After completing his PhD he worked as a postdoctoral fellow at Harvard Medical School before being appointed to Assistant Professor in the Department of Animal Biology at the University of Pennsylvania. 9 years later he came to Boston University. He lists his research interests as mechanisms controlling self-renewal, proliferation and differentiation of adult stem cells; intrinsic and extrinsic regulation of stem cells and niche; role of stem cells during development, homeostasis, regeneration and disease; generation of mutant mice as models for stem cell-mediated diseases and development of therapeutic strategies in regenerative medicine. He has had an illustrious career and in 2010 he was nominated for the Pfizer Distinguished Teaching Award.