Manipulation of dHb9-expressing Motor Neurons Results in Eclosion Defects. Marcus A. Toral, Soumya Banerjee, David Conway, Joyce Fernandes. Miami University, Oxford, OH.

   As the fruit fly develops from a larva into a morphologically distinct adult, existing neural circuits must be remodeled during a period of metamorphosis to allow for the acquisition of new behaviors. Corresponding to this behavioral switch in motor control from the abdomen to the thorax, there is a dramatic reduction and expansion, respectively, to the abdominal and thoracic segments of the central nervous system. In this context our lab has been investigating the involvement of dHb9 expressing motor neurons (MNs) in eclosion behavior. Work in our lab has revealed that the this subset of MNs includes two that innervate larval muscle fibers (MFs) 12 and 13, which are present in abdominal segments A1 and A2 and persist through metamorphosis to aid in eclosion (Kimura and Truman, 1990). To test the role of these dHb9 expressing MNs in eclosion, we have selectively manipulated them during metamorphosis. Through GAL4-UAS targeted activation of the cell death gene Reaper (rpr), Diphtheria Toxin (DT1), and Shibire (shiTS), we initiate apoptotic pathways and functional blockades in dHb9 cells, subsequently analyzing the effects at both the behavioral and cellular levels. We have determined thus far that the dHb9 subset plays a significant, but non-essential role in eclosion. In 100% of flies that failed to eclose, we observed no dHb9-positive innervation to MF13 in A2 (n=20). From this, we have determined that innervation of adult MF13 in A2 is the most important contribution of the dHb9 subset to proper eclosion. Additionally, preliminary data suggests that the early time period prior to the formation of the adult innervation pattern (0h-48h after pupation) is most critical to the formation of this neural circuit. Next, we will be employing the use of another functional blocking mechanism, Tetanus Toxin (TTX), more closely monitoring eclosion behavior defects with video recordings, and utilizing the extensive descriptions of dHb9 cellular identity gained from our previous work to link observed defects to the absence of individual dHb9 cells and their corresponding muscle targets.