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JAKMIP1 Is a Novel Component of an FMRP-Associated RNP Complex and Regulates Neuronal Translation

Friday, 3 May 2013: 11:45
Chamber Hall (Kursaal Centre)
J. M. Berg1, L. Chen2, A. Oguro-Ando3, J. L. Stein4, J. A. Miller2, A. A. Vashisht5, E. P. Kite2, A. Li2, O. Penagarikano6, J. A. Wohlschlegel5 and D. H. Geschwind7, (1)Program in Neuroscience IDP; Semel Institute for Neuroscience and Human Behavior; Program in Neurogenetics, Department of Neurology, The University of California, Los Angeles, Los Angeles, CA, (2)Department of Neurology, The University of California, Los Angeles, Los Angeles, CA, (3)UCLA, Los Angeles, CA, (4)Department of Neurology; Program in Neurogenetics, The University of California, Los Angeles, Los Angeles, CA, (5)Biological chemistry, The University of California, Los Angeles, Los Angeles, CA, (6)University of California at Los Angeles, Los Angeles, CA, (7)Semel Institute for Neuroscience and Human Behavior; Department of Neurology; Program in Neurogenetics; Center for Autism Research and Treatment and Center for Neurobehavioral Genetics, University of California at Los Angeles, Los Angeles, CA
Background The regulation of neuronal translation is crucial for proper neuronal development and function and is among several biological processes implicated in autism spectrum disorders (ASD).  Janus kinase and microtubule-interacting protein 1 (JAKMIP1) is dysregulated in ASD subjects with Fragile X syndrome, (dup)15q, and idiopathic ASD. However, its role in brain development is unknown.

Objectives:   We used an unbiased approach to characterize JAKMIP1’s protein interactome. We identified an interaction with the FMRP-associated translational complex and are interested in the mechanism and purpose of the FMRP-JAKMIP1 interaction, JAKMIP1’s association and regulation of FMRP mRNA translational targets, and JAKMIP1’s role in neuronal translation.

Methods : We used Multidimensional Protein Identification Technology (MudPIT) to identify JAKMIP1’s proteomic interactome.  To test JAKMIP1’s presence in polyribosomes, we conducted polyribosome fractionation, immunoprecipitation from a BacTRAP neural cell line expressing eGFP-tagged polyribosomes, and immunocytochemistry of JAKMIP1 and poly(A)-binding protein 1 (PABPC1) in neurons. To test JAKMIP1’s association with FMRP mRNA targets, we conducted quantitative RTPCR with RNA from JAKMIP1 immunoprecipitation.  We tested JAKMIP1’s translational control of a subset of these targets by protein analysis at synaptosomal membranes in neural systems with reduced JAKMIP1.  We used fluorescence non-canonical amino acid tagging (FUNCAT) to assess translation in neurons lacking JAKMIP1.

Results:   We show that JAKMIP1 is present in the polyribosome fraction and binds FMRP protein as well as several of its mRNA targets, including Fmr1 and PSD95, both of which have increased expression in synaptosomal membranes upon Jakmip1 knockdown. Furthermore, we show that neurons from Jakmip1 knockout mice show significantly reduced nascent translation.

Conclusions : These results identify JAKMIP1 as a new protein involved in the regulation of neuronal translation and show that it interacts with the process of FMRP-related translational control.  Elucidation of the precise molecular interactions occurring within the JAKMIP1 and FMRP-associated complex, its relationship to neuronal activity, as well as the interaction of JAKMIP1 with the transport machinery are exciting new directions that we are exploring.

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