In vitro development of spontaneously activated bovine oocytes

Liposome-encapsulated diacyl glycerol and inositol triphosphate-induced delayed oocyte activation and poor development of parthenotes

Objective:

To explore the ability of diacyl glycerol (DAG) and inositol triphosphate (IP3), two major secondary messengers in the calcium signaling pathway, in activating oocytes.

Material and Methods:

Oocyte cumulus complex obtained from superovulated Swiss albino mice were incubated in M16 medium with liposome-encapsulated 1,2-Dipalmitoyl-sn-glycerol (LEDAG) and/or IP3 for 3 h. Strontium chloride was used as positive control. The activation potential, ploidy status, and blastocyst rate was calculated.

Results:

Both DAG and IP3, individually, induced activation in ~98% of oocytes, which was significantly higher (p<0.01) than activation induced by strontium chloride (60%). Delayed pronucleus formation and a higher percentage of diploid parthenotes was observed in oocytes activated with LEDAG and/or IP3. However, these embryos failed to progress beyond the 6-8–cell stage. Only when the medium was supplemented with LEDAG (5 μg/mL) and IP3 (10 μg/mL) could activated oocytes progress till the blastocyst stage (5.26%), which was lower than the blastocyst rate in the positive controls (13.91%).

Conclusion:

The results of the present study indicate that DAG and IP3 can induce delayed oocyte activation and poor development of parthenotes in vitro.

The oxidative stress adaptor p66Shc is required for permanent embryo arrest in vitro

BACKGROUND

Excessive developmental failure occurs during the first week of in vitro embryo development due to elevated levels of cell death and arrest. We hypothesize that permanently arrested embryos enter a stress-induced "senescence-like" state that is dependent on the oxidative stress-adaptor and lifespan determinant protein p66Shc. The aim of this study was to selectively diminish p66Shc gene expression in bovine oocytes and embryos using post-transcriptional gene silencing by RNA-mediated interference to study the effects of p66Shc knockdown on in vitro fertilized bovine embryos.

RESULTS

Approximately 12,000-24,000 short hairpin (sh)RNAi molecules specific for p66Shc were microinjected into bovine germinal vesicle stage oocytes or zygotes. Experiments were comprised of a control group undergoing IVF alone and two groups microinjected with and without p66Shc shRNAi molecules prior to IVF. The amount of p66Shc mRNA quantified by Real Time PCR was significantly (P < 0.001) lowered upon p66Shc shRNAi microinjection. This reduction was selective for p66Shc mRNA, as both histone H2a and p53 mRNA levels were not altered. The relative signal strength of p66Shc immuno-fluorescence revealed a significant reduction in the number of pixels for p66Shc shRNAi microinjected groups compared to controls (P < 0.05). A significant decrease (P < 0.001) in the incidence of arrested embryos upon p66Shc shRNAi microinjection was detected compared to IVF and microinjected controls along with significant reductions (P < 0.001) in both cleavage divisions and blastocyst development. No significant differences in p66Shc mRNA levels (P = 0.314) were observed among the three groups at the blastocyst stage.

CONCLUSION

These results show that p66Shc is involved in the regulation of embryo development specifically in mediating early cleavage arrest and facilitating development to the blastocyst stage for in vitro produced bovine embryos.

In vitro development of human oocytes after parthenogenetic activation or intracytoplasmic sperm injection

OBJECTIVE

To compare directly in vitro developmental competence between parthenogenetically activated and intracytoplasmic sperm injection (ICSI)-fertilized oocytes.

DESIGN

For each patient, three metaphase II oocytes were randomized to the ICSI procedure, while n-3 were allocated to parthenogenetic activation.

SETTING

University hospital infertility unit.

PATIENTS

Thirty-eight patients, aged 35.2 +/- 3.3 years (mean +/- SD) selected for ICSI.

INTERVENTIONS

After 1 hour from denudation, oocytes were either fertilized by ICSI (n = 114) or chemically activated (n = 104). Fertilized and activated oocytes were cultured for up to 3 and 5 days, respectively.

MAIN OUTCOME MEASURES

Development rate, cell number, and morphological grade during culture.

