Think globally, act locally: Redefining organellar membrane environments through cryo-electron tomography

Early enthusiasm for the "cellular revolution" in cryo-electron tomography (cryo-ET) was largely driven by the promise of resolving protein structures in native environments. However, a parallel trajectory has emerged that centers less on structure determination and instead on quantitative information about the nanoscale organization of organelle membranes and associated macromolecules. Together, these advances have shifted the field from descriptive visualization toward conceptual insight, and in the process, redefined what "local" means in organelle biology. In this review, I highlight recent studies that show how cryo-ET has illuminated specialized organelle membrane states defined by geometry, bilayer properties, protein patterning, and molecular sociology. These innovations reveal insights into membrane microenvironments and further establish cryo-ET as a bridge between structural and cell biology.