Publications

Abstract

Mutations of the FOXP2 gene cause a severe speech and language disorder, providing a molecular window into the neurobiology of language. Individuals with FOXP2 mutations have structural and functional alterations affecting brain circuits that overlap with sites of FOXP2 expression, including regions of the cortex, striatum, and cerebellum. FOXP2 displays complex patterns of expression in the brain, as well as in non-neuronal tissues, suggesting that sophisticated regulatory mechanisms control its spatio-temporal expression. However, to date, little is known about the regulation of FOXP2 or the genomic elements that control its expression. Using chromatin conformation capture (3C), we mapped the human FOXP2 locus to identify putative enhancer regions that engage in long-range interactions with the promoter of this gene. We demonstrate the ability of the identified enhancer regions to drive gene expression. We also show regulation of the FOXP2 promoter and enhancer regions by candidate regulators – FOXP family and TBR1 transcription factors. These data point to regulatory elements that may contribute to the temporal- or tissue-specific expression patterns of human FOXP2. Understanding the upstream regulatory pathways controlling FOXP2 expression will bring new insight into the molecular networks contributing to human language and related disorders.

Abstract

Intellectual disability (ID) is a severe neurodevelopmental disorder with genetically heterogeneous causes. Large-scale sequencing has led to the identification of many gene-disrupting mutations; however, a substantial proportion of cases lack a molecular diagnosis. As such, there remains much to uncover for a complete understanding of the genetic underpinnings of ID. Genetic variants present in non-coding regions of the genome have been highlighted as potential contributors to neurodevelopmental disorders given their role in regulating gene expression. Nevertheless the functional characterization of non-coding variants remains challenging. We describe the identification and characterization of de novo non-coding variation in 3′UTR regulatory regions within an ID cohort of 50 patients. This cohort was previously screened for structural and coding pathogenic variants via CNV, whole exome and whole genome analysis. We identified 44 high-confidence single nucleotide non-coding variants within the 3′UTR regions of these 50 genomes. Four of these variants were located within predicted miRNA binding sites and were thus hypothesised to have regulatory consequences. Functional testing showed that two of the variants interfered with miRNA-mediated regulation of their target genes, AMD1 and FAIM. Both these variants were found in the same individual and their functional consequences may point to a potential role for such variants in intellectual disability.

Abstract

Understanding the genetic factors underlying neurodevelopmental and neuropsychiatric disorders is a major challenge given their prevalence and potential severity for quality of life. While large-scale genomic screens have made major advances in this area, for many disorders the genetic underpinnings are complex and poorly understood. To date the field has focused predominantly on protein coding variation, but given the importance of tightly controlled gene expression for normal brain development and disorder, variation that affects non-coding regulatory regions of the genome is likely to play an important role in these phenotypes. Herein we show the importance of 3 prime untranslated region (3'UTR) non-coding regulatory variants across neurodevelopmental and neuropsychiatric disorders. We devised a pipeline for identifying and functionally validating putatively pathogenic variants from next generation sequencing (NGS) data. We applied this pipeline to a cohort of children with severe specific language impairment (SLI) and identified a functional, SLI-associated variant affecting gene regulation in cells and post-mortem human brain. This variant and the affected gene (ARHGEF39) represent new putative risk factors for SLI. Furthermore, we identified 3′UTR regulatory variants across autism, schizophrenia and bipolar disorder NGS cohorts demonstrating their impact on neurodevelopmental and neuropsychiatric disorders. Our findings show the importance of investigating non-coding regulatory variants when determining risk factors contributing to neurodevelopmental and neuropsychiatric disorders. In the future, integration of such regulatory variation with protein coding changes will be essential for uncovering the genetic causes of complex neurological disorders and the fundamental mechanisms underlying health and disease

