 50F-treated group at GVBD than in the other groups; the 5F-, 10F-, and 100F-treated groups were higher than the control; and the 50F-treated group was highest at MII. The abundance of GDF9 and BMP15 transcript at GVBD and BMP15 and CCNB1 transcripts at MII increased in the 10F-treated group. Cleavage rate, blastocyst formation rate, and total cell number were significantly higher in the 5F- to 50F-treated groups. These results demonstrate that FGF10 markedly improves cumulus cell expansion, oocyte maturation, and subsequent embryo development. Mol. Reprod. Dev. 84: 67-75, 2017. © 2016 Wiley Periodicals, Inc.

Cytoplasmic Determination of Meiotic Spindle Size Revealed by a Unique Inter-Species Germinal Vesicle Transfer Model

Spindle sizes are different in diverse species and cell types. In frogs, the meiotic spindle size is positively correlated with the egg cell volume. Across species, relatively small mouse oocytes (70–80 μm) have a relatively large spindle while larger pig oocytes (about 120 μm) have a considerably smaller spindle. In this study we investigated whether species-specific oocyte spindle size was determined by cytoplasmic or nuclear factors. By exchanging the germinal vesicle between mouse and pig oocytes, we obtained two kinds of reconstructed oocytes: one with mouse ooplasm and pig GV (mCy-pGV oocyte), and the other with pig ooplasm and mouse GV (pCy-mGV oocyte). We show that the MII spindle size of the mCy-pGV oocyte is similar to that of the mouse meiotic spindle and significantly larger than that of the pig meiotic spindle. The timing of oocyte maturation also followed that of the species from which the oocyte cytoplasm arose, although some impact of the origin of the GV was observed. These data suggest that spindle size and the timing of meiotic progression are governed by cytoplasmic components rather than cytoplasmic volume and GV materials.

The Extracellular Calcium-Sensing Receptor (CASR) Regulates Gonadotropins-Induced Meiotic Maturation of Porcine Oocytes

Gonadotropins and epidermal growth factor (EGF) play crucial roles in promoting oocyte maturation. The regulatory network downstream of these key factors is not well understood. The present study was designed to investigate the role of the calcium-sensing receptor (CASR) in porcine oocyte in vitro maturation. CASR expression was up-regulated in oocytes matured in gonadotropin-containing medium. Cortical distribution of CASR was enhanced with gonadotropins but not EGF. Supplementation of a CASR agonist (NPS R-568) in the gonadotropin (FSH and/or LH)-containing maturation medium significantly enhanced oocyte nuclear maturation. Addition of NPS2390, a CASR antagonist, compromised oocyte nuclear maturation. Furthermore, increased cortical distribution and decreased expression of CASR was observed after the NPS R-568 treatment. Oocytes treated with NPS R-568 had higher concentration of CYCLIN B1, decreased reactive oxygen species, and increased glutathione levels, indicative of advanced cytoplasmic maturation. In contrast, NPS2390 treatment compromised oocyte cytoplasmic maturation. A higher blastocyst formation rate after parthenogenetic activation was observed when oocytes were matured in the presence of the CASR agonist, NPS R-568. MAPK3/1 phosphorylation was increased during in vitro maturation and after NPS R-568 treatment, and decreased following CASR antagonist supplementation. Taken together, our data showed that the CASR is a gonadotropin-regulated factor that promotes porcine oocyte maturation in a MAPK-dependent manner.

The influence of N-acetyl-l-cysteine on damage of porcine oocyte exposed to zearalenone in vitro

Zearalenone (ZEA), one of the mycotoxins produced by Fusarium fungi, impacts porcine reproduction by interfering with the estrogen signaling pathway. Previous studies have shown that ZEA inhibits porcine oocyte maturation through the formation of aberrant spindle. To explore the effect of ZEA on porcine oocyte meiotic maturation, the extent of both nuclear and cytoplasmic maturation was examined in this study. Compared with control group, presence of ZEA (3 μM) during oocyte maturation, significantly inhibited the polar body extrusions from 71% to 51%, and significantly increased intracellular reactive oxygen species (ROS) level (12.01 vs. 5.89). Intracellular glutathione (GSH) content in ZEA treatment group was lower than in the control group (1.08 pmol/oocyte vs. 0.18 pmol/oocyte), and cortical granules of cortical area distributed oocytes were reduced (88% vs. 62%). ZEA decreases cumulus expansion in both morphology and mRNA level (HAS2, PTX3, TNFAIP6 and CX43). Addition of N-acetyl-l-cysteine (NAC) to the oocyte maturation media reversed the ZEA-induced inhibition of polar body extrusion (from 69% to 81%), up-regulated ROS (from 7.9 to 6.5), down-regulated GSH content (from 0.16 to 0.82 pmol/oocyte) and recovered cumulus cells expansion in morphology and mRNA level. It is concluded that ZEA affects both oocyte nucleus and cytoplasmic maturation during in vitro maturation, and NAC can reverse these damages to some extent.

