The role of TEK and TIE receptor tyrosine kinases in murine cardiovascular development

grantor: University of TorontoTEK and TIE are related receptor tyrosine kinases (RTKs) expressed in endothelial cells (ECs) and their precursors, the angioblasts, during embryogenesis. The focus of this thesis is an analysis of the function of TEK and TIE in the murine vascular system. The studies presented strongly suggest a primary requirement for both receptors in the expansion and maintenance of the vasculature, but not for vasculogenesis, the initial differentiation of ECs. The function of 'Tie' was investigated using a gene targeting strategy. The development of embryos lacking functional TIE arrested in midgestation as a result of widespread hemorrhage and edema, a phenotype attributed to loss of inter-endothelial cell integrity in the microvasculature. Furthermore, mosaic analysis confirmed a cell-autonomous requirement for TIE at midgestation in the capillaries of organs that are vascularized by sprouting of pre-existing ECs (angiogenesis) but that TIE is dispensable for 'in situ' differentiation of ECs (vasculogenesis). Possible redundancy in the TEK and TIE signalling pathways was investigated in embryos homozygous mutant for both 'Tek' and 'Tie '. Vasculogenesis proceeds normally in embryos lacking both receptors, but such embryos die early in gestation of multiple cardiovascular defects. Chimeric analysis of 'Tek' and 'Tie' deficient embryos revealed an absolute requirement for TEK in early heart development whereas the receptors are dispensable for the initial assembly of the rest of the vasculature. In contrast, both receptors are required in the microvasculature of most organs during late organogenesis and in most blood vessels of the adult. This analysis identified essential functions for TEK and TIE in quiescent endothelium and indicates that they play ongoing roles in maintaining the integrity of the vasculature in the adult. Finally, the molecular basis for EC specific expression of 'Tek ' was addressed by deletion analysis of the 'Tek' promoter in transgenic mice. This investigation identified a short genomic region that directed reporter gene expression in a manner that accurately reflected the expression of the endogenous 'Tek' gene in early embryogenesis.Ph.D