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Landon SM, Baker K, Macpherson LJ. Give-and-take of gustation: the interplay between gustatory neurons and taste buds. Chem Senses 2024; 49:bjae029. [PMID: 39078723 PMCID: PMC11315769 DOI: 10.1093/chemse/bjae029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/11/2024] Open
Abstract
Mammalian taste buds are highly regenerative and can restore themselves after normal wear and tear of the lingual epithelium or following physical and chemical insults, including burns, chemotherapy, and nerve injury. This is due to the continual proliferation, differentiation, and maturation of taste progenitor cells, which then must reconnect with peripheral gustatory neurons to relay taste signals to the brain. The turnover and re-establishment of peripheral taste synapses are vital to maintain this complex sensory system. Over the past several decades, the signal transduction and neurotransmitter release mechanisms within taste cells have been well delineated. However, the complex dynamics between synaptic partners in the tongue (taste cell and gustatory neuron) are only partially understood. In this review, we highlight recent findings that have improved our understanding of the mechanisms governing connectivity and signaling within the taste bud and the still-unresolved questions regarding the complex interactions between taste cells and gustatory neurons.
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Affiliation(s)
- Shannon M Landon
- Department of Neuroscience, Developmental and Regenerative Biology, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX, United States
| | - Kimberly Baker
- Department of Neuroscience, Developmental and Regenerative Biology, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX, United States
- 59th Medical Wing: Surgical and Technological Advancements for Traumatic Injuries in Combat: 204 Wagner Ave, San Antonio, TX 78211, United States
| | - Lindsey J Macpherson
- Department of Neuroscience, Developmental and Regenerative Biology, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX, United States
- Brain Health Consortium, The University of Texas at San Antonio, San Antonio, TX, United States
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Doyle ME, Premathilake HU, Yao Q, Mazucanti CH, Egan JM. Physiology of the tongue with emphasis on taste transduction. Physiol Rev 2023; 103:1193-1246. [PMID: 36422992 PMCID: PMC9942923 DOI: 10.1152/physrev.00012.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
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 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, and 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 address the effect of systemic disease on tongue structure and function, especially in relation to taste.
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Affiliation(s)
- Máire E Doyle
- Diabetes Section/Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
| | - Hasitha U Premathilake
- Diabetes Section/Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
| | - Qin Yao
- Diabetes Section/Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
| | - Caio H Mazucanti
- Diabetes Section/Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
| | - Josephine M Egan
- Diabetes Section/Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
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Witt M. Anatomy and development of the human taste system. HANDBOOK OF CLINICAL NEUROLOGY 2019; 164:147-171. [DOI: 10.1016/b978-0-444-63855-7.00010-1] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/11/2023]
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Shandilya J, Gao Y, Nayak TK, Roberts SGE, Medler KF. AP1 transcription factors are required to maintain the peripheral taste system. Cell Death Dis 2016; 7:e2433. [PMID: 27787515 PMCID: PMC5133999 DOI: 10.1038/cddis.2016.343] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Revised: 08/30/2016] [Accepted: 09/26/2016] [Indexed: 01/07/2023]
Abstract
The sense of taste is used by organisms to achieve the optimal nutritional requirement and avoid potentially toxic compounds. In the oral cavity, taste receptor cells are grouped together in taste buds that are present in specialized taste papillae in the tongue. Taste receptor cells are the cells that detect chemicals in potential food items and transmit that information to gustatory nerves that convey the taste information to the brain. As taste cells are in contact with the external environment, they can be damaged and are routinely replaced throughout an organism's lifetime to maintain functionality. However, this taste cell turnover loses efficiency over time resulting in a reduction in taste ability. Currently, very little is known about the mechanisms that regulate the renewal and maintenance of taste cells. We therefore performed RNA-sequencing analysis on isolated taste cells from 2 and 6-month-old mice to determine how alterations in the taste cell-transcriptome regulate taste cell maintenance and function in adults. We found that the activator protein-1 (AP1) transcription factors (c-Fos, Fosb and c-Jun) and genes associated with this pathway were significantly downregulated in taste cells by 6 months and further declined at 12 months. We generated conditional c-Fos-knockout mice to target K14-expressing cells, including differentiating taste cells. c-Fos deletion caused a severe perturbation in taste bud structure and resulted in a significant reduction in the taste bud size. c-Fos deletion also affected taste cell turnover as evident by a decrease in proliferative marker, and upregulation of the apoptotic marker cleaved-PARP. Thus, AP1 factors are important regulators of adult taste cell renewal and their downregulation negatively impacts taste maintenance.
