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Evolution of epithelial sodium channels: current concepts and hypotheses
Lukas Wichmann1, Mike Althaus2
1Institute for Animal Physiology, Justus Liebig University, Giessen, Germany.
Summary
Epithelial sodium channels (ENaCs) are crucial for vertebrate osmoregulation. Their evolution in tetrapods likely involved adaptations for freshwater and terrestrial life, with proton sensitivity aiding freshwater osmoregulation and protease regulation supporting lung liquid homeostasis.
Area of Science:
- Vertebrate Evolution
- Physiology
- Molecular Biology
Background:
- Vertebrate evolution involved adapting to freshwater and terrestrial environments, necessitating osmoregulatory mechanisms for ion and water balance.
- Sodium homeostasis is vital, with epithelial sodium channels (ENaCs) playing a key role in reabsorbing sodium in tetrapod kidneys and lungs.
- ENaCs are vertebrate-specific cation channels, but their evolutionary history within the degenerin/ENaC family requires further investigation.
Purpose of the Study:
- To review current understanding of ENaC phylogeny and the evolution of regulatory motifs.
- To explore the role of ENaCs in osmoregulation during tetrapod terrestrialization.
- To discuss the potential functions of ENaC orthologs in fishes and atypical isoforms in mammals.
Main Methods:
- Phylogenetic analysis of ENaC sequences.
- Comparative genomics to identify conserved and divergent motifs.
- Literature review of existing research on ENaC function and regulation.
Main Results:
- ENaCs are vertebrate-specific, with limited knowledge on their evolutionary origins within the degenerin/ENaC family.
- Specific sequence motifs regulating ENaC function emerged during tetrapod adaptation to land.
- Distinct regulation and expression patterns of ENaC isoforms exist in tetrapod vertebrates.
Conclusions:
- Ancestral proton-sensitive ENaCs may have facilitated freshwater osmoregulation.
- Protease-regulated ENaCs likely evolved for lung liquid homeostasis in terrestrial tetrapods.
- Further research is needed on ENaC orthologs in fishes and atypical isoforms in mammals.
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