Apoptosis and in vitro development of preimplantation porcine embryos derived in vitro or by nuclear transfer

Apoptosis occurs during preimplantation development in both in vivo- and in vitro-produced embryos, and it may contribute to embryonic loss. The present study investigated the development of porcine nuclear transfer (NT) embryos reconstructed by using fetal fibroblasts as compared to embryos produced by in vitro fertilization (IVF). The onset and the frequency of apoptosis in NT and IVF embryos were examined via morphological and nuclear changes and TUNEL assay. The NT blastocysts had a similar number of nuclei as compared to IVF blastocysts and appeared to be morphologically similar. Relative to IVF embryos, the NT embryos had a lower cleavage rate (42.7% vs. 71.0%) and a lower developmental rate (11.1% vs. 28.6%) to the blastocyst stage. The earliest positive TUNEL signals were detected in the NT embryos on Day 5 of culture. The percentage of cells undergoing apoptosis in the NT embryos was higher than that of the IVF embryos and increased with time in vitro. Some of the abnormal morphological changes observed during early development related to apoptosis. Cytoplasmic fragmentation, developmental arrest, and nuclear condensation were typical characteristics of embryos undergoing apoptosis. Some mechanisms of the apoptotic pathway were triggered by changes in the NT embryos. The developmental rates of NT embryos might be improved by identifying specific apoptotic pathways and then intervening in these pathways to improve development.     

Full-term development of mouse blastomere nuclei transplanted into enucleated two-cell embryos

The nuclei from four- and eight-cell mouse embryos were transplanted into enucleated two-cell embryos. It was found that such embryos not only developed to the blastocyst stage in vitro (72% and 35%), but also developed to full term (22% and 8%) after transfer to recipient mice. However, development of embryos which contained nuclei from the inner cell mass was not observed. Since the development of enucleated zygotes which contain advanced nuclei is limited (the present study; McGrath and Solter: Science, 226:1317-1319, '84; Robl, Gilligan, Critser, and First: Biol. Reprod., 34:733-739, '86), it appears that cytoplasmic factors are important for the development of nuclei from advanced cells.     

Differential development of rabbit embryos derived from parthenogenesis and nuclear transfer

Parthenogenetic development (PA) is often used as a model to investigate activation protocols for nuclear transfer (NT) embryos. The objective of this study was to compare the development, as well as the dynamics of the nuclear materials and microtubules of PA and NT embryos following similar activation treatment. Our results demonstrate that, during parthenogenesis, activation through either electrical pulses or chemical stimulation alone resulted in low cleavage rates and compromised development. A combination of two sets of electrical pulses and a 2-h-exposure to chemical activation medium (5 microg/ml cycloheximide (CHX) and 2 mM 6-dimethylaminopurine (6-DMAP) in KSOM+0.1% BSA) could effectively activate rabbit oocytes, and resulted in a 99% (n = 73) cleavage rate with greater than 60% (n = 73) developing to blastocysts at day 4. However, the same activation protocol following NT resulted in only 65-72% of oocytes cleaved (depending on donor cell type), with less than 20% developing to the blastocyst stage. The differences observed between NT and PA embryos subjected to the same activation protocol were also evident in terms of the time required for their development to the blastocyst stage, as well as the cell numbers present in blastocysts at day 6. Furthermore, laser confocal microscopy revealed that pronuclear formation in the NT embryos was delayed by comparison to that in the parthenotes. In conclusion, our study suggests that an effective protocol for parthenogenesis cannot promise a comparable outcome for NT embryos.     

Effect of two activation treatments and age of blastomere karyoplasts on in vitro development of bovine nuclear transfer embryos

