NEAT1_1-encoded microprotein PSNEAT1 drives rDNA transcription via phase separation with WRN

Nuclear enriched abundant transcript 1 (NEAT1) has two isoforms that serve as core structural components of paraspeckles. Although the regulatory functions of NEAT1 as a noncoding RNA are well established, it has remained unclear whether the short polyadenylated isoform, NEAT1_1, encodes a functional microprotein. Herein, we identify NEAT1_1 encodes a microprotein, which we name PSNEAT1 (phase-separating NEAT1 microprotein). PSNEAT1 localizes to the fibrillar center of nucleolus, where it enhances ribosomal DNA (rDNA) transcription, ribosome biogenesis, and tumor growth. Notably, depletion of PSNEAT1 results in pronounced nucleolar disorganization. Mechanistically, PSNEAT1 directly binds both rDNA and the DNA helicase WRN, thus facilitating WRN recruitment to nucleolus by liquid-liquid phase separation (LLPS). Collectively, our study reveals an LLPS-dependent mechanism by which the NEAT1_1-encoded microprotein PSNEAT1 regulates nucleolar structure and function.