Biology subjects

Bird, A. P.

Publications and source records attributed to Bird, A. P..

7 recordsLinked to original sources

bioRxiv2025

Translational reading frame determines the pathogenicity of C-terminal frameshift deletions in MeCP2: an alternative therapeutic approach

Mutations in the MECP2 gene cause the severe neurological disorder Rett syndrome. A cluster of frameshift-causing C-terminal deletions (CTDs) lead to loss of [~]100 amino acids at the C-terminus of the MeCP2 protein, and account for approximately 10% of RTT-causing mutations. The pathogenicity of C-terminal deletions (CTDs) is unexpected, as this C-terminal domain is non-essential in mice. Utilising databases of pathogenic and benign human MECP2 mutations, we find that some individuals with apparently typical CTDs do not exhibit Rett syndrome, confirming that C-terminal truncations are not intrinsically pathogenic. Using human DNA sequence data and mouse models, we demonstrate that pathogenicity results from a drastic reduction in MeCP2 levels and is determined by the presence of the short amino acid motif proline-proline-stop (-PPX) at the C-terminus, which results from a shift to the +2 reading frame. Individuals with CTDs that shift to the +1 frame avoid this motif and do not develop Rett syndrome. Mutating the stop codon of the PPX motif to tryptophan rescues MeCP2 expression and RTT-like phenotypes in a CTD mouse model. Finally, we demonstrate that an adenine base editor can efficiently introduce this tryptophan substitution in cultured cells. Overall, our findings uncover a simple and reliable prognostic distinction between benign and pathogenic CTDs and provide proof-of-concept for an editing strategy that potentially corrects all disease-causing CTD mutations.

genetics↗

bioRxiv2025

Dysfunction of a SET3-like complex underlies a family of related neurological disorders

TBLR1 is a subunit of the NCoR corepressor complex that is mutated in a range of neurodevelopmental disorders. Here, we report that TBLR1 functions as a molecular scaffold that physically connects ANKRD11 and SETD5 - two of the most frequently mutated proteins in neurodevelopmental disorders - and links them to the rest of the NCoR complex. The resulting assembly resembles the yeast SET3 complex (SET3C) - a transcriptional regulator. Pathogenic missense mutations in TBLR1, ANKRD11 and SETD5 disrupt this assembly, and an engineered mutation that specifically abolishes SETD5 incorporation into SET3C causes severe developmental impairments in mice. Disruptions of mammalian SET3C components cause highly correlated changes in gene expression - including upregulation of already highly transcribed genes. Together, our results reveal that failure of transcriptional regulation by SET3C is a convergent molecular basis for a family of neurodevelopmental disorders.

molecular biology↗

bioRxiv2022

Structural analysis of SALL4 zinc-finger domain reveals a link between AT-rich DNA binding and Okihiro syndrome

Spalt-like 4 (SALL4) maintains vertebrate embryonic stem cell identity and is required for the development of multiple organs, including limbs. Mutations in SALL4 are associated with Okihiro syndrome and SALL4 is also a known target of thalidomide. SALL4 protein has a distinct preference for AT-rich sequences, recognised by a pair of zinc fingers at the C-terminus. However, unlike many characterised zinc finger proteins, SALL4 shows flexible recognition with many different combinations of AT-rich sequences being targeted. SALL4 interacts with the NuRD corepressor complex which potentially mediates repression of AT-rich genes. We present a crystal structure of SALL4 C-terminal zinc fingers with an AT-rich DNA sequence, which shows that SALL4 uses small hydrophobic and polar side chains to provide flexible recognition in the major groove. Missense mutations reported in patients that lie within the C-terminal zinc fingers reduced overall binding to DNA but not the preference for AT-rich sequences. Furthermore, these mutations altered association of SALL4 with AT-rich genomic sites, providing evidence that these mutations are likely pathogenic.

biochemistry↗

bioRxiv2021

Convergent Cerebrospinal Fluid Proteomes and Metabolic Ontologies in Humans and Animal Models of Rett Syndrome

