Limits...
The loss of taste genes in cetaceans.

Zhu K, Zhou X, Xu S, Sun D, Ren W, Zhou K, Yang G - BMC Evol. Biol. (2014)

Bottom Line: The sequence characteristics and evolutionary analyses of taste receptor genes suggested that nearly all cetaceans may have lost all taste modalities except for that of salt.Our results suggest that cetaceans have lost four of the basic taste modalities including sour, sweet, umami, and most of the ability to sense bitter tastes.The integrity of the candidate salt taste receptor genes in all the cetaceans examined may be because of their function in Na(+) reabsorption, which is key to osmoregulation and aquatic adaptation.

View Article: PubMed Central - PubMed

Affiliation: Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, 210023, China. zhukangli1989@163.com.

ABSTRACT

Background: Five basic taste modalities, sour, sweet, bitter, salt and umami, can be distinguished by humans and are fundamental for physical and ecological adaptations in mammals. Molecular genetic studies of the receptor genes for these tastes have been conducted in terrestrial mammals; however, little is known about the evolution and adaptation of these genes in marine mammals.

Results: Here, all five basic taste modalities, sour, sweet, bitter, salt and umami, were investigated in cetaceans. The sequence characteristics and evolutionary analyses of taste receptor genes suggested that nearly all cetaceans may have lost all taste modalities except for that of salt.

Conclusions: This is the first study to comprehensively examine the five basic taste modalities in cetaceans with extensive taxa sampling. Our results suggest that cetaceans have lost four of the basic taste modalities including sour, sweet, umami, and most of the ability to sense bitter tastes. The integrity of the candidate salt taste receptor genes in all the cetaceans examined may be because of their function in Na(+) reabsorption, which is key to osmoregulation and aquatic adaptation.

Show MeSH

Related in: MedlinePlus

Variations in three salt taste receptor genes. Variations in all completely and partially (80%) conserved residues are shown with respect to rat (Rattus norvegicus) homologous sequence. Light green bar indicates completely conserved sites, and light purple bar indicates 80% or greater conserved sites. Black words below indicate conserved residues in rat ENaCα, β and γ, respectively, if the residues are the same in the three genes, we use only one symbol. Numbers indicate the location of residues in rat ENaCα. Residues in red indicate variations in ENaCγ, while residues in dark purple indicate variations in ENaCα. Bracket denotes selective sites, and arrow denotes amiloride binding site.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC4232718&req=5

Fig2: Variations in three salt taste receptor genes. Variations in all completely and partially (80%) conserved residues are shown with respect to rat (Rattus norvegicus) homologous sequence. Light green bar indicates completely conserved sites, and light purple bar indicates 80% or greater conserved sites. Black words below indicate conserved residues in rat ENaCα, β and γ, respectively, if the residues are the same in the three genes, we use only one symbol. Numbers indicate the location of residues in rat ENaCα. Residues in red indicate variations in ENaCγ, while residues in dark purple indicate variations in ENaCα. Bracket denotes selective sites, and arrow denotes amiloride binding site.

Mentions: No inactivating mutation was identified in any of these three genes. Furthermore, we have identified multiple conserved residues in cetaceans that are essential for channel function. These conserved residues reside in motifs that include the conserved proline-rich motifs containing PPPXYXXL residues in the C-terminus, HG residues in the N-terminus, FPXXTXC in post-M1 (first transmembrane domain), completely conserved residues in the second transmembrane domain (M2), and conserved Cys-rich domains in the extracellular loop [74]. All of these conserved motifs are essential for channel function, for example post-M2 and M2 constitute the outer pore entry and selectivity filter [74], conserved HG in the N-terminus plays an important role in gating [75], Cys-rich domains are vital for tertiary structure of the extracellular loop [76], and conserved proline-rich motifs in the C terminus take part in channel ubiquitination, endocytosis, and degradation of the ENaC [77,78]. Based on sequence alignments, Scnn1a, Scnn1b and Scnn1g possessed all these conserved amino acids, except for a conserved HG in the N-terminus of Scnn1a, a conserved FPXXTXC in post-M1, and two important residues in the Cys-rich domains of Scnn1b; however these omissions are likely to be because of our incomplete gene amplification. Interestingly, we identified a variable residue, γV591I, in the completely conserved M2 motif in the baiji. Among residues with 80% or greater conservation in M2, we identified a γV590I variation in toothed whales, a γV593I variation in all toothed whales except for the beaked whale (Mesoplodon densirostris), and a αM596V variation in cetaceans (Figure 2). These substitutions probably affect the formation of the channel pore based on their distribution in pre-M2 and M2, which are known to participate in the formation of the channel pore. Even though we could not identify all conserved sequences owing to incomplete amplification, the above analyses strongly suggested that the salt taste genes were intact.Figure 2


The loss of taste genes in cetaceans.

