A study of Notch signalling in developmental angiogenesis.
Doctoral thesis, UCL (University College London).
Blood vessel patterning during angiogenesis is a guided process. Endothelial tip cells located at the end of vascular sprouts are important for vessel guidance. One of the aims of my studies is to determine how endothelial tip cell formation is regulated. Previous studies have shown that the Notch ligand, Delta-like 4 (Dll4), is prominently expressed in tip cells, therefore suggesting a role of Notch signalling in its regulation. In the mouse, suppression of Notch signalling by pharmacological inhibition of γ-secretase or genetic deletion of one Dll4 allele resulted in excessive endothelial tip cell formation and a poorly-patterned, hyperdense vessel network. Induction of Notch signalling by Jagged1 peptide treatment led to a decrease in tip cell formation and a sparse vessel network. Thus, the Notch pathway negatively regulates tip cell formation to promote a non-sprouting endothelial stalk cell. The Notch-regulated ankyrin repeat protein, Nrarp, is a Notch target gene that is highly expressed in stalk cells and endothelial cells located at vessel branchpoints. Deletion of Nrarp in mouse and morpholino knockdown of nrarp-a and nrarp-b in zebrafish resulted in decreased endothelial cell proliferation and junctional instability, leading to ectopic vessel regression and the formation of a sparse vessel network. In endothelial cells, loss of Nrarp function increased Notch signalling but decreased Wnt signalling, thereby confirming its role as a negative and positive modulator of Notch and Wnt signalling, respectively. Mice null for Lymphoid enhancer factor 1 (Lef1) or deficient in endothelial Ctnnb1 also displayed increased vessel regression and decreased vessel density, suggesting a role of canonical Wnt/β-catenin signalling in maintaining vessel stability. In conclusion, my studies show that Notch signalling regulates endothelial tip cell formation and vessel stability to fine-tune vessel patterning. Furthermore, I demonstrate that Nrarp provides a molecular link to Wnt signalling to regulate vessel stability.
|Title:||A study of Notch signalling in developmental angiogenesis|
|Open access status:||An open access version is available from UCL Discovery|
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