Cell lineage analyses of epithelia and blood vessels in chimeric mouse embryos by use of an embryonic stem cell line expressing the β-galactosidase gene

We have established an embryonic stem (ES) cell line, MS1-EL4, which has the potential to make various tissues in chimeric embryos and, at the same time, expresses the β-galactosidase gene which was introduced as a good cell marker. To examine cell behavior and lineage during embryogenesis, we injected MS1-EL4 cells into host blastocysts and recovered chimeric embryos at various developmental stages. We examined the distribution of the MS1-EL4 cell derivatives by staining whole embryos with X-gal and by making serial paraffin sections. So far we have obtained the following results: (1) the MS1-EL4 cell line is useful for studying cell lineages because of its ubiquitous expression at least until the mid-gestation stage; (2) cells of the primitive ectoderm and its derivative epithelial tissues continue to intermingle with each other until the late primitive streak stage. Then, at early somite stages, cells of various epithelia stop intermingling and give rise to small coherent clones; (3) blood vessels of the yolk sac are formed by local aggregation of the ancestor cells and those of the embryo proper by proliferation and sprouting from fewer angiogenic cells.