Regeneration of endoderm from primitive ectoderm in the mouse embryo: fact or artifact?
The publishers regret that there is an error on page 323 of this article. The last paragraph should read as follows:
The fact that individual 5th day primitive ectoderm cells can give rise to both somatic cells and functional gametes (Gardner, 1978a) argues that they retain genomic totipotency. Nevertheless, results obtained in the present study and in earlier blastocyst injection experiments (Gardner & Rossant, 1979; Gardner, 1982) do not support the conclusion that these cells remain undetermined until 2 days or so after implantation. Rather, they suggest that both primitive ectoderm and primitive endoderm cells become restricted to mutually exclusive lineages more or less synchronously, some time between 
and 
days post coitum. So far, extraembryonic-endoderm-like cells have only been obtained unequivo-cally from primitive ectoderm following its exposure to conditions of terato-carcinogenesis (Graham, 1977). In view of current ignorance of events underlying this process and uncertainty as to whether the target for neoplastic conversion is the primitive ectoderm cell itself or one of its lineal descendants, it is not clear what relevance, if any, such findings have to the problem of stability of ectodermal determination. There are also indications that primitive-endoderm-derived cells may exhibit metaplasia in certain circumstances (Lu, Sobis, Van Hove & Vandeputte, 1984). Nevertheless, it would appear that both types of mature ICM cell have undergone sufficiently stable differentiation by the late blastocyst stage to render their interconversion during subsequent embryogenesis a most unlikely event.
