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Rodney Stewart

Assistant Professor of Oncological Sciences

B.S. University of Melbourne, Australia

Ph.D. Yale University

Research

References

 

Rodney Stewart's Lab Page

Rodney Stewart's PubMed Literature Search

Research

Metastasis is the leading cause of death in cancer patients. Our ability to treat metastatic disease is hampered by our limited understanding of the mechanisms that drive metastasis, and thus the development of targeted therapies. Tumor cells become metastatic by acquiring genetic and epigenetic alterations that confer the ability to survive passage through the bloodstream, extravasate through the capillary endothelium, and proliferate into secondary tumors at distant sites. The stages of metastasis closely resemble the cellular events that occur during normal development, such as formation of the vertebrate neural crest, where progenitor cells delaminate from the dorsal neural tube by undergoing an epithelial-mesenchymal transition (EMT), and then actively migrate throughout the embryo. It is therefore not surprising that genes controlling key events during neural crest development are also aberrantly activated during metastasis, such as the Snail and Twist family of transcription factors. However, how "re-activation" of these embryonic transcription factor programs in tumor cells leads to metastasis remains unclear, due in part to our incomplete knowledge of the downstream effectors of these genes in both normal cell migration and metastasis.

Research in my laboratory involves identifying novel genes and signaling pathways that regulate neural crest migration and analyzing the consequence of their misregulation in animal models of cancer. The forward genetic capacity and exceptional imaging qualities of zebrafish provide a unique opportunity to identify new genes and pathways that control cell migration and metastasis in vivo. Establishing new metastasis models using these approaches will be crucial for developing and testing new therapeutic strategies that target metastatic cells. Current projects in the lab are:

Genetic and Chemical Screens in Zebrafish: To identify genetic mechanisms that control neural crest migration, we perform forward genetic and chemical screens with transgenic zebrafish that have fluorescently-labeled neural crest cells. Thus, we are able to identify mutants and drugs that disrupt embryonic cell migration in real time using simple imaging systems. One of the projects in the lab is to map and clone the genes affected in these mutants to determine the molecular mechanism(s) underlying the migration phenotypes. Another project involves screening through defined compound libraries to identify chemicals that inhibit EMT and cell migration in embryos containing GFP-labeled neural crest cells.

Defining Signaling Pathways that Regulate Neural Crest Cell Migration: To define the signaling pathways that control cell migration, we perform microarray screens in zebrafish foxd3- and snail1-deficient embryos, which have defined neural crest migration defects. Using this approach we have identified several novel genes that potentially function downstream of these neural crest transcription factors to promote cell migration. Current projects in the lab involve performing knockdown and overexpression studies to order these genes into genetic pathways and determine their role during normal embryonic cell migration.

Establishing Metastasis Models in Zebrafish: The optically clear zebrafish embryos and adult pigment mutants allow fluorescently labeled cells and tumors to be monitored using real-time imaging techniques. In addition, oncogenic signaling pathways underlying tumor formation are highly conserved in zebrafish, and a number of zebrafish cancer models are now established. Current projects available in the lab are to generate zebrafish metastasis models by co-expressing neural crest genes in tumors, such as melanoma, neuroblastoma and schwannoma. These projects involve generating transgenic animals in different genetic backgrounds and using cell transplantation experiments to determine cell autonomous and non-autonomous mechanisms of cell migration and metastasis.

Above: Zebrafish mutants with neural crest migration defects. Below: Zebrafish neural crest-derived tumor.

 

References