The overall goal of the Program Project is to elucidate the complex interactions between the cellular and genetic control mechanisms which regulate the early stages of mammalian development. During the series of cleavage division which leads from zygote to blastocyst, sequential activation of the embryonic genome occurs concomitantly with the first overt signs of differentiation of trophectoderm and the origins of embryonic tissues. By the blastocyst stage, the embryo contains the lineage precursors of all embryonic and extraembryonic tissues. To determine the nature of these early and crucial differentiation events, we propose the following experimental approaches: 1) Through the joint effort of all investigators, genetic probes which reflect the gene expression at each developmental stage will be developed. These probes will be used to identify the corresponding gene products and to begin the analysis of their function. 2) By transient or permanent introduction into embryos of specific genes and/or their products, the functional role of these genes will be determined. 3) Nuclear transfer embryos will be analysed to determine the reasons for their developmental failure and for identifying the genes involved. Part of this approach will involve analysis of specific and gene regulation during gametogenesis. 4) The role of growth controlling molecules (including growth factors and their receptors and oncogenes) in regulating the growth and differentiation patterns in early embryos including trophectoderm and inner cell mass will be studied. The role of protein phosphorylation in regulating the transcriptional activity of the embryonic gene will be examined. 5) Establishment of cell lineages and the cell lineage specific gene expression will be explored by injection of suitable DNA markers and by in situ hybridization with specific probes. 6) Differentiation of trophectoderm, trophoblast and inner cell mass will be studied by identifying genes and gene products specific for those tissues, by determining their role and by attempting to specifically alter or abolish this first differentiation event in mouse embryogenesis. In view of the accessibility of trophectoderm tissue, the readily characterized sequence of developmental events involved in trophectoderm formation.
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