TEL-AML1 transgenic zebrafish model of precursor B cell acute lymphoblastic leukemia

Abstract

Acute lymphoblastic leukemia (ALL) is a clonal disease that evolves through the accrual of genetic rearrangements and͞or mutations within the dominant clone. The TEL-AML1 (ETV6-RUNX1) fusion in precursor-B (pre-B) ALL is the most common genetic rearrangement in childhood cancer; however, the cellular origin and the molecular pathogenesis of TEL-AML1-induced leukemia have not been identified. To study the origin of TEL-AML1-induced ALL, we generated transgenic zebrafish expressing TEL-AML1 either ubiquitously or in lymphoid progenitors. TEL-AML1 expression in all lineages, but not lymphoid-restricted expression, led to progenitor cell expansion that evolved into oligoclonal B-lineage ALL in 3% of the transgenic zebrafish. This leukemia was transplantable to conditioned wildtype recipients. We demonstrate that TEL-AML1 induces a B cell differentiation arrest, and that leukemia development is associated with loss of TEL expression and elevated Bcl2͞Bax ratio. The TEL-AML1 transgenic zebrafish models human pre-B ALL, identifies the molecular pathways associated with leukemia development, and serves as the foundation for subsequent genetic screens to identify modifiers and leukemia therapeutic targets.stem cell ͉ translocation ͉ childhood cancer ͉ genetics T he TEL-AML1 fusion generated by the t(12, 21)(p13;q22) chromosomal translocation is present in 25% of childhood pre-B acute lymphoblastic leukemia (ALL), making it the most common genetic rearrangement in childhood cancer (1-3). The translocation fuses the first five exons of the Ets transcription factor TEL (also known as ETV6) in-frame to nearly the entire AML1 gene (also known as RUNX1). Retrospective studies in twins with pre-B ALL, as well as Guthrie cards studies from 567 normal newborns (4), reveal that the TEL-AML1 fusion occurs in utero, with a protracted time course for leukemia development (5, 6).Murine studies involving TEL-AML1 suggest that this fusion protein confers a low transforming ability. Transgenic mice expressing TEL-AML1 from the Ig heavy chain promoter (E) did not develop any hematological disorder (7). Mice transplanted with bone marrow cells transduced with retroviral vectors expressing TEL-AML1 developed a preleukemic state without occult leukemia (8-10). The incidence of leukemia in such mice increased only in the presence of cooperating mutations (11).The cell initially transformed by TEL-AML1 remains to be elucidated; however, in ALL patients, the TEL-AML1 fusion event precedes differentiation of lymphoid progenitors to pre-B cells (12). This finding confines the origin of pre-B ALL to a B-lineage restricted progenitor(s) (4) or a multipotent hematopoietic stem cell (HSC) with preferential B-lymphoid clonal expansion (13).We used the zebrafish to study TEL-AML1 leukemogenesis for several reasons. First, the zebrafish has well conserved genetic processes controlling hematopoesis (14, 15). Second, zebrafish develop tumors that are histologically similar to human tumors (16)(17)(18)(19)(20). The lymphoid expression of mouse c-Myc led to...

Catch of the day: zebrafish as a human cancer model

“…Overexpression of TEL-AML1 led to the development of infiltrating B-lineage leukemia while rag2-mediated Notch overexpression resulted in T-cell leukemia. Both cancers also displayed similar properties with respect to mammals (Sabaawy et al, 2006;Chen et al, 2007).…”

“…In a separate study, the same group showed that irradiation or dexamethasone-induced apoptosis of fish leukemic cells is dependent on bcl-2 gene function that also operates in mammalian forms of leukemia (Langenau et al, 2005b). Two independent studies used a similar approach to induce different subtypes of leukemia mediated by overexpression of the aberrant TEL-AML1 fusion protein using the ubiquitous b-actin promoter or overexpression of Notch using the rag2 promoter (Sabaawy et al, 2006;Chen et al, 2007). Overexpression of TEL-AML1 led to the development of infiltrating B-lineage leukemia while rag2-mediated Notch overexpression resulted in T-cell leukemia.…”

Co-injection strategies to modify radiation sensitivity and tumor initiation in transgenic Zebrafish

“…To capitalize on the powerful developmental and genetic tools available in zebrafish, researchers have created numerous zebrafish tumor models (Langenau et al, 2003Yang et al, 2004;Berghmans et al, 2005;Patton et al, 2005;Haramis et al, 2006;Sabaawy et al, 2006;Le et al, 2007). The ultimate goal of the majority of this work is to identify pathways that modify disease states.…”

Leukemia-associated genetic aberrations in mesenchymal stem cells of children with acute lymphoblastic leukemia

“…Transgenic TEL-AML1 expression did not induce leukemia either in vitro using human HSC, or in vivo using transgenic mice and zebrafish models, but increased the self-renewal of B-cell progenitors and the number of HSC (19)(20)(21)(22)(23). Twin studies and analysis of cord blood samples demonstrates that the childhood leukemia development is initiated in utero (24,25).…”