Genomic mapping and expression patterns of C380, OK6 and D42 enhancer trap lines in the larval nervous system of Drosophila

Since its description more than fifteen years ago, the GAL4-UAS system of heterologous transgenic expression has found universal and widespread use in Drosophila research, making it a uniquely powerful analytical tool. Several hundreds of enhancer-trap GAL4 “driver” lines have since been used to express proteins of interest in specific spatio-temporal domains. However, the identities of enhancer elements that regulate GAL4 expression in vivo are often not known. Here, I report the mapping of three GAL4 lines commonly used as motor neuron drivers. Sequencing of genomic DNA flanking these three P-element transposon insertions, C380 (BG380), OK6 and D42, shows that these insertions lie upstream of the futsch, Rapgap1and toll-6 genes, respectively. Of the three, OK6-GAL4 (Rapgap1) expression is most restricted to motor neurons, while C380-GAL4 and D42-GAL4 also show prominent expression in the peripheral nervous system, including body wall sensory neurons. Next, I use available antibodies to Futsch and Rapgap1 to determine the extent to which expression patterns of these genes overlap with one another, and show that all three GAL4 lines express strongly in the nervous system, albeit with clear differences. Finally, I test if the highly restricted expression pattern of Futsch is maintained in six other species of Drosophilids (D. yakuba, D. ananassae, D. pseudoobscura, D. simulans, D. willistoni and D. virilis). My results suggest conserved control of Futsch expression across species, most likely through upstream cis-acting elements. A comparative anatomy of the larval central nervous systems and peripheral innervation in these Drosophilid species as revealed by contemporary immunohistochemical markers is also presented.