Role of c‐Jun N‐terminal kinase activation in blastema formation during planarian regeneration

Abstract

The robust regenerative abilities of planarians absolutely depend on a unique population of pluripotent stem cells called neoblasts, which are the only mitotic somatic cells in adult planarians and are responsible for blastema formation after amputation. Little is known about the molecular mechanisms that drive blastema formation during planarian regeneration. Here we found that treatment with the c-Jun N-terminal kinase (JNK) inhibitor SP600125 blocked the entry of neoblasts into the M-phase of the cell cycle, while allowing neoblasts to successfully enter S-phase in the planarian Dugesia japonica. The rapid and efficient blockage of neoblast mitosis by treatment with the JNK inhibitor provided a method to assess whether temporally regulated cell cycle activation drives blastema formation during planarian regeneration. In the early phase of blastema formation, activated JNK was detected prominently in a mitotic region (the ''postblastema'') proximal to the blastema region. Furthermore, we demonstrated that undifferentiated mitotic neoblasts in the postblastema showed highly activated JNK at the single cell level. JNK inhibition by treatment with SP600125 during this period caused a severe defect of blastema formation, which accorded with a drastic decrease of mitotic neoblasts in regenerating animals. By contrast, these animals still retained many undifferentiated neoblasts near the amputation stump. These findings suggest that JNK signaling plays a crucial role in feeding into the blastema neoblasts for differentiation by regulating the G2 ⁄ M transition in the cell cycle during planarian regeneration.

A LIM-homeobox gene is required for differentiation of Wnt-expressing cells at the posterior end of the planarian body

“…In previous studies, PiwiA protein has been found to be expressed, not only in stem cells which are expressing piwiA mRNA, but also in post-mitotic progeny: the stem cell-derived cells (Guo et al, 2006;Yoshida-Kashikawa et al, 2007;Scimone et al, 2010). The blastema cells are almost all post-mitotic cells, as indicated by the absence of mitotic cell markers (Salvetti et al, 2000;Eisenhoffer et al, 2008;Tasaki et al, 2011a;Tasaki et al, 2011b). Therefore, the DjPiwiA protein-expressing cells in the blastema are most likely to be stem cell-derived cells.…”

A Survey of the Molecular Basis for the Generation of Functional Dopaminergic Neurons from Pluripotent Stem Cells: Insights from Regenerative Biology and Regenerative Medicine

“…The cells that participate in blastema formation already exist from the proliferative state, and a portion of these cells start to form the brain rudiment [25,26]. Therefore, the commitment of DA neurons may immediately occur after brain rudiment and brain pattern formation.…”

“…Subsequently, a blastema (a mass of cells derived from pluripotent stem cells) is formed by mitogen-activated protein (MAP) kinase activation 24 hours after amputation [25,26]. It has been revealed that blastema cells are supplied from the post-blastema region via mitosis from G2-phase pluripotent stem cells.…”

Drosophila as a model of wound healing and tissue regeneration in vertebrates

“…It has also been shown that the Scribble (Scrib) complex, an important determinant of apicobasal polarity, contributes to epithelial cell migration and fusion during both development and wound healing in mammals by recruiting the small GTPases Cdc42, Rac and the serinethreonine kinase Pak to the leading edge (LE) of migrating cells (Murdoch et al, 2003;Zarbalis et al, 2004;Humbert et al, 2006;Dow et al, 2007;Bahri et al, 2010). JNK signaling is required for regeneration after wounding in zebrafish (Kawakami, 2010, for review), and it plays a crucial role in the differentiation of blastema neoblasts by regulating the G2/ M cell cycle transition during planarian regeneration (Tasaki et al, 2011). Finally, it was shown that expression of Wnt target genes was stimulated by JNK activation, accelerating tumorigenesis (Sancho et al, 2009).…”