Motor neuron regulates Indirect muscle patterning through EGF ligands. Kumar Vishal, Lindsay Grainger, Mary Turvy, Joyce Fernandes. Dept Zoology, Maimi Univ, Oxford, OH.

   Unlike embryonic myogenesis, many aspects of adult myogenesis require innervation. One example is seen during development of the thoracic indirect flight muscles (IFMs) where denervation affects IFM is reduces myoblast proliferation and also causes loss of the organizer cell specific marker dumbfounded. These results suggest that motor neurons may act through organizer cells to regulate myogenesis (Fernandes and Keshishian, 2005). However, the natures of signals involved in this communication remain to be elucidated. Our overall goal is to understand how EGF signaling is involved in cell -cell communication during IFM myogenesis. We find that have shown that blocking EGF receptor in the receiving cells (organizer cell and myoblasts) alters muscle patterning. Disrupting the pathway in organizer cells led to a reduction in the number of one groups of IFMs (DLMs), 6DLMs are seen in 5% of the manipulate animals. Blocking the pathway in myoblast causes a less severe reduction in the number of DLM fibers, 6DLMs are seen in 60-65% of experimental animals. Dorsoventral muscles (DVM) profiles are also altered in both cases. These results suggest that the organizer cell is the primary receiving cell during IFM myogenesis. Based on these results, in this study we are testing the role of motor neuron as a primary signaling cell. We will manipulate the EGF ligands in the motor neuron using an RNAi approach. Effects of this manipulation will be examined on adult muscle profile. We will also examine muscle patterning during pupal stages to determine what aspects of patterning are disrupted. Myoblast proliferation will be monitored by BrdU incorporation assay, whereas fusion of myoblasts to form nascent fibers will be studied using antibodies to the transcription factor, erect wing. Our preliminary studies to block EGF ligand vein, suggest that muscle patterning is disrupted in 50% of cases. Since, IFM myogenesis shares a striking similarity to vertebrate skeletal muscles on their dependence on innervation; this study will help in a better understanding of the neuronal control of myogenesis.