ELL3 (elongation factor for RNA polymerase II 3) is a transcription elongation factor with multifaceted roles in developmental and cellular regulation. Functionally, ELL3 enhances the catalytic rate of RNA polymerase II transcription elongation and serves as a component of the super elongation complex (SEC) 1. In embryonic stem cells, ELL3 marks both active and poised enhancers, establishing proper RNA polymerase II occupancy at developmentally regulated genes in a cohesin-dependent manner, and is required for recruiting P-TEFb during differentiation 2. ELL3 also regulates LINE-1 transposon enhancers to control naïve pluripotency by modulating the AKT pathway 3. Clinically, ELL3 dysfunction has significant disease implications. Maternal ELL3 loss-of-function causes oocyte aneuploidy and early miscarriage by localizing to the spindle during meiosis and coordinating with TPX2 to ensure proper KIF11 motor function and chromosome 15 4. ELL3 acts as a critical regulator of stem cell fate through the p53-Bcl2 axis, where suppression induces senescence while overexpression promotes apoptosis 5. In cancer, ELL3 overexpression stimulates breast cancer proliferation, drug resistance, and cancer stem cell properties via MEK/ERK signaling 6. ELL3 dysregulation also contributes to multiple sclerosis pathogenesis by affecting oligodendrocyte function through miRNA synthesis modulation 7.