Rho-associated coiled-coil containing kinase inhibitor improves outcomes of direct-transfer slow-cooled bovine blastocysts

Direct-transfer slow-cooling cryopreservation is a widely used method for bovine embryo cryopreservation. However, the transfer of cryopreserved embryos is associated with reduced pregnancy rates. Rho-associated coiled-coil containing kinase inhibitor (ROCKi) has shown promise in improving the viability of post-warmed vitrified bovine embryos. Our objective was to investigate the effects of ROCKi treatment prior to slow-cooling or after cryopreservation on embryo viability. In vitro produced bovine embryos (n = 571) were randomly assigned to one of five groups: No-cryopreservation control group (NC-C), C-C group were cryopreserved by slow-rate cooling without ROCKi at any point, R-C group were incubated with ROCKi for 2 h before cryopreservation, C-R group were not exposed to ROCKi prior to cryopreservation but were cultured with ROCKi after cryopreservation, and R-R group were exposed to ROCKi before and after cryopreservation. Treatment group was significantly associated with blastocoel re-expansion, hatching, and degeneration (P < 0.0001). Blastocoel re-expansion rates were lower (P < 0.05) in the C-C (75.2 ± 4.2%) and R-C (85.2 ± 4.7%) groups compared with the NC-C (99.0 ± 0.7%), C-R (94.7 ± 2.6%) and the R-R (94.5 ± 2.9%) groups. The median time to re-expansion was significantly slowest in the C-C group (650, 560-915 min), followed by the R-C group (538, 421-611 min), then the C-R and R-R groups were similar (291, 261-361 and 321, 271-371 min) and the NC-C group was the fastest (196, 161-230 min) (P < 0.05). Similarly, the post-thaw hatching rate was lower, and the median time to hatching slower in the C-C (58.1 ± 7.0%, 2,033, 1634-2820 min) and R-C (65.7 ± 6.9%, 1,853, 1494-2356 min) groups compared with the NC-C (81.7 ± 6.0%, 1,309, 1084-1514 min), C-R (77.2 ± 6.5%, 1,384, 1013-1754 min) and R-R (82.0 ± 5.3%, 1,209, 943-1424 min) groups. ROCKi supplementation after cryopreservation resulted in fewer degenerated embryos (C-R = 8.9 ± 2.8%, and R-R 7.1 ± 2.8%) compared to the C-C (26.8 ± 4.3%) and R-C (17.9 ± 5.7%) groups. Exposure to ROCKi both before cryopreservation and after-cryopreservation yielded the best outcomes, similar to NC-C control group without cryopreservation, and significantly better than the C-C control group without supplements. Exposure to ROCKi after cryopreservation demonstrated greater benefits compared to exposure before cryopreservation alone. These findings suggest that ROCKi can potentially enhance cryosurvival of bovine embryos.

Cryopreservation of engineered hair follicle germs for hair regenerative medicine

Hair regenerative medicine must involve practical procedures, such as cryopreservation of tissue grafts. This can aid in evaluating tissue safety and quality, as well as transportation to a clinic and multiple transplants. Hair follicle germs (HFGs), identified during in vivo development, are considered effective tissue grafts for hair regenerative medicine. However, to the best of our knowledge, methods for cryopreserving HFGs have not been explored yet. This study investigated the efficacy of slow vitrification methods for freezing HFGs. Cryoprotectants such as dimethyl sulfoxide (DMSO) and carboxylated poly-l-lysine were used for vitrification. The results indicate that DMSO vitrification yielded the most efficient de novo hair regeneration in mouse skin, comparable to that of non-cryoprotected HFGs. A microfinger was fabricated to scale up the cryopreservation method, considering that thousands of tissue grafts were required per patient in clinical practice. The microfinger can be used for a series of processes, holding the HFG, replacing it with a cryopreservation solution, freezing it in liquid nitrogen, thawing it in a warm medium, and transplanting it into the skin. Although de novo hair regeneration by HFGs cryopreserved using microfingers was reduced by approximately 20 % compared to those cryopreserved using flat plates for fertilized eggs, it exceeded 50 %. These findings demonstrate that vitrification with DMSO and microfingers could be a useful approach for the cryopreservation of tissue grafts in hair regenerative medicine for hair loss.

