Genomic Organization and Differential Signature of Positive Selection in the Alpha and Beta Globin Gene Clusters in Two Cetacean Species

Abstract

The hemoglobin of jawed vertebrates is a heterotetramer protein that contains two α- and two β-chains, which are encoded by members of α- and β-globin gene families. Given the hemoglobin role in mediating an adaptive response to chronic hypoxia, it is likely that this molecule may have experienced a selective pressure during the evolution of cetaceans, which have to deal with hypoxia tolerance during prolonged diving. This selective pressure could have generated a complex history of gene turnover in these clusters and/or changes in protein structure themselves. Accordingly, we aimed to characterize the genomic organization of α- and β-globin gene clusters in two cetacean species and to detect a possible role of positive selection on them using a phylogenetic framework. Maximum likelihood and Bayesian phylogeny reconstructions revealed that both cetacean species had retained a similar complement of putatively functional genes. For the α-globin gene cluster, the killer whale presents a complement of genes composed of HBZ, HBK, and two functional copies of HBA and HBQ genes, whereas the dolphin possesses HBZ, HBK, HBA and HBQ genes, and one HBA pseudogene. For the β-globin gene cluster, both species retained a complement of four genes, two early expressed genes—HBE and HBH—and two adult expressed genes—HBD and HBB. Our natural selection analysis detected two positively selected sites in the HBB gene (56 and 62) and four in HBA (15, 21, 49, 120). Interestingly, only the genes that are expressed during the adulthood showed the signature of positive selection.

Myoglobin oxygen affinity in aquatic and terrestrial birds and mammals

“…Elevated concentrations of respiratory pigments have obvious adaptive advantages for maintaining aerobic metabolism in diving birds and mammals, and recent studies have examined the potential adaptive molecular evolution of the functional properties of these pigments Soegaard et al, 2012;Helbo and Fago, 2012;Schneuer et al, 2012;Mirceta et al, 2013). Oxygen binding globin proteins are obvious candidates for molecular adaptation in diving animals that experience regular hypoxia (Nery et al, 2013a) and Mb has experienced an increased rate of evolution in cetaceans (Nery et al, 2013b). Dasmeh et al (2013) found that mutations that increase Mb protein-fold stability are positively selected for in cetaceans, and this increase in protein stability is positively correlated with Mb concentration.…”

Beluga whale pVHL enhances HIF-2α activity via inducing HIF-2α proteasomal degradation under hypoxia

“…Compared to hypoxic tolerance in terrestrial mammals, such as plateau and cave mammals which adapt to chronic hypoxia, cetaceans have adapted to fluctuating oxygen [22, 23], but how this occurs is unclear [24, 25]. …”

Beta‐globin gene evolution in the ruminants: evidence for an ancient origin of sheep haplotype B

“…To more precisely identify the possible origin of haplotype B , we collected the sequences of the beta‐globin loci from all of the available ruminant genomes as well as from the killer whale and bottlenosed dolphin, which like the ruminants also belong to the cetartiodactyls (Nery et al . ). The pig and wild Bactrian camel were also used as outgroups.…”