Survival of rabbit embryos after culture or culture/freezing

Five-hundred-and-ninety-five rabbit embryos at the 2- to 4-cell stage were cultured for 48 h to the morula stage. One-hundred-and-sixty-three embryos were transferred directly after culture while the rest (432) were frozen to −196°C. The development of these embryos was tested by transfer into synchronized pseudopregnant recipients or into pseudopregnant recipients 24 h before synchrony. The results were determined at day 17 of pregnancy. The transfer of cultured embryos into synchronized recipients gave a higher survival rate than transfer into asynchronized recipients (51 vs. 15%; P<0.05). The freezing of cultured embryos affected in vitro and in vivo development. Only 56% of the frozen-thawed morulae developed to the blastocyst stage compared with 89% in the control group (P<0.005). The survival rate after synchronous transfer was only 14%. Our results indicate that rabbit embryos need asynchronous conditions when they are frozen and cultured. Embryo survival rate was enhanced by 38% (P<0.07) when these cultured frozen-thawed embryos were transferred into pseudopregnant recipients in an earlier physiological stage (−24 h).     

Blastocyst formation by pig embryos resulting from in-vitro fertilization of oocytes matured in vitro

Follicular oocytes collected from prepubertal gilts at a local slaughter house were matured (36 h), fertilized and developed in vitro. Of 785 embryos, 190 (24%) embryos cleaved to the 2-4 cell stages with blastomeres of regular size by 33 h after insemination. These cleaved embryos were surgically transferred into the oviducts of 4 synchronized recipient gilts and recovered from the uterine horns 4 or 7 days later: 13 morulae, 2 blastocysts and 1 expanded blastocyst were recovered after 4 days and 3 hatched blastocysts were recovered 7 days after transfer. Re-culture in vitro sustained further development of morulae recovered 4 days after transfer: 11 of 13 morulae had developed to the blastocyst/hatched blastocyst stages. Overall, 17 of 190 (9%) embryos developed to the blastocyst stage. The results indicate that pig oocytes can be matured and fertilized in vitro, and subsequently develop to the blastocyst stage.     

Developmental ability of bovine embryos after nuclear transfer based on the nuclear source: in vivo versus in vitro

Bovine nuclear transfer embryos reconsitituted from in vitro-matured recipient oocyte cytoplasm and different sources of donor nuclei (in vivo, in vitro-produced or frozen-thawed) were evaluated for their ability to develop in vitro. Their cleavage rate and blastocyst formation are compared with those of control IVF embryos derived from the same batches of in vitro-matured oocytes that were used for nuclear transfer and were co-cultured under the same conditions on bovine oviducal epithelial cell monolayers for 7 d. Using fresh donor morulae as the source of nuclei resulted in 30.2% blastocyst formation (150 497 ), which was similar to that of control IVM-IVF embryos (33.8% blastocysts, 222 657 ). When IVF embryos were used as the source of nuclei for cloning, a slightly lower blastocyst formation rate (22.6%, 41 181 ) was obtained but not significantly different from that using fresh donor morulae. Nuclear transfer embryos derived from vitrified donor embryos showed poor development in vitro (7.1%, 11 154 ). No difference in morphology or cell number was observed after 7 d of co-culture between blastocysts derived from nuclear transfer or control IVF embryos. The viability of 34 in vitro-developed nuclear transfer blastocysts was tested in vivo and resulted in the birth of 11 live calves (32.3%).     

Nuclear transfer in cattle using in vivo-derived vs. in vitro-produced donor embryos: Effect of developmental stage

