The relationship between oxygen consumption rate and viability of in vivo-derived pig embryos vitrified by the micro volume air cooling method

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.

Insemination of recipient sows improves the survival to term of vitrified and warmed porcine expanded blastocysts transferred non-surgically

This study was performed to evaluate reproductive performance after non‐surgical embryo transfer (Ns‐ET) of 10–15 porcine expanded blastocysts (ExBs) that had been vitrified and warmed (V/W) using the micro volume air cooling (MVAC) method. The effect of asynchrony between the donor and recipient estrous cycle was investigated. Ns‐ET was conducted in recipients whose estrous cycle was asynchronous to that of donors by a delay of 2, 1, or 0 days. In the 2‐day and 1‐day groups, the similar farrowing rates (27.3% and 25.0%) and survival rates to term (13.9% and 15.7%) were obtained after Ns‐ET of V/W ExBs. None of the recipients in 0‐day group farrowed. Artificial insemination (AI) prior to Ns‐ET was then evaluated. Ten–15 V/W ExBs were transferred non‐surgically to 12 recipients whose estrous cycles were asynchronous to that of donors by a 2‐day delay. All of the recipients produced piglets, and all (100.0%) delivered piglets were derived from the transferred V/W ExBs. The survival rate of V/W ExBs to term was 25.2%. These results demonstrate that Ns‐ET of V/W ExBs using MVAC can facilitate piglet production, even if 10–15 embryos are transferred. Moreover, piglets were obtained stably when AI was performed prior to Ns‐ET.

Phospholipid composition and resistance to vitrification of in vivo blastocyst of a Brazilian naturalized porcine breed

ABSTRACT Piau porcine blastocysts were submitted to MALDI-TOF to identify the main phospholipids (PL). After that, in vivo blastocysts (D6) were vitrified (n=52), non-vitrified were used as control (n=42). After warming, blastocysts were in vitro cultured to assess re-expansion and hatching at 24 and 48 hours. Finally, at 48 hours, hatched blastocysts were submitted to RT-qPCR searching for BCL2A1, BAK, BAX and CASP3 genes. For MALDI-TOF, the ion intensity was expressed in arbitrary units. Blastocyst development was compared by Qui-square (P< 0.05). Among the most representative PL was the phosphatidylcholine [PC (32:0) + H]+; [PC (34:1) + H]+ and [PC (36:4) + H]+. Beyond the PL, MALDI revealed some triglycerides (TG), including PPL (50:2) + Na+, PPO (50:1) + Na+, PLO (52:3) + Na+ and POO (52:2) + Na. Re-expansion did not differ (P> 0.05) between fresh or vitrified blastocysts at 24 (33.3%; 32.7%) or 48 hours (2.4%; 13.5%). Hatching rates were higher (P< 0.05) for fresh compared to vitrified at 24 (66.7%; 15.4%) and 48 hours (97.6%; 36.0%). BAX was overexpressed (P< 0.05) after vitrification. In conclusion, Piau blastocysts can be cryopreserved by Cryotop. This study also demonstrated that the apoptotic pathway may be responsible for the low efficiency of porcine embryo cryopreservation.

Expression of the T85A mutant of zebrafish aquaporin 3b improves post-thaw survival of cryopreserved early mammalian embryos

While vitrification has become the method of choice for preservation of human oocytes and embryos, cryopreservation of complex tissues and of large yolk-containing cells, remains largely unsuccessful. One critical step in such instances is appropriate permeation while avoiding potentially toxic concentrations of cryoprotectants. Permeation of water and small non-charged solutes, such as those used as cryoprotectants, occurs largely through membrane channel proteins termed aquaporins (AQPs). Substitution of a Thr by an Ala residue in the pore-forming motif of the zebrafish (Dario rerio) Aqp3b paralog resulted in a mutant (DrAqp3b-T85A) that when expressed in Xenopus or porcine oocytes increased their permeability to ethylene glycol at pH 7.5 and 8.5. The main objective of this study was to test whether ectopic expression of DrAqp3b-T85A also conferred higher resistance to cryoinjury. For this, DrAqp3b-T85A + eGFP (reporter) cRNA, or eGFP cRNA alone, was microinjected into in vivo fertilized 1-cell mouse zygotes. Following culture to the 2-cell stage, appropriate membrane expression of DrAqp3b-T85A was confirmed by immunofluorescence microscopy using a primary specific antibody directed against the C-terminus of DrAqp3b. Microinjected 2-cell embryos were then cryopreserved using a fast-freezing rate and low concentration (1.5 M) of ethylene glycol in order to highlight any benefits from DrAqp3b-T85A expression. Notably, post-thaw survival rates were higher (P<0.05) for T85A–eGFP-injected than for -uninjected or eGFP-injected embryos (73±7.3 vs. 28±7.3 or 14±6.7, respectively). We propose that ectopic expression of mutant AQPs may provide an avenue to improve cryopreservation results of large cells and tissues in which current vitrification protocols yield low survival.