Zebrafish as a Biosensor for Studying Tumorigenesis

Bioscience Technology

100 Enterprise Drive
Rockaway, NJ, 07866

Zebrafish as a Biosensor for Studying Tumorigenesis

by Tanuja Koppal, PhD

Over 150 years ago Rudolph Virchow proposed a remarkably insightful theory that implied that cancer cells arise from embryo-like cells. Current cancer stem cell theory also suggests that cancer arises from a sub-population of tumor stem cells. Several studies have shown aggressive tumor cells to behave like stem cells and to share many embryonic characteristics.

Recent research published by Mary Hendrix and her group at Northwestern University in Chicago has shown that aggressive tumor cells also “speak an embryonic language” and communicate with embryonic progenitor cells. Hendrix has used the embryonic zebrafish as a model to study such cellular interactions between human melanoma cells and embryonic zebrafish progenitor cells. “We are using the embryonic zebrafish model as a biosensor for how human tumor cells can interact with an embryonic microenvironment,” she says. Her research findings using this model first appeared in the August 2006 issue of Nature Medicine and more recent studies were published in the April 2007 issue of Nature Reviews Cancer

“This discovery was pretty serendipitous,” says Hendrix. It was surprising to find that fluorescently labeled melanoma cells injected into very early developing blastula-stage zebrafish embryos never formed a tumor. “This very early developmental stage can be used to study the suppressive effects of the zebrafish embryonic microenvironment on tumorigenicity,” says Hendrix. However, tumor cells transplanted into the embryos at a later stage did form tumors.

Green fluorescent protein labeled aggressive human metastatic melanoma cells are injected into blastula-stage zebrafish embryos 3 hours post fertilization (hpf), either at the region(s) of the animal pole, resulting in an abnormal cranial outgrowth, or at the yolk margin, resulting in the formation of a secondary body axis (12 hpf ). Melanoma tumorigenicity is inhibited in the embryonic zebrafish microenvironment for up to 3 months in the adult fish. (Source: Mary J.C. Hendrix)

Techniques like whole-mount immunochemistry, followed by confocal microscopy and in situ hybridization of zebrafish sections, showed the presence of various ectopic structures in the embryos, which depended on where the tumor cells were transplanted, in the animal pole or the blastoderm margin. “In one case it [tumor cells] instructed the [zebrafish embryonic] cells to form abnormal cranial tissue and in another case a complete secondary body axis was formed,” says Hendrix.

“After we found that the tumor cells were instructing the zebrafish progenitor cells we asked ourselves the question, what factor would be responsible for the formation of ectopic structures?.” A review of the literature showed that developmental biologists had looked at the role of a protein called Nodal in early development. Nodal is an embryonic morphogen and a member of the transforming growth factor (TGF-beta) superfamily of proteins. Earlier experiments had shown that addition of Nodal RNA or DNA to different embryonic structures induced the formation of ectopic structures. “That’s how we worked our way backwards to making this observation,” she says.

This phenomenon of ectopic outgrowth induction was seen associated only with the most aggressive tumor cells

the more aggressive the cancer, the more the amount of Nodal present. “What this means is that highly aggressive tumor cells appear to be recapitulating an embryonic program by aberrantly expressing this embryonic morphogen,” says Hendrix. Nodal was also found to be absent in normal adult tissue and only seen expressed in human embryonic stem cells and in placental cells. More recently Nodal has been found in other types of cancers like breast and testicular cancers. “This observation has allowed us to appreciate the merging of developmental biology and cancer biology and the convergence of embryonic and tumorigenic pathways,” says Hendrix.

Metastatic melanoma, which develops from the transformation of skin pigment cells or melanocytes, has a mortality rate of more than 80% and a median survival of less than 7.5 months. Hence, Hendrix is keen to find ways to validate Nodal as a biomarker for assessing melanoma progression and as a possible therapeutic target for treating aggressive types of cancer. Studies to understand the regulation and activation of Nodal are now underway in the lab. “As we begin to manipulate the signaling pathways centered around Nodal, we would be able to ask specific questions about the ability of the tumor cells to interact with the zebrafish microenvironment.”

“I think there might be other embryonic programs that are aberrantly recapitulated by aggressive tumor cells that we have yet to discover,” says Hendrix. “We are now talking to different groups in the US to see how we could translate this discovery to a clinical trial.”

Mary Hendrix, PhD, serves as the President and Scientific Director for the Children's Memorial Research Center at Northwestern University’ Feinberg School of Medicine in Chicago. Her research is focused on identifying genes and cellular pathways involved in cancer metastasis. “I have always looked at cancer as an abnormal embryonic phenomenon,” says Hendrix. “I have made observations about the plasticity of cancer that are grounded in the principles of embryology and developmental biology.”

Hendrix received her B.S. degree in biology from Shepherd University and her PhD. in anatomy from George Washington University. She then did her postdoctoral research at Harvard Medical School in the department of anatomy and cell biology. “I was trained as a developmental biologist and received some extraordinary training from Dr. Elizabeth Hay at Harvard Medical School,” says Hendrix. After leaving Harvard she became very interested in studying cancer biology and joined the faculty at the University of Arizona where she rose to the rank of Professor. She then moved to the Pediatric Research Institute at the St. Louis University School of Medicine and later to the University of Iowa where she was the head of the department of anatomy and cell biology.

Mary J.C. Hendrix, Ph.D., is President and Scientific Director at the Children's Memorial Research Center, Northwestern University.

Mary J.C. Hendrix, PhD,serves as President and Scientific Director for the Children’s Memorial Research Center at Northwestern University’ Feinberg School of Medicine in Chicago. Her research is focused on identifying genes and cellular pathways involved in cancer metastasis. “I have always looked at cancer as an abnormal embryonic phenomenon,” says Hendrix. “I have made observations about the plasticity of cancer that are grounded in the principles of embryology and developmental biology.”

Hendrix received her B.S. degree in biology from Shepherd University and her PhD. in anatomy from George Washington University. She then did her postdoctoral research at Harvard Medical School in the department of anatomy and cell biology. “I was trained as a developmental biologist and received some extraordinary training from Dr. Elizabeth Hay at Harvard Medical School,” says Hendrix. She became very interested in studying cancer biology and joined the faculty at the University of Arizona. Dr. Hendrix also held positions at the Pediatric Research Institute at the St. Louis University School of Medicine, and at the University of Iowa where she was the head of the department of anatomy and cell biology.