Tumorhead is a gene from Xenopus laevis that has been identified as a positive regulator of cell proliferation during the development of the ectodermal germ layer. In addition, our lab has shown that tumorhead exhibits a dynamic pattern of sub-cellular localization, shuttling from the cytoplasm to the nucleus during development. There is suggestive evidence correlating the shift in tumorhead localization with changes in the cell cycle. To date, the molecular mechanism by which tumorhead affects cell proliferation during embryonic development, as well as the physiological significance of its dynamic sub-cellular localization are unclear. The specific aims of my proposal are the following: (1) To identify tumorhead interacting proteins that may lead to define the molecular pathway through which it functions. To accomplish this we will try to isolate the tumorhead protein complex through the use of immunoaffinity chromatography, followed by identification of protein partners through the use of mass spectrometry. (2) To determine if tumorhead's dynamic sub-cellular localization is a mechanism for regulating its ability to promote cell proliferation. This will be studied through the use of tumorhead mutants with altered subcellular localization in tumorhead functional analyses.