Multiple loss-of-function variants of taste receptors in modern humans

Effects of chronic unpredictable mild stress-induced depression on bitter taste receptor expression in mice

OBJECTIVE

With the rapid increase in the pace of life, people are facing increasing pressures of all kinds, and depression has gradually become a serious psychological disorder in human society, strongly affecting normal social and physiological activities. Depression can disrupt an individual's taste perception and potentially result in taste disorders by affecting and altering taste receptors. This disruption can consequently impact their food preferences and overall eating experiences.

DESIGN

In this study, we used the chronic unpredictable mild stress (CUMS) method to establish a depression model in male C57BL/6 J mice and explored the changes in taste receptor expression in the lingual circumvallate papillae (CP) to elucidate the effects of depression on taste. After 6 weeks of CUMS, behavioral performance evaluations, such as forced swim, open field, and elevated plus maze tests, were conducted in depression model mice. A further two-bottle choice test was subsequently performed to determine the effect of depression on bitter taste, and the expression of bitter taste receptors in the lingual CP was detected via immunofluorescence staining.

RESULTS

In this study, we found for the first time that mice with CUMS-induced depression had decreased bitter taste sensitivity through a two-bottle choice test and demonstrated that the expression of T2r5, a receptor related to bitter taste perception, and the expression of secondary taste signaling proteins in the lingual CP were significantly decreased in mice exposed to CUMS, as determined via qRTPCR and immunofluorescence staining.

CONCLUSIONS

Our study highlights how CUMS influences the perception of bitterness in the peripheral taste system, potentially elucidating stress-induced changes in eating habits.

Genetic history of Cambridgeshire before and after the Black Death

The extent of the devastation of the Black Death pandemic (1346-1353) on European populations is known from documentary sources and its bacterial source illuminated by studies of ancient pathogen DNA. What has remained less understood is the effect of the pandemic on human mobility and genetic diversity at the local scale. Here, we report 275 ancient genomes, including 109 with coverage >0.1×, from later medieval and postmedieval Cambridgeshire of individuals buried before and after the Black Death. Consistent with the function of the institutions, we found a lack of close relatives among the friars and the inmates of the hospital in contrast to their abundance in general urban and rural parish communities. While we detect long-term shifts in local genetic ancestry in Cambridgeshire, we find no evidence of major changes in genetic ancestry nor higher differentiation of immune loci between cohorts living before and after the Black Death.

Ecological Sensing Through Taste and Chemosensation Mediates Inflammation: A Biological Anthropological Approach

Ecological sensing and inflammation have evolved to ensure optima between organism survival and reproductive success in different and changing environments. At the molecular level, ecological sensing consists of many types of receptors located in different tissues that orchestrate integrated responses (immune, neuroendocrine systems) to external and internal stimuli. This review describes emerging data on taste and chemosensory receptors, proposing them as broad ecological sensors and providing evidence that taste perception is shaped not only according to sense epitopes from nutrients but also in response to highly diverse external and internal stimuli. We apply a biological anthropological approach to examine how ecological sensing has been shaped by these stimuli through human evolution for complex interkingdom communication between a host and pathological and symbiotic bacteria, focusing on population-specific genetic diversity. We then focus on how these sensory receptors play a major role in inflammatory processes that form the basis of many modern common metabolic diseases such as obesity, type 2 diabetes, and aging. The impacts of human niche construction and cultural evolution in shaping environments are described with emphasis on consequent biological responsiveness.

TAS2R20 variants confer dietary adaptation to high-quercitrin bamboo leaves in Qinling giant pandas