The yield and quality of (a) parthenogenetic blastocysts produced by two activation treatments (cycloheximide [CHX] or 6-dimethylaminopurine [DMAP]) and (b) nuclear transfer blastocysts generated using these two activation treatments and three different ages of karyoplast derived from day 3, 4, or 5 in vitro produced donor embryos, were examined in order to define an optimal nuclear transfer protocol. The two activation protocols comprised calcium ionophore followed by either CHX or DMAP. Parthenogenetic blastocyst yields were greater (P < 0.001) following activation with DMAP than CHX (59.7 +/- 5.1 vs. 31.4 +/- 4.5 [mean +/- SEM]). In contrast, nuclear transfer blastocyst rates per fused embryo were lower (P < 0.0001) using cytoplasts activated with DMAP. The individual rates using day 3, 4, and 5 donors and using CHX and DMAP activation treatments were 31.9 +/- 5.0, 31.7 +/- 6.2, 20.4 +/- 7.3 and 27.8 +/- 4.7, 20.1 +/- 7.5, 12.7 +/- 8.3, respectively. Blastocyst rate per fused embryo was negatively correlated (P = 0.0091) with the total number of blastomeres per donor embryo. Despite this inverse relationship, the calculated potential blastocyst yield per donor embryo was positively correlated (P < 0.0048) to karyoplast age. The individual potential yields on days 3, 4, and 5 and for the two activation protocols (CHX and DMAP) were 4.7 +/- 0.8, 7.2 +/- 1.2, 10.1 +/- 2.1 and 3.8 +/- 0.8, 5.5 +/- 2.1, 7.3 +/- 4.1, respectively. One possible explanation for the observed inverse relationship is that differentiation events during early cleavage are able to reduce the ability of the cytoplast to reprogram the transferred karyoplast and hence reduce blastocyst yields. The mechanism that mediates the differential effect of the CHX and DMAP on blastocysts yields between parthenogenetic and nuclear transfer embryos remains to be elucidated. In conclusion, the results indicate that although activation of oocytes with DMAP can produce a higher percentage of blastocysts, CHX activation is superior for use in nuclear transfer.     

Fragmentation and development of preimplantation porcine embryos derived by parthenogenetic activation and nuclear transfer

Fragmentation occurs during early developmental stages of electrically activated oocytes and nuclear transfer (NT) embryos. It might contribute to the low developmental rate of porcine NT embryos. The present study was conducted to investigate whether the addition of sugars such as sorbitol or sucrose suppresses fragmentation and supports the development of electrically activated oocytes and NT embryos. The activated oocytes were cultured in Porcine Zygote Medium-3 (PZM-3) supplemented with sorbitol or sucrose for 2 days after electric activation, and then cultured in the PZM-3 for the remaining 4 days. The osmolarities of PZM-3, PZM-3 supplemented with 0.05 or 0.1 M sorbitol, and PZM-3 with 0.05 M sucrose were 269 +/- 6.31, 316 +/- 3.13, 362 +/- 4.37, and 315 +/- 5.03 mOsm, respectively. When parthenogentically activated oocytes were cultured in PZM-3 supplemented with 0.05 M sorbitol or sucrose for the first 2 days and then cultured in PZM-3 without sugar, a significantly higher (P < 0.05) cleavage rate and blastocyst rate were observed. Interestingly, addition of sugar to PZM-3 for 2 days reduced the fragmentation rate compared to PZM-3 without sugar. In NT embryos, sugar addition into PZM-3 increased the fusion rate (84.2% +/- 6.07 vs. 95.1% +/- 2.52), cleavage rate (67.6% +/- 5.80 vs. 77.3% +/- 3.03), and developmental rate to the blastocyst stage (10.2% +/- 0.79 vs. 19.4% +/- 1.77). There was no significant difference between treatments for the number of the blastocysts. In addition the fragmentation rate was reduced compared to PZM-3 without sorbitol (26.1 +/- 4.30 vs. 14.5 +/- 1.74). In conclusion, increasing the osmolarity of PZM-3 through addition of either sorbitol or sucrose for 48 hr increased the cleavage and developmental rate to the blastocyst stage by reducing the fragmentation rate through increasing osmolarity.     

Early development in utero of bovine nuclear transfer embryos using early G1 and G0 phase cells

Bovine somatic cell nuclear transfer (NT) embryos can develop to normal calves, but the success rates are still quite low. Recently, enhanced development of bovine NT embryos to full term has been achieved using fibroblasts at the early G1 phase instead of cells at the quiescent (G0) phase. In the present study, we examined the morphological development in utero of NT embryos using early G1 phase cells (eG1-NT embryos) and G0 phase cells (G0-NT embryos). We produced eG1- and G0-NT blastocysts, and then they were transferred to recipient heifers for transient development in utero up to day 14 of gestation. In vitro-fertilized (IVF), parthenogenetic and artificially inseminated (AI) embryos were used as controls. The rate of formation of embryonic disks of the recovered embryos was the same among the groups of eG1-NT, IVF, and AI embryos (p>0.05). The formation rate in eG1-NT embryos was significantly higher than that in G0-NT embryos (p<0.05). The lengths of eG1-NT embryos were the same as those of IVF, parthenogenetic, and AI embryos (p>0.05), but significantly shorter than those of G0-NT embryos (p<0.01). We conclude that the morphological development of day 14 embryos derived from eG1-NT embryos was mostly similar to that of AI embryos, but that the morphological development of G0-NT embryos was abnormally large and different from that of AI and eG1-NT embryos.     

