Biology subjects

Biggs, D.

Publications and source records attributed to Biggs, D..

6 recordsLinked to original sources

bioRxiv2026

Aperiodic exponent ceases to track changes in propofol dose at deep surgery-level hypnotic depths

BackgroundAccurately tracking hypnotic depth during surgery is key to deliver personalized and precise anaesthesia. The aperiodic exponent of electroencephalographic (EEG) data has shown great promise as a marker of the balance between excitatory and inhibitory cortical activity and of hypnotic depth. In humans, this relation has been mostly evidenced by pairwise comparisons between awake and superficial anaesthesia states. However, it is unclear if this relation is also present across deeper hypnotic depths. Here we examined the relation between aperiodic exponent and hypnotic depth across different surgery-level propofol doses. MethodsThe present was an exploratory prospective observational analytical study where we recorded high-density EEG data from patients before surgery and during continuous target-controlled propofol infusions with different intraoperative target concentrations. We evaluated the relation between steady-state propofol dose and several EEG features including aperiodic exponent and spectral band powers. ResultsAll EEG measures were different when comparing awake versus anaesthesia conditions. At surgery-level hypnotic depths, some spectral band powers continued to track propofol dose displaying either with positive (delta R2 = 0.23, p = 0.001) or negative correlations (alpha R2 = 0.36, p < 0.001; beta R2 = 0.045, p < 0.001). Importantly, the aperiodic exponent was not associated with propofol doses absolute value (R2 = 0.011, p = 0.43) or with its relative change (R2 = 0.011, p = 0.51). ConclusionsOur results suggest that the relation between aperiodic exponent and excitatory/inhibitory balance is circumscribed to more superficial hypnotic depths than those typically employed for surgery.

neuroscience↗

bioRxiv2025

C9orf72 polyGA knock-in mice exhibit mild motor and proteomic changes consistent with ALS/FTD

A GGGGCC repeat expansion in C9orf72 is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The repeat expansion is translated into five different dipeptide repeat proteins: polyGA, polyGP, polyGR, polyAP and polyPR. To investigate the effect of polyGA, which is the most abundant dipeptide repeat protein in patient brains, we used CRISPR/Cas9 to insert 400 codon-optimized polyGA repeats immediately downstream of the mouse C9orf72 start codon. This generated (GA)400 knock-in mice driven by the endogenous mouse C9orf72 promoter, coupled with heterozygous C9orf72 reduction. (GA)400 mice develop subtle pathology including mild motor dysfunction characterized by impaired rotarod performance. Quantitative proteomics revealed polyGA expression caused protein alterations in the spinal cord, including changes in previously identified polyGA interactors. Our findings show that (GA)400 mice are a complementary in vivo model to better understand C9ALS/FTD pathology and determine the specific role of single DPRs in disease.

neuroscience↗

bioRxiv2025

Generation of C9orf72h370 mice, an intron 1 humanised C9orf72 repeat-expansion knock-in model

An autosomal dominant GGGGCC repeat expansion in intron 1 of the C9orf72 gene is the most common genetic cause of both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Here, we set out to engineer a gene targeted mouse model harbouring a pathogenic length humanised C9orf72 repeat expansion allele, in order to model pathological mechanisms in a physiological context. In human disease, pathogenic repeats typically range from the hundreds to thousands of units in length, representing a considerable challenge for cellular and in vivo model generation given the instability of GC rich and repetitive DNA sequences during molecular cloning. To overcome this challenge, we developed new methodology to synthetically and iteratively build pure GGGGCC repeats within a linear vector system, which we then seamlessly and scarlessly embedded within the native human genomic sequence. This created a gene targeting DNA vector for homologous recombination of the human sequence in mouse embryonic stem cells. We used this novel targeting vector to generate a new gene targeted mouse allele, C9orf72h370, that for the first time has mouse C9orf72 intron 1 scarlessly replaced with human intron 1 including a pure (GGGGCC)370 hexanucleotide repeat expansion. We confirm that the mouse model expresses human intron 1-derived RNA and produces dipeptide repeat proteins derived from the GGGGCC repeat expansion. We now provide this model as a new freely available resource for the field. In addition, we demonstrate the utility of our cloning method for engineering diverse repeat expansion sequences for modelling other disorders, such as Fragile X Syndrome.

molecular biology↗

bioRxiv2023

Shieldin and CST co-orchestrate DNA polymerase-dependent tailed-end joining reactions independently of 53BP1-governed repair pathway choice