Discovery of porcine maternal factors related to nuclear reprogramming and early embryo development by proteomic analysis

Background

Differentiated cell nuclei can be reprogrammed to a pluripotent state in several ways, including incubation with oocyte extracts, transfer into enucleated oocytes, and induced pluripotent stem cell technology. Nuclear transfer-mediated reprogramming has been proven to be the most efficient method. Maternal factors stored in oocytes have critical roles on nuclear reprogramming and early embryo development, but remain elusive.

Results

In this study, we showed most of porcine oocytes became nuclear matured at 33 h of IVM and the rate had no significant difference with oocytes at 42 h of IVM (p > 0.05). Moreover, the cleavage and blastocyst rates of SCNT and PA embryos derived from 42O were significantly higher than that of 33O (p < 0.05). But 33O could sustain IVF embryo development with higher cleavage and blastocyst rates comparing to 42O (p < 0.05). To clarify the development potential difference between 33O and 42O, 18 differentially expressed proteins were identified by proteomic analysis, and randomly selected proteins were confirmed by Western blot. Bioinformatic analysis of these proteins revealed that 33O highly synthesized proteins related to fertilization, and 42O was rich in nuclear reprogramming factors.

Conclusions

These results present a unique insight into maternal factors related to nuclear reprogramming and early embryo development.

Electronic supplementary material

The online version of this article (doi:10.1186/s12953-015-0074-5) contains supplementary material, which is available to authorized users.

The effects of human recombinant granulocyte-colony stimulating factor treatment during in vitro maturation of porcine oocyte on subsequent embryonic development

Granulocyte colony-stimulating factor (G-CSF) is required for proliferation, differentiation, and survival of cells. It is also a biomarker of human oocyte developmental competence for embryo implantation. In humans, the G-CSF concentration peaks during the ovulatory phase of the ovarian cycle. In this study, the expressions of G-CSF and its receptor were analyzed by polymerase chain reaction in granulosa cells (GCs), CL, cumulus cells (CCs), and oocytes. Cumulus-oocyte complexes were aspirated from antral follicles of 1 to 3 mm (small follicles) and 4 to 6 mm (medium follicles). Cumulus-oocyte complexes from two kinds of follicles were matured in protein-free maturation medium supplemented with various concentrations of G-CSF (0, 10, and 100 ng/mL). By real-time polymerase chain reaction, the expressions of G-CSF and its receptor were detected in GCs, CL, CCs, and oocytes. Interestingly, the G-CSF transcript levels were significantly lower in oocytes than in the other cell types, whereas the G-CSF receptor transcript levels in oocytes were similar to those in GCs. After 44 hours of IVM, no differences in the rate of nuclear maturation were detected; however, the intracellular reactive oxygen species levels in oocytes from both groups of follicles matured with 10 ng/mL of human recombinant G-CSF (hrG-CSF) groups were significantly lower (P < 0.05). After parthenogenetic activation, the cleavage rates were significantly (P < 0.05) higher in 100 ng/mL hrG-CSF-treated small (63.3%) follicles than in 0, 10 ng/mL hrG-CSF-treated small (38.6% and 49.0%, respectively) follicles and 0 ng/mL hrG-CSF-treated medium (52.1%) follicles, and the cleavage rates were significantly (P < 0.05) higher in 10 ng/mL hrG-CSF-treated medium (76.3%) follicles than in all other groups. The blastocyst formation rates were significantly (P < 0.05) higher in 100 ng/mL hrG-CSF-treated small (31.2%) follicles than in 0 and 10 ng/mL hrG-CSF small (10.4% and 15.6%, respectively) follicles, and the 10 ng/mL hrG-CSF medium (45.7%) follicle was significantly (P < 0.05) higher than in all other groups. The total cell number in blastocysts from the 10 ng/mL hrG-CSF medium (106.5) follicles was significantly (P < 0.05) increased compared to 0, 10, 100 ng/mL hrG-CSF small (55.0, 73.7 and 59.5, respectively) follicles and 0, 100 ng/mL hrG-CSF-treated medium (82.5 and 93.5, respectively) follicles. After IVF, the blastocysts stage was significantly (P < 0.05) increased in 10 ng/mL hrG-CSF-treated medium (36.4%) follicles. Fertilization efficiency was significantly high in 100 ng/mL of small (29.1%) and 10 ng/mL of medium (44.0%) follicles. We also examined the Bcl2 and ERK2 transcript levels and found that they were significantly higher in the small and medium follicle treatment groups. In conclusion, these results indicate that hrG-CSF improve the viability of porcine embryos.

