Biology subjects

Frazer, J. K.

Publications and source records attributed to Frazer, J. K..

6 recordsLinked to original sources

bioRxiv2024

The axillary lymphoid organ - an external, experimentally accessible immune organ in the zebrafish

Lymph nodes and other secondary lymphoid organs play critical roles in immune surveillance and immune activation in mammals, but the deep internal locations of these organs make it challenging to image and study them in living animals. Here, we describe a previously uncharacterized external immune organ in the zebrafish ideally suited for studying immune cell dynamics in vivo, the axillary lymphoid organ (ALO). This small, translucent organ has an outer cortex teeming with immune cells, an inner medulla with a mesh-like network of fibroblastic reticular cells along which immune cells migrate, and a network of lymphatic vessels draining to a large adjacent lymph sac. Noninvasive high-resolution imaging of transgenically marked immune cells can be carried out in the lobes of living animals, and the ALO is readily accessible to external treatment. This newly discovered tissue provides a superb model for dynamic live imaging of immune cells and their interaction with pathogens and surrounding tissues, including blood and lymphatic vessels. TeaserA newly characterized external zebrafish lymphoid organ provides a powerful model for live imaging of immune cell dynamics

developmental biology↗

bioRxiv2023

Diverse Epithelial Lymphocytes in Zebrafish Revealed Using a Novel Scale Biopsy Method

Zebrafish are a compelling model to study lymphocytes because zebrafish and humans have similar adaptive immune systems. Human and zebrafish lymphocyte types are conserved, but many aspects of zebrafish lymphocyte biology remain uninvestigated, including lymphocytes in peripheral tissues, like epidermis. Here, we report the first study focused on zebrafish scale epidermal lymphocytes. Zebrafish scales represent a source to longitudinally sample live fish. We developed a novel biopsy technique, collecting scales to analyze epithelial lymphocytes from several fluorescently-labeled lines. We imaged scales via confocal microscopy and demonstrated multiple lymphocyte types in scales/epidermis, quantifying them flow cytometrically. We profiled gene expression of scale, thymic, and marrow lymphocytes from the same animals, revealing B- and T-lineage signatures. Single-cell qRT-PCR and RNA sequencing (scRNAseq) show not only canonical B and T cells, but also novel lymphocyte populations not described previously. To validate longitudinal scale biopsies, we serially sampled scales from fish treated with dexamethasone (DXM), demonstrating epidermal lymphocyte responses. To analyze cells functionally, we employed a bead-ingestion assay, showing thymic, marrow, and epidermal lymphocytes have phagocytic activity. In summary, we establish a non-lethal technique to obtain zebrafish lymphocytes, providing the first quantification, expression profiling, and functional data from epidermal lymphocytes in the zebrafish model. SummaryThis study describes a new biopsy method to acquire zebrafish lymphocytes for ex vivo studies, without euthanasia. Expression profiles of individual lymphocytes from multiple zebrafish transgenic lines reveal diverse lymphocyte populations, including novel cells expressing genes of both the B- and T-lineages.

immunology↗

bioRxiv2023

Dynamic Changes in Lymphocyte Populations Establish Zebrafish as a Thymic Involution Model

The thymus is the site of T lymphocyte development and T cell education to recognize foreign, but not self, antigens. B cells also reside and develop in the thymus, although their functions are less clear. During thymic involution, a process of lymphoid atrophy and adipose replacement linked to sexual maturation, thymocytes decline. However, thymic B cells decrease far less than T cells, such that B cells comprise [~]1% of human neonatal thymocytes, but up to [~]10% in adults. All jawed vertebrates possess a thymus, and we and others have shown zebrafish (Danio rerio) also have thymic B cells. Here, we investigated the precise identities of zebrafish thymic T and B cells and how they change with involution. We assessed the timing and specific details of zebrafish thymic involution using multiple lymphocyte-specific, fluorophore-labeled transgenic lines, quantifying the changes in thymic T- and B-lymphocytes pre- vs. post-involution. Our results prove that, as in humans, zebrafish thymic B cells increase relative to T cells post-involution. We also performed RNA sequencing (RNA-seq) on D. rerio thymic and marrow lymphocytes of four novel double-transgenic lines, identifying distinct populations of immature T and B cells. Collectively, this is the first comprehensive analysis of zebrafish thymic involution, demonstrating its similarity to human involution, and establishing the highly genetically- manipulatable zebrafish model as a template for involution studies.

