Publications

Abstract

Mutations of FOXP2 in 7q31 cause a rare disorder involving speech apraxia, accompanied by expressive and receptive language impairments. A recent report described a child with speech and language deficits, and a genomic rearrangement affecting chromosomes 7 and 11. One breakpoint mapped to 7q31 and, although outside its coding region, was hypothesised to disrupt FOXP2 expression. We identified an element 2 kb downstream of this breakpoint with epigenetic characteristics of an enhancer. We show that this element drives reporter gene expression in human cell-lines. Thus, displacement of this element by translocation may disturb gene expression, contributing to the observed language phenotype.

Abstract

Theories addressing the biological basis of language must be built on
an appreciation of the ways that molecular and neurobiological substrates
can contribute to aspects of human cognition. Here, we lay out
the principles by which a genome could potentially encode the necessary
information to produce a language-ready brain. We describe
what genes are; how they are regulated; and how they affect the formation,
function, and plasticity of neuronal circuits. At each step,
we give examples of molecules implicated in pathways that are important
for speech and language. Finally, we discuss technological advances
in genomics that are revealing considerable genotypic variation in
the human population, from rare mutations to common polymorphisms,
with the potential to relate this variation to natural variability
in speech and language skills. Moving forward, an interdisciplinary
approach to the language sciences, integrating genetics, neurobiology,
psychology, and linguistics, will be essential for a complete understanding
of our unique human capacities.

Abstract

Background Bats are able to employ an astonishingly complex vocal repertoire for navigating their environment and conveying social information. A handful of species also show evidence for vocal learning, an extremely rare ability shared only with humans and few other animals. However, despite their potential for the study of vocal communication, bats remain severely understudied at a molecular level. To address this fundamental gap we performed the first transcriptome profiling and genetic interrogation of molecular networks in the brain of a highly vocal bat species, Phyllostomus discolor. Results Gene network analysis typically needs large sample sizes for correct clustering, this can be prohibitive where samples are limited, such as in this study. To overcome this, we developed a novel bioinformatics methodology for identifying robust co-expression gene networks using few samples (N=6). Using this approach, we identified tissue-specific functional gene networks from the bat PAG, a brain region fundamental for mammalian vocalisation. The most highly connected network identified represented a cluster of genes involved in glutamatergic synaptic transmission. Glutamatergic receptors play a significant role in vocalisation from the PAG, suggesting that this gene network may be mechanistically important for vocal-motor control in mammals. Conclusion We have developed an innovative approach to cluster co-expressing gene networks and show that it is highly effective in detecting robust functional gene networks with limited sample sizes. Moreover, this work represents the first gene network analysis performed in a bat brain and establishes bats as a novel, tractable model system for understanding the genetics of vocal mammalian communication.

Abstract

Speech requires precise motor control and rapid sequencing of highly complex vocal musculature. Despite its complexity, most people produce spoken language effortlessly. This is due to activity in distributed neuronal circuitry including cortico-striato-thalamic loops that control speech-motor output. Understanding the neuro-genetic mechanisms that encode these pathways will shed light on how humans can effortlessly and innately use spoken language and could elucidate what goes wrong in speech-language disorders.
FOXP2 was the first single gene identified to cause speech and language disorder. Individuals with FOXP2 mutations display a severe speech deficit that also includes receptive and expressive language impairments. The underlying neuro-molecular mechanisms controlled by FOXP2, which will give insight into our capacity for speech-motor control, are only beginning to be unraveled. Recently FOXP2 was found to regulate genes involved in retinoic acid signaling and to modify the cellular response to retinoic acid, a key regulator of brain development. Herein we explore the evidence that FOXP2 and retinoic acid signaling function in the same pathways. We present evidence at molecular, cellular and behavioral levels that suggest an interplay between FOXP2 and retinoic acid that may be important for fine motor control and speech-motor output.
We propose that retinoic acid signaling is an exciting new angle from which to investigate how neurogenetic mechanisms can contribute to the (spoken) language ready brain.

Abstract

Disrupted in schizophrenia 1 (DISC1) is a leading candidate susceptibility gene for schizophrenia, bipolar disorder, and recurrent major depression, which has been implicated in other psychiatric illnesses of neurodevelopmental origin, including autism. DISC1 was initially identified at the breakpoint of a balanced chromosomal translocation, t(1;11) (q42.1;14.3), in a family with a high incidence of psychiatric illness. Carriers of the translocation show a 50% reduction in DISC1 protein levels, suggesting altered DISC1 expression as a pathogenic mechanism in psychiatric illness. Altered DISC1 expression in the post-mortem brains of individuals with psychiatric illness and the frequent implication of non-coding regions of the gene by association analysis further support this assertion. Here, we provide the first characterisation of the DISC1 promoter region. Using dual luciferase assays, we demonstrate that a region -300bp to -177bp relative to the transcription start site (TSS) contributes positively to DISC1 promoter activity, whilst a region -982bp to -301bp relative to the TSS confers a repressive effect. We further demonstrate inhibition of DISC1 promoter activity and protein expression by FOXP2, a transcription factor implicated in speech and language function. This inhibition is diminished by two distinct FOXP2 point mutations, R553H and R328X, which were previously found in families affected by developmental verbal dyspraxia (DVD). Our work identifies an intriguing mechanistic link between neurodevelopmental disorders that have traditionally been viewed as diagnostically distinct but which do share varying degrees of phenotypic overlap.