Increasing the cAMP concentration during in vitro maturation of pig oocytes improves cumulus maturation and subsequent fertilization in vitro

Porcine IVF faces various problems such as incomplete cytoplasmic maturation of the oocyte and polyspermy. Previous studies proved the importance of cAMP in regulating nuclear and cytoplasmic maturation of oocytes. This study investigated the effect of the cAMP-modulating agents 3-isobutyl-1-methylxanthine (IBMX) and dibutyryl cAMP sodium salt (dbcAMP) on several parameters during in vitro production of porcine embryos. First, we wanted to see if oocyte collection in IBMX could meiotically arrest oocytes and, as such, improve synchronization of nuclear and cytoplasmic maturation. To this end, cumulus-oocyte complexes (COCs) were collected from gilts in HEPES-buffered Tyrode balanced salt solution medium with 0.5-mM IBMX or without IBMX. At the end of oocyte collection, the effect of IBMX on chromatin configuration was evaluated. However, no differences could be observed in nuclear configuration between IBMX- and IBMX+ oocytes (P > 0.05). Second, we added dbcAMP during IVM to improve cytoplasmic maturation and evaluated cumulus expansion (lack of adhesion), a disintegrin and metalloproteinase with thrombospondin-like repeats (ADAMTS-1) levels in cumulus cells, fertilization, and blastocyst rates. Cumulus-oocyte complexes were matured in modified North Carolina State University medium 37 with or without 1-mM dbcAMP. Frozen-thawed, epididymal, boar spermatozoa were used for IVF. After IVF, presumed zygotes were cultured for 7 days in North Carolina State University medium 23. Penetration rate decreased in dbcAMP+ (57.3%) compared with dbcAMP- (67.8%), but the polyspermy rate also decreased (43.3% vs. 53.4%, respectively) leading to an increased normal fertilization rate (56.7% vs. 46.6%, respectively; P < 0.05). Only 7.2% of the COCs showed adhesion in dbcAMP+ which was lower than 15.7% in dbcAMP- (P < 0.05) probably because of an upregulation of the ADAMTS-1 protein by dbcAMP. When the adherent oocytes were removed during maturation, no difference could be detected between the blastocyst rate of dbcAMP- and dbcAMP+ (17.1% and 21.0% on Day 7, respectively; P > 0.05). In conclusion, the use of IBMX during collection did not cause a meiotic arrest. Using dbcAMP during IVM caused a greater normal fertilization rate, a lower rate of adherent COCs during IVM, higher levels of ADAMTS-1 in cumulus cells, and an equal blastocyst rate after screening out adherent COCs. These findings contribute to a better understanding of cAMP involvement in porcine oocyte maturation and provide a basis to develop an improved system with less polyspermy and higher blastocyst rates.

Zinc regulates meiotic resumption in porcine oocytes via a protein kinase C-related pathway

Zinc is an extremely important trace element that plays important roles in several biological processes. However, the function of zinc in meiotic division of porcine oocytes is unknown. In this study, we investigated the role of zinc during meiotic resumption in in vitro matured porcine oocytes. During meiotic division, a massive release of zinc was observed. The level of free zinc in the cytoplasm significantly increased during maturation. Depletion of zinc using N, N, N′, N′-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN), a Zn²⁺ chelator, blocked meiotic resumption in a dose dependent manner. The level of phosphorylated mitogen activated protein kinase (MAPK) and p34^cdc2 kinase activity were reduced when zinc was depleted. Moreover, zinc depletion reduced the levels of phosphorylated protein kinase C (PKC) substrates in a dose dependent manner. Real-time PCR analysis showed that expression of the MAPK- and maturation promoting factor related genes C-mos, CyclinB1, and Cdc2 was downregulated following zinc depletion. Treatment with the PKC agonist phorbol 12-myristate 13-acetate (PMA) increased phosphorylation of PKC substrates and MAPK and increased p34^cdc2 kinase activity. This rescued the meiotic arrest, even in the presence of TPEN. Activation of PKC by PMA increased the level of zinc in the cytoplasm. These data demonstrate that zinc is required for meiotic resumption in porcine oocytes, and this appears to be regulated via a PKC related pathway.

