In a new publication in the Journal of Cell Biology, Jan van der Beek et al. use Correlative Light-Electron Microscopy (CLEM) to study key proteins of the endo-lysosomal system. Rab5, Rab7, APPL1 and EEA1 mark distinct populations of endosomes. However, the ultrastructural features of these subpopulations have been difficult to elucidate since classic immunolabeling with gold particles fails to detect the identifying proteins. Optimization of a CLEM protocol on sections was able to overcome this limitation, successfully linking Rab5, Rab7, APPL1 and EEA1 to ultrastructural characteristics. Surprisingly, EEA1 labels a subset of endosomes with late-stage morphology, considerably broadening the distribution of this protein in the endo-lysosomal system.

Jan van der Beek, Cecilia de Heus, Nalan Liv, and Judith Klumperman. 2022. “Quantitative Correlative Microscopy Reveals the Ultrastructural Distribution of Endogenous Endosomal Proteins.” The Journal of Cell Biology 221(1).