Cell migration is a highly integrated, multistep process that underlies normal development, repair of injured tissue, and the progression of diseases such as cancers and atherosclerosis. Cells utilize key signaling proteins, notably protein kinases, to regulate changes in cell division and cell shape for proper migration. The Drosophila Tribbles protein functions to restrict cell division and promote protein turnover during the cell migration process and is related to the TRB family of proteins that includes human SKIP-1, which when mutated is associated with an aggressive form of leukemia called acute myelogenous leukemia (AML). An important, but unresolved question is whether these proteins act as kinases to attach phosphate molecules to target proteins or rather as a pseudokinases to regulate signaling indirectly. To address this, the PI's laboratory will use a powerful genetic model system to express normal and mutated versions of Tribbles and examine effects on cell structure and protein turnover. The outcome of these experiments will shed light on the molecular function of Tribbles during normal development and the work proposed will train undergraduates and graduate students in cutting edge approaches to understand the genetic basis of development with implications for human disease.
Intellectual merit How do animals achieve their characteristic sizes? During normal development, cells grow to a certain size and then cell division is triggered to split the cell in two. This process repeats until an organ is built. However it is unclear how cells coordinate their growth and division with the rate of growth in other tissues. Moreover, body sizes vary impressively between closely related animal species, and species-specific adaptations show incredible size scaling. For example, the human hand and the bat wing are vastly different in size despite being built of digits similar in number and arrangement. Tissue size is adjusted to both nutrient availability and a host of environmental pressures including temperature and O2 levels and size is subject to intense evolutionary selection pressure with consequences for mate selection, predation and tolerance to environmental changes. The mechanisms coordinating this developmental plasticity are incompletely understood, and include integration of cues from hormones regulating the timing of growth and insulin adjusting growth to energy intake. Model systems such as the fruit fly Drosophila have provided important insights into how cells and tissues balance the activities of multiple signaling pathways to establish a body pattern. Under this award, we have studied the role of the fly gene tribbles in controlling the two key contributors to tissue size: cell proliferation and cell growth. It has been well established that the cell cycle pathway controls cell division, and cell growth regulated by the insulin signaling pathway. Previously, it was shown that the Tribbles protein binds the protein cdc25 phosphatase, a key component of the cell cycle pathway, to block cell division. We developed a computer-based tool to document the effect of Tribbles on wing cell growth and then applied this tool in a genetic screen to search for new Tribbles targets. From this approach, we identified the gene Akt1, a key mediator of insulin signaling in all animals. Our results show that the gene Tribbles blocks insulin signaling by binding Akt1 and reducing its ability to transmit the insulin signal. As a result, animal size is linked to Tribbles levels: the animal is small when Tribbles levels are high and conversely animals are large when Tribbles levels low. Because genes identical to Tribbles are found in all animals, our studies of the role of Tribbles in fly cell growth and proliferation will offer insight into the genetic basis of animal diversity, the mechanism of evolution, the effect of environmental conditions on a developmental program, and the underlying causes of developmental aberrations and metabolic disease. Broader Impacts The project has supported an ongoing program to train students in molecular and cell biological approaches to dissect conserved developmental mechanisms in a model organism. The department places a strong emphasis on teaching biology through research, and the lab trains graduate and undergraduate students, many with non-traditional backgrounds, at a state university located in an urban setting. The PI has had strong success in attracting minority students, and the PI has used NSF support to (1) implement a laboratory course (Biol 312WL, Laboratory in Developmental Biology, Genetics and Cell Biology), (2) recruit well-trained undergraduates from this course to perform research sponsored by a campus-wide SEARCH (Students Engaged in Artistic and Academic Research) scholar program and (3) sponsor the research of high school teachers and students. We have developed an important piece of software, Fijiwings, which automates the collection of data regarding tissue and cell size. Fijiwings is freely available at http://sourceforge.net/projects/fijiwings/, and has been downloaded by scientists worldwide over 500 times. To disseminate our work, students publish their research in scientific journals and present their results at national and regional meetings and the PI co-organized the regional Midwest Drosophila Research Conference for 2012 and 2013.