RESULTS

The two groups showed no significant differences between rates of fertilization and parthenogenetic activation, development, and blastomere number on days 2 and 3 of culture. However, parthenotes showed a lower morphological grade, and a significantly lower proportion went on cleaving to day 3, when only activated rather than total numbers of oocytes were considered. On day 5 after activation, nine oocytes (8.6%) reached the blastocyst stage, representing 12.9% of parthenotes.

CONCLUSIONS

Since most parameters examined in this study were similar between activated and fertilized oocytes, parthenogenetic activation may be a useful tool for the preclinical evaluation of experimental procedures.

Cloning: Eight Years After Dolly

It is now 8 years since the birth of Dolly, the first animal produced by nuclear transfer using a donor cell population established from an adult animal. During this time, the technique of nuclear transfer has been successfully applied to a range of mammalian species for the production of offspring using a plethora of donor cell types derived from both foetal and adult tissues. In addition, when coupled with genetic manipulation of the donor cells, transgenic offspring have been produced with a range of genetic modifications including gene knockouts and gene knockings. Despite the apparent successes of the technology, the efficiency of development to live offspring has remained low and developmental abnormalities still occur. The objectives of this paper are to review some of the successes and failures of the nuclear transfer procedure since the production of Dolly. In particular, we will review the major steps in the procedure and discuss studies from our laboratory and others which have modified the procedure in ways which may impact on development.

Chromosomal abnormalities: a potential quality issue for cloned cattle embryos

Nuclear transfer in cattle is associated with high levels of embryonic mortality and often with congenital malformation. Chromosomal abnormalities are a well-known cause of pregnancy failure and congenital malformation in humans, but their relative contribution to pregnancy failure and congenital malformation in cloned embryos and calves is largely unknown. This paper reviews existing literature on the chromosomal constitution of bovine embryos produced by fertilization in vivo and in vitro, parthenogenetic activation, and nuclear transfer. The published data suggest that chromosomally abnormal cells are common in embryos; however, the frequency reported varies with the method of embryo production. The most frequently observed deviation from the diploid karyotype was mixoploidy resulting from aberrant cell division causing polyploidy in a variable proportion of the embryo's cells.

Bovine parthenogenesis is characterized by abnormal chromosomal complements: implications for maternal and paternal co-dependence during early bovine development

The present study was conducted to examine the karyotypes of parthenogenetic bovine embryos arising from the application of standard oocyte activation and diploidization methods. Bovine cumulusoocyte complexes were collected and matured in vitro for 24 hr prior to oocyte activation with either 5 microM ionomycin or 7% ethanol for 5 min. Groups of activated oocytes were further treated with 5 micrograms/ml cytochalasin D or 1.9 mM 6-dimethylaminopurine (DMAP) for 6 hr. Cleavage varied significantly (P < .05) among the treatment groups with 68.0% of the ethanol- and DMAP-treated oocytes dividing. Blastocyst development did not vary with 18.4 +/- 2.5% of all treated oocytes progressing to this stage. Blastocyst development did not occur in groups subjected to oocyte activation alone. Blastocysts displayed haploid (2.3%), diploid (11.4%), tetraploid (40.9%), octaploid (4.5%), and mixoploid chromosomal complements (40.9%). Two-cell stage parthenogenotes resulting from ethanol or ionomycin treatment alone displayed haploid (66.7%), diploid (16.7%), tetraploid (4.2%), and mixoploid (12.5%) complements. Our results demonstrate that diploid bovine parthenogenotes arising from these procedures are a minority, with the majority of parthenogenotes displaying polyploid and mixoploid chromosomal complements. The events contributing to these abnormal chromosomal complements occur as early as completion of the first cell cycle, possibly linking these events with the absence of a paternally supplied centrosome.