Improvement of post-thaw quality and fertilizing ability of bull spermatozoa using Rho kinase inhibitor in freezing extender

In this study, it was hypothesized that the addition of an appropriate concentration of Y-27632 (a ROCK inhibitor) to the freezing extender prevents cryopreservation-induced apoptosis and improves embryonic development after in vitro fertilization (IVF). Semen samples were collected from five fertile Simmental bulls using an artificial vagina twice a week for 4 weeks. Selected samples were pooled and diluted with Tris-egg-yolk-glycerol (TEYG) extender containing different concentrations of Y-27632 (0, 10, 20, 30, and 40 μM) and then frozen in liquid nitrogen. After thawing, computer-assisted semen analysis (CASA), plasma membrane integrity, and acrosome intactness were evaluated in terms of morphological abnormalities, intracellular generation of reactive oxygen species (ROS), DNA fragmentation, phosphatidylserine (PS) externalization, and apoptotic-related gene expression. Finally, groups of frozen and thawed spermatozoa were used for bovine oocyte IVF. The results show that the semen extender at a concentration of 20 μM Y-27632 effectively improved total motility (TM), curvilinear velocity (VCL), as well as the plasma membrane and acrosome integrity compared to the control group (p < 0.05). Intracellular ROS levels were significantly (p < 0.05) lower in samples treated with 30 μM Y-27632 compared to the control specimen. Furthermore, supplementation of the semen extender with 20 μM Y-27632 resulted in more viable spermatozoa compared with the control group (p < 0.05). According to qRT-PCR results, the expression levels of BAX and CASPASE-9 genes in samples treated with 30 μM Y-27632 were significantly downregulated, while the expression of BCL2 was increased compared to the control (p < 0.05). The results of IVF demonstrated that the treatment of frozen-thawed spermatozoa with 20 μM Y-27632 increased blastocyst rates compared to the control group (p < 0.05). In conclusion, the addition of 20 μM Y-27632 into the freezing extender can improve the functionality and the fertilizing capacity of frozen spermatozoa due to its antioxidative and anti-apoptotic properties.

Cryodevices developed for minimum volume cooling vitrification of bovine oocytes

Unfertilized bovine oocytes can be efficiently cryopreserved only when an extremely rapid cooling rate (>20,000°C/min) is applied to oocytes with a very limited amount of surrounding vitrification solution. This protocol is defined as minimum volume cooling (MVC) vitrification. Various types of cryodevices, such as open pulled straw, Cryoloop, and Cryotop, have been developed to accelerate the cooling efficacy. Furthermore, hollow fibers with nano-scale pores, triangle nylon mesh sheets, and multilayer silk fibroin sheets have been optimized for the loading of large quantities of oocytes and/or the subsequent removal of excess vitrification solution, without requiring skillful operation to transfer individual oocytes using fine capillaries. This article provides an up-to-date review of cryodevices suitable for the MVC vitrification of bovine oocytes at the immature (germinal vesicle-) and mature (metaphase II-) stages.

Cryopreservation of Gametes and Embryos and Their Molecular Changes

The process of freezing cells or tissues and depositing them in liquid nitrogen at -196 °C is called cryopreservation. Sub-zero temperature is not a physiological condition for cells and water ice crystals represent the main problem since they induce cell death, principally in large cells like oocytes, which have a meiotic spindle that degenerates during this process. Significantly, cryopreservation represents an option for fertility preservation in patients who develop gonadal failure for any condition and those who want to freeze their germ cells for later use. The possibility of freezing sperm, oocytes, and embryos has been available for a long time, and in 1983 the first birth with thawed oocytes was achieved. From the mid-2000s forward, the use of egg vitrification through intracytoplasmic sperm injection has improved pregnancy rates. Births using assisted reproductive technologies (ART) have some adverse conditions and events. These risks could be associated with ART procedures or related to infertility. Cryopreservation generates changes in the epigenome of gametes and embryos, given that ART occurs when the epigenome is most vulnerable. Furthermore, cryoprotective agents induce alterations in the integrity of germ cells and embryos. Notably, cryopreservation extensively affects cell viability, generates proteomic profile changes, compromises crucial cellular functions, and alters sperm motility. This technique has been widely employed since the 1980s and there is a lack of knowledge about molecular changes. The emerging view is that molecular changes are associated with cryopreservation, affecting metabolism, cytoarchitecture, calcium homeostasis, epigenetic state, and cell survival, which compromise the fertilization in ART.

