Leukemia

Leukemia is the most common cancer of childhood, and great strides have been made in its treatment, so that currently most efforts go into devising more targeted therapies, rather than broad-spectrum chemotherapy, thus limiting the side-effects of the treatment. In order to be able to achieve this goal, we need to have a better understanding of the molecular mechanism underlying this disease.
Leukemia can be generated in zebrafish by injecting a construct containing murine c-myc under the zebrafish Rag-2 promoter at the one-cell stage (Fig. 1). These experiments were carried out in transgenic zebrafish, where the Rag-2 promoter drives GFP, allowing the visualization of the leukemic process. This demonstrates that this oncogenic mechanism is conserved throughout vertebrate evolution. Another strategy is to tag leukemic cells with luciferase (Fig. 2). Given its high signal-to-noise ratio luciferase can be advantageous in adult zebrafish, when weak signals need to be detected.

Thus the zebrafish model can be used to contribute to our understanding of the molecular origins of leukemias. In a forward genetic screen using the lck-promoter GFP transgenic line, where all T cells are GFP positive, we will examine adult zebrafish for expansion of the GFP signal from the thymus, as shown in Figure 1. Demonstration of leukemic transformation is done by clonal analysis, FACS sorting and transplantation experiments. Bona fide leukemic mutants, which either have activation of an oncogene or inactivation of a tumor suppressor, will be positionally cloned.

Established leukemic models can then be used for small molecule screens, looking for novel compounds with anti-leukemic activity (Fig. 3).