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Affiliation(s)
- Jayasha Shandilya
- Department of Biological Sciences, University at Buffalo, Buffalo, NY 14260, USA
| | - Yankun Gao
- Department of Biological Sciences, University at Buffalo, Buffalo, NY 14260, USA
| | - Tapan K Nayak
- Department of Physiology & Biophysics, University at Buffalo, Buffalo, NY 14214, USA
| | - Stefan G E Roberts
- Department of Biological Sciences, University at Buffalo, Buffalo, NY 14260, USA
| | - Kathryn F Medler
- Department of Biological Sciences, University at Buffalo, Buffalo, NY 14260, USA
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5
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Feng P, Huang L, Wang H. Taste bud homeostasis in health, disease, and aging. Chem Senses 2013; 39:3-16. [PMID: 24287552 DOI: 10.1093/chemse/bjt059] [Citation(s) in RCA: 93] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The mammalian taste bud is an onion-shaped epithelial structure with 50-100 tightly packed cells, including taste receptor cells, supporting cells, and basal cells. Taste receptor cells detect nutrients and toxins in the oral cavity and transmit the sensory information to gustatory nerve endings in the buds. Supporting cells may play a role in the clearance of excess neurotransmitters after their release from taste receptor cells. Basal cells are precursor cells that differentiate into mature taste cells. Similar to other epithelial cells, taste cells turn over continuously, with an average life span of about 8-12 days. To maintain structural homeostasis in taste buds, new cells are generated to replace dying cells. Several recent studies using genetic lineage tracing methods have identified populations of progenitor/stem cells for taste buds, although contributions of these progenitor/stem cell populations to taste bud homeostasis have yet to be fully determined. Some regulatory factors of taste cell differentiation and degeneration have been identified, but our understanding of these aspects of taste bud homoeostasis remains limited. Many patients with various diseases develop taste disorders, including taste loss and taste distortion. Decline in taste function also occurs during aging. Recent studies suggest that disruption or alteration of taste bud homeostasis may contribute to taste dysfunction associated with disease and aging.
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Affiliation(s)
- Pu Feng
- Monell Chemical Senses Center, 3500 Market Street, Philadelphia, PA 19104, USA.
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6
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Abstract
Taste loss in human patients following radiotherapy for head and neck cancer is a common and significant problem, but the cellular mechanisms underlying this loss are not understood. Taste stimuli are transduced by receptor cells within taste buds, and like epidermal cells, taste cells are regularly replaced throughout adult life. This renewal relies on progenitor cells adjacent to taste buds, which continually supply new cells to each bud. Here we treated adult mice with a single 8 Gy dose of x-ray irradiation to the head and neck, and analyzed taste epithelium at 1-21 d postirradiation (dpi). We found irradiation targets the taste progenitor cells, which undergo cell cycle arrest (1-3 dpi) and apoptosis (within 1 dpi). Taste progenitors resume proliferation at 5-7 dpi, with the proportion of cells in S and M phase exceeding control levels at 5-6 and 6 dpi, respectively, suggesting that proliferation is accelerated and/or synchronized following radiation damage. Using 5-bromo-2-deoxyuridine birthdating to identify newborn cells, we found that the decreased proliferation following irradiation reduces the influx of cells at 1-2 dpi, while the robust proliferation detected at 6 dpi accelerates entry of new cells into taste buds. In contrast, the number of differentiated taste cells was not significantly reduced until 7 dpi. These data suggest a model where continued natural taste cell death, paired with temporary interruption of cell replacement, underlies taste loss after irradiation.