To determine the best developmental stage of donor embryos for yielding the highest number of clones per embryo, we compared the efficiencies of nuclear transfer when using blastomeres from morulae or morulae at cavitation, or when using inner-cell-mass cells of blastocysts as nuclear donors. This comparison was done both on in vivo-derived and in vitro-produced donor embryos. In experiment 1, with in vivo-derived donor embryos, nuclei from morulae at cavitation supported the development of nuclear transfer embryos to the blastocyst stage (36%) at a rate similar to that of nuclei from morulae (27%), blastomeres from morulae at cavitation being superior (P < 0.05) to inner-cell-mass cells from blastocysts (21%). The number of blastocysts per donor embryo was significantly (P < 0.05) higher when using nuclei from morulae at cavitation (15.7 ± 4.1) rather than nuclei from morulae (9.8 ± 5.5) or blastocysts (6.3 ± 3.3). With in vitro-produced donor embryos (experiment 2), nuclei from morulae yielded slightly more blastocysts (32%) than nuclei from morulae at cavitation (29%), both stages being superior to nuclei from blastocysts (15% development to the blastocyst stage). Morulae at cavitation yielded a higher number of cloned blastocysts per donor embryo (11.5 ± 5.9) than did morulae (9.3 ± 3.2) and blastocysts (3.3 ± 1.4). Transfer of cloned embryos originating from in vivo-derived morulae, morulae at cavitation, and blastocysts resulted in four pregnancies (10%), three pregnancies (7%), and one (17%) pregnancy on day 45. The corresponding numbers of calves born were 3 (4%), 3 (7%), and 0, respectively. After transfer of blastocysts derived from in vitro nuclear donor morulae (n = 16) and morulae at cavitation (n = 7), two (20%) and two (50%) recipients, respectively, were pregnant on day 45. However, transfer of seven cloned embryos from in vitro donor blastocysts to three recipients did not result in a pregnancy. Using in vitro-produced donor embryos, calves were only obtained from morula-stage donors (13%). Our results indicate that the developmental stage of donor embryos affects the efficiency of nuclear transfer, with morulae at cavitation yielding a high number of cloned blastocysts. © 1996 Wiley-Liss, Inc.     

Survival of frozen-thawed sheep embryos cryopreserved at cleavage stages

This study evaluated the effect of freezing-thawing procedures on the viability of sheep embryos cryopreserved at various developmental stages. The survival rates of frozen-thawed embryos were compared with non-frozen counterparts. Embryos were recovered from the oviduct and uterus, at different days of the early luteal phase, and were classified at six different developmental stages: 2- to 4-cell (n = 72), 5- to 8-cell (n = 73), 9- to 12-cell (n = 70), early morulae (n = 42), morulae (n = 41), and blastocyst (n = 70). For each early cleavage stage and blastocysts, approximately half of the embryos, were frozen immediately by slow freezing with an ethylene glycol-based solution. The remaining embryos were cultured to the hatched blastocyst stage. All morulae and compact morulae were frozen after recovery with the same protocol. Cryoprotectants were removed using 1M sucrose solution, and then warmed the embryos were cultured to the hatched stage in a standardized in vitro culture. Embryo developmental stage had a significant effect on the ability to hatch following freezing (P<0.0001). The cryotolerance of the embryos fitted a regression (r2 = 0.908), increasing linearly from 2- to 4-cell embryos (17.1%) to morula stage (46.3%) and in a quadratic regression from the morula to the blastocyst stage (83.7%). Frozen early cleavage stage embryos had a significantly lower viability than their fresh counterparts (23.1 vs 83.1%; P<0.0001), with a similar rate of viability between fresh or frozen blastocysts (92.5 vs 83.7%). In conclusion, early sheep embryos are very sensitive to freezing per se and the survival rates following conventional freezing improve as embryo developmental stage progresses.     

Hypotaurine requirement for in vitro development of golden hamster one-cell embryos into morulae and blastocysts, and production of term offspring from in vitro-fertilized ova.

Almost 30 years after the first successful in vitro fertilization (IVF) in golden hamsters (Mesocricetus auratus), we report that IVF hamster embryos can develop in a chemically defined, protein-free culture medium into morulae and blastocysts, and produce normal offspring after transfer to recipients. When examined 96 h post-insemination, 82% (160/200) of IVF ova had cleaved to at least 2 cells, 55% (97/200) had developed beyond the 4-cell stage, and 22% (38/200) had developed into morulae/blastocysts. In vitro development of IVF embryos to greater than or equal to 8 cells was absolutely dependent on hypotaurine. Twenty living offspring were produced from transfer of IVF embryos to recipients, with an overall success rate of 5% and 17% for oviductal (2-cell) and uterine (8-cell/morulae) transfers, respectively. In vivo-fertilized pronucleate embryos collected 3 h after egg activation were less able to develop in vitro than embryos collected only 6 h later, revealing a critical influence of the oviduct within the first hours of embryo development. Hypotaurine partly compensated for the decreased oviductal exposure of early 1-cell embryos. Establishment of a key role for hypotaurine in hamster embryo development, support of IVF embryos to morula/blastocyst stages in vitro, and production of living offspring after IVF embryo transfer are significant steps towards the goal of obtaining comparative data on preimplantation embryogenesis.     

