Biology subjects

Anderson, C. J.

Publications and source records attributed to Anderson, C. J..

25 records · Page 2Linked to original sources

bioRxiv2022

Slc9a6 mutation causes Purkinje cell loss and ataxia in the spontaneous shaker rat

BackgroundThe shaker rat carries a naturally occurring mutation leading to progressive ataxia characterized by Purkinje cell (PC) loss. We previously reported on fine-mapping the shaker locus to the long arm of the rat X chromosome. In this work, we sought to identify the mutated gene underlying the shaker phenotype and confirm its identity by functional complementation. MethodsWe fine-mapped the candidate region and analyzed cerebellar transcriptomes to identify deleterious variants. We generated an adeno-associated virus (AAV) targeting solute carrier family 9, member A6 (Slc9a6) expression to PCs using a mouse L7-6 (L7) promoter, as well as a control green fluorescent protein (GFP)-expressing virus. We administered AAVs prior to the onset of PC degeneration through intracerebroventricular injection and evaluated the molecular, cellular, and motor phenotypes. ResultsWe identified a XM_217630.9 (Slc9a6):c.[191_195delinsA] variant in the Slc9a6 gene that segregated with disease. This mutation is predicted to generate a truncated sodium-hydrogen exchanger 6 (NHE6) protein, p.(Ala64Glufs*23). Administration of AAV9-PHP.eB expressing rat Slc9a6 prior to symptom onset reduced the shaker motor, molecular, and cellular phenotypes. InterpretationSlc9a6 is mutated in shaker and also in human Christianson syndrome, an epileptic encephalopathy. AAV-based gene therapy may be a viable therapeutic strategy for Christianson syndrome, and the shaker rat model may aid in therapeutic development.

neuroscience↗

bioRxiv2020

Defining the impact of deep brain stimulation contact size and shape on neural selectivity

BackgroundUnderstanding neural selectivity is essential for optimizing medical applications of deep brain stimulation (DBS). We previously showed that modulation of the DBS waveform can induce changes in orientation-based selectivity, and that lengthening of DBS pulses or directional segmentation can reduce preferential selectivity for large axons. In this work, we sought to answer a simple, but important question: how do the size and shape of the contact influence neural selectivity? MethodsWe created multicompartment neuron models for several axon diameters and used finite element modeling with standard-sized cylindrical leads to determine the effects on changing contact size and shape on axon activation profiles and volumes of tissue activated. Contacts ranged in size from 0.04 to 16 mm2, compared with a standard size of 6 mm2. ResultsWe found that changes in contact size induce substantial changes in orientation-based selectivity in the context of a cylindrical lead, and rectangular shaping of the contact can alter this selectivity. Smaller contact sizes were more effective in constraining neural activation to small, nearby axons representative of grey matter. However, micro-scale contacts enable only limited spread of neural activation before exceeding standard charge density limitations; further, energetic efficiency is optimized by somewhat larger contacts. InterpretationsSmall-scale contacts are optimal for constraining stimulation in nearby grey matter and avoiding orientation-selective activation. However, given charge density limitations and energy inefficiency of micro-scale contacts, our results suggest that contacts about half the size of those on segmented clinical leads may optimize efficiency and charge density limitation avoidance.

neuroscience↗

bioRxiv2020

Influence of the artificial sodium saccharin sweetener Sucram(R) on the microbial community composition in the rumen content and attached to the rumen epithelium in dairy cattle: A pilot study

The products of rumen microbial fermentations are considered essential for animal growth and performance. Changes in these microbial communities can have major effects on animal growth and performance. Saccharin-based artificial sweeteners can be included in livestock diets to increase palatability and encourage feed intake. Despite the importance of the rumen microbial fermentation, little or no research is available regarding how saccharin-based artificial sweeteners affect rumen content and rumen epithelial microbial communities. The aim of this study was to identify changes in both the rumen content and rumen epithelial microbial communities in response to the supplementation of Sucram(R), a sodium-saccharin-based sweetener (Pancosma S.A./ADM Groups, Rolle, Switzerland) during standard, non-stress conditions using 16SrRNA gene amplicon sequencing. The rumen epithelial and rumen content microbiota of five Holstein-Friesian milking dairy cattle were compared before (baseline, BL) and after a 28-day supplementation of Sucram(R). Illumina MiSeq-based 16S rRNA gene sequencing was conducted, and community analysis revealed significant changes in the abundance of specific phylotypes when comparing BL to Sucram(R) experimental groups. Sucram(R) did not have a significant effect on overall rumen microbial community structure between experimental groups. Statistically significant changes in microbial community composition following Sucram(R) supplementation were observed most consistently across a number of bacterial taxa in the rumen epithelium, while fewer changes were seen in the rumen content. Predicted genomic potentials of several significantly different OTUs were mined for genes related to feed efficiency and saccharin degradation. Operational taxonomic units (OTUs) classified as Prevotella and Sharpea were significantly (p<0.05) increased in samples supplemented with Sucram(R), whereas a reduction in abundance was seen for OTUs classified as Treponema, Leptospiraceae, Ruminococcus and methanogenic archaea. This is the first study to report an effect of Sucram(R) on ruminant microbial communities, suggesting possible beneficial impacts of Sucram(R) on animal health and performance that may extend beyond increasing feed palatability.

