B. Avery
University of Copenhagen
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by B. Avery.
Biology of Reproduction | 2003
Jakob O. Gjørret; Hiemke M. Knijn; S.J. Dieleman; B. Avery; Lars-Inge Larsson; Poul Maddox-Hyttel
Abstract The postimplantation developmental potential of embryos can be affected by various forms of cell death, such as apoptosis, at preimplantation stages. However, correct assessment of apoptosis is needed for adequate inference of the developmental significance of this process. This study is the first to investigate the independent chronological occurrence of apoptotic changes in nuclear morphology and DNA degradation (detected by the TUNEL reaction) and incidences of nuclei displaying these features at various preimplantation stages of bovine embryos produced both in vivo and in vitro. Different elements of apoptosis were observed at various developmental stages and appeared to be differentially affected by in vitro production. Nuclear condensation was observed from the 6-cell stage in vitro and the 8-cell stage in vivo, whereas the TUNEL reaction was first observed at the 6-cell stage in vitro and the 21-cell stage in vivo. Morphological signs of other forms of cell death were also observed in normally developing embryos produced both in vivo and in vitro. The onset of apoptosis seems to be developmentally regulated in a stage-specific manner, but discrete features of the apoptotic process may be differentially regulated and independently modulated by the mode of embryo production. Significant differences in indices of various apoptotic features were not evident between in vivo- and in vitro-produced embryos at the morula stage, but such differences could be observed at the blastocyst stage, where in vitro production was associated with a higher degree of apoptosis in the inner cell mass.
Theriogenology | 1991
B. Avery; V. Madison; T. Greve
In vitro fertilized bovine embryos were karyotyped at Day 7 and Day 8 post insemination. The results showed that the percentage of males (sex ratio) was dependent on the developmental stage. Among expanded blastocysts (the most advanced embryos), the sex ratio was 100%, followed by 89% for expanding blastocysts, 75% for blastocysts, and 40% for young blastocysts, all analyzed at Day 7. For embryos karyotyped at Day 8, the sex ratio was 20%. The average mitotic index for all in vitro fertilized embryos was 3.5%. These results suggest that the apparent relationship between sex and developmental rate could be used as a method for noninvasive sexing of in vitro fertilized embryos.
Animal Reproduction Science | 1992
Valerie Madison; B. Avery; Torban Greve
Abstract These experiments were conducted to determine whether the compactness and quantity of follicle cells (corona radiata and cumulus cells) could be used as criteria for the selection of immature bovine oocytes for their developmental potential in vitro. Oocytes were divided into three categories: (I) oocytes surrounded by compact, multi-layers of follicle cells; (2) oocytes with compact layers of corona radiata cells only; (3) oocytes with less compact and fewer layers of follicle cells. The frequencies of normal penetration, cleavage to the 6–16-cell stage on Day 3 post-insemination and blastocyst formation by Day 8–10 were the endpoints for evaluation. Oocytes of each category underwent normal penetration at a similar frequency. Greater proportions of oocytes in Categories 1 and 2 cleaved (38.1% and 36.9%, respectively), compared to those in Category 3 (27.0%) (P = 0.014 and P = 0.010, respectively). Oocytes of Category 1 developed to the blastocyst stage at a significantly greater frequency than oocytes of Category 3 (24.5% and 14.9%, respectively, P = 0.010). The rate of blastocyst development for Category 2 was similar to that of Categories 1 and 3. The results presented indicate that visual assessment of the follicle cell investment surrounding immature bovine oocytes can be used to select oocytes most capable of embryonic development in vitro following maturation and fertilization in vitro.
