Proliferation pattern during rostrum regeneration of the symbiotic flatworm Paracatenula galateia: a pulse-chase-pulse analysis.
The remarkable totipotent stem-cell-based regeneration capacities of the Platyhelminthes have brought them into the focus of stem cell and regeneration research. Although selected platyhelminth groups are among the best-studied invertebrates, our data provide new insights into regenerative processes in the most basally branching group of the Platyhelminthes, the Catenulida. The mouth- and gutless free-living catenulid flatworm Paracatenula galateia harbors intracellular bacterial symbionts in its posterior body region, the trophosome region, accounting for up to 50% of the volume. Following decapitation of this flatworm, we have analyzed the behavior of the amputated fragments and any anterior and posterior regeneration. Using an EdU-pulse-chase/BrdU-pulse thymidine analog double-labeling approach combined with immunohistochemistry, we show that neoblasts are the main drivers of the regeneration processes. During anterior (rostrum) regeneration, EdU-pulse-chase-labeled cells aggregate inside the regenerating rostrum, whereas BrdU pulse-labeling before fixation indicates clusters of S-phase neoblasts at the same position. In parallel, serotonergic nerves reorganize and the brain regenerates. In completely regenerated animals, the original condition with S-phase neoblasts being restricted to the body region posterior to the brain is restored. In contrast, no posterior regeneration or growth of the trophosome region in anterior fragments cut a short distance posterior to the brain has been observed. Our data thus reveal interesting aspects of the cellular processes underlying the regeneration of the emerging catenulid-bacteria symbiosis model P. galateia and show that a neoblast stem cell system is indeed a plesiomorphic feature of basal platyhelminths.
Department of Marine Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria. Uli.Dirks@gmx.de
Ulrich
U
Dirks
Harald R
HR
Gruber-Vodicka
Bernhard
B
Egger
Jörg A
JA
Ott
D000818:Animals; D049109:Cell Proliferation; D007150:Immunohistochemistry; D010986:Platyhelminths / Q000033:anatomy & histology* / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D012038:Regeneration; D016196:S Phase; D013234:Stem Cells / Q000166:cytology