Midline Functions within the Notch-Delta Signaling Pathway Regulating Interommatidial Bristle Complex Formation within the Developing Eye of Drosophila . Sandra M. Leal, Sudeshna Das. Dept Biological Sci, Univ Southern Mississippi, Hattiesburg, MS.

   The Drosophila midline (mid) gene encodes a highly conserved invertebrate ortholog of the mammalian Tbx20 transcription factor gene and is essential for proper development of the embryonic central nervous system (CNS). At present, the exact mechanisms by which mid regulates CNS development are not completely understood. Thus, to resolve mid function, we have been using the Drosophila eye as a practical model system to efficiently undertake a genetic modifier screen and RNAi methodology to identify mid-interacting genes for subsequent translational studies in CNS tissues. One mid-interacting gene we identified from the screen, extramacrochaetae (emc), functions within the Notch-Delta signaling pathway specifying the fates of sensory organ precursor cells (SOPs). We carried out genetic epistasis studies to confirm that mid functions within the Notch-Delta signaling pathway critical for specifying SOPs. SOPs give rise to mechanosensory bristle complexes that are each composed of a shaft, socket, neuron and sheath cell. Based upon the results of these studies, we propose a model suggesting that mid regulates the specification of pI neuroblasts that differentiate into SOPs. Since emc and mid are widely expressed in the embryonic CNS, we are now examining whether they interact within unique subsets of neurons to specify their fates.