Using EC and ES cell culture to study early development: recent observations on Indian hedgehog and Bmps

Despite great technological advances in the study of mammalian development in the past two decades, certain problems in early development, such as how the extraembryonic lineages are established, have remained intractable. We suggest that teratocarcinoma (EC) and embryonic stem cells (ES) remain useful in vitro tools for studying some of these problems. We present a continuation of our studies on the role of IHH-based signaling in early development and demonstrate that the IHH N-peptide is expressed in the outer visceral endoderm cells of both the EC and ES-derived embryoid body. We also show that Bmp2 is upregulated and Bmp4 downregulated during the differentiation of F9 EC cells into embryoid bodies, whereas both genes are upregulated when J7 ES cells differentiate into embryoid bodies. We also examine the spatial localization of Ihh, Bmp2, and Bmp4 in day 6.5-7.0 and 7.5-8.0 embryos by in situ hybridization analysis. These data support the EC temporal expression data in that all 3 genes are expressed in visceral endoderm. Bmp4 expression appears to be limited to extraembryonic regions, where mesoderm as well as visceral endoderm are stained. Ihh and Bmp2 are expressed in extraembryonic tissues and the embryo proper. Functional roles for the observed expression patterns are discussed.