Our labs new pre-print is now available here on BioRxiv. It is one of many papers the lab has contributed too which are available as pre-prints before publication.
In this study we thought hard about ways in which we could identify self-renewing stem cells in the ongoing absence of planarian transgenesic approaches. One cell biology phenotype that we thought would be useful to trace cells that are definitely capable of undergoing multiple rounds of cell division was endoreplication or endocycling, where cells go through the cell cycle but without completing M-phase and actually dividing. This results in cells of increased ploidy and DNA content.
To do this in planarians we knocked down condensin complex proteins as this have been shown to induce endocycling in other systems. Analysing these RNAi phenotypes in planarians allowed us to establish that only certain neoblasts, those of the previously described sigma class (van Wolfswinkel, 2014), are enlarged due to increased DNA content. This, in agreement with original the description of these cells, provides strong evidence these are the self-renewing stem cell population in planarians. Other stem cells that were identified by expression heterogeneity (van Wolfswinkel, 2014) don’t ever appear to undergo more than one round of the cell cycle, so these may need to reclassified as transit amplifying progeny, capable of a single division rather then included in the stem cell compartment.