Drosophila Tempura, a putative protein prenyltransferase, regulate synaptic growth and synaptic transmission. Kuchuan Chen¹, Wu-Lin Charng¹, Shinya Yamamoto¹, Nele Haelterman¹, Guang Lin^2,4, Hugo Bellen^1,2,3,4. 1) Program in Developmental Biology; 2) Dept of Molecular and Human Genetics; 3) Dept of Neuroscience; 4) Howard Hughes Medical Institute; Jan and Dan Duncan Neurological Research Institute, Baylor College of Medicine, Houston, TX.

   Neurons require efficient and specialized vesicle trafficking for their proper development and function. Small Rab GTPases are key regulators of this vesicular transport system. Mutations in Rab proteins or their regulators have been shown to be associated with several neurological diseases. In a forward genetic screen of the Drosophila X chromosome, we isolated 8 alleles of an uncharacterized gene that we named tempura. Our current data (see abstract by Wu-Lin Charng et al.) indicate that tempura is a subunit of geranylgeranyl transferase II (GGT II), an enzyme involved in the covalent attachment of 20-carbon geranylgeranyl groups to Rab GTPases. This lipid modification functions as a membrane anchor for Rabs and is paramount for the function and subcellular localization of the Rab proteins. To investigate the role of tempura in the nervous system, we examined the larval neuromuscular junction (NMJ) in these mutants. Interestingly, loss of tempura causes a severe morphological defect in the larval NMJ. The axon terminal boutons are less branched and more clustered, suggesting that tempura plays an important role in synaptic growth. To determine if tempura is required for proper synaptic function, we performed FM1-43 assays and electrophysiological recording. The size of the excitatory junction potential (EJP) in tempura mutants is comparable to controls, suggesting normal exocytosis. However, FM1-43 fluorescence is reduced in tempura mutants, indicating impaired endocytosis of synaptic vesicles. To examine the expression pattern of tempura, we created transgenic fly with a genomically tagged gene. Surprisingly, tempura is highly expressed in glial cells in L3 instar larvae. These data suggest that tempura may play a role in glial cells that regulate neuronal development and function via non-autonomous pathway.