In vitro development of preimplantation porcine nuclear transfer embryos cultured in different media and gas atmospheres

This study investigated the effect of culture media and gas atmospheres on the development of porcine nuclear transfer embryos. Oocytes derived from a local abattoir were matured for 42-44 h and enucleated. Fetal fibroblasts were prepared from a Day 35 porcine fetus. Confluent stage fetal fibroblasts were introduced into the perivitelline space of enucleated oocytes. Fusion and activation were induced simultaneously with two direct current (1.2 kV/cm for 30 micros) in 0.3 M mannitol medium. For parthenogenetic activation, the same pulses were used. In Experiment 1, parthenogenetically activated oocytes were cultured in North Carolina State University-23 (NCSU-23), Porcine Zygote Medium-3 (PZM-3), or Beltsville Embryo Culture Medium-3 (BECM-3). Parthenogenetically activated oocytes cultured in PZM-3 had a higher (P < 0.05) developmental rate to the blastocyst stage (15.2% versus 3.7-9.6%) as compared to BECM-3 or NCSU-23. The number of nuclei in Day 6 blastocysts was higher (P < 0.05) in PZM-3 (23.6) and NCSU-23 (21.4) than BECM-3 (14.2). In Experiment 2, parthenogenetically activated oocytes were cultured in NCSU-23 under a gas atmosphere of 5% CO(2) in air for 6 days (T1), 5% CO(2), 5% O(2), 90% N(2) for 6 days (T2), 5% CO(2) in air for 3 days, then 5% CO(2), 5% O(2), 90% N(2) for 3 days (T3), or 5% CO(2), 5% O(2), 90% N(2) for 3 days, then 5% CO(2) in air for 3 days (T4). Blastocyst formation rates were not different among treatments (12.9 =/-3.6 %, 13.5 +/- 4.2%, 10.8+/-2.4%, and 12.6+/-2.7%, respectively). However, T2 (36.7+/-2.9) and T3 (33.8+/-3.0) resulted in more nuclei per blastocyst than T1 (23.2+/-2.1) or T4 (26.0+/-2.1 ). In Experiment 3, reconstructed porcine nuclear transfer (NT) embryos were cultured in NCSU-23 or PZM-3 under a gas atmosphere of 5% CO(2) in air or 5% CO(2), 5% O(2), 90% N(2). Developmental rates to blastocyst stage for porcine NT embryos cultured in NCSU-23 under a gas atmosphere of 5% CO(2) in air or 5% CO(2), 5% O(2), 90% N(2) were 7.2+/-1.4% and 12.3+/-1.4%, and the number of nuclei was 12.2=/-0.8% and 19.4+/-1.0, respectively. NT embryos cultured in PZM-3 under a gas atmosphere of 5% CO(2) in air or 5% CO(2), 5% O(2), 90% N(2) had developmental rates to blastocyst stage of 18.8+/-1.9 %, and 17.8+/-3.8% the nuclei number was 20.9 +/- 1.9 and 21.9+/-3.3, respectively. NT embryos cultured in NCSU-23 had a higher developmental rate to the blastocyst stage in 5% CO(2), 5% O(2), 90% N(2) than in 5% CO(2) in air (P < 0.05). Regardless of gas atmospheres, NT embryos cultured in PZM-3 had a higher developmental rate (18.3 =/- 1.7% versus 16.9 +/- 1.2%) and nuclei number (21.4 +/-1.8 versus 16.9 +/- 1.2) than in NCSU-23 (P < 0.05). In conclusion, a gas atmosphere of 5% CO(2), 5% O(2), 90% N(2) supported a higher development rate of porcine NT embryos than 5% CO(2) in air when the porcine NT embryos were cultured in NCSU-23. Furthermore, regardless of atmosphere, PZM-3 supported a higher development rate of porcine nuclear transfer embryos than NCSU-23.     

