LINE-1, the NORth star of nucleolar organization

Long interspersed element-1 (LINE-1) retrotransposons are abundant transposable elements in mammals and significantly influence chromosome structure, chromatin organization, and 3D genome architecture. In this issue of Genes & Development , Ataei et al. (doi:10.1101/gad.351979.124) identify a homininae-specific LINE-1 element within nucleolar ogranizer regions (NORs) that is specifically transcribed in naïve human embryonic stem cells. Deletion or silencing of this element disrupts nucleolar organization and function and alters cellular identity. These findings provide novel insights into the role of retrotransposons in genome organization and suggest that individual LINE-1 elements may have evolved specialized roles.