Identification and characterization of an oocyte factor required for porcine nuclear reprogramming

Nuclear reprogramming of somatic cells can be induced by oocyte factors. Despite numerous attempts, the factors responsible for successful nuclear reprogramming remain elusive. In the present study, we found that porcine oocytes with the first polar body collected at 42 h of in vitro maturation had a stronger ability to support early development of cloned embryos than porcine oocytes with the first polar body collected at 33 h of in vitro maturation. To explore the key reprogramming factors responsible for the difference, we compared proteome signatures of the two groups of oocytes. 18 differentially expressed proteins between these two groups of oocytes were discovered by mass spectrometry (MS). Among these proteins, we especially focused on vimentin (VIM). A certain amount of VIM protein was stored in oocytes and accumulated during oocyte maturation, and maternal VIM was specifically incorporated into transferred somatic nuclei during nuclear reprogramming. When maternal VIM function was inhibited by anti-VIM antibody, the rate of cloned embryos developing to blastocysts was significantly lower than that of IgG antibody-injected embryos and non-injected embryos (12.24 versus 22.57 and 21.10%; p < 0.05), but the development of in vitro fertilization and parthenogenetic activation embryos was not affected. Furthermore, we found that DNA double strand breaks dramatically increased and that the p53 pathway was activated in cloned embryos when VIM function was inhibited. This study demonstrates that maternal VIM, as a genomic protector, is crucial for nuclear reprogramming in porcine cloned embryos.

Follicular fluid leptin concentrations and expression of leptin and leptin receptor in the equine ovary and in vitro-matured oocyte with reference to pubertal development and breeds

There is no published information about follicular-fluid leptin concentrations or the presence of leptin and leptin receptor in the equine ovary or oocyte. Three groups of mares - adult draft mares, draft fillies and adult Standardbred mares - were included in the study. Leptin and leptin receptor were detected in all immature oocytes by immunofluorescence with higher intensity in oocytes from draft mares compared with draft fillies and Standardbred mares. After in vitro maturation a higher proportion of oocytes reached metaphase II in draft mares than in draft fillies and Standardbred mares, and in all groups both leptin and leptin receptor became localised in the oocyte cortex but with higher immunopositivity in draft mares compared with draft fillies and Standardbred mares. These intensities were confirmed by the expression profiles of leptin and leptin receptor mRNA. Moreover, leptin was detected in ovarian blood vessels in all three types of animal and within the corpora lutea in adult mares. Serum and follicular-fluid concentrations of leptin were similar in draft and Standardbred mares but higher in draft mares than in draft fillies. This study supports the hypothesis that expression of leptin and leptin receptor mRNA and the rate of maturation can be related either to adiposity or to puberty.

Expression of INHβA and INHβB proteins in porcine oocytes cultured in vitro is dependent on the follicle size

The current study aimed to investigate differential expression of inhibin βA (INHβA) and inhibin βB (INHβB) in porcine oocytes before or after in vitro maturation (IVM) isolated from follicles of various sizes. Porcine oocytes isolated from large, medium and small follicles (40 from each) were used to study the INHβA and INHβB protein expression pattern using western blot analysis before or after 44 h of oocyte IVM. An increased expression of INHβA was found in oocytes collected from large and medium follicles compared with small follicles before or after IVM (P < 0.001, P < 0.05, respectively). Similarly, higher INHβB levels were observed in oocytes recovered from large follicles compared with small (P < 0.01). As INHβA and INHβB are expressed in both porcine follicular somatic cells and oocytes, it can be assumed that these transforming growth factor beta (TGFβ) superfamily factors are involved in the regulation of molecular bi-directional pathways during follicle and oocyte development, and can be recognized as markers of follicle and oocyte maturation. Moreover, the current study clearly demonstrated that inhibin expression is substantially associated with porcine follicle growth and development.

The dynamics of connexin expression, degradation and localisation are regulated by gonadotropins during the early stages of in vitro maturation of swine oocytes

Gap junctional communication (GJC) plays a primordial role in oocyte maturation and meiotic resumption in mammals by directing the transfer of numerous molecules between cumulus cells and the oocyte. Gap junctions are made of connexins (Cx), proteins that regulate GJC in numerous ways. Understanding the dynamic regulation of connexin arrangements during in vitro maturation (IVM) could provide a powerful tool for controlling meiotic resumption and consequently in vitro development of fully competent oocytes. However, physiological events happening during the early hours of IVM may still be elucidated. The present study reports the dynamic regulation of connexin expression, degradation and localization during this stage. Cx43, Cx45 and Cx60 were identified as the main connexins expressed in swine COC. Cx43 and Cx45 transcripts were judged too static to be a regulator of GJC, while Cx43 protein expression was highly responsive to gonadotropins, suggesting that it might be the principal regulator of GJC. In addition, the degradation of Cx43 expressed after 4.5 h of IVM in response to equine chorionic gonadotropin appeared to involve the proteasomal complex. Cx43 localisation appeared to be associated with GJC. Taken together, these results show for the first time that gonadotropins regulate Cx43 protein expression, degradation and localisation in porcine COC during the first several hours of IVM. Regulation of Cx43 may in turn, via GJC, participate in the development of fully competent oocytes.

