Determination of Optimal Conditions for Parthenogenetic Activation and Subsequent Development of Rat Oocytes In Vitro

Selection of Rattus norvegicus cumulus-oocyte complex for vitrification by brilliant cresyl blue

The influence of the method of evaluating developmentally competent oocytes on their viability after cryopreservation still needs to be better understood. The objective of this study was to determine the cleavage and embryo developmental rates after parthenogenetic activation of cumulus-oocyte complexes (COCs) selected by different concentrations of brilliant cresyl blue (BCB) and cryopreservation. In the first experiment, COCs were separated into groups and incubated for 1 h in medium containing BCB (13 μM, 16 μM, or 20 μM). The control group was not exposed to BCB staining. In the second experiment, COCs were divided into four groups: 13 μM BCB(+), 13 μM BCB(-), fresh control (selected by morphologic observation and immediately in vitro matured) and vitrified control (selected by morphologic evaluation, vitrified, and in vitro matured). In the first experiment, the 13 μM BCB group displayed greater development rates at the morula stage (65.45%, 36/55) when compared with the other groups. In the second experiment, cleavage (47.05%, 72/153) and morula development (33.55%, 51/153) of the control group of fresh COCs were increased compared with the other groups. However, when comparing morula rates between vitrified COC control and BCB(+) groups, the BCB(+) group had better results (19.23%, 5/26 and 64.7%, 11/17, respectively). Our best result in rat COC selection by BCB staining was obtained using a concentration of 13 μM. This selection could be a valuable tool to improve vitrification outcomes, as observed by the BCB(+) group that demonstrated better results compared with the vitrified COC control.

Removal of sperm tail using trypsin and pre-activation of oocyte facilitates intracytoplasmic sperm injection in mice and rats

We examined various methods to enhance the accessibility of intracytoplasmic sperm injection (ICSI) technology to more users by making the technique easier, more efficient, and practical. First, the methods for artificially removing the mouse sperm tail were evaluated. Trypsin treatment was found to efficiently remove the sperm tails. The resultant sperm cells had a lower oocyte activation capacity; however, the use of activated oocytes resulted in the same fecundity as that of fresh, untreated sperm. Pre-activated oocytes were more resistant to physical damage, showed higher survival rates, and required less time per injection. Testing this method in rats yielded similar results, although the oocyte activation method was different. Remarkably, this method resulted in higher birth rates of rat progeny than with conventional methods of rat ICSI. Our method thereby streamlines mouse and rat ICSI, making it more accessible to laboratories across many disciplines.

Performing ICSI within 4 hours after denudation optimizes clinical outcomes in ICSI cycles

BACKGROUND

The study aimed to investigate whether and how general and partial time intervals between processes, from human chorionic gonadotrophin (HCG) trigger to intracytoplasmic sperm injection (ICSI), affected the laboratory and reproductive outcomes in ICSI cycles.

METHODS

This was a retrospective data analysis of 3602 women who underwent ICSI treatment cycles using partner or donor sperms, performed at Reproduction Medicine Center of Tongji Hospital of Tongji Medical College of Huazhong University of Science and Technology (Wuhan, China) between October 2016 and September 2018. The clinical pregnancy rate was the major outcome in the study. The fertilization and available embryo rates were secondary outcomes.

RESULTS

Data from 3602 consecutive fresh ICSI cycles was analysed. Multivariate linear regression and logistic regression analysis of factors related to fertilization and clinical pregnancy rates showed that fertilization rate (P = 0.001) and clinical pregnancy rate (P = 0.037) were significantly associated with denudation (DN)-ICSI interval. Long DN-ICSI interval was associated with higher rate of fertilization than short DN-ICSI interval but significantly decreased clinical pregnancy rate when the interval is over 4 h (P < 0.05).

CONCLUSIONS

DN-ICSI time interval can act as an independent predictor for clinical outcomes in ICSI cycles. The optimal time for ICSI is within 4 h after oocyte denudation for excellent laboratory and reproductive outcomes in ICSI cycles.

The timing of cumulus cell removal for intracytoplasmic sperm injection influences the capability of embryonic development

PURPOSE

To determine whether the presence of intact cumulus cells during the preincubation period for ICSI should be considered as a critical factor in fertilization and embryonic development.

METHODS

The cohort of this prospective randomized study was limited to infertile women younger than 39 years of age who underwent controlled ovarian stimulation for ICSI between October 2013 and May 2015 and whose embryos were to be incubated until day 5. Women with estradiol levels of <2000 pmol/L on the day of HCG injection were excluded. Cumulus cells were removed immediately after OPU in Group A and at 120 minutes after OPU in Group B. ICSI was performed with all mature oocytes, and fertilized oocytes were cultured to the blastocyst stage. Maturation, fertilization, blastocyst, good quality blastocyst, pregnancy, live birth, and miscarriage rates were compared.