Abstract

Purpose: Factors affecting the efficacy of therapeutic monoclonal antibodies (mAb) directed to the epidermal growth factor receptor (EGFR) remain relatively unknown, especially in glioma. Experimental Design: We examined the efficacy of two EGFR-specific mAbs (mAbs 806 and 528) against U87MG-derived glioma xenografts expressing EGFR variants. Using this approach allowed us to change the form of the EGFR while keeping the genetic background constant. These variants included the de2-7 EGFR (or EGFRvIII), a constitutively active mutation of the EGFR expressed in glioma. Results: The efficacy of the mAbs correlated with EGFR number; however, the most important factor was receptor activation. Whereas U87MG xenografts expressing the de2-7 EGFR responded to therapy, those exhibiting a dead kinase de2-7 EGFR were refractory. A modified de2-7 EGFR that was kinase active but autophosphorylation deficient also responded, suggesting that these mAbs function in de2-7 EGFR–expressing xenografts by blocking transphosphorylation. Because de2-7 EGFR–expressing U87MG xenografts coexpress the wild-type EGFR, efficacy of the mAbs was also tested against NR6 xenografts that expressed the de2-7 EGFR in isolation. Whereas mAb 806 displayed antitumor activity against NR6 xenografts, mAb 528 therapy was ineffective, suggesting that mAb 528 mediates its antitumor activity by disrupting interactions between the de2-7 and wild-type EGFR. Finally, genetic disruption of Src in U87MG xenografts expressing the de2-7 EGFR dramatically enhanced mAb 806 efficacy. Conclusions: The effective use of EGFR-specific antibodies in glioma will depend on identifying tumors with activated EGFR. The combination of EGFR and Src inhibitors may be an effective strategy for the treatment of glioma.

Abstract

Mutations in FOXP2, a member of the forkhead family of transcription factor genes, are the only known cause of developmental speech and language disorders in humans. To date, there are no known targets of human FOXP2 in the nervous system. The identification of FOXP2 targets in the developing human brain, therefore, provides a unique tool with which to explore the development of human language and speech. Here, we define FOXP2 targets in human basal ganglia (BG) and inferior frontal cortex (IFC) by use of chromatin immunoprecipitation followed by microarray analysis (ChIP-chip) and validate the functional regulation of targets in vitro. ChIP-chip identified 285 FOXP2 targets in fetal human brain; statistically significant overlap of targets in BG and IFC indicates a core set of 34 transcriptional targets of FOXP2. We identified targets specific to IFC or BG that were not observed in lung, suggesting important regional and tissue differences in FOXP2 activity. Many target genes are known to play critical roles in specific aspects of central nervous system patterning or development, such as neurite outgrowth, as well as plasticity. Subsets of the FOXP2 transcriptional targets are either under positive selection in humans or differentially expressed between human and chimpanzee brain. This is the first ChIP-chip study to use human brain tissue, making the FOXP2-target genes identified in these studies important to understanding the pathways regulating speech and language in the developing human brain. These data provide the first insight into the functional network of genes directly regulated by FOXP2 in human brain and by evolutionary comparisons, highlighting genes likely to be involved in the development of human higher-order cognitive processes.

Abstract

We previously discovered that mutations of the human FOXP2 gene cause a monogenic communication disorder, primarily characterized by difficulties in learning to make coordinated sequences of articulatory gestures that underlie speech. Affected people have deficits in expressive and receptive linguistic processing and display structural and/or functional abnormalities in cortical and subcortical brain regions. FOXP2 provides a unique window into neural processes involved in speech and language. In particular, its role as a transcription factor gene offers powerful functional genomic routes for dissecting critical neurogenetic mechanisms. Here, we employ chromatin immunoprecipitation coupled with promoter microarrays (ChIP-chip) to successfully identify genomic sites that are directly bound by FOXP2 protein in native chromatin of human neuron-like cells. We focus on a subset of downstream targets identified by this approach, showing that altered FOXP2 levels yield significant changes in expression in our cell-based models and that FOXP2 binds in a specific manner to consensus sites within the relevant promoters. Moreover, we demonstrate significant quantitative differences in target expression in embryonic brains of mutant mice, mediated by specific in vivo Foxp2-chromatin interactions. This work represents the first identification and in vivo verification of neural targets regulated by FOXP2. Our data indicate that FOXP2 has dual functionality, acting to either repress or activate gene expression at occupied promoters. The identified targets suggest roles in modulating synaptic plasticity, neurodevelopment, neurotransmission, and axon guidance and represent novel entry points into in vivo pathways that may be disturbed in speech and language disorders.