Interspecies nuclear transfer of Tibetan antelope using caprine oocyte as recipient

Interspecies nuclear transfer is an invalulable tool for studying nucleus-cytoplasm interactions; and at the same time, it provides a possible alternative to clone endangered animals whose oocytes are difficult to obtain. In the present study, we investigated the possibility of cloning Tibetan antelope embryos using abattoir-derived caprine oocytes as recipients. Effects of culture conditions, enucleation timing, and donor cell passages on the in vitro development of Tibetan antelope-goat cloned embryos were studied. Maternal to zygotic transition timing of interspecies Tibetan antelope embryos was also investigated using two types of cloned embryos, Tibetan antelope-rabbit and Tibetan antelope-goat embryos. Our results indicate that: (1) goat oocyte is able to reprogram somatic cells of different genus and supports development to blastocyst in vitro. (2) Coculture system supported the development of Tibetan antelope-goat embryos to blastocyst rate stage (4.0%), while CR1aa alone did not. (3) When MII phase enucleated caprine cytoplast and TII phase enucleated caprine cytoplast were used as recipients, the fusion rate and blastocyst rate of hybrid embryos were not statistically different (73.9% vs. 67.4%; 4.0% vs. 1.1%). (4) When donor cells at 3-8 passages were used, 2.9% hybrid embryos developed to blastocysts, while none developed to blastocysts when cells at 10-17 passages were used. (5) There may be a morula-to-blastocyst block for Tibetan antelope-goat, while there may be an 8- to 16-cell block for Tibetan antelope-rabbit embryos.     

Effects of transferring in vitro-cultured rabbit embryos to recipient oviducts on mucin coat deposition, implantation and development

A mucin coat is deposited on rabbit embryos during passage through the oviduct; rabbit blastocysts cultured from the 1-cell stage in vitro have no mucin coat. When cultured blastocysts are transferred to recipients, the lack of mucin coat might account in part for subsequent failure of pregnancy. We have investigated the possibility that mucin coat deposition is induced following transfer of in vitro 72 h-cultured blastocysts to oviducts of asynchronous or synchronous recipients. One-cell embryos were collected by flushing oviducts 19-20 h post-coitus and were cultured in vitro for 72 h until they reached the blastocyst stage. The blastocysts were transferred to the oviducts of recipients that were synchronized either with the donors (synchronous) or 1 day later than the donors (asynchronous). They were recovered after 24-48 h and the mucin coat thickness and embryo degeneration rate were measured. The degeneration rate of blastocysts recovered from uteri of synchronous recipients was higher than that from asynchronous recipients (72.2% vs 40.0%). The mucin coats around embryos recovered from oviducts of asynchronous recipients after 48 h were thicker than those from synchronous recipients. More asynchronous recipients were pregnant and gave birth to more pups than synchronous recipients. These results indicate that the oviducts of asynchronous recipients secreted more mucin around the transferred embryos, causing higher rates of implantation of the in vitro-cultured blastocysts.     

The survival of whole and bisected rabbit morulae after cryopreservation by the vitrification method

The survival of whole and bisected rabbit morulae cryopreserved by the vitrification method was investigated. The embryos were loaded in a column of vitrification solution (VS, a mixture of 25% glycerol and 25% 1, 2-propanediol in PBS+16% calf serum), which was located between two columns of 1 M sucrose solution in a plastic straw. The embryos were frozen by being plunged into liquid nitrogen and thawed in a water bath at 20 degrees C. Two methods of loading embryos into straws were used: the single and double column vitrification solution methods. The embryonic survival rates between these two methods were compared. Seventy-one (86.6%) out of 82 morulae vitrified in double column straws developed into the blastocyst stage in vitro. Eleven (18.3%) live fetuses were obtained after the transfer of 60 frozen-thawed morulae to four recipients. By contrast, the survival rate (36.5%, 27 74 ) of embryos vitrified in the single column straws was significantly lower (P<0.05). The vitrification solution of the single column straws became opaque, indicating ice-crystal formation, upon thawing in 5 of 11 straws, which was assumed to have damaged the embryos. More than 80% (29 36 ) of the bisected morulae frozen and thawed in the double column straws developed to the blastocyst stage in vitro when cryoprotectant was diluted stepwise with 1 M and 0.25 M sucrose solution. When the cryoprotectant was removed by one-step dilution with 1 M sucrose solution, swelling in blastomeres was observed and the development rate of the recovered embryos decreased (45.8%, 11 24 ). These results indicate that the vitrification method employed in our experiment is not only efficient for the cryopreservation of rabbit morulae, but it can also be used for the preservation of bisected rabbit morulae, which had not been successful using previous methods.     

