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PubMed1978

Factors affecting the binding of polycyclic aromatic hydrocarbons to human embryo cells, and transformable and non-transformable hamster embryo cells.

The effects of various factors, including population doubling number, percent of confluence, serum concentration and storage in liquid nitrogen on the binding of several polycyclic aromatic hydrocarbons to human and hamster embryo cells were studied. The binding of 7,12-dimethylbenz[a]-anthracene (DMBA) to hamster embryo cells DNA, RNA and protein was maximal after 22 h of treatment. In contrast, binding to human embryo cell macromolecules increased for at least 55 h. Treatment of hamster embryo cells at 100% confluence resulted in much less binding than treatment at 70% confluence, whereas with human embryo cells the binding increased, or remained constant, following treatment at the greater confluence. The transforming frequency of hamster embryo cells decreases with increasing population doubling number. Accordingly, we found that the binding of DMBA to hamster embryo DNA, RNA and protein decreased approximately 100-fold between population doubling numbers 8 and 20. In transformable cell cultures, DMBA was bound to hamster embryo cell DNA to a greater extent than to RNA or protein. The binding of DMBA to nucleic acids was much greater than binding by either dibenz[a,h]anthracene (DB[a,h]A) or dibenz-[a,c]anthracene (DB[a,c]A), both of which had low binding values at all population doubling numbers tested. Therefore, the best correlation of binding with carcinogenicity and transforming activity was observed with DMBA. Storage of hamster embryo cells in liquid nitrogen did not alter their binding characteristics. Binding of all three hydrocarbons to human embryo cell nucleic acids was low during all population doubling numbers studied, while binding to cellular protein increased until population doubling number 70 and then decreased sharply.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1990

Spatial distribution of the capacity to initiate a secondary embryo in the 32-cell embryo of Xenopus laevis.

To examine the spatial distribution of dorsal determinants in the early embryos of Xenopus laevis, individual cells from the 32-cell embryo were transplanted into the same tier of the ventral side of a synchronous recipient. Their abilities to initiate a secondary embryo were measured by the incidence of secondary embryos and by the length of the secondary axis relative to the primary embryo. The ability was found to be localized in all cells (A1, B1, C1, and D1) of the dorsal most column and in the vegetal cells (C2 and D2) of the dorsolateral column. Transplanted C1 (subequatorial) cells caused the highest incidence of a secondary embryo and the average relative length of the secondary embryo was also greatest. Effectiveness decreased in the order: D1, B1, D2, C2, and A1. When these results were compared with Dale and Slack's fate map of the 32-cell embryo, it was concluded that the distribution of dorsal determinants is unique and does not coincide with the prospective regions for any tissues, though it is somewhat similar to the prospective region of dorsal endoderm or notochord. From these results it seems that dorsal determinants do not determine a particular tissue in an embryo but rather the "dorsal" region of an embryo.

Animals↗
PubMed1995

In vitro murine embryotoxicity of cyclophosphamide in embryos co-cultured with maternal hepatocytes: development and application of a murine embryo-hepatocyte co-culture model.

The technique of whole embryo culture provides a sensitive model to evaluate both the effects, and their underlying mechanisms, of drugs and environmental chemicals on embryonic development, independent of maternal influences. However, before teratogenic expression, many teratogens must be enzymatically bioactivated to toxic reactive intermediates. To detect such proteratogens, the embryo culture model may need to be coupled with an exogenous bioactivating system if maternal and/or placental metabolism is involved. We developed a similar embryo-hepatocyte co-culture system using embryos and maternal hepatocytes from mice, which often are more sensitive than rats to chemical teratogens, and which may have a balance of phase II drug metabolising enzymes more similar to humans. This murine system was then used to evaluate the relative maternal and embryonic contributions to cyclophosphamide embryopathy. Day 9.5 (morning of plug = day 1) murine embryos were co-cultured for 24 h in vitro with primary cultures of murine maternal hepatocytes (> 85% viability). Murine embryos were exposed to cyclophosphamide concentrations (0, 7.5, 15, 25 micrograms/ml), similar to those used in rat embryo culture studies. Murine embryos co-cultured with murine maternal hepatocytes developed normally, as did embryos exposed to cyclophosphamide in the absence of hepatocytes. Maternal hepatocytes were necessary for the expression of cyclophosphamide embryotoxicity, which was concentration-dependent, as demonstrated by increasing severity of reductions in crown rump length, yolk sac diameter and somite number. These results show that the co-culture of murine maternal hepatocytes and embryos is feasible, and suggest that maternal bioactivation is required for murine cyclophosphamide embryopathy.

