C. E. Farin*, P. W. Farin†, and J. A. Piedrahita§
*Department of Animal Science, †Department of Population Health and Pathobiology, and §Department of Molecular Biomedical Sciences, North Carolina State University, Raleigh 27695-7621
ABSTRACT The establishment of in vitro fertilization and culture systems for mammalian embryos has facilitated the application of embryo technologies in research, industry, and clinical settings. Furthermore, the advent of cloning by nuclear transfer has significantly enhanced the potential for genetic modification of livestock. Based on studies in cattle, sheep, and mice, it has become apparent that embryos produced using these systems can differ in morphology and developmental potential compared with embryos produced in vivo. Referred to as “large offspring syndrome,” these abnormalities in the development of fetuses, placentas, and offspring are particularly evident following transfer of cloned embryos, but they also occur in pregnancies from embryos produced using in vitro culture alone. The objective of this review is to examine the effects of in vitro production and cloning on bovine embryo and fetal development. Literature pertaining to preimplantation embryo, conceptus, and fetal development, as well as gene expression occurring at each of these three stages, is reviewed. Physiologic and genetic mechanisms that contribute to large offspring syndrome also are discussed.Key Words: Bovine, Cloning, Fetus, In Vitro Embryo Production, Insulin-like Growth Factors
© 2004, by the American Society of Animal Science. All rights reserved.
J. Anim. Sci. 2004. 82(E. Suppl.):E53-E62
Implications
Production of livestock embryos using in vitro systems represents a low-cost alternative to production of embryos in vivo. Furthermore, the use of cloning provides an alternative method for propagating genetically valuable animals and facilitates techniques for genome modification. Embryos produced using in vitro production and cloning systems can differ in morphology and developmental potential from those produced in vivo. Similarly, conceptuses, fetuses, and offspring resulting from in vitro-produced or cloned embryos can differ in their morphology, physiology, and expression of developmentally important genes compared with in vivo controls. Mechanisms proposed to explain how laboratory environments influence development of in vitro-produced and cloned embryos focus on the modification of epigenetic patterns that can affect gene expression without altering primary DNA sequences. Understanding these mechanisms will facilitate the refinement of IVP and cloning systems and the production of embryos comparable to in vivo.
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