Totipotency and normal differentiation of single teratocarcinoma cells cloned by injection into blastocysts.

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Abstract
A definitive test for developmental totipotency of mouse malignant teratocarcinoma cells was conducted by cloning singly injected cells in genetically marked blastocysts. Totipotency was conclusively shown in an adult mosaic female whose tumor-strain cells had made substantial contributions to all of the wide range of its somatic tissues analyzed; the clonally propagated cell lineage had differentiated in numerous normal directions. The test cells were from cores of embryoid bodies of a euploid, chromosomally male (X/Y), ascites tumor grown only in vivo by transplantation for 8 yr. The capacity of cells from the same source to differentiate, in a phenotypic male, into reproductively functional sperms, was shown previously. Cells from this transplant line provide material suitable for projected somatic and germ-like genetic analyses of mammalian differentiation based on cycling of mutation-carrying tumor cells through developing embryos. In some animals obtained from single-cell injections, tumor-derived cells were sporadically distributed in developmentally unrelated tissues. These cases can be accounted for by delayed and haphazard cellular integration, and by a marked degree of sustained cellular developmental flexibility in early mammalian development, irrespective of certain classical germ-layer designations. All mosaic mice obtained have thus far been free of teratomas. In 1 case, the injected stem cell contributed only to the pancreas and gave rise to a malignancy resembling pancreatic adenocarcinoma. The high modal frequency of euploidy in these individually tested cells tends to indicate that a near-normal chromosome complement is sufficient for total restoration of orderly gene expression in a normal embryonic environment; it may also be necessary for teratoma stem-cell proliferation to be terminated there.