53BP1 regulates DNA end-joining in lymphocytes, diversifying immune antigen receptors. This involves nucleosome-bound 53BP1 at DNA double-stranded breaks (DSBs) recruiting RIF1 and shieldin, a poorly understood DNA-binding complex. The 53BP1-RIF1-shieldin axis is pathological in BRCA1-mutated cancers, blocking homologous recombination (HR) and driving illegitimate non-homologous end-joining (NHEJ). However, how this axis regulates DNA end-joining and HR suppression remains unresolved. We investigated shieldin and its interplay with CST, a complex recently implicated in 53BP1-dependent activities. Immunophenotypically, mice lacking shieldin or CST are equivalent, with class-switch recombination co-reliant on both complexes. ATM-dependent DNA damage signalling underpins this cooperation, inducing physical interactions between these complexes that reveal shieldin as a DSB-responsive CST adaptor. Furthermore, DNA polymerase {zeta} functions downstream of shieldin, establishing DNA fill-in synthesis as the physiological function of shieldin-CST. Lastly, 53BP1 suppresses HR and promotes NHEJ in BRCA1-deficient mice and cells independently of shieldin. These findings showcase the resilience of the 53BP1 pathway, achieved through the collaboration of chromatin-bound 53BP1 complexes and DNA end-processing effector proteins.

molecular biology↗

bioRxiv2023

PolyGR and polyPR knock-in mice reveal a conserved neuroprotective extracellular matrix signature in C9orf72 ALS/FTD neurons

A GGGGCC repeat expansion in C9orf72 is the most common genetic cause of ALS and FTD (C9ALS/FTD). The presence of dipeptide repeat (DPR) proteins, generated by translation of the expanded repeat, is a major pathogenic feature of C9ALS/FTD pathology, but their most relevant effects in a physiological context are not known. Here, we generated C9orf72 DPR knock-in mouse models characterised by physiological expression of 400 codon-optimised polyGR or polyPR repeats, and heterozygous C9orf72 reduction. (GR)400 and (PR)400 knock-in mice exhibit cortical neuronal hyperexcitability, age-dependent spinal motor neuron loss and progressive motor dysfunction, showing that they recapitulate key features of C9FTD/ALS. Quantitative proteomics revealed an increase in extracellular matrix (ECM) proteins in (GR)400 and (PR)400 spinal cord, with the collagen COL6A1 the most increased protein. This signature of increased ECM proteins was also present in C9ALS patient iPSC-motor neurons indicating it is a conserved feature of C9ALS/FTD. TGF-{beta}1 was one of the top predicted regulators of this ECM signature and polyGR expression in human iPSC-neurons was sufficient to induce TGF-{beta}1 followed by COL6A1, indicating TGF-{beta}1 is one driver of the ECM signature. Knockdown of the TGF-{beta}1 or COL6A1 orthologue in Drosophila dramatically and specifically exacerbated neurodegeneration in polyGR flies, showing that TGF-{beta}1 and COL6A1 protect against polyGR toxicity. Altogether, our physiological C9orf72 DPR knock-in mice have revealed a neuroprotective and conserved ECM signature in C9FTD/ALS.

neuroscience↗

bioRxiv2020

A functional overlap between actively transcribed genes and chromatin boundary elements

Mammalian genomes are subdivided into large (50-2000 kb) regions of chromatin referred to as Topologically Associating Domains (TADs or sub-TADs). Chromatin within an individual TAD contacts itself more frequently than with regions in surrounding TADs thereby directing enhancer-promoter interactions. In many cases, the borders of TADs are defined by convergently orientated boundary elements associated with CCCTC-binding factor (CTCF), which stabilises the cohesin complex on chromatin and prevents its translocation. This delimits chromatin loop extrusion which is thought to underlie the formation of TADs. However, not all CTCF-bound sites act as boundaries and, importantly, not all TADs are flanked by convergent CTCF sites. Here, we examined the CTCF binding sites within a [~]70 kb sub-TAD containing the duplicated mouse -like globin genes and their five enhancers (5-R1-R2-R3-Rm-R4-1-2-3). The 5 border of this sub-TAD is defined by a pair of CTCF sites. Surprisingly, we show that deletion of the CTCF binding sites within and downstream of the -globin locus leaves the sub-TAD largely intact. The predominant 3 border of the sub-TAD is defined by a steep reduction in contacts: this corresponds to the transcribed 2-globin gene rather than the CTCF sites at the 3-end of the sub-TAD. Of interest, the almost identical 1- and 2-globin genes interact differently with the enhancers, resulting in preferential expression of the proximal 1-globin gene which behaves as a partial boundary between the enhancers and the distal 2-globin gene. Together, these observations provide direct evidence that actively transcribed genes can behave as boundary elements. Significance StatementMammalian genomes are complex, organised 3D structures, partitioned into Topologically Associating Domains (TADs): chromatin regions that preferentially self-interact. These chromatin interactions are thought to be driven by a mechanism that continuously extrudes chromatin loops, forming structures delimited by chromatin boundary elements and reflecting the activity of enhancers and promoters. Boundary elements bind architectural proteins such as CCCTC-binding factor (CTCF). Previously, an overlap between the functional roles of enhancers and promoters has been shown. However, whether there is overlap between enhancers/promoters and boundary elements is not known. Here, we show that actively transcribed genes can also behave as boundary elements, similar to CTCF boundaries. In both cases, multi-protein complexes bound to these regions may stall the process of chromatin loop extrusion.

genomics↗