Djnedd4L Is Required for Head Regeneration by Regulating Stem Cell Maintenance in Planarians

SUMOylation and ubiquitylation are homologous processes catalyzed by homologous enzymes, and they are involved in nearly all aspects of eukaryotic biology. Planarians, which have the remarkable ability to regenerate their central nervous system (CNS), provide an excellent opportunity to investigate the molecular processes of CNS regeneration in vivo. In this study, we analyzed gene expression profiles during head regeneration with an RNA-seq-based screening approach and found that Djnedd4L and Djubc9 were required for head regeneration in planarians. RNA interference targeting of Djubc9 caused the phospho-H3 mitotic cells to decrease in quantity, or even become absent as a part of the Djubc9 RNAi phenotype, which also showed the collapse of the stem cell lineage along with the reduced expression of epidermal differentiation markers. Furthermore, we found that Djnedd4L RNAi induced increased cell division and promoted the premature differentiation during regeneration. Taken together, our findings show that Djubc9 and Djnedd4L are required for stem cell maintenance in the planarian Dugesia japonica, which helps to elucidate the role of SUMOylation and ubiquitylation in regulating the regeneration process.