Shining a light on protein networks in speech and language [Invited talk]

FOXP1 and FOXP2 are transcription factors with important roles in brain development. FOXP2 was the first gene to be clearly implicated in speech/language disorder. Sequence variants cause a monogenic form of speech disorder, of which the predominant feature is developmental verbal dyspraxia. Heterozygous FOXP1 mutations have been reported in individuals with autism and intellectual disability accompanied by severe speech/language problems. At the protein level, FOXP1 and FOXP2 are co-expressed in similar neural circuits and can dimerize, with the potential to co-regulate downstream targets, including those involved in language development. In our work, we use these two transcriptions factors as a gateway into protein networks that may underlie the formation of brain circuits important for speech/language development. Although several putative FOXP interactors have been previously identified, many await further functional validation. We developed a bioluminescence resonance energy transfer (BRET) system to assess FOXP dimerization in live cells. HEK293 cells were transiently transfected with pairs of FOXP expression constructs fused to either Renilla luciferase or YFP and resonance energy transfer was measured between the two fusion proteins. The BRET method was first validated by analyzing FOXP homo- and heterodimerization. We then investigated the functional effects of known FOXP2 and FOXP1 variants identified in disorders affecting speech/language. Furthermore, we assessed protein-protein interactions between FOXP2 variants and previously identified putative interactors. In summary, we have developed a robust functional assay which allows qualitative and quantitative assessment of FOXP protein-protein interactions, thereby providing insight into the pathways underlying complex neurodevelopmental disorders such as autism and speech/language impairment