This project will build on our substantial expertise in studying the formation of functional brain wiring patterns to investigate the molecular mechanisms that control neural-vascular co-patterning in the developing brain. The co-ordinated development of neuronal and vascular networks is a prerequisite for normal nervous system architecture and function. Angiogenic sprouts invade the developing neural tube from a perineuronal vascular plexus and extend towards the ventricular surface where they branch and anastomose to form a subventricular vascular plexus. Once established the nascent neuronal vascular network continues to expand and remodel to meet the metabolic demand of the growing neural tissue. Accurate navigation of developing axons therefore requires that avascular areas are created and maintained to provide spaces for axon growth, or that axons activate mechanisms that enable them to navigate through an environment already populated by vessels. In initial experiments we found evidence that both of these processes act in concert to control neurovascular co-patterning. We have found that the ventral midline region of the neural tube, where many brain commissures develop, is relatively devoid of vessel sprouts creating vessel-free regions for axon growth. We have also found that axons are able to navigate around the rare vessels that form in this region to ensure accurate axon navigation towards their targets. The molecular mechanisms underlying the spatial patterning of vessels in the CNS as well as the avoidance of vessels by developing nerves have not, as yet, been established. Pro-angiogenic factors, such as VEGF-A are expressed strongly at the ventral midline of the neural tube, indicating that inhibitory factors must act in this region to prevent blood vessel ingression. The identity of these inhibitory signals is not known currently.
The aims of this project are to:
(1) Investigate the molecular mechanisms that create avascular regions at the ventral midline region of the developing CNS where brain commissures develop.
(2) Investigate the mechanism that enable growing axons to navigate around blood vessels positioned along their path.
We will use expression databases, immunohistochemistry and in situ hybridisation to screen mouse and zebrafish embryos for candidate antiangiogenic factors expressed in patterns consistent with a lack of vessel sprouting into the ventral midline of the neural tube. To determine the functional importance of identified candidates in controlling blood vessel patterning, we will use our established in vitro assays of vessel outgrowth in combination with in vivo analyses of blood vessel development in genetic mutants. We will also analyse nerve and vessel patterning using confocal imaging followed by 3D reconstructions and use live imaging of neuronal and vascular development.
These experiments will expand our understanding of the mechanisms required for the normal co-ordinated development of neural and vascular networks in the developing CNS. Through identification of factors that limit blood vessel sprouting, this work may lead to the identification of novel therapeutics for treatment of vascular disease. The findings will also be relevant to understanding the regenerative processes essential for reestablishment of functional neuronal and vascular networks following disease or damage to the adult CNS.
Erskine, L. Francois, U., Denti, L., Joyce A., Tillo, M, Bruce, F., Vargesson, N., and Ruhrberg, C. (2017). Dual role for neuropilin 1 and VEGF-A signalling in nerves and blood vessels to shape axon projections in the developing CNS. Development 144, 2504-2516.
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Erskine, L., Reijntjes, S., Pratt, T., Schwarz, Q., Denti, L., Schwarz, Q, Vieira, J. M., Alakakone, B., Shewan, D. and Ruhrberg, C. (2011). VEGF signalling through Neuropilin 1 guides commissural axon crossing at the optic chiasm. Neuron 70, 951-965.