Identifying Molecular Signatures Underlying Preleukemic Clonal Expansion

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Project Summary Clonal expansion occurs when the progeny of a cell excessively increases in number. It plays a crucial role in theearly phase of many hematopoietic disorders such as myeloproliferative disorders, myelodysplastic syndromes, and leukemias. During disease genesis, clonal expansion is often initiated by somatic mutations,which in turn allow the accumulation of additional molecular changes that lead to disease progression. However, not all clonal expansions lead to blood disorders or leukemia. Recent studies show that hematopoietic stem and progenitor cells (HSPCs) commonly exhibit clonal expansion after bone marrow transplantation and in healthy elderly without any apparent disease. Little is known about the differences between normal and preleukemic clonal expansion, particularly with respect to the molecular events underlying their differences. The proposed research project will address the hypothesis that preleukemic clonal expansion is associated with distinct gene expression and/or epigenetic characteristics in addition to the known leukemia-associated mutations, such as Tet2 mutations. Clonal expansion will be tracked using a genetic barcoding technology in Tet2 inducible knockout mice. Moreover, the genetic barcoding technology is integrated with droplet-based single cell RNA-sequencing (scRNA- seq) and with single cell assay for transposable accessible chromatin-sequencing (scATAC-seq) to identify molecular events that are associated with the distinct clonal expansion. The identified molecular signatures of pre-leukemic clonal expansion will be functionally tested using the dCas9-KRAB mouse model. The proposed study compares cellular expansion across different clones to identify rare cellular and molecular events associated with Tet2-induced pre-leukemic clonalexpansion. These experiments will reveal the key molecular drivers that trigger preleukemic clonal expansion undetectable using conventional assays of bulk cell populations. The findings will help improve diagnosis of hematopoietic diseases, particularly TET2 related diseases, and may identify new therapeutic targets for their treatments.