The impacts of laser zona thinning on hatching and implantation of vitrified-warmed mouse embryos

Thinning or Opening: A Randomized Sibling-Embryo Pilot Trial on the Efficacy of Two Laser-Assisted Hatching Modes During the Extended Culture of Highly Fragmented Cleavage Embryos

A randomized sibling-embryo pilot trial investigated whether two ways of laser-assisted hatching result in different blastulation and clinical outcomes after extended in vitro culture process of highly fragmented day-3 cleavage embryos. From 92 couples, a total of 315 highly fragmented day-3 embryos (the fragmentation >25%) were recruited and randomized into laser-assisted zona thinning (LAT, n=157) and opening (LAO, n=158) groups, and then underwent a blastocyst culture in vitro. The main endpoint measurements including blastocyst formation and grading as well as the clinical pregnancy after blastocyst transfer were obtained during the treatment procedure of in vitro fertilization and embryo transfer, and then analyzed with generalized estimating equation (GEE) and/or time-to blastocyst analysis models. A total of 166 day-3 embryos developed into blastocyst stage (52.70%), of which 97 were viable blastocysts (30.79%), and 42 top-quality ones (13.33%). LAT did not have any inferior or superior to LAO in the endpoints of either total, viable, top-quality or hatched blastocyst formation, with the ORs (95%CI) from GEE model as 0.89 (0.55-1.45), 0.71 (0.42-1.21), 1.12 (0.56-2.25) and 0.68 (0.42-1.12) respectively for LAT treatment. And the time-to-blastocyst analysis showed a similar result. Additionally, no difference in clinical outcomes after blastocyst transfer was found between the two groups. The author concluded that when applying the LAHs during the extended culture of highly fragmented embryos, both LAT and LAO can generate a promising clinical outcome, and the LAT operation be equivalent to the LAO. Future well-designed, multiple-center, larger-sample investigations are required to ascertain above conclusion.

An investigation of the effects of laser-assisted zona pellucida drilling on the preimplantation mouse embryo and the competency of embryo implantation

OBJECTIVE

To investigate the impact of laser-assisted zona pellucida (ZP) drilling on the mouse embryo, with particular emphasis on molecular mechanisms, and the efficiency of embryo attachment capability using an in vitro model of implantation.

DESIGN

Experimental study.

SETTING

Academic research laboratory.

ANIMAL(S)

C57BL/6JOlaHsd mouse embryos and B6C3F1 × B6D2F1 mouse embryos.

INTERVENTION(S)

Eight-cell stage mouse embryos were randomly assigned to a laser-assisted ZP drilling group (n = 343), ZP partial drilling group (n = 312), ZP quarter thinning group (n = 289), and control group (n = 353). Embryos were cultured in vitro from E2.5 to E4.5 for 48 hours. To investigate the capacity to implant, E4.5 embryos (laser-assisted drilling group [n = 46], ZP partial drilling group [n = 28], ZP quarter thinning group [n = 26], and control group [n = 36]) were then transferred onto an attachment model on the basis of Ishikawa cells and cultured for another 72 hours.

MAIN OUTCOME MEASURE(S)

Blastocyst formation, hatching status, and hatching morphology at E4.5. Blastocyst cell components, the extent of apoptosis in embryonic cells (DNA fragmentation, caspase-3 activation, and expression of apoptosis-related genes), the expression of heat shock protein 70, and differentially expressed genes (DEGs) generated by RNA sequencing. Fully hatched embryo rate and stable attachment rate in the in vitro attachment model.

RESULT(S)

There were no significant differences between the laser-assisted ZP manipulation groups and control group with respect to the formation of blastocysts, cell number, embryonic cell apoptosis, and cellular stress. All 3 of the laser-assisted ZP manipulations significantly increased the hatching rate at E4.5 compared with the control group, especially the ZP drilling group. However, only the ZP drilling group was associated with a significantly higher proportion of "8"-shaped hatching blastocysts. Furthermore, RNA sequencing identified 48 DEGs between blastocysts from the laser-assisted drilling group and control group; the metabolic pathways were significantly enriched in these DEGs. In addition, there were no significant differences between the laser-assisted ZP manipulation groups and control group with respect to the rate of stable attachment at E7.5, although a significantly higher entrapment rate was observed in the ZP drilling group.

CONCLUSION(S)

Laser-assisted ZP manipulations did not induce cellular apoptosis or stress in mouse blastocysts. Nevertheless, for the first time, we found that laser-assisted ZP drilling could alter the embryonic transcriptome and may affect metabolic activity. Furthermore, although laser-assisted ZP manipulations can enhance the initiation of hatching, it is evident that ZP drilling comes with a potential risk of embryo entrapment.

Cryopreservation of Porcine Embryos: Recent Updates and Progress

Cryopreservation of embryos is important for long-distance embryo transfer and conservation of genetic resources. Porcine research is important for animal husbandry and biomedical research. However, porcine embryos are difficult to cryopreserve because of their high cytoplasmic lipid content and sensitivity to chilling stress. Vitrification is more efficient than slow freezing, and vitrification is mostly used in embryo cryopreservation. So far, the vitrification process of porcine embryos has been continuously improved, resulting in improved survival rates of warmed embryos and farrowing rates after the transplant procedure. It is worth noting that automatic vitrification has made great progress, which is expected to promote the standardization and application of vitrification. In this article, the vitrification process of porcine embryos at the blastula stage and early development stages is reviewed in detail. In addition, the efficiency of different vitrification systems was compared. In addition, we summarize technology that can improve the survival rate of cryopreserved porcine embryos, such as delipidation methods (including physical delipidation and chemical delipidation) and medium improvements (including chemically defined media and adding antioxidants). Meanwhile, gene expression changes during cryopreservation are also elaborated.

Evaluation of the impact of laser-assisted hatching techniques on the hatching process of mouse blastocysts using time-lapse microscopy

OBJECTIVE

To study the effect of zona opening (ZO) and 2 zona thinning (ZT) techniques on the hatching process of mouse embryos using a last-generation laser system and time-lapse microscopy (TLM).

DESIGN

Prospective randomized study.

SETTING

Private research center.

ANIMALS

A total of 267 F1 hybrid (B6/CBA) mice embryos were included.

INTERVENTION(S)

Morulae were randomly selected and the zona pellucida (ZP) manipulated using a laser system according to 4 experimental groups: control (ZP intact, n = 59), ZO (25 μm hole, n = 70), ZT25 (25% perimeter thinned, n = 71), and ZT35 (35% perimeter thinned, n = 67). Embryo development was monitored by TLM until day 6.

MAIN OUTCOME MEASURE(S)

Time to first breach the ZP, hatching time, time to complete hatching, multiple breaching, multiple hatching, loss of cells, hole size, and embryo quality were analyzed.

RESULT(S)

No significant differences in the proportion of completely hatched embryos were found among groups. However, the time (average hours ± SD) to complete hatching was significantly delayed in the control group compared with all laser-treated groups: 118.3 ± 9.5 hours in the ZT25 group, 116.6 ± 8.7 hours in the ZT35 group, and 120.4 ± 9.9 hours in the ZO group. The applied laser techniques did not interfere with the quality of the blastocysts at day 5/6 of culture.

CONCLUSION(S)

ZO, ZT25, and ZT35 embryos hatched significantly earlier than the zona intact group without increasing the multiple hatching rates, suggesting an improvement of the hatching process. This study found that the pattern of the hatching process after ZT and ZO differs.