microbiology↗

bioRxiv2019

Pervasive lesion segregation shapes cancer genome evolution

Cancers arise through the acquisition of oncogenic mutations and grow through clonal expansion1, 2. Here we reveal that most mutagenic DNA lesions are not resolved as mutations within a single cell-cycle. Instead, DNA lesions segregate unrepaired into daughter cells for multiple cell generations, resulting in the chromosome-scale phasing of subsequent mutations. We characterise this process in mutagen-induced mouse liver tumours and show that DNA replication across persisting lesions can generate multiple alternative alleles in successive cell divisions, thereby increasing both multi-allelic and combinatorial genetic diversity. The phasing of lesions enables the accurate measurement of strand biased repair processes, the quantification of oncogenic selection, and the fine mapping of sister chromatid exchange events. Finally, we demonstrate that lesion segregation is a unifying property of exogenous mutagens, including UV light and chemotherapy agents in human cells and tumours, which has profound implications for the evolution and adaptation of cancer genomes.

cancer biology↗

bioRxiv2019

Preclinical immunoPET imaging of glioblastoma-infiltrating myeloid cells using Zirconium-89-labeled anti-CD11b antibody

PurposeGlioblastoma is a lethal brain tumor, heavily infiltrated by tumor-associated myeloid cells (TAMCs). TAMCs are emerging as a promising therapeutic target as they suppress antitumor immune responses and promote tumor cell growth. Quantifying TAMCs using non-invasive immunoPET could facilitate patient stratification for TAMC-targeted treatments and monitoring of treatment efficacy. As TAMCs uniformly express the cell surface marker, integrin CD11b, we evaluated a 89Zr-labeled anti-CD11b antibody for non-invasive imaging of TAMCs in a syngeneic orthotopic mouse glioma model.\n\nProceduresA human/mouse cross-reactive anti-CD11b antibody (clone M1/70) was conjugated to a DFO chelator and radiolabeled with Zr-89. PET/CT and biodistribution with or without a blocking dose of anti-CD11b Ab were performed 72 hours post-injection of 89Zr-anti-CD11b Ab in mice bearing established orthotopic syngeneic GL261 gliomas. Flow cytometry and immunohistochemistry of dissected GL261 tumors were conducted to confirm the presence of CD11b+ TAMCs.\n\nResultsSignificant uptake of 89Zr-anti-CD11b Ab was detected at the tumor site (SUVmean = 2.60 {+/-} 0.24) compared with the contralateral hemisphere (SUVmean = 0.6 {+/-} 0.11). Blocking with a 10-fold lower specific activity of 89Zr-anti-CD11b Ab markedly reduced the SUV in the right brain (SUVmean = 0.11 {+/-} 0.06), demonstrating specificity. Spleen and lymph nodes (myeloid cell rich organs) also showed high uptake of the tracer, and biodistribution analysis correlated with the imaging results. CD11b expression within the tumor was validated using flow cytometry and immunohistochemistry, which showed high CD11b expression primarily in the tumoral hemisphere compared to the contralateral hemisphere.\n\nConclusionThese data establish that 89Zr-anti-CD11b Ab immunoPET targets CD11b+ cells (TAMCs) with high specificity in a mouse model of GBM, demonstrating the potential for non-invasive quantification of tumor infiltrating CD11b+ immune cells during disease progression and immunotherapy in patients with GBM.

immunology↗

bioRxiv2019

Neural Selectivity, Efficiency, and Dose Equivalence in Deep Brain Stimulation through Pulse Width Tuning and Segmented Electrodes.

BackgroundAchieving deep brain stimulation (DBS) dose equivalence is challenging, especially with pulse width tuning and directional contacts. Further, the precise effects of pulse width tuning are unknown.\n\nMethodsWe created multicompartment neuron models for two axon diameters and used finite element modeling to determine extracellular influence from standard and segmented electrodes. We analyzed axon activation profiles and calculated volumes of tissue activated.\n\nResultsLong pulse widths focus the stimulation effect on small, nearby fibers, suppressing white matter tract activation (responsible for some DBS side effects) and improving battery utilization. Directional leads enable similar benefits to a greater degree. We derive equations for equivalent activation with pulse width tuning and segmented contacts.\n\nInterpretationsWe find agreement with classic studies and reinterpret recent articles concluding that short pulse widths focus the stimulation effect on small, nearby fibers, decrease side effects, and improve power consumption. Our field should reconsider shortened pulse widths.

neuroscience↗

bioRxiv2018

Structural basis for activation of Dot1L methyltransferase on the nucleosome by histone H2BK120 ubiquitylation

Histone H3 lysine 79 (H3K79) methylation is enriched on actively transcribed genes, and its misregulation is a hallmark of leukemia. Methylation of H3K79, which resides on the structured disk face of the nucleosome, is mediated by the Dot1L methyltransferase. Dot1L activity is part of a trans-histone crosstalk pathway, requiring prior histone H2B ubiquitylation of lysine 120 (H2BK120ub) for optimal activity. However, the molecular details describing both how Dot1L binds to the nucleosome and why Dot1L is activated by H2BK120 ubiquitylation are unknown. Here we present the cryo-EM structure of Dot1L bound to a nucleosome reconstituted with a site-specifically ubiquitylated H2BK120. The structure reveals that Dot1L engages the nucleosome acidic patch using an arginine anchor and occupies a conformation poised for methylation. Ubiquitin directly interacts with Dot1L and is positioned as a clamp on the nucleosome interacting region of Dot1L. Using our structure, we identify point mutations that disrupt the nucleosome-specific and ubiquitin-dependent activities of Dot1L. This study establishes a path to better understand Dot1L function in normal and leukemia cells.

biophysics↗