Meeting Abstract

P3.142  Tuesday, Jan. 6  Neoblasts in Catenulida MERLIE, S.A.**; RYAN, K.A.*; SMITH III, J.P.; Winthrop University; Winthrop University; Winthrop University merlies2@winthrop.edu

Our current understanding of the stem-cell (neoblast) system in Platyhelminthes comes primarily from a wealth of experiments on regeneration in members of the Tricladida, supplemented by studies of members of other groups. To date, there are relatively few studies of the neoblasts in the potentially-primitive Catenulida. Accordingly, we have carried out M-phase (anti-phosphoH3) and putative S-phase (anti-PCNA) labeling experiments in Stenostomum virginianum and Catenula lemnae, supplementing these light-microscopic histochemical studies with electron microscopy. We have also studied neoblast dynamics in starved and fed S. virginianum. Neoblasts were observed in the gastrodermis and parenchyma of both species by both light-microscopic immunohistochemistry and by electron microscopy. In addition, S. virginianum was found to possess neoblasts in the epidermis, consistent with previous light- and electron-microscopic observations of dividing cells in the epidermis of various catenulid species. Following prolonged starvation, neoblast mitoses in S. virginianum recovered in a biphasic fashion, with mitoses peaking at 3 hours and 24 hours post-feeding, in a pattern reminiscent of that in triclad flatworms. Collectively, these data support the hypothesis that the neoblast stem-cell system may be a synapomorphy for the Platyhelminthes. (Supported by a Grant from the Winthrop University Research Council)