Cell allocation and chromosomal complement of parthenogenetic and IVF bovine embryos

Considerable concerns exist regarding the quality of parthenogenetically activated embryos in terms of sufficient numbers of cells comprising the inner cell mass (ICM) and trophectoderm (TE) and the ploidy. Therefore, these two parameters were used to assess the quality of embryos derived from parthenogenetic activation by using calcium ionophore A23187 (CaI) followed by either 6-dimethylaminopurine (6-DMAP, 3.5 hr or 6.5 hr) or cycloheximide (CHX) plus cytochalasin D (CD). The conventional in vitro (IVF) produced embryos served as a control. Double staining of the parthenogenetic blastocysts showed that the total cell number (TC) of embryos from the 6-DMAP 3.5 hr (87.0 +/- 5.3) and CHX+CD (79.0 +/- 6.1) groups was not different (P > 0.05), but was lower than that of control embryos (116.0 +/- 5.8, P < 0.001). The mean ratios of inner cell mass (ICM) and trophectoderm (TE) cells in the 6-DMAP 3.5 hr group (0.57 +/- 0.04) and the control IVF group (0.50 +/- 0. 02) did not differ significantly. Both were higher than those of the CHX+CD group (0.36 +/- 0.02; P < 0.05). Further analysis of chromosomal compositions of developing stage embryos at day four after IVF or parthenogenetic activation demonstrated that prolonged treatment with 6-DMAP for 6.5 hr resulted in a significantly lower percentage of diploid embryos and a significantly higher percentage of abnormal ploidy embryos compared to treatment with 6-DMAP for 3.5 hr or with CHX and IVF. In conclusion, parthenogenetic activation of bovine oocytes with CaI followed by 6-DMAP for 3.5 hr could produce better quality embryos in terms of total cell numbers, the number of cells allocated to the ICM, and the ploidy of embryos.

Activation regimens to prepare bovine oocytes for intracytoplasmic sperm injection

Activation of bovine oocytes to produce a single haploid pronucleus in preparation for intracytoplasmic sperm injection (ICSI) has been investigated with various combinations of ionomycin and 6-dimethylaminopurine (DMAP). Effects were evaluated by immunocytochemical staining, chromosomal analysis and assessment of development in vitro. Oocytes matured in vitro were exposed to: ionomycin alone (single or repeated treatments, Groups 1 and 2 respectively), ionomycin followed by DMAP (immediately or after a 3-h delay, Groups 3 and 4), or no treatment (control, Group 5). They were then co-cultured in M199 with bovine oviductal epithelial cells. Activation rates were not significantly different among groups but significantly fewer oocytes in Group 3 extruded a second polar body than in Groups 1, 2, and 4. Most parthenotes (60% to 80%) in Groups 1, 2, and 4 were haploid, whereas 82% in Group 3 were mixoploid or polyploid. Most of the parthenotes (88%) in Group 4 formed a single pronucleus besides extruding the second polar body and were therefore more suitable for ICSI than those of Groups 1 and 2 in which condensed chromosomes predominated. The respective rates of oocyte cleavage in Groups 1 to 4 were 24%, 36%, 70%, and 75%; corresponding blastocyst rates were 1%, 5%, 17%, and 8%. There were significantly fewer cells in the parthenotes of Groups 1, 2, and 4 than of Group 3, or of embryos produced by in vitro fertilization. Thus, delaying the addition of DMAP after ionomycin decreases chromosomal abnormalities and produces a high proportion of activated oocytes suitable for ICSI.

Cytogenetic analysis of bovine parthenotes after spontaneous activation in vitro

We conducted a cytogenetic study of bovine parthenotes derived from oocytes matured and cultured in vitro. In vitro maturation was carried out by culturing follicular oocytes for 24 h in TCM199 supplemented with estrous cow serum (ECS) and hormones at 39 degrees C in 5% CO2. Matured oocytes were incubated for 20 h in sperm TALP without the addition of spermatozoa, after which they were cultured in maturation droplets for 48 to 72 h. Spontaneous activation occurred in 9.5% of the matured oocytes. Cytogenetic analysis of 24 parthenotes revealed that 62.5% exhibited a normal, diploid chromosome complement. The remaining 37.5% had various ploidy anomalies: haploidy (25%), triploidy (4.2%) and tetraploidy (8.3%). Parthenotes exhibited different developmental stages. The number of blastomeres ranged from 2 to 8 within a parthenote. Only 1 parthenote was comprised 9 to 16 cells. The results showed that spontaneous parthenogenetic activation which occurs in an IVM/IVF system may interfere with embryo production efficiency.