Biology subjects

Harrison, L. C.

Publications and source records attributed to Harrison, L. C..

7 recordsLinked to original sources

bioRxiv2024

The molecular basis of immunosuppression by soluble CD52 is defined by interactions of N-linked and O-linked glycans with HMGB1 Box B

AbstractHuman soluble CD52 is a short glycopeptide comprising 12 amino acids (GQNDTSQTSSPS) which functions as an immune regulator by sequestering the pro-inflammatory high mobility group box protein 1 (HMGB1) and supressing immune responses. Recombinant CD52 has been shown to act as a broad anti-inflammatory agent, dampening both adaptive and innate immune responses. This short glycopeptide is heavily glycosylated, with a complex sialylated N-linked glycan at N3 and reported O- linked glycosylation possible on several serine and threonine residues. Previously we demonstrated that specific glycosylation features of CD52 are essential for its immunosuppressive function, with terminal -2,3-linked sialic acids required for binding to the inhibitory SIGLEC-10 receptor leading to T-cell suppression. Using high resolution mass spectrometry, we have further characterised the N- and O-linked glycosylation of Expi293 recombinantly produced CD52 at a glycopeptide and released glycan level, accurately determining glycan heterogeneity of both N- and O-linked glycosylation, and localising the site of O-glycosylation to T8 with high confidence and direct spectral evidence. This detailed knowledge of CD52 glycosylation informed the construction of a model system, which we analysed by molecular dynamics simulations to understand the mechanism of recognition and define interactions between bioactive CD52, HMGB1 and the SIGLEC-10 receptor. Our results confirm the essential role of glycosylation, more specifically hyper-sialylation, in the function of CD52, and identify at the atomistic level specific interactions between CD52 glycans and the Box B domain of HMGB1 that determine recognition, and the stability of the CD52/HMGB1 complex. These insights will inform the development of synthetic CD52 as an immunotherapeutic agent.

molecular biology↗

bioRxiv2021

Functional analysis of Mmd2 and related PAQR genes during sex determination in mice

Sex determination in eutherian mammals is controlled by the Y-linked gene Sry, which drives the formation of testes in male embryos. Despite extensive study, the genetic steps linking Sry action and male sex determination remain largely unknown. Here, we focused on Mmd2, a gene that encodes a member of the progestin and adipoQ receptor (PAQR) family. We show that Mmd2 is expressed during the sex-determining period in XY but not XX gonads, specifically in the Sertoli cell lineage which orchestrates early testis development. Analysis of knockout mice deficient in Sox9 and Sf1 revealed that Mmd2 operates downstream of these known sex-determining genes. However, when we used CRISPR to ablate Mmd2 in the mouse, fetal testis development appeared to progress normally. To determine if other genes might have compensated for the loss of Mmd2, we identified the closely related PAQR family members Paqr8 and Mmd as also being expressed during testis development. We used CRISPR to generate mouse strains deficient in Paqr8 and Mmd, but both knockout lines appeared phenotypically normal and fertile. Finally, we generated Mmd2;Mmd and Mmd2;Paqr8 double-null embryos and again observed normal testis development. These results may reflect functional redundancy among these factors. Our findings highlight the difficulties involved in identifying genes with a functional role in sex determination and gonadal development through expression screening and loss-of-function analyses of individual candidate genes, and may help to explain the paucity of genes in which variations have been found to cause human disorders/differences of sex development.

developmental biology↗

bioRxiv2020

Chromosomes distribute randomly to, but not within, human neutrophil nuclear lobes

The proximity pattern and radial distribution of chromosome territories within spherical nuclei are well understood to be random and non-random, respectively. Whether this distribution pattern is conserved in the partitioned or lobed nuclei of polymorphonuclear cells is unclear. Here we use chromosome paint technology and a novel high-throughput imaging analysis pipeline to examine the chromosome territories of all 46 chromosomes in hundreds of single human neutrophils - an abundant and famously polymorphonuclear immune cell. By comparing the distribution of chromosomes to randomly shuffled controls, and validating with orthogonal chromosome conformation capture technology, we show for the first time that all human chromosomes randomly distribute to neutrophil nuclear lobes, while maintaining a non-random radial distribution within these lobes. Furthermore, by leveraging the power of this vast dataset, we are able to reveal characteristics of chromosome territories not detected previously. For example, we demonstrate that chromosome length correlates with three-dimensional volume not only in neutrophils but other human immune cells. This work demonstrates that chromosomes are largely passive passengers during the neutrophil lobing process, but are able to maintain their macro-level organisation within lobes. Furthermore, the random distribution of chromosomes to the naturally partitioned nuclear lobes suggests that specific transchromosomal interactions are unimportant in mature neutrophils.

immunology↗

bioRxiv2020

Acidosis, Zinc and HMGB1 in Sepsis: A Common Connection Involving Sialoglycan Recognition