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Shin YK, Cong WN, Cai H, Kim W, Maudsley S, Egan JM, Martin B. Age-related changes in mouse taste bud morphology, hormone expression, and taste responsivity. J Gerontol A Biol Sci Med Sci 2011; 67:336-44. [PMID: 22056740 DOI: 10.1093/gerona/glr192] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Normal aging is a complex process that affects every organ system in the body, including the taste system. Thus, we investigated the effects of the normal aging process on taste bud morphology, function, and taste responsivity in male mice at 2, 10, and 18 months of age. The 18-month-old animals demonstrated a significant reduction in taste bud size and number of taste cells per bud compared with the 2- and 10-month-old animals. The 18-month-old animals exhibited a significant reduction of protein gene product 9.5 and sonic hedgehog immunoreactivity (taste cell markers). The number of taste cells expressing the sweet taste receptor subunit, T1R3, and the sweet taste modulating hormone, glucagon-like peptide-1, were reduced in the 18-month-old mice. Concordant with taste cell alterations, the 18-month-old animals demonstrated reduced sweet taste responsivity compared with the younger animals and the other major taste modalities (salty, sour, and bitter) remained intact.
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Affiliation(s)
- Yu-Kyong Shin
- Laboratory of Clinical Investigation, Diabetes Section, National Institute on Aging, Baltimore, MD 21224, USA
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Harrison TA, Smith Adams LB, Moore PD, Perna MK, Sword JD, Defoe DM. Accelerated turnover of taste bud cells in mice deficient for the cyclin-dependent kinase inhibitor p27Kip1. BMC Neurosci 2011; 12:34. [PMID: 21507264 PMCID: PMC3110126 DOI: 10.1186/1471-2202-12-34] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2010] [Accepted: 04/20/2011] [Indexed: 12/02/2022] Open
Abstract
Background Mammalian taste buds contain several specialized cell types that coordinately respond to tastants and communicate with sensory nerves. While it has long been appreciated that these cells undergo continual turnover, little is known concerning how adequate numbers of cells are generated and maintained. The cyclin-dependent kinase inhibitor p27Kip1 has been shown to influence cell number in several developing tissues, by coordinating cell cycle exit during cell differentiation. Here, we investigated its involvement in the control of taste cell replacement by examining adult mice with targeted ablation of the p27Kip1 gene. Results Histological and morphometric analyses of fungiform and circumvallate taste buds reveal no structural differences between wild-type and p27Kip1-null mice. However, when examined in functional assays, mutants show substantial proliferative changes. In BrdU incorporation experiments, more S-phase-labeled precursors appear within circumvallate taste buds at 1 day post-injection, the earliest time point examined. After 1 week, twice as many labeled intragemmal cells are present, but numbers return to wild-type levels by 2 weeks. Mutant taste buds also contain more TUNEL-labeled cells and 50% more apoptotic bodies than wild-type controls. In normal mice, p27 Kip1 is evident in a subset of receptor and presynaptic taste cells beginning about 3 days post-injection, correlating with the onset of taste cell maturation. Loss of gene function, however, does not alter the proportions of distinct immunohistochemically-identified cell types. Conclusions p27Kip1 participates in taste cell replacement by regulating the number of precursor cells available for entry into taste buds. This is consistent with a role for the protein in timing cell cycle withdrawal in progenitor cells. The equivalence of mutant and wild-type taste buds with regard to cell number, cell types and general structure contrasts with the hyperplasia and tissue disruption seen in certain developing p27Kip1-null sensory organs, and may reflect a compensatory capability inherent in the regenerative taste system.
