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Show 230 Priscilla Auduong Spinal Muscular Atrophy (SMA) is the most commonly inherited cause of death in children (Park, Kariya, & Monani, 2010 for review). This disease is characterized by a loss of motor neurons which leads to muscle degeneration, paralysis, and eventual death by respiratory failure (Monani, 2005 for review). More than ninety percent of the children born with this disease die; SMA occurs at a rate of 1 in 6,000 to 10,000 live births with a carrier frequency of 1 in 40 people (Kolb & Kissel, 2011 for review). SMA is a result of the loss of a gene known as Survival of Motor Neurons (SMN) (Burghes & Beattie, 2009 for review). We hypothesize that SMN is required in motor neurons for proper axonal extension and synapse formation/maintenance, and in muscles to ensure proper innervation. Using Drosophila melano-gaster, we examined the requirements for SMN in motor neuronal development using RNA inter-ference (RNAi) and forward genetics. Our results indicate that, as in higher organisms, a complete depletion of SMN kills the embryo very early in development. Embryos were collected and in-jected with varying concentrations of double-stranded RNA (dsRNA) that specifically targeted the Drosophila SMN transcript for degradation. Embryos were allowed to develop to late stages of development and were then filleted, fixed, stained and imaged on a confocal microscope. Using the open-source software, Image J (http://rsbweb.nih.gov/ij/), measurements of motor neurons were collected for each image. Identical experiments were conducted for genetic mutants lack-ing either the SMN gene as a whole, or portions of it. Gain of function data indicated no aberrant patterns of neuromuscular junction formation or maintenance, suggesting that additional SMN is not detrimental to the organism. Because dsRNA can be injected in the fly at varying concentrations, we were able to generate ti-tratable loss of function phenotypes. We observed in pilot studies that 1) SMN is required for axo-nal extension, but not for motor neuron formation or cell fate specification, 2) that motor axons often fail to extend to their muscle target fields and typically fail to form synapses, as evidenced by 3) prolonged observation of myopodia which are membranous extensions from the surface of embryonic muscles that typically retract once contact with the growth cones are made. We are currently expanding our model of SMA pathology for subsequent second site modifier screens. SPINAL MUSCULAR ATROPHY MODELED IN DROSOPHILA MELANOGASTER Priscilla Auduong (Kelley Murphy, Alice Schmid) Department of Human Genetics University of Utah honors college spring 2012 Kelley Murphy Alice Schmid |
