We have examined the myogenic potential of human embryonic stem (hES) cells in a xeno-transplantation animal model. Here we show that precursors differentiated from hES cells can undergo myogenesis in an adult environment and give rise to a range of cell types in the myogenic lineage. This study provides direct evidences that hES cells can regenerate both muscle and satellite cells in vivo and are another promising cell type for treating muscle degenerative disorders in addition to other myogenic cell types.

It has previously been shown that human ␤ -microseminoprotein enhances development of mesodermal structures in the chick embryo. The present study was carried out to elucidate the mechanism of action of human ␤ -microseminoprotein in the chick embryo. ␤ -Microseminoprotein brought about significant modulation of expression of Brachyury in gastrulating embryos. In approximately 50% of the treated embryos, Brachyury expression was enhanced around the Hensen's node. These cells not only expressed higher levels of Brachyury , but also appeared to switch off Brachyury expression prematurely, postinvagination. The spatial modulation of Brachyury is not clearly reflected in the northern blots, indicating that ␤ -microseminoprotein treatment results in redistribution of available transcripts or that the upregulation is compensated for by early switching off of Brachyury postinvagination. Because higher levels of Brachyury during gastrulation are believed to result in early exit of cells from the primitive streak, ␤ -microseminoprotein treatment appeared to have stimulated morphogenetic movements by upregulating Brachyury around the Hensen's node. This deduction was confirmed by scanning electron microscopic analysis that showed that altered morphogenetic movements accompany modulation of Brachyury . The specific responses elicited by ␤ -microseminoprotein indicate presence of a structurally related molecule in the chick. By western blotting, similar molecules were indeed detected in the chicken seminal plasma and in chick embryos. These data strongly suggest that ␤ -microseminoprotein-related molecule(s) participates in mesoderm formation in the chick embryo.