Developmental capacities of two-cell mouse embryos frozen by three methods

Ice nucleating agents allow embryo freezing without manual seeding

Embryo slow freezing protocols include a nucleation induction step called manual seeding. This step is time consuming, manipulator dependent and hard to standardize. It requires access to samples, which is not always possible within the configuration of systems, such as differential scanning calorimeters or cryomicroscopes. Ice nucleation can be induced by other methods, e.g., by the use of ice nucleating agents. Snomax is a commercial preparation of inactivated proteins extracted from Pseudomonas syringae. The aim of our study was to investigate if Snomax can be an alternative to manual seeding in the slow freezing of mouse embryos. The influence of Snomax on the pH and osmolality of the freezing medium was evaluated. In vitro development (blastocyst formation and hatching rates) of fresh embryos exposed to Snomax and embryo cryopreserved with and without Snomax was assessed. The mitochondrial activity of frozen-thawed blastocysts was assessed by JC-1 fluorescent staining. Snomax didn't alter the physicochemical properties of the freezing medium, and did not affect embryo development of fresh embryos. After cryopreservation, the substitution of manual seeding by the ice nucleating agent (INA) Snomax did not affect embryo development or embryo mitochondrial activity. In conclusion, Snomax seems to be an effective ice nucleating agent for the slow freezing of mouse embryos. Snomax can also be a valuable alternative to manual seeding in research protocols in which manual seeding cannot be performed (i.e., differential scanning calorimetry and cryomicroscopy).

An attempt of cryopreservation of mouse embryos at the ACTREC laboratory animal facility in India

Cryopreservation is the long-term storage of viable cells/tissue in liquid nitrogen. The present study was conducted to freeze 8-cell- to morula-stage mouse embryos from the ACTREC Laboratory Animal Facility using a "slow freezing and fast revival" method. In all, 4,088 embryos were collected from 495 donor female mice of ten different strains. An average recovery of 8 embryos per donor mouse were recorded. Of the 4,088 embryos, 3,946 embryos of normal morphology were frozen in 173 straws. They were cooled down using a controlled-rate freezing assembly, and the straws were directly plunged into liquid nitrogen for long-term storage. Out of these 3,946 frozen embryos, 2,650 were found to be viable after fast revival. The highest survival rate, 81%, was recorded in B6D2F1 hybrid mice, whereas the lowest rate, 51%, was recorded in the S/RV/Cri-ba mutant strain. Out of 2,650 viable embryos, 2,359 embryos (89%) developed to the blastocyst stage after 24 h of incubation in a CO(2) incubator. The developed blastocysts were transferred surgically into 101 pseudopregnant female mice, of which 49 (48.5%) females were found to be pregnant. The highest percentage of pregnancy, 75%, was recorded in C57BL/6NCrl and NIH-III mice, whereas no pregnant recipients were recorded in Ptch, C3H/HeNCrl and NOD SCID mice. Based on the deliveries of these 49 females, an average of 4 young were delivered per female. Improvement in efficiency of freezing, thawing, and surgical transfer of embryos into pseudopregnant females is one of the challenges in such studies.

Effect of a programmed short-term stimulation protocol on the replacement of cryopreserved embryos

PURPOSE

Through problems in the management of embryo thawings and transfers, we investigated in a comparative study the use of the natural cycle and of a programmed short-term stimulation protocol as preparation method for the replacement of cryopreserved embryos. To date, 117 embryos have been thawed, and 60 (51%) survived with > or = 50% intact blastomeres.

METHODS

In 31 cases, replacement of the frozen-thawed embryos was planned in the natural cycle (group A) and in nine cases in the stimulated cycle (group B). In group A, 16 replacements could be performed (cancellation rate 48%). Six transfers took place on weekends (37%). Two clinical pregnancies could be established (13% per replacement). In group B, there were no canceled cycles (p < 0.025). All thawings and transfers could be conducted between Monday and Friday. In one case, the single one frozen embryo was degenerated after thawing.

RESULTS

Thus, eight replacements could be performed which resulted in three clinical pregnancies (38% per replacement, n.s.) and one biochemical pregnancy.

CONCLUSIONS

Based on our results, we conclude that a programmed short-term protocol not only provides viable embryos with a good cryopreservation potential, but it is also a reliable preparation method for the replacement of frozen-thawed embryos.