SUMMARY
A survey of the current knowledge on stem cells and cell proliferation in turbellarians is presented,
with special focus on recent results obtained by the authors when studying cell kinetics and
cultivating neoblasts from various species. Differentiated somatic cells do not divide in flatworms.
In these animals neoblasts constitute a proliferative compartment. These cells are rather uniform
when viewed through a light microscope, but constitute a heterogeneous population comprising
actual stem cells, progenitors and early differentiation stages. Cell kinetics were monitored by the
incorporation of 5-bromo-2'-deoxyuridine and by immunocytochemical staining for mitoses in the
marine microturbellarians Macrostomum, Microstomum and Convolutriloba. Distribution patterns of
proliferating cells within the body were documented, and a tentative interpretation of the
differences observed is given. Correlations to the nervous system and the mode of reproduction
seem to exist. To analyse neoblasts quantitatively and establish primary cultures, neoblasts from
the freshwater planarians (triclads) Dugesia and Schmidtea were isolated, purified and subjected to
various culture conditions, with the ultimate but not yet achieved goal of establishing a permanent
stem cell line. The role of stem cells in flatworms is compared with the situation in mammals, with
special focus on embryogenesis, germline and strategies of cell renewal.
KEY WORDS
BrdU labelling; cell cultures; cell proliferation; neoblasts; germline; stem cells
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