Animals↗
PubMed2000

Impact of reducing the number of embryos transferred from three to two in women under the age of 35 who produced three or more high-quality embryos.

OBJECTIVE: To investigate the effect of a reduction in the number of good-quality embryos transferred in patients <35 years of age on pregnancy and multiple pregnancy rate. DESIGN: Prospective observational study with historical controls. SETTING: Academic tertiary referral unit. PATIENT(S): Three hundred eight patients <35 years of age undergoing IVF-ET. INTERVENTION(S): For patients who had three or more good quality embryos available for transfer, those in group 1 were given the option to have either two or three embryos replaced, whereas those in group 2 were allowed a maximum of two embryos transferred. In both groups, patients who had less than three good-quality embryos had the option to have three embryos transferred. MAIN OUTCOME MEASURE(S): Pregnancy and multiple pregnancy rates. RESULT(S): Patients in group 1, compared with those in group 2, had significantly more embryos (3 vs. 2) of significantly higher cumulative embryo score (31 vs. 24) transferred. This resulted in significantly higher multiple (57.8% vs. 30.8%) and triplet (15.6% vs. 1.4%) pregnancy rates in group 1. However, no difference in overall clinical pregnancy rate (37.2% vs. 41.2%) or live birth rate (28.1% vs. 29.4%) was observed between group 1 and 2. CONCLUSION(S): In women <35 years of age, who have three or more good-quality embryos available for transfer, a maximum of two embryos should generally be transferred.

Adult↗
PubMed1992

Human embryo biopsy on the 2nd day after insemination for preimplantation diagnosis: removal of a quarter of embryo retards cleavage.

OBJECTIVE: To assess any reduction in viability and development in vitro after biopsy of a quarter of the cells of human embryos on day 2 after insemination. DESIGN: A prospective study in which normally fertilized surplus embryos of good morphology with two to eight cells approximately 48 hours after insemination were randomly allocated to a control or biopsied group, respectively. SETTING: In vitro fertilization (IVF) unit and laboratories of the Hammersmith Hospital, Institute of Obstetrics and Gynaecology, London University. PATIENTS, PARTICIPANTS: One hundred twenty-nine embryos from 28 infertile IVF patients. INTERVENTIONS: Follicular aspiration by ultrasound-guided transvaginal puncture and embryo biopsy by micromanipulative procedures. MAIN OUTCOME MEASURE(S): Pyruvate uptake and cell number at the blastocyst stage. RESULTS: Embryo biopsy did not have an adverse effect on either the proportion developing to the blastocyst stage (50% [32 of 64] and 47.7% [31 of 65] for the control and biopsied groups, respectively) or embryo viability, measured indirectly through pyruvate uptake. However, the proportion of embryos that reached the morula stage after day 4 (retarded embryos) was significantly higher (44%, 11 of 25 versus 8.7%, 2 of 23) in the biopsied group. The total number of cells (29.6 +/- 3.1 versus 62.4 +/- 4.7), numbers of inner cell mass (7.7 +/- 2.2 versus 24.5 +/- 1.4) and trophectoderm (24.0 +/- 5.2 versus 45.0 +/- 6.4) cells, and the inner cell mass:trophectoderm ratio (34.7 +/- 7.9 versus 59.5 +/- 11.7) were strikingly reduced at the blastocyst stage in the biopsied group. This reduction was greater in embryos that reached the morula stage after day 4. CONCLUSIONS: More investigation is needed to assess whether the detrimental effects observed were because of the biopsy method used in this study or to a high sensitivity of human embryos at early stages to manipulation in vitro.

