Deficiency of genomic reprogramming in trophoblast stem cells following nuclear transfer.

To examine the genomic reprogrammability of trophoblast stem (TS) cells using a nuclear transfer technique, we produced TS cloned embryos using five TS cell lines from three strains of mice (ICR, B6D2F1, and B6CBF1) as donors and observed developmental ability during preimplantation development. The developmental rates of the TS cloned embryos that developed to the two-cell, four- to eight-cell, morula, and blastocyst stages were 58-83%, 0-38.6%, 0-21.3%, and 0-15.9%, respectively, indicating that more than 50% of TS cloned embryos arrested at the two-cell stage. These TS cloned two-cell embryos were expressed low level of Dappa3 (also known as PGC7/Stella), indicating that zygotic gene activation (ZGA) was disrupted in these embryos. However, a small portion of the TS cloned embryos (0-15.9%) reached the blastocyst stage. In these TS cloned blastocysts, the numbers of trophectoderm (TE) and inner cell mass (ICM) cells were 31.9 ± 4.6 and 12.1 ± 3.0, respectively, which were not significantly different from those in the fertilized embryos. In addition, the gene expression analysis showed that Oct3/4, and Cdx2, which are ICM- and TE-specific marker genes, respectively, and Dppa3, and Hdac1, which are zygotic gene activation-related genes, were expressed in TS cloned blastocysts at the same levels as in the fertilized blastocysts. These results indicate that although TS cloned embryos are able to differentiate into ICM cells, the genomic reprogrammability of TS cells is very low following nuclear transfer.