Chinese scientists have made a significant breakthrough in the understanding of the nucleolus, a structure in the nucleus with crucial functions. Their findings could have implications for the diagnosis and treatment of related diseases, such as cancer and rare conditions including Diamond-Blackfan anemia and Treacher Collins syndrome. The nucleolus, responsible for producing and processing ribosomal RNA in humans and animals, has been studied in detail by researchers from Shanghai’s Center for Excellence in Molecular Cell Science at the Chinese Academy of Sciences. Using ultrahigh resolution living cell microscopic imaging technology, the team discovered that in addition to the previously thought three-layer structure, there is an additional layer of spherical shell area, named the PDFC, that wraps outside the dense fiber component (DFC). Newly produced ribosomal RNA needs to pass through this layer, which acts as a “monitoring station,” to complete final ribosomal assembly. The protein URB1, present in the monitoring station, is key to regulating the folding and processing of newborn ribosomal RNA. Without URB1, ribosomal RNA swarms into the granular component (GC) zone with unremoved ends, making the cell unable to function normally. The study’s corresponding author, Chen Lingling, said that the research could have a significant impact on cell biology and embryonic development. The paper was published in the journal Nature.