Molecular Reproduction and Development | 1996
Dorthe Viuff; B. Avery; T. Greve; W.A. King; Poul Hyttel
The objectives of this study on in vitro produced bovine two‐ and four‐cell embryos were (1) to investigate the uptake of 3H‐uridine through the plasma membrane, (2) to characterize the pattern of RNA synthesis during the second cell cycle, and (3) to measure the incorporation of 3H‐uridine into de novo synthesized RNA. A total of 200 embryos were incubated with 3H‐uridine for 15, 30, 60 (two‐ and four‐cell embryos), 120 (four‐cell embryos), 180 (two‐cell embryos), and 240 min (two‐ and four‐cell embryos), respectively. 3H‐uridine uptake reached a maximum by 30 min in two‐cell embryos, whereas four‐cell embryos reached a maximum at 120 min. A total of 440 two‐cell embryos were isolated 27–33 hr postinsemination (hpi), and 90 of these were incubated for 10 hr with 3H‐uridine (200 μCi/ml). The remainder were incubated with 3H‐uridine for 3 hr starting at 0–3 (n = 54), 3–6 (n = 75), 6–9 (n = 77), or 9–12 (n = 77) hr after cleavage to the two‐cell stage. Control two‐cell embryos (n = 67) were incubated with 3H‐uridine supplemented with 5 mg/ml of unlabelled uridine for 10 hr (inhibition control), or they were incubated with 3H‐uridine for 10 hr and RNase treated (100 μg/ml post fixation (RNase control). Subsequently, the embryos were processed for autoradiography. The long‐term incubation revealed transcription (autoradiographically labelled nuclei) in a total of 77% of the two‐ and four‐cell embryos. No transcription was observed in any of the 3 hr incubation groups. The RNase control embryos lacked labelling of the nuclei, whereas the inhibition control embryos only showed markedly reduced labelling. Finally, total RNA extraction was performed on a total of 336 two‐cell embryos that were incubated with 3H‐uridine or 3H‐uridine supplemented with unlabelled uridine for 2, 5, or 10 hr. It was possible to detect an increasing amount of labelled RNA after the 2, 5, and 10 hr incubation periods, and it was possible to inhibit this incorporation competitively. Together the data demonstrate a low level of transcription during the second cell cycle without a well‐defined transcriptional peak.
Theriogenology | 1996
Mette Schmidt; T. Greve; B. Avery; Jean-François Beckers; José Sulon; H.B. Hansen
Pregnancy, parturition and calf survival following the transfer of embryos produced in vitro were monitored. A total of 44 blastocysts was transferred in pairs to 1 uterine horn ipsilateral to the corpus luteum (CL) of 22 synchronized heifers. At Day 42 of development 14 recipients (64%) were pregnant; the calving rate was also 64%. The twinning rate was 9/14 at Day 42 and 7/14 at birth, for an overall fetal mortality rate of 9%. The average gestation length was 281 and 275 d for single and twin pregnancies, respectively. Blood samples from recipients were collected for determination of bovine pregnancy associated glycoprotein (bPAG) from 2 wk after transfer and throughout the pregnancy. During the first trimester of pregnancy, the bPAG concentration was significantly higher in twin than in single bearing heifers, and the perinatal increase in bPAG was correlated positively with the total weight of the fetus(es). The percentage of male calves was 43%. The birth weight of twin individuals was 25 +/- 1 kg, which was 78% of the birthweight of the singletons (32 +/- 2 kg). One singleton calf was oversized, weighing 58 kg (80% more than the median weight of the other singletons). Stillbirths occurred in 21% of the twins, butin none of the singletons. Calf mortality during the first 14 d was higher for twins (4/11) than for singletons (1/7) due to infections and cerebellar hypoplasia. Karyotyping the calves detected no cytogenetically recognizable abnormalities. All calves were negative for BVD virus and IBR antibodies. The results of this study showed that although the incidence of fetal loss was low, there was an unacceptable high perinatal mortality of the calves. Thus it is likely that the blood supply through the placenta of animals pregnant with twins was impaired or it is possible that these fetuses and calves had increased stress susceptibility caused by the in vitro conditions. Furthermore, the birth of 1 oversized calf, 2 calves with cerebellar hypoplasia and 5 calves succumbing to infections seems to indicate that a proportion of in vitro produced calves may suffer from factors inherent in the in vitro production system.
