Kismet-dependent regulation of glutamate receptors at the Drosophila Neuromuscular Junction. Rupa Ghosh¹, Srikar Vegesna¹, Hong Boa³, Bing Zhang³, Faith Liebl², Daniel Marenda¹. 1) Drexel University, Philadelphia, PA; 2) Univ of Southern Illinois at Edwardsville, IL; 3) Univ of Oklahoma, OK.

   CHARGE syndrome (CS) is a developmental disorder with a birth incidence of 1:8000-12,000 worldwide. CS affects multiple organ systems such as the eye, ear, heart, facial nerve, nose, CNS and the reproductive system. Additionally, 90% of CS patients exhibit hypotonia & motor co-ordination defects. Two-thirds of the disorder are caused due to haploinsufficiency of the Chromodomain DNA Helicase Binding Protein (CHD7). CHD7 is an epigenetic transcription factor and its Drosophila homolog is Kismet. We reduced kis function in a tissue-specific manner by RNAi using the GAL4-UAS system. We analyzed behavior by a ubiquitous and motorneuron - specific reduction of Kismet protein. This led to a Held-out-wing phenotype and reduced larval and adult locomotion and motor co-ordination. From microarray data, reduced Kismet protein showed a significant upregulation of glutamate biosynthesis genes and downregulation of glutamate receptor subunits. Drosophila neuromuscular junction (NMJ) synapses are glutamatergic in nature. Glutamatergic synapses in Drosophila conduct fast synaptic transmission, which form the basis of locomotion. The analysis of NMJ morphology in 3rd instar larvae with ubiquitous reduction of Kismet protein led to pre-synaptic changes that are most likely compensatory in nature, such as increased branching of the NMJ synapse. We also found a significant reduction of GluRIIC mRNA and relative fluorescent intensity. Further, our electrophysiology results suggested decreased synaptic transmission of the NMJ synapse of muscle 6/7. Taken together, our data is the first to identify GluRs as a downstream target of kismet function. It also indicates that Kismet affects the pre-synaptic component of the NMJ and effects on the post-synaptic side are more likely secondary to the pre-synaptic defects. This study will help better understand the role of Kismet during development and may be extended to the function of CHD7 in humans and CS.