Trypanosomatid flagellates such as Trypanosoma brucei and T. cruzi have long fascinated cell biologists because their endocytic traffic is confined to a single invagination of the plasma membrane called the flagellar pocket. This unusual geometry makes them powerful models for testing how universal the principles of membrane trafficking really are. Previous work had catalogued many components of clathrin-mediated endocytosis in these parasites, but the composition and evolutionary standing of their ESCRT machinery remained incompletely resolved. In animals and fungi, a subcomplex called ESCRT-0, built around the Vps27/Hrs and STAM proteins, recognises ubiquitylated substrates and hands them to the downstream complexes. Whether trypanosomes possess anything comparable has been an open question.

The team approached the problem from two directions: comparative genomics across the eukaryotic tree and experimental biochemistry in the parasite itself. Using hidden Markov model searches and reciprocal best BLAST analyses, they surveyed hundreds of genomes from every major eukaryotic supergroup for orthologs of candidate sorting proteins. In parallel, they engineered procyclic-form T. brucei cells to express an endogenous GFP-tagged version of Vps23, the Tsg101 orthologue that anchors the ESCRT-I complex. Affinity purification followed by quantitative mass spectrometry then pulled down the proteins that travel with TbVps23 in living cells, allowing the researchers to confirm predicted partners and uncover unexpected ones.

The most striking biochemical discovery was that trypanosome ESCRT-I is not the canonical heterotetramer familiar from yeast and animals. Instead, the purification identified two novel Vps23-interacting proteins, encoded by adjacent open reading frames Tb927.11.2020 and Tb927.11.2030, that travel stoichiometrically with the core subunits. These proteins are specific to trypanosomes, with no obvious homologues outside the kinetoplastid lineage, and their association with Vps23 indicates that the trypanosome ESCRT-I subcomplex is a heteropentamer. The finding adds a new tier of compositional divergence to a complex long considered structurally conserved, and it underscores how evolutionary flexibility can be woven into even the most fundamental cellular machines.

Equally consequential is the team’s answer to the question of what serves as the trypanosome ESCRT-0 analogue. Rather than a Vps27/STAM pair, which the analyses confirmed is absent from most non-opisthokont lineages, the parasites employ Tom1, a protein carrying the VHS and GAT domains that is broadly distributed across eukaryotes. The researchers demonstrated that trypanosome Tom1, termed TbTom1, colocalises with TbVps23 at endosomal membranes and interacts with a kinetoplastid-specific partner protein the authors nicknamed Jerry, a multi-domain protein studded with three FYVE domains, lipid-binding modules that recognise endosomal phosphoinositides. Together, Tom1 and Jerry appear to fulfil the substrate-recognition role that ESCRT-0 plays in fungi and animals, but through entirely different molecular parts.

Structural predictions reinforced the ancient pedigree of this arrangement. AlphaFold3 modelling of TbTom1 revealed a compact, well-ordered VHS helical bundle linked to a GAT domain, closely superimposable on the VHS domain of human TOM-1, while the remaining regions of the protein are predicted to be intrinsically disordered. This architecture supports the authors’ proposal that Tom1 is the ancestral VHS-GAT-domain-containing cargo adaptor, present in the last common ancestor of eukaryotes and retained across supergroups, whereas the Vps27/Hrs-STAM system of ESCRT-0 is a later innovation restricted to animals and fungi. By mapping the occurrence of Tom1 and Jerry orthologues across the Euglenozoa, the researchers showed that Tom1 is universally retained within the phylum while Jerry is absent from diplonemids, tracing a lineage-specific layer of specialisation on top of a conserved core.

The experimental evidence connecting these proteins to endocytic function came from cellular phenotyping. Cells expressing tagged versions of TbTom1 or TbJerry showed significantly enlarged flagellar pockets, with morphometric analysis of DAPI-stained cells revealing a marked increase in pocket area compared with the parental line, and tagged TbJerry cells additionally displaying a subtle nozzle-like distortion of the pocket. Because the flagellar pocket is the sole site of endocytosis in trypanosomes, such expansion implies a direct perturbation of membrane uptake and trafficking throughput. The phenotypes were measured across individual cloned lines and validated by immunoblotting of endogenous tags, giving the morphological data a firm molecular footing.

Curiously, the machinery appears dispensable for parasite viability in laboratory culture. RNA interference targeting TbTom1 in bloodstream-form cells reduced transcript levels by roughly 65 percent yet left proliferation unimpaired over an eight-day course, and mass spectrometric profiling of the silenced proteome showed that overall protein composition shifted only modestly. Concanavalin A uptake assays, which track soluble cargo from the flagellar pocket through endosomes to the lysosome, proceeded indistinguishably in TbTom1-depleted cells and controls. The authors interpret this resilience as evidence of redundancy or adaptability within the trypanosome sorting network rather than irrelevance of Tom1, a pattern consistent with the plasticity that their comparative analyses document throughout the system.

