A screen for new genes mediating synaptic transmission. X. Guo , K.E. Zinsmaier. Department of Neuroscience, 234d Stemmler Hall, University of Pennsylvania School of Medicine, Philadelphia, PA19104-6974, USA.

   Although many proteins of the machinery mediating neurotransmitter release have been identified, some important components are still missing. To gain a better understanding of the molecular mechanisms underlying synaptic transmission, we conducted a F1 screen for lethal mutations disrupting vision in Drosophila, using the EGUF recombination system (Stowers & Schwarz, 1999, Genetics 152, 1631). This method accomplishes the generation of mutant F1 flies whose eyes are homozygous for a potentially lethal mutation while the remaining body is heterozygous. We screened 13,000 male F1 flies for phototaxis by using a countercurrent apparatus. Initially, 173 "blind" lines have been identified, which are mostly homozygous lethal. Half of these "blind" lines exhibit morphologically abnormal eyes under EGUF conditions, while the other half exhibit morphologically normal eyes. Some of the mutations have been examined for a defect in synaptic transmission by electrophysiological recordings at the NMJ of 3rd instar larvae. Line 682 shows normal EJP amplitudes at low stimulation frequency, while at a high stimulation frequency EJPs completely fail within 20 sec. Simultaneously, the frequency of spontaneously occurring mEJPs increases dramatically. In another line, termed 936, EJP amplitudes are reduced by about 60%. During high frequency stimulation at 10 Hz, EJP amplitudes significantly facilitate to 135% of the original response, while EJPs in control become depressed to 80%. A more detailed and systematic study of both and further mutations is currently in progress.