Biology of Reproduction | 2000
Dorthe Viuff; T. Greve; B. Avery; Poul Hyttel; Per B. Brockhoff; Preben D. Thomsen
Abstract Availability of embryos of high quality is required to obtain satisfactory embryonic developmental rates and normal calves following transfer of in vitro-produced (IVP) bovine embryos. One relevant quality parameter is the frequency of chromosome aberrations, which can be evaluated using multicolor fluorescent in situ hybridization (FISH) with chromosome 6- and chromosome 7-specific probes in cattle. In this study, interphase nuclei (n = 3805) were analyzed from 426 bovine IVP embryos. We found that 73%, 72%, 81%, and 58% of the embryos from Days 2, 3, 4, and 5 post-insemination (pi), respectively, displayed a normal diploid chromosome number in all cells. When looking at the types of chromosome aberrations, the percentages of mixoploidy at Days 2, 3, 4, and 5 pi were 22%, 15%, 16%, and 42%, respectively, whereas the percentages of polyploidy (i.e., all nuclei in an embryo were analyzed and were polyploid) were 5%, 13%, 3%, and 0%, respectively. In conclusion, numerical chromosome aberrations were detected as early as Day 2 pi. The development of polyploid embryos is slow and is apparently arrested during the third cell cycle, whereas the mixoploid embryos seem to continue development.
Molecular Reproduction and Development | 1998
B. Avery; Anders Hay-Schmidt; Poul Hyttel; T. Greve
The developmental competence of bovine follicular oocytes that had been meiotically arrested with the phosphokinase inhibitor 6‐dimethylaminopurine (6‐DMAP) was studied. After 24 h in vitro culture with 2 mM 6‐DMAP, 85 ± 12% of the oocytes were at the germinal vesicle stage compared to 97 ± 3% at the start of culture (P > 0.05). After release of the 6‐DMAP inhibition, followed by 24 h IVM, 82 ± 18% were at MII stage, compared with 93 ± 7% in the control group (P > 0.05). The 6‐DMAP oocytes displayed a much higher frequency of abnormal MII configurations than the control oocytes (67% vs 23%; P < 0.0001). In addition spontaneous oocyte activation was more frequent than among control oocytes (5% vs 0.3%; P 0.0006). After IVF of 6‐DMAP oocytes, normal fertilization was lower (76 ± 8% vs 89 ± 7%; P < 0.01), oocyte activation higher (11 ± 5% vs 2 ± 2%; P < 0.01), and polyspermy slightly but not significantly higher (8 ± 7% vs 4 ± 4%; P > 0.05), compared with the control group. Cleavage was lower (61 ± 13% vs 81 ± 6%; P < 0.001), as well as day 8 blastocyst formation (17 ± 7% vs 36 ± 8%; P < 0.001). The MII kinetics was different for 6‐DMAP and control oocytes. Maximum MII levels were reached at 22 h IVM in both groups, but 50% MII was reached at 17 h in 6‐DMAP oocytes, compared to 20 h in control oocytes. Ultrastructure of MII oocytes was similar in the two groups, but in 6‐DMAP oocytes the ooplasmic vesicle pattern at GV was at a more advanced stage than in control oocytes. In conclusion, 6‐DMAP exposure of GV oocytes prior to IVM induce asynchronous cytoplasmic maturation, leading to aberrant MII kinetics. Thus, at the time of insemination a smaller cohort of oocytes will be at the optimal stage for normal fertilization and subsequent blastocyst development. Mol. Reprod. Dev. 50:334–344, 1998.