Expression and cellular distribution of INHA and INHB before and after in vitro cultivation of porcine oocytes isolated from follicles of different size

Cumulus-oocyte-complexes (COCs) were collected from small (<3 mm), medium (3-5 mm), and large (>5 mm) porcine follicles, and the INHA and INHB expression and cellular localization were studied. Developmentally competent (BCB+) COCs were cultured for 44 h. Samples of mRNA were isolated before and after in vitro maturation (IVM) from oocytes collected from follicles of different size for RQ-PCR assay. The INHA and INHB protein distribution within the oocytes was observed by confocal microscopy. INHA mRNA expression was increased in oocytes from large compared to medium and small follicles before IVM (P < 0.001), and to oocytes of small follicles after IVM (P < 0.001). The INHB expression was not different before IVM, but the IHNB mRNA level was gradually higher in oocytes from large follicles after IVM (P < 0.01). INHA was not differently expressed before IVM; however, in large follicle oocytes the protein was distributed in the peripheral area of the cytoplasm; in oocytes from small follicles it was in the entire cytoplasm. After IVM, INHA was strongly expressed in oocytes from small follicles and distributed particularly in the zona pellucida (ZP). Similarly and both before and after IVM, INHB protein was highly expressed in small follicle oocytes and within the cytoplasm. In summary, INHs can be recognized as a marker of porcine oocyte quality.

Expression of RNA-binding proteins DND1 and FXR1 in the porcine ovary, and during oocyte maturation and early embryo development

The porcine oocyte and early embryo are transcriptionally quiescent following germinal vesicle breakdown in the oocyte and prior to activation of the embryonic genome, at approximately the 4-cell stage of development. Despite a lack of new transcription, mRNA and protein repertoires are subject to regulation during this time. One potential mechanism of regulation is through the functional activity of miRNAs and/or the presence of specific RNA-binding proteins. Both DND1 (dead end homolog 1) and FXR1 (fragile-X-mental retardation-related protein 1) are RNA-binding proteins that have been demonstrated to impact miRNA-mediated, post-transcriptional gene regulation. The objective was to characterize the presence and the expression changes in DND1 and FXR1 during pig oocyte maturation and early embryo development. DND1 and FXR1 expression were evaluated in oocytes and cumulus cells during meiotic progression and in 4-cell stage embryos using quantitative RT-PCR, Western blot analysis, and immunostaining. These data demonstrate DND1 and FXR1 mRNA are expressed in the maturing oocyte and early in vitro-fertilized embryos, with significantly less DND1 in 4-cell stage embryos as compared to germinal vesicle and metaphase II-arrested oocytes. Based on immunohistochemistry, DND1 protein abundance is greater in secondary follicles in comparison to primary and tertiary follicles. Using ribonucleoprotein immunoprecipitation from germinal vesicle-stage oocytes, DND1 was demonstrated to interact with several mRNAs associated with pluripotency. This work provides a better understanding of the biological relevance of DND1 and FXR1 during female gametogenesis and embryo development in pigs.

Advances on in vitro production and cryopreservation of porcine embryos

There have been intensive attempts to establish reliable in vitro production (IVP) and cryopreservation methods of embryos in pigs. Although a great deal of progress has been made, current IVP systems and cryopreservation still suffer from insufficient cytoplasmic abilities of in vitro matured oocytes, polyspermic fertilization, poor quality of in vitro produced embryos and low efficiency of embryo cryopreservation. Compared to other mammalian species, pig oocytes and embryos are characterized by large amounts of lipid content stored mainly in the form of lipid droplets in the cytoplasm. This fact has a negative influence on biotechnological applications on porcine oocytes and embryos. In this review, we will discuss recent studies about methods and techniques for modifying porcine embryo IVP system and embryo cryopreservation that produces high quality of pig blastocysts using in vitro maturation, in vitro fertilization, in vitro culture, microsurgical manipulation, addition of protein, the use of cytoskeleton stabilizing agents and various physical methods. The presented methods and techniques make it possible to modify the characteristics of oocytes and embryos and thus may become major tools in mammalian gamete and embryo agricultural or biotechnological applications in the future.

