Injury-induced transcription in the planarian outer epithelium is critical for tissue regeneration

Planarian flatworms have an extraordinary regenerative capacity; even a small, asymmetrical fragment of amputated planarian tissue can recreate an entirely new animal. The planarian field has made significant progress in identifying specific genes and cell types required for this complex process, but substantially less is known about the molecular mechanisms that convert a significant physical injury (e.g., head amputation) into the expression of specific genes in particular cell types. One tissue in which this question is particularly relevant is the planarian epidermis, a single-layer, mucociliary epithelium with similarities to the epithelia of mammalian airways. This epithelium plays an essential, early role in planarian regeneration as the cells surrounding the wound site must quickly stretch and extend to cover the wound area after injury. We hypothesized that these injury-induced morphological changes activate the transcription of genes with essential functions in the regenerative process. To best detect these transcriptional changes, we developed a rapid method for isolating the planarian outer epithelium and prepared ribodepleted RNA-sequencing libraries from samples isolated at multiple time points after tissue amputation. One gene we both identified using these methods and found to be functionally important for regeneration is a putative planarian homolog of vertebrate Shoc2. SHOC2 is an essential scaffolding protein that mediates specific, context-dependent activation of the ERK1/2 signaling pathway (J O_SCPLOWANGC_SCPLOW O_SCPLOWANDC_SCPLOWG O_SCPLOWALPERINC_SCPLOW2016). Notably, the ERK1/2 pathway is known to be activated after injury and required for regeneration in multiple species (M O_SCPLOWANUELC_SCPLOW et al. 2006; O O_SCPLOWWLARNC_SCPLOWet al. 2017; T O_SCPLOWOMASSOC_SCPLOWet al. 2023). These findings suggest that these epithelial datasets have the potential to uncover many functionally relevant and possibly highly conserved genes that play fundamental roles in animal regeneration.