Ross L. Cagan

Research

Patterning of the Drosophila eye

One of the fundamental interests of the laboratory is exploration of epithelial patterning. How does an initially random collection of undifferentiated cells mature into a precise and functional organized epithelium? The developing Drosophila eye is an elegant model for studying epithelial patterning and, incidentally, is one of nature's most beautiful structures (Figure). We have used genetics, biochemistry, histology, laser ablation studies, disc culturing, microarrays, and computational modeling to explore how these epithelial cells move within the epithelium to find their final positions.

Figure 5.  The adult fly eye.

Mutations in the transmembrane adhesion proteins Rst and Hbs lead to a failure of IPCs to move into their correct niches. We find that their adhesion to each other across neighboring cells provides the ‘attraction’ that helps move cells to their proper niches. This involves adhesion but also actin cytoskeleton rearrangement, and we have identified many factors that mediate this cytoplasmic process. The result is dynamic cell movement, important for eye patterning; similar mechanisms may be at play in our cancer metastasis models. As we further explore the developing fly eye, we are beginning to integrate adhesion, signal transduction, and cell biology to achieve a more complete and useful understanding of the mechanisms that direct epithelial patterning.

For more information, please visit the Cagan Laboratory website.

A different approach to disease

Cancer has proven a difficult disease to achieve significant long-term advances in patient survival; improvements in survival are often measured in months. Diabetes has not fare much better. My laboratory has undertaken a genetic and drug screening approach targeting cancer and diabetes utilizing the fruitfly Drosophila. Our basic approach has been to use the advantages of the fly to take a whole animal approach to disease. We use an integrated approach: genes and drugs identified in flies are then brought to rodent and ultimately to clinical trials; sequencing and histological data from humans are then brought back to our fly models to allow us to develop increasingly sophisticated fly models.

MEN2: My laboratory has developed a Drosophila model for Multiple Endocrine Neoplasia Type 2 (MEN2) and related MTC. Targeting oncogenic Ret to the eye, we phenocopied many aspects of the human syndrome (Figure). With this model in hand, we utilized a classical genetic modifier screen to identify 140 factors that function in the oncogenic process (Figure). We used this data to predict two candidate human susceptibility loci that are commonly deleted in MEN2 patients with secondary pheochromocytomas.

Figure 1. Adult fly eyes, Left; a normal eye, Right; An eye expressing an oncogenic (cancer-causing) form of Ret. The eye is small and 'rough', reflecting defects in the underlying epithelium.

Metastasis:  One regulator of oncogenic Ret was Csk, the major inhibitor of Src activity. Src is perhaps the original oncogene, and has been implicated in metastasis. Working in flies, we demonstrated that activating Src sets up a ‘metastatic boundary’ of cells that migrate away specifically from the tumor's edge (Figure); we have implicated multiple factors in this ‘metastasis’. Working with pathologists, we have established evidence from histological sections that human solid tumors share many of these same molecular/spatial aspects present in our fly models (Figure). Currently, we are using human tumor sequencing data to alter multiple oncogenes/tumor suppressors with the goal of designing more sophisticated models of human tumorigenesis.

Figure 2.  Fly Src-mediated ‘tumors’ in the wing epithelium (left) lose E-cadherin (green) at tumor edges (brackets); human Squamous Cell Carcinomas (right) share this loss of E-cadherin (brown).

Diabetes: We have established a collaboration with Tom Baranski's laboratory to create a model system for diabetes. Flies placed on a high-carbohydrate diet demonstrate a broad range of defects that share important properties with human diabetics: hemolymph glucose levels rise to levels similar to uncontrolled diabetics and pathways important in human diabetes progression modify diet-mediated fly phenotypes.

Our efforts are directed at three aspects of diabetes. First, our histology and lipid mass spec results indicate that changes in the lipid profiles of our ‘diabetic’ flies phenocopy changes in humans (Figure). Second, our genetic screens have identified 170 modifiers of the media-induced phenotype. Finally, we have explored the effects of ‘flyabetes’ on heart and kidney function (Figure), the two major sources of organ failure in type 2 diabetic patients. Our goal is an effective whole-animal approach to understanding and treating diabetes and metabolic syndrome.

Figure 3.  Fly heart (center, green) and fly kidney ‘nephrocyte’ (red). These fail on a high sugar diet.

Drug Screening: My laboratory has developed a novel method of high-throughput drug screening using our fly models, robotics, and compound libraries. Through our feeding paradigms, we provided whole animal validation (Figure) that helped identify ZD6474 as a useful tool for treating MEN2 patients; the compound has completed Phase III and holds promise to be the first approved chemotherapeutic for MEN2. We have now expanded these efforts to other diseases including metastasis and, working with medicinal chemists, to novel classes of compounds. Importantly, the inhibitors we identified in flies show efficacy in standard mouse models of oncogenic growth and metastasis. With these whole animal approaches, we hope to identify lead compounds that maximize efficacy and bioavailability while minimizing whole animal toxicity.

Figure 4.  Feeding flies the chemical kinase inhibitor ZD6474 led to rescue of the Ret-mediated tumorigenic phenotype.

For more information, please visit the Cagan Laboratory website.