Advances in biotechnology in recent decades have revolutionized our understanding of early mammalian development and promise to provide ever more finely tuned and precisely targeted techniques for genetic enhancement of domestic animal species. In demonstrating what is both technically and biologically possible, not only in mice but also in larger animal species, research has provided hope that previously intractable diseases and genetic defects can be successfully combated. Crucial to this research is the ability to culture oocytes, embryos and somatic cells in vitro and to sustain their development without inducing adverse short- or long-term consequences. There is a need to refine current culture strategies in farm animal species to avoid jeopardizing their dependent technologies. A key to resolving current limitations of culture strategies is to identify, acknowledge and then address those features of in vitro culture that compromise early regulation of mammalian development. The aim of this review is to appraise critically in vitro embryo and somatic cell production strategies in the context of their impact on developmental competence and normality at embryonic, fetal and later stages. In addition, effects of physically manipulating embryos and cells, most notably via nuclear and gene transfer technologies, are considered with a view to identifying how detrimental consequences can be avoided.
TG McEvoy, JJ Robinson and KD Sinclair
LE Young, KD Sinclair and I Wilmut
Bovine and ovine embryos exposed to a variety of unusual environments prior to the blastocyst stage have resulted in the development of unusually large offspring which can also exhibit a number of organ defects. In these animals, the increased incidence of difficult parturition and of fetal and neonatal losses has limited the large-scale use of in vitro embryo production technologies commonly used in humans and other species. Four different situations have been identified that result in the syndrome: in vitro embryo culture, asynchronous embryo transfer into an advanced uterine environment, nuclear transfer and maternal exposure to excessively high urea diets. However, programming of the syndrome by all of these situations is unpredictable and not all of the symptoms described have been observed universally. Neither the environmental factors inducing the large offspring syndrome nor the mechanisms of perturbation occurring in the early embryo and manifesting themselves in the fetus have been identified.
CA Maltin, MI Delday, KD Sinclair, J Steven and AA Sneddon
The possibility that early fetal programming affects health or disease status in adult life has been considered in relation to tissues such as the cardiovascular system but not with respect to skeletal muscle. Since muscle mass and function are important for life, it is pertinent to ask whether events during the development of muscle in utero can affect the performance of the tissue in later life. This review discusses the factors that influence muscle performance, outlines the current understanding of myogenesis and examines how manipulations alter myogenic outcome after birth. The performance of muscle is determined by the number, type and size of the muscle fibres, these in turn being affected by a number of factors, and the evidence indicates that the proportions of types of muscle fibre have a heritable component. The formation of muscle occurs early in embryogenesis and it appears that the major impacts on myogenesis are associated with extremes of treatment or embryo manipulations. The impact of extremes of treatment or embryo manipulations on myogenesis is seen in the secondary fibres whereas primary fibres appear to be insensitive or protected. Overall, the opportunities for manipulation of myogenesis in utero to improve adult performance are limited.
PG Pushpakumara, RS Robinson, KJ Demmers, GE Mann, KD Sinclair, R Webb and DC Wathes
Early mammalian embryo development in vitro can be enhanced by co-culture with oviductal cells and by the addition of insulin-like growth factors (IGFs). This study examined the expression patterns of the oviductal IGF system in cattle in relation to the number of days after oestrus and the presence or absence of embryos. Oviducts were collected from: (i) 66 nulliparous heifers on day 3, day 6 or day 16 after insemination and from (ii) ten non-pregnant, lactating cows on day 0 or day 1 of the oestrous cycle. Oviducts were coiled, frozen whole and sectioned for in situ hybridization. Expression patterns of mRNAs encoding IGF-I, IGF-II, type 1 IGF receptor (IGF-1R), and the IFG binding proteins (IGFBP)-1, -3 and -5 were determined from autoradiographs. Separate measurements were made for the mucosa and muscle layers of the infundibulum, ampulla and isthmus. None of the parameters measured differed between heifers with or without the presence of an embryo. mRNAs encoding IGF-I and IGF-1R were present in the mucosa and muscle of all three oviductal regions, and the highest value of IGF-I mRNA was measured in heifers on day 3. IGF-II mRNA was expressed predominantly in the muscle wall. IGFBP-1 mRNA was not detectable, whereas mRNAs encoding IGFBP-3 and -5 were expressed in both the muscle and mucosa. IGFBP-3 expression was higher in cows on day 0 and day 1 of the oestrous cycle than in heifers on day 3, day 6 and day 16 after insemination. A peak of IGFBP-5 expression was reached on day 6. Locally or systemically produced IGFs, regulated by IGFBPs, may act directly on the embryo or indirectly via modulation of oviductal secretions and muscular activity to influence the success of early embryo development.