MAPK3 at the Autism-Linked Human 16p11.2 Locus Influences Precise Synaptic Target Selection at Drosophila Larval Neuromuscular Junctions
Sang Mee Park1, Hae Ryoun Park1,2, and Ji Hye Lee1,2,*
1Department of Oral Pathology and BK21Plus Project, School of Dentistry, Pusan National University, Yangsan 50612, Korea, 2Institute of Translational Dental Sciences, Pusan National University, Yangsan 50612, Korea
*Correspondence: jihyelee@pusan.ac.kr
Received December 13, 2016; Revised January 22, 2017; Accepted January 23, 2017.; Published online February 15, 2017.
© Korean Society for Molecular and Cellular Biology. All rights reserved.

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ABSTRACT
Proper synaptic function in neural circuits requires precise pairings between correct pre- and post-synaptic partners. Errors in this process may underlie development of neuropsychiatric disorders, such as autism spectrum disorder (ASD). Development of ASD can be influenced by genetic factors, including copy number variations (CNVs). In this study, we focused on a CNV occurring at the 16p11.2 locus in the human genome and investigated potential defects in synaptic connectivity caused by reduced activities of genes located in this region at Drosophila larval neuromuscular junctions, a well-established model synapse with stereotypic synaptic structures. A mutation of rolled, a Drosophila homolog of human mitogen-activated protein kinase 3 (MAPK3) at the 16p11.2 locus, caused ectopic innervation of axonal branches and their abnormal defasciculation. The specificity of these phenotypes was confirmed by expression of wild-type rolled in the mutant background. Albeit to a lesser extent, we also observed ectopic innervation patterns in mutants defective in Cdk2, Gaq, and Gp93, all of which were expected to interact with Rolled MAPK3. A further genetic analysis in double heterozygous combinations revealed a synergistic interaction between rolled and Gp93. In addition, results from RT-qPCR analyses indicated consistently reduced rolled mRNA levels in Cdk2, Gaq, and Gp93 mutants. Taken together, these data suggest a central role of MAPK3 in regulating the precise targeting of presynaptic axons to proper postsynaptic targets, a critical step that may be altered significantly in ASD. 
Keywords: 16p11.2, autism, copy number variations, Drosophila, MAPK3


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