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Affiliation(s)
- Theresa A Harrison
- Department of Anatomy and Cell Biology, Quillen College of Medicine, East Tennessee State University, Johnson City, TN, USA.
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Cohn ZJ, Kim A, Huang L, Brand J, Wang H. Lipopolysaccharide-induced inflammation attenuates taste progenitor cell proliferation and shortens the life span of taste bud cells. BMC Neurosci 2010; 11:72. [PMID: 20537148 PMCID: PMC2898829 DOI: 10.1186/1471-2202-11-72] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2009] [Accepted: 06/10/2010] [Indexed: 11/18/2022] Open
Abstract
Background The mammalian taste bud, a complex collection of taste sensory cells, supporting cells, and immature basal cells, is the structural unit for detecting taste stimuli in the oral cavity. Even though the cells of the taste bud undergo constant turnover, the structural homeostasis of the bud is maintained by balancing cell proliferation and cell death. Compared with nongustatory lingual epithelial cells, taste cells express higher levels of several inflammatory receptors and signalling proteins. Whether inflammation, an underlying condition in some diseases associated with taste disorders, interferes with taste cell renewal and turnover is unknown. Here we report the effects of lipopolysaccharide (LPS)-induced inflammation on taste progenitor cell proliferation and taste bud cell turnover in mouse taste tissues. Results Intraperitoneal injection of LPS rapidly induced expression of several inflammatory cytokines, including tumor necrosis factor (TNF)-α, interferon (IFN)-γ, and interleukin (IL)-6, in mouse circumvallate and foliate papillae. TNF-α and IFN-γ immunoreactivities were preferentially localized to subsets of cells in taste buds. LPS-induced inflammation significantly reduced the number of 5-bromo-2'-deoxyuridine (BrdU)-labeled newborn taste bud cells 1-3 days after LPS injection, suggesting an inhibition of taste bud cell renewal. BrdU pulse-chase experiments showed that BrdU-labeled taste cells had a shorter average life span in LPS-treated mice than in controls. To investigate whether LPS inhibits taste cell renewal by suppressing taste progenitor cell proliferation, we studied the expression of Ki67, a cell proliferation marker. Quantitative real-time RT-PCR revealed that LPS markedly reduced Ki67 mRNA levels in circumvallate and foliate epithelia. Immunofluorescent staining using anti-Ki67 antibodies showed that LPS decreased the number of Ki67-positive cells in the basal regions surrounding circumvallate taste buds, the niche for taste progenitor cells. PCR array experiments showed that the expression of cyclin B2 and E2F1, two key cell cycle regulators, was markedly downregulated by LPS in the circumvallate and foliate epithelia. Conclusions Our results show that LPS-induced inflammation inhibits taste progenitor cell proliferation and interferes with taste cell renewal. LPS accelerates cell turnover and modestly shortens the average life span of taste cells. These effects of inflammation may contribute to the development of taste disorders associated with infections.
