Identification and characterisation of axon guidance genes in Drosophila melanogaster

• Main Author: Hayward, Neil Martin
• Published: University of Cambridge 2000
• Subjects: 591.35
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603902

From a collection of lines in which a GAL4 enhancer trap vector is randomly inserted in the genome, five lines were selected based on the restricted expression of GAL4 in the pioneer neurons. Three genes flanking the insertion were successfully cloned by plasmid rescue, and remarkably all are involved in signalling pathways: (i) <I>foraging </I>is a cGMP-dependent protein kinase, with an established role regulating larval behaviour. However, using antibodies made in this study, <I>foraging </I>is not detectable in pioneer neurons, and gain- and loss-of-function experiments show no defects in axon guidance. Given that <I>foraging </I>regulates axonal conductance in larval neurons, it may yet have an embryonic role in pioneer neurons, but at a low expression level. (ii) <I>FKBP12</I> is a cytoplasmic suppressor of TGF-β signalling. I have shown it to be expressed in neurons where it is localised to axons, and is thus ideally placed for a guidance molecule. I have shown that a potential ligand for this pathway, <I>dpp</I>, is expressed in longitudinal glia, and ectopic expression of <I>dpp</I> can attract axons. (iii) <I>Dfer</I> is a cytoplasmic tyrosine kinase, which I have shown to be expressed in pioneers neurons (dMP2 and MP1). By eliminating <I>Dfer</I> function (using RNAi and a deficiency), I have shown the gene plays a role in guiding axons in the CNS, to prevent longitudinal axons from crossing the midline. <I>Dfer </I>also acts in motor neurons at choice points in the periphery. Continuing analyses of <I>Dfer</I> function should provide an insight into the cytoplasmic processes involved in receiving and interpreting inter-cellular axon guidance signals.