Using iPSCs to Model Angelman and Chromosome 15q11.2-q13 Duplication (Dup15q) Syndromes

Background: Angelman syndrome (AS) is a neurodevelopmental disorder with profound impacts on cognitive function, speech/language, and seizure susceptibility that is most frequently caused by deletions of maternal chromosome 15q11.2-q13.   Autism is frequently diagnosed in individuals with AS.  Conversely, duplications of maternal chromosome 15q11.2-q13 are one of the most common cytogenetic anomalies associated with autism.   Cognitive function, speech/language, and seizure susceptibility is also impacted in individuals with Dup15q syndrome.   Disruption in the copy number of one gene, UBE3A, underlies both disorders. 

Objectives: To develop human iPSC models of AS and Dup15q syndromes to 1.) understand the local gene regulation underlying these disorders, 2.) to identify cellular phenotypes associated with both disorders, and 3.) to test potential therapeutic approaches to restore normal 15q gene expression. 

Methods: iPSCs from AS and Dup15q patients were generated from patient fibroblast, cord blood, or peripheral blood samples using retrovirus, lentivirus, episomal, and sendai virus reprogramming methods.  Genome editing using CRISPR/CAS9 technology was used to modulate gene regulation.  iPSCs were differentiated into forebrain cortical neurons using an embryoid body-based or monolayer protocol.  RT-qPCR and RNA-Seq were used to quantify local and global gene expression.  Microscopy and electrophysiology were used to investigate cellular phenotypes. 

Results: We have generated iPSCs from several individuals with AS and Dup15q syndromes and have differentiated them into forebrain cortical neurons.   We have genetically corrected AS iPSCs and have modulated expression of UBE3A in iPSCs and neurons using a variety of methods. We compared 15q gene expression between the different iPSC lines as well as from their neuronal derivatives.  We found that gene expression closely followed copy number in iPSCs, but deviated somewhat from copy number in iPSC-derived neurons.  Early electrophysiology experiments and examination of dendritic spine morphology corroborate a defect in neuronal development.   

Conclusions: Human iPSCs derived from individuals with AS and Dup15q syndrome provide an attractive model to study gene expression and cellular phenotypes of neurodevelopmental disorders, including ASD.  They can be used to gain important insight into the neuronal development deficits underlying these autism-related disorders, as well as to test potential therapeutic approaches.