RUNX1 is a member of the core-binding factor family of transcription factors and is indispensable for the establishment of definitive hematopoiesis in vertebrates. RUNX1 is one of the most frequently mutated genes in a variety of hematological malignancies. Germ line mutations in RUNX1 cause familial platelet disorder with associated myeloid malignancies. Somatic mutations and chromosomal rearrangements involving RUNX1 are frequently observed in myelodysplastic syndrome and leukemias of myeloid and lymphoid lineages, that is, acute myeloid leukemia, acute lymphoblastic leukemia, and chronic myelomonocytic leukemia. More recent studies suggest that the wild-type RUNX1 is required for growth and survival of certain types of leukemia cells. The purpose of this review is to discuss the current status of our understanding about the role of RUNX1 in hematological malignancies.

CRISPR/Cas9 has emerged as a versatile genome-engineering tool that relies on a single guide RNA (sgRNA) and the Cas9 enzyme for genome editing. Simple, fast and economical methods to generate sgRNAs have made targeted mutagenesis routine in cultured cells, mice, zebrafish and other model systems. Pre-screening of sgRNAs for target efficacy is desirable both for successful mutagenesis and minimizing wasted animal husbandry on targets with poor activity. Here, we describe an easy, quick and cost-effective fluorescent polymerase chain reaction (PCR)-based method, CRISPR Somatic Tissue Activity Test (CRISPR-STAT), to determine target-specific efficiency of sgRNA. As a proof of principle, we validated our method using 28 sgRNAs with known and varied levels of germline transmission efficiency in zebrafish by analysis of their somatic activity in injected embryos. Our data revealed a strong positive correlation between the fluorescent PCR profiles of the injected embryos and the germline transmission efficiency. Furthermore, the assay was sensitive enough to evaluate multiplex gene targeting. This method is easy to implement by laboratories with access to a capillary sequencer. Although we validated the method using CRISPR/Cas9 and zebrafish, it can be applied to other model systems and other genome targeting nucleases.

Fanconi Anemia (FA) is a genomic instability syndrome resulting in aplastic anemia, developmental abnormalities, and predisposition to hematological and other solid organ malignancies. Mutations in genes that encode proteins of the FA pathway fail to orchestrate the repair of DNA damage caused by DNA interstrand crosslinks. Zebrafish harbor homologs for nearly all known FA genes. We used multiplexed CRISPR/Cas9-mediated mutagenesis to generate loss-of-function mutants for 17 FA genes: fanca, fancb, fancc, fancd1/brca2, fancd2, fance, fancf, fancg, fanci, fancj/brip1, fancl, fancm, fancn/palb2, fanco/rad51c, fancp/slx4, fancq/ercc4, fanct/ube2t, and two genes encoding FA-associated proteins: faap100 and faap24. We selected two indel mutations predicted to cause premature truncations for all but two of the genes, and a total of 36 mutant lines were generated for 19 genes. Generating two independent mutant lines for each gene was important to validate their phenotypic consequences. RT-PCR from homozygous mutant fish confirmed the presence of transcripts with indels in all genes. Interestingly, 4 of the indel mutations led to aberrant splicing, which may produce a different protein than predicted from the genomic sequence. Analysis of RNA is thus critical in proper evaluation of the consequences of the mutations introduced in zebrafish genome. We used fluorescent reporter assay, and western blots to confirm loss-of-function for several mutants. Additionally, we developed a DEB treatment assay by evaluating morphological changes in embryos and confirmed that homozygous mutants from all the FA genes that could be tested (11/17), displayed hypersensitivity and thus were indeed null alleles. Our multiplexing strategy helped us to evaluate 11 multiple gene knockout combinations without additional breeding. Homozygous zebrafish for all 19 single and 11 multi-gene knockouts were adult viable, indicating FA genes in zebrafish are generally not essential for early development. None of the mutant fish displayed gross developmental abnormalities except for fancp^-/- fish, which were significantly smaller in length than their wildtype clutch mates. Complete female-to-male sex reversal was observed in knockouts for 12/17 FA genes, while partial sex reversal was seen for the other five gene knockouts. All adult females were fertile, and among the adult males, all were fertile except for the fancd1 mutants and one of the fancj mutants. We report here generation and characterization of zebrafish knockout mutants for 17 FA disease-causing genes, providing an integral resource for understanding the pathophysiology associated with the disrupted FA pathway. Deficiencies in repair of DNA damage can cause diseases such as Fanconi anemia (FA), which is characterized by birth defects, bone marrow failure, anemia, leukemia and other cancers. A set of proteins constitute the FA pathway and together orchestrate the DNA repair process. Inactivation of one or more gene(s) encoding the proteins of the DNA repair pathway in an animal model would enable us to study the functions of these proteins in maintenance of normal cellular functions and the overall health of an individual in the absence of function. We systematically targeted the FA pathway in zebrafish using CRISPR/Cas9. We generated 36 fish lines with loss-of-function mutations in 19 FA pathway genes and showed that all survive to adulthood. We did not notice obvious morphological changes except in fancp gene-inactivated fish, which were smaller in length. However, all mutant fish were either exclusively or in majority male. Unlike reduced fertility among FA patients, all adult mutant fish were fertile, except for the fancd1 and fancj knockout males. These mutant zebrafish will serve as a huge resource for the scientific community to study the role of FA proteins in fish development, DNA repair, and as models for FA disease.

