Colorful clones in the blood Stem cells in regenerating tissues such as the blood can acquire mutations that enable a growth advantage, increasing the chance of developing cancer. It is unclear how such diverse mutations promote clonal fitness. Avagyan et al . generated a platform in zebrafish to label clones with unique hues while inducing mutations in genes implicated in human blood disorders. Mutations in some genes caused clones to expand over time, resulting in clonal dominance. Progenitors in the dominant clone expressed anti-inflammatory factors to resist the inflammatory environment produced by their own mature progeny, leading to a self-perpetuating cycle promoting clonal fitness. Targeting these resistance pathways may be used to abate clonal hematopoiesis and prevent its associated pathology. —BAP

Until recently, molecular imaging using magnetic resonance (MR) has been limited by the modality’s low sensitivity, especially with non-proton nuclei. The advent of hyperpolarized (HP) MR overcomes this limitation by substantially enhancing the signal of certain biologically important probes through a process known as external nuclear polarization, enabling real-time assessment of tissue function and metabolism. The metabolic information obtained by HP MR imaging holds significant promise in the clinic, where it could play a critical role in disease diagnosis and therapeutic monitoring. This review will provide a comprehensive overview of the developments made in the field of hyperpolarized MR, including advancements in polarization techniques and delivery, probe development, pulse sequence optimization, characterization of healthy and diseased tissues, and the steps made towards clinical translation.

Germline heterozygous mutations in GATA2 are associated with a syndrome characterized by cytopenias, atypical infections, and increased risk of hematologic malignancies. Here, we generated a zebrafish mutant of gata2b that recapitulated the myelomonocytopenia and B-cell lymphopenia of GATA2 deficiency syndrome. Using single-cell assay for transposase accessible chromatin with sequencing of marrow cells, we showed that loss of gata2b led to contrasting alterations in chromosome accessibility in early myeloid and lymphoid progenitors, associated with defects in gene expression. Within the myeloid lineage in gata2b mutant zebrafish, we identified an attenuated myeloid differentiation with reduced transcriptional priming and skewing away from the monocytic program. In contrast, in early lymphoid progenitors, gata2b loss led to accumulation of B-lymphoid transcription factor accessibility coupled with increased expression of the B-cell lineage-specification program. However, gata2b mutant zebrafish had incomplete B-cell lymphopoiesis with loss of lineage-specific transcription factor accessibility in differentiating B cells, in the context of aberrantly reduced oxidative metabolic pathways. Our results establish that transcriptional events in early progenitors driven by Gata2 are required to complete normal differentiation.

Our lives begin with 1 cell, then 2, then 4, then the trillion cell adult, comprised of cell lineages, tissues, organs. How does this occur? Examination in numbers of cells, N, Cellular Phylodynamics, revealed two previously unappreciated processes: UNI-GROWTH, the slowing of growth that occurs as we become larger, caused by fewer cells dividing, captured by the Universal Mitotic Fraction and Universal Growth Equations, with accuracy confirmed for 13 species, including nematodes, mollusks, and vertebrates; and ALLO GROWTH, the creation of body parts from Founder Cells, captured by the Cellular Allometric Growth Equation, which describes mitotic expansion by Cell-Heritable change in the Cell Cycle Time. These equations can generate cell lineage approximations, bringing the power of coalescent theory to developmental biology.

No abstract

The establishment of in vitro cultures of zebrafish cancer cells has expanded the potential of zebrafish as a disease model. However, the lack of effective methods for gene delivery and genetic manipulation has limited the experimental applications of these cultures. To overcome this barrier, we tested and optimized vesicular stomatitis virus glycoprotein (VSV-G) pseudotyped lentiviral and retroviral vector transduction protocols. We show that lentivirus successfully and efficiently transduced zebrafish melanoma cell lines in vitro, allowing antibiotic selection, fluorescence-based sorting, and in vivo allotransplantation. In addition, injection of concentrated lentiviral particles into embryos and tumors established the feasibility of in vivo gene delivery.

No abstract

Myeloid neoplasms, including myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML), are clonal hematopoietic disorders that arise from abnormal hematopoietic stem and progenitor cells (HSPCs)with acquired somatic mutations. To follow the hematopoietic output of HSPC clones endogenously, we have developed a novel marking strategy in which each HSPC clone is labeled in a unique fluorescent hue. The transgenic zebrafish line Zebrabow uses a Cre/lox system where stochastic recombination of multiple transgenic insertions harboring three fluorescent proteins (dTomato, YFP and CFP) provide stable and heritable color barcodes. Tissue-specificity is ensured by tamoxifen-induced Cre activation under the draculin promoter which is highly expressed in zebrafish HSPCs throughout development. The result of Zebrabow labeling is a collection of colored blood cells, which are grouped by their hue, and largely cluster in various groups, each representing a clonal population of cells that arise from a specific HSPC. To induce clonal hematopoietic states in zebrafish assessed by color dominance in hematopoietic cells, we introduced combinations of known genetic mutations founds in MDS and AML into Zebrabow embryos. Embryos at the 1-cell stage were injected with combinations of mutations and HSPC color labeling was performed at 36 to 48 hours post fertilization, during peak emergence of definitive blood stem cells from the dorsal aorta. The injected mutations were grouped by known co-occurence in patients with MDS and AML. The transgenic overexpression of Jak2V617F, FLT3ITD, IDH2R140Q, HOXA9 or HOXB4 under the zebrafish blood-specific promoter draculin, was combined with somatic mutagenesis of endogenous tet2, asxl1, dnmt3a, ezh2, ptena/b and tp53 via the CRISPR/Cas9 system. Mosaic combinations of these mutations resulted in the expansion of single color clones, contributing to ≥30% of granulocytes, with concomittant myeloid expansion in a third of these zebrafish. The majority of zebrafish exhibiting clonal expansion harbored frame-shift mutations in asxl1 with >25% variant allelic frequency identified by next-generation sequencing. Similarly, combinations including Jak2V617F, tet2, or asxl1 mutations lead to single color expansion in kidney marrow cells in 30% of injected zebrafish, with the occasional presence of a blast-like population of cells in the marrow and spleen. We have successfully modeled early stages of clonal hematopoietic expansion with myeloproliferation in the presence of Jak2V617F and asxl1 deletion using the unique color barcoding system in zebrafish. Disclosures Zon: Marauder Therapeutics: Equity Ownership, Other: Founder; Scholar Rock: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Other: Founder; Fate, Inc.: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Other: Founder.