Zhu K, Zhou X, Xu S, Sun D, Ren W, Zhou K, Yang G - BMC Evol. Biol. (2014)

Variations in three salt taste receptor genes. Variations in all completely and partially (80%) conserved residues are shown with respect to rat (Rattus norvegicus) homologous sequence. Light green bar indicates completely conserved sites, and light purple bar indicates 80% or greater conserved sites. Black words below indicate conserved residues in rat ENaCα, β and γ, respectively, if the residues are the same in the three genes, we use only one symbol. Numbers indicate the location of residues in rat ENaCα. Residues in red indicate variations in ENaCγ, while residues in dark purple indicate variations in ENaCα. Bracket denotes selective sites, and arrow denotes amiloride binding site.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4232718&req=5

Fig2: Variations in three salt taste receptor genes. Variations in all completely and partially (80%) conserved residues are shown with respect to rat (Rattus norvegicus) homologous sequence. Light green bar indicates completely conserved sites, and light purple bar indicates 80% or greater conserved sites. Black words below indicate conserved residues in rat ENaCα, β and γ, respectively, if the residues are the same in the three genes, we use only one symbol. Numbers indicate the location of residues in rat ENaCα. Residues in red indicate variations in ENaCγ, while residues in dark purple indicate variations in ENaCα. Bracket denotes selective sites, and arrow denotes amiloride binding site.
Mentions: No inactivating mutation was identified in any of these three genes. Furthermore, we have identified multiple conserved residues in cetaceans that are essential for channel function. These conserved residues reside in motifs that include the conserved proline-rich motifs containing PPPXYXXL residues in the C-terminus, HG residues in the N-terminus, FPXXTXC in post-M1 (first transmembrane domain), completely conserved residues in the second transmembrane domain (M2), and conserved Cys-rich domains in the extracellular loop [74]. All of these conserved motifs are essential for channel function, for example post-M2 and M2 constitute the outer pore entry and selectivity filter [74], conserved HG in the N-terminus plays an important role in gating [75], Cys-rich domains are vital for tertiary structure of the extracellular loop [76], and conserved proline-rich motifs in the C terminus take part in channel ubiquitination, endocytosis, and degradation of the ENaC [77,78]. Based on sequence alignments, Scnn1a, Scnn1b and Scnn1g possessed all these conserved amino acids, except for a conserved HG in the N-terminus of Scnn1a, a conserved FPXXTXC in post-M1, and two important residues in the Cys-rich domains of Scnn1b; however these omissions are likely to be because of our incomplete gene amplification. Interestingly, we identified a variable residue, γV591I, in the completely conserved M2 motif in the baiji. Among residues with 80% or greater conservation in M2, we identified a γV590I variation in toothed whales, a γV593I variation in all toothed whales except for the beaked whale (Mesoplodon densirostris), and a αM596V variation in cetaceans (Figure 2). These substitutions probably affect the formation of the channel pore based on their distribution in pre-M2 and M2, which are known to participate in the formation of the channel pore. Even though we could not identify all conserved sequences owing to incomplete amplification, the above analyses strongly suggested that the salt taste genes were intact.Figure 2

Bottom Line: The sequence characteristics and evolutionary analyses of taste receptor genes suggested that nearly all cetaceans may have lost all taste modalities except for that of salt.Our results suggest that cetaceans have lost four of the basic taste modalities including sour, sweet, umami, and most of the ability to sense bitter tastes.The integrity of the candidate salt taste receptor genes in all the cetaceans examined may be because of their function in Na(+) reabsorption, which is key to osmoregulation and aquatic adaptation.

View Article: PubMed Central - PubMed

Affiliation: Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, 210023, China. zhukangli1989@163.com.

ABSTRACT

Background: Five basic taste modalities, sour, sweet, bitter, salt and umami, can be distinguished by humans and are fundamental for physical and ecological adaptations in mammals. Molecular genetic studies of the receptor genes for these tastes have been conducted in terrestrial mammals; however, little is known about the evolution and adaptation of these genes in marine mammals.

Results: Here, all five basic taste modalities, sour, sweet, bitter, salt and umami, were investigated in cetaceans. The sequence characteristics and evolutionary analyses of taste receptor genes suggested that nearly all cetaceans may have lost all taste modalities except for that of salt.

Conclusions: This is the first study to comprehensively examine the five basic taste modalities in cetaceans with extensive taxa sampling. Our results suggest that cetaceans have lost four of the basic taste modalities including sour, sweet, umami, and most of the ability to sense bitter tastes. The integrity of the candidate salt taste receptor genes in all the cetaceans examined may be because of their function in Na(+) reabsorption, which is key to osmoregulation and aquatic adaptation.

Show MeSH
Related in: MedlinePlus