Abstract

Endomembrane system compartments are characteristic of eukaryotic cells, supporting functions including protein synthesis, post-translational modifications and protein/lipid targeting. As such, the endomembrane system has important roles in signalling, and defective vesicle transport is associated with a variety of diseases. While these functions are mostly studied in an evolutionarily narrow sampling of model organisms, comparative genomics can be used to examine the system in non-model organsisms and to trace proteins and cellular traits to their roots. What has emerged from these studies is that the origin of these compartments can be traced back to the origin of the eukaryotic cell, which is estimated to have occurred over one billion years ago, indicating spectacular cellular complexity prior to expansion of the eukaryotic lineages. This provides a challenge in terms of explaining how these early eukaryotes arose. These studies also highlight that complexity can arise in multiple ways during evolution. The patterns of complexity generation will be illustrated by examples from studies of the tethering complexes (mediating vesicle fusion specificity), the retromer complex (involved in retrograde traffic from the endosome or lysosome to the Golgi complex), and factors shaping the endoplasmic reticulum.