The research led by Associate Professor Hidenori Nishihara and Professor Yoshiro Ishimaru, as described in the publication in Nature Ecology & Evolution on December 13, 2023, is a significant contribution to our understanding of taste perception and the evolutionary history of sweet tastes receptors.
The identification of five new groups within the TAS1R family through a genome-wide survey of jawed vertebrates, including major fish groups, provides valuable insights into the diversity and evolution of taste receptors. The TAS1R family, responsible for encoding taste receptor type 1 (T1R), plays a crucial role in detecting sweet tastes and umami tastes in mammals. Understanding the genetic variations within this family across different species contributes to unraveling the evolutionary history of taste perception.
The absence of the typical TAS1R gene pattern in coelacanth and cartilaginous fishes, with the identification of ‘taxonomically unplaced’ TAS1R genes, highlights the complexity of taste receptor evolution. This suggests that our understanding of taste receptor evolution might be incomplete and underscores the importance of studying a broad range of species to capture the full diversity of taste perception mechanisms.
The broader implications of this research extend to the understanding of feeding habits and dietary preferences in various organisms. By investigating taste receptors, researchers can gain insights into the evolution of life on Earth, as taste perception is intricately linked to identifying healthful foods and avoiding potentially harmful substances.
The collaborative effort involving researchers from Kindai University, Meiji University, The Jikei University School of Medicine, the National Institute of Genetics, and The University of Tokyo demonstrates the significance of interdisciplinary collaboration in advancing our understanding of complex biological processes.
“Our study revealed that as compared to most modern vertebrates, the vertebrate ancestor possessed more T1Rs. These findings challenge the paradigm that only three T1R family members have been retained during evolution,” states Prof. Nishihara.
The identification and categorization of novel taste receptor genes, TAS1R4, TAS1R5, TAS1R6, TAS1R7, and TAS1R8, by the research team led by Associate Professor Hidenori Nishihara and Professor Yoshiro Ishimaru provide a more nuanced understanding of taste receptor evolution across different species.
The distribution of these new genes among various species with a common ancestor sheds light on the complexity and diversity of taste perception mechanisms. TAS1R4, for example, was found in lizards, axolotl, lungfishes, coelacanth, bichir, and cartilaginous fishes but was absent in mammals, birds, crocodilians, turtles, and teleost fishes. This suggests a unique evolutionary trajectory for TAS1R4 in certain lineages of vertebrates.
The observation of TAS1R5 in axolotl, lungfishes, and coelacanth, with a close evolutionary relationship to TAS1R1 and TAS1R2, indicates a shared ancestry between these genes. Understanding these evolutionary relationships provides insights into the genetic basis of taste perception and how certain taste receptors have evolved over time.
The exclusive presence of TAS1R6 in cartilaginous fishes, evolving from the same ancestral gene as TAS1R1, TAS1R2, and TAS1R5, highlights the intricate and dynamic nature of taste receptor evolution. This finding suggests that TAS1R6 has a unique role in the taste perception of cartilaginous fishes.
The presence of TAS1R7 in axolotl and lizards, and TAS1R8 in bichir and lungfishes, with the determination that these genes originated in the common ancestor of jawed vertebrates, further enriches our understanding of the molecular basis of taste perception in different species.
Moreover, the discovery of diversity within existing TAS1R genes, such as TAS1R3A and TAS1R3B in bony vertebrates and the diversification of TAS1R2 into TAS1R2A and TAS1R2B challenges previous assumptions about the simplicity of taste receptor gene groups. This complexity underscores the need for a more nuanced approach to studying taste perception, considering the varied genetic adaptations that different species have undergone.
“We found that the TAS1R phylogenetic tree comprises of a total of 11 TAS1R clades, revealing an unexpected gene diversity,” attaches Prof. Nishihara.
The research led by Associate Professor Hidenori Nishihara and Professor Yoshiro Ishimaru unveils a fascinating timeline of taste receptor gene evolution. The study suggests that the first TAS1R gene emerged in jawed vertebrates approximately 615-473 million years ago. Through subsequent duplications, the common ancestor of bony vertebrates developed nine taste receptor genes (TAS1R1,2A, 2B, 3A, 3B, 4, 5, 7, and 8). Over time, certain lineages experienced the loss of specific TAS1R genes, resulting in the retention of only three TAS1Rs (TAS1R1, TAS1R2A, and TAS1R3A) in mammals and teleost fishes. This evolutionary perspective highlights the dynamic nature of taste receptor gene evolution, providing valuable insights into the molecular adaptations that have shaped the sensory systems of diverse vertebrate species.
Professor Nishihara unveils practical applications arising from the sweet tastes study, “These findings make it easier for us to deduce the taste preferences of diverse vertebrates. This, in turn, can have potential applications such as the development of pet foods and attractants tailored to the preferences of fish, amphibians, and reptiles.”
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