Publications

Abstract

ARHGEF39 was previously implicated in developmental language disorder (DLD) via a functional polymorphism that can disrupt post-transcriptional regulation by microRNAs. ARHGEF39 is part of the family of Rho guanine nucleotide exchange factors (RhoGEFs) that activate small Rho GTPases to regulate a wide variety of cellular processes. However, little is known about the function of ARHGEF39, or how its function might contribute to neurodevelopment or related disorders. Here, we explore the molecular function of ARHGEF39 and show that it activates the Rho GTPase RHOA and that high ARHGEF39 expression in cell cultures leads to an increase of detached cells. To explore its role in neurodevelopment, we analyse published single cell RNA-sequencing data and demonstrate that ARHGEF39 is a marker gene for proliferating neural progenitor cells and that it is co-expressed with genes involved in cell division. This suggests a role for ARHGEF39 in neurogenesis in the developing brain. The co-expression of ARHGEF39 with other RHOA-regulating genes supports RHOA as substrate of ARHGEF39 in neural cells, and the involvement of RHOA in neuropsychiatric disorders highlights a potential link between ARHGEF39 and neurodevelopment and disorder. Understanding the GTPase substrate, co-expression network, and processes downstream of ARHGEF39 provide new avenues for exploring the mechanisms by which altered expression levels of ARHGEF39 may contribute to neurodevelopment and associated disorders.

Abstract

Relationships among laurasiatherian clades represent one of the most highly disputed topics in mammalian phylogeny. In this study, we attempt to disentangle laurasiatherian interordinal relationships using two independent genome-level approaches: (1) quantifying retrotransposon presence/absence patterns, and (2) comparisons of exon datasets at the levels of nucleotides and amino acids. The two approaches revealed contradictory phylogenetic signals, possibly due to a high level of ancestral incomplete lineage sorting. The positions of Eulipotyphla and Chiroptera as the first and second earliest divergences were consistent across the approaches. However, the phylogenetic relationships of Perissodactyla, Cetartiodactyla, and Ferae, were contradictory. While retrotransposon insertion analyses suggest a clade with Cetartiodactyla and Ferae, the exon dataset favoured Cetartiodactyla and Perissodactyla. Future analyses of hitherto unsampled laurasiatherian lineages and synergistic analyses of retrotransposon insertions, exon and conserved intron/intergenic sequences might unravel the conflicting patterns of relationships in this major mammalian clade.

Abstract

Progress in genome sequencing now enables the large-scale generation of reference genomes. Various international initiatives aim to generate reference genomes representing global biodiversity. These genomes provide unique insights into genomic diversity and architecture, thereby enabling comprehensive analyses of population and functional genomics, and are expected to revolutionize conservation genomics.

Abstract

Vocal learning, the ability to produce modified vocalizations via learning from acoustic signals, is a key trait in the evolution of speech. While extensively studied in songbirds, mammalian models for vocal learning are rare. Bats present a promising study system given their gregarious natures, small size, and the ability of some species to be maintained in captive colonies. We utilize the pale spear-nosed bat (Phyllostomus discolor) and report advances in establishing this species as a tractable model for understanding vocal learning. We have taken an interdisciplinary approach, aiming to provide an integrated understanding across genomics (Part I), neurobiology (Part II), and transgenics (Part III). In Part I, we generated new, high-quality genome annotations of coding genes and noncoding microRNAs to facilitate functional and evolutionary studies. In Part II, we traced connections between auditory-related brain regions and reported neuroimaging to explore the structure of the brain and gene expression patterns to highlight brain regions. In Part III, we created the first successful transgenic bats by manipulating the expression of FoxP2, a speech-related gene. These interdisciplinary approaches are facilitating a mechanistic and evolutionary understanding of mammalian vocal learning and can also contribute to other areas of investigation that utilize P. discolor or bats as study species.

Abstract

Forkhead box P2 (FOXP2) is a highly conserved transcription factor that has been implicated in human speech and language disorders and plays important roles in the plasticity of the developing brain. The pattern of nucleotide polymorphisms in FOXP2 in modern populations suggests that it has been the target of positive (Darwinian) selection during recent human evolution. In our study, we searched for evidence of selection that might have followed FOXP2 adaptations in modern humans. We examined whether or not putative FOXP2 targets identified by chromatin-immunoprecipitation genomic screening show evidence of positive selection. We developed an algorithm that, for any given gene list, systematically generates matched lists of control genes from the Ensembl database, collates summary statistics for three frequency-spectrum-based neutrality tests from the low-coverage resequencing data of the 1000 Genomes Project, and determines whether these statistics are significantly different between the given gene targets and the set of controls. Overall, there was strong evidence of selection of FOXP2 targets in Europeans, but not in the Han Chinese, Japanese, or Yoruba populations. Significant outliers included several genes linked to cellular movement, reproduction, development, and immune cell trafficking, and 13 of these constituted a significant network associated with cardiac arteriopathy. Strong signals of selection were observed for CNTNAP2 and RBFOX1, key neurally expressed genes that have been consistently identified as direct FOXP2 targets in multiple studies and that have themselves been associated with neurodevelopmental disorders involving language dysfunction.