MECP2 loss-of-function mutations cause Rett syndrome, a disorder that results from a disrupted brain transcriptome. How these transcriptional defects are decoded into a disease proteome remains unknown. We studied the proteome in Rett syndrome cerebrospinal fluid (CSF) across vertebrates. We identified a consensus proteome and ontological categories shared across Rett syndrome cerebrospinal fluid (CSF) from three species, including humans. Rett CSF proteomes enriched proteins annotated to HDL lipoproteins, complement, mitochondria, citrate/pyruvate metabolism, as well as synapse compartments. We used these prioritized and shared ontologies to select analytes for orthogonal quantification. These studies independently validated our proteome and ontologies. Ontologically selected CSF hits had genotypic discriminatory capacity as determined by Receiver Operating Characteristic (ROC) analysis and distinguished Rett from a related neurodevelopmental disorder, CDKL5 deficiency disorder. We propose that Mecp2 mutant CSF proteomes and ontologies inform novel putative mechanisms and biomarkers of disease. We suggest that Rett syndrome is a metabolic disorder impacting synapse function.

neuroscience↗

bioRxiv2020

Neuronal non-CG methylation is an essential target for MeCP2 function

SUMMARYDNA methylation is implicated in neuronal biology via the protein MeCP2, mutation of which causes Rett syndrome. MeCP2 recruits the NCOR1/2 corepressor complexes to methylated cytosine in the CG dinucleotide, but also to non-CG methylation, which is abundant specifically in neuronal genomes. To test the biological significance of its dual binding specificity, we replaced the MeCP2 DNA binding domain with an orthologous domain whose specificity is restricted to mCG motifs. Knock-in mice expressing the domain-swap protein displayed severe Rett syndrome-like phenotypes, demonstrating that interaction with sites of non-CG methylation, specifically the mCAC trinucleotide, is critical for normal brain function. The results support the notion that the delayed onset of Rett syndrome is due to the late accumulation of both mCAC and its reader MeCP2. Intriguingly, genes dysregulated in both Mecp2-null and domain-swap mice are implicated in other neurological disorders, potentially highlighting targets of particular relevance to the Rett syndrome phenotype.Competing Interest StatementThe authors have declared no competing interest.View Full Text

genetics↗

bioRxiv2018

A mutation-led search for novel functional domains in MeCP2

Most missense mutations causing Rett syndrome affect domains of MeCP2 that have been shown to either bind methylated DNA or interact with a transcriptional co-repressor complex. Several mutations, however, including the C-terminal truncations that account for ~10% of cases, fall outside these characterised domains. We studied the molecular consequences of four of these \"non-canonical\" mutations in cultured neurons and mice to see if they reveal additional essential domains without affecting known properties of MeCP2. The results show that the mutations partially or strongly deplete the protein and also in some cases interfere with co-repressor recruitment. These mutations therefore impact the activity of known functional domains and do not invoke new molecular causes of Rett syndrome. The finding that a stable C-terminal truncation does not compromise MeCP2 function raises the possibility that small molecules which stabilise these mutant proteins may be of therapeutic value.

molecular biology↗

bioRxiv2016

Domains of methylated CAC and CG target MeCP2 to tune transcription in the brain

Mutations in the gene encoding the methyl-CG binding protein MeCP2 cause neurological disorders including Rett syndrome. The di-nucleotide methyl-CG (mCG) is the canonical MeCP2 DNA recognition sequence, but additional targets including non-methylated sequences have been reported. Here we use brain-specific depletion of DNA methyltransferase to show that DNA methylation is the primary determinant of MeCP2 binding in mouse brain. In vitro and in vivo analyses reveal that MeCP2 binding to non-CG methylated sites in brain is largely confined to the tri-nucleotide sequence mCAC. Structural modeling suggests that mCG and mCAC may be interchangeable as minimal structural perturbation of MeCP2 accompanies binding. MeCP2 binding to chromosomal DNA in mouse brain is proportional to mCG + mCAC density and defines domains within which transcription is sensitive to MeCP2 occupancy. The results suggest that MeCP2 interprets patterns of mCAC and mCG in the brain to negatively modulate transcription of genes critical for neuronal function.

molecular biology↗