Mixl1 regulatory networks in development and disease

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the School of School of Molecular Sciences, Faculty of Science, Technology and Engineering, La Trobe University, Bundoora.

Mixl1 is an essential transcription factor in embryonic viability and normal development of a range of mesoderm and endoderm derivatives, and is more commonly being used as a marker of directed progenitor differentiation and induced pluripotent cell reprogramming. However, little is known of the specific molecular pathways regulated by Mixl1. Understanding these molecular pathways may assist in developing accurate reprogramming and directed differentiation technology, and novel diagnostic and therapeutic tools for haematological malignancies associated with abnormal MIXL1 re-expression in adult tissues. This project focused on Mixl1 transcriptional networks during early mouse embryogenesis and human haematological malignancies. Our transcriptional profiling of Mixl1-null mouse gastrulas and Mixl1-overexpressing mouse ES cells contradicted some previous suggestions of Mixl1 involvement in lineage specification, and identified a novel role for Mixl1 in regulation of EMT and morphogenetic cell movements, and potential for progenitor cell priming and maintenance. Additionally, we consider the function of Mixl1 may change over different developmental stages, and suggest models for these various functions, including evidence for identified potential novel direct transcriptional targets. Mixl1-overexpressing ES cells were also valuable to identify potential novel transcriptional targets in MIXL1-expressing haematological malignancies. We identified MIXL1 overexpression in subsets of Acute myeloid leukemia (AML), Burkitt lymphoma (BL) and Diffuse large B-cell lymphoma (DL-BCL), suggesting that MIXL1 may contribute to a range of haematological malignancy types. EGR1 and MSI2, which were validated as candidate direct MIXL1 transcriptional targets in Mixl1-overexpressing mouse ES cells, were significantly upregulated in AML samples showing MIXL1 overexpression, suggesting the ability to identify molecular subtypes within a disease group, for developing novel and improved diagnostic, prognostic and treatment methods.