The Nucleolar Remodeling is Required for the of Mouse Fibroblasts Reprogramming to iPSC [ATAC-Seq]

The nucleolus is a membraneless organelle responsible for ribosome biogenesis, perinuclear heterochromatin formation, and genome stability regulation. However, how cell fate decision occurs, including early embryonic development, ESC differentiation, and tumorigenesis, remains poorly understood at the nucleolar level. It has been observed that large nucleoli and rDNA hyperactivity are common in pluripotent stem cells and tumor cells, while the nucleolus shrinks and rDNA transcriptional activity decrease during lineage commitment. iPSCs nucleolar size and rDNA transcriptional activity are greater than that before reprogramming. It remains unclear how and when the differentiated cell nucleoli convert to the stem cell nucleoli during iPSC reprogramming.In this study, we found that nucleolar remodeling, manifested as enlarged nucleolus, activation of rDNA transcription, enhanced activity of nucleolar organizing regions (NORs), and conversion of reticular nucleolar ultrastructure into low-granular, is an early and stage-specific event that occurs during iPSCs reprogramming. Our study highlights the importance of rDNA transcriptional activity in the early stages of iPSC reprogramming, which is crucial for nucleolar remodeling and regaining stemness. Interfering rDNA transcription hinders nucleolar remodeling, which has disastrous consequences for chromatin remodeling in early stage of iPSC reprogramming and iPSCs establishment. Moreover, our results revealed a nucleolar regulation on chromatin accessibility during iPSC reprogramming and identified some candidate genes (Mybl2, Bard1 and other chromosome related genes) that might be associated with iPSC reprogramming, which may apply to nucleolar remodeling in other cell fated decision. Overall design: Comparative gene expression profiling analysis of ATAC-seq data for 4F2A cells(+DOX,48h) that treated by DMSO or CX-5461 for 1 hour at reprogramming begainning.