Identification and Characterization of Genes Involved Sensory Organ Patterning in Drosophila Adult Legs

The generation of morphological diversity among homologous animal structures is known to be controlled by the homeotic (Hox) genes. However, the molecular mechanisms underlying Hox gene function are not fully understood. This thesis addresses this issue by using the Drosophila adult legs as a model system. The Drosophila adult has three pairs of legs, one pair on each of its three thoracic segment, the T1, T2 and T3 segments. Each leg is identical but differs in size, shape and in the sense organ pattern. Our focus is on the differences in sensory organ patterns among the legs from different segments. The leg sensory organs include a group of small mechanosensory bristles (mCs), which on the T2 leg are precisely arranged in longitudinal rows, called the L-row bristles. The T1 and T3 legs also have L-rows, but in addition to the L-rows, T1 and T3 legs have mCs organized in transverse rows oriented orthogonal to the L-rows, which are called T-rows. The T-rows are found at specific positions along the circumference and proximal/distal axis of T1 and T3 legs. In addition, male T1 legs have a modified T-row called the sex comb, which consists of a group of peg like bristles and is used in mating. Our focus is on the mechanisms that generate the T1 leg specific T-row and sex comb pattern. Previous research in the lab has revealed the role of Drosophila Hox gene, Sex combs reduced (Scr), in generating segment-specific sense organ patterns on the T1 leg by modulating the presumably default L-row patterning pathway. Scr function is necessary for T-row and sex comb development, but our studies suggest that Scr function, alone, is insufficient to form T-rows and sex combs and that additional genes are required for T-row/sex comb development. The goal of my research was to identify genes that function either downstream and/or in parallel to Scr to specify a T-row/sex comb fate. To do this we initiated an in vivo RNAi screen and identified several new genes that are required to form the T1 leg T-row and sex comb pattern.