Year 3

Stem cells are the building blocks during development of organisms as varied as plants and humans. In addition, adult or “tissue” stem cells provide for the maintenance and regeneration of tissues, such as blood and skin throughout the lifetime of an individual. The ability of stem cells to contribute to these processes depends on their unique ability to divide and generate both new stem cells (self-renewal) as well as specialized cell types (differentiation).
A thorough understanding of the factors that regulate self-renewal programs will be essential for the expansion and long-term maintenance of adult stem cells in culture, a necessary step towards the successful use of stem cells in regenerative medicine and tissue replacement therapies. In some tissues, cells that have already begun to specialize can revert or “de-differentiate” and assume stem cell properties, including the ability to self-renew. De-differentiation of specialized cells could provide a “reservoir” of cells that could act to replace stem cells lost due to wounding or aging. This proposal seeks to uncover the mechanisms that are utilized to regulate the process of de-differentiation and to compare these to the mechanisms that endow stem cells with the ability to self-renew using the fruit fly Drosophila melanogaster as well as pluripotent human cells. Understanding the mechanisms by which partially differentiated cells can re-acquire self-renewal potential and how these programs are utilized during the normal course of tissue maintenance and repair could provide powerful strategies for regenerative medicine by stimulating inherent self-repair programs normally present within tissues and organs.
In the most recent funding period, we have characterized the role of a gene called multiple sex combs (msx), which plays a role in regulating the switch between proliferation and differentiation via control of proteins that are essential for proper DNA compaction and, consequently gene expression. Because the function of this gene is conserved in human cells, we speculate that understanding the function of this gene will provide insight into additional mechanisms that regulate the behavior of human stem cells. IN addition, we have characterized the role of human Igf-II mRNA binding protein 1 (hIMP1) in pluripotent human cells and during early neural differentiation. Lastly, we have developed a system for investigating maintenance and regeneration of specialized stem cell microenvironments in the Drosophila male germ line. Regeneration of stem cell environments (also known as ‘niches’) must accompany the expansion of stem cells required for tissue repair. Thus, investigating this process will lead to the identification of genes and pathways that regulate regeneration of stem cells in more complex mammalian tissues.