Establishing a New Zebrafish Model to Study Malignant Transformation in Myeloproliferative Disorders

Myeloproliferative diseases (MPDs) are a group of hematological malignancies characterized by the abnormal increase of different blood cells in peripheral blood and in other hematological organs. The molecular pathways involved in disease pathogenesis and progression as well as in drug sensitivity and resistance are not fully elucidated yet. Given the physiological similarity to mammals, the zebrafish (ZF) could accelerate the study of the molecular basis of these diseases. In the last decade several human leukaemia associated oncogenes have been transiently over-expressed in ZF embryos in order to perturb the myelo-erythroid compartment, with the aim to create experimental models to discover new molecular pathways that can became potential targets for new chemical compounds.

We took advantage of the binary Gal4/UAS system to express oncogenic human HRAS in the ZF hematopoietic compartment. We used the tg(MAZe) driver line, a specific transgenic line that allows random mosaic expression of Gal4-VP16 after heat shock^(hs) treatment⁽¹⁾. This driver line was mated with a tg(UAS:eGFP-HRASV12)⁽²⁾ responder line in order to mimic somatic events leading to human oncogene expression.

Surprisingly a single heat shock at 30hpf, (referred here as HRASV12^hs) induces human HRASV12 expression in hematopoietic progenitors as judged by the expansion of the hematopoietic tissue. Histological analysis showed an increased number of monocytes/macrophages. Blood smear of HRASV12^hs larvae showed the expansion of blasts and myeloid precursors. Quantitative analysis of gene expression highlights a remarkable increase of myelo-erythroid restricted genes associated with a slight increase of staminality markers (pu1, mpx, lmo2, mpl, CD41 and c-myb). Moreover fish raised to adulthood developed hyper-plastic kidney marrow, the site of definitive haematopoiesis, the equivalent of mammalian bone marrow.

The combination of hyper-proliferation of blood cells associated with the expansion of the hematopoietic compartment that we found in this model reproduces the pathological features of human myeloproliferative disorders. This study shows that it is possible to drive the expression of leukemia associated oncogenes to the hematopoietic compartment in developing ZF thus reproducing some of the features of human blood malignancies in an in vivo model. Our Group is now testing different driver lines in order to induce oncogene expression in earliest hematopoietic progenitors and is focusing on different responder lines expressing human oncogenes involved in hematopoietic malignancies.

No relevant conflicts of interest to declare.