RESULTS

There were no significant differences in maturation, fertilization, blastocyst, pregnancy, live birth, or miscarriage rates between Groups A and B. However, the percentage of good quality blastocysts was significantly higher in Group B than Group A (52.0% vs 33.1%).

CONCLUSIONS

Intact cumulus cells should be maintained during the preincubation period, as they are important to embryonic development after fertilization.

Generation of transgenic marmosets using a tetracyclin-inducible transgene expression system as a neurodegenerative disease model

Controllable transgene expression systems are indispensable tools for the production of animal models of disease to investigate protein functions at defined periods. However, in nonhuman primates that share genetic, physiological, and morphological similarities with humans, genetic modification techniques have not been well established; therefore, the establishment of novel transgenic models with controllable transgene expression systems will be valuable tools to understand pathological mechanism of human disease. In the present study, we successfully generated transgenic marmosets using a tetracyclin-inducible transgene expression (tet-on) system as a neurodegenerative disease model. The mutant human ataxin 3 gene controlled by the tet-on system was introduced into marmoset embryos via lentiviral transduction, and 34 transgene-introduced embryos were transferred into the uteri of surrogate mothers. Seven live offspring (TET1-7) were obtained, of which four were transgenic. Fibroblasts from TET1 and 3 revealed that inducible transgene expression had occurred after treatment with 10 μg/mL of doxycycline, while treatment with doxycycline via drinking water resulted in 1.7- to 1.8-fold inducible transgene expression compared with before treatment. One transgenic second-generation offspring (TET3-3) was obtained from TET3, and doxycycline-inducible transgene expression in its fibroblasts showed that TET3-3 maintained a high transgene expression level that matched its parent. In conclusion, we established a novel transgenic marmoset line carrying the mutant human ataxin 3 gene controlled by the tet-on system. The development of nonhuman primate models with controllable transgene expression systems will be useful for the identification of disease biomarkers and evaluation of the efficacy and metabolic profiles of therapeutic candidates.

Effects of chemical combinations on the parthenogenetic activation of mouse oocytes

The aim of this study was to identify an optimal method for the parthenogenetic activation of mouse oocytes. Ethanol (EH), strontium chloride (SrCl₂) and ionomycin calcium salt were each combined with cytochalasin B to induce the parthenogenetic activation of CD-1^® mouse oocytes. Among the EH combination groups, the blastocyst formation and hatching rates of the group that was activated with EH and CB for 5 min were significantly higher compared with those of the groups that were activated for 7 and 10 min (P<0.05). Among the SrCl₂ combination groups, the blastocyst formation and hatching rates of the group that was activated with SrCl₂ and CB for 30 min were significantly higher compared with those of the groups that were activated for 1 and 2 h (P<0.05). Among the ionomycin calcium salt combination groups, the blastocyst formation and hatching rates of the group that was activated with ionomycin and CB for 3 min were higher compared with those of the groups that were activated for 5 and 7 min (P<0.05). Compared with the other two combinations, the experimental indicators of the EH combination groups were notably superior (P<0.05). For combined activation, simultaneous activation with two substances was significantly more effective than successive activation (P<0.05). For combined activation with EH and cytochalasin B in mouse oocytes, 5 min of parthenogenetic activation had significant advantages with regard to cleavage, blastocyst formation and blastocyst hatching rates. In addition, the activation rate of combined activation was higher than that of single activators. For combined activation, the simultaneous application of two activators has a superior effect.

Rat eggs cannot wait: Spontaneous exit from meiotic metaphase-II arrest

Mammalian eggs await fertilisation while arrested at the second metaphase stage of meiotic division. A network of signalling pathways enables the establishment and maintenance of this metaphase-II arrest. In the absence of fertilisation, mammalian eggs can spontaneously exit metaphase II when parthenogenetically stimulated, or sometimes without any obvious stimulation. Ovulated rat eggs abortively release from metaphase-II arrest once removed from egg donors. Spontaneously activated rat eggs extrude the second polar body and proceed to the so-called metaphase III-'like' stage, with clumps of condensed chromatin scattered in the egg cytoplasm. It is still unclear what makes rat eggs susceptible to spontaneous activation; however, a vague picture of the signalling pathways involved in the process of spontaneous activation is beginning to emerge. Such cell cycle instability is one of the major reasons why it is more difficult to establish nuclear transfer in the rat. This review examines the known predisposing factors and biochemical mechanisms involved in spontaneous activation. The strategies used to prevent spontaneous metaphase-II release in rat eggs will also be discussed.

