Advances in understanding tissue regenerative capacity and mechanisms in animals

There is much to learn regarding how and why tissue regeneration occurs. A synthesis of efforts using different model systems and maturing tools will unite strengths and perspectives towards this goal.Regenerative capacity is a complex trait dependent on the ability to access high-fidelity morphogenetic programmes after injury. It is distributed unequally among species and, within individuals, among their tissues.Mammalian regenerative capacity is influenced by developmental stage, and is usually greater prenatally than postnatally. Ageing adult mammals display reduced regenerative capacity in tissues like liver, blood, pancreas and skeletal muscle compared with younger cohorts.Source tissue for regeneration is commonly derived from the activity of undifferentiated stem or progenitor cells, or by dedifferentiation or transdifferentiation from differentiated cells. Regenerative sources and mechanisms differ by tissue type and injury type.Mechanisms acting locally often initiate growth from regenerative sources. For example, the epithelial cover of an injury can mature into a paracrine stimulator of regenerative growth, or stressed or dying cells can release signals that stimulate their replacement by the activity of progenitor cells.Signals operating from areas away from an injury or systemically as circulating factors can also influence the initiation and targeting of tissue regeneration.Positional memory is the process by which adult cells spared from injury maintain information necessary to replace structures of the correct size and shape. It is likely that this property is contributed to by the maintenance of developmental patterning factors in adult tissues.