No abstract

The efficiency of cloning by somatic cell nuclear transfer (SCNT) is poor in livestock with w5% of transferred cloned embryos developing to term. SCNT is associated with gross placental structural abnormalities. We aimed to identify defects in placental histology and gene expression in failing ovine cloned pregnancies to better understand why so many clones generated by SCNT die in utero. Placentomes from SCNT pregnancies (nZ9) and age matched, naturally mated controls (nZ20) were collected at two gestational age ranges (105-134 days and 135-154 days; termZ147 days). There was no effect of cloning on total placental weight. However, cloning reduced the number of placentomes at both gestational ages (105-134 days: control 55.0G4.2, clone 44.7G8.0 and 135-154 days: control 72.2G5.1, clone 36.6G5.1; P!0.001) and increased the mean individual placentome weight (105-134 days: control 10.6G1.3 g, clone 18.6G2.8 g and 135-154 days: control 6.6G0.6 g, clone 7.0G2.0 g; P!0.02). Placentomes from cloned pregnancies had a significant volume of shed trophoblast and fetal villous hemorrhage, absent in controls, at both gestational age ranges (P!0.001) that was shown to be apoptotic by activated caspase-3 immunoreactivity. Consequently, the volume of intact trophoblast was reduced and the arithmetic mean barrier thickness of trophoblast through which exchange occurs was altered (P!0.001) at both gestational age ranges in clones. In addition, cloning reduced placental expression of key genes in placental differentiation and function. Thus, cloning by SCNT results in both gross and microscopic placental abnormalities. We speculate that trophoblast apoptosis, shedding, and hemorrhage may be causal in fetal death in ovine clones. Reproduction (2007) 133 243-255

No abstract

Central to this review is the knowledge that, in some livestock species, the environment in which fertilization and embryo development occurs influences not only preimplantation embryo development but also the phenotype of resulting offspring. This knowledge is based on in-vitro studies where the induced changes in the embryo can result in an array of developmental abnormalities after transfer including fetal overgrowth. Whilst such findings are of immediate relevance to assisted reproduction in the human, they also raise another equally important but less obvious issue. Can the in-vivo environments in which fertilization and embryo development normally occur be influenced by exogenous factors (either physical or chemical) in such a way that long-term development is adversely affected? In a global environment of increased use of synthetic chemicals and increased production of pollutants, it is an issue of growing relevance. This review examines technical information that is pertinent to these issues together with a brief assessment of some possible molecular mechanisms responsible for aberrant development. The review concludes with an assessment of the clinical significance of the findings.

The aim of this study was to compare serum-starved and non-starved donor cells in sheep nuclear transfer with a special emphasis on cloning outcomes. Sheep oocytes, derived either in vivo or in vitro, were fused with cultured serum-starved or actively growing adult granulosa cells. Resulting blastocysts were transferred to recipients fresh or after vitrification, and subsequent pregnancies followed to term. Donor cell treatment did not significantly affect preimplantation development, pregnancy rates, fetal loss or neonate survival rates. Of 22 lambs born, ten survived the immediate perinatal period but all succumbed at various timepoints within the first few weeks of life. The results of the study suggest that the use of serum-starved cells offers no advantages or disadvantages to cloning outcomes. Neither were significant differences in outcomes observed when using either in vivo- or in vitro-derived oocytes or embryos transferred fresh or after vitrification. Yet, these results continue to highlight problems associated with somatic cell cloning as indicated by offspring mortality. It remains unclear whether the high offspring mortality in the current study was related to species, associated with the cell lines used or the result of other causes.