Sensitivity to bitter tastes provides animals with an important means of interacting with their environment and thus, influences their dietary preferences. Genetic variants encoding functionally distinct receptor types contribute to variation in bitter taste sensitivity. Our previous study showed that two nonsynonymous sites, A52V and Q296H, in the TAS2R20 gene are directionally selected in giant pandas from the Qinling Mountains, which are speculated to be the causative base-pair changes of Qinling pandas for the higher preference for bamboo leaves in comparison with other pandas. Here, we used functional expression in engineered cells to identify agonists of pTAS2R20 (i.e., giant panda's TAS2R20) and interrogated the differences in perception in the in vitro responses of pTAS2R20 variants to the agonists. Our results show that pTAS2R20 is specifically activated by quercitrin and that pTAS2R20 variants exhibit differences in the sensitivity of their response to the agonist. Compared with pTAS2R20 in pandas from other areas, the receptor variant with A52V and Q296H, which is most commonly found in Qinling pandas, confers a significantly decreased sensitivity to quercitrin. We subsequently quantified the quercitrin content of the leaves of bamboo distributed in the Qinling Mountains, which was found to be significantly higher than that of the leaves of bamboo from panda habitats in other areas. Our results suggest that the decreased sensitivity to quercitrin in Qinling pandas results in higher-quercitrin-containing bamboo leaves to be tasting less bitter to them and thus, influences their dietary preference. This study illustrates the genetic adaptation of Qinling pandas to their environments and provides a fine example of the functional effects of directional selection in the giant panda.

TAS2R38 Bitterness Receptor Genetic Variation and Risk of Gastrointestinal Neoplasm: A Meta-Analysis

Genetic variation in TAS2R38 bitterness taste receptor could alter the efficacy of molecular sensing, hence may be associated with cancer risk. Thus, we performed a meta-analysis to verify the association between the risk of gastrointestinal (GI) neoplasm and TAS2R38 genetic variation. Studies with TAS2R38 diplotype distribution and GI neoplasm phenotypes were searched from PubMed, EMBASE and SCOPUS, and five articles including eight studies were finally selected. The association between diplotype and neoplasm risk was estimated with summarized odds ratios (ORs) and 95% confidence intervals (CIs), applying of fixed- or random-effects models. The findings suggested TAS2R38 diplotype was not associated with GI neoplasms susceptibility [AVI vs. PAV: OR = 1.03 (95%CI: 0.97-1.09), AVI/PAV vs. PAV/PAV: OR = 1.05, (95%CI: 0.94-1.17), AVI/* vs. PAV/PAV: OR = 1.04 (95%CI: 0.94-1.16)]. Because of the presence of heterogeneity under the two genetic models (AVI/AVI vs. PAV/PAV and AVI/AVI vs. PAV/*), further subgroup analyses by ethnicity and neoplasm type were performed. However, results failed to show the neoplasm risk was altered by diplotype. In conclusion, the meta-analysis indicates that TAS2R38 diplotype minimally modified the GI neoplasm risk. Given the limited study size and resources, further well-designed and larger studies are required to validate the true effect of TAS2R38 polymorphisms on neoplasm risk.

Human Knockout Carriers: Dead, Diseased, Healthy, or Improved?

Whole-genome and whole-exome sequence data from large numbers of individuals reveal that we all carry many variants predicted to inactivate genes (knockouts). This discovery raises questions about the phenotypic consequences of these knockouts and potentially allows us to study human gene function through the investigation of homozygous loss-of-function carriers. Here, we discuss strategies, recent results, and future prospects for large-scale human knockout studies. We examine their relevance to studying gene function, population genetics, and importantly, the implications for accurate clinical interpretations.

Premature termination codons in modern human genomes

The considerable range of genetic variation in human populations may partly reflect distinctive processes of adaptation to variable environmental conditions. However, the adaptive genomic signatures remain to be completely elucidated. This research explores candidate loci under selection at the population level by characterizing recently arisen premature termination codons (PTCs), some of which indicate a human knockout. From a total of 7595 participants from two population exome projects, 246 PTCs were found where natural selection has resulted in new alleles with a high frequency (from 1% to 96%) of derived alleles and various levels of population differentiation (F_ST = 0.00139–0.626). The PTC genes formed protein and regulatory networks limited to 15 biological processes or gene families, of which seven categories were previously unreported. PTC mutations have a strong tendency to be introduced into members of the same gene family, even during modern human evolution, although the exact nature of the selection is not fully known. The findings here suggest the ongoing evolutionary plasticity of modern humans at the genetic level and also partly provide insights into common human knockouts.