9202417 Maul This proposal requests the funds for a confocal microscope to be used by a multi-user group. The major users will utilize the instrument in projects over the long term. Projects include the 3D reconstruction of changing chromosomal domains during differentiation and of specific and newly found nuclear domains, the changing inter- relationships of cells during development or induced differentiation by retinoic acids or by coculture in skin reconstruction, the different distribution of mRNA in whole developing embryos, and the relative localization of specific genes in the intact nucleus (mapping). Aside from these larger projects minor projects have been identified and initiated by different laboratories at The Wistar Institute in particular in the developing structural biology program. These will be supervised by the principal investigator. Projects are diverse and need an efficient way to study cell or tissue architecture in the 0.1 to 1 m range in specimens that have a thickness of 0.1-1-mm. Confocal microscopy in its advanced state provides us with the means to achieve our goals.