Hematopoietic perturbation in zebrafish expressing a tel-jak2a fusion.

OBJECTIVE: Various TEL-JAK2 fusions have been identified in patients with lymphoblastic and myeloid leukemias that result in constitutive activation of the JAK2 kinase domain. Such fusions can mediate factor-independent growth of hematopoietic cell lines and induction of malignancy in mouse models. MATERIALS AND METHODS: To assess whether zebrafish could be utilized as a suitable model for the study of myeloid oncogenesis, we generated a zebrafish tel-jak2a fusion oncoprotein based on that seen in a case of chronic myeloid leukemia. This was transiently expressed in zebrafish embryos under the control of the spi1 promoter, which is strongly active in myeloid precursors. RESULTS: Visual, histological, and molecular analysis revealed disruption of normal embryonic hematopoiesis, including perturbation of the myeloid and erythroid lineages. CONCLUSION: These results indicate that the zebrafish tel-jak2a oncoprotein is functional, and suggest that this organism will be useful for the experimental study of myeloid malignancy.

The zebrafish spi1 promoter drives myeloid-specific expression in stable transgenic fish.

The spi1 (pu.1) gene has recently been identified as a useful marker of early myeloid cells in zebrafish. To enhance the versatility of this organism as a model for studying myeloid development, the promoter of this gene has been isolated and characterized. Transient transgenesis revealed that a 5.3 kilobase promoter fragment immediately upstream of the spi1 coding sequence was sufficient to drive expression of enhanced green fluorescent protein (EGFP) in injected embryos in a manner that largely recapitulated the native spi1 gene expression pattern. This fragment was successfully used to produce a germ line transgenic line of zebrafish with EGFP-expressing myeloid cells. These TG(spi1:EGFP)pA301 transgenic zebrafish represent a valuable tool for further studies of myeloid development and its perturbation.

Tyrosine residues of the granulocyte colony-stimulating factor receptor transmit proliferation and differentiation signals in murine bone marrow cells.

Granulocyte colony-stimulating factor (G-CSF) is the major regulator of granulopoiesis and acts through binding to its specific receptor (G-CSF-R) on neutrophilic granulocytes. Previous studies of signaling from the 4 G-CSF-R cytoplasmic tyrosine residues used model cell lines that may have idiosyncratic, nonphysiological responses. This study aimed to identify specific signals transmitted by the receptor tyrosine residues in primary myeloid cells. To bypass the presence of endogenous G-CSF-R, a chimeric receptor containing the extracellular domain of the epidermal growth factor receptor in place of the entire extracellular domain of the G-CSF-R was used. A series of chimeric receptors containing tyrosine mutations to phenylalanine, either individually or collectively, was constructed and expressed in primary bone marrow cells from G-CSF-deficient mice. Proliferation and differentiation responses of receptor-expressing bone marrow cells stimulated by epidermal growth factor were measured. An increased 50% effective concentration to stimulus of the receptor Y(null) mutant indicated that specific signals from tyrosine residues were required for cell proliferation, particularly at low concentrations of stimulus. Impaired responses by mutant receptors implicated G-CSF-R Y(764) in cell proliferation and Y(729) in granulocyte differentiation signaling. In addition, different sensitivities to ligand stimulation between mutant receptors indicated that G-CSF-R Y(744) and possibly Y(729) have an inhibitory role in cell proliferation. STAT activation was not affected by tyrosine mutations, whereas ERK activation appeared to depend, at least in part, on Y(764). These observations have suggested novel roles for the G-CSF-R tyrosine residues in primary cells that were not observed previously in studies in cell lines.