Stimulus-triggered enhancement of chilling tolerance in zebrafish embryos.

BACKGROUND: Cryopreservation of zebrafish embryos is still an unsolved problem despite market demand and massive efforts to preserve genetic variation among numerous existing lines. Chilled storage of embryos might be a step towards developing successful cryopreservation, but no methods to date have worked. METHODS: In the present study, we applied a novel strategy to improve the chilling tolerance of zebrafish embryos by introducing a preconditioning hydrostatic pressure treatment to the embryos. In our experiments, 26-somites and Prim-5 stage zebrafish embryos were chilled at 0°C for 24 hours after preconditioning. Embryo survival rate, ability to reach maturation and fertilizing capacity were tested. RESULTS: Our results indicate that applied preconditioning technology made it possible for the chilled embryos to develop normally until maturity, and to produce healthy offspring as normal, thus passing on their genetic material successfully. Treated embryos had a significantly higher survival and better developmental rate, moreover the treated group had a higher ratio of normal morphology during continued development. While all controls from chilled embryos died by 30 day-post-fertilization, the treated group reached maturity (~90-120 days) and were able to reproduce, resulting in offspring in expected quantity and quality. CONCLUSIONS: Based on our results, we conclude that the preconditioning technology represents a significant improvement in zebrafish embryo chilling tolerance, thus enabling a long-time survival. Furthermore, as embryonic development is arrested during chilled storage this technology also provides a solution to synchronize or delay the development.

Stress tolerance and transcriptional response in mouse embryos treated with high hydrostatic pressure to enhance cryotolerance.

Sublethal high hydrostatic pressure (HHP) treatment of cells was reported to enhance stress tolerance and to increase post-thawing survival after cryopreservation in mouse, swine and cattle. The goal of this study was to define if HHP stress tolerance depends on the embryos' stage of development and culture conditions, to describe long term in vivo effects and transcriptional alterations of selected stress related genes. Studies showed that impacts greater than 60 MPa caused blastomere and membrane injuries to the two-cell stage embryos, while even 80 MPa was well tolerated by blastocysts. HHP treatment caused significant upregulation of Azin1, Sod2 and Gadd45g genes, detected by RT-qPCR. The transfer of HHP treated blastocysts revealed normal in vivo development and reproductive function in a two generation study. The cell type and the embryos' development stage shall be taken into account when optimizing sublethal HHP stress treatment protocol of different cells.

Pregnancy achieved by transfer of a single blastocyst selected by time-lapse monitoring.

Appropriate selection of a single blastocyst for transfer decreases the risk of multiple gestations. By using a compact time-lapse microscope system placed inside a regular incubator, combined with a microwell embryo culture dish, the development of all the embryos from a patient was continuously monitored by obtaining images at 10 min intervals. The embryos were not moved during the time-lapse observation. The system was switched off completely between image acquisitions in order to avoid exposure to electromagnetic radiation. The analysis of time-lapse records was used to choose a single blastocyst for transfer, which resulted in a singleton pregnancy and birth of a healthy boy on term.

Prediction of in-vitro developmental competence of early cleavage-stage mouse embryos with compact time-lapse equipment.

Single blastocyst transfer is regarded as an efficient way to achieve high pregnancy rates and to avoid multiple pregnancies. Risk of cancellation of transfer due to a lack of available embryos may be reduced by early prediction of blastocyst development. Time-lapse investigation of mouse embryos shows that the time of the first and second cleavage (to the 2- and 3-cell stages, respectively) has a strong predictive value for further development in vitro, while cleavage from the 3-cell to the 4-cell stage has no predictive value. In humans, embryo fragmentation during preimplantation development has been associated with lower pregnancy rates and a higher incidence of developmental abnormalities. Analysis of time-lapse records shows that most fragmentation is reversible in the mouse and is resorbed in an average of 9 h. Daily or bi-daily microscopic checks of embryo development, applied routinely in human IVF laboratories, would fail to detect 36 or 72% of these fragmentations, respectively. Fragmentation occurring in a defined time frame has a strong predictive value for in-vitro embryo development. The practical compact system used in the present trial, based on the 'one camera per patient' principle, has eliminated the usual disadvantages of time-lapse investigations and is applicable for the routine follow-up of in-vitro embryo development.