Key discoveries on cellular regeneration.

• Position: Body Clock

Complementary discoveries that break new ground on efforts to turn back the body's clock on cellular activity--paving the way for a better understanding of stem cells, tissue growth, and regeneration--have been made by two groups of scientists at the Children's Medical Center Research Institute at the University of Texas Southwestern Medical Center, Dallas.

A team led by Sean Morrison, professor of pediatrics, has identified an RNA-binding protein called IMP1 that promotes stem cell self-renewal during fetal development. Self-renewal is the process by which stem cells divide to make more stem cells, which is important for the growth of tissues during fetal development and the regeneration of tissues throughout adult life.

At the same time, researchers, including Hao Zhu, assistant professor of pediatrics and internal medicine, have shown that another RNA-binding protein, Lin28a, also promotes tissue repair by reactivating a metabolic state reminiscent of the juvenile developmental stage.

Morrison's investigation identified a set of genes, including IMP1, that are turned on only within time-limited windows, and control developmental switches in stem cell properties between fetal development and adulthood. IMP1 is turned off during late fetal development, partly as a consequence of increasing expression of a third family of RNA-binding molecules called let-7 microRNAs. Importantly, let-7 microRNAs are turned on during late fetal development in part due to declining expression of Lin28a.

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