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Affiliation(s)
- Zachary J Cohn
- Monell Chemical Senses Center, Philadelphia, PA 19104-3308, USA
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Ichimori Y, Ueda K, Okada H, Honma S, Wakisaka S. Histochemical changes and apoptosis in degenerating taste buds of the rat circumvallate papilla. ACTA ACUST UNITED AC 2010; 72:91-100. [PMID: 20009345 DOI: 10.1679/aohc.72.91] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The present study was designed to examine the histochemical changes and occurrence of apoptosis in taste buds of rat circumvallate papillae following bilateral transection of the glossopharyngeal nerve. Following transection of the glossopharyngeal nerve, the number of taste buds was not altered until post-operative day 3 (PO3), but decreased significantly thereafter. The number of cells within a taste bud, however, decreased significantly from PO2. In normal, uninjured animals, approximately 15.4%, 9.0%, and 7.7% of taste bud cells were labeled with antibodies for phospholipase C beta2 subunit (PLCbeta2), a marker for type II cells, neural cell adhesion molecule (NCAM), a marker for type III cells, and Jacalin, a marker for type IV cells, respectively. Following gustatory nerve injury, the ratio of cells expressing markers of type III and type IV decreased gradually from PO2, and Jacalin-labeled taste bud cells disappeared on PO3. Under normal conditions, immunoreactivity for single-strand DNA (ssDNA), a marker of apoptosis, was detected in the nuclei of PLC beta2-immunoreactive cells and cells showing no labeling for PLCbeta2, NCAM, or Jacalin. On PO1, the number of taste bud cells showing ssDNA immunoreactivity increased to double that of normal uninjured animals; these ssDNA-immunoreactive cells were also labeled with NCAM and Jacalin as well as PLCbeta2. The present results suggest that denervation of the gustatory nerve causes apoptosis in all types of taste bud cells, resulting in the rapid degeneration of taste buds.
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Affiliation(s)
- Yasuo Ichimori
- Department of Oral Anatomy and Developmental Biology, Osaka University Graduate School of Dentistry, Suita, Osaka, Japan
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Ueda K, Ichimori Y, Maruyama H, Murakami Y, Fujii M, Honma S, Wakisaka S. Cell-type specific occurrence of apoptosis in taste buds of the rat circumvallate papilla. ACTA ACUST UNITED AC 2008; 71:59-67. [PMID: 18622094 DOI: 10.1679/aohc.71.59] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The present study employed immunohistochemistry for single-stranded DNA (ssDNA) to detect apoptotic cells in taste buds of the rat circumvallate papilla. Double-labeling of ssDNA and markers for each cell type - phospholipase C beta2 (PLCbeta2) and alpha-gustducin for type II cells, neural cell adhesion molecule (NCAM) for type III cells, and Jacalin for type IV cells - was also performed to reveal which types of cells die by apoptosis. We detected approximately 16.8% and 14.0% of ssDNA-immunoreactive nuclei among PLCbeta2-immunoreactive and alpha-gustducinimmunoreactive cells, respectively, but rarely found ssDNA-immunoreactive cells among NCAM-immunoreactive or Jacalin-labeled cells, indicating that type II cells die by apoptosis. We also applied double labeling of ssDNA and human blood group antigen H (AbH) - which mostly labels type I cells as well as other cell types - and found that approximately 78% of ssDNA-immunoreactive cells were labeled with AbH, indicating that apoptosis also occurs in type I cells. The present results revealed that apoptosis occurs in both type I cells (dark cells) and type II cells (light cells), suggesting that there are two major cell lineages (dark cell and light cell lineages) for the differentiation of taste bud cells. In summury, type IV cells differentiate into dark and light cells and type III cells differentiate to type II cells within the light cell line.
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Affiliation(s)
- Katsura Ueda
- Department of Oral Anatomy and Developmental Biology, Osaka University Graduate School of Dentistry, Osaka, Japan
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Coyle CA, Strand SC, Good DJ. Reduced activity without hyperphagia contributes to obesity in Tubby mutant mice. Physiol Behav 2008; 95:168-75. [PMID: 18619628 DOI: 10.1016/j.physbeh.2008.05.014] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2007] [Revised: 05/22/2008] [Accepted: 05/23/2008] [Indexed: 10/22/2022]
Abstract
The Tub gene was originally identified as a spontaneous mutation in C57Bl/6J mice, and associated with adult-onset obesity (Tub MUT mice). Although the original Tub MUT mouse was identified over 15 years ago, there have been few reports on the animal's food intake, body fat percentage or energy expenditure. In this study, we report food intake, body weight from 5-20 weeks, body fat, body temperature and three different measures of physical activity behavior. Tub MUT mice display reduced food intake, uncharacteristic of many obese mouse models, and reduced voluntary wheel running with normal home cage ambulatory behavior. We conclude that motivation for food and exercise is an underlying defect in TUB MUT mice.