Broadly, the study reframes how biologists should think about the early ESCRT machinery. Evidence that Tom1 functions within the ESCRT pathway of trypanosomes supplies the fourth eukaryotic supergroup in which such a role has been demonstrated, and the authors argue that Tom1, not Vps27/STAM, is likely part of the pan-eukaryotic early ESCRT apparatus. At the same time, the heteropentameric ESCRT-I complex and the kinetoplastid-restricted Jerry protein illustrate how individual lineages continue to elaborate and customise the machinery, echoing earlier discoveries such as the plant-specific FREE1 adaptor, whose orthologues the team also surveyed across embryophytes. Evolution, in this view, has conserved the skeleton of the sorting system while repeatedly rebuilding its sensory apparatus.

For parasitologists, the implications extend toward intervention. Trypanosomes depend on relentless endocytic turnover of their variant surface glycoproteins and invariant surface receptors to evade the immune system, and any component that is parasite-specific, such as the novel ESCRT-I subunits or Jerry, represents a potential Achilles heel that host proteins do not share. Conversely, the conserved Tom1-dependent pathway offers a benchmark against which the animal and fungal systems can be reinterpreted, potentially correcting an animal-centric bias that has coloured membrane trafficking research for decades. What this study makes clear is that the deepest lessons about how eukaryotic cells move their membranes may come not from yeast or human tissue culture, but from an ancient parasite whose cellular geography forces every molecular handoff to happen in one remarkable pocket of membrane.

Subject of Research: The composition and evolution of the ESCRT endosomal sorting system in trypanosome parasites

Article Title: The trypanosome ESCRT system possesses both novel components and under-recognised pan-eukaryotic features

Article References: Padilla-Mejia, N. E., Durante, I. M., Záhonová, K., Stříbrná, E., Heller, J., Dacks, J. B., Lukeš, J., & Field, M. C. (2026). The trypanosome ESCRT system possesses both novel components and under-recognised pan-eukaryotic features. BMC Biology. https://doi.org/10.1186/s12915-026-02730-4

Image Credits: AI Generated

DOI: 10.1186/s12915-026-02730-4

Keywords: ESCRT, endocytosis, trypanosomes, Trypanosoma brucei, Tom1, Vps23, flagellar pocket, protein trafficking, endosomes, eukaryotic evolution, VHS domain, FYVE domain

The fundamental concept underlying the study involves measuring the evolutionary distance from the First Eukaryotic Common Ancestor (FECA) to the Last Eukaryotic Common Ancestor (LECA), normalized by the median branch length within eukaryotes, to adjust for differing evolutionary rates. Essentially, this normalized stem length serves as a molecular clock that hypothetically times gene acquisitions from prokaryotic donors to eukaryotes. Prior research had suggested that proteins with alphaproteobacterial ancestry—mitochondria’s bacterial progenitors—exhibited significantly shorter stems compared to genes derived from archaea, thereby implying a late mitochondrial acquisition.

However, when Tobiasson and colleagues applied this framework to an expansive dataset comprising 5,850 normalized stem lengths, the patterns proved far more complex than previously appreciated. The distribution showed a sharp peak near 0.05, mirroring trends from earlier research but revealing nuanced deviations that challenge simple temporal interpretations. Notably, alphaproteobacterial stems shorter than 0.3 were longer than those of Asgard archaeal origin, while stems surpassing 0.35 reversed this relation, appearing shorter than Asgard stems on average. This bimodal and statistically robust relationship calls into question the straightforward use of stem lengths as proxies for acquisition timing.

Interestingly, genes traced back to cyanobacteria, which are known contributors to plastids but not mitochondria, exhibited similar but less pronounced patterns, suggesting a broader evolutionary phenomenon beyond mitochondrial symbiogenesis. This observation integrates well with emerging perspectives that multiple prokaryotic lineages contributed variably to early eukaryotic genetics, complicating the notion of a singular, simple lineage acquisition event.

By narrowing the scope to specific gene categories with clearly defined ancestries—ribosomal proteins of archaeal origin and oxidative phosphorylation components from alphaproteobacteria—the team discerned an amplification of these complex trends. Despite the expectation that genes acquired simultaneously during mitochondrial endosymbiosis would display uniform stem lengths, the data revealed variances spanning orders of magnitude. This inconsistency fundamentally undermines the reliability of normalized stem lengths as mere chronological markers of gene incorporation.

The investigators propose an alternative interpretation rooted in the evolutionary pressures faced by newly acquired genes. Genes inherited from Asgard archaea, hypothesized to be closely related to the protoeukaryotic host, were likely already adapted to the cellular milieu of the evolving eukaryotic cell. In contrast, genes of bacterial origin—whether from alphaproteobacteria or other sources—would have required extensive adaptation post-acquisition, effectively elongating their molecular stems. This adjustment phase introduces substantial evolutionary change that inflates inferred stem lengths, conflating acquisition age with functional integration.

