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

Abstract

SUMMARYPlanarians have high regenerative ability, which is dependent on pluripotent adult somatic stem cells called neoblasts. Recently, canonical Wnt/-catenin signaling was shown to be required for posterior specification, and Hedgehog signaling was shown to control anterior-posterior polarity via activation of the Djwnt1/P-1 gene at the posterior end of planarians. Thus, various signaling molecules play an important role in planarian stem cell regulation. However, the molecular mechanisms directly involved in stem cell differentiation have remained unclear. Here, we demonstrate that one of the planarian LIM-homeobox genes, Djislet, is required for the differentiation of Djwnt1/P-1-expressing cells from stem cells at the posterior end. RNA interference (RNAi)-treated planarians of Djislet [Djislet(RNAi)] show a tail-less phenotype. Thus, we speculated that Djislet might be involved in activation of the Wnt signaling pathway in the posterior blastema. When we carefully examined the expression pattern of Djwnt1/P-1 by quantitative real-time PCR during posterior regeneration, we found two phases of Djwnt1/P-1 expression: the first phase was detected in the differentiated cells in the old tissue in the early stage of regeneration and then a second phase was observed in the cells derived from stem cells in the posterior blastema. Interestingly, Djislet is expressed in stem cell-derived DjPiwiA-and Djwnt1/P-1-expressing cells, and Djislet(RNAi) only perturbed the second phase. Thus, we propose that Djislet might act to trigger the differentiation of cells expressing Djwnt1/P-1 from stem cells.

Localization of planarian β-CATENIN-1 reveals multiple roles during anterior-posterior regeneration and organogenesis

“…This observation supports the hypothesis that the wnt1 ligand, secreted by the newly formed posterior organizer, is the morphogen that sustains nuclear translocation of β-CATENIN-1 at the posterior pole during regeneration (Adell et al, 2009;Petersen and Reddien, 2009b). Later on, the nested expression of the other posterior Wnt ligands would control the re-establishment and maintenance of the gradient (Hayashi et al, 2011;Lander and Petersen, 2016;März et al, 2013;Scimone et al, 2016;Sureda-Gómez et al, 2015) (Fig. 6A).…”

teashirt is required for head-versus-tail regeneration polarity in planarians

“…Anterior and posterior poles are small clusters of cells at the head and tail tip, respectively, and are required for normal planarian head and tail regeneration and PCG expression (Felix and Aboobaker, 2010;Hayashi et al, 2011;Blassberg et al, 2013;Chen et al, 2013;Scimone et al, 2014b;Vásquez-Doorman and Petersen, 2014;Vogg et al, 2014). However, in contrast to teashirt RNAi, inhibition of either anterior or posterior pole formation does not cause a reversal of the head-tail regeneration choice.…”

JNK Signaling is necessary for a Wnt and stem cell dependent regeneration program

“…This early wnt1 expression is required for stem cells at the posterior wound site to differentiate to form a Wnt gene-expressing pole in the regenerating blastema (Petersen and Reddien, 2009b). Active Hh signalling is required for early wound-induced Wnt gene expression and a number of other genes have now been shown to be required for the formation of the stem cell-dependent phase of later Wnt gene expression (Blassberg et al, 2013;Chen et al, 2013;Currie and Pearson, 2013;Hayashi et al, 2011;Marz et al, 2013;Rink et al, 2009;Yazawa et al, 2009). In junl-1(RNAi) worms, the early phase of wound-induced wnt1 expression was not affected and was equivalent to that observed for control animals at both anterior and posterior wounds ( Fig.…”

“…In particular, Smed-islet (Hayashi et al, 2011), Smed-pitx (Currie and Pearson, 2013;Marz et al, 2013) and Smed-pbx (Blassberg et al, 2013;Chen et al, 2013) have all been shown to be required for correct posterior regeneration. In all cases these genes are necessary for the stem celldependent phase of wnt1 expression and the subsequent activation of Smed-wnt11-2 and Smed-wnt11-5.…”

“…Although Wnt and Hh signalling are clearly central players in controlling anterior-posterior polarity in planarians, a number of other genes have also been shown to be required for this process, by potentially interacting with these pathways (Blassberg et al, 2013;Chen et al, 2013;Currie and Pearson, 2013;Hayashi et al, 2011;Marz et al, 2013), and to be required for the stem cell-dependent phase of wnt1 expression and subsequent activation of Smed-wnt11-2 and Smed-wnt11-5. In this report it has been shown that JNK (A) Double Smed-ptc/junl-1(RNAi) and Smed-apc/junl-1(RNAi) resulted in tails forming at every wound site (xt), compared with the tailless animals (a) that result after Smed-junl-1/gfp(RNAi) ( ptc/gfp xt=53/66, ptc/junl-1 xt=67/69, apc/gfp xt=40/40, apc/junl-1 xt=40/40, gfp/gfp n=86/86, junl-1/gfp a=95/101, as scored for tails at both ends for the ptc knockdowns and tails at the posterior for gfp and junl-1).…”