In vitro development to blastocysts of early porcine embryos produced in vivo or in vitro

The objective of this study was to compare the development of porcine embryos from the 2- and 4-cell stages to the blastocyst stage after in vivo or in vitro fertilization and in vivo or in vitro culture. Early-stage embryos were collected either from superovulated gilts 36 h after the second mating or after in vitro fertilization (IVF) of in vivo-matured oocytes, both followed by in vitro culture to the blastocyst stage. Blastocysts collected from superovulated donors served as controls. In the first experiment, a total of 821 2- and 4-cell embryos derived from in vivo-fertilized oocytes was cultured either in medium NCSU 23, modified Whittens' medium or modified KRB for 5 d. Significantly (P < 0.05 and P < 0.001) more embryos overcame the 4-cell block and developed to the blastocyst stage in medium NCSU 23 than in the 2 other culture media. Hatching was only observed in medium NCSU 23. In the second experiment, embryos derived from in vivo-matured oocytes fertilized in vitro were cultured in medium NCSU 23. Of 1869 mature oocytes 781 (41.8%) cleaved within 48 h after in vitro fertilization. A total of 715 embryos was cultured to the morula and blastocyst stages, and 410 (57.3%) overcame the developmental block stage, with 358 embryos (50.1%) developing to the morula and blastocyst stages. None of the embryos hatched, and the number of nuclei was significantly (P < 0.05) lower compared with that of in vivo-fertilized embryos (18.9 +/- 9.8 vs 31.2 +/- 5.8). In the third experiment, 156 blastocysts derived from in vitro fertilization and 276 blastocysts derived from in vivo fertilization and in vitro culture were transferred into synchronized recipients, while 164 blastocysts were transferred immediately after collection into 6 recipients, resulting in a pregnancy rate of 83.3%, with 35 piglets (on average 7.0) born. From the in vitro-cultured embryos, 58.3% (7/12) of the recipients remained pregnant at Day 35 after transfer, but only 33.3% maintained pregnancy to term, and 14 piglets (on average 3.5) were born. In contrast, the transfer of embryos derived from in vitro-fertilized oocytes did not result in pregnancies. It is concluded that 1) NCSU 23 is superior to modified Whittens' medium and modified KRB and 2) blastocysts derived from in vitro fertilization have reduced viability as indicated by the lower number of nuclei and failure to induce pregnancy upon transfer into recipients.     

Effect of leukemia inhibitory factor on bovine embryos produced in vitro under chemically defined conditions

The objective of these experiments was to assess putative embryotrophic effects of leukemia inhibitory factor (LIF) on bovine preimplantation development in chemically defined media. Recombinant human LIF was added to embryo culture media at a concentration of 100 ng/ml. When added for culture of morulae LIF had no positive effect on the proportion of embryos reaching the blastocyst stage. However, LIF significantly reduced development to the blastocyst stage when added for culture of 4-cell stage embryos (P<0.05). In contrast, a positive effect was found for progression of blastocyst development. In vitro blastocyst hatching rates were significantly improved in the presence of LIF (P<0.02). Number of total cells and of inner cell mass (ICM) cells were increased in LIF-treated blastocysts. In vitro survival of frozen-thawed blastocysts was not improved by adding LIF to morula stage embryos before cryopreservation. The pregnancy rate after direct transfer of cryopreserved LIF-treated embryos was not different from that for untreated control embryos. Data indicate that addition of LIF has no major beneficial effect on bovine embryos produced in these chemically defined conditions.     