Biopsy↗
PubMed1998

Secondary donation of frozen embryos is more common after pregnancy initiation with donated eggs than after in vitro fertilization-embryo transfer and gamete intrafallopian transfer.

OBJECTIVE: To determine the availability of donated cryopreserved embryos. DESIGN: Retrospective review. SETTING: Community hospital-based donor oocyte program. PATIENT(S): Eighty-nine consecutive infertile couples and women who had 94 sets of embryos cryopreserved after pregnancy initiation with unfertilized donated eggs between January 1, 1991 and December 31, 1996. INTERVENTION(S): Cryopreservation of fertilized ova or cleaving embryos. MAIN OUTCOME MEASURE(S): Disposition of frozen embryos as of June 1, 1997. RESULT(S): Of the 94 sets of frozen embryos, 52 (55.3%) were thawed into the original recipient. At an average of 30 months since the treatment cycle, 26 (27.7%) sets of embryos remain in storage. Of the 16 sets of embryos not thawed for transfer, 11 sets (11.7%) were donated and 5 sets (5.3%) were destroyed. The fraction of spare embryos donated was much higher after pregnancy initiation with unfertilized donated eggs than after IVF-ET and GIFT (68.8% versus 19.1%, respectively). CONCLUSION(S): Couples and women who did not use their frozen embryos after pregnancy initiation with unfertilized donated eggs were twice as likely to donate them as to have them destroyed. Secondary donation of cryopreserved embryos was much more common after pregnancy initiation with unfertilized donated eggs than after standard IVF-ET and GIFT.

Adult↗
PubMed1999

Sibling embryo blastocyst development correlates with the in vitro fertilization day 3 embryo transfer pregnancy rate in patients under age 40.

OBJECTIVE: To examine the IVF day 3-ET pregnancy rate in patients under 40 with sibling embryo blastocyst development, compared with similar patients without blastocyst formation. DESIGN: Retrospective analysis. SETTING: Academic infertility center. PATIENT(S): One hundred twenty-five IVF day 3-ET patients under 40 with sibling embryos for extended culture. INTERVENTION(S): Extended culture of nontransferred sibling embryos for blastocyst development. MAIN OUTCOME MEASURE(S): Pregnancy and multiple gestation rates, number of oocytes, embryos formed, and embryos transferred. RESULT(S): Thirty-eight percent of patients became pregnant. Forty-eight percent of patients had sibling embryos develop to blastocyst. The blastocyst group had more oocytes retrieved (17.4+/-6.6 versus 14.4+/-5.6), more embryos formed (11.2+/-4.2 versus 8.8+/-3.2), and a higher clinical pregnancy rate (60% versus 18%) than the group without blastocyst development. CONCLUSION(S): Blastocyst transfer has been shown to improve implantation rates and reduce the risk of multiple gestations from assisted reproductive technology. Sibling embryo blastocyst development may reflect superior embryo quality, as manifested by increased IVF-ET pregnancy rates. In addition to predicting pregnancy in the current cycle, sibling embryo blastocyst development may provide information about the potential for fresh blastocyst transfer in subsequent cycles and help to identify patients at risk for multiple gestations.

Adult↗
PubMed2000

Embryo cryopreservation at the pronuclear stage and efficient embryo use optimizes the chance for a liveborn infant from a single oocyte retrieval.

