Cloning of two neurally expressed genes found adjacent to P[GAL4]307, a marker of the giant fibre circuit, in Drosophila melanogaster
The enhancer trap line P[GAL4]307 was isolated on the basis of expression in the giant fibres. It has proved to be an elegant marker of giant fibres in adult Drosophila. The giant fibres (GFs) are part of a simple circuit in the fly's central nervous system (eNS) that mediate a light-off escape response involving a jump and wing beat. Detailed analysis of the adult expression pattern, using antibodies to the products of the genetic elements used in enhancer trapping, has revealed that all the major components of the escape circuit are clearly detectable. Subsequently, the development of this circuit has been traced using the same antibody staining techniques, revealing the timing of circuit establishment and the developmental profiles of each component neuron. To complete this profile the birthdating of the GFs has been attempted. The overall aim of this section of work was to map the circuit from the first cell division producing the major neurons in embryos, through establishment of the circuit in pupae to full development of the active circuit in adults. The second major section of work has been the cloning of genes from DNA surrounding the P-element insertion. An important facet of P-element design is the ability to use it to remove the genomic DNA from around the site of insertion. A probe created from a fragment of this genomic DNA has been used to screen a library. This yielded a eDNA that, in combination with subsequently isolated cDNAs, forms a contiguous stretch of DNA approximately 4Kb in length. A translation of the eDNA has revealed homology with proteins from a range of eukaryotes from yeast to humans. These may form a family of elongation initiation co-factors. On the basis of homology with an Arabidopsis thaliana gene argonaute, this new Drosophila gene has been named diomedes. The genomic region has also been sequenced, revealing another gene close to diomedes. This new gene, LD07701, appears to be full length, and is unusual because it may be a non-coding RNA. Both genes isolated have neural expression in embryos, larvae and pupae, although it appears neither is the gene whose expression is reflected by the enhancer trap pattern.