Abstract

Sensory systems experience a trade-off between maximizing the
detail and amount of sampled information. Thistrade-off is particularly
pronounced in sensorysystemsthat are highlyspecialised fora single
task and thus experience limitations in other tasks. We hypothesised
that combining sensory input from multiple streams of information
may resolve this trade-off and improve detection and sensing
reliability. Specifically, we predicted that perceptive limitations
experienced by animals reliant on specialised active echolocation
can be compensated for by the phylogenetically older and less
specialised process of passive hearing. We tested this hypothesis in
greater horseshoe bats, which possess morphological and neural
specialisations allowing them to identify fluttering prey in dense
vegetation using echolocation only. At the same time, their
echolocation system is both spatially and temporally severely
limited. Here, we show that greater horseshoe bats employ passive
hearing to initially detect and localise prey-generated and other
environmental sounds, and then raise vocalisation level and
concentrate the scanning movements of their sonar beam on the
sound source for further investigation with echolocation. These
specialised echolocators thus supplement echo-acoustic information
with environmental acoustic cues, enlarging perceived space beyond
their biosonar range. Contrary to our predictions, we did not find
consistent preferences for prey-related acoustic stimuli, indicating the
use of passive acoustic cues also for detection of non-prey objects.
Our findings suggest that even specialised echolocators exploit a
wide range of environmental information, and that phylogenetically
older sensory systems can support the evolution of sensory
specialisations by compensating for their limitations.

Abstract

Although humans are unmatched in their capacity to produce
speech and learn language, comparative approaches in diverse
animalmodelsareabletoshedlightonthebiologicalunderpinnings
of language-relevant traits. In the study of vocal learning, a trait
crucial for spoken language, passerine birds have been the
dominant models, driving invaluable progress in understanding the
neurobiology and genetics of vocal learning despite being only
distantly related to humans. To date, there is sparse evidence that
our closest relatives, nonhuman primates have the capability to
learn new vocalisations. However, a number of other mammals
have shown the capacity for vocal learning, such as some
cetaceans, pinnipeds, elephants, and bats, and we anticipate that
with further study more species will gain membership to this
(currently) select club. A broad, cross-species comparison of vocal
learning, coupled with careful consideration of the components
underlying this trait, is crucial to determine how human speech and
spoken language is biologically encoded and how it evolved. We
emphasise the need to draw on the pool of promising species that
havethusfarbeenunderstudiedorneglected.Thisisbynomeansa
call for fewer studies in songbirds, or an unfocused treasure-hunt,
but rather an appeal for structured comparisons across a range of
species, considering phylogenetic relationships, ecological and
morphological constrains, developmental and social factors, and
neurogenetic underpinnings. Herein, we promote a comparative
approachhighlightingtheimportanceofstudyingvocallearningina
broad range of model species, and describe a common framework
for targeted cross-taxon studies to shed light on the biology and
evolution of vocal learning.

Abstract

Bats are gregarious, highly vocal animals that possess a broad repertoire of social vocalisations. For in-depth studies of their vocal behaviours, including vocal flexibility and vocal learning, it is necessary to gather repeatable evidence from controlled laboratory experiments on isolated individuals. However, such studies are rare for one simple reason: eliciting social calls in isolation and under operant control is challenging and has rarely been achieved. To overcome this limitation, we designed an automated setup that allows conditioning of social vocalisations in a new context, and tracks spectro-temporal changes in the recorded calls over time. Using this setup, we were able to reliably evoke social calls from temporarily isolated lesser spear-nosed bats (Phyllostomus discolor). When we adjusted the call criteria that could result in food reward, bats responded by adjusting temporal and spectral call parameters. This was achieved without the help of an auditory template or social context to direct the bats. Our results demonstrate vocal flexibility and vocal usage learning in bats. Our setup provides a new paradigm that allows the controlled study of the production and learning of social vocalisations in isolated bats, overcoming limitations that have, until now, prevented in-depth studies of these behaviours.

Abstract

Language, humans’ most distinctive trait, still remains a ‘mystery’ for evolutionary theory. It is underpinned by a universal infrastructure—cooperative turn-taking—which has been suggested as an ancient mechanism bridging the existing gap between the articulate human species and their inarticulate primate cousins. However, we know remarkably little about turn-taking systems of non-human animals, and methodological confounds have often prevented meaningful cross-species comparisons. Thus, the extent to which cooperative turn-taking is uniquely human or represents a homologous and/or analogous trait is currently unknown. The present paper draws attention to this promising research avenue by providing an overview of the state of the art of turn-taking in four animal taxa—birds, mammals, insects and anurans. It concludes with a new comparative framework to spur more research into this research domain and to test which elements of the human turn-taking system are shared across species and taxa.

