Autism Spectrum Disorders (ASD) are heritable neurodevelopmental disorders, affecting one in 88 children and involving hundreds of genes. The study of convergent biological pathways and simpler, monogenic forms of ASD are useful tools in understanding ASD. Fragile X syndrome (FXS) meets both criteria, as FMRP, the protein disrupted in FXS, regulates neuronal translation, a biological convergence point in autism, and is caused by a single gene mutation. Our group recently identified JAKMIP1 as downstream of both FMRP and CYFIP1, a regulator of FMRP-dependent translation at the synapse, in patient, in vitro and in vivo studies. However, little is known about JAKMIP1's developmental function in the CNS, and more specifically its relationship with FMRP.
To ascertain JAKMIP1's function, we determined when and where JAKMIP1 was expressed during brain development and used a gel free mass spectrometry, Multidimensional Protein Identification Technology (MudPIT), to uncover JAKMIP1's developmental protein interactome. We conducted gene ontology analysis of high confidence interactors to determine JAKMIP1 function via guilt-by association and validated top targets by co-immunoprecipitation. These studies predicted a role for JAKMIP1 in FMRP translational control during postnatal brain development. We confirmed this by showing that JAKMIP1 binds to FMRP protein and associates with and regulates well-established FMRP mRNA targets, including PSD95, which showed decreased expression at synaptosomal membranes and unloading from translational complexes in Jakmip1 KO mice. Gene expression profiling of postnatal Jakmip1 KO mouse brains implicates JAKMIP1 in regulating FMRP mRNA targets, as Jakmip1 KO brain expression profiles show statistical overlap with high confidence FMRP RNA binding partners.
We validated JAKMIP1's role in translation and membership in translational complexes through in vivo polyribosome fractionation in mice administered puromycin or with Jakmip1 knockout, JAKMIP1 co-immunoprecipitation with eGFP-tagged polyribosomes, and colocalization of JAKMIP1 with translational complexes in neurons. We found that JAKMIP1 is expressed in polyribosomes in vivo and in vitro, contributes to the protein makeup of translational complexes in vivo, and regulates neuronal translation. To test if disruptions in JAKMIP1 function translate into FXS and ASD related behaviors, we generated a Jakmip1 knockout mouse. We found that loss of Jakmip1 leads to behavioral abnormalities overlapping those of Fmr1 knockout mice and mouse models of ASD, including restrictive and repetitive behaviors, impaired social behavior and altered anxiety profiles.
Taken together, these studies demonstrate a major role for JAKMIP1 in neurological development involving FMRP-related translational control critical for establishing and/or maintaining normal social, repetitive, and anxiety-associated behavior.