A key developmental transition occurs in erythroid cells around the time of birth characterized by the switch from fetal to adult hemoglobin (from 1232 to 1222). This switch is of critical pathophysiologic significance for sickle cell disease and 2-thalassemia, as persistent elevations of fetal hemoglobin (HbF) levels ameliorate these diseases. Genome-wide association studies of HbF levels led to the discovery of the BCL11A transcriptional repressor as a major effector of the hemoglobin switch. BCL11A inhibition represents a promising novel strategy for HbF reactivation. Genetic variation is predicted to affect regulatory elements influencing the expression of BCL11A, and thereby HbF level. Preliminary data indicate that the BCL11A locus possesses discrete chromatin signatures. This proposal tests the hypothesis that the BCL11A locus is subject to lineage-specific and developmental stage-specific layers of epigenetic regulation. Functional variants at the BCL11A locus that affect HbF expression are likely to reside within regulatory regions. The specific aims of this proposal are to: 1) investigate mechanisms of BCL11A transcriptional regulation promoting the fetal-to-adult developmental transition; and 2) functionally evaluate regulatory elements at the BCL11A locus. Dr. Daniel E. Bauer, M.D., Ph.D., a fellow at Children's Hospital Boston, has outlined a 5-year career development plan that will build upon his clinical background in pediatric hematology/oncology and research background in the study of hematopoiesis to establish himself as an independent investigator in pediatric hematology/oncology at a large academic medical center. Under the mentorship of Dr. Stuart H. Orkin, M.D., a recognized leader in the fields of hematopoiesis and epigenetics, Dr. Bauer seeks to apply genetic and epigenetic approaches to the study of BCL11A regulation in the physiologic hemoglobin switch. An Advisory Committee of internationally recognized experts in the field will oversee his transition to independence. This plan is ideally carried out in the Division of Hematology/Oncology at Children's Hospital Boston, given its distinguished record of training physician-scientists in a rich, collaborative, and supportive environment. At the completion of the 5-year plan, Dr. Bauer will launch a career as an independent investigator with a focus on the epigenetics of hematopoietic cell fate control using hemoglobin switching as a model. In summary, this proposal aims to investigate human genetic variation and epigenetic mechanisms that influence the regulation of the BCL11A locus within the adult erythroid context. Increased knowledge of mechanisms underlying the hemoglobin switch upstream of BCL11A will inform the development of novel therapeutics targeting HbF reactivation in sickle cell disease and ?-thalassemia. Furthermore, identifying these molecular pathways will contribute to an improved basic understanding of lineage specification and ontogeny.