Evolution and diversification of the nuclear envelope

Eukaryotic cells arose over 1.5 billion years ago, with the endomembrane system a central feature, facilitating evolution of specialised intracellular compartments. Endomembranes include the nuclear envelope (NE) that divides the cytoplasm from the nucleoplasm. The NE possesses universal features, specifically a double lipid bilayer membrane, nuclear pore complexes (NPCs), and continuity with the endoplasmic reticulum, indicating a common evolutionary origin. However, the levels of specialisation between eukaryotic lineages remains unclear, despite clear evidence for distinct mechanisms underpinning various nuclear activities. Several distinct modes of molecular evolution facilitate organellar diversification and include gene loss (sculpting), replacement/repurposing (backfilling), paralog expansion and emergence of novel genes in specific lineages. To understand mechanisms that apply to the NE, we exploited previously described proteome datasets of purified nuclear envelopes from model systems for comparative analysis. We find enrichment of core nuclear functions amongst the most widely conserved proteins, which account for a small fraction of the total, while the largest cohorts are likely lineage-specific. This, together with consideration of additional published studies, suggests that, despite a common origin, the NE has evolved as a highly diverse organelle with significant lineage-specific functionality.