Molecular regulation of blood development and leukaemia

The ability of embryonic stem (ES) cells to proliferate indefinitely in-vitro and under the right conditions, to differentiate to form any cell type found in the adult body, a property known as pluripotency, provides an exciting avenue for examining the molecular regulation of normal blood development in-vitro. We have established a cell based system that mimics normal embryonic and adult blood production in the laboratory environment, allowing us to manipulate and monitor the expression of specific genes. Using this approach, we have identified the Mixl1 homeobox gene as a master control gene in mesoderm-blood differentiation and have generated genetically manipulated mice and stem cell lines to dissect the molecular pathway regulated by Mixl1 in normal blood development and leukaemia (Hart et al., 2002, Glaser et al., 2006 ).

We have identified Leukaemia patients with re-activated Mixl1 homeobox gene expression and identified a novel transcriptional signature in the specific leukaemia subtypes where Mixl1 has been re-activated. Leukaemias with elevated Mixl1 gene expression will be correlated with clinical findings and patient history to determine the diagnostic and prognostic significance of this discovery. Mixl1 and the gene regulatory network activated by this homeobox transcription factor may represent an important new class of molecular targets for future leukaemia diagnostics and therapeutics.

The mouse Mixl1 gene was modified in embryonic stem cells by replacing the gene with an enhanced green fluorescent protein (eGFP) reporter gene. When embryonic stem cells carrying the Mixl1-eGFP reporter are differentiated into embryoid bodies in vitro, they begin to express the eGFP reporter gene in mesoderm-blood progenitors, enabling identification, characterisation and manipulation of early mesoderm-blood progenitors and the genes that control them.