The development of tissue explant and embryonic stem cell derived models to investigate the molecular and cellular mechanisms that coordinate vertebrate haematopoiesis and angiogenesis

Understanding the processes that control the formation of blood (haematopoiesis), and blood vessels (vasculogenesis and angiogenesis) in vivo has huge clinical importance. The complex three-dimensional architecture of blood vessels is dynamic and aberrant regulation of either the growth or function of the vascular system may potentiate the spread of tumours, resulting in failure of physiological processes such as implantation and placental development, leading to a range of angiogenesis associated disorders for example diabetic retinopathy. Both embryonic and adult haematopoiesis are also three-dimensional, dynamic processes in which deregulation may result in blood disorders or leukaemia. The experiments herein describe my contribution to investigations into the molecular mechanisms involved in haematopoiesis and angiogenesis over a period of approximately 15 years, taking advantage of technical advances as they became available and adapting them to specific cell models. For example, microarray technology has facilitated discovery of new pathways and transcripts implicated in normal and pathological angiogenesis; central to this mechanism is the role of vascular endothelial growth factor (VEGF), a mitogen specific to endothelial cells. Chromosome immunoprecipitation (ChIP) technology subsequently revealed pathways of early mesoderm formation and the importance of gastrulation in this process. Transcriptional targets of the T-box transcription factor Brachyury were subsequently determined. Throughout this work, the human female reproductive tract provided a unique resource, as one of the rare sites of physiological angiogenesis with which to investigate endothelial cell biology and haematopoiesis. Embryonic stem cell-derived embryoid bodies subsequently proved to be an excellent model for the study of early blood vessel development in three dimensions (2003-5), and to follow early mesoderm development (2006-2010). Targets of Brachyury revealed the close association between blood vessel development, haematopoiesis and early mesoderm formation via a common haemangioblast precursor for blood and endothelial cell lineages. Data gathered by myself, and colleagues, from gene expression and transcription factor analysis is now being used to create lineage codes or routemaps for differentiation of stem cells to mature cells in-vitro and it is now possible to produce mature megakaryocytes and erythrocytes in vitro. The current challenge is to produce fully functional human platelets and enucleated red blood cells. Combined with the use of autologous induced pluripotent stem cells (iPSCs) this makes patientspecific tailoring of cell-based therapies a real possibility.