A. Thomas Look
We are studying cancer genetics using the zebrafish animal model as an in vivo system, in combination with RNAi knockdown of critical genes in human tumor cell lines, to dissect developmental pathways subverted in human leukemias and solid tumors. The zebrafish model is an established system for studying vertebrate embryogenesis, organogenesis and disease. A powerful attribute of the zebrafish is its capacity for discovery of novel pathways by performing large-scale forward genetic and small molecule screens on transparent, readily accessible embryos. In addition, transient gene knockdown in the zebrafish embryo can readily be performed using antisense morpholino injections, to quickly analyze gene function and determine epistatic relationships in vivo. Thus, the zebrafish is an ideal system for identifying novel genes involved in cancer, as their discovery is based on unbiased phenotypic assays and can uncover genes that are either activated (oncogenes) or inactivated (tumor suppressors) during malignant transformation. Using genome-wide mutagenesis screening strategies in conjunction with transgenic approaches we are also generating zebrafish models of leukemias, brain tumors, and neuroblastoma.
Zebrafish myelopoiesis is very similar to that in humans and we are using the model to study the pathogenesis of two important human diseases - myelodysplastic syndrome and acute myeloid leukemia. A second screen is underway to uncover genes disrupted in neuroblastoma, the most common extra-cranial solid tumor of children. These embryonic tumors arise in the peripheral sympathetic nervous system (PSNS) and most of the genes regulating both PSNS development and neuroblastoma formation have yet to be identified. Through these screens we have identified new genes required for normal myelopoiesis and PSNS development and are currently studying their respective contributions to neoplastic pathogenesis. Cell death mechanisms also contribute to malignant transformation and p53, a critical regulator of DNA repair and apoptosis, is the most commonly mutated gene among all cancers. We have isolated a mutant p53 zebrafish line that is tumor-prone, and we have recently used this line to discover a new apoptotic pathway that is induced by DNA damage and bypasses p53, which is triggered by the loss or inactivation of Chk1.
We have also shown that human T-cell leukemias can be divided into five major subtypes based on the expression of oncogenes that initiate malignant transformation, and in addition, have generated transgenic zebrafish lines overexpressing Myc that develop T-Cell leukemia, recapitulating the most prevalent of these human T-ALL subtypes. We are now conducting one of the first “cancer-related” modifier screens in a vertebrate system to identify both enhancers and suppressors of T-cell leukemia. Chemical and genetic modifier screens using tumor-prone zebrafish lines may ultimately reveal mutant genes or drugs that can suppress or modify disease progression. We hope to identify such modifiers that can either promote specific aspects of the malignancy, such as genomic instability or metastasis, or that delay or suppress tumor onset. Through the combination of these approaches we hope to uncover novel genes and targets for the development of small molecule inhibitors and new cancer therapies.
Mayer Building, Room 630
44 Binney Street
Boston, MA 02115