Isolation and characterization of embryonic stem-like cells from canine blastocysts

Embryonic stem (ES) cells are pluripotent cells with the capacity to generate any type of cell. Here we describe the isolation of ES-like cells from canine blastocysts. Canine embryos were collected from beagle bitches at day 11-16 of first estrus. A total of 80 normal embryos were obtained from 15 dogs. Of the embryos, 13 were at the morulae stage, 39 at the blastocyst stage, and 28 at the hatched blastocyst stage. The inside of morulae or inner cell masses (ICMs) of blastocysts were isolated mechanically, and cultured onto mouse embryonic fibroblasts (MEF) as feeder layers. Primary cell colonies were formed in 0% (0/13) of morulae, 25.6% (10/39) of blastocysts, and 67.9% (19/28) of hatched blastocysts. These colonies were separated either by enzymatic dissociation or by mechanical disaggregation. Dissociation with collagenase resulted in immediate differentiation, but with mechanical disaggregation these cells remained undifferentiated, and two ES-like cell lines (cES1, cES2) continued to grow in culture after eight passages. These cells had typical stem cell-like morphology and expressed specific markers such as alkaline phosphatase activity, stage specific embryonic antigen-1 and Oct-4. These cells formed embryoid bodies (EBs) in a suspension culture; extended culture of EBs resulted in the formation of cystic EBs. When the simple EBs were cultured on tissue culture plates, they differentiated into several types of cells including neuron-like, epithelium-like, fibroblast-like, melanocyte-like, and myocardium-like cells. These observations indicate that we successfully isolated and characterized canine ES-like cells.     

Viable Transgenic Goats Derived from Skin Cells

The current study was undertaken to evaluate the possibility of expanding transgenic goat herds by means of somatic cell nuclear transfer (NT) using transgenic goat cells as nucleus donors. Skin cells from adult, transgenic goats were first synchronized at quiescent stage (G0) by serum starvation and then induced to exit G0 and proceed into G1. Oocytes collected from superovulated donors were enucleated, karyoplast-cytoplast couplets were constructed, and then fused and activated simultaneously by a single electrical pulse. Fused couplets were either co-cultured with oviductal cells in TCM-199 medium (in vitro culture) or transferred to intermediate recipient goat oviducts (in vivo culture) until final transfer. The resulting morulae and blastocysts were transferred to the final recipients. Pregnancies were confirmed by ultrasonography 25-30 days after embryo transfer. In vitro cultured NT embryos developed to morulae and blastocyst stages but did not produce any pregnancies while 30% (6/20) of the in vivo derived morulae and blastocysts produced pregnancies. Two of these pregnancies were resorbed early in gestation. Of the four recipients that maintained pregnancies to term, two delivered dead fetuses 2-3 days after their due dates, and two recipients gave birth to healthy kids at term. Fluorescence in situ hybridization (FISH) analysis confirmed that both kids were transgenic and had integration sites consistent with those observed in the adult cell line.     

Vitrification of Mouse Embryos at Various Stages by Open-Pulled Straw (OPS) Method

This study was performed to pursue the optimal condition for the cryopreservation of mouse morulae by a two-step OPS method and to investigate the feasibility of the optimal condition for vitrification of embryos at other developmental stages. First, the mouse morulae were vitrified in OPS using one-step procedure—that is, embryos were vitrified after direct exposure to EDFS30 (15% ethylene glycol (EG), 15% dimethyl sulfoxide (DMSO), Ficoll and sucrose), or two-step method—that is, embryos were first pretreated in 10%E+10%D (10% EG and 10% DMSO in mPBS) for 30 sec, then exposed to EDFS30 for 15 to 60 sec, respectively. After vitrification and warming, the embryos were morphologically evaluated and assessed by their development to blastocysts, expanded/hatched blastocysts, or to term after transfer. The result showed that all the vitrified-warmed morulae had similar blastocyst rate compared to that of control (91.7% vs. 100%), and the highest developmental rate to expanded blastocysts (100%) or hatched blastocysts (62.3%) was observed when the morulae were pretreated with 10%E+10%D for 0.5 min, exposed to EDFS30 for 25 sec before vitrification and warming in 0.5 M sucrose for 5 min. After transfer, the survival rate (33.1%) in vivo of the vitrified morulae was higher (P > 0.05) than that of the fresh embryos (24.6%). Secondly, embryos at different stages were cryopreserved and thawed following the above program. Most (93.4 to 100%) of the embryos recovered after vitrification were morphologically normal at all the developmental stages. The blastocyst rates of the vitrified one-cell (52.5 to 66.7%) and the two-cell (63.3 to 68.9%) embryos were lower (P < 0.05) than those of the vitrified four-cell embryos (81.7 to 86.4%), the eight-cell embryos (90.0 to 93.3%), morulae (96.7 to 100%), and the expanded blastocysts rate (98.3 to 100.0%) of the vitrified early blastocysts. The highest survival rate in vivo of vitrified embryos were from the early blastocysts (40.4%), which was similar to that of fresh embryos (48.6%). The data demonstrate that the optimal protocol for the cryopreservation of morulae was suitable for the four-cell embryos to early blastocyst stages and that the early blastocyst stage is the most feasible stage for mouse embryo cryopreservation under our experimental conditions.     