Abstract

Disorders of speech and language are highly heritable, providing strong
support for a genetic basis. However, the underlying genetic architecture is complex,
involving multiple risk factors. This chapter begins by discussing genetic loci associated
with common multifactorial language-related impairments and goes on to
detail the only gene (known as FOXP2) to be directly implicated in a rare monogenic
speech and language disorder. Although FOXP2 was initially uncovered in
humans, model systems have been invaluable in progressing our understanding of
the function of this gene and its associated pathways in language-related areas of the
brain. Research in species from mouse to songbird has revealed effects of this gene
on relevant behaviours including acquisition of motor skills and learned vocalisations
and demonstrated a role for Foxp2 in neuronal connectivity and signalling,
particularly in the striatum. Animal models have also facilitated the identification of
wider neurogenetic networks thought to be involved in language development and
disorder and allowed the investigation of new candidate genes for disorders involving
language, such as CNTNAP2 and FOXP1. Ongoing work in animal models promises
to yield new insights into the genetic and neural mechanisms underlying human
speech and language

Abstract

Neurodevelopmental disorders that disturb speech and language are highly heritable. Isolation of the underlying genetic risk factors has been hampered by complexity of the phenotype and potentially large number of contributing genes. One exception is the identification of rare heterozygous mutations of the FOXP2 gene in a monogenic syndrome characterised by impaired sequencing of articulatory gestures, disrupting speech (developmental verbal dyspraxia, DVD), as well as multiple deficits in expressive and receptive language. The protein encoded by FOXP2 belongs to a divergent subgroup of forkhead-box transcription factors, with a distinctive DNA-binding domain and motifs that mediate hetero- and homodimerisation. FOXP1, the most closely related member of this subgroup, can directly interact with FOXP2 and is co-expressed in neural structures relevant to speech and language disorders. Moreover, investigations of songbird orthologues indicate that combinatorial actions of the two proteins may play important roles in vocal learning, leading to the suggestion that human FOXP1 should be considered a strong candidate for involvement in DVD. Thus, in this study, we screened the entire coding region of FOXP1 (exons and flanking intronic sequence) for nucleotide changes in a panel of probands used earlier to detect novel mutations in FOXP2. A non-synonymous coding change was identified in a single proband, yielding a proline-to-alanine change (P215A). However, this was also found in a random control sample. Analyses of non-coding SNP changes did not find any correlation with affection status. We conclude that FOXP1 mutations are unlikely to represent a major cause of DVD.

Abstract

Childhood syndromes disturbing language development are common and display high degrees of heritability. In most cases, the underlying genetic architecture is likely to be complex, involving multiple chromosomal loci and substantial heterogeneity, which makes it difficult to track down the crucial genomic risk factors. Investigation of rare Mendelian phenotypes offers a complementary route for unravelling key neurogenetic pathways. The value of this approach is illustrated by the discovery that heterozygous FOXP2 (where FOX is forkhead box) mutations cause an unusual monogenic disorder, characterized by problems with articulating speech along with deficits in expressive and receptive language. FOXP2 encodes a regulatory protein, belonging to the forkhead box family of transcription factors, known to play important roles in modulating gene expression in development and disease. Functional genetics using human neuronal models suggest that the different FOXP2 isoforms generated by alternative splicing have distinct properties and may act to regulate each other's activity. Such investigations have also analysed the missense and nonsense mutations found in cases of speech and language disorder, showing that they alter intracellular localization, DNA binding and transactivation capacity of the mutated proteins. Moreover, in the brains of mutant mice, aetiological mutations have been found to disrupt the synaptic plasticity of Foxp2-expressing circuitry. Finally, although mutations of FOXP2 itself are rare, the downstream networks which it regulates in the brain appear to be broadly implicated in typical forms of language impairment. Thus, through ongoing identification of regulated targets and interacting co-factors, this gene is providing the first molecular entry points into neural mechanisms that go awry in language-related disorders