Supporting this hypothesis, genes involved in genetic information processing, which one might expect to be ancient and stable, surprisingly exhibited shorter than average stem lengths, indicating a complex interplay between evolutionary conservation and functional adaptation. Meanwhile, genes associated with metabolically dynamic systems, such as oxidative phosphorylation, demonstrated dramatically extended stem lengths, consistent with prolonged adaptive evolution.

These findings necessitate a reconceptualization of stem length metrics and their interpretive power. They suggest that molecular clocks in gene trees may predominantly reflect the varying tempos of post-acquisition evolutionary adaptation rather than the chronological order of acquisition events. Thus, the evolutionary narrative of eukaryogenesis emerges as a dynamic mosaic shaped both by the timing of gene acquisitions and the diverse evolutionary pressures acting on individual genes.

This research further emphasizes the dominant role of Asgard archaea in shaping the eukaryotic lineage, lending support to theories positing Asgard archaea as the protoeukaryotic host lineage. The data contravene simplistic models of eukaryogenesis based solely on timing inferred from stem lengths and instead point to a multifactorial scenario wherein gene origin, cellular context, and functional adaptation interplay to shape the genome.

Moreover, the study highlights the limitations of phylogenetic normalization techniques when applied across deep evolutionary timescales. The extensive variability observed suggests caution in extrapolating gene tree branch lengths to infer precise historical events, especially given complex biological phenomena such as horizontal gene transfer, gene loss, and convergent evolution.

Ultimately, this work represents a significant leap in our understanding of the evolutionary dynamics underlying the origin of eukaryotes and mitochondria. It calls for refined analytical frameworks that integrate evolutionary rate heterogeneity, functional adaptation, and phylogenomic context. Future research grounded in these principles promises to unravel the intricate evolutionary history of one of life’s defining transitions.

Tobiasson et al.’s findings invite a reassessment of the molecular clocks traditionally employed in evolutionary biology, urging a more nuanced appreciation of the forces shaping gene evolution. As scientists recalibrate their tools and interpretive models, insights from this study will undoubtedly reverberate across evolutionary research, informing not only the origin of eukaryotes but broader paradigms of genome evolution.

This work exemplifies how interdisciplinary approaches blending phylogenetics, molecular evolution, and comparative genomics can challenge entrenched hypotheses and foster innovative perspectives on complex biological phenomena. In doing so, it paves the way for a more integrated and dynamic understanding of life’s earliest, most transformative episodes.

Subject of Research: Evolutionary timing and origins of core eukaryotic genes in relation to Asgard archaea and alphaproteobacteria during eukaryogenesis.

Article Title: Dominant contribution of Asgard archaea to eukaryogenesis.

Article References:
Tobiasson, V., Luo, J., Wolf, Y.I. et al. Dominant contribution of Asgard archaea to eukaryogenesis. Nature (2026). https://doi.org/10.1038/s41586-025-09960-6

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41586-025-09960-6

At the heart of eukaryotic sophistication lies the endomembrane system: a dynamic compilation of membrane-bound organelles orchestrating material transport, biosynthesis, and intracellular recycling. This system encompasses the endoplasmic reticulum (ER), Golgi apparatus, plasma membrane, and the endolysosomal components such as endosomes, lysosomes, and autophagosomes. By scrutinizing the genealogical origins and diversification timing of vesicle trafficking protein families—integral to the movement and sorting of cargo within vesicular carriers—the researchers have established a chronological sequence of compartment emergence. Intriguingly, the duplicated genes involved in trafficking between the ER, Golgi, and plasma membrane stand among the oldest, dating from approximately 2.9 to 2.1 billion years ago.

These ancestral gene duplications predominantly originated from archaeal lineages, particularly from the Asgard group known to be closely related to eukaryotes. Protein families such as SNARE proteins (like STX5), Rab GTPases (including RAB19, RAB30, and RAB33 variants), and COPI and COPII coat proteins reflect an early elaboration of trafficking machinery essential for developing fundamental membrane-bound compartments. The tight clustering of duplication events suggests a concerted and contemporaneous expansion of gene families dedicated to establishing the ER, Golgi, and plasma membrane compartments, suggesting a major evolutionary innovation phase during the early eukaryotic lineage.

In stark contrast, vesicle trafficking components tailored exclusively to the endolysosomal system appear to have diversified later, initiating around 2.4 billion years ago. This endomembrane subdivision, critical for digestion and recycling within the cell, is reflected by duplication events in genes encoding specialized SNARE proteins (STX7, STX12) and Rab GTPases (RAB7A, RAB9A/B), alongside ABC transporters and chloride channel proteins integral to organellar function. The later emergence of these world-defining compartments substantiates the hypothesis that eukaryotic cellular complexity was sculpted progressively, layering new specialized functions atop an existing membrane trafficking framework.