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Affiliation(s)
- Christopher A Coyle
- Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst, MA 01003, United States
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Guagliardo NA, Hill DL. Fungiform taste bud degeneration in C57BL/6J mice following chorda-lingual nerve transection. J Comp Neurol 2007; 504:206-16. [PMID: 17626272 PMCID: PMC2811721 DOI: 10.1002/cne.21436] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Taste buds are dependent on innervation for normal morphology and function. Fungiform taste bud degeneration after chorda tympani nerve injury has been well documented in rats, hamsters, and gerbils. The current study examines fungiform taste bud distribution and structure in adult C57BL/6J mice from both intact taste systems and after unilateral chorda-lingual nerve transection. Fungiform taste buds were visualized and measured with the aid of cytokeratin 8. In control mice, taste buds were smaller and more abundant on the anterior tip (<1 mm) of the tongue. By 5 days after nerve transection taste buds were smaller and fewer on the side of the tongue ipsilateral to the transection and continued to decrease in both size and number until 15 days posttransection. Degenerating fungiform taste buds were smaller due to a loss of taste bud cells rather than changes in taste bud morphology. While almost all taste buds disappeared in more posterior fungiform papillae by 15 days posttransection, the anterior tip of the tongue retained nearly half of its taste buds compared to intact mice. Surviving taste buds could not be explained by an apparent innervation from the remaining intact nerves. Contralateral effects of nerve transection were also observed; taste buds were larger due to an increase in the number of taste bud cells. These data are the first to characterize adult mouse fungiform taste buds and subsequent degeneration after unilateral nerve transection. They provide the basis for more mechanistic studies in which genetically engineered mice can be used.
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Affiliation(s)
- Nick A Guagliardo
- Department of Psychology, University of Virginia, Charlottesville, Virginia 22904-4400, USA
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Hayato R, Ohtubo Y, Yoshii K. Functional expression of ionotropic purinergic receptors on mouse taste bud cells. J Physiol 2007; 584:473-88. [PMID: 17702819 PMCID: PMC2277161 DOI: 10.1113/jphysiol.2007.138370] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Neurotransmitter receptors on taste bud cells (TBCs) and taste nerve fibres are likely to contribute to taste transduction by mediating the interaction among TBCs and that between TBCs and taste nerve fibres. We investigated the functional expression of P2 receptor subtypes on TBCs of mouse fungiform papillae. Electrophysiological studies showed that 100 microm ATP applied to their basolateral membranes either depolarized or hyperpolarized a few cells per taste bud. Ca(2+) imaging showed that similarly applied 1 mum ATP, 30 microm BzATP (a P2X(7) agonist), or 1 microm 2MeSATP (a P2Y(1) and P2Y(11) agonist) increased intracellular Ca(2+) concentration, but 100 microm UTP (a P2Y(2) and P2Y(4) agonist) and alpha,beta-meATP (a P2X agonist except for P2X(2), P2X(4) and P2X(7)) did not. RT-PCR suggested the expression of P2X(2), P2X(4), P2X(7), P2Y(1), P2Y(13) and P2Y(14) among the seven P2X subtypes and seven P2Y subtypes examined. Immunohistostaining confirmed the expression of P2X(2). The exposure of the basolateral membranes to 3 mm ATP for 30 min caused the uptake of Lucifer Yellow CH in a few TBCs per taste bud. This was antagonized by 100 microm PPADS (a non-selective P2 blocker) and 1 microm KN-62 (a P2X(7) blocker). These results showed for the first time the functional expression of P2X(2) and P2X(7) on TBCs. The roles of P2 receptor subtypes in the taste transduction, and the renewal of TBCs, are discussed.