Blood pH is tightly regulated between 7.35-7.45, with values below 7.3 during sepsis being associated with lactic acidosis, low serum zinc, and release of proinflammatory HMGB1 from activated and/or necrotic cells. Using an ex vivo whole blood system to model lactic acidosis, we show that while HMGB1 does not engage leukocyte receptors at physiological pH, lowering pH with lactic acid facilitates binding. At normal pH, micromolar zinc supports plasma sialoglycoprotein binding by HMGB1, which is markedly reduced when pH is adjusted with lactic acid to sepsis levels. Glycan array studies confirmed zinc and pH-dependent HMGB1 binding to sialoglycans typical of plasma glycoproteins. Thus, proinflammatory effects of HMGB1 are suppressed via plasma sialoglycoproteins until drops in pH and zinc release HMGB1 to trigger downstream immune activation. Significance StatementHMGB1 sequestered by plasma sialoglycoproteins at physiological pH is released when pH and zinc concentrations fall in sepsis.

immunology↗

bioRxiv2020

Activation-induced re-organization of chromatin in human T cells

Remodelling of chromatin architecture is known to regulate gene expression and has been well characterized in cell lineage development but less so in response to cell perturbation. Activation of T cells, which triggers extensive changes in transcriptional programs, serves as an instructive model to elucidate how changes in genome organization orchestrate gene expression in response to cell perturbation. To characterize coordinate changes at different levels of chromatin architecture, we analysed chromatin accessibility, chromosome conformation and gene expression after activation of human T cells. T cell activation led to widespread changes in chromatin interactions and accessibility that were mostly shared between CD4+ and CD8+ T cells. Differential chromatin interactions were associated with upregulation or downregulation of linked target genes. Moreover, activation was associated with the formation of shorter chromatin interactions, partitioning of topologically associating domains (TADs) and acquisition of new TAD boundaries characterized by higher nucleosome occupancy, and lower chromatin accessibility and gene expression. These findings render an integrated and multiscale characterization of activation-induced re-organization of chromatin architecture underlying gene transcription in human T cells.

genetics↗

bioRxiv2017

No kissing in the nucleus: Unbiased analysis reveals no evidence of trans chromosomal regulation of mammalian immune development

It has been proposed that interactions between mammalian chromosomes, or transchromosomal interactions (also known as kissing chromosomes), regulate gene expression and cell fate determination. Here we aimed to identify novel transchromosomal interactions in immune cells by high-resolution genome-wide chromosome conformation capture. Although we readily identified stable interactions in cis, and also between centromeres and telomeres on different chromosomes, surprisingly we identified no gene regulatory transchromosomal interactions in either mouse or human cells, including previously described interactions. We suggest that advances in the chromosome conformation capture technique and the unbiased nature of this approach allow more reliable capture of interactions between chromosomes than previous methods. Overall our findings suggest that stable transchromosomal interactions that regulate gene expression are not present in mammalian immune cells and that lineage identity is governed by cis, not trans chromosomal interactions.

genomics↗

bioRxiv2017

Influence of fecal collection conditions and 16S rRNA gene sequencing protocols at two centers on human gut microbiota analysis

BackgroundTo optimise fecal sampling and analysis yielding reproducible microbiome data, and gain further insight into sources of its variation, we compared different collection conditions and 16S rRNA gene sequencing protocols in two centers. Fecal samples were collected on three sequential days from six healthy adults and placed in commercial collection tubes (OMNIgeneGut OMR-200) at room temperature or in sterile 5 ml screw-top tubes in a home fridge or home freezer for 6-24 h, before transfer at 4{degrees}C to the laboratory and storage at - 80{degrees}C within 24 hours. Replicate samples were shipped on dry ice to centers in Australia and the USA for DNA extraction and sequencing of the V4 region of the 16S rRNA gene, using different PCR protocols. Sequences were analysed with the QIIME pipeline and Greengenes database at the Australian center and with an in-house pipeline and SILVA database at the USA center.\n\nResultsVariation in gut microbiome composition and diversity was dominated by differences between individuals. Minor differences in the abundance of taxa were found between collection-processing methods and day of collection. Larger differences were evident between the two centers, including in the relative abundances of genus Akkermansia, in phylum Verrucomicrobiales, and Bifidobacteria in Actinobacteria.\n\nConclusionsCollection with storage and transport at 4{degrees}C within 24 h is adequate for 16S rRNA analysis of the gut microbiome. However, variation between sequencing centers suggests that cohort samples should be sequenced by the same method in one center. Differences in handling, shipping and methods of PCR gene amplification and sequence analysis in different centers introduce variation in ways that are not fully understood. These findings are particularly relevant as microbiome studies shift towards larger population-based and multicenter studies.

bioinformatics↗