title: New evidence for monozygotic twins in the mouse: twinning initiated in the late blastocyst can account for mirror image asymmetries.
abstract: The 11.5-day twin mice reported here support one of the classically described mechanisms for mammalian monozygotic twinning: subdivision of the blastocyst inner cell mass at the stage of proamnion cavitation. This particular method for monozygotic twinning has the attraction of providing a hypothesis for mirror image translocation of asymmetric traits. Monozygotic twins in laboratory rodents at or near parturition have not been identified and only two prior descriptions, for 7.5- and 9.5-day mouse embryos, have been found in the literature. Experimentally induced twins having identical heredity, i.e., clones, would enable study of heritable and environmental regulation of the components of discordance. A set of twin mouse embryos at 11.5 days of gestation within a common yolk sac, and with shared vitelline and allantoic circulations, provides direct evidence that monozygotic twin mice can survive rotation within the common yolk sac and suggests a reasonable probability that they can survive to term.
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000502:physiology*; D005260:Female; D006801:Humans; D051379:Mice / Q000196:embryology / Q000235:genetics*; D011247:Pregnancy; D012399:Rotation; D013997:Time Factors; D014427:Twins; D014430:Twins, Monozygotic; D014817:Vitelline Membrane / Q000098:blood supply