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Affiliation(s)
- Ryotaro Hayato
- Kyushu Institute of Technology, Hibikino 2-4, Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Kitakyushu 808-0196, Japan
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Oakley B, Witt M. Building sensory receptors on the tongue. ACTA ACUST UNITED AC 2005; 33:631-46. [PMID: 16217619 DOI: 10.1007/s11068-005-3332-0] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2005] [Accepted: 04/05/2005] [Indexed: 12/01/2022]
Abstract
Neurotrophins, neurotrophin receptors and sensory neurons are required for the development of lingual sense organs. For example, neurotrophin 3 sustains lingual somatosensory neurons. In the traditional view, sensory axons will terminate where neurotrophin expression is most pronounced. Yet, lingual somatosensory axons characteristically terminate in each filiform papilla and in each somatosensory prominence within a cluster of cells expressing the p75 neurotrophin receptor (p75NTR), rather than terminating among the adjacent cells that secrete neurotrophin 3. The p75NTR on special specialized clusters of epithelial cells may promote axonal arborization in vivo since its over-expression by fibroblasts enhances neurite outgrowth from overlying somatosensory neurons in vitro. Two classical observations have implicated gustatory neurons in the development and maintenance of mammalian taste buds--the early arrival times of embryonic innervation and the loss of taste buds after their denervation in adults. In the modern era more than a dozen experimental studies have used early denervation or neurotrophin gene mutations to evaluate mammalian gustatory organ development. Necessary for taste organ development, brain-derived neurotrophic factor sustains developing gustatory neurons. The cardinal conclusion is readily summarized: taste buds in the palate and tongue are induced by innervation. Taste buds are unstable: the death and birth of taste receptor cells relentlessly remodels synaptic connections. As receptor cells turn over, the sensory code for taste quality is probably stabilized by selective synapse formation between each type of gustatory axon and its matching taste receptor cell. We anticipate important new discoveries of molecular interactions among the epithelium, the underlying mesenchyme and gustatory innervation that build the gustatory papillae, their specialized epithelial cells, and the resulting taste buds.
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Affiliation(s)
- Bruce Oakley
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109, USA
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Fan L, Girnius S, Oakley B. Support of trigeminal sensory neurons by nonneuronal p75 neurotrophin receptors. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2004; 150:23-39. [PMID: 15126035 DOI: 10.1016/j.devbrainres.2004.02.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 02/19/2004] [Indexed: 01/06/2023]
Abstract
The p75 neurotrophin receptor (p75NTR) binds all four mammalian neurotrophins, including neurotrophin-3 (NT-3) required for the development of select sensory neurons. This study demonstrated that many gustatory and somatosensory neurons of the tongue depend upon p75NTR. Each of thousands of filiform papillae at the front of the tongue as well as each somatosensory prominence at the back of the tongue has a small cluster of p75NTR-positive epithelial cells that is targeted by somatosensory innervation. This expression of p75NTR by epithelial target cells required NT-3 but not adult innervation. NT-3-secreting cells were adjacent to the p75NTR-positive target cells of each somatosensory organ, as demonstrated in NT-3(lacZneo) transgenic mice. In NT-3 null mutant mice, there were few lingual somatosensory neurons. In p75NTR null mutant mice, the lingual somatosensory axons were likewise absent or had deficient terminal arborizations. Cell culture indicated that substrate p75NTR can influence neuronal outgrowth. Specifically, dissociated trigeminal sensory neurons more than doubled their neurite lengths when grown on a lawn of p75NTR-overexpressing fibroblasts. This enhancement of neurite outgrowth by fibroblast p75NTR raises the possibility that epithelial target cell p75NTR may help to promote axonal arborization in vivo. The co-occurrence in p75NTR null mice of a 35% reduction in geniculate ganglion taste neurons and a shortfall of taste buds is consistent with the established role of gustatory innervation in prompting mammalian taste receptor cell differentiation.
