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Planarians can reproduce either sexually or asexually. Asexual animals reproduce by dividing into two, with both head and tail fragments regrowing into complete animals. All planarians also can accomplish this feat if cut into two surgically. New tissues and organs are created by neoblasts adult stem cells that share certain characteristics with embryonic stem cells and can differentiate into essentially all cells found in adult animals. A similar process occurs in normal intact adults, in which neoblast progeny cells continually replace aged cells. Additionally, if nutrition is limited, planarians can exhibit de-growth eliminating cells while maintaining the form and function of the various organ systems of the animals. The genetic and molecular mechanisms underlying these capabilities are almost completely unknown.
Reddien is working to create a body of knowledge and research tools that will establish the planarian as a model organism to study the molecular genetics of regeneration. (The classic invertebrate model organisms, the Drosophila fruit fly and C. elegans worm, cannot efficiently regenerate tissues as adults.) He and co-workers developed methods for high-throughput RNA interference (RNAi), which employs customized RNAs to silence production of proteins from a given gene. Exploiting these methods, Reddien then led the first large-scale study of gene function in planarians, discovering multiple genes needed for regeneration.
In addition to tackling the challenges of regeneration, his work should aid a more general understanding of stem cells.
Reddien joined Whitehead Institute in 2005. He obtained his PhD in biology from the Massachusetts Institute of Technology, and carried out his undergraduate studies in molecular biology at the University of Texas at Austin.
Selected Publications
Peter W. Reddien, Néstor J. Oviedo, Joya R. Jennings, James C. Jenkin, and Alejandro Sánchez Alvarado. 2005. SMEDWI-2 is a PIWI-like protein that regulates planarian stem cells for regeneration and homeostasis. Science 310: 1327-1330.
Reddien PW, Bermange AL, Murfitt KJ, Jennings JR, Sánchez Alvarado A. 2005. Identification of genes needed for regeneration, stem cell function, and tissue homeostasis by systematic gene perturbation in planaria. Dev Cell. 8(5):635-49.
Reddien PW, Sánchez Alvarado A. 2004. Fundamentals of planarian regeneration. Ann. Review Cell and Dev. Bio. 20: 735-757.
Newmark PA, Reddien PW, Cebria F, Sánchez Alvarado A. 2003. Ingestion of bacterially expressed double-stranded RNA inhibits gene expression in planarians. Proc Natl Acad Sci 100 Suppl 1:11861-5.
Lundquist EA, Reddien PW, Hartwieg E, Horvitz HR, Bargmann CI. 2001. Three C. elegans Rac proteins and several alternative Rac regulators control axon guidance, cell migration and apoptotic cell phagocytosis. Development 128(22):4475-88.
Reddien PW, Cameron S, Horvitz HR. 2001. Phagocytosis promotes programmed cell death in C. elegans. Nature 412(6843):198-202.
Reddien PW, Horvitz HR. 2000. CED-2/CrkII and CED-10/Rac control phagocytosis and cell migration in Caenorhabditis elegans. Nat Cell Biol. 2(3):131-6.
Shaham S, Reddien PW, Davies B, Horvitz HR. 1999. Mutational analysis of the Caenorhabditis elegans cell-death gene ced-3. Genetics 153(4):1655-71. | 