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Abstract A key question in evolutionary biology concerns the relative importance of different sources of adaptive genetic variation, such as de novo mutations, standing variation, and introgressive hybridization. A corollary question concerns how allelic variants derived from these different sources may influence the molecular basis of phenotypic adaptation. Here, we use a protein-engineering approach to examine the phenotypic effect of putatively adaptive hemoglobin (Hb) mutations in the high-altitude Tibetan wolf that were selectively introgressed into the Tibetan mastiff, a high-altitude dog breed that is renowned for its hypoxia tolerance. Experiments revealed that the introgressed coding variants confer an increased Hb–O2 affinity in conjunction with an enhanced Bohr effect. We also document that affinity-enhancing mutations in the β-globin gene of Tibetan wolf were originally derived via interparalog gene conversion from a tandemly linked β-globin pseudogene. Thus, affinity-enhancing mutations were introduced into the β-globin gene of Tibetan wolf via one form of intragenomic lateral transfer (ectopic gene conversion) and were subsequently introduced into the Tibetan mastiff genome via a second form of lateral transfer (introgression). Site-directed mutagenesis experiments revealed that the increased Hb–O2 affinity requires a specific two-site combination of amino acid replacements, suggesting that the molecular underpinnings of Hb adaptation in Tibetan mastiff (involving mutations that arose in a nonexpressed gene and which originally fixed in Tibetan wolf) may be qualitatively distinct from functionally similar changes in protein function that could have evolved via sequential fixation of de novo mutations during the breed’s relatively short duration of residency at high altitude.
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Gene Turnover and Diversification of the α- and β-Globin Gene Families in Sauropsid
The genes that encode the α- and β-chain subunits of vertebrate hemoglobin have served as a model system for elucidating general principles of gene family evolution, but little is known about patterns of evolution in amniotes other than mammals and birds. Here, we report a comparative genomic analysis of the α- and β-globin gene clusters in sauropsids (archosaurs and nonavian reptiles). The objectives were to characterize changes in the size and membership composition of the α- and β-globin gene families within and among the major sauropsid lineages, to reconstruct the evolutionary history of the sauropsid α- and β-globin genes, to resolve orthologous relationships, and to reconstruct evolutionary changes in the developmental regulation of gene expression. Our comparisons revealed contrasting patterns of evolution in the unlinked α- and β-globin gene clusters. In the α-globin gene cluster, which has remained in the ancestral chromosomal location, evolutionary changes in gene content are attributable to the differential retention of paralogous gene copies that were present in the common ancestor of tetrapods. In the β-globin gene cluster, which was translocated to a new chromosomal location, evolutionary changes in gene content are attributable to differential gene gains (via lineage-specific duplication events) and gene losses (via lineage-specific deletions and inactivations). Consequently, all major groups of amniotes possess unique repertoires of embryonic and postnatally expressed β-type globin genes that diversified independently in each lineage. These independently derived β-type globins descend from a pair of tandemly linked paralogs in the most recent common ancestor of sauropsids.
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- Award ID(s):
- 1736026
- PAR ID:
- 10058052
- Date Published:
- Journal Name:
- Genome biology and evolution
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 1759-6653
- Page Range / eLocation ID:
- 344–358
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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