developmental biology↗

bioRxiv2022

p66Shc is an apoptotic rheostat whose targeted ROS inhibition improves MI outcomes

p66Shc is an oxidoreductase that responds to cell stress by translocating to mitochondria, where p66Shc produces pro-apoptotic reactive oxygen species (ROS). This study identifies ROS-active p66Shc as a monomer that produces superoxide anion independent of metal ions, inhibits cytochrome c peroxidase, and is regulated by environmental condition-induced structural changes. p66Shc anti-apoptotic functions, including: cytochrome c reduction, increased electron transport chain activity, and caspase cascade inhibition were also discovered. This study also demonstrates that p66Shc is a stress-dependent rheostat of apoptosis, regulated by p66Shc-mortalin complexes. These complexes decrease pro-apoptotic ROS production, without blocking p66Shc-mediated cytochrome c reduction. However, stress disrupts p66Shc-mortalin interactions, promoting apoptosis. Tipping p66Shcs apoptotic balance toward anti-apoptotic functions by genetic knockdown or p66Shc-selective ROS inhibition decreased pro-apoptotic effects and improved outcomes in zebrafish myocardial infarction models, representing a potential new myocardial infarction treatment with promising results.

biochemistry↗

bioRxiv2019

Targeted sequencing of candidate genes of dyslipidemia in Punjabi Sikhs: Population-specific rare variants in GCKR promote ectopic fat deposition

Dyslipidemia is a well-established risk factor for cardiovascular diseases. Although, advances in genome-wide technologies have enabled the discovery of hundreds of genes associated with blood lipid phenotypes, most of the heritability remains unexplained. Here we performed targeted resequencing of 13 bona fide candidate genes of dyslipidemia to identify the underlying biological functions. We sequenced 940 Sikh subjects with extreme serum levels of hypertriglyceridemia (HTG) and 2,355 subjects were used for replication studies; all 3,295 participants were part of the Asian Indians Diabetic Heart Study. Gene-centric analysis revealed a burden of variants for increasing HTG risk in GCKR (p=2.1x10-5), LPL (p=1.6x10-3) and MLXIPL (p=1.6x10-2) genes. Of these, three missense and damaging variants within GCKR were further examined for functional consequences in vivo using a transgenic zebrafish model. All three mutations were South Asian population-specific and were largely absent in other multiethnic populations of the Exome Aggregation Consortium. We built different transgenic models of human GCKR with and without mutations and analyzed the effects of dietary changes in vivo. Despite the short-term feeding, profound phenotypic changes were apparent in hepatocyte histology and fat deposition associated with increased expression of GCKR in response to a high fat diet (HFD). Liver histology of the GCKRmut showed severe fatty metamorphosis which correlated with ~7 fold increase in the mRNA expression in the GCKRmut fish even in the absence of a high fat diet. These findings suggest that functionally disruptive GCKR variants not only increase the risk of HTG but may enhance ectopic lipid/fat storage defects in the absence of obesity and HFD. To our knowledge, this is the first transgenic zebrafish model of a putative human disease gene built to accurately assess the influence of rare genetic changes and their phenotypic consequences in vivo.

genetics↗

bioRxiv2018

Simultaneous B and T cell acute lymphoblastic leukemias in zebrafish driven by transgenic MYC: implications for oncogenesis and lymphopoiesis

Precursor-B cell acute lymphoblastic leukemia (pre-B ALL) is the most common pediatric cancer, but there are no useful zebrafish pre-B ALL models. We describe the first highly-penetrant zebrafish pre-B ALL, driven by human MYC. Leukemias express B lymphoblast-specific genes and are distinct from T cell ALL (T-ALL)--which these fish also develop. Zebrafish pre-B ALL shares in vivo features and expression profiles with human pre-B ALL, and these profiles differ from zebrafish T-ALL or normal B and T cells. These animals also exhibit aberrant lymphocyte development. As the only robust zebrafish pre-B ALL model and only example where T-ALL also develops, this model can reveal differences between MYC-driven pre-B vs. T-ALL and be exploited to discover novel pre-B ALL therapies.\n\nStatement of significanceWe describe the first robust zebrafish pre-B ALL model in MYC-transgenic animals known to develop T-ALL, revealing the only animal model with both human ALL types. We also describe aberrant multi-lineage lymphopoiesis. This powerful system can be used to study MYC-driven leukemogenesis and discover new pre-B ALL targeted therapies.

cancer biology↗