Single-Cell Resolution of MET- and EMT-Like Programs in Osteoblasts During Zebrafish Fin Regeneration

Abstract

While humans have limited potential for limb regeneration, some vertebrates can regenerate bony appendages following amputation. During zebrafish fin regeneration, mature osteoblasts at the amputation stump dedifferentiate and migrate to the blastema, where they re-enter the cell cycle and then re-differentiate to form new bone. Osteoblastic cells differentially exhibit mesenchymal and epithelial characteristics during fin regeneration, however little is known about how these transitions occur. Here, we performed single-cell RNA-sequencing (scRNA-seq) studies to elucidate osteoblastic transcriptional programs during zebrafish caudal fin regeneration. In contrast to existing scRNA-seq resources, our dataset captures a large number of osteoblastic cells, allowing for their in-depth analysis. We found osteoprogenitors are enriched with components associated with the epithelial-to-mesenchymal transition (EMT) and its reverse, mesenchymal-to-epithelial transition (MET). In trajectory analyses, osteoblastic cells solely expressed EMT components, or transiently expressed MET components prior to expressing those for EMT. We found that cdh11, a cancer EMT marker, is expressed during osteoblast dedifferentiation. We also found that esrp1, a regulator of alternative splicing in epithelial cells whose expression is important for MET, is expressed in a subset of osteoprogenitors during outgrowth. This study provides a valuable single cell resource for the study of osteoblastic cells during zebrafish fin regeneration, and identifies MET- and EMT-associated components which may be important for successful appendage regeneration.