Physiology of the tongue with emphasis on taste transduction.

The tongue is a complex multifunctional organ that interacts and senses both interoceptively and exteroceptively. Although it is easily visible to almost all of us it is relatively understudied and what is in the literature as regards taste mechanisms is often contradictory or is not comprehensively reported. The tongue is both a motor and a sensory organ: motor in that it is required for speech and mastication, and sensory in that it receives information to be relayed to the central nervous system pertaining to the safety and quality of the contents of the oral cavity. Additionally, the tongue and its taste apparatus form part of an innate immune surveillance system. For example, loss or alteration in taste perception can be an early indication of infection as became evident during the present global SARS-CoV-2 pandemic. Here we particularly emphasize the latest updates in the mechanisms of taste perception, taste bud formation and adult taste bud renewal, the presence, and effects of hormones on taste perception, review the understudied lingual immune system with specific reference to SARS-CoV-2, discuss nascent work on tongue microbiome, as well as addressing the effect of systemic disease on tongue structure and function, especially in relation to taste.

Human SARS-CoV-2 has evolved to increase U content and reduce genome size.

Infections caused by SARS-CoV-2 have brought great harm to human health. After transmission for over two years, SARS-CoV-2 has diverged greatly and formed dozens of different lineages. Understanding the trend of its genome evolution could help foresee difficulties in controlling transmission of the virus. In this study, we conducted an extensive monthly survey and in-depth analysis on variations of nucleotide, amino acid and codon numbers in 311,260 virus samples collected till January 2022. The results demonstrate that the evolution of SARS-CoV-2 is toward increasing U-content and reducing genome-size. C, G and A to U mutations have all contributed to this U-content increase. Mutations of C, G and A at codon position 1, 2 or 3 have no significant difference in most SARS-CoV-2 lineages. Current viruses are more cryptic and more efficient in replication, and are thus less virulent yet more infectious. Delta and Omicron variants have high mutability over other lineages, bringing new threat to human health. This trend of genome evolution may provide a clue for tracing the origin of SARS-CoV-2, because ancestral viruses should have lower U-content and probably bigger genome-size.

Human Type II Taste Cells Express Angiotensin-Converting Enzyme 2 and Are Infected by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2).

Chemosensory changes are well-reported symptoms of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The virus targets cells for entry by binding of its spike protein to cell-surface angiotensin-converting enzyme 2 (ACE2). It is not known whether ACE2 is expressed on taste receptor cells (TRCs), or whether TRCs are infected directly. in situ hybridization probe and an antibody specific to ACE2 indicated presence of ACE2 on a subpopulation of TRCs (namely, type II cells in taste buds in taste papillae). Fungiform papillae of a SARS-CoV-2+ patient exhibiting symptoms of coronavirus disease 2019 (COVID-19), including taste changes, were biopsied. Presence of replicating SARS-CoV-2 in type II cells was verified by in situ hybridization. Therefore, taste type II cells provide a potential portal for viral entry that predicts vulnerabilities to SARS-CoV-2 in the oral cavity. The continuity and cell turnover of a patient's fungiform papillae taste stem cell layer were disrupted during infection and had not completely recovered 6 weeks after symptom onset. Another patient experiencing post-COVID-19 taste disturbances also had disrupted stem cells. These results demonstrate the possibility that novel and sudden taste changes, frequently reported in COVID-19, may be the result of direct infection of taste papillae by SARS-CoV-2. This may result in impaired taste receptor stem cell activity and suggest that further work is needed to understand the acute and postacute dynamics of viral kinetics in the human taste bud.

Prevalence, Risk Factors, and Clinical Correlates of Insomnia in China College Student During the COVID-19.

Objective: The 2019 novel coronavirus disease (COVID-19) broke out in Hubei Province and spread rapidly to the whole country, causing huge public health problems. College students are a special group, and there is no survey on insomnia among college students. The purpose of this study was to investigate the incidence and related factors of insomnia in college students during the period of COVID-19. Method: A total of 1,086 college students conducted a cross-sectional study through the questionnaire star platform. The survey time was from February 15 to February 22, 2020. The collected information included demographic informatics and mental health scale, Athens Insomnia Scale (AIS) to assess sleep quality, Self-Reporting Questionnaire-20 (SRQ-20) to assess general psychological symptoms, Chinese perceived stress scale (CPSS) to assess stress. We used logistic regression to analyze the correlation between related factors and insomnia symptoms. Results: The prevalence of insomnia, general psychological symptoms and stress were 16.67, 5.8, and 40.70%, respectively. Multivariate logistic regression analysis showed that gender (OR = 1.55, p = 0.044, 95% CI = 1.00-2.41), general psychological symptoms (OR = 1.49, p < 0.01, 95% CI = 1.40-1.60) and living in an isolation unit (OR = 2.21, p = 0.014, 95% CI = 1.17-4.16) were risk factors for insomnia of college students. Conclusion: Our results show that the insomnia is very common among college students during the outbreak of covid-19, and the related factors include gender, general psychological symptoms and isolation environment. It is necessary to intervene the insomnia of college students and warrants attention for mental well-being of college students.

Human SARS-CoV-2 has evolved to reduce CG dinucleotide in its open reading frames.

The outbreak of COVID-19 has brought great threat to human health. Its causative agent is a severe acute respiratory syndrome-related coronavirus which has been officially named SARS-CoV-2. Here we report the discovery of extremely low CG abundance in its open reading frames. We found that CG reduction in SARS-CoV-2 is achieved mainly through mutating C/G into A/T, and CG is the best target for mutation. Meanwhile, 5'-untranslated region of SARS-CoV-2 has high CG content and is capable of forming an internal ribosome entry site (IRES) to recruit host ribosome for translating its RNA. These features allow SARS-CoV-2 to reproduce efficiently in host cells, because less energy is consumed in disrupting the stem-loops formed by its genomic RNA. Notably, genomes of cellular organisms also have very low CG abundance, suggesting that mutating C/G into A/T occurs universally in all life forms. Moreover, CG is the dinucleotide related to CpG island, mutational hotspot and single nucleotide polymorphism in cellular organisms. The relationship between these features is worthy of further investigations.