Biology of Reproduction | 2005
Morten Vejlsted; B. Avery; Mette Schmidt; T. Greve; Natalie Alexopoulos; Poul Maddox-Hyttel
Abstract The epiblast represents the final embryonic founder cell population with the potential for giving rise to all cell types of the adult body. The pluripotency of the epiblast is lost during the process of gastrulation. Large animal species have a lack of specific markers for pluripotency. The aim of the present study was to characterize the bovine epiblast cell population and to provide such markers. Bovine Day 12 and Day 14 embryos were processed for transmission-electron microscopy or immunohistochemistry. In Day 12 embryos, two cell populations of the epiblast were identified: one constituting a distinctive basal layer apposing the hypoblast, and one arranged inside or above the former layer, including cells apposing the Rauber layer. Immunohistochemically, staining for the octamer-binding transcription factor 4 (OCT4, also known as POU5F1), revealed a specific and exclusive staining of nuclei of the complete epiblast. Colocalization of vimentin and OCT4 was demonstrated. Only trophectodermal cells stained for alkaline phosphatase. Staining for the proliferation marker Ki-67 was localized to most nuclei throughout the epiblast. A continuous staining for zonula occludens-1 protein was found between cells of the trophectoderm and hypoblast but was not evident in the epiblast. A basement membrane, detected by staining for laminin, formed a “cup-like” structure in which the epiblast was located. The ventrolateral sides of the cup appeared to be incomplete. In conclusion, the bovine epiblast includes at least two cell subpopulations, and OCT4 was shown, to our knowledge for the first time, to be localized exclusively to epiblast cells in this species.
Biology of Reproduction | 2000
J. Laurincik; P.D. Thomsen; Anders Hay-Schmidt; B. Avery; T. Greve; R.L. Ochs; Poul Hyttel
Abstract The aim of the present investigation was to describe the basic cell biology of the postfertilization activation of rRNA genes using in vitro-produced bovine embryos as a model. We used immunofluorescence confocal laser scanning microscopy and transmission electron microscopy to study nucleolar development in the nuclei of embryos up to the fifth postfertilization cell cycle. During the first cell cycle (1-cell stage), fibrillarin, upstream binding factor (UBF), nucleolin (C23), and RNA polymerase I were localized to distinct foci in the pronuclei, and, ultrastructurally, compact spherical fibrillar masses were the most prominent pronuclear finding. During the second cell cycle (2-cell stage), the findings were similar except for a lack of nucleolin and RNA polymerase I labeling. During the third cell cycle (4-cell stage), fibrillarin, UBF, nucleophosmin, and nucleolin were localized to distinct foci. Ultrastructurally, spherical fibrillar masses that developed a central vacuole over the course of the cell cycle were observed. Early in the fourth cell cycle (8-cell stage), fibrillarin, nucleophosmin, and nucleolin were localized to small bodies that with time developed a central vacuole. UBF and topoisomerase I were localized to clusters of small foci. Ultrastructurally, spherical fibrillar masses with a large eccentric vacuole and later small peripheral vacuoles were seen. Late in the fourth cell cycle, nucleophosmin and nucleolin were localized to large shell-like bodies; and fibrillarin, UBF, topoisomerase I, and RNA polymerase I were localized to clusters of small foci. Ultrastructurally, a presumptive dense fibrillar component (DFC) and fibrillar centers (FCs) were observed peripherally in the vacuolated spherical fibrillar masses. Subsequently, the presumptive granular component (GC) gradually became embedded in the substance of this entity, resulting in the formation of a fibrillo-granular nucleolus. During the fifth cell cycle (16-cell stage), a spherical fibrillo-granular nucleolus developed from the start of the cell cycle. In conclusion, the nucleolar protein compartment in in vitro-produced preimplantation bovine embryos is assembled over several cell cycles. In particular, RNA polymerase I and topoisomerase I are detected for the first time late during the fourth embryonic cell cycle, which coincides with the first recognition of the DFC, FCs, and GC at the ultrastructural level.
Theriogenology | 1989
B. Avery; A. Bak; Mette Schmidt
The purpose of this study was to determine whether a correlation between embryonic cleavage rates and sex ratios in dairy cattle could be substantiated. Embryos were collected at Day 7 after estrus following superovulation and artificial insemination. Embryos from flushings where at least two different developmental stages within the same flushing could be identified were examined. A total of 476 such embryos was transferred to recipients and 110 calves were born. The sex effect was only demonstrable in flushings yielding embryos of at least three different developmental stages. The sex ratios from this group were 32%, 58% and 62% in the slow, intermediate and fast developing groups of embryos, respectively. The deviations were not significant (P = 0.084). Only 23% of the flushings provided embryos that fell into this cathegory, which limits the use of differential cleavage rates as a sexing method, unless additional embryo culture is introduced to the technique.