OBJECTIVE: To estimate the potential for a liveborn in our program achieved through either fresh or frozen embryos derived from a single oocyte retrieval. DESIGN: Retrospective analysis. SETTING: A tertiary referral reproductive medicine unit. PATIENT(S): All consecutive patients undergoing oocyte retrieval from January 1, 1996, to June 30, 1997. INTERVENTION(S): All couples undergoing IVF-ET at our center are counseled about a specific embryo transfer number after oocyte retrieval based on demographic and historical factors. Only this specified number of embryos is retained in culture. All normally fertilized (2PN) oocytes exceeding this number are immediately cryopreserved at the pronuclear stage. For couples who do not conceive after fresh embryo transfers, frozen embryo transfers are subsequently performed by usually thawing only the number of embryos intended for transfer, thereby conserving remaining embryos for further potential frozen embryo cycles. MAIN OUTCOME MEASURE(S): Liveborn delivery per oocyte retrieval.39.0 years were 61.2%, 59.7%, and 18.5%, respectively. CONCLUSION(S): For women <39 years of age, the efficient use of embryo cryopreservation at the pronuclear stage and economical embryo utilization policies results in cumulative chances for a liveborn exceeding 60%.

Adult↗
PubMed1998

The characterization of bovine embryos obtained from prepubertal calf oocytes and their viability after non surgical embryo transfer.

We have previously shown that the addition of epidermal growth factor (EGF) during in vitro maturation was capable of stimulating the cytoplasmic maturation of cow and calf oocytes. The aim of the present study was to compare calf and cow blastocysts produced in the presence of EGF in terms of total cell number and cell distribution between trophectoderm (TE) and inner cell mass (ICM), pattern of protein synthesis, and ability to establish pregnancy after embryo transfer to recipients. For all experiment, embryos at Day 7 were obtained from IVM/IVF/IVC oocytes. No significant differences were noted in total cell number (cow = 138 +/- 46 vs calf = 142 +/- 59; mean +/- SD) or ICM and TE cell number between calf (ICM = 35 +/- 19, TE = 107 +/- 52) and cow (ICM = 38 +/- 21, TE = 99 +/- 32) blastocysts, nor in the ICM/total cell number ratio (cow = 0.27 +/- 11, calf = 0.25 +/- 12). No differences were noted in the constitutive and the neosynthetic protein profiles between cow and calf embryos obtained in vitro. The results of embryo transfer, showed that there was higher pregnancy loss following transfer of calf compared with cow embryos. After Day 35, the rate of pregnancy decreases, with only 22% of calf embryos maintaining pregnancy until calving compared with 39% for cow embryos. In conclusion, it would seem that embryos originating from calf oocytes are less capable of establishing pregnancies than embryos obtained from adult oocytes, although this difference was not significant. This low viability cannot be explained by differences in cell number or by the protein profiles identified between these 2 groups of embryos.

Abortion, Spontaneous↗
PubMed2006

Contribution of embryo cryopreservation to elective single embryo transfer in IVF-ICSI.

Single embryo transfer is the best way to reduce the risk of multiple pregnancy in IVF-intracytoplasmic sperm injection (ICSI). Between June 2002 and December 2004, all patients (first cycle, female age <38 years) were offered the choice between having one (SET) or two (DET) embryos transferred. Among 493 couples, 428 had at least two good quality embryos, and among them, 32% opted for SET. The SET and DET populations were not comparable (patients in the SET group were younger and had more oocytes retrieved), and therefore a paired, case-control analysis was performed involving 130 SET couples and 130 DET couples, matched according to the female partners' ages and the numbers of embryos available. All of the SET patients, and 82% of the DET group, had at least one embryo cryopreserved, (3.9 versus 2.8 embryos). The option of SET was continued for the frozen-thawed embryo transfers. The pregnancy rate following embryo transfer was significantly lower after SET compared with DET for both fresh (27.6 versus 36.9%; P < 0.05) and frozen-thawed (14.4 versus 23.5%) embryos. However, the cumulative live birth rates following the transfer of fresh and frozen embryos were identical between the two groups (43 versus 45%), with a high prevalence of twins following DET (34 versus 0%).

Adult↗
PubMed2003

Assessment of mammalian embryo quality: what can we learn from embryo morphology?