Preimplantation development of rabbit embryos after transfer of embryonic nuclei into different cytoplasmic environment

The development of nuclear-transfer oocytes and zygotes was tested in the rabbit. Metaphase II oocytes and zygotes in the early pronuclear stage were treated with a cytoskeletal inhibitor (cytochalasin D), enucleated, and subsequently fused either with single blastomeres from eight- and 16-cell stages (oocytes and zygotes) or with pronuclei-containing karyoplasts (zygotes only). Also, nonenucleated zygotes were fused with 1/8 blastomeres. Fusion was performed by means of an electric field. Development of reconstituted embryos was monitored mainly in vitro, but a certain number of embryos developed from oocytes and zygotes receiving nuclei from eight-cell stages were also transferred into pseudopregnant does. Development of nuclear-transfer oocytes was distinctly better than that of nuclear-transfer zygotes, since 16.9% and 9.5% oocytes vs. 8.1% and 3.7% zygotes carrying eight- and 16-cell nuclei, respectively, developed to the blastocyst stage. Two advanced but already dead fetuses were found after transfer of 27 four-cell embryos obtained after fusion of oocytes with 1/8 blastomeres. No implantations were observed after transfer of 25 four-cell embryos developed from enucleated zygotes receiving eight-cell nuclei. These findings indicate that, in the rabbit, some nuclei from 16-cell embryos are still capable of promoting at least preimplantation development. Comparison between the developmental abilities of oocyte- and zygote-derived nuclear-transfer embryos also suggests that the cytoplasmic environment of recipient cell is more crucial for the development of reconstituted embryos than the stage of introduced nuclei (at least up to the 16-cell stage). The majority of pronuclear exchange embryos (69.9%) and 40% of nonenucleated zygotes receiving eight-cell nuclei were able to develop to the blastocyst stage. This latter observation indicates, similarly as with mouse, a supporting role of residual pronuclei for participation of an eight-cell nucleus in the development of reconstituted zygotes.     

Effects of thioredoxin on the preimplantation development of bovine embryos

Thioredoxin (TRX) is an ubiquitous protein disulfide reductase, which is known to be involved in the implantation development of mouse embryos. In the present study, recombinant human TRX was used to evaluate its effect on the promotion of preimplantation development of bovine embryos derived from in vitro maturation and fertilization. Supplementation of the medium 24h post insemination with TRX significantly (P<0.05) enhanced the frequency of development to the blastocyst stage in 5% O(2) concentration. The optimal concentration was 0.5 microg/ml (P<0.05, compared with 0, 0.1 and 1.0 microg/ml). This effect of TRX was evident only when added around the time of the first cleavage stage (24 h post insemination); no promotion was found with treatment at 6h (one-cell) or 44 h (six- to eight-cell) after insemination. Moreover, it is of interest that even with the best combination of the dose and timing of TRX treatment (0.5 microg/ml, at 24 h post insemination), no promotion of development was observed when embryos were cultured under 20% O(2). However, a preincubation of TRX in the culture medium under 20% oxygen for 24h did not diminish the promoting effect in the subsequent TRX treatment under optimal conditions, thus suggesting that the possible oxidation of TRX alone may not be the reason for the disappearance of the effect under a high oxygen concentration. These results indicate that TRX does improve the development of bovine embryos in vitro, though unlike the general reducing reagents such as beta-mercaptoethanol or cysteamine, TRX may have to exert its effect at specific times and in more physiologic oxygen environments.     

Effects of opioids on the development of preimplantation mouse embryos

Opioid peptide DAGO, agonist of opiate mu-receptors and naloxone antagonist of mu-, delta- and kappa-receptors in concentration 3 x 10 M inhibit embryonic development of CBA mice. Inhibition was stage-specific with maximal effect after addition of opioids to zygotes: in the presence of Naloxone no more than 6.7% of embryos reached morula and blastula stages and in the presence of DAGO--36.8%. The other embryos were arrested at two-, four- or, sometimes even, at eight-cell stages without any signs of fragmentation. Four and eight-cell embryos were less sensitive to drug action. Inhibitory effects of these opioids were reduced when they were added simultaneously to zygotes. Agonist of opiate delta-receptors, opioid peptide DADLe, failed to affect embryonic development.     