Dynamic oxygen enhances oocyte maturation in long-term follicle culture

Traditionally, follicles have been grown in standard incubators with atmospheric oxygen concentration. However, preantral follicles exist in the avascular cortex of the ovary. This study examines the effectiveness of an oxygen delivery protocol that more closely mimics the in vivo environment of the ovary on oocyte viability, maturation, parthenogenetic activation, and fertilization from in vitro cultured rat preantral follicles. Of 54 oocytes cultured in the dynamic oxygen environment, 35 were viable while only 22 of 50 oocytes cultured within an ambient oxygen concentration remained viable (p < 0.05). Germinal vesicle breakdown was observed in 56% of oocytes from the dynamic oxygen group compared to 30% of oocytes from the ambient oxygen group (p < 0.05). Parthenogenetic activation was observed in a significant number of oocytes from the dynamic oxygen group, while none of the oocytes from the ambient oxygen group activated (p < 0.05). However, the proportions of oocytes from the dynamic oxygen group that remained viable underwent germinal vesicle breakdown, and activated were still significantly less than those from the in vivo control group (p < 0.05). Fertilization of the oocytes from the dynamic oxygen group was confirmed through a successful trial of intracytoplasmic sperm injection.

The effect of the time interval between injection and parthenogenetic activation on the spindle formation and the in vitro developmental potential of somatic cell nuclear-transferred rat oocytes

We examined the optimal conditions for somatic cell nuclear transfer (SCNT) in the rat. First, we examined the effect of preincubation time before activation on SCNT rat oocytes produced in the presence of MG132 with regard to spindle formation and the potential to develop into blastocysts. The spindles of SCNT oocytes continued to elongate with an increase in the culture duration and, in approximately half of oocytes, the chromosomes were distributed along the spindles at 120 min after incubation. Such abnormal spindle formation in SCNT oocytes is a possible reason for the low developmental potential of SCNT rat oocytes. To inhibit the formation of abnormal spindle formation, we examined secondly the developmental potential of rat SCNT oocytes that had been preincubated with nocodazole and demecolcine instead of MG132. The developmental rates in SCNT oocytes, however, were decreased. For successful rat somatic cell cloning, two steps might be required: (1) to culture the somatic cell nuclei for a sufficient time in MII oocyte cytoplasm to enhance nuclear reprogramming; and (2) to induce normal spindle formation with normal chromosomal construction.

A combined treatment with ethanol and 6-dimethylaminopurine is effective for the activation and further embryonic development of oocytes from Sprague-Dawley and Wistar rats

In nuclear-transferred or round spermatid-injected oocytes, artificial activation is required for further development in mammals. Although strontium chloride is widely used as the reagent for inducing oocyte activation in mice, the optimal method for oocyte activation remains controversial in rats because ovulated rat oocytes are spontaneously activated in vitro before artificial activation is applied. In our previous study, we found that cytostatic factor activity, which is indispensable for arrest at the MII stage, is potentially low in rats and that this activity differs greatly between two outbred rats (Slc: Sprague-Dawley (SD) and Crj: Wistar). Therefore, it is necessary to establish an optimal protocol for oocyte activation independent of strains. Given that comparative studies of the in vitro development of oocytes activated by different activation protocols are very limited, we compared four different protocols for oocyte activation (ethanol, ionomycin, strontium and electrical pulses) in two different SD and Wistar rats. Our results show that oocytes derived from SD rats have significantly higher cleavage and blastocyst formation than those from Wistar rats independent of activation regimes. In both types of rat, ethanol treatment provided significantly higher developmental ability at cleavage and blastocyst formation compared to the other activation protocols. However, the initial culture in a fertilization medium (high osmolarity mR1ECM) for 24 h showed a detrimental effect on the further in vitro development of parthenogenetic rat oocytes. Taken together, our results show that ethanol treatment is the optimal protocol for the activation of rat oocytes in SD and Wistar outbred rats. Our data also suggest that high-osmolarity media are inadequate for the in vitro development of parthenogenetically activated oocytes compared with fertilized oocytes.

