Advances in cell, developmental and molecular biology, and the discovery of regeneration-competent cells in many non-regenerating mammalian tissues, have given impetus to systematic investigations that will enable us to regenerate these tissues by cell transplantation or the pharmaceutical induction of regeneration from the body's own tissues. A significant avenue of research is the identification of the soluble and insoluble signals and their transduction pathways that govern the proliferation and differentiation of regeneration-competent cells, and the signals that inhibit their activity...