 |
 |
| Ihor Lemischka |
The focus of our research is to understand the molecular and cellular nature of the undifferentiated stem cell "states", and how such states are altered during a change in cell fate. The underlying rationale for our studies is that the complement of gene-products and their inter-relationships that exist in stem cells accounts for their remarkable abilities to balance self-renewal and differentiation decision processes. We study both adult and embryonic stem (ES) cells, primarily from the mouse, but also from the human. As a first step, we have comprehensively identified most, if not all gene-products that are expressed in highly purified hematopoietic stem cell (HSC). We performed similar analyses in mouse ES cells. Such molecular "signatures" provide parts-lists that are available to the stem cells. The challenge has been to functionally address the roles that these molecules play in mediating the biological properties of HSC and ES cells. Further, we would like to understand how these molecular components are "wired" into regulatory signaling and transcriptional networks.
To explore these issues we have utilized a number of global gene-expression perturbation technologies, such as inhibitory short hairpin RNA (shRNA). We have successfully down regulated the expression levels of candidate regulatory molecules in both HSC and ES cells. A number of these play crucial regulatory roles in processes such as self-renewal, proliferation, and differentiation. We have further developed strategies that allow the analyses of cell-fate change dynamics at multiple biochemical and molecular levels in response to defined and precisely controlled changes in the expression levels of key regulatory molecules. These strategies have provided the first in-depth view of how a cell-fate decision actually occurs at the transcriptional, post-transcriptional, translational, and post-translational levels. An important aspect of our overall efforts is computational and quantitative analyses. We anticipate that our approach will yield a systems biology level description and understanding of stem cell decision processes. This in turn, will have profound implications in future efforts focused on applying basic stem cell research in translational as well as clinical contexts.
| Kateri Moore |
There is a cellular milieu that surrounds and supports the blood forming or hematopoietic stem cell. Throughout adult life these stem cells are present within the bone marrow and are thought to be located in apposition to the endosteal surface of the bone. Stromal cellular elements provide a unique microenvironmental space or niche that mediates the extrinsic molecular signals involved in the balance of self-renewal and commitment decisions of stem cells. My work is focused on defining the most primitive stem cell microenvironmental niche at the cellular and molecular level. Our previous studies have shown that a cell line, AFT024, can maintain competitive repopulating stem cell activity that is qualitatively and quantitatively identical to that present in freshly purified cells. We suggest that the AFT024 stromal cell line provides a unique and positively acting molecular milieu that maintains self-renewing stem cells. To isolate the components of this milieu we have constructed a subtracted cDNA library enriched for molecules preferentially expressed in this supporting line. We have assembled a biological process oriented Web-based interface, the Stromal Cell Database (StroCDB). Candidate genes from this database are being tested in gain and loss of function studies and are being used to develop mouse models. These genetically modified mice provide model systems to both manipulate and visualize stem cells and their niches in vivo under normal homeostasis and/or after systemic and/or specific microenvironmental perturbation. In addition, we are investigating the "molecular cross-talk" that occurs when stem cells and stromal cells interact under a variety of conditions. This research will provide invaluable insights into the intrinsic and extrinsic mechanisms that balance the self-renewal and differentiation of hematopoietic stem cells and perhaps of all stem cells.