KANSL1 condensates drive spatial assembly of NSL complex

The non-specific lethal (NSL) complex is a well-characterized chromatin-modifying complex that binds to gene promoters particularly those of housekeeping genes to regulate their transcription. Dysregulation of NSL complex subunits has been causally linked to developmental defects, intellectual disability, and oncogenesis. To date, the NSL complex has been shown to comprise at least seven evolutionarily conserved subunits (KANSL1, KANSL2, KANSL3, WDR5, MCRS1, KAT8, and PHF20), along with two associated subunits (OGT and HCF1). However, the molecular mechanism governing its assembly remains poorly understood. Among its components, KANSL1 serves as the essential scaffolding subunit, playing indispensable roles in both the structural integrity and functional regulation of the complex. However, the molecular mechanism underlying this regulation remains elusive. Here, we report that KANSL1 undergoes liquid-liquid phase separation (LLPS) mediated by its intrinsically disordered region 4 (IDR4), a C-terminal segment spanning residues 733–857. IDR4-dependent LLPS of KANSL1 promotes the recruitment of KANSL2 and KANSL3, enabling assembly of the intact NSL complex. Moreover, this LLPS is essential for the histone acetyltransferase activity of the NSL complex and for the subsequent transcriptional regulation of its target genes. Furthermore, we demonstrate that KANSL1 LLPS governs the proliferation and migration of HeLa cells. Collectively, our findings uncover a self-regulated assembly mechanism of the NSL complex orchestrated by its scaffolding subunit KANSL1 and broaden the mechanistic understanding of how LLPS contributes to multi-protein complex formation and epigenetic gene regulation.