Presence of cleaved caspase 3 in swine embryos of different developmental capacities produced by parthenogenetic activation

This study assessed the presence of cleaved caspase 3 (CC3) during the in vitro development of swine embryos produced by parthenogenetic activation (PA). Embryos with high and low capacity to develop into blastocysts and the exposure to a caspase inhibitor (z-DEVD-fmk) were used to investigate the effect of CC3 on embryo development. The blastocyst rate (64.3% vs. 16.4%) and the average number of nuclei per blastocyst (39.7 vs. 19.8) were significantly higher (P < 0.05) in early- (before 24 hr) compared to late- (between 24 and 48 hr) cleaving embryos after PA. CC3 was mainly detected in the cytoplasm of Day-2 and -4 embryos, but was primarily localized in the nucleus of Day-5 and -6 embryos. The fluorescence signal for CC3 relative to negative controls was significantly higher (P < 0.05) in early- (2.42-fold) compared to late-cleaving (1.39-fold) embryos at Day 2 of culture. Treatment with z-DEVD-fmk during the first 24 or 48 hr of the culture period resulted in more embryos developing into blastocysts compared to the control group (55.8% and 55.1% vs. 37%, respectively; P < 0.05). This study confirmed the presence of CC3 in PA embryos from the two-cell to the blastocyst stage, and revealed that CC3 cellular-localization changed during embryo development. CC3 was shown to be more abundant in early-cleaving and more developmentally competent embryos compared to late-cleaving and less developmentally competent embryos. The inhibition of caspase activity at the beginning, but not at the end, of the culture period affected development of PA embryos.

Synergistic effect of porcine follicular fluid and dibutyryl cyclic adenosine monophosphate on development of parthenogenetically activated oocytes from pre-pubertal gilts

This study investigated the effect of porcine follicular fluid (PFF) and dibutyryl cyclic adenosine monophosphate (dbcAMP) during in vitro maturation (IVM) of porcine oocytes on meiotic maturation, fertilization and embryo development, and compared the effect of supplementing the embryo culture media with PFF or foetal bovine serum (FBS) on embryo development. Oocytes from pre-pubertal gilts were IVM for 44 h, and parthenogenetically activated or in vitro-fertilized. Embryos were cultured in porcine zygote medium (PZM3) for 7 days. Cleavage and blastocyst rates were evaluated at 48 h and 7 days of culture. The supplementation of the IVM medium with 25% PFF and 1 mm dbcAMP for the first 22 h resulted in more (p < 0.05) embryos developing to the blastocyst stage as compared with the inclusion of dbcAMP alone. The dbcAMP + PFF combination increased (p < 0.05) the average number of nuclei per blastocyst as compared with either of these components alone or in its absence. A synergistic effect of dbcAMP + PFF during IVM was also reflected in the capacity of oocytes to regulate sperm penetration and prevent polyspermy, as twice as many oocytes from the control group were penetrated by more than one sperm as compared with those matured in the presence of both dbcAMP and PFF. The supplementation of PZM3 with 10% FBS from days 5 to 7 of culture significantly improved the total cell quantity in embryos derived either from control or dbcAMP + PFF matured oocytes. There was no effect on the total cell quantity when FBS was replaced by the same concentration of PFF. These studies showed that dbcAMP, PFF and FBS can improve both the quantity (57.3% vs 41.5%) and quality (74.8 vs 33.3 nuclei) of porcine blastocysts derived from oocytes recovered of pre-pubertal gilts.

Physiological function of hyaluronan in mammalian oocyte maturation

Despite its structural simplicity, hyaluronan exhibits a broad spectrum of biological activities. Cumulus expansion observed during oocyte maturation in mammals is also induced by hyaluronan accumulation in cumulus-oocyte complexes. It has been demonstrated that this volumetric change in cumulus-oocyte complexes correlates with the progression of oocyte maturation. We have investigated the molecular mechanism of oocyte maturation in mammals, focusing on hyaluronan accumulation in cumulus-oocyte complexes during cumulus expansion. In this review, we describe the physiological function of hyaluronan, emphasizing the progression of oocyte maturation in mammals based on our previous findings.

The effects of macromolecular and serum supplements and oxygen tension during bovine in vitro procedures on kinetics of oocyte maturation and embryo development

Aiming to standardize in vitro production of bovine embryos and to obtain supplements to replace serum in culture media, this study evaluated the nuclear maturation kinetics and embryonic development in bovine after in vitro maturation (IVM) and culture (IVC) with several macromolecules (animal origin: bovine serum albumin (BSA), fetal calf serum (FCS); synthetic: polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), Ficoll, and Knockout) at two oxygen tensions (20% and 5% O(2)). Regarding nuclear kinetics, neither the presence of the expected stage (metaphase I, transition anaphase to telophase, and metaphase II) at each evaluation moment (6, 18, and 24 h after IVM, respectively) nor the accelerated polar body emission (at 18 h after IVM) related developmental competence to blastocyst stage when different supplements were compared. Independently of supplement, cleavage rates at 20% O(2) (61.6-79.2%) were higher than at 5% O(2) (38.9-58.7%). At 20% O(2), higher blastocyst and hatching rates, respectively, were obtained in treatments BSA, FCS, Knockout, and control group (IVM with FCS and IVC with BSA + FCS, 14.0-23.5% and 6.8-15.4%) in comparison to PVA, PVP, and Ficoll (0%). The same was observed at 5% O(2) for blastocyst rates with BSA, FCS, Knockout, and control (5.4-16.8%) and for hatching rates with BSA, FCS, and control (2.0-11.1%). We can conclude that producing bovine embryos at 20% O(2) during the entire IVP process resulted in higher developmental rates than at 5% O(2). In addition, while defined macromolecules PVA, PVP, and Ficoll were not suitable for embryonic development, the synthetic serum Knockout was able to replace serum and albumin for IVP in bovine at 20% O(2).