Vitrification of mouse embryos at various stages by open-pulled straw (OPS) method

This study was performed to pursue the optimal condition for the cryopreservation of mouse morulae by a two-step OPS method and to investigate the feasibility of the optimal condition for vitrification of embryos at other developmental stages. First, the mouse morulae were vitrified in OPS using one-step procedure-that is, embryos were vitrified after direct exposure to EDFS30 (15% ethylene glycol (EG), 15% dimethyl sulfoxide (DMSO), Ficoll and sucrose), or two-step method-that is, embryos were first pretreated in 10%E + 10%D (10% EG and 10% DMSO in mPBS) for 30 sec, then exposed to EDFS30 for 15 to 60 sec, respectively. After vitrification and warming, the embryos were morphologically evaluated and assessed by their development to blastocysts, expanded/hatched blastocysts, or to term after transfer. The result showed that all the vitrified-warmed morulae had similar blastocyst rate compared to that of control (91.7% vs. 100%), and the highest developmental rate to expanded blastocysts (100%) or hatched blastocysts (62.3%) was observed when the morulae were pretreated with 10%E + 10%D for 0.5 min, exposed to EDFS30for 25 sec before vitrification and warming in 0.5 M sucrose for 5 min. After transfer, the survival rate (33.1%) in vivo of the vitrified morulae was higher (P > 0.05) than that of the fresh embryos (24.6%). Secondly, embryos at different stages were cryopreserved and thawed following the above program. Most (93.4 to 100%) of the embryos recovered after vitrification were morphologically normal at all the developmental stages. The blastocyst rates of the vitrified one-cell (52.5 to 66.7%) and the two-cell (63.3 to 68.9%) embryos were lower (P < 0.05) than those of the vitrified four-cell embryos (81.7 to 86.4%), the eight-cell embryos (90.0 to 93.3%), morulae (96.7 to 100%), and the expanded blastocysts rate (98.3 to 100.0%) of the vitrified early blastocysts. The highest survival rate in vivo of vitrified embryos were from the early blastocysts (40.4%), which was similar to that of fresh embryos (48.6%). The data demonstrate that the optimal protocol for the cryopreservation of morulae was suitable for the four-cell embryos to early blastocyst stages and that the early blastocyst stage is the most feasible stage for mouse embryo cryopreservation under our experimental conditions.     

Reduced survival in utero from transferred mouse blastocysts compared with morulae

Studies on the survival of mouse embryos revealed that fewer offspring were produced when blastocysts, rather than morulae, were transferred to foster mothers. Approximately 8–10 h after fertilization F1 hybrid eggs (C57BL/6J × LT/Sv) were collected and cultured to morulae (day 4) or blastocysts (day 5 ) before transfer into uteri of day 3 foster mothers. A few recipients were killed on day 8 of gestation and deciduae were examined histologically. Embryos developing from transferred morulae were found to lie deep within the deciduae and were surrounded by numerous, large blood islands. Conversely, embryos developing from transferred blastocysts implanted more distally to the maternal blood vessels with only a few blood islands surrounding the embryos. These observations, suggesting abnormal implantation with insufficient embyro nourishment, were confirmed when uteri of foster mothers were examined on day 19 of gestation. Although the proportion of implantations from transferred morulae or blastocysts was similar (42 % and 47%, respectively), significantly more of the implantations were resorbed after transfer of blastocysts (78%) as compared with morulae (15%). These results demonstrate that transfer of day 5 cultured blastocysts into uteri of foster mothers increases embryonic mortality as a consequence of improper implantation.     

