Embryonic development entails a complex program of events that must be executed in a precise and ordered fashion. Much of the coordination of these events is achieved by the directive instructions of extracellular signaling molecules that serve to activate or repress transcription of specific gene subsets and ultimately influence the proliferative state or identity of the target cell. Because these signaling molecules have a profound effect on cell growth and differentiation, it is imperative that the expression of these molecules be rigorously and specifically regulated. Thus, elucidation of the regulatory mechanisms that govern differential expression of these signaling molecules is fundamental to an understanding of the process of development. The goal of this research project is to elucidate the mechanisms which determine the extremely discrete temporal and spatial pattern of expression of the FGF-4 gene during embryonic development. FGF-4, a member of the FGF family of growth factors, is an important signaling molecule which has been shown to be essential for at least two stages of embryogenesis, post-implantation mouse development and growth and patterning of the limb. One aspect of the specificity of FGF-4 gene expression is determined by a cell-specific enhancer, which can promote transcription only in undifferentiated embryonal carcinoma (EC) and embryonal stem (ES) cells. This element interacts with two specific transcriptional regulators, Sox2 and Oct-3, which are coexpressed in EC and ES cells, and in the inner cells mass (ICM) of the blastocyst, the first site of FGF-4 expression during development. We plan 1) to determine the mechanism by which these two transcriptional regulators, Oct-3 and Sox2, synergize to activate expression of the FGF-4 gene. 2) To identify and characterize new distinct regulatory elements governing FGF-4 expression during later stages of embryonic development and the signal and factors influencing their activity. 3) FGF-4 null embryos do not develop beyond implantation, thus precluding the assessment of its role in later development. We will utilize the knowledge obtained from the studies identifying the specific regulatory DNA elements driving the expression of the FGF-4 gene to bypass the early lethality of FGF-4 null embryos and further investigate the role of FGF-4 in embryonic development, particularly the myotomes and the limb bud.
