Incubation of sperm heads impairs fertilization and early embryo development following intracytoplasmic sperm injection (ICSI) by decreasing oocyte activation in mice

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.

DNA methylation and gene expression changes in mouse pre- and post-implantation embryos generated by intracytoplasmic sperm injection with artificial oocyte activation

BACKGROUND

The application of artificial oocyte activation (AOA) after intracytoplasmic sperm injection (ICSI) is successful in mitigating fertilization failure problems in assisted reproductive technology (ART). Nevertheless, there is no relevant study to investigate whether AOA procedures increase developmental risk by disturbing subsequent gene expression at different embryonic development stages.

METHODS

We used a mouse model to explore the influence of AOA treatment on pre- and post-implantation events. Firstly, the developmental potential of embryos with or without AOA treatment were assessed by the rates of fertilization and blastocyst formation. Secondly, transcriptome high-throughput sequencing was performed among the three groups (ICSI, ICSI-AOA and dICSI-AOA groups). The hierarchical clustering and Principal Component Analysis (PCA) analysis were used. Subsequently, Igf2r/Airn methylation analysis were detected using methylation-specific PCR sequencing following bisulfite treatment. Finally, birth rate and birth weight were examined following mouse embryo transfer.

RESULTS

The rates of fertilization and blastocyst formation were significantly lower in oocyte activation-deficient sperm injection group (dICSI group) when compared with the ICSI group (30.8 % vs. 84.4 %, 10.0 % vs. 41.5 %). There were 133 differentially expressed genes (DEGs) between the ICSI-AOA group and ICSI group, and 266 DEGs between the dICSI-AOA group and ICSI group. In addition, the imprinted gene, Igf2r is up regulated in AOA treatment group compared to control group. The Igf2r/Airn imprinted expression model demonstrates that AOA treatment stimulates maternal allele-specific mehtylation spreads at differentially methylated region 2, followed by the initiation of paternal imprinted Airn long non-coding (lnc) RNA, resulting in the up regulated expression of Igf2r. Furthermore, the birth weight of newborn mice originating from AOA group was significantly lower compared to that of ICSI group. The pups born following AOA treatment did not show any other abnormalities during early development. All offspring mated successfully with fertile controls.

CONCLUSIONS

AOA treatment affects imprinted gene Igf2r expression and mehtylation states in mouse pre- and post-implantation embryo, which is regulated by the imprinted Airn. Nevertheless, no significant differences were found in post-natal growth of the pups in the present study. It is hoped that this study could provide valuable insights of AOA technology in assisted reproduction biology.

Ionomycin-induced mouse oocyte activation can disrupt preimplantation embryo development through increased reactive oxygen species reaction and DNA damage

Oocyte activation induced by calcium oscillations is an important process in normal fertilization and subsequent embryogenesis. In the clinical-assisted reproduction, artificial oocyte activation (AOA) is an effective method to improve the clinical outcome of patients with null or low fertilization rate after ICSI. However, little is known about the effect of AOA on preimplantation embryo development in cases with normal fertilization by ICSI. Here, we used ionomycin at different concentrations to activate oocytes after ICSI with normal sperm and evaluated energy metabolism and preimplantation embryo development. We found that a high concentration of ionomycin increased the frequency and amplitude of calcium oscillation patterns, affecting the balance of mitochondrial energy metabolism, leading to increased reactive oxygen species (ROS) and decreased ATP. Eventually, it increases DNA damage and decreases blastocyst formation. In addition, the addition of vitamin C to the culture medium ameliorated the increase in ROS and DNA damage and rescued the abnormal embryo development caused by excessive ionomycin activation. This study provides a perspective that the improper application of AOA may have adverse effects on preimplantation embryo development. Thus, clinical AOA treatment should be cautiously administered.

Dynamic alterations in H4K12 acetylation during meiotic maturation and after parthenogenetic activation of mouse oocytes

The aim of the study was to investigate the continuous changing pattern of H4K12 acetylation, and the expression levels of histone acetyltransferases (HATs) and histone deacetyltransferases (HDACs) in mouse oocytes during meiosis and after parthenogenetic activation (PA). The immunofluorescence results showed hyperacetylation of lysine-12 on histone H4 (H4K12) in the germinal vesicle (GV) oocytes that then decreased during germinal vesicle breakdown (GVBD), and disappeared in metaphase II (MII). However, it reappeared in the early 1-cell embryos derived after 4 h of PA. The expression levels of some selected HATs and HDACs also validated the changing pattern of H4K12 acetylation during meiosis and PA. In conclusion, H4K12 is deacetylated in GVBD and MII, and re-hyperacetylated after PA.

Andrographolide disrupts meiotic maturation by blocking cytoskeletal reorganisation and decreases the fertilisation potential of mouse oocytes

Andrographolide (AG) is a diterpenoid lactone isolated from the stem and leaves of Andrographis paniculata Nees that is used for the effective treatment of infectious diseases in Asian countries. Previous studies have reported adverse effects of AG on female fertility in rodents; however, the underlying mechanisms are unknown. The aim of the present study was to investigate the effects of AG on the IVM of mouse oocytes and their fertilisation potential. Immature oocytes incubated for 6, 14 or 24h in medium containing 5, 10 or 20μM AG showed time- and dose-dependent decreases in maturation rates compared with the control group. Immunostaining revealed that AG exposure disrupted spindle organisation and migration, as well as actin cap formation and cytokinesis. Furthermore, most oocytes exposed to 20μM AG underwent apoptosis, and the few oocytes exposed to 5 or 10μM AG that reached MII exhibited lower fertilisation rates after intracytoplasmic sperm injection. The findings of the present study suggest that AG may disrupt mouse oocyte meiotic maturation by blocking cytoskeletal reorganisation, and may thus have an adverse effect on female fertility.

Effect of genistein added to bull semen after thawing on pronuclear and sperm quality

The aim of this research was to study the effect of different genistein treatments on bull sperm after thawing on pronuclear formation after in vitro fertilization (IVF) and on different sperm quality variables. Three experiments were performed. In Experiment 1, three treatments (Control, sperm incubation for 1h at 37 °C with or without genistein) and two sperm concentrations during IVF (1 or 3 × 10(6)sperm/mL) were evaluated to study the influence of genistein on pronuclear formation (PNF). Sperm incubation for 1h before IVF reduced PNF regardless of sperm concentration. However, after sperm incubation and with 3 × 10(6)sperm/mL in IVF, the genistein treatment group had greater fertilization rates than the untreated group. In Experiment 2, six treatments plus the control group were performed to study the effect of genistein (presence or not) and incubation conditions (30 min at 37 °C, 1h at 27 °C or at 37 °C) on PNF using 3 × 10(6)sperm/mL for IVF. When incubation time was reduced to 30 min, PNF rate from the genistein treatment group was no different from either the control group or in the group in which incubation occurred for 1h at 27 °C. In Experiment 3, the effect of several genistein treatments (control; genistein treatment for 30 min of incubation at 37 °C; genistein treatment for 1h of incubation at 27 °C) on sperm motility, viability and DNA fragmentation were evaluated. Genistein did not improve sperm motility and, depending on the experimental group or time, it either reduced or had no effect on sperm motility. Genistein treatment did not improve sperm viability after 5h of incubation. However, genistein treatment for 1h at 27 °C decreased sperm DNA fragmentation compared with the control group after 5h of sperm incubation. In conclusion, the treatment of bull sperm with genistein for 1h at 27 °C could decrease sperm DNA fragmentation, although PNF rate after IVF and sperm motility were reduced.