Stuart H. Orkin

The laboratory utilizes multidisciplinary approaches to understand how mammalian cells choose specific fates and how mutations in important transcriptional regulators lead to developmental defects or malignancy. Recent and ongoing work falls into several overlapping areas. First, while many of the essential hematopoietic transcription factors are identified, how they act in the context of other factors within progenitors is less well understood. Hence, we are using biochemical and molecular approaches to address the function of these factors. Second, we are employing engineered mice to dissect the genetic pathogenesis of two forms of leukemia with distinctive biology. These include "standard" pre-B cell leukemia of childhood associated with the TEL-AML1 translocation and acute megkaryocytic (M7) leukemia in Down syndrome patients initiated by somatic mutation of GATA-1. Third, we are asking whether some of the lessons of hematopoiesis may be applied to consideration of the pathogenesis of solid tumors. In this context, we have developed a model of sporadic human breast cancer of the secretory variety that allows for identification and isolation of the target cells in which oncogenic transformation is initiated. Finally, the fundamental properties of stem cells--pluripotency and self-renewal--are being addressed from a biochemical perspective in mouse embryonic stem (ES) cells. Through affinity purification of critical regulators of ES cell fate (nanog and Oct4) followed by mass spectrometry, we have identified proteins that associate in complexes and assembled a preliminary "interactome" map. In the future, we will pursue the functions of the associated proteins in order to unravel the biochemistry of ES fate specification. This strategy may ultimately suggest how directed manipulation of somatic cells to an ES cell fate might be achieved.