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Van Wolfswinkel lab

RNA biology of stem cells
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It takes Schmidtea about 10 days to regenerate a head (including a brain!) or the entire posterior part of the body. The new tissue, which is formed by new cell division of the neoblasts, is initially visible as an unpigmented ougrowth called the blastema.
Sexual reproduction in Schmidtea takes much longer than regeneration. The embryos develop inside the egg capsule and hatch only after 2 to 3 weeks. After that it takes them several weeks to become sexually mature again.
Schmidtea has a complex body morphology with several localized and organized cell types. The left image shows the intestinal tract in green. The pharynx, which also functions as an anus, is connected to the intestine at its anterior end, and is shown in green in the middle image. The magenta cells in the left and the middle image are the neurons, viewed from the dorsal and the ventral side respectively. The right image shows the muscle cells in green, and the protonephrydia (simple kidneys) in magenta.
The neoblasts, here shown in green, are present throughout most of the body of Schmidtea. These are the only dividing cells in the planarian body, as shown by BrdU incorporation during DNA duplication (top, magenta), or by phosphorylation of histone 3 which marks the mitotic phase (bottom, magenta).
Not all neoblasts are the same. Some neoblasts are pluripotent, but others are already specialized into a specific lineage. Shown here are isolated neoblasts of two different classes (green and magenta).
Three different stages of epidermal cell differentiation are shown in green, yellow and magenta respectively. During differentiation the cells move outward towards the outer surface of the animal.
Neoblast classes do not represent different cell cycle stages. Both neoblast classes shown above ( in green and magenta) can be in the mitotic phase of cell cycle, as indicated by the phosphorylation of histone H3 (shown in yellow).

Department of Molecular Cellular and Developmental Biology

Yale University