Department of Biological Sciences,University of Warwick,Coventry, CV4 7AL.,
The GFS is a neural circuit of the adult fly that is involved in the light-off escape response. We wish to isolate genes involved in its development, maintenance and connectivity. The Giant Fibres (GF) descend from the brain, through the cervical connective, into the prothoracic neuromere (T1). They then pass into the mesothoracic neuromere (T2) where they dive ventrally and bend. In T2 they make two synapses, one with the peripherally synapsing interneurons (PSIs) that drive the dorsal longitudinal muscle motorneurons (DLMns) and thus the wing muscles, and the second with the tergotrochantral motorneuron (TTMn) that stimulates extension of the middle leg. Several P[GAL4] enhancer trap lines that mark the adult GF and other parts of the GFS have been generated. One of these lines, P[GAL4]-307, has been used to follow the development of these large interneurons. The distinctive cell bodies of the GF can be distinguished in the larval brain, and by late 3rd instar larvae the Giant Fibre projections can be seen on the T1-T2 border. After 14 hours post puparium the axons have entered T2. By 48 hours the circuit appears to be complete. We can elucidate the birth of the GF and other neurons in the GFS by incorporating BUdR at various time points during development. A double labelling procedure, enabling dedection of the final division giving rise to the GF, is being conducted i.e. by the co-localisation of BUdR and LacZ from the enhancer trap. Data will be presented on such experiments. The P[GAL4] enhancer trap has been localised to 50B/C. Four lethal imprecise excisions have been generated and a molecular analysis of the enhancer trap is in progress.