title: Cell renewal and apoptosis in macrostomum sp. [Lignano].
abstract: In platyhelminths, all cell renewal is accomplished by totipotent stem cells (neoblasts). Tissue maintenance is achieved in a balance between cell proliferation and apoptosis. It is known that in Macrostomum sp. the epidermis undergoes extensive cell renewal. Here we show that parenchymal cells also exhibit a high rate of cell turnover. We demonstrate cell renewal using continuous 5'bromo-2-deoxyuridine (BrdU) exposure. About one-third of all cells are replaced after 14 days. The high level of replacement requires an equivalent removal of cells by apoptosis. Cell death is characterized using a combination of three methods: (1). terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL), (2). specific binding of phosphatidyl-serine to fluorescent-labelled annexin V and (3). identification of apoptotic stages by ultrastructure. The number of cells observed in apoptosis is insufficient to explain the homeostasis of tissues in Macrostomum. Apoptosis-independent mechanisms may play an additional role in tissue dynamics.
authors.affiliation: Institute of Zoology and Limnology, University of Innsbruck, Technikerstrasse 25, A-6020, Innsbruck, Austria.
authors.forename: K
authors.initials: K
authors.lastname: Nimeth
authors.forename: P
authors.initials: P
authors.lastname: Ladurner
authors.forename: R
authors.initials: R
authors.lastname: Gschwentner
authors.forename: W
authors.initials: W
authors.lastname: Salvenmoser
authors.forename: R
authors.initials: R
authors.lastname: Rieger
mesh_terms: D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D017209:Apoptosis / Q000502:physiology*; D001973:Bromodeoxyuridine / Q000494:pharmacology; D002455:Cell Division / Q000502:physiology; D020287:In Situ Nick-End Labeling; D008854:Microscopy, Electron; D013234:Stem Cells / Q000648:ultrastructure; D014419:Turbellaria / Q000166:cytology*
chemical_list: D000963:Antimetabolites; D001973:Bromodeoxyuridine