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Schmidtea mediterranea: a system for comparative studies of embryogenesis and regeneration

Regeneration, the replacement of lost or damaged tissues to restore organ function, remains one of the most poorly understood processes in developmental biology. The origin and regulation of cells that make regeneration possible in different systems are largely obscure. How similar or distinct developmental processes are during embryogenesis and regeneration remains to be determined. In fact, few experimental systems are available to systematically study these issues. Here, we lay the foundation for formal comparison of molecular processes and gene function during embryogenesis and regeneration in S. mediterranea (Smed), a free-living freshwater planarian species uniquely suited to address the relationship between developmental plasticity and regeneration competency.

Smed flatworms are bilaterally symmetric, triploblastic animals that possess a wide variety of differentiated cell types and organ systems. Smed are stable diploids that exist as two biotypes: asexual animals that reproduce by fission, and obligate cross-fertilizing hermaphrodites that reproduce sexually (Newmark and Sánchez Alvarado, 2002; Newmark et al., 2008). Smed embryos are direct developers: newborn hatchlings grow and mature into adult worms without an intervening larval stage (Sánchez Alvarado, 2003). At hatching, juveniles are sexually immature but otherwise possess a body plan grossly similar to the adult hermaphrodite (Sánchez Alvarado, 2003; Wang et al., 2007). These flatworms are renowned for their remarkable regenerative potential: following amputation, small tissue fragments from adult worms of either biotype re-form complete, properly patterned individuals within one to two weeks. Regeneration is dependent on neoblasts, an abundant, cycling somatic cell population comprised of pluripotent stem cells and lineage-primed progenitors. All differentiated tissues in adult planaria, including the germline, are maintained and re-made from neoblast progeny.

The Sánchez Alvarado laboratory at the Stowers Institute for Medical Research is pioneering efforts to study Smed embryogenesis. This website accompanies our manuscript, “Embryonic origin of adult stem cells required for tissue homeostasis and regeneration,” and contains the molecular staging series and molecular fate mapping atlas for Smed embryogenesis described in our publication.


More Information

To learn more about the Smed sexual biotype and our planarian culturing conditions, please visit the “About our worms” page.

For more information about the salient features of freshwater flatworm embryogenesis, please visit the “Planarian embryogenesis crash course” page.

Our molecular staging resource associates unique gene expression signatures with chronological age, embryo morphology, representative images and written summaries of key developmental events to holistically describe and define prototypes for each stage.

Our molecular fate mapping atlas describes temporary embryonic tissue types and definitive organ system development.

Interested in examining expression trends for your favorite genes during embryogenesis? Search using names, putative function, or expression patterns with Gene Search. Identify homologous Smed sequences for genes of interest using BLAST.



Newmark, P.A., and Sánchez Alvarado, A. (2002). Not your father's planarian: a classic model enters the era of functional genomics. Nat Rev Genet 3, 210-219.

Newmark, P.A., Wang, Y., and Chong, T. (2008). Germ cell specification and regeneration in planarians. Cold Spring Harb Symp Quant Biol 73, 573-581.

Sánchez Alvarado, A. (2003). The freshwater planarian Schmidtea mediterranea: embryogenesis, stem cells and regeneration. Curr Opin Genet Dev 13, 438-444.

Wang, Y., Zayas, R.M., Guo, T., and Newmark, P.A. (2007). nanos function is essential for development and regeneration of planarian germ cells. Proc Natl Acad Sci U S A 104, 5901-5906.