Increasing the rate of blastocyst formation and hatching from in vitro-produced bovine zygotes

This study was designed to identify parameters that would facilitate early selection of superior embryos, as well as to define culture conditions that could increase the proportion of embryos proceeding to the blastocyst stage. In the first experiment, the developmental potential of bovine embryos that had reached different stages of development after 60 h of culture following insemination was assessed. No 2-cell embryos underwent further cleavage. Of the 4-cell embryos (n = 188) only 12.2% progressed to the blastocyst stage, while 62.5% of 8-cell embryos (n = 480) did so (P < 0.01). In a further experiment, the effects of conditioning the culture medium (TCM 199) either with Buffalo rat liver cells (BRLC) or bovine oviductal epithelial cells (BOEC) and the effects of co-culture with either of these 2 cell types were examined. The percentage of 8-cell embryos proceeding to the morula and blastocyst stages was independent of cell type and culture system. However, BOEC-conditioned medium supported significantly lower production of blastocysts than any of the other culture methods. Only 24.1% of the former proceeded to the blastocyst stage after the full 10 d of culture, and only 3% hatched, values that were significantly lower than in the other 3 groups (P < 0.01). Among the latter, 44% progressed to the blastocyst stage in BRLC-conditioned medium while 44 and 46% reached that endpoint after co-culture with BOEC or BRL cells, respectively. The percentages that hatched among these were 28.2, 31 and 28.5%, respectively.

Expression of two transgenes in in vitro matured and fertilized bovine zygotes after DNA microinjection

Bovine zygotes produced by in vitro maturation-in vitro fertilization (IVM-IVF) were examined for their potential to serve as recipients of transgenes. Pronuclei, which were maximally visible at about 22 h after IVF, were injected with a SV40-LacZ construct (pSVON). Injected zygotes had lower cleavage rates (49.1%, n = 1162, P < 0.01) than did either noninjected controls (87.4%, n = 1420) or noninjected zygotes in which pronuclei were not visible (67.6%, n = 803). Zygotes that were injected into their pronuclei cleaved as well as zygotes injected cytoplasmically. At 48 h after injection, when most embryos had reached the four- and eight-cell stages, more zygotes in the pronuclear group (22.7%, n = 125) stained positively for LacZ than did zygotes in the cytoplasmic group (8.0%, n = 125). A group of zygotes injected into the pronucleus with pSVON was cultured for 9 days. More morulae (10.8%, n = 134) than blastocysts (3.2%, n = 31) expressed the LacZ gene, indicating that silencing of expression occurred as development progressed. Another group of zygotes was injected with a beta-actin-LacZ gene construct (pbActinLacZ) and, of the embryos assayed at 48 h, 10.6% (n = 255) stained positively. At 9 days, 36.3% of morulae (n = 91) and 21% of blastocysts (n = 33) expressed the transgene. Almost all putative transgenic embryos injected with either construct showed a mosaic pattern of LacZ expression, with an average of only 2-3 cells staining at the eight-cell stage and the majority of cells in positive blastocysts showing no evidence of expression.

Expression of bovine trophoblast interferons by in vitro-derived blastocysts is correlated with their morphological quality and stage of development

Bovine embryos, whether produced naturally or by in vitro techniques, exhibit considerable variability in morphological quality and develop at different rates. Our objectives have been to determine whether initial expression of trophoblast interferon (IFN-tau) was a reflection of conceptus stage of development or age and whether there was an effect of embryo quality on the amount of IFN-tau produced. Early blastocysts (N = 187) were selected at the onset of blastocoele formation and cultured individually. Embryo quality (excellent, good, or fair: E, G, or F) and developmental stage (early, expanded and hatched blastocysts: BL, EBL, and HBL, respectively) were used in a 3 x 3 factorial complete randomized block design, each block (n = 4) consisting of batches of embryos produced from oocytes in different collections. Quality and developmental stage of embryos and IFN-tau released into the medium were assessed every 24 h. Production of IFN-tau (units/embryo/24 h) was greater (P < 0.01) among hatched blastocysts (HBL; 0.91 +/- 0.08) than expanded blastocysts (EBL; 0.23 +/- 0.04) and early blastocysts (BL; 0.05 +/- 0.08). Embryos of similar developmental stage but differing by 2 days in age released equal amounts of IFN-tau. Expression of antiviral activity increased (P < 0.05) from 27% to 57% to 100% as development proceeded from BL to EBL and to HBL respectively. More IFN-tau was produced by HBL graded G (1.0 +/- 0.1) or E (1.3 +/- 0.1) than by those of F quality (0.5 +/- 0.1). All blastocysts, whatever their quality and developmental stage, contained IFN-tau mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of bovine trophoblast interferon in conceptuses derived by in vitro techniques

Expression of the trophoblast interferon, bovine trophoblast protein-1 (bTP-1), has been studied in embryos produced by in vitro maturation-in vitro fertilization (IVM-IVF). No bTP-1 production was noted until after embryos had reached the expanded blastocyst stage and had begun to hatch (Days 8-9 post-fertilization). Single blastocysts comprising 115 +/- 22 cells released 1.0 +/- 0.1 units of interferon activity/24 h. Amplification of conceptus mRNA by reverse transcription-polymerase chain reaction procedure with bTP-1-specific oligonucleotides confirmed that bTP-1 transcripts were present in blastocysts but were not detectable at earlier stages. Although cultured blastocysts produced by IVM-IVF procedures continued to secrete bTP-1 for a few days, they failed to attach to the substratum and form outgrowths, and soon lost structural integrity. However, when Day 8 blastocysts/morulae were transferred to the uteri of synchronized cows, recovered 4 days later, and placed into individual cultures, they attached and formed outgrowths that produced large amounts of bTP-1 (greater than 2000 units/culture/24 h after 14 days). Embryos thus first expressed bTP-1 when a functional trophectoderm was first formed, and induction did not require a period of in vivo development. However, continued viability of the blastocyst and bTP-1 production were not sustained in vitro and may require some exposure to the uterine environment.