Efficiency of in vitro fertilization is influenced by the meiotic competence of porcine oocytes and time of their maturation

The effect of meiotic competence of oocytes and time of their maturation on the efficiency of fertilization was studied in pigs. Cycling gilts with synchronized estrous cycles were used as oocyte donors. To obtain oocytes with different meiotic competence, oocytes were recovered separately from small and medium follicles in the early, middle and late luteal or early follicular phase. They were matured for 40 h, 43 h or 47 h and fertilized by spermatozoa of a proven boar. The penetration and monospermy rates, and total efficiency of fertilization were assessed. The same data were related to the follicle size, with or without regard to the phase, and to the maturation time. Regardless of the phase and the time of maturation, the monospermy rate and total efficiency of fertilization were significantly lower for the small follicle-derived oocytes than for the medium follicle-derived oocytes (38.5±10.4% vs 63.1±7.0% and 24.7±6.3% vs 42.5±3.8%). With regard to the phase, in the small follicle-derived oocytes, the monospermy rate increased significantly (P<0.05) from the early luteal to the late luteal phase (from 25.4±2.4% to 46.4±3.9%) and remained unchanged in the early follicular phase. A similar tendency was observed in the total efficiency of fertilization. No differences were found in either of these parameters in medium follicle-derived oocytes in the late luteal and early follicular phase. With regard to the time of maturation, the total efficiency of fertilization was significantly higher (P<0.05) in the small follicle-derived oocytes matured for 47 h than in those matured for 40 h (27.7±7.4% vs. 20.5±6.1%) and in the medium follicle-derived oocytes matured for 40 h as compared with those matured for 47 h (47.1±1.9% vs. 32.7±1.1%). With regard to the phase and the time of maturation, the differences were significant only in the late luteal and early follicular phases. It can be concluded that greater meiotic competence of porcine oocytes positively influences monospermy rate and total efficiency of fertilization process. However adequate time of maturation is an important factor for oocytes with different meiotic competence to improve the IVF procedure.

Short-term preservation of porcine oocytes in ambient temperature: novel approaches

The objective of this study was to evaluate the feasibility of preserving porcine oocytes without freezing. To optimize preservation conditions, porcine cumulus-oocyte complexes (COCs) were preserved in TCM-199, porcine follicular fluid (pFF) and FCS at different temperatures (4°C, 20°C, 25°C, 27.5°C, 30°C and 38.5°C) for 1 day, 2 days or 3 days. After preservation, oocyte morphology, germinal vesicle (GV) rate, actin cytoskeleton organization, cortical granule distribution, mitochondrial translocation and intracellular glutathione level were evaluated. Oocyte maturation was indicated by first polar body emission and spindle morphology after in vitro culture. Strikingly, when COCs were stored at 27.5°C for 3 days in pFF or FCS, more than 60% oocytes were still arrested at the GV stage and more than 50% oocytes matured into MII stages after culture. Almost 80% oocytes showed normal actin organization and cortical granule relocation to the cortex, and approximately 50% oocytes showed diffused mitochondria distribution patterns and normal spindle configurations. While stored in TCM-199, all these criteria decreased significantly. Glutathione (GSH) level in the pFF or FCS group was higher than in the TCM-199 group, but lower than in the non-preserved control group. The preserved oocytes could be fertilized and developed to blastocysts (about 10%) with normal cell number, which is clear evidence for their retaining the developmental potentiality after 3d preservation. Thus, we have developed a simple method for preserving immature pig oocytes at an ambient temperature for several days without evident damage of cytoplasm and keeping oocyte developmental competence.

Induction of oocyte maturation by hyaluronan-CD44 interaction in pigs

In most mammals, the oocyte is surrounded with compact multilayers of cumulus cells; these form cumulus-oocyte complexes (COCs). During oocyte maturation, the COCs dramatically expand and this is termed "cumulus expansion". We have previously demonstrated that cumulus expansion is the result of hyaluronan synthesis and accumulation in the extracellular space between cumulus cells in the COCs and that hyaluronan accumulation within the COCs affects oocyte maturation. We have also demonstrated that CD44, the principal hyaluronan receptor, is expressed in the COCs during cumulus expansion and that the interaction between hyaluronan and CD44 appears to be closely related to gap junctional communication of the COCs during the process of meiotic resumption. Based on our previous studies, we review herein that the physiological significance and the molecular mechanism of cumulus expansion for porcine oocyte maturation.

