Advances in genetics and genomics have improved our understanding of autism spectrum disorders. As many genes have been implicated, we look to points of convergence among these genes across biological systems to better understand and treat these disorders.

Rare maternally inherited duplications at 15q11-13 are observed in about 1% of individuals with an Autism Spectrum Disorder (ASD), making it among the most common causes of ASD. 15q11-13 comprises a complex region, and because this CNV encompasses many genes, it is important to explore individual genotypephenotype relationships. Cytoplasmic FMR1 interacting protein 1 (CYFIP1) is of particular interest because of its interaction with FMRP, its upregulation in transformed lymphoblastoid cell lines from patients with duplications at 15q11-13 and ASD, and the presence of smaller overlapping deletions of CYFIP1 in patients with schizophrenia and intellectual disability. Here, we confirm that CYFIP1 is upregulated in transformed lymphoblastoid cell lines, and demonstrate its upregulation in postmortem brain from 15q11-13 duplication patients for the first time. To investigate how increased CYFIP1 dosage might predispose to neurodevelopmental disease, we studied the consequence of its overexpression in multiple systems. We show that overexpression of CYFIP1 results in morphological abnormalities including cellular hypertrophy in SY5Y cells and differentiated mouse neuronal progenitors. We validate these results in vivo by generating a BAC transgenic mouse, which over-expresses CYFIP1 under the endogenous promotor, observing an increase in the proportion of mature dendrite spines and dendritic spine density. Gene expression profiling at embryonic day 15 suggested dysregulation of mTOR signaling, which was confirmed at the protein level. Importantly, similar evidence of mTOR-related dysregulation was seen in brains from 15q11-13 duplication patients with ASD. Finally, treatment of differentiated mouse neuronal progenitors with an mTOR inhibitor (rapamycin) rescued the morphological abnormalities resulting from CYFIP1 overexpression. Together, these data show that CYFIP1 overexpression results in specific cellular phenotypes, and implicate modulation by mTOR signaling, further emphasizing its role as a potential convergent pathway in some forms of ASD.

SUMMARY Autism spectrum disorder is a heritable, common neurodevelopmental disorder with diverse genetic causes. Several studies have implicated protein synthesis as one among several of its potential convergent mechanisms. We originally identified janus kinase and microtubule-interacting protein 1 (JAKMIP1) as differentially expressed in patients with distinct syndromic forms of ASD, Fragile X Syndrome and 15q duplication syndrome. Here, we provide multiple lines of evidence that JAKMIP1 is a component of polyribosomes and an RNP translational regulatory complex that includes fragile X mental retardation protein, DEAD box helicase 5, and poly(A) binding protein, cytoplasmic 1. JAKMIP1 loss dysregulates neuronal translation during synaptic development, affecting glutamatergic NMDAR signaling, and results in social deficits, stereotyped activity, abnormal postnatal vocalizations, and other autistic-like behaviors in the mouse. These findings define an important and novel role for JAKMIP1 in neural development and further highlight pathways regulating mRNA translation during synaptogenesis in the genesis of neurodevelopmental disorders.

Background CYFIP1, a protein that interacts with FMRP and regulates protein synthesis and actin dynamics, is overexpressed in Dup15q syndrome as well as autism spectrum disorder (ASD). While CYFIP1 heterozygosity has been rigorously studied due to its loss in 15q11.2 deletion, Prader-Willi and Angelman syndrome, the effects of CYFIP1 overexpression, as is observed in patients with CYFIP1 duplication, are less well understood. Methods We developed and validated a mouse model of human CYFIP1 overexpression ( CYFIP1 OE) using qPCR and western blot analysis. We performed a large battery of behavior testing on these mice, including ultrasonic vocalizations, three-chamber social assay, home-cage behavior, Y-maze, elevated plus maze, open field test, Morris water maze, fear conditioning, prepulse inhibition, and the hot plate assay. We also performed RNA sequencing and analysis on the basolateral amygdala. Results Extensive behavioral testing in CYFIP1 OE mice reveals no changes in the core behaviors related to ASD: social interactions and repetitive behaviors. However, we did observe mild learning deficits and an exaggerated fear response. Using RNA sequencing of the basolateral amygdala, a region associated with fear response, we observed changes in pathways related to cytoskeletal regulation, oligodendrocytes, and myelination. We also identified GABA-A subunit composition changes in basolateral amygdala neurons, which are essential components of the neural fear conditioning circuit. Conclusion Overall, this research identifies the behavioral and molecular consequences of CYFIP1 overexpression and how they contribute to the variable phenotype seen in Dup15q syndrome and in ASD patients with excess CYFIP1. Electronic supplementary material The online version of this article (10.1186/s13229-019-0278-0) contains supplementary material, which is available to authorized users.

No abstract