Abstract
ABSTRACT Eukaryotic cells arose ~1.5 billion years ago, with the endomembrane system a central feature, facilitating evolution of intracellular compartments. Endomembranes include the nuclear envelope (NE) dividing the cytoplasm and nucleoplasm. The NE possesses universal features: a double lipid bilayer membrane, nuclear pore complexes (NPCs), and continuity with the endoplasmic reticulum, indicating common evolutionary origin. However, levels of specialization between lineages remains unclear, despite distinct mechanisms underpinning various nuclear activities. Several distinct modes of molecular evolution facilitate organellar diversification and to understand which apply to the NE, we exploited proteomic datasets of purified nuclear envelopes from model systems for comparative analysis. We find enrichment of core nuclear functions amongst the widely conserved proteins to be less numerous than lineage-specific cohorts, but enriched in core nuclear functions. This, together with consideration of additional evidence, suggests that, despite a common origin, the NE has evolved as a highly diverse organelle with significant lineage-specific functionality.
Highlights
Eukaryotes are estimated to have arisen over one and a half billion years ago – an event considered to be one of the major evolutionary transitions [1,2,3]
Reconstructions from comparative genomics have established an overall pattern of conserva tion of endomembrane-system genes among all major lineages of eukaryotes including plants, protists, amoebae, animals and fungi, implying inheritance from a complex common ancestor [14]
It suggests that a widely conserved, complex set of NEA proteins may exist, corre sponding to the conservation of the nuclear envel ope (NE) itself
Summary
Eukaryotes are estimated to have arisen over one and a half billion years ago – an event considered to be one of the major evolutionary transitions [1,2,3]. At some point following the divergence from the archaeal lineage, the protoeukaryote began to acquire features typical of eukaryotic cells, including a tubulin-based flagellum, an endomembrane system, a cytoskeleton and the mitochondrion. This period of evolution produced a complex Last Eukaryotic Common Ancestor (LECA) that possessed a large diversity of compartments exceeding the complement of many extant unicellular organisms. The remaining structures/orga nelles in eukaryotic cells, including the nucleus, are considered to be endogenously-derived, i.e. arising through evolution and expansion in the gene complement of the proto-eukaryote; the proteins defining various organelles have clear vertical descent from an archaeal ancestor. Reconstruction of the evolution of endogenouslyderived organelles relies on the identification and analysis of marker genes/proteins that define specific organelles and their sub-structures
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