Showing papers by "Ian Wilmut published in 1993"

Nuclear-cytoplasmic interactions during the first cell cycle of nuclear transfer reconstructed bovine embryos: implications for deoxyribonucleic acid replication and development

Abstract: The present study investigated the decay of maturation-promoting factor (MPF) activity in electrically activated in vitro-matured bovine oocytes and examined the influence of the cell cycle stage of both the donor nucleus and the recipient cytoplasm upon the morphology and DNA synthesis potential of the donor nucleus in reconstructed embryos The decay of MPF activity was studied both biochemically in electrically activated in vitro-matured oocytes and by morphological examination of nuclear structure in reconstructed bovine embryos As measured by H1 kinase activity in groups of 10 oocytes, the level of MPF declined rapidly to 30 +/- 4% (of the maximum level in unactivated control oocytes) at 60 min and reached a basal level of 20 +/- 6% at 120 min This level of activity was then maintained until at least 9 h postactivation In contrast, when MPF activity was assayed by morphological examination of nuclei in individual reconstructed embryos, the decline in activity occurred over a period of 9 h postactivation DNA synthesis of nuclei arrested at the G1/S border and in G2 phases of the cell cycle was examined in embryos reconstructed at the time of oocyte activation, ie, when MPF levels were maximal, and by fusion 10 h postactivation, when no MPF activity could be detected All nuclei transferred at the time of oocyte activation underwent nuclear envelope breakdown (NEBD) and subsequent DNA synthesis However, when nuclei were transferred 10 h after activation, no NEBD was observed in any nuclei Nuclei arrested at the G1/S border or nuclei in S phase when transferred in the absence of NEBD underwent DNA synthesis, while no DNA synthesis was observed in G2 nuclei transferred into this cytoplasmic environment The results presented show that all nuclei, regardless of cell cycle stage, undergo DNA replication when transplanted into metaphase II (MeII) cytoplasts in which MPF activity is high From these observations we would suggest that one factor that may contribute to the present low frequency of development of bovine nuclear transfer embryos is the ploidy of the reconstructed embryo after the first cell cycle In order to maintain correct ploidy of the reconstructed embryo, only G1 nuclei should be transferred at the time of activation, when MPF levels are high In contrast, when the integrity of the nuclear membrane is maintained by transfer at 10 h postactivation, when MPF activity is absent, the rereplication of G2 nuclei is prevented and correct ploidy of the reconstructed embryo may be maintained

Effect of recombinant bovine somatotropin on the superovulatory response to pregnant mare serum gonadotropin in heifers.

Abstract: Treatment of mature heifers with recombinant bovine somatotropin (BST) increases the number of ovarian follicles of 2-5 mm in diameter. This study was carried out to investigate whether the increase in the number of small follicles induced by BST treatment can enhance the superovulatory response. In the first experiment, 24 heifers were assigned, in a randomized block design, to four treatment groups: 1) control; 2) BST; 3) pregnant mare serum gonadotropin (PMSG); 4) BST+PMSG. On Day 7 of the estrous cycle, animals in groups 2 and 4 received injections of 320 mg BST (in a sustained release formulation), while heifers in groups 1 and 3 received 10 ml saline. Five days later heifers in groups 3 and 4 were treated with a single dose of 2000 IU PMSG to induce superovulation. Embryos were recovered nonsurgically on Days 6-8 of the following cycle, and all heifers underwent laparoscopy on Day 9 to assess ovulation rate. In a second experiment, 24 heifers were assigned randomly to four treatment groups: 1) PMSG (1000 IU); 2) BST (320 mg) + PMSG (1000 IU); 3) PMSG (2000 IU); 4) BST (320 mg) + PMSG (2000 IU), and then treated as for experiment I. In both experiments, all heifers were scanned daily using real-time ultrasound from the day before BST injection until the day of ovulation to monitor dynamics of ovarian follicular growth and development, and blood samples were collected daily throughout the experimental period for measurement of peripheral progesterone, estradiol-17 beta, growth hormone (GH), and insulin-like growth factor-I (IGF-I).(ABSTRACT TRUNCATED AT 250 WORDS)

Reproductive performance in relation to uterine and embryonic traits during early gestation in Meishan, large white and crossbred sows

Abstract: Previous studies have shown that females of the Chinese Meishan breed and of their F1 cross with European Large White pigs are very prolific, producing about four more piglets per litter than control Large White females The main cause of this prolificacy is enhanced prenatal survival for a given ovulation rate in Meishan and F1 females and this is controlled by genes of the mother, not those of the conceptus The objectives of this study were to determine whether genotypic differences in embryo survival were apparent in the period immediately after attachment and to compare embryonic and uterine development at this time Sows in their third parity (20 Large White, 14 Meishan, 25 Large White x Meishan F1 and 25 Meishan x Large White F1) were killed 20-22 days after mating and their reproductive tracts recovered for further study There were significant differences between the purebred sows, and crossbred sows were approximately intermediate for the number of corpora lutea (207 +/- 09, 278 +/- 11, 224 +/- 08 and 233 +/- 08 for the four genotypes, respectively), the number of embryos (152 +/- 09, 234 +/- 11, 172 +/- 08 and 188 +/- 08, respectively) and the proportionate embryo survival (074 +/- 004, 084 +/- 004, 078 +/- 003 and 082 +/- 003, respectively) There was a negative association within genotype between embryo survival and the number of corpora lutea Adjusting for the genotypic difference in the number of corpora lutea increased the genotypic differences in embryo survival(ABSTRACT TRUNCATED AT 250 WORDS)