Use of melatonin as an inhibitor of apoptotic process for cryopreservation of zebrafish (Danio rerio) embryos

This study investigated the use of melatonin to arrest the effects of apoptosis in vitrified zebrafish (D. rerio) embryos. Dechorionated embryos at 22-24 somite-stage were divided (n = 60/treatment) into a non-vitrified (Control Group, 0 M melatonin) and vitrified treatments with 0 M (T1), 1 µM (T2) and 1 mM of melatonin (T3). For vitrified treatments, a solution methanol/propylene glycol based was used and the embryos stored in -196 °C for a week. After thaw, survival rate, scanning electron microscopy, expression of anti (bcl-2) and pro-apoptotic (bax/caspase-3) genes, reactive oxygen species (ROS) formation and DNA fragmentation analyses were performed. No live embryos were obtained from vitrified treatments, observing a rapid degeneration immediately after thawing, with the vitelline layer rupture and leakage of its content, followed by breakdown of epithelial cells and melanisation of the tissue. Regarding the apoptotic process, T3 had the highest relative gene expression, for the three genes (P < 0.05) furthermore, T2 had similar expression of pro-apoptotic genes to CG (P < 0.05). ROS formation revealed that CG presented lower percentage of embryo surface area affected (3.80 ± 0.40%) (P < 0.05), in contrast, no differences were found among the other groups. T1 was most significantly (P < 0.05) damaged by DNA fragmentation. The vitrified groups with melatonin had similar damage levels of CG (P > 0.05). The inclusion of 1 µM of melatonin in the vitrifying solution, countered the effects of apoptotic process in post-thaw embryos, suggesting its utility in cryopreserving fish embryos.

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.

The role of Rho-associated kinase inhibitor, Y-27632 on primary culture of ovine spermatogonial stem cells

The access to sufficient numbers of spermatogonial stem cells (SSCs) is a prerequisite for the study of their regulation and further biomanipulation. Rho kinase (ROCK) belongs to a family of serine/threonine kinases and involves in a wide range of fundamental cellular functions. The aim of the present study was to study the effect of ROCK inhibitor, Y-27632 (0.1-40 µM), during the primary culture of ovine SSCs. SSCs were collected from 3-5-month-old’s lamb testes. The viability of SSCs, the apoptosis assay of SSCs, the intracellular reactive oxygen species (ROS) analysis, and the SSCs markers and apoptosis-related gene expressions were detected by MTT reduction assay, Annexin V–FITC/ Propidium Iodide (PI) dual staining, flow cytometry and real-time-PCR studies, respectively. Morphological analyses indicated that the 5-10 µM Y-27632 had an optimal effect on the number of presumptive SSCs colonies and the area covered by them after a 10 days culture. The cell viability, apoptosis and necrosis of SSCs after 10 days’ culture were not affected in comparison with the control group, and the 20 µM of Y-27632 resulted in significantly decreased cell viability (P<0.05) and an increased necrosis of cells. On day 10 after culture, the expression of P53 was decreased with an increase from 0 to 10 µM in the Y-27632 dose. In the 20 µM Y-27632 group, the expressions of P53 and Bax were higher and the Bcl-2 was lower than other groups and these values were significantly different from 5 and 10 µM Y-27632 groups (P<0.05). The level of intracellular ROS was decreased with an increase in the Y-27632 dose from 5 to 20 µM in comparison with the control group. In conclusion, the present study demonstrated that Y-27632 at a concentration of 5-10 µM provided optimal culture conditions for the primary culture of ovine SSCs.