Abstract

Genes including FOXP2, FOXP1 and CNTNAP2, have been implicated in human speech and language phenotypes, pointing to a role in the development of normal language-related circuitry in the brain. Although speech and language are unique human phenotypes, a comparative approach is possible by addressing language-relevant traits in animal model systems. One such trait, vocal learning, represents an essential component of human spoken language, and is shared by cetaceans, pinnipeds, elephants, some birds and bats. Given their vocal learning abilities, gregarious nature, and reliance on vocalisations for social communication and navigation, bats represent an intriguing mammalian system in which to explore language-relevant genes. We used immunohistochemistry to detail the distribution of FoxP2, FoxP1 and Cntnap2 proteins, accompanied by detailed cytoarchitectural histology in the brains of two vocal learning bat species; Phyllostomus discolor and Rousettus aegyptiacus. We show widespread expression of these genes, similar to what has been previously observed in other species, including humans. A striking difference was observed in the adult Phyllostomus discolor bat, which showed low levels of FoxP2 expression in the cortex, contrasting with patterns found in rodents and non-human primates. We created an online, open-access database within which all data can be browsed, searched, and high resolution images viewed to single cell resolution. The data presented herein reveal regions of interest in the bat brain and provide new opportunities to address the role of these language-related genes in complex vocal-motor and vocal learning behaviours in a mammalian model system.

Abstract

Bats are unique among mammals, possessing some of the rarest mammalian adaptations, including true self-powered flight, laryngeal echolocation, exceptional longevity, unique immunity, contracted genomes, and vocal learning. They provide key ecosystem services, pollinating tropical plants, dispersing seeds, and controlling insect pest populations, thus driving healthy ecosystems. They account for more than 20% of all living mammalian diversity, and their crown-group evolutionary history dates back to the Eocene. Despite their great numbers and diversity, many species are threatened and endangered. Here we announce Bat1K, an initiative to sequence the genomes of all living bat species (n∼1,300) to chromosome-level assembly. The Bat1K genome consortium unites bat biologists (>132 members as of writing), computational scientists, conservation organizations, genome technologists, and any interested individuals committed to a better understanding of the genetic and evolutionary mechanisms that underlie the unique adaptations of bats. Our aim is to catalog the unique genetic diversity present in all living bats to better understand the molecular basis of their unique adaptations; uncover their evolutionary history; link genotype with phenotype; and ultimately better understand, promote, and conserve bats. Here we review the unique adaptations of bats and highlight how chromosome-level genome assemblies can uncover the molecular basis of these traits. We present a novel sequencing and assembly strategy and review the striking societal and scientific benefits that will result from the Bat1K initiative.

Abstract

Heterozygous mutations of the Forkhead-box protein 2 (FOXP2) gene in humans cause childhood apraxia of speech. Loss of Foxp2 in mice is known to affect striatal development and impair motor skills. However, it is unknown if striatal excitatory/inhibitory balance is affected during development and if the imbalance persists into adulthood. We investigated the effect of reduced Foxp2 expression, via a loss-of-function mutation, on striatal medium spiny neurons (MSNs). Our data show that heterozygous loss of Foxp2 decreases excitatory (AMPA receptor-mediated) and increases inhibitory (GABA receptor-mediated) currents in D1 dopamine receptor positive MSNs of juvenile and adult mice. Furthermore, reduced Foxp2 expression increases GAD67 expression, leading to both increased presynaptic content and release of GABA. Finally, pharmacological blockade of inhibitory activity in vivo partially rescues motor skill learning deficits in heterozygous Foxp2 mice. Our results suggest a novel role for Foxp2 in the regulation of striatal direct pathway activity through managing inhibitory drive.

