19-P035 Cellular and molecular dynamics of stem cell differentiation during planarian regeneration

After limb amputation, urodele amphibians can regenerate lost parts perfectly throughout their life. However, Xenopus laevis shows its characteristic limb regenerative ability. Although Xenopus tadpole has the capacity to regenerate their limbs after amputation, after amputation of a froglet (a small frog after metamorphosis) limb, it can regenerate only a spike-shaped cartilage which has no pattern. Considering that the spike has no joint along the PD axis and that limb amputation at any level (e.g. wrist and elbow) results in the same spike structure, positional information along the PD axis seems not to be reflected correctly during froglet limb regeneration. In this study, we investigated the PD axis formation during limb regeneration in X. laevis. We compared expression pattern, and expression level of hoxa11 and hoxa13 between tadpole blastema and froglet blastema. Furthermore, weperformed cell sorting assay using blastemal cells that were derived from different amputation levels along the PD axis. We found that expression domains of hoxa11 and hoxa13 were never separated and that expression level of hoxa13 was very low in the froglet blastema. We also found that sorting out along the PD axis was never observed in the froglet blastema. These data indicate that re-expression of hoxa11 and hoxa13 occurs during spike formation, but that morphogenesis along the PD axis is obviously defected. We also discuss that inappropriate and inharmonious shift of timing between pattern formation (i.e. separation of hoxa11 and hoxa13 domains) and cell differentiation (i.e. chondrogenesis) may be involved in the PD pattern defect.