ATAC-Seq of Xenopus tail regeneration

Mammals possess limited regeneration capabilities, where the few examples of scarless healing tend to be restricted to early development. In light of this, it is of great interest to study animals that can faithfully regrow complete appendages, and uncover the biological properties that facilitate this process. Xenopus tropicalis tadpoles are excellent vertebrate models of regeneration, as they rapidly recover lost tails within just one week post amputation. Though we have some understanding of what pathways are required for tail regeneration, we have yet to systematically chronicle the regulatory events that coordinate this specialized response to injury. Here, we highlight a striking phenomenon in Xenopus regeneration, whereby nuclei within the fin epithelium of an amputated tail change shape in a dramatic and stereotyped manner during regeneration. We assess chromatin accessibility dynamics through ATAC-Seq of nine time points of regeneration, and find that large scale changes in chromatin state are highly correlated to changes in nuclear shape. To identify critical regulators of these chromatin dynamics, we describe and apply a machine learning method, PFBoost, which integrates information from motifs underlying dynamically accessible ATAC-Seq peaks and differentially expressed transcription factors from time-matched RNA-Seq data to predict chromatin state. To functionally evaluate PFBoost-predicted regeneration regulators, we developed an inducible CRISPRi system utilizing the FKBP derived destabilizing domain, and knockdown expression of these regulators during the early hours of regeneration. With this methodology, we identified and describe two novel regulators of regeneration, spib and chd8. We provide not only an abundant resource for chromatin dynamics in tail regeneration, but also chronicle an intriguing mechanism of regeneration regulation in the form of nuclear shape change and coordinate changes in chromatin state. Overall design: Profiling of chromatin accessibility across nine time points in tadpole tail regeneration; sequenced in duplicate via Illumina HiSeq and NextSeq. Please note that each *combined_reps.bw file was generated from both replicates and is linked to the corresponding 'rep1' sample records.