Beyond membrane trafficking, the study reveals that the endoplasmic reticulum’s membrane biogenesis pathways testify to an intimate genetic interplay across domains of life. Archaeal-derived gene duplications, such as those involving the SRD5A1 and STT3 paralogs, predate substantial bacterial gene duplications involved in lipid biosynthesis, illustrating a temporally overlapping integration. Notably, bacterial-origin genes like ACSL1, GPAT, LPCAT, and SPTLC families, fundamental to synthesizing membrane lipids, underwent duplications roughly contemporaneous with archaeal duplications. This confluence implies a gradual metabolic synchronization whereby archaeal genetic frameworks were supplemented and functionally enhanced by bacterial biochemical pathways long before the Last Eukaryotic Common Ancestor (LECA).

The origins of these bacterial contributions extend beyond alphaproteobacteria, traditionally associated with mitochondrial ancestry. Gene phylogenies of certain lipid biosynthesis enzymes point to potential acquisition from other bacterial groups such as Myxococcota, suggesting a broader bacterial involvement in shaping eukaryotic membranes. This multifaceted bacterial gene integration underscores a complex, possibly stepwise, membrane transition during eukaryote formation, challenging simpler, mitochondrion-centric views of membrane evolution.

Membrane transporters essential for the digestive endolysosomal compartments further complicate the evolutionary narrative. Chloride channels (CLCs), solute carrier families (SLCs), and ATP-binding cassette (ABC) transporters show duplication signatures contemporaneous with compartment diversification, aligning functional specialization with structural emergence. The bacterial origins of these transporters—including some from alpha-proteobacteria and others tracing back to non-alphaproteobacterial bacteria—reveal an extensive drawing from bacterial gene pools to equip the evolving endolysosomal system.

This integrative approach—tracing gene family duplications and their origins—provides a refined temporal framework situating the mitochondrial endosymbiosis event. Alphaproteobacterial gene families diversified within approximately 200 million years following the mitochondrial founding event, concordant with a hypothesis that mitochondrial acquisition catalyzed significant genomic and cellular innovation. The timing aligns with the later phases of endomembrane system elaboration, suggesting that mitochondrial integration was pivotal for subsequent internal complexity, energy metabolism, and compartmental specialization.

Fundamentally, these findings depict eukaryogenesis as an extended evolutionary tango, where gene duplications and horizontal gene transfers forged a cellular mosaic. This mosaic seamlessly incorporated archaeal endomembrane components with bacterial lipid synthesis and metabolic functions, assembling a multifunctional intracellular infrastructure of unprecedented complexity. The stepwise accumulation of gene products tailored for specific compartments echoes a blueprint in which genetic innovation through duplication directly fashioned novel organelles and cellular capabilities.

Importantly, the study’s data addresses longstanding debates around the role of phagocytosis in mitochondrial acquisition. The identification of an early digestive endolysosomal system suggests that phagocytic processes evolved from pre-existing endocytic and recycling machinery, countering the notion that phagocytosis emerged solely as a mechanism to engulf the proto-mitochondrial endosymbiont. This layered evolutionary scenario strengthens the view that the eukaryotic cell’s interior landscapes were already undergoing diversification when mitochondria were ensnared.

In sum, this research transcends traditional phylogenetic reconstructions by quantitatively dating gene duplications and correlating them with compartment-specific functions. It illuminates the nuanced choreography underpinning the eukaryotic cell’s emergence, emphasizing that the intricate dance of gene duplication, domain fusion, and lateral gene transfer forged the cellular grandeur seen today. Such insights not only deepen our understanding of cellular evolution but also open new investigative pathways in evolutionary cell biology and the origin of complex life.

These revelations compel the scientific community to rethink eukaryotic evolution as a deeply intertwined saga of archaeal and bacterial genetic interdependencies, staged over billions of years. The orchestration of this evolutionary symphony through gene duplication mechanisms underscores duplication as a driving force for cellular complexity. Future investigations inspired by this approach may unravel further the genomic riddles encoding the fundamental innovations that distinguish eukaryotes from their prokaryotic ancestors, propelling our quest to unravel life’s profound origins.

Subject of Research: Evolutionary assembly of eukaryotes; gene duplications in vesicle trafficking and membrane biology during eukaryogenesis.

Article Title: Dated gene duplications elucidate the evolutionary assembly of eukaryotes.

Article References:
Kay, C.J., Spang, A., Szöllősi, G.J. et al. Dated gene duplications elucidate the evolutionary assembly of eukaryotes. Nature (2025). https://doi.org/10.1038/s41586-025-09808-z

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41586-025-09808-z