Functional investigation of microRNA pathways in human speech and language disorders

Thesis

The forkhead-box protein P2 (FOXP2) is a transcription factor implicated in an inherited human speech and language disorder. A heterozygous R553H mutation in the gene is associated with a monogenic form of developmental verbal dyspraxia. Reduced functional dosage in mice brains causes altered synaptic plasticity in cortico-striatal circuits, and impairs motor learning. Genome-wide in vivo ChIP–chip screens for Foxp2 binding in the developing mouse brain have identified a set of microRNAs (miRNAs) whose promoter regions were occupied by Foxp2. Thus, I employed microarray expression profiling to identify microRNAs regulated by Foxp2 in the embryonic mouse brain. Interestingly, the microarray results were divergent from in vitro effects of Foxp2/FOXP2 on these microRNAs, suggesting that regulation of these microRNAs is context-specific. In light of the regulation of MIR137 by FOXP2, I went on to study a putative genetic network involving FOXP2, TCF4, CNTNAP2 and MIR137. While TCF4, CNTNAP2 and MIR137 each are regulated in vitro by FOXP2, the regions bound by FOXP2 were insufficient to generate the anticipated transcriptional regulation when cloned upstream of a reporter gene. To test if FOXP2-regulated microRNAs are risk factors for specific language impairment (SLI), I performed candidate association analyses on a large family-based cohort of SLI probands. I also identified 5 common variants and 3 rare variants in predicted microRNA binding sites in the 3' UTR from the exomes of 48 of these probands. I tested them for association with SLI in the larger cohort. rs72727021, lying in the miR-192/215 binding site of the C9ORF100 3' UTR, was significantly associated with nonword repetition in the SLI cohort (p-value = 2.75 X 10^-4). Testing of rs72727021 and the 3 rare variants with a luciferase reporter assay revealed that 2 rare variants affected gene expression levels independently of the microRNA, suggesting that these 2 microRNA binding sites might be risk factors contributing to the SLI phenotype. FOXP2/Foxp2 is likely to act through microRNAs to generate and fine-tune neural gene expressionpatterns that underlie neuronal function and neural circuits important for vocal learning, and for human speech and language.

Authors: Ho, J

• Publication date: 2014
• DOI: 10.5287/ora-44gmjbrnd
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: Oxford University, UK
• Language: English
• Keywords: microRNAs; exome sequencing; microarray; FOXP2
• Subjects: Language and cognitive development; Neuroscience; Neurogenetics