Improved postimplantation development of rabbit nuclear transfer embryos by activation with inositol 1,4,5-trisphosphate

Cloned rabbit embryos are characterized by their extremely poor postimplantation development, despite their high survivability until the blastocyst stage in vitro. This study examined whether the developmental failure of cloned rabbit embryos in vivo can be overcome by technical improvements to the activation protocol. Freshly collected cumulus cells were transferred into enucleated oocytes by intracytoplasmic injection. One to two hours later, the oocytes were activated by electroporation with Ca(2+) or inositol 1,4,5-trisphosphate (IP3), which is known to induce repeated rises in intracellular Ca(2+), as in normal fertilization. After transfer of embryos at the two- to four-cell stages, well-defined implantation sites with remnant fetal tissue were observed at term (day 28) only in the IP3-stimulation groups (0.9% and 5.8% per transferred embryo for single and triple stimulation groups, respectively). When some recipients in the same group were examined at days 16-20, a viable cloned fetus (day 19) with normal organogenesis was obtained. These findings clearly demonstrate that the oocyte activation protocol using IP3 enhances the postimplantation development of nuclear-transferred rabbit embryos.     

Preimplantational embryo development and incidence of blastomere apoptosis in bovine somatic cell nuclear transfer embryos reconstructed with long-term cultured donor cells

This study was performed to investigate whether types and/or age of donor cells affect preimplantational embryo development and the incidence of apoptosis in bovine somatic cell nuclear transfer (SCNT) embryos. Bovine fetal or adult ear fibroblasts were isolated, cultured in vitro and categorized into fresh or long-term cultured cells in terms of population doublings (PD): in fetal fibroblasts, <16 being considered fresh and >50 being long-term cultured; in adult ear fibroblasts, <16 being considered fresh and >30 being long-term cultured. Bovine oocytes from slaughterhouse ovaries were matured in TCM-199, enucleated and reconstructed by SCNT. The reconstructed oocytes were fused, chemically activated, and cultured in modified synthetic oviduct fluid (mSOF) at 39 degrees C in a humidified atmosphere of 5% CO(2) air for 7 days. The early development of SCNT embryos was monitored under a microscope and the quality of blastocysts was assessed by differential counting of inner cell mass (ICM) and trophectoderm (TE) cells and by apoptosis detection in blastomeres using a terminal deoxynucleotidyl transferase-mediated d-UTP nick end-labeling (TUNEL) assay. As results, types and/or age of donor cells did not affect the rate of blastocyst formation and the number of ICM and TE cells. However, a significant increase in apoptotic blastomeres was observed in SCNT embryos reconstructed with long-term cultured fetal or adult ear fibroblasts compared to those in SCNT embryos derived from fresh fetal or adult ear fibroblasts. In conclusion, these results indicated that the long-term culture of donor cells caused increased the incidence of apoptosis in bovine SCNT embryos but did not affect the developmental competence and the cell number of blastocysts.     

Effects of vascular endothelial growth factor on porcine preimplantation embryos produced by in vitro fertilization and somatic cell nuclear transfer