Effects of Short-Term Inhibition of Rho Kinase on Dromedary Camel Oocyte In Vitro Maturation

Simple Summary

Our results revealed, for the first time, that short-term inhibition of Rho-associated protein kinases (ROCK) for 4 h prior to in vitro maturation (IVM) in a biphasic IVM approach improved oocyte nuclear maturation, producing more MII oocyte, through modulating the expression of cytokinesis- and antiapoptosis-related mRNA transcripts. This positive result suggests ROCK inhibitor as a potential candidate molecule to exploit in the control of oocyte meiotic maturation.

Abstract

This is the first report on a biphasic in vitro maturation (IVM) approach with a meiotic inhibitor to improve dromedary camel IVM. Spontaneous meiotic resumption poses a major setback for in vitro matured oocytes. The overall objective of this study was to improve in vitro maturation of dromedary camel oocytes using ROCK inhibitor (Y-27632) in a biphasic IVM to prevent spontaneous meiotic resumption. In the first experiment, we cultured immature cumulus–oocyte complexes (COCs, n = 375) in a prematuration medium supplemented with ROCK inhibitor (RI) for 2 h, 4 h, 6 h, and 24 h before submission to normal in vitro maturation to complete 28 h. The control was cultured for 28 h in the absence of RI. In the first phase of experiment two, we cultured COCs (n = 480) in the presence or absence (control) of RI for 2 h, 4 h, 6 h, and 24 h, and conducted real-time relative quantitative PCR (qPCR) on selected mRNA transcripts. The same was done in the second phase, but qPCR was done after completion of normal IVM. Assessment of nuclear maturation showed that pre-IVM for 4 h yielded an increase in MII oocyte (54.67% vs. 26.6% of control; p < 0.05). As expected, the same group showed the highest degree (2) of cumulus expansion. In experiment 2, qPCR results showed significantly higher expression of ACTB and BCL2 in the RI group treated for 4 h when compared with the other groups. However, their relative quantification after biphasic IVM did not reveal any significant difference, except for the positive response of BCL2 and BAX/BCL2 ratio after 4 and 6 h biphasic IVM. In conclusion, RI prevents premature oocyte maturation and gave a significantly positive outcome during the 4 h treatment. This finding is a paradigm for future investigation on dromedary camel biphasic IVM and for improving the outcome of IVM in this species.

The protective effect of Leucosporidium-derived ice-binding protein (LeIBP) on bovine oocytes and embryos during vitrification

Ice-binding proteins (IBPs) facilitate organism survival under extreme conditions by inhibiting thermal hysteresis and ice recrystallization. IBPs have been widely used as cryoprotectants to cryopreserve mammalian gametes and embryos. In the present study, we evaluated the protective effects of an Arctic yeast, Leucosporidium sp. AY30 derived ice-binding protein (LeIBP), on the vitrification of bovine metaphase II (MII) oocytes and embryos. When oocytes and embryos were frozen using the two-step vitrification method, the survival rate was significantly increased in the presence of LeIBP. The LeIBP supplementation decreased the levels of intracellular reactive oxygen species (ROS) and enhanced mitochondrial functions in the vitrified-warmed oocytes. Furthermore, LeIBP improved the developmental potential and suppressed apoptosis of the embryos derived from vitrified-warmed oocytes. Collectively, these data indicate that LeIBP can be used as a promising cryoprotectant to prevent cryoinjury during vitrification in bovine oocytes.

Rescue of vitrified-warmed bovine mature oocytes by short-term recovery culture with resveratrol

Resveratrol, a well-known antioxidant, has been reported to protect mouse metaphase-II (M - II) stage oocytes from vitrification injuries when used as a treatment during a series of vitrification processes. The present study was conducted to investigate whether short-term treatment of post-warm bovine mature oocytes with resveratrol can increase blastocyst formation rate following in vitro fertilization and culture. Bovine denuded M - II oocytes were vitrified-warmed using Cryotop® or nylon mesh (pore size = 37 μm) as a cryodevice. The post-warm oocytes were treated for 2 h with 1 μM resveratrol in recovery culture medium. The resveratrol treatment had no harmful influence on morphological survival and cleavage rate of the oocytes vitrified-warmed with Cryotop® or nylon mesh. In the Cryotop® vitrification series, blastocyst formation rate of resveratrol-treated post-warm oocytes (39.0%) was not significantly different from that of non-treated post-warm oocytes (31.7%). However in the nylon mesh vitrification series, there was a significant increase in the blastocyst yield (42.4% vs. 31.3%, P < 0.05) when post-warm oocytes were treated with resveratrol. Blastocyst yield from fresh control oocytes was 49%. Levels of reactive oxygen species were comparable between post-warm and fresh control M - II oocytes, and decreased in oocytes after recovery culture with resveratrol. Mitochondrial activity of post-warm oocytes was restored to the pre-vitrification level during the recovery culture regardless of resveratrol supplementation. Thus, short-term recovery culture with resveratrol can rescue bovine M - II oocytes vitrified-warmed on a nylon mesh cryodevice.