Increasing glucose in KSOMaa basal medium on culture Day 2 improves in vitro development of cloned caprine blastocysts produced via intraspecies and interspecies somatic cell nuclear transfer

This study was conducted to evaluate the efficiency of potassium simplex optimization medium with amino acids (KSOMaa) as a basal culture medium for caprine intraspecies somatic cell nuclear transfer (SCNT) and caprine-bovine interspecies somatic cell nuclear transfer (iSCNT) embryos. The effect of increased glucose as an energy substrate for late stage development of cloned caprine embryos in vitro was also evaluated. Enucleated caprine and bovine in vitro matured oocytes at metaphase II were reconstructed with caprine ear skin fibroblast cells for the SCNT and iSCNT studies. The cloned caprine and parthenogenetic embryos were cultured in either KSOMaa with 0.2 mM glucose for 8 days (Treatment 1) or KSOMaa for 2 days followed by KSOMaa with additional glucose at a final concentration of 2.78 mM for the last 6 days (Treatment 2). There were no significant differences in the cleavage rates of SCNT (80.7%) and iSCNT (78.0%) embryos cultured in KSOMaa medium. Both Treatment 1 and Treatment 2 could support in vitro development of SCNT and iSCNT embryos to the blastocyst stage. However, the blastocyst development rate of SCNT embryos was significantly higher (P < 0.05) in Treatment 2 compared to Treatment 1. Increasing glucose for later stage embryo development (8-cell stage onwards) during in vitro culture (IVC) in Treatment 2 also improved both caprine SCNT and iSCNT embryo development to the hatched blastocyst stage. In conclusion, this study shows that cloned caprine embryos derived from SCNT and iSCNT could develop to the blastocyst stage in KSOMaa medium supplemented with additional glucose (2.78 mM, final concentration) and this medium also supported hatching of caprine cloned blastocysts.     

Cloning of bovine embryos by multiple nuclear transfer

The in vitro development of multiple generation bovine nuclear transferred embryos to blastocysts and their survival ability after freezing and thawing were examined. Parent donor embryos which had 20 to 50 cells were recovered from superovulated cows. Follicular oocytes matured in vitro were used as recipient oocytes. The recipient oocytes enucleated at 22 to 24 h after the onset of maturation were preactivated at 33 h. Enucleated oocytes with a donor blastomere were fused 9 h after activation by an electric stimulus and the fused oocytes were cultured in vitro (first generation). Reconstituted oocytes that had developed to the 8- to 16-cell stage 3 to 4 d after fusion were used as donor embryos for the next generation. Recloning procedures were performed twice (second and third generations). The proportion of recipient oocytes successfully fused with a blastomere increased with the cycle of nuclear transfer. Eighty to 86% of fused oocytes developed to the 2-cell stage and there was no significant difference with the generation. The proportion of reconstituted embryos receiving blastomeres derived from first generation embryos had higher developmental ability in vitro, than those derived from other generations (43 vs 31% for 8 to 16-cell stage, 37 vs 20 and 21% for blastocyst stage). The number of cloned blastocysts increased with repeated nuclear transfer (once: 6.2 +/- 4.3, twice: 19.8 +/- 9.2 and three times: 30.0 +/- 14.7) but varied greatly with each parent donor embryo. The in vitro viability of cloned blastocysts after freezing and thawing (59%) was low but not significantly different from that obtained for in vitro fertilized blastocysts (72%). After transfer of either fresh or frozen-thawed cloned blastocysts to 21 recipients, 10 of them were pregnant on Day 60. Four and 3 offspring were produced from 20 fresh and 14 frozen-thawed blastocysts,respectively.     

Effect of stage of development on survival of mouse embryos frozen-thawed rapidly

Embryos were recovered on Day 4 of pregnancy from superovulated random-bred OF₁ Swiss albino mice. They were classified into four categories based on their stage of development: expanding blastocyst, blastocyst, early blastocyst, and compacted morula. They were then cooled at 2 °C/min from ?7 to ?25 °C in a freezing medium containing 1.36 M glycerol and 0.25 M sucrose in phosphate-buffered saline (PBS). At ?25 °C, they were plunged into LN₂ and thawed a few hours later in water at 20 °C. After washing in PBS, recovered embryos were cultured for 20 to 24 hr and the number of embryos that had developed normally was recorded. The results showed a clear effect of the stage of development on survival. Survival of expanding blastocysts and blastocysts was very low (1.4 and 21.8%, respectively) compared to that of early blastocysts and compacted morulae (69.4 and 73.5%). The more differentiated stage of the blastocyst (two kinds of cells) and the presence of a blastocoelic cavity may explain the differences observed under our cooling conditions. As a further test of viability, 93 blastocysts that had developed in culture for 20 hr from 153 frozen-thawed early blastocysts and compacted morulae (60.8%) were transferred to 8 recipient mice. Seven became pregnant, yielding $\text{38}\text{82}$ normal live young (46.3%).