This study examined the effects of vascular endothelial growth factor (VEGF) on porcine embryos produced by in vitro fertilization (IVF) and somatic cell nuclear transfer (SCNT) at different developmental stages. Four sets of experiments were performed. In the first, supplementation of the in vitro culture medium with 5 ng/mL VEGF was suitable for porcine IVF embryo development, and the blastocyst formation rate was significantly higher than the control and other groups (57.73 ± 6.78% (5 ng/mL VEGF) vs. 43.21 ± 10.22% (control), 42.16 ± 10.24% (50 ng/mL VEGF) and 41.91 ± 11.74% (500 ng/mL VEGF); P < 0.05). The total cell number after supplementation with 5 ng/mL VEGF was significantly higher than the control and other groups (151.85 ± 39.77 (5 ng/mL VEGF) vs. 100.00 ± 34.43 (control), 91.2 ± 31.51 (50 ng/mL VEGF), and 112.53 ± 47.66 (500 ng/mL VEGF); P < 0.05). In the second experiment, when VEGF was added at different developmental stages of IVF derived embryos (early stage, days 1-3, late stage, days 4-7), the blastocyst formation rate and total cell number were significantly higher at the late stage (47.71 ± 9.13% and 131.5 ± 20.70, respectively) than in the control (34.32 ± 7.44% and 85.50 ± 20.41, respectively) and at the early stage (33.60 ± 5.78% and 86.75 ± 25.10, respectively; P < 0.05). There was no significant difference in the blastocyst development rate or total cell number between the whole culture period (days 1-7) and the late stage culture period after supplementation with 5 ng/mL VEGF (P > 0.05). In the third experiment, the cleavage rate was significantly higher when SCNT embryos were cultured with VEGF during the whole culture period than in the late stage (63.56 ± 15.52% vs. 39.72 ± 4.94%; P < 0.05), but there was no significant difference between the control and the early stage culture period (P > 0.05). The blastocyst formation rate was significantly higher at the late stage culture period with VEGF than at the early stage culture period (34.40 ± 15.06% vs. (16.07 ± 5.01%; P < 0.05). There was no significant difference in the total cell number between the groups (P > 0.05). In experiment 4, using real-time PCR, VEGF mRNA expression was detected in all the developmental stages of IVF and SCNT embryos, but the expression level varied according to the developmental stage. VEGF receptor, KDR mRNA was detected in all stages IVF and SCNT embryos. However, flt-1 mRNA was not expressed in all embryonic stages of IVF and SCNT embryos. These data suggest that VEGF supplementation at the late embryonic developmental stage might improve the developmental potential of both IVF and SCNT preimplantation porcine embryos through its receptors.     

Relationship between nuclear remodeling and development in nuclear transplant rabbit embryos.

The present study characterized the profile of nuclear remodeling in nuclear transplant rabbit embryos and investigated the relationship between chromatin behavior after transfer and embryo development. The developmental potential and pattern of remodeling of donor nuclei from cleavage-, morula-, and blastocyst- (inner cell mass ICM, and trophectoderm, TE) stage donors were evaluated. In addition, we determined whether a modification in the synchrony between blastomere fusion and oocyte activation altered the profile of nuclear remodeling and affected development of reconstituted embryos. Development to blastocysts was similar with 8- and 32-cell-stage donor nuclei (42% and 33%, respectively, p greater than 0.1). However, it was reduced with ICM transplants (17%, p less than 0.05), and development of TE transplants did not progress beyond the 8-cell stage. Upon blastomere fusion into nonactivated oocyte cytoplasm, nuclear remodeling was characterized by premature chromosome condensation (PCC), followed by pronuclear (PN) formation and swelling. PCC occurred synchronously within 1.2-1.5 h post-fusion with all stages of donor nuclei (p greater than 0.1). PN formation in 8- and 32-cell transplants occurred approximately 4 h after fusion, and was synchronous to that of female pronuclei in activated oocytes; however, it was delayed in ICM and TE transplants (p less than 0.01). With all stages of donor nuclei, final nuclear diameter was similar to, or larger than, that of female pronuclei. Fusion to activated oocyte cytoplasm, as opposed to nonactivated cytoplasm, prevented PCC and extensive nuclear swelling (16.0 +/- 0.7 vs. 30 +/- 0.7 microns, respectively, p less than 0.01). Nuclear diameter in early embryos was smaller (p less than 0.01), and development to blastocysts was reduced (p less than 0.05). The results indicate that remodeling of the donor nucleus is not essential for development to blastocysts; however, it is beneficial. Furthermore, complete reprogramming seems possible only after remodeling of the donor nucleus, i.e., PCC in nonactivated cytoplasm, followed by nuclear swelling upon activation of the oocyte.     

Studies on preimplantation development of buffalo embryos

A total of 71 lactating and nonlactating buffalo-cows of the Murrah breed and F(1)-F(3) crossbreds of Murrah x Bulgarian buffalo were used for a year as donors of embryos after a preliminary treatment for superovulation induction with pregnant mare serum gonadotrophin (PMSG) or follicle stimulating hormone (FSH) in combination with prostaglandin F-2 alpha analog (PGF-2 alpha) according to general application procedures in cows. From 36 to 72 h following prostaglandin injection, the buffalo-cows were checked with the help of a teaser bull for detection of estrus. The animals in estrus were inseminated twice either naturally or artificially with frozen semen. Nonsurgical flushing of the uterine horns was done in 45 of the buffalo-cows between 108 and 162 h after the onset of estrus. After slaughter the uterine horns and oviducts of the other 26 animals were flushed separately between 74 and 108 h after the beginning of estrus. Seven late morulae and eight hatched blastocysts were recovered between 114 and 116 h from the onset of estrus as a result of nonsurgical flushing. All of the 40 embryos recovered after 117 h were in the hatched blastocyst stage. As a result of flushing the oviducts and the uterine horns of slaughtered donors between 74 and 100 h, eggs were obtained only from the oviducts, while flushing conducted between 102 and 108 yielded eggs from both the oviducts and the uterine horns.     