Quantity and quality of embryos collected from mice passively immunized against estradiol

The objective of this study was to determine the effects of passive immunization against estradiol on the occurrence and timing of estrus, ovulation and fertilization rates and on early embryonic development in mice. Swiss Webster female mice were randomly assigned to one of the three treatment groups to be injected with 0.1 ml saline (control; n=15), 0.1 ml anti-estradiol antisera (high dose: n=17) or 0.1 ml antiestradiol antisera diluted 1:10 with saline (low dose; n=17) at seven weeks of age. Immediately after injection mice were placed with males and observed daily for the presence of vaginal plugs for 10 d. Three days after vaginal plugs were observed, mice were terminated and the uteri were removed and flushed to determine the number and quality of unfertilized ova and embryos. No differences were observed in the timing of vaginal plug formation, the proportion of mice with vaginal plugs, or the mean number of unfertilized ova or embryos collected from each treatment group. However, the proportion of excellent or good quality embryos was reduced in the high dosage treatment. It was concluded from this study that passive immunization of mice against estradiol did not increase the number of embryos obtained from mice and that a high dosage of antisera against estradiol reduced embryo quality. These results provide evidence that alterations in levels of estradiol may adversely affect embryonic development.

Deep freezing of mouse one-cell embryos and oocytes using different cryoprotectants

The objective of this study was to compare iso-osmolar concentrations (1.5 M) of 1,2-propanediol, glycerol, dimethylsulphoxide and a combination of 1 M propanediol + 0.5M glycerol (PDGLY) as cryoprotectants for murine ovulated oocytes and one-cell embryos. A higher (P < 0.01) percentage of one-cell embryos developed to the two-cell stage when frozen-thawed with 1,2-propanediol (83%) as compared with glycerol (43%), dimethylsulfoxide (51%) or PDGLY (7%). Data recalculated on the basis of two-cell embryos/number of normal one-cell embryos after thawing indicated no differences among single cryoprotectant groups. More (P < 0.01) frozen-thawed, in-vitro fertilized oocytes developed to the two-cell stage when 1,2-propanediol (35%) was used as cryoprotectant as compared with glycerol (15%). Freezing-thawing resulted in a reduced number of two-cell embryos after oocytes were fertilized in-vitro as compared with fresh oocytes. 1,2-propanediol was a better cryoprotectant than glycerol, dimethylsulphoxide or PDGLY for deep freezing of murine oocytes or one-cell embryos.

Effect of one-step sucrose dilution of glycerol on in-vitro development of frozen-thawed mouse embyros

Several glycerol (GLY) dilution treatments were compared using frozen-thawed early blastocysts from Swiss Webster mice. These treatments consisted of 0.00 (0.00S n = 68), 0.25 (0.25S n = 67), 0.50 (0.50S n = 76), 0.75 (0.75S n = 66), 1.00 (1.00S n = 59), and 1.25 (1.25S n = 60) M of sucrose to remove GLY from embryos in one step. Then the one step procedure was compared with a three-step GLY dilution treatment (C n = 66). Embryos were exposed to 1.5 M of GLY in three-steps, frozen according to a standard freezing technique and stored at -196 degrees C. Embryos were thawed in a 37 degrees C water bath, pooled, and those graded good or excellent were randomly assigned to the experimental groups. The blastocysts were cultured in Whitten's medium microdrops under paraffin oil in a water saturated 5% CO(2) air atmosphere at 37 degrees C. The proportion (%) of embryos developing to expanded blastocysts was lowest (P < 0.05) in treatment 0.00S (63.1 +/- 4.0). The 0.25S (72.0 +/- 4.3) and 0.50S (75.0 +/- 3.1) 0.75S (79.0 +/- 4.4) treatments yielded a similar percentage of expanded blastocysts. The 1.00S treatment (87.0 +/- 4.0) was similar to 0.75S and 1.25S (98.3 +/- 4.0) treatments. The C treatment was superior (P < 0.05) to dilutions done with < 0.75 M sucrose, similar to 0.75S and 1.00S, and inferior (P < 0.05) to 1.25S. This later treatment yielded the highest percentage of expanded blastocysts. The percentage of embryos that hatched in treatments 0.00S, 0.25S, 0.50S, 0.75S and C was lower (P < 0.05) compared to 1.00S and 1.25S. The percentage of embryos and hatched blastocysts increased linearly (P < 0.01) from 0.0 to 1.25 M sucrose. Dilution of GLY with 1 or 1.25 M sucrose yielded better results compared with lower sucrose concentrations or the three-step GLY removal procedure.