Abstract

Neurodevelopmental disorders have a strong genetic component, but despite widespread efforts, the specific genetic factors underlying these disorders remain undefined for a large proportion of affected individuals. Given the accessibility of exome-sequencing, this problem has thus far been addressed from a protein-centric standpoint; however, protein-coding regions only make up ∼1-2% of the human genome. With the advent of whole-genome sequencing we are in the midst of a paradigm shift as it is now possible to interrogate the entire sequence of the human genome (coding and non-coding) to fill in the missing heritability of complex disorders. These new technologies bring new challenges, as the number of non-coding variants identified per individual can be overwhelming, making it prudent to focus on non-coding regions of known function, for which the effects of variation can be predicted and directly tested to assess pathogenicity. The 3’UTRome is a region of the non-coding genome that perfectly fulfils these criteria and is of high interest when searching for pathogenic variation related to complex neurodevelopmental disorders. Herein, we review the regulatory roles of the 3’UTRome as binding sites for microRNAs, RNA binding proteins or during alternative polyadenylation. We detail existing evidence that these regions contribute to neurodevelopmental disorders and outline strategies for identification and validation of novel putatively pathogenic variation in these regions. This evidence suggests that studying the 3’UTRome will lead to the identification of new risk factors, new candidate disease genes and a better understanding of the molecular mechanisms contributing to NDDs.

Abstract

Past events like fluctuations in population size and post-glacial colonization processes may influence the relative importance of genetic drift, migration and selection when determining the present day patterns of genetic variation. We disentangle how drift, selection and migration shape neutral and adaptive genetic variation in 12 moor frog populations along a 1700 km latitudinal gradient. We studied genetic differentiation and variation at a MHC exon II locus and a set of 18 microsatellites.
Results

Using outlier analyses, we identified the MHC II exon 2 (corresponding to the β-2 domain) locus and one microsatellite locus (RCO8640) to be subject to diversifying selection, while five microsatellite loci showed signals of stabilizing selection among populations. STRUCTURE and DAPC analyses on the neutral microsatellites assigned populations to a northern and a southern cluster, reflecting two different post-glacial colonization routes found in previous studies. Genetic variation overall was lower in the northern cluster. The signature of selection on MHC exon II was weaker in the northern cluster, possibly as a consequence of smaller and more fragmented populations.
Conclusion

Our results show that historical demographic processes combined with selection and drift have led to a complex pattern of differentiation along the gradient where some loci are more divergent among populations than predicted from drift expectations due to diversifying selection, while other loci are more uniform among populations due to stabilizing selection. Importantly, both overall and MHC genetic variation are lower at northern latitudes. Due to lower evolutionary potential, the low genetic variation in northern populations may increase the risk of extinction when confronted with emerging pathogens and climate change.

Abstract

A commentary on
FOXP2 drives neuronal differentiation by interacting with retinoic acid signaling pathways

by Devanna, P., Middelbeek, J., and Vernes, S. C. (2014). Front. Cell. Neurosci. 8:305. doi: 10.3389/fncel.2014.00305

Abstract

Understanding the biological foundations of language is vital to gaining insight into how the capacity for language may have evolved in humans. Animal models can be exploited to learn about the biological underpinnings of shared human traits, and although no other animals display speech or language, a range of behaviors found throughout the animal kingdom are relevant to speech and spoken language. To date, such investigations have been dominated by studies of our closest primate relatives searching for shared traits, or more distantly related species that are sophisticated vocal communicators, like songbirds. Herein I make the case for turning our attention to the Chiropterans, to shed new light on the biological encoding and evolution of human language-relevant traits. Bats employ complex vocalizations to facilitate navigation as well as social interactions, and are exquisitely tuned to acoustic information. Furthermore, bats display behaviors such as vocal learning and vocal turn-taking that are directly pertinent for human spoken language. Emerging technologies are now allowing the study of bat vocal communication, from the behavioral to the neurobiological and molecular level. Although it is clear that no single animal model can reflect the complexity of human language, by comparing such findings across diverse species we can identify the shared biological mechanisms likely to have influenced the evolution of human language. Keywords