Embryo morphology assessment, however imperfect it may be, is at present the most popular method for embryo selection prior to transfer, both in human and bovine assisted reproduction. A major difference between human and bovine embryos is the fact that in the latter, assessment of morphology is jeopardized by the opacity of the blastomeres, which is caused by lipid droplet accumulation. This opacity makes it difficult to assess nuclear and nucleolar morphology, aspects which can easily be evaluated in human zygotes or early cleaving embryos. However, recent research which focused on correlation between bovine embryo morphology and embryonic ultrastructure, gene expression and cryoresistance, has provided evidence that much more can be deduced from mere embryo morphology than previously thought. Morphological features such as colour of the blastomeres, the extent of compaction, timing of blastocyst formation and expansion and diameter of the embryo at hatching can be linked with embryo quality. On the other hand, cattle embryos of deviant chromosomal constitution or with aberrant genetic make-up cannot be selected against by means of the current morphological techniques. Possible solutions include the visualization of bovine pronuclei at the zygote stage by means of ultracentrifugation or multiphoton laser scanning microscopy, and adjustment of genetic analysis in order to reconstruct embryo genetic make-up starting from the biopsy material.

Animals↗
PubMed1997

Perifusion culture system for bovine embryos: improvement of embryo development by use of bovine oviduct epithelial cells, an antioxidant and polyvinyl alcohol.

Three experiments were conducted in an attempt to improve a continuous flow-perifusion system capable of maintaining embryo development for long periods of time. Bovine embryos (8-16 cells) obtained from static co-culture with cumulus cells in a serum-free medium were perifused in an ACUSYST-S cell culture incubator. Culture chambers of the incubator consisted of a 0.2-mL unit (Chamber 1) connected to a 1.5-mL unit (Chamber 2), with the outflow from Chamber 1 routed to the inlet to Chamber 2. A bovine embryo culture medium supplemented with 3 mg mL-1 bovine serum albumin (BSA) and 25 mM HEPES was used as a perifusion culture medium (PCM). Embryos were perifused in Chamber 2 for 24, 48 and 72 h and further co-cultured in a static system up to 216 h after insemination. In Experiment 1, conditioning PCM with frozen-thawed bovine oviduct epithelial cells (BOEC) placed in Chamber 1 enhanced (P < 0.05) blastocyst formation of embryos in Chamber 2, after 24, 48 and 72 h of perifusion culture. The proportion of blastocysts was not further increased by placing BOEC in Chamber 2 along with the embryos. In Experiment 2, embryos were perifused with PCM conditioned with BOEC in Chamber 1 for 48 h or 72 h. A higher proportion of perifused embryos developed to the blastocyst stage after addition of 25 U mL-1 or 50 U mL-1 of superoxide dismutase (SOD) to PCM than in its absence. However, blastocyst formation of embryos perifused for 72 h was not increased after addition of 50 U mL-1 SOD compared with its absence. In Experiment 3, the proportions of morulae and blastocysts were not decreased by replacement of 3 mg mL-1 BSA with 1 mg mL-1 polyvinyl alcohol (PVA) in a BOEC-conditioned medium containing 50 U mL-1 SOD after perifusion for 48 h. In conclusion, PCM conditioning with BOEC and addition of an antioxidant to the perifusion medium improved the developmental capacity of perifused embryos. PVA is an adequate replacement for BSA in the perifusion medium.

Animals↗
PubMed2003

FISH analysis for chromosomes 13, 16, 18, 21, 22, X and Y in all blastomeres of IVF pre-embryos from 144 randomly selected donated human oocytes and impact on pre-embryo morphology.