Follicular, oocyte and embryo features related to metabolic status in primiparous lactating does fed with high-fibre rearing diets

Fertility of primiparous lactating does in the early postpartum (pp) period is very low mainly due to pronounced deficient energy intake, influencing oocyte and embryo developmental competence. The hypothesis used in this work was that high-lignin fibre diet supplied during the rearing period could increase feed intake and, consequently, improve the reproductive physiology and metabolic status of primiparous does in the early pp period. Diets with high-lignin [HL: 15.8% dry matter (DM)] or standard-lignin content (SL: 4.9% DM) were supplied until parturition time. No diet effects in serum oestradiol, progesterone concentrations and follicle categories were found in the histological study. Metaphase II rate of in vitro-matured oocytes was significantly higher in the SL vs the HL group (p < 0.001). Cytoplasmically degenerated oocytes (in terms of abnormal distribution of cortical granules) and follicular atresia rate were significantly lower in the SL group than in the HL group (p < 0.05 and p < 0.005 respectively). In addition, HL-fed does showed lower number of viable embryos and higher rate of retarded in vivo-recovered embryos compared with the SL group (p < 0.05). Neither in vitro embryo development of viable embryos nor conception rate was significantly different between groups. Feed intake increased during the first pregnancy in the HL group (p < 0.05), but not during early lactation. Serum protein, non-esterified fatty acid and leptin concentrations, as well as estimated body composition were similar in does fed with both diets. In conclusion, the enhancement of reproductive management by using highly lignified products in rearing diets does not seem to report physiological reproductive benefits affecting oocyte maturation rate and embryo viability in primiparous lactating does.

Sonic hedgehog promotes porcine oocyte maturation and early embryo development

In the present study, we investigated the effects of the Sonic hedgehog (Shh) protein on porcine oocyte maturation and early embryo development. Immunohistochemistry showed activation of Shh signalling in cumulus–oocyte complexes (COCs), as reflected by Patched (Ptc), Smoothened (Smo) and Gli1 expression in oocytes, cumulus cells and granulosa cells, particularly those of small follicles (<2 mm in diameter). Western blot analysis showed Smo expression in COCs and in denuded oocytes derived from small and medium (3–7 mm)-sized follicles. Small follicles contained the highest concentration of Shh in follicular fluid compared with medium-sized and large (>7 mm in diameter) follicles. Supplementation with Shh (0.5 or 1 μg mL–1) enhanced oocyte maturation compared with the control group (92.4% and 90.4% v. 81.9%, respectively; P < 0.05). This effect was reversed by the simultaneous addition of cyclopamine (1–2 μm), an Shh inhibitor. Similar to intact COCs, denuded COCs showed enhanced maturation following Shh supplementation. Furthermore, cyclin B1 content, extracellular signal-regulated kinase 1/2 phosphorylation, intracellular calcium release, blastocyst rate and total cell numbers were greater (P < 0.05) in oocytes matured in the presence of 0.5 and 1 μg mL–1 Shh compared with control oocytes. The findings of the present study provide the first evidence that the Shh signalling pathway is active, or at least partially activated, in the porcine ovary and is likely to promote oocyte cytoplasmic and nuclear maturation, as well as subsequent in vitro development, although the underlying mechanisms remain to be elucidated.

Testosterone potentially triggers meiotic resumption by activation of intra-oocyte SRC and MAPK in porcine oocytes

The role of androgen and androgen receptors (ARs) in males has been well established. This steroid and its receptor also exist in follicles, but their functions are still unclear. In this study, using a culture system containing a low dose of hypoxanthine, we revealed the positive contribution of testosterone to oocyte meiotic resumption. By performing ultracentrifugation to allow clear visualization of porcine germinal vesicles, our results provide evidence that mitogen-activated protein kinase (MAPK) in the oocyte itself but not in cumulus cells was activated before germinal vesicle breakdown (GVBD) after testosterone treatment. We further explored the signal cascade of testosterone-triggered GVBD and showed significant contributions of AR to testosterone-induced MAPK activation and GVBD. By using a potent and selective inhibitor of SRC and detecting activation of the kinase, we found that testosterone activated SRC in oocytes but not in cumulus cells and that SRC (as an essential upstream molecule of MAPK) mediated this testosterone- and AR-promoted reinitiation of meiosis. The present findings propose an undefined signaling pathway and suggest the potential competence of testosterone for meiotic resumption in mammalian oocytes.