Vertebrates evolved mechanisms for sodium conservation and gas exchange in conjunction with migration from aquatic to terrestrial habitats. Epithelial Na+ channel (ENaC) function is critical to systems responsible for extracellular fluid homeostasis and gas exchange. ENaC is activated by cleavage at multiple specific extracellular polybasic sites, releasing inhibitory tracts from the channel’s α and γ subunits. We found that proximal and distal polybasic tracts in ENaC subunits coevolved, consistent with the dual cleavage requirement for activation observed in mammals. Polybasic tract pairs evolved with the terrestrial migration and the appearance of lungs, coincident with the ENaC activator aldosterone, and appeared independently in the a and g subunits. In summary, sites within ENaC for protease activation developed in vertebrates when renal Na+ conservation and alveolar gas exchange was required for terrestrial survival.
Source data for figures 1 and 2 are provided in Supplementary Data. Source data for trait evolution analysis, Figures 3 and Figure 4 are provided as image and Microsoft Excel files. Images and source data of electrophysiology traces in Figure 3 are provided at the Zenodo data repository (10.5281/zenodo.5790375).
Figure 3-source data 2Zenodo, doi:10.5281/zenodo.5790375.
- Ossama B Kashlan
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Animal experimentation: This study was performed in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. All of the animals were handled according to approved institutional animal care and use committee (IACUC) protocols (#20037084 and #21018704) of the University of Pittsburgh. All surgery was performed following tricaine methane sulfonate anesthesia and sacrifice, and every effort was made to minimize suffering.
- Kenton J Swartz, National Institute of Neurological Disorders and Stroke, National Institutes of Health, United States
- Received: November 23, 2021
- Accepted: December 28, 2021
- Accepted Manuscript published: January 5, 2022 (version 1)
© 2022, Wang et al.
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