TGF-beta coordinates changes in Keratin gene expression during complex tissue regeneration

Zebrafish larval tail regeneration can be broadly broken down into three phases: wound repair, initiation of regeneration and redevelopment of the tail. We and others have shown that activation of the Hedgehog and TGF-beta signalling pathways is required to trigger tail regeneration. In this study we initially focus on these two pathways to better understand their role regeneration. We have found that Hedgehog signalling acts upstream of the TGF-beta pathway by activating transcription of the TGF-beta ligand tgfb1a. We have identified differentially expressed genes that are regulated after tail excision as well as those that are dependent upon TGF-beta signalling. From this analysis we found that Keratin genes fall into two categories of co-expression: one set that is upregulated by TGF-beta signalling after injury (krtup) and a second set that is downregulated (krtdown). We have mapped the expression of a representative member of krtup (krt97) and krtdown (krt5) sets during development and regeneration and show that krt97 is found in epithelia that is moving and krt5 is expressed in epithelia that is stationary. To see whether these two sets show co-expression more broadly, we analysed single cell RNA sequencing data and found that krts also fall into the same categories during zebrafish development. Based upon our results we propose that the krtup set may allow for collective epithelial migration while the krtdown set may inhibit mobility. These results reveal one mechanism by which TGF-beta may initiate regeneration and could help to explain how changes in cytoskeletal composition influence cell movement during development and repair.