Prions are unique in biology in that they represent heritable or infectious elements that appear to be devoid of nucleic acids. The formation of prions involves the conversion of a normal soluble host prion protein to an abnormal, insoluble form. In the transmissible spongiform encephalopathies (TSE or prion diseases), a group of mammalian neurodegnerative diseases that includes Creutzfeldt-Jakob disease in humans and BSE, the abnormal prion protein is closely associated with infectivity and has been proposed to be the infectious TSE agent. In yeast, prions are responsible for the non-Mendelian heritability of certain phenotypes. The unique challenge in prion research, and the focus of this session, is to understand how a host-derived protein may be responsible for the different aspects of TSE disease in mammals and non-genetic heritable elements in yeast.

Stem cells have been identified in a variety of tissues at different developmental stages. Stem cells offer novel therapeutic avenues to treating diseases as well as a source of cells for large scale genomic analysis. We have chosen three speakers who will address specific aspects of stem cell biology. Dr. Panchison will present his results on how to regulate stem cell differentiation using bone morphogenetic proteins. Dr. Lumelsky will present her results on using ES cells to generate a specific population of differentiated cells the pancreatic islet cells. Dr. Becker will describe how microarray technology can be combined with our ability to grow purified populations of stem and precursor cells to identify new regulators of stem cell growth or new functions of known genes.