Toll-7 and Toll-6: central nervous system functions as Drosophila neurotrophin receptors

Abstract

The Drosophila Toll receptor is crucial for dorsoventral patterning in embryos, and for innate immunity. Toll also functions during central nervous system development, promoting neuronal survival and targeting. There are nine Toll paralogues in Drosophila, and it is unknown whether any of these also function in the CNS. Toll’s ligand, Spz, has an NGF domain. NGF is a vertebrate neurotrophin - a growth factor that regulates the development and function of the nervous system. Drosophila Neurotrophin 1 (DNT1), identified by homology to the vertebrate neurotrophin BDNF, and DNT2 are paralogues of spz. The three DNTs – DNT1, DNT2 and spz – are structural and functional homologues of vertebrate neurotrophins, and they promote neuronal survival, targeting and synaptogenesis in Drosophila. However, the receptors for DNT1 and DNT2 are unknown.
Here, using a combination of in situ hybridisations and reporters that drive GFP expression, I investigate the expression of Toll paralogues in the Drosophila nervous system. By generating null mutant flies and gain-of-function transgenic flies, I examine genetic interactions between Tolls and DNTs. I also investigate the rolls of these receptors in adult locomotion, axon targeting and cell survival. Finally, in cell culture, I test whether DNTs can signal through Tolls to activate NFκB.