Fishing with a Transgenic Line: Using Zebrafish to Elucidate Mechanisms and Therapeutics in NUP98-NSD1 AML

The NUP98-NSD1 (NND1) translocation is a fusion oncogene recently identified in pediatric acute myeloid leukemia (AML), where it occurs in approximately 16% of patients. NND1 predicts a dismal prognosis, with a 4-year event-free survival <10%. The mechanism of action of NND1 may be through the activation of the posterior homeobox gene, HOXA9.  NND1 patients often harbour an internal tandem duplication of fms-like tyrosine kinase 3 (FLT3-ITD), another genetic lesion associated with poor prognosis. Co-expression of NND1 and FLT3-ITD results in worse survival than either aberration in isolation. NND1 may be sufficient to produce a myeloproliferative phenotype, but the interaction with FLT3-ITD activates essential downstream signaling pathways necessary for AML pathogenesis. A better understanding of the mechanisms by which NND1 dysregulates hematopoiesis and interacts with FLT3-ITD is fundamental to developing targeted therapies to improve the outcome in this disease.

The zebrafish has been established as a robust and reliable model of hematologic malignancies, with conserved genetics and ease of genetic interrogation. Our group previously generated a transgenic zebrafish model expressing the related fusion oncogene, NUP98-HOXA9, in which embryos had anemia and expansion of myeloid cells, and adult fish exhibited a myeloproliferative neoplasm (MPN). Using this model, we discovered novel downstream epigenetic regulators that could be targeted therapeutically and restore normal embryonic hematopoiesis. Moreover, the up-regulated genes that we identified correlated with features of high-risk AML in human datasets, highlighting the translational relevance of this human disease model and justifying the employment of this approach to investigate NND1-driven AML (Deveau et al, Leukemia 2015).

Plasmid constructs have been generated that incorporate human NND1 into the zebrafish using the Tol2 system, with detection by green fluorescent protein (GFP) expression. Injection of CMV-NND1-sGFP revealed strong GFP expression from 24-48 hours post fertilization (hpf) ubiquitously and in hematopoietic cells. Whole-mount in situ hybridization experiments of plasmid-injected embryos have shown that, similar to the NUP98-HOXA9 model, embryos expressing NND1 develop a pre-leukemic state, with a decrease in red blood cell marker expression (gata1) and an increase in myeloid marker expression (l-plastin). Currently no animal models exist for NND1 AML. Our initial studies have revealed a myeloproliferative phenotype in zebrafish embryos, providing an in vivo tool for further genetic and epigenetic interrogation, as well as a preclinical platform for novel drug discovery in this disease.