Silk fibroin sheet multilayer suitable for vitrification of in vitro-matured bovine oocytes

Minimum volume cooling (MVC) procedure has been successfully applied to vitrify mammalian oocytes, but high skill of capillary pipetting is required to load the oocytes on a cryodevice with a minimal volume (<1 μL) of vitrification solution (VS). Here we report a novel cryodevice for bovine oocyte vitrification, silk fibroin (SF) sheet multilayer, of which spontaneous absorption property can eliminate pipette operation for removal of excess VS. Based on physical stability and scanning electron microscopic observation, the SF sheet prepared from 1.5% (wt/vol) fibroin solution was selected and layered around a polypropylene strip (0.1-mm thickness, 0.7-mm width, 10-mm depth). Ten denuded bovine mature oocytes were loaded onto the SF sheet multilayer with 2-3 μL of the VS, and then cooled rapidly by plunging into liquid nitrogen. Nylon mesh (NM) device with square opening 37-μm length of a side and commercially available Cryotop® (CT) device were used as controls, and the minimization of VS volume was performed by paper towel absorption and capillary aspiration, respectively. In SF, NM and CT groups, post-warming oocyte recovery rates were 99.5, 99.1 and 100%, and the morphological survival rates were 99.7, 94.5 and 99.0%, respectively. Subsequent IVF and 8-days IVC resulted in comparable blastocyst yields among the three groups (25.5, 25.0 and 26.1% in SF, NM and CT groups, respectively). These results suggest that SF sheet multilayer is a useful cryodevice for bovine matured oocytes in MVC vitrification because VS volume surrounding the oocytes can be easily minimized through its absorption property.

Effect of Cytochalasin B Treatment on the Improvement of Survival Rate in Vitrified Pig Oocyte

To improve survival rates of vitrified pig oocytes, the treatment of cytoskeletal stabilizer on an appropriate time is one of the possible approaches. However, the exact treatment timing and effect of cytoskeletal stabilizer such as cytochalasin B (CB) is not well known during oocyte vitrification procedures. Thus, the present study was conducted to determine optimal treatment timing of CB during vitrification and warming procedures. In experiment 1, the survival rates of the post-warming pig oocytes were analyzed by fluorescein diacetate (FDA) assays with 4 classifications. In results, post-warming oocytes showed significantly (p<0.05) decreased number of alive oocytes (31.8% vs. 86.4%) compared to fresh control. In detail, the significant difference (p<0.05) was found only in strong fluorescence (18.2% vs. 70.5%) not in intermediate fluorescence groups (13.6% vs. 15.9%). In experiment 2, CB was treated before (CB-Vitri) and after (Vitri-CB) vitrification. In results, group of Vitri-CB showed significantly (p<0.05) higher (91.6%) survival rates compared to group of CB-Vitri (83.7%), significantly (p<0.05) and comparable with group of Vitri Control (88.7%) by morphological inspection. In FDA assay results, group of Vitri-CB showed significantly (p<0.05) higher (44.2%) survival rates compared to groups of CB-Vitri (36.7%) and Vitri Control (35.1%). In conclusion, the increased survival rates of post-warming pig oocyte treated with Vitri-CB method are firstly described here. The main finding of present study is that the CB treatment during recovery could be helpful to refresh the post-warming pig oocyte resulting its improved survival rates.

