The assembly of a mature vascular network involves coordinated endothelial cell (EC) shape changes, including a process of EC elongation. How EC elongation is dynamically regulated in vivo is not fully understood. Here, we generated a zebrafish mutant, deficient for the integrin adaptor protein Talin1. Using a new Focal Adhesion (FA) marker line, expressing endothelial Vinculinb-eGFP, we demonstrated that EC FAs function dynamically and are lost in our talin1 mutants, allowing us to uncouple the primary roles of FAs in ECs morphogenesis, from the secondary effects that occur due to systemic vessel failure or loss of blood flow. Talin1 loss led to compromised F-actin rearrangements, perturbed EC elongation and disrupted cell-cell junction linearisation in vessel remodelling. Finally, chemical induction of actin polymerisation restored FA dynamics and EC elongation during vascular morphogenesis. Together, we have identified that FAs are essential for EC elongation and junction linearisation in flow pressured vessels and influence actin polymerisation in cellular morphogenesis. These observations can explain the severely compromised vessel beds and vascular leakage observed in mutant models that lack integrin signalling.

Medulloblastoma (MB) is an embryonal-derived lesion arising in the cerebellum, contributing to 20% of childhood brain tumours and 63% of intracranial embryonal tumours. Currently, standard of care includes surgical resection and chemotherapy, used in conjunction with radiation. While these treatments have significantly improved survival rates, the therapy side effects are detrimental to survivors’ quality of life. Furthermore, relapse occurs in 30% of patients and unfortunately these are untreatable and therefore fatal for 95% of patients. It is presumed that in patients that present with a recurrent tumour, initial treatment has been ineffective. A major cause of this can be the heterogenous vasculature in and around the tumour. Recent studies have identified that the blood brain barrier (BBB), in the context of MB, is highly heterogenous with differences in BBB cellular composition and integrity between MB sub-types and within single tumours. It remains unclear however, how these vascular differences emerge and what the primary defects are. This gap in our knowledge is mainly due to the lack of models that allow long-term live imaging. We have established a xenograft approach to examine human MB tumour cells in zebrafish embryonal brains. We have validated that human Medulloblastoma cells of the Group 3 (Gp3) MB subgroup, are viable in zebrafish brains. This work has also identified that in the presence of these human Gp3 MB tumour cells, the local vasculature becomes dysmorphic and tortuous over time. Timelapse imaging of these tumour and vasculature interactions demonstrates that there is a rapid and long ranging angiogenic response with new vessel sprouts growing towards the tumour cells. By utilising our large range of transgenic zebrafish lines, we will continue investigating how MB cells interact and alter distinctive BBB cell types and how these changes impact vessel function.