Mechanisms mediating axon outgrowth in the Drosophila CNS

We are dependent on our nervous system functioning correctly for us to move, think, learn, speak and control our bodies. To do this, all our nerve cells must connect together in the brain and to the parts of the body they control. Most of this 'wiring together' happens during the growth and development of the embryo during pregnancy. To do this each nerve cell must extend a long process, called an axon, over large distances and through complex environments to find and connect to its appropriate partners. Each axon is guided when to turn and which way to grow to reach its partner by sensing specific chemicals or molecular 'cues' in different parts of the body. These signals are detected by 'receptor' proteins at the tip of the growing axon. The activity of these receptors signal information into the axon to direct its growth. To enable this to happen efficiently the nerve cell has to co-ordinate its internal organisation with that of the external signals. By studying these processes we will understand better how the nervous system is formed and we can apply this knowledge to aiding the development of strategies to repair the nervous system of patients who have suffered neural injury or disease.

We want to find the molecules that work to control the growth of the axon to guide it along its pathways. We know already that many of the same molecules and receptors in mammals are also present in smaller animals like the fruitfly Drosophila where they do the same job but on a simpler scale. We are using Drosophila to characterise the signalling processes that function within the axon to organise internal signals that facilitate the axon's ability to respond to external signals. We have found that two proteins called Mud and Frizzled have a role in this process. We wish to understand the precise mechanisms of action of these proteins and how they facilitate the targeted growth of axons in the central nervous system. We know that similar molecules are also active during the development of the mammalian nervous system. By using Drosophila we can rapidly identify the mechanims by which these molecules act and the partners that are necessary for their activity. Also use of Drosophila allows us to reduce the need to sacrifice large numbers of mice in research. Once we have found out how these molecules work in Drosophila we will inform other researchers so that the molecules can be tested in other model systems. We need this information both to learn how the nervous system is made and to find out what molecules might be useful in helping us to repair neural injuries or diseases that lead to paralysis or neural degeneration. Unfortunately mammals cannot repair nerve damage that occurs in the brain, our hope is that by identifying the molecules that were originally used to drive and direct nerve cell growth in the embryo we can re-supply these molecules to help nerve cell regeneration in people.

The formation of the nervous system requires that a large number of neurons establish a precise pattern of connectivity. Both vertebrates and invertebrates face the same formidable task of establishing an intricate pattern of axon pathways and many of the molecules identified to date which regulate axon guidance are highly conserved between species. However, we still have only a rudimentary understanding of how these processes are coordinated. To fully understand this process and to aid regenerative strategies it is necessary to identify additional genes involved in wiring and elucidate their cellular functions and molecular interactions. To enable a full recovery of the nervous system not only do affected neural cells need to be replaced but severed connections must be repaired, this makes the identification and characterization of the molecules expressed during embryogenesis that direct the formation of axonal pathways of particular importance. We have identified previously undescribed roles for Mud and Frizzled to direct axon outgrowth at the Drosophila midline where they function as intracellular participants in netrin-independent signaling pathways and may play a role in the early symmetry breaking events that prefigure the determination of initial extension decisions. This proposal aims to understand the molecular mechanisms by which they function. We will establish whether Mud functions to orient microtubules within axons via an interaction with dynein/dynactin and whether its centrosomal location is essential for its activity. We will use a recombineering strategy to perform a structure/function analysis of Mud to identify the functional domains necessary for it to direct axon outgrowth. We further aim to establish whether Frizzled requires additional components of the PCP pathway and or whether the PCP proteins have separable roles to direct axon growth. Finally we will examine whether Mud and Frizzled function in the same or separable pathways.

The research in this proposal will have a number of beneficiaries including academia, the public and potentially UK business.
Academia
The prinipal beneficiaries of this research will be international acadamic researchers in a number of fields leading to an enhanciment the knowledge economy, contributing to the global understanding of developmental biology and developing skilled researchers. Investigators in my immediate discipline will benefit from the insights this research will provide into the molecules required to allow nerve cells to extend their axons precisely to their target cells within the central nervous system. Researchers interested in signal transduction may also benefit from this research as it could reveal the signalling pathways linking extrinsic signals to intrinsic patterning. Additionally researchers in regenerative medicine investigating methodologies to exploit stem cells will benefit from any novel observations we make regarding proteins required to direct nerve growth. Similarly knowledge generated from our work will benefit researchers in health science hoping to understand the molecular basis of congenital neural disease where a greater knowledge of the types of molecules utilised during development is required to inform candidate gene studies or identification of possible targets for therapeutics.
Society
The research work proposed in this work will extend our knowledge of the development of the nervous system, potentially identify mechanisms to aid regenerative medicine and may uncover targets that could be used in develop therapies for neurodevelopmental disorders. Our work will thus benefit UK society and culture, we will ensure that members of the public benefit by allowing access to and understanding of our work by engaging in activities that communicate or share our work with the public. We will seek media coverage opportunities by providing press releases. We also plan to provide benefit by participating in activities that promote and explain our research to school students and their parents. These will include presentations and advice on careers in science to students at schools and widening participation events. . Future activities will include presentation for the London Science Festival, a research day with colleagues as part of Brain Awareness Week and a presentation for the British Association Science Festival.
Health and Wealth
Although it is not envisioned that the proposed research will directly lead to exploitable results it is possible that we will uncover pathways that are disrupted in neurodevelopmental diseases. We will discuss our research results and the reagents we develop with Kings Business and Innovation, an in-house service that advises King's College academics on pathways for the commercial impact and exploitation of academic research. Services provided include the identification, protection and licensing of IP, support and advice on creating companies or identifying commercial partnerships and identifying partners for the development and sale of reagents. We will seek the advice of Kings Business and Innovation to identify the best pathways to achieve commercial impact from the knowledge generated in this proposal.