BACKGROUND: The data are compiled from two multicentre, prospectively randomized studies on the effect of follicular fluid meiosis-activating sterol (FF-MAS) on human oocytes. The donated oocytes were exposed either to test doses of FF-MAS or to control solutions. The data from the control groups are presented with chromosomal status of the embryos correlated to embryo morphology. METHODS: The study includes 144 randomly selected donated human oocytes. The nucleus from each blastomere was fixed separately and fluorescence in-situ hybridization (FISH) using seven probes (13, 16, 18, 21, 22, X and Y) was performed. RESULTS: Analysis of 103 pre-embryos containing 479 blastomeres resulted in 424 blastomeres with clear FISH signals. Of these blastomeres, 55% were normal diploid and 45% were abnormal. At a pre-embryonic level, 53% were classified as normal containing >or=50% normal blastomeres while 31% of the pre-embryos were classified as uniformly normal. Abnormality rate was significantly increased in the pre-embryos with unevenly sized blastomeres and with increasing degree of fragmentation at 68 h after fertilization. Applying criteria for good embryo quality significantly increased the rate of chromosomally normal pre-embryos from 53 to 75%. CONCLUSIONS: The data demonstrate the high degree of genetic heterogeneity in a randomly selected pool of donated pre-embryos from an IVF programme. Further, we found that uniformity of blastomere size, degree of fragmentation and cleavage kinetics reflect the cytogenetic status of the pre-embryo and are therefore important in the selection of pre-embryos.

Blastomeres↗
PubMed1998

Autocrine mediators are required to act on the embryo by the 2-cell stage to promote normal development and survival of mouse preimplantation embryos in vitro.

Autocrine mediators released by the early embryo are implicated in the support of embryo development. Their mechanisms and timing of action, however, are uncertain. This study shows that their action is necessary during the 2-cell stage of development, at which time they do not act as classical growth factors, having no impact on the rate of cell-cycle progression. Rather, they act as survival factors, protecting embryos from subsequent cell death. Culture of zygotes for the first 48 h after insemination (but not the first 24 h only) at a high concentration of 1 embryo/microl before transfer to a concentration of 1 embryo/100 microl significantly improved development compared with culture at the lower concentration for 120 h. By contrast, if the initial 48 h of culture was at 1 embryo/100 microl, subsequent culture at 1 embryo/microl caused no improvement. Platelet-activating factor (PAF) supplementation (0.186 microM) of media for the 48-h period after insemination (but not 24 h only) improved the development of embryos cultured at low embryo concentrations (1 embryo/10 microl) even when transferred to PAF-free media for the subsequent 72-h culture period. The ability of PAF to mimic the effects of higher embryo density implicates embryo-derived PAF as one of the autocrine mediators stimulating early embryo development. The cell death that occurred at low embryo concentration had a mixed phenotype: some cells had lost membrane integrity whereas others had intact membranes but punctate or fragmented chromatin. It is concluded that the action of autocrine diffusible factors, including PAF, are necessary during the 2-cell stage for subsequent survival and normal development of embryos to the blastocyst stage.

Animals↗
PubMed1995

Before I was an embryo, I was a pre-embryo: or was I?

Issues surrounding human embryos are poignant and profound. Should research be conducted on them? Should they be discarded? Should they be donated to infertile couples? The Warnock Report was a landmark in providing guidelines limiting experimentation on human embryos to the first 14 days after fertilization, at which time implantation of the embryo is complete and the primitive streak has appeared. However, these embryological features were not considered sufficiently distinctive to bestow upon this 14-day period a separate classification. This situation changed when, in 1986, Anne McLaren suggested the use of the terms 'pre-embryo' or 'conceptus' to designate "the entire product of the fertilized egg up to the end of the implantation stage" and the term 'embryo' for "that small part of the pre-embryo or conceptus, first distinguishable at the primitive streak stage, that later develops into the foetus." In this paper we look critically at the term 'pre-embryo', and we shall present the case for an alternative set of terms, namely, embryo-placenta and embryo-fetus. We consider this latter to be biologically-based terminology, that does not have any connotation of restricted moral value as the term pre-embryo does for some.

Beginning of Human Life↗
PubMed2001

Generation of single-copy transgenic mouse embryos directly from ES cells by tetraploid embryo complementation.

