Our laboratory is interested in the growth, development and integrity of animal tissues. We study multiple organs, trying to identify common principles, and we extend these investigations to cancer and injury repair. In most organs, different cell types are generated by stem cells—cells that also make copies of themselves and thereby maintain the tissue. An optimal balance between the number of stem and differentiated cells is essential for the proper function of organs. Locally acting signals are important to maintain this balance in a spatially-organized manner, and these signals are key to understanding the regulation of growth. A common theme linking our work is Wnt signals. Work from many laboratories, including our own, has shown that Wnt proteins are essential to control stem cells. How this is achieved is far from clear and is the subject of studies in the lab, both in vivo and in cell culture. In vivo, a particular question we address is how physiological changes such as those occurring during hormonal stimuli, injury or programmed tissue degeneration have an impact on the self-renewal signals and on stem cell biology.