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Reduction of paraoxonase expression followed by inactivation across independent semiaquatic mammals suggests stepwise path to pseudogenization

May 5, 2023

Convergent adaptation to the same environment by multiple lineages frequently involves rapid evolutionary change at the same genes, implicating these genes as important for environmental adaptation. Such adaptive molecular changes may yield either change or loss of protein function; loss of function can eliminate newly deleterious proteins or reduce energy necessary for protein production. We previously found a striking case of recurrent pseudogenization of the Paraoxonase 1 (Pon1) gene among aquatic mammal lineages—Pon1 became a pseudogene with genetic lesions, such as stop codons and frameshifts, at least four times independently in aquatic and semiaquatic mammals. Here, we assess the landscape and pace of pseudogenization by studying Pon1 sequences, expression levels, and enzymatic activity across four aquatic and semiaquatic mammal lineages: pinnipeds, cetaceans, otters, and beavers. We observe in beavers and pinnipeds an unexpected reduction in expression of Pon3, a paralog with similar expression patterns but different substrate preferences. Ultimately, in all lineages with aquatic/semiaquatic members, we find that preceding any coding-level pseudogenization events in Pon1, there is a drastic decrease in expression, followed by relaxed selection, thus allowing accumulation of disrupting mutations. The recurrent loss of Pon1 function in aquatic/semiaquatic lineages is consistent with a benefit to Pon1 functional loss in aquatic environments. Accordingly, we examine diving and dietary traits across pinniped species as potential driving forces of Pon1 functional loss. We find that loss is best associated with diving activity and likely results from changes in selective pressures associated with hypoxia and hypoxia-induced inflammation.

Publication Year 2023
Title Reduction of paraoxonase expression followed by inactivation across independent semiaquatic mammals suggests stepwise path to pseudogenization
DOI 10.1093/molbev/msad104
Authors Allie M. Graham, Jerrica M. Jamison, Marisol Bustos, Charlotte Cournoyer, Alexa Michaels, Jason S. Presnell, Rebecca Richter, Daniel E. Crocker, Ari Fustukjian, Margaret Hunter, Lorrie D. Rea, Judit Marsillach, Clement E. Furlong, Wynn K. Meyer, Nathan L. Clark
Publication Type Article
Publication Subtype Journal Article
Series Title Molecular Biology and Evolution
Index ID 70245589
Record Source USGS Publications Warehouse
USGS Organization Wetland and Aquatic Research Center