BACKGROUND: Transgenic mice have been used extensively to analyze gene function. Unfortunately, traditional transgenic procedures have only limited use in analyzing alleles that cause lethality because lines of founder mice cannot be established. This is frustrating given that such alleles often reveal crucial aspects of gene function. For this reason techniques that facilitate the generation of embryos expressing such alleles would be of enormous benefit. Although the transient generation of transgenic embryos has allowed limited analysis of lethal alleles, it is expensive, time consuming and technically challenging. Moreover a fundamental limitation with this approach is that each embryo generated is unique and transgene expression is highly variable due to the integration of different transgene copy numbers at random genomic sites. RESULTS: Here we describe an alternative method that allows the generation of clonal mouse embryos harboring a single-copy transgene at a defined genomic location. This was facilitated through the production of Hprt negative embryonic stem cells that allow the derivation of embryos by tetraploid embryo complementation. We show that targeting transgenes to the hprt locus in these ES cells by homologous recombination can be efficiently selected by growth in HAT medium. Moreover, embryos derived solely from targeted ES cells containing a single copy LacZ transgene under the control of the alpha-myosin heavy chain promoter exhibited the expected cardiac specific expression pattern. CONCLUSION: Our results demonstrate that tetraploid embryo complementation by F3 hprt negative ES cells facilitates the generation of transgenic mouse embryos containing a single copy gene at a defined genomic locus. This approach is simple, extremely efficient and bypasses any requirement to generate chimeric mice. Moreover embryos generated by this procedure are clonal in that they are all derived from a single ES cell lines. This facilitates the comparative analysis of lethal alleles and thereby advances our ability to analyze gene function in mammals.

Alleles↗
PubMed2005

The formation of primordial germ cells from germline cells in spherical embryos derived from the blastodisc of 2-cell embryos in goldfish, Carassius auratus.

The property of primordial germ cells (PGCs) in fragmented goldfish embryos was investigated. When 1- and 2- cell embryos were cut at several perpendicular levels at the animal-vegetal axis, cells expressing vas mRNA were observed in the resultant embryos derived from all kinds of animal fragments. Blastodisc fragments from the 1- to 2-cell stage developed to spherical embryos containing yolk body with a yolk syncytial layer (YSL). Germ ring and no tail expression were not observed in the spherical embryo. When the spherical embryo labeled with tracer dye or GFP-nos1 3'UTR mRNA was transplanted onto the animal part of the blastoderm in a host embryo at the blastula stage, PGCs of spherical embryo origin were detected around the gonadal ridges in the resultant embryos which developed normally. These results suggest that small animal fragments should contain factors sufficient for PGC differentiation and that PGCs differentiate without mesoderm induction, since mesoderm is not induced in a spherical embryo.

Animals↗
PubMed1991

Using embryo sexing within closed mixed multiple ovulation and embryo transfer schemes for selection on dairy cattle.

Two types of multiple ovulation and embryo transfer schemes that included bull progeny testing were compared. In the juvenile schemes, embryos were collected at 16 to 18 mo of age without sexing, whereas, in the adult schemes, donors were chosen based on their first lactation record, and their embryos were systematically sexed. With the latter schemes, natural calves obtained at the first two calvings could compete with embryo transfer calves to be replacements. The optimal structure of this scheme was derived algebraically for the same number of transferred embryos as in the juvenile schemes. Predicted asymptotic annual genetic gains, after stabilization of genetic parameters taking into account the Bulmer effect, were found to be slightly in favor of the adult schemes for a given set of parameters (overall number of transferred embryos, number of embryos per collection, and embryo survival rate). In the adult schemes, the nucleus sizes were much larger than in the juvenile schemes, which allowed a higher selection differential on male paths, thus compensating for the longer generation interval. Asymptotic rate of genetic gain for Monte Carlo simulations were about 10 and 7% lower for juvenile and adult schemes, respectively, but still higher (20%) than the predicted value for the corresponding conventional scheme. Consequently, adult schemes with embryo sexing can be an efficient alternative to juvenile schemes without embryo sexing.

Animals↗