Developmental capacity of ferret embryos by nuclear transfer using G0/G1-phase fetal fibroblasts

With the ultimate goal of establishing experimental protocols necessary for cloning ferrets, the present study has established parameters for the reconstruction of ferret embryos by nuclear transfer (NT) using G0/G1-phase donor fetal fibroblasts. Cumulus-oocyte complexes were harvested from superovulated ferrets and cultured in maturation medium for 24 h. Matured oocytes were then enucleated and injected with the fibroblast nuclei derived from 14-16-h serum-starved cells. Reconstructed embryos were then activated by a combination of electric pulses and chemical stimulations. Subsequently, the reconstructed and activated embryos were either cultured in vitro or transferred to pseudopregnant ferrets to evaluate their developmental capacity in vitro and in vivo. Our results demonstrated that 56.3% of reconstructed embryos (n = 187) cleaved, while 26.0% and 17.6% developed to morula and blastocyst phases in vitro, respectively. The blastocysts derived from NT embryos demonstrated normal morphology by differentially staining as compared to normal blastocysts developed in vivo following fertilization. In vivo developmental studies at 21 days posttransplantation demonstrated 8.8% of reconstructed embryos (n = 91) implanted into the uterine lining of recipients, while 3.3% formed fetuses. However, reconstructed embryos (n = 387) failed to develop to term (42 days). These results demonstrate donor nuclei of G0/G1-phase fetal fibroblast cells can be reprogrammed to support the development of reconstructed ferret embryos in vitro and in vivo; however, a significant third-trimester block occurs preventing full-term development.     

Expression of adipokines in preimplantation rabbit and mice embryos

Recent studies point to a role for adipokines in reproduction. Leptin is involved in embryo metabolism and may participate in embryo-maternal crosstalk. Little is known about potential roles of other adipokines in reproduction. We therefore studied the expression of adiponectin and pathway members during the pre- and periimplantation period in rabbits and mice. Adiponectin protein is localized in glandular epithelium of the rabbit endometrium on day 6 and 8 p.c. and in mouse endometrium on day 3.5 and 5 p.c. Rabbit, but not mice blastocysts express adiponectin mRNA. Adiponectin receptors one and two, adiponectin paralogues and PPARs were found in both species. Both, trophoblast and embryoblast were adiponectin positive. Real time PCR for adipoR1 and adipoR2 in rabbit blastocysts of different gastrulation stages at day 6 p.c. revealed a specific switch in expression: Expression was high in the trophoblast in early stages and in the embryoblast shortly prior to implantation. In conclusion, during the pre- and periimplantation period, members of the adiponectin pathway are expressed in endometrium and blastocysts, with a specific expression pattern in the embryonic disk of the gastrulating rabbit blastocyst, giving support to a role of the adipokine network in blastocyst differentiation and embryo-maternal interactions.     

Sexing of preimplantation mouse embryos by measurement of X-linked gene dosage in a single blastomere

Single blastomeres were isolated from zona-free 8-cell mouse embryos and assayed for X-linked hypoxanthine phosphoribosyl transferase (HPRT) activity and autosome-linked adenine phosphoribosyl transferase (APRT) activity. At this stage of development both X chromosomes are active in female embryos. Hence, a bimodal distribution of HPRT: APRT ratios, corresponding to male (XY) and female (XX) biopsied samples, was observed due to the 2-fold difference in gene dosage for HPRT activity. Batches of putative male and female embryos identified in this way were transferred to pseudopregnant recipient females. Development of the seven-eighths embryos was equivalent to that of control zona-free intact embryos. Sex determination by measurement of X-linked gene dosage was accurate and rapid enough to allow transfer of embryos of known sex without the need for cryopreservation.