A method for culture of micromanipulated sheep embryos and its use to produce monozygotic twins

Abstract

MICROSURGICAL techniques have proved valuable for investigations of the regulatory capacity of early mammalian embryos, including the developmental potential of single blastomeres from two-, four- and eight-celled embryos (see ref. 1 for review). However, the usefulness of radical microsurgery in experiments on early cleavage stages has been restricted largely to species in which such young embryos may be cultured in vitro, notably the mouse, as, in most instances, embryos less advanced than the late morula stage fail to survive in vivo if the zona pellucida has been removed or substantially damaged^2–6. There has been no satisfactory method for culture in vitro of early cleavage stages in the sheep, and consequently there have been few reports of attempts to micromanipulate early sheep embryos^7–9. I describe here a method whereby micromanipulated eggs can be protected during their early development in vivo and its use in an investigation of the developmental potential of single blastomeres from two-celled sheep embryos with the aim of producing monozygotic twins. The method involves coating the eggs with agar after microsurgery so as to seal defects produced in the zona pellucida.