In a remarkable discovery that sheds new light on evolutionary dynamics in aquatic organisms, researchers at the Institute of Science Tokyo have uncovered how the European eel has regained the capability to transport a broad range of solutes through its cell membranes, a function believed to be lost in its ancestors. This breakthrough revolves around the aquaporin 10 (Aqp10) gene family, which encodes crucial membrane channel proteins responsible for selectively allowing water and various small uncharged molecules to permeate cellular barriers. The study, published in the prestigious journal Genome Biology and Evolution, reveals that gene duplication followed by strategic mutation has resurrected ancestral-like membrane permeability in European eels, reversing a long-standing evolutionary loss.
Aquaporins are integral membrane proteins that act as selective channels for water and a variety of solutes, including glycerol, urea, and boric acid, enabling cells to maintain homeostasis and adapt to fluctuating environmental conditions. Among aquaporins, Aqp10 stands out for its ability to transport both water and non-ionic solutes, though different variants of this protein exhibit distinct permeability profiles. Historically, the common ancestor of ray-finned fishes possessed two main Aqp10 genes: aqp10.1 and aqp10.2. Notably, aqp10.1 encoded channels with broad solute transport capabilities, whereas aqp10.2 coded for aquaporins with more selective permeability.
During evolutionary history, eels diverged from their ray-finned relatives and underwent a significant genomic shift, losing all variants of the aqp10.1 gene responsible for broad solute permeation. This gene loss theoretically imposed limitations on their physiological adaptability. However, contrary to expectations, the lineage leading to the European eel (Anguilla species) has remarkably circumvented this constraint. Instead of retaining a single aqp10.2 gene variant like many other eel relatives, such as congers and morays, European eels have undergone tandem gene duplication events, expanding the aqp10.2b gene subgroup into three distinct paralogs: aqp10.2b1, aqp10.2b2, and aqp10.2b3.
The Institute of Science Tokyo team conducted a series of meticulous functional assays using Xenopus oocytes as an experimental system to characterize the solute permeability of these duplicated genes. Results demonstrated a fascinating bifurcation in functionality: while aqp10.2b1 maintained narrow solute selectivity consistent with its ancestral counterpart, the paralogs aqp10.2b2 and aqp10.2b3 had re-evolved broad solute permeability, effectively recapitulating the original function of the now-lost aqp10.1 gene. This indicates a robust example of birth-and-death evolution—a process encompassing gene loss, duplication, mutation, and functional divergence—within the acutely specialized aquaporin gene family of the European eel.
At the molecular level, the regained permeability characteristics were traced to a pivotal single amino acid substitution within the aquaporin channel’s aromatic/arginine (ar/R) selectivity filter, a structural motif critical for determining the size and chemical nature of transported solutes. This filter consists of four amino acids that create a highly specific pore architecture influencing solute passage. The research team pinpointed the substitution of a tyrosine residue with glycine at the third position of the filter in the paralogs aqp10.2b2 and b3—a mutation that fundamentally altered the pore environment, broadening its selectivity and enabling permeability to molecules such as urea and boric acid.
This nuanced understanding of the ar/R selectivity filter’s role in aquaporin function underscores the delicate interplay between protein structure and physiological adaptation. The European eel’s aquaporin gene family showcases a vivid evolutionary narrative wherein loss of function is not an irreversible dead end but rather an opportunity for molecular innovation through gene duplication and targeted mutation. Such evolutionary plasticity offers adaptive advantages in navigating challenging environments and may reflect broader trends in genome evolution among aquatic vertebrates.
Moreover, this discovery intensifies our comprehension of molecular evolution, exemplifying how ancestral gene functions can be resurrected via genomic rearrangements, which ultimately shape organismal biology. The European eel’s unique aquaporin gene complement highlights the importance of gene duplication as an evolutionary mechanism facilitating diversification and resilience. This adaptive reconfiguration allows the eel to regulate the transport of various solutes critical for osmoregulation, waste elimination, and metabolic processes, especially as the species migrates through diverse aquatic habitats.
The findings also enrich the discourse on the evolutionary trajectory of Anguilliformes, a group that, despite losing the broadly permeable aqp10.1 gene, did not remain constrained by this loss. Instead, the evolution of multiple aqp10.2b paralogs demonstrates nature’s capacity to explore genetic novelty and functional restoration. This dynamic birth-and-death cycle within gene families such as aquaporins is emblematic of broader molecular evolutionary processes shaping vertebrate adaptability.
This study carries impactful implications beyond fundamental evolutionary biology. Understanding aquaporin gene evolution and function can elucidate how aquatic organisms manage osmotic challenges, influence their ecological interactions, and respond to environmental pressures like salinity fluctuations. The research enriches potential applied domains such as aquaculture optimization, conservation biology, and biomimetic engineering of selective membrane channels.
The collaboration between the Institute of Science Tokyo, The University of Tokyo, and Shinshu University underpins the interdisciplinary rigor of this work, encompassing molecular genetics, evolutionary biology, and physiological experimentation. By integrating gene analysis, structural biology, and functional assessment, the researchers provide a comprehensive portrait of how gene duplication and mutation contribute to the functional repertoire of membrane proteins critical to aquatic life.
In the broader context of molecular genetics, this research highlights the subtle yet profound effects single amino acid changes can impose within a protein, reshaping its transport specificity and expanding biological functionality. This nuanced molecular adaptability, controlled by relatively minor genetic events, speaks to the elegant complexity inherent in biological systems.
Overall, the resurrection of broad solute permeability in European eel aquaporins exemplifies evolutionary ingenuity, demonstrating how gene loss is not necessarily an endpoint but, through duplication and mutation, can pave the way for functional diversification and adaptation. This work underscores the importance of genome evolution studies for understanding physiological resilience and evolutionary innovation in aquatic vertebrates.
Subject of Research: Animals
Article Title: Loss and Gain of Aqp10 Paralogs with Broad Solute Selectivity in Anguillid Eels
News Publication Date: 12-Sep-2025
Web References: https://academic.oup.com/gbe/article/17/10/evaf169/8251923
References: DOI 10.1093/gbe/evaf169
Image Credits: Institute of Science Tokyo
Keywords: Genome evolution, molecular evolution, gene duplication, aquaporins, evolutionary biology, molecular genetics, aquatic animals, organismal biology, genetic analysis, aquatic ecology, physiology, Anguillid eels
Tags: adaptive evolution in fishancestral membrane permeability restorationAqp10 gene family researchaquaporin gene mutationaquatic homeostasis mechanismsEuropean eel gene duplicationevolution of aquaporin proteinsgenetic evolution in eelsGenome Biology and Evolution publicationmembrane channel proteins functionselective transport of solutessolute permeability in aquatic organisms