Recently, it has been shown that targeted mutagenesis using zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs) can be used to generate knockout zebrafish lines for analysis of their function and/or developing disease models. A number of different methods have been developed for the design and assembly of gene-specific ZFNs and TALENs, making them easily available to most zebrafish researchers. Regardless of the choice of targeting nuclease, the process of generating mutant fish is similar. It is a time-consuming and multi-step process that can benefit significantly from development of efficient high throughput methods. In this study, we used ZFNs assembled through either the CompoZr (Sigma-Aldrich) or the CoDA (context-dependent assembly) platforms to generate mutant zebrafish for nine genes. We report our improved high throughput methods for 1) evaluation of ZFNs activity by somatic lesion analysis using colony PCR, eliminating the need for plasmid DNA extractions from a large number of clones, and 2) a sensitive founder screening strategy using fluorescent PCR with PIG-tailed primers that eliminates the stutter bands and accurately identifies even single nucleotide insertions and deletions. Using these protocols, we have generated multiple mutant alleles for seven genes, five of which were targeted with CompoZr ZFNs and two with CoDA ZFNs. Our data also revealed that at least five-fold higher mRNA dose was required to achieve mutagenesis with CoDA ZFNs than with CompoZr ZFNs, and their somatic lesion frequency was lower (<5%) when compared to CopmoZr ZFNs (9–98%). This work provides high throughput protocols for efficient generation of zebrafish mutants using ZFNs and TALENs.

ATP6V1H is a component of a large protein complex with vacuolar ATPase (V-ATPase) activity. We identified two generations of individuals in which short stature and osteoporosis co-segregated with a mutation in ATP6V1H. Since V-ATPases are highly conserved between human and zebrafish, we generated loss-of-function mutants in atp6v1h in zebrafish through CRISPR/Cas9-mediated gene knockout. Homozygous mutant atp6v1h zebrafish exhibited a severe reduction in the number of mature calcified bone cells and a dramatic increase in the expression of mmp9 and mmp13. Heterozygous adults showed curved vertebra that lack calcified centrum structure and reduced bone mass and density. Treatment of mutant embryos with small molecule inhibitors of MMP9 and MMP13 significantly restored bone mass in the atp6v1h mutants. These studies have uncovered a new, ATP6V1H-mediated pathway that regulates bone formation, and defines a new mechanism of disease that leads to bone loss. We propose that MMP9/MMP13 could be therapeutic targets for patients with this rare genetic disease. Osteoporosis, a major health problem worldwide, is characterized by low bone mineral density (BMD) and a propensity to fracture. Genetic factors are clearly the major determinants of BMD, but their identification and contribution to osteoporosis risk have been difficult to assess in humans. Genome-wide association studies (GWAS) have identified numerous sequence variants that influence BMD. The loci identified to date, however, account for only a small fraction of the total variation in BMD. Through analysis of a pedigree with an undiagnosed disease in which affected members have markedly low bone mass, we identify a novel and critical bone formation pathway, mediated through the gene ATP6V1H. Zebrafish lacking apt6vh1 demonstrate loss of bone mass, and exhibit increased mmp9 and mmp13 levels; inhibition of mmp9 and mmp13 led to the rescue of bone density defects. Here we show that happloinsufficiency of ATP6V1H is associated with osteoporosis in both humans and zebrafish. This study exemplifies the value of studying rare diseases to understand prevalent ones.

CRISPRz (http://research.nhgri.nih.gov/CRISPRz/) is a database of CRISPR/Cas9 target sequences that have been experimentally validated in zebrafish. Programmable RNA-guided CRISPR/Cas9 has recently emerged as a simple and efficient genome editing method in various cell types and organisms, including zebrafish. Because the technique is so easy and efficient in zebrafish, the most valuable asset is no longer a mutated fish (which has distribution challenges), but rather a CRISPR/Cas9 target sequence to the gene confirmed to have high mutagenic efficiency. With a highly active CRISPR target, a mutant fish can be quickly replicated in any genetic background anywhere in the world. However, sgRNA's vary widely in their activity and models for predicting target activity are imperfect. Thus, it is very useful to collect in one place validated CRISPR target sequences with their relative mutagenic activities. A researcher could then select a target of interest in the database with an expected activity. Here, we report the development of CRISPRz, a database of validated zebrafish CRISPR target sites collected from published sources, as well as from our own in-house large-scale mutagenesis project. CRISPRz can be searched using multiple inputs such as ZFIN IDs, accession number, UniGene ID, or gene symbols from zebrafish, human and mouse.