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Our species exhibits great diversity in various traits. Such diversity is the outcome of the evolutionary journey of our ancestors. We are working to elucidate the evolutionary history of biological diversity in modern humans through various approaches, including phenotypic measurement experiments on human individuals, measurement of DNA base sequences and chemical modification states from experimental participants, molecular biology experiments, and population genetic analyses.
Variation in the brown adipose tissue activity
Variation in the brown adipose tissue activity
Brown adipose tissue (BAT), an energy-dissipating tissue in mammals, plays an important role in the maintenance of body temperature under cold stress and is attracting attention as a potential target for the prevention and treatment of obesity. It is well known that there are significant individual differences in BAT activity among Japanese people. To conceive the role of genome variation and its evolutionary history in shaping this diversity, we are conducting a series of physiological and genetic studies.
Genetic variation of β2 adrenergic receptor is associated with BAT activity in East Asian adults
Genetic variation of β2 adrenergic receptor is associated with BAT activity in East Asian adults
BAT thermogenesis is known to be enhanced by cold stimuli, and it has long been recognized that β-adrenergic receptors (β-AR) mediate this effect. In particular, studies using rodents have suggested that type 3 β-AR expressed in BAT plays a central role; however, it remains unclear which β-AR subtype is important in humans. We used techniques such as PET-CT, infrared thermal imaging, and near-infrared time-resolved spectroscopy to measure the diversity of BAT activity in adults under cold conditions in vivo and found that this diversity is associated with a single-nucleotide polymorphism of the type 2 β-AR, rather than the type 3 β-AR. These findings suggest that there are species differences in BAT between humans and rodents (Ishida et al., 2024).
ΔTempは、BAT活性を示す。数値が大きいほどBAT活性が高い。
Unexpected diveristy of BAT activity in East Asians
Unexpected diveristy of BAT activity in East Asians
It has been known that BAT activity is highly diverse among Japanese people, but it was not known how this diversity compares to that of closely related populations in neighboring regions. We conducted a study in which adult men and women of Japanese or Chinese origin were subjected to cold stimulation under identical conditions, and measured brown BAT activity using infrared thermal imaging. The results revealed that Japanese individuals had lower BAT activity than Chinese individuals, and that this trend was particularly pronounced during the summer months (Ishida and Nakayama., 2025).
Application of methylome analyses in anthropology
Application of methylome analyses in anthropology
The human body exhibits various physiological responses to maintain homeostasis when the external environment changes. Additionally, repeated exposure to the same stimulus leads to physiological adaptation to that stimulus. Such processes involve changes in gene expression patterns at the cellular level. DNA methylation, a stable form of DNA modification involved in gene expression regulation, allows us to assess cellular states even from nucleic acid samples where RNA analysis is difficult. We have successfully identified various stress-related traces associated with a nomadic lifestyle in immune cells of Mongolians by quantitatively analyzing genome-wide DNA methylation states in DNA samples collected nearly 10 years ago (Inaba et al. 2022). Currently, we are applying this technology to hypobaric and hypoxic exposure experiments in artificial climate chambers and field surveys of high-altitude populations with the aim of elucidating the mechanisms of adaptation to high altitudes, one of the most challenging environments for humans.
Evolution of common diseases
Evolution of common diseases
We all experience various illnesses throughout our lives. Many of these illnesses are multifactorial genetic disorders, which are caused by a combination of environmental factors and multiple genetic factors. We are investigating how genomic diversity, which influences susceptibility to such illnesses, has been shaped during human evolution using methods such as natural selection detection analysis based on human population genome data. Previously, we reported that genes associated with visceral fat accumulation in Japanese individuals had undergone natural selection related to adaptation to cold environments, and that recent natural selection experienced by Mongolians was strongly associated with obesity susceptibility in this population. Recently, we discovered that polymorphisms contributing to myopia susceptibility have evolved under the influence of natural selection related to regional differences in light intensity and immune function during human dispersal (Xia and Nakayama 2023).
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