Direct comparison of Cryotop® vitrification and Bicell® freezing on recovery of functional rat pancreatic islets

Two protocols, Bicell^® freeze-thawing and Cryotop^® vitrification-warming, were compared for suitability in cryopreserving rat pancreatic islets (101-150 μm in mean diameter). Immediate survival rates of post-thaw and post-warm islets (50 and 57%, respectively), assessed by FDA/PI double staining, were lower than that of fresh control islets (90%). Most of the PI-positive dead cells were detected in peripheral area of post-warm islets, and were removed after subsequent 24 h culture (survival rate; 85% vs 59% in post-thaw islets). Quantitative PCR analysis showed that Bicell^® freeze-thawing compromised expression of genes relating to β-cell function (Pdx1 and Glut2), but not to one of apoptotic pathways (Bax/Bcl2 ratio). Expression of these genes was maintained in islets before and after the Cryotop^® vitrification-warming. Values of stimulus index (SI) for 20 mM/3 mM glucose-stimulated insulin secretion were 6.7, 1.9 and 3.9 in fresh control, post-thaw and post-warm islets, respectively. The SI values after 24 h culture were 4.1, 1.9 and 3.1, respectively. Larger islets (>150 μm in diameter) had comparable survival rates, but lower SI values after Cryotop^® vitrification-warming when compared to smaller counterparts. These results suggest that rat pancreatic islets can be cryopreserved by Cryotop^® vitrification-warming rather than Bicell^® freeze-thawing, without considerable loss of in vitro β-cell function.

Microtubule assembly crucial to bovine embryonic development in assisted reproductive technologies

Centrosome integrity and microtubule network are crucial to the events around fertilization, including pronuclear development, migration and fusion, and the first mitotic division. The present review highlights the importance of bull spermatozoal centrosomes to function as a microtubule‐organizing center for successful fertilization and the subsequent embryonic development. Spermatozoal centrosomes need to be blended with ooplasmic pericentriolar materials accurately to nucleate and organize the sperm aster. Dysfunction of the spermatozoal centrosomes is associated with fertilization failure, which has been overcome with supplemental stimuli for oocyte activation following intracytoplasmic sperm injection in humans. Even though the spermatozoal centrosomes are functionally intact, abnormal sperm aster formation was frequently observed in vitrified‐warmed bovine oocytes, with delayed pronuclear development and migration. Treatment of the post‐warm oocytes with Rho‐associated coiled‐coil kinase inhibitor or α‐tocopherol inhibited the incidence of the abnormal aster formation, resulting in higher blastocyst yields following in vitro fertilization and culture. Thus, understanding of centrosomal function made it possible to improve the performance of advanced reproductive technologies.

Melatonin inhibits apoptosis and improves the developmental potential of vitrified bovine oocytes

Vitrification of oocytes has been shown to be closely associated with increased levels of reactive oxygen species (ROS) and apoptotic events. However, little information is available the effect of melatonin on the ROS levels and apoptotic events in vitrified oocytes. Therefore, we studied the effect of melatonin on ROS and apoptotic events in vitrified bovine oocytes by supplementing vitrification solution or in vitro maturation (IVM) and vitrification solution with 10(-9) m melatonin. We analyzed the ROS, mitochondrial Ca(2+) (mCa(2+) ) and membrane potential (ΔΨm), externalization of phosphatidylserine (PS), caspase-3 activation, DNA fragmentation, mRNA expression levels of Bax and Bcl2 l1, and developmental potential of vitrified bovine oocytes. Vitrified bovine oocytes exhibited increased levels of ROS, mCa(2+) , Bax mRNA, and caspase-3 protein and higher rates of PS externalization and DNA fragmentation, and decreased ΔΨm and Bcl2 l1 mRNA expression level. However, melatonin supplementation in vitrification solution or IVM and vitrification solution significantly decreased the levels of ROS, mCa(2+) , Bax mRNA expression, and caspase-3 protein, and PS externalization and DNA fragmentation rates, and increased the ΔΨm and Bcl2 l1 mRNA expression level in vitrified oocytes, resulting in an increased developmental ability of vitrified bovine oocytes after parthenogenetic activation. The developmental ability of vitrified oocytes with melatonin supplementation in IVM and vitrification solution was similar to that of fresh ones. This study showed that supplementing the IVM and vitrification medium or vitrification medium with 10(-9) m melatonin significantly decreased the ROS level and inhibited apoptotic events of vitrified bovine oocytes, consequently increasing their developmental potential.

