Background

Planarians are bilaterally symmetric platyhelminthes, members of the superphylum lophotrochozoa. There are terrestrial, marine, and freshwater planarians. They prey predominantly upon injured insects, insect larvae, and other invertebrates. Planarians are triploblastic and acoelomated animals that lack circulatory, skeletal, and respiratory systems (Figure 1A). These animals have the amazing ability to restore any missing part of their body after an amputation in a few days (Reddien and Alvarado, 2004; Salo, 2006); and to grow and degrow depending of the environmental conditions and food availability (Baguñá and Romero, 1981). These characteristics are due to the presence of an adult stem cell population – called neoblasts – that is able to give rise to any planarian cell type (Reddien and Alvarado, 2004; Salo, 2006). The high regenerative capacity of planarians, with the presence of a unique totipotent stem cell system, provides an ideal model for studying cell renewal, regeneration, and stem cell regulation. Schmidtea mediterranea is the most common planarian species used in molecular biology to perform molecular and cellular studies, because it presents special features that optimize research. For instances, they are easily maintained as a stable clonal line in the laboratory due to their robust ability to regenerate, which allows a uniform genetic background and minimizes the experimental variability. Here we detail the protocol used in our laboratory to maintain the planarian species Schmidtea mediterranea.