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Affiliation(s)
- Lixin Fan
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, 3124 Natural Science Building, 830 N. University Ave., Ann Arbor, MI 48109-1048, USA
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Yee CL, Jones KR, Finger TE. Brain-derived neurotrophic factor is present in adult mouse taste cells with synapses. J Comp Neurol 2003; 459:15-24. [PMID: 12629664 DOI: 10.1002/cne.10589] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Brain-derived neurotrophic factor (BDNF), one of the members of the nerve growth factor family of neurotrophins, is expressed in developing gustatory papillae and is thought to be the neurotrophin that supports gustatory innervation during development. BDNF expression does not cease after development but continues in some taste cells of adult mice. To determine which types of taste cells produce BDNF, we undertook an immunohistochemical study of taste cells in BDNF(LacZ) gene targeted "knock-in" adult mice. In these mice, beta-galactosidase (beta-gal) immunoreactivity is an indicator of cells that produce BDNF transcripts. In the tongues of adult BDNF(LacZ) mice, beta-gal (BDNF) is present in long slender taste cells, as well as pyriform taste cells. Bromodeoxyuridine labeling experiments in BDNF(LacZ) mice indicate that BDNF is not present in taste cells that are younger than 3 days postmitotic. BDNF mainly colocalizes with markers of type II and type III taste cells: ubiquitin carboxyl terminal hydrolase (PGP 9.5), serotonin (5-HT), neural cell adhesion molecule (N-CAM), synaptic associated protein of 25 kDa (SNAP-25), and to a lesser extent with alpha-gustducin. beta-Gal immunoreactivity is not associated with blood group H antigen, a marker of type I taste cells. We conclude that BDNF is absent from basal cells and type I (blood group H antigen immunoreactive) taste cells but is present in differentiated type II and type III taste cells. The presence of SNAP-25 in BDNF-expressing cells suggests a role for BDNF in synaptic formation and transmission.
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Affiliation(s)
- Cindy L Yee
- Rocky Mountain Taste and Smell Center, Denver, Colorado 80262, USA.
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18
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Sun H, Oakley B. Development of anterior gustatory epithelia in the palate and tongue requires epidermal growth factor receptor. Dev Biol 2002; 242:31-43. [PMID: 11795938 DOI: 10.1006/dbio.2001.0526] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We characterized the gustatory phenotypes of neonatal mice having null mutations for epidermal growth factor receptor (egfr(-/-)), brain-derived neurotrophic factor (bdnf(-/-)), or both. We counted the number and diameter of fungiform taste buds, the prevalence of poorly differentiated or missing taste cells, and the incidence of ectopic filiform-like spines, each as a function of postnatal age and anterior/posterior location. Egfr(-/-) mice and bdnf(-/-) mice had similar reductions in the total number of taste buds on the anterior portions of the tongue and palate. Nonetheless, there were significant differences in their gustatory phenotypes. EGFR deficiency selectively impaired the development of anterior gustatory epithelia in the mouth. Only bdnf(-/-) mice had numerous taste buds missing from the foliate, vallate, and posterior fungiform papillae. Only egfr(-/-) fungiform taste papillae had robust gustatory innervation, markedly reduced cytokeratin 8 expression in taste cells, and a high incidence of a filiform-like spine. Egfr/bdnf double-null mutant mice had a higher frequency of failed fungiform taste bud differentiation. In bdnf(-/-) mice taste cell development failed because of sparse gustatory innervation. In contrast, in young egfr(-/-) mice the abundance of axons innervating fungiform papillae and the normal numbers of geniculate ganglion neurons implicate gustatory epithelial defects rather than neural defects.
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Affiliation(s)
- Hanshi Sun
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, 3127 Natural Science Building, Ann Arbor, Michigan 48109-1048, USA
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Kishi M, Emori Y, Tsukamoto Y, Abe K. Changes in cell morphology and cell-to-cell adhesion induced by extracellular Ca2+ in cultured taste bud cells. Biosci Biotechnol Biochem 2002; 66:484-