Overcoming MIII arrest from spontaneous activation in cultured rat oocytes

The rat oocyte spontaneously activates under a wide variety of conditions. This process progresses to MIII arrest that is not responsive to parthenogenetic activation and development. Insofar as activation involves extrusion of the second polar body (PBII), we set out to determine if preventing this step by inhibiting microfilaments would change the course of spontaneous activation (SA). In particular, how long does the effect of SA persist while retaining reversibility of PBII extrusion once inhibitors are removed? We wanted to determine if the eggs would be responsive to parthenogenetic activation and capable of resuming development once a permanent inhibition is achieved. We set out to determine whether SA would depend on the ovular age of oocytes. Inhibiting of PBII extrusion was achieved by affecting microtubules with demecolcine or nocodazole or actin filaments with cytochalasin B (CB) and cytochalasin D (CD). We found that all oocytes undergo SA and progression to MIII; however, the rapidity of spontaneous activation is a function of the ovular age of the oocyte. The resumption of the meiosis period changes dramatically from 20 to 180 min with decreasing ovular age. We established that suppression of PB formation can be effectively achieved in oocytes of younger ovular age, and that inhibition of PB extrusion became irreversible after 3.5 h of treatment. We established that drug-treated oocytes could undergo subsequent reactivation and in vitro development to blastocysts. The rate of in vitro development of cytochalasin-treated group was comparable to parthenogenetic controls, while nocodazole and demecolcine produced oocytes that developed at lower frequencies. Thus, the application of the microfilament inhibiting drugs helps to overcome the negative effect of SA that results in MIII arrest. Here we also show optimized parthenogenetic stimulation that resulted in development to the blastocyst stage at frequency comparable to development of fertilized embryos.

Oocyte spontaneous activation in different rat strains

Oocyte spontaneous activation (OSA) has been reported to occur during in vitro culture of ovulated rat oocytes. The objective of this study was to compare the rate of oocyte spontaneous activation and the level of maturation promoting factor (MPF) activity in oocytes from different strains. Twelve strains were selected from two commercial sources. Females were superovulated and oocytes collected 17 h after hCG injection. Denuded oocytes were cultured in M16 medium under oil at 37 degrees C and 5% CO(2) in air. The proportion of activated oocytes was determined after 6 h of in vitro culture. Data were compared by analysis of variance (ANOVA), considering each animal as an experimental unit. MPF activity was determined in oocytes from the different strains at 0, 1.5, and 3 h after oocyte collection. The log ratio of the MPF activity at 1.5 and 3 h relative to 0 hours for each animal was analyzed by ANOVA. While significant (p < 0.01) differences were observed between strains in the rate of OSA, there were no differences between strains in the level of MPF during the time points measured (p > 0.3).

Embryonic Stem Cells from Parthenotes

While human embryonic stem cells (hESCs) hold tremendous therapeutic potential, they also create societal and ethical dilemmas. Adult and placental stem cells represent two alternatives to the hESC, but may have technical limitations. An additional alternative is the stem cell derived from parthenogenesis. Parthenogenesis is a reproductive mechanism that is common in lower organisms and produces a live birth from an oocyte activated in the absence of sperm. However, parthenogenetic embryos will develop to the blastocyst stage and so can serve as a source of embryonic stem cells. Parthenogenetic ESCs (pESCs) have been shown to have the properties of self-renewal and the capacity to generate cell derivatives from the three germ layers, confirmed by contributions to chimeric animals and/or teratoma formation when injected into SCID mice. Therefore, this mechanism for generating stem cells has the ethical advantage of not involving the destruction of viable embryos. Moreover, the cells do not involve the union of male and female and so genetic material will be derived exclusively from the female oocyte donor (with the attendant potential immunological advantages). This chapter describes the biology underlying parthenogenesis, as well as provides detailed technical considerations for the production of pESCs.

Optimal Conditions for Successful In Vitro Fertilization and Subsequent Embryonic Development in Sprague-Dawley Rats1

The present study was conducted to determine the optimal conditions for successful in vitro fertilization (IVF) in Sprague-Dawley (SD) rats. The IVF of oocytes from SD and Wistar rats was compared in different fertilization media (mR1ECM, IVF-20, and modified Krebs-Ringer bicarbonate solution [mKRB]), and IVF conditions were then optimized for oocytes of the SD strain. Results showed that in mR1ECM medium, fertilization rates were markedly lower in SD rats (15%) than in the Wistar strain (73%), although this response was significantly improved by increasing the NaCl concentration. In addition, fertilization rates in SD rats were higher in modified IVF-20 (73%) than in IVF-20 (18%) and mKRB (53%). In contrast, fertilization rates in Wistar rats were higher in IVF-20 and modified IVF-20 than in mKRB (78%, 74%, and 36%, respectively). Further investigation concerning the effects of the NaCl supplementation (10- 40 mM) in IVF-20 on the fertilization of oocytes in the SD strain indicated that significantly higher percentages of oocytes were fertilized in IVF-20 supplemented with 30 mM NaCl (66%) and developed to the blastocyst stage (47%) in vitro. After transfer, embryos derived from this IVF system developed to term at a percentage comparable to that of in vivo-fertilized controls. In conclusion, differences exist in optimal IVF conditions between rat strains, and a modified culture medium has been successfully developed for assessment of the developmental competence of oocytes in SD rats.