Multiple aster formation is frequently observed in bovine oocytes retrieved from 1-day stored ovaries

We have recently reported that multiple aster formation after in vitro fertilization (IVF) was one of the factors that negatively affected the developmental competence of vitrified-warmed bovine matured oocytes, and that short-term culture of the post-warm oocytes with an inhibitor of Rho-associated coiled-coil kinase (ROCK) suppressed the multiple aster formation and improved the blastocyst yield. The present study was conducted to investigate whether increased multiple aster formation following IVF was involved in impaired developmental competence of stored ovary-derived bovine oocytes. Oocytes retrieved from 1-day stored ovaries had lower developmental potential to day 8 blastocysts when compared with those from fresh ovaries (37 versus 63%). Immunostaining of α-tubulin 10 h post-IVF revealed that a higher incidence of multiple aster formation occurred in oocytes retrieved from stored ovaries than from fresh ovaries (31 versus 15%). Treatment of post-in vitro maturated (post-IVM) oocytes with ROCK inhibitor for 2 h significantly suppressed the incidence of multiple aster formation (10 versus 32% in the control group). However, the suppression effect of ROCK inhibitor on multiple aster formation in IVM/IVF oocytes did not improve blastocyst yield from stored ovary-derived oocytes (41 versus 37% in the control group). These results suggested that the higher incidence of multiple aster formation by bovine ovary storage was not responsible for the decreased developmental competence of IVF oocytes.

High revivability of vitrified-warmed bovine mature oocytes after recovery culture with α-tocopherol

The objective of this study was to investigate whether developmental competence of vitrified-warmed bovine oocytes can be improved by antioxidant treatment during recovery culture. In experiment 1, one of the two antioxidants (either l-ascorbic acid or α-tocopherol) was added as a supplement to the recovery culture medium to which postwarming oocytes were exposed for 2 h before IVF. The exposure to α-tocopherol had a positive effect on rescuing the oocytes as assessed by the blastocyst yield 8 days after the IVF (35.1-36.3% vs 19.2-25.8% in untreated postwarming oocytes). Quality of expanding blastocysts harvested on Day 8 was comparable between α-tocopherol-treated vitrification group and fresh control group in terms of total cell number and chromosomal ploidy. In experiment 2, level of reactive oxygen species, mitochondrial activity, and distribution of cortical granules in α-tocopherol-treated postwarming oocytes were assessed. No obvious differences from the control data were found in these parameters. However, the treatment with α-tocopherol increased the percentage of zygotes exhibiting normal single aster formation (90.3% vs 48.0% in untreated postwarming oocytes; 10 h post-IVF). It was concluded that α-tocopherol treatment of vitrified-warmed bovine mature oocytes during recovery culture can improve their revivability, as shown by the high blastocyst yield and the higher mean total cell number in the blastocysts.

Recent progress in cryopreservation of bovine oocytes

Principle of oocyte cryoinjury is first overviewed and then research history of cryopreservation using bovine oocytes is summarized for the last two decades with a few special references to recent progresses. Various types of cryodevices have been developed to accelerate the cooling rate and applied to the oocytes from large domestic species enriched with cytoplasmic lipid droplets. Two recent approaches include the qualitative improvement of IVM oocytes prior to the vitrification and the short-term recovery culture of vitrified-warmed oocytes prior to the subsequent IVF. Supplementation of L-carnitine to IVM medium of bovine oocytes has been reported to reduce the amount of cytoplasmic lipid droplets and improve the cryotolerance of the oocytes, but it is still controversial whether the positive effect of L-carnitine is reproducible. Incidence of multiple aster formation, a possible cause for low developmental potential of vitrified-warmed bovine oocytes, was inhibited by a short-term culture of the postwarm oocytes in the presence of Rho-associated coiled-coil kinase (ROCK) inhibitor. Use of an antioxidant α-tocopherol, instead of the ROCK inhibitor, also supported the revivability of the postwarm bovine oocytes. Further improvements of the vitrification procedure, combined with pre- and postvitrification chemical treatment, would overcome the high sensitivity of bovine oocytes to cryopreservation.