Cryopreservation affects the quality of in vitro produced bovine embryos at the molecular level.

There are still immense differences in the quality of in vitro produced embryos compared to their in vivo generated counterparts. These differences include a higher sensitivity of in vitro produced embryos towards cryopreservation. The quality of such embryos has been evaluated by morphological examination as well as the assessment of total cell numbers, pregnancy rates and in few cases through the analysis of their gene expression. The aim of the present study was to determine whether different cryopreservation methods have an influence on the quality of in vitro produced embryos after thawing. Bovine blastocysts were produced in a standard culture system (SOFaa). Having reached the stage of an expanding blastocyst on day 7, embryos were randomly either vitrified (n = 106) or cryopreserved conventionally (n = 131). Reexpansion (24h post thawing; 86/106 [81.1 ± 20.3%] of the vitrified embryos, 104/131 [79.4 ± 16.5%] of the conventionally cryopreserved embryos respectively) and hatching rates (48 h post thawing; 67/106 [63.2 ± 24.5%] of the vitrified embryos, 80/131 [61.1 ± 29.3%] of the conventionally cryopreserved embryos respectively) were similar. No significant differences in total cell numbers as well as live-dead cell ratio could be seen in hatched blastocysts of either cryopreservation group as well as in a control group (embryos cultured up to the stage of a hatched blastocyst and not cryopreserved by either method). Additionally, RT-qPCR was used to assess the relative abundance of eight developmentally important genes (HSPA1A, SLC2A1, SLC2A3, DSC2, CDH1, TJP1, DNMT3A, IFNT2) in hatched embryos of all groups. The results revealed significant differences in 4 of 8 (HSPA1A, SLC2A1, TJP1, DSC2) gene transcripts when comparing vitrified embryos to embryos of the control group and in 6 of 8 gene transcripts (HSPA1A, SLC2A1, TJP1, SLC2A3, DNMT3A, IFNT2) when comparing slow frozen embryos to embryos of the control group. Furthermore, the comparison of vitrified embryos to those frozen conventionally solely showed significant differences in the relative abundance of IFNT2. These results indicate that although not visible in gross morphology, but in the relative amount of gene transcripts, vitrification may be the more suitable method to cryopreserve in vitro produced bovine embryos cultured in SOF media.

Stinshoff H ，Wilkening S ，Hanstedt A ，Brüning K ，Wrenzycki C ... -  《-》

Higher survival rate of vitrified and thawed in vitro produced bovine blastocysts following culture in defined medium supplemented with beta-mercaptoethanol.

The present study was conducted to compare bovine embryo developmental quality, after culture in different defined culture media, up to blastocyst stage, and subsequently cultured in media supplemented with beta-mercaptoethanol (beta-ME) following blastocyst vitrification and thawing. In part one of this study, presumptive zygotes were randomly allocated into the following media: (1) CR1, (2) KSOM, (3) SOF, and (4) sequential KSOM-SOF. In the second part of the study, blastocysts derived from four different culture media were subjected to a solid surface vitrification (35% (v/v) ethylene glycol+0.5M Sucrose+5% (w/v) Polyvinylpyrrolidone (PVP), and tested for the effect of beta-ME on their post-vitrification survival. Following thawing, blastocysts were cultured with or without beta-ME. Culture medium had no effect on cleavage rates; however, a significantly greater number of zygotes cultured in KSOM, KSOM-SOF, or SOF developed to the 8-cell stage, compared with those cultured in CR1. A greater proportion of the zygotes cultured in SOF or KSOM-SOF reached blastocysts, than did those cultured in CR1 or KSOM. The use of sequential KSOM-SOF significantly increased total cell numbers of Day 7 expanded-blastocysts when compared to those cultured in CR1, KSOM, or SOF. Addition of beta-ME into culture media after vitrification and thawing improved blastocyst survival, hatching rates, and total cell numbers of blastocysts. In conclusion, supplementation of beta-ME into culture medium after vitrification and thawing significantly increased blastocyst survival, hatching rates, and their total cell numbers. These results suggest that vitrified IVF embryos should be thawed and briefly cultured in beta-ME medium prior to embryo transfer.

Nedambale TL ，Du F ，Yang X ，Tian XC ... -  《ANIMAL REPRODUCTION SCIENCE》

Comparison on in vitro fertilized bovine embryos cultured in KSOM or SOF and cryopreserved by slow freezing or vitrification.

The objectives of this study were to identify an improved in vitro cell-free embryo culture system and to compare post-warming development of in vitro produced (IVP) bovine embryos following vitrification versus slow freezing. In Experiment 1, non-selected presumptive zygotes were randomly allocated to four medium treatments without co-culture: (1) SOF + 5% FCS for 9 days; (2) KSOM + 0.1% BSA for 4 days and then KSOM + 1% BSA to Day 9; (3) SOF + 5% FCS for 4 days and then KSOM + 1% BSA to Day 9; and (4) KSOM + 0.1% BSA for 4 days and then SOF + 5% FCS to Day 9. Treatment 4 (sequential KSOM-SOF culture system) improved (P > 0.05) morulae (47%), early blastocysts (26%), Day-7 blastocysts (36%), cell numbers, as well as total hatching rate (79%) compared to KSOM alone (Treatment 2). Embryos cultured in KSOM + BSA alone developed slowly and most of them hatched late on Day 9, compared to other treatments. In Experiment 2, the sequential KSOM-SOF culture system was used and Day-7 blastocysts were subjected to following cryopreservation comparison: (1) vitrification (VS3a, 6.5 M glycerol); or (2) slow freezing (1.36 M glycerol). Warmed embryos were cultured in SOF with 7.5% FCS. Higher embryo development and hatching rates (P < 0.05) were obtained by vitrification at 6h (71%), 24h (64%), and 48h (60%) post-warming compared to slow freezing (48, 40, and 31%, respectively). Following transfer of vitrified embryos to synchronized recipients, a 30% pregnancy rate was obtained. In conclusion, replacing KSOM with SOF after 4 days of culture produced better quality blastocysts. Vitrification using VS3a may be used more effectively to cryopreserve in vitro produced embryos than the conventional slow freezing method.

Nedambale TL ，Dinnyés A ，Groen W ，Dobrinsky JR ，Tian XC ，Yang X ... -  《THERIOGENOLOGY》

Osmotic challenge and expression of aquaporin 3 and Na/K ATPase genes in bovine embryos produced in vitro.

The aim of this study was to evaluate the effect of culture media and stage of development in the osmotic ability of in vitro-fertilized bovine embryos and the expression of aquaporin 3 (Aqp3) and Na/K ATPase isoform 1 (ATPAse1) genes in embryos (i) with different ability to undergo rehydration and (ii) following vitrification. In experiment 1, in vitro fertilized presumptive zygotes were co-cultured in SOFaac or modified CR2aa medium and embryos at blastocyst and expanded blastocyst stages at day 7 post-insemination were exposed to NaCl hypertonic medium (900 mOsm) for 5 min following 120 min of culture in isotonic medium in order to evaluate dehydration and rehydration, respectively. No difference (P>0.05) on blastocyst rate was found between CR2aa and SOFaac medium but embryos co-cultured in SOFaac medium underwent greater (P<0.05) dehydration. Embryos at expanded blastocyst stage underwent greater dehydration but slower rehydration than embryos at blastocysts stage (P<0.05). In the experiment 2, the amount of Aqp3 and ATPase1 transcripts were quantified in blastocysts with high or low rehydration after exposure to hypertonic medium. No difference (P>0.05) on relative amount of transcripts was found in either genes. In the experiment 3, expanded blastocysts produced in a co-culture system were vitrified, warmed and then cultured for 72 h for analysis of embryo survival and amount of Aqp3 and ATPase1 transcripts. Lower (P<0.05) embryo survival rate was found for vitrified-warmed embryos (57.9%) than for their fresh counterparts (84.6%). There was no difference on expression of ATPase1 gene but lower (P<0.01) amount of Aqp3 transcripts was found in the vitrified-warmed embryos. In conclusion, embryo ability to undergo shrinkage and swelling is influenced by medium used in a co-culture system and by embryo stage. Rehydrating ability of embryos after exposure to NaCl hypertonic medium is not associated with variations on expression of Aqp3 and ATPase1 genes, but the vitrification can alter gene expression of in vitro-fertilized bovine embryos produced in a co-culture system.

Camargo LS ，Boite MC ，Wohlres-Viana S ，Mota GB ，Serapiao RV ，Sa WF ，Viana JH ，Nogueira LA ... -  《-》

Serum free embryo culture medium improves in vitro survival of bovine blastocysts to vitrification.

The aim of this study was to examine the effects of co-culture with Vero cells during the in vitro maturation (IVM) and three culture media, B2+5% fetal calf serum (FCS) on Vero cells, synthetic oviduct fluid (SOF)+5% FCS, and SOF+20 gL(-1) bovine serum albumin (BSA), on the developmental competence of the embryos and their ability to survive vitrification/warming. We also tested the effect of morphological quality and the age of the embryo on its sensitivity to vitrification. The IVM system neither affects the embryo development up to Day 7 nor survival rates after vitrification. The culture of embryos in SOF+FCS and in Vero cells+B2 allowed obtaining more Day 6 and Day 7 blastocysts, and a higher % of Day 7 blastocysts vitrified than culture in SOF+BSA. Contrarily, on Day 8, more blastocysts were vitrified in SOF+BSA than in SOF+FCS. Blastocysts quality affected development after vitrification/warming, and Day 7 embryos showed higher survival rates than their Day 8 counterparts. Day 7 blastocysts produced in Vero cells or in SOF+BSA survived at higher rates than those produced in SOF+FCS at 24 and 48 h after warming. Embryo culture with BSA allows obtaining hatching rates after vitrification/warming higher than those obtained after co-culture with Vero cells in B2 and FCS. Moreover, this system provides hatching rates from Day 8 blastocysts comparable to those obtained on Day 7 in Vero cells. Further studies, including embryo transfer to recipients, are needed to clarify factors affecting the freezability of in vitro produced bovine embryos.

Gómez E ，Rodríguez A ，Muñoz M ，Caamaño JN ，Hidalgo CO ，Morán E ，Facal N ，Díez C ... -  《THERIOGENOLOGY》