| The molecular events that regulate the progression of adipocyte differentiation have been well elucidated, however there is little information about the early events that surround the initiation of adipocyte differentiation from preadipocytes, as well as the commitment of a pluripotent stem cell to the adipose lineage. This dissertation has investigated the role of GATA transcription factors in regulating early stages of adipogenesis. Their unique expression pattern and function in white preadipocytes indicate that GATA factors play a prominent role in gating the initiation of adipocyte differentiation. Similarly, we have discovered through gain and loss of function studies that GATA-2 prevents brown preadipocytes from achieving their mature phenotype with respect to functional mitochondria physiology and expression of genes related to thermogenesis, but did not strongly impact adipogenic genes or adipocyte markers found in white adipocytes. We have also examined whether GATA proteins contribute to lineage commitment of adipocytes from a pluripotent precursor. Interestingly, disruption of GATA-2 in totipotent stem cells did not inhibit development of adipose tissue in vivo, or the formation of brown adipocytes from pluripotent cells in vitro. These findings suggest distinct roles for GATA proteins at two different stages of development: lineage commitment and terminal differentiation. To further elaborate on the mechanism by which GATA regulates adipocyte differentiation, we have mapped the domains that participate in the interaction between GATA transcription factors and the C/EBP family of proteins, and demonstrate that loss of interaction prevents GATA from suppressing adipogenesis, independent of its ability to bind DNA and regulate gene transcription. We have additionally identified that GATA interaction with a known co-factor, FOG-1, also contributes to GATA action. Taken together, these findings allude to the assembly of a multifactorial complex in preadipocytes where GATA factors associate with target DNA as well as C/EBPalpha and FOG-1. An increased understanding of how GATA factors regulate adipocyte differentiation beginning from a progenitor cell provides important insight to the process of adipose tissue formation in vivo , which can be applied toward the design of novel anti-obesity therapies. |
