Determinants of GATA1-mediated gene regulation during erythroid maturation

Abstract

Hematopoiesis has long been used as a model system to study development and lineage decision-making. Within this branch of development, erythropoiesis is the process through which mature red blood cells arise from progenitor cells. In this context, GATA1 is widely considered to be the master transcription factor for erythropoiesis, controlling the expression of a vast majority of the genes involved in red blood cell maturation. GATA1 dysfunction has been shown to cause several human disorders, including anemias and thalassemias, and has been linked to the onset of various types of leukemia. GATA1 has been shown to function as both a gene activator and repressor, posing the question of how it distinguishes between various categories of genes and regulates them. In this thesis, we apply a combination of systems and molecular biology approaches in order to gain a better understanding of various regulatory mechanisms centered around GATA1. In the main study of this thesis, we uncover a new physical interaction between GATA1 and the cohesin complex, which has previously been involved in establishing three-dimensional chromatin architecture in the nucleus. We collected chromatin interaction data in a murine cell line model for erythropoiesis, and identified tens of thousands of DNA looping events in both progenitor and differentiated cells. Integration of these chromatin interaction maps with gene expression and transcription factor occupancy datasets revealed new principles underlying gene regulation, and suggests that GATA1 plays a major role in orchestrating the 3D organization of the differentiating erythroid cell. In a second study, we identify a new feedback mechanism which facilitates the replacement of GATA2, a transcription factor expressed at earlier stages of hematopoiesis, by GATA1. We show that Fbw7, an ubiquitin ligase protein trans-activated by GATA1, targets GATA2 for proteosomal degradation, thus reducing its halflife and leading to more efficient GATA factor switching. Finally, in a last section, we characterize the GATA1 -interacting transcription factors zfp281 and zfp148, and show that they play functionally redundant roles in erythroid development. Altogether, this thesis presents new insights into GATA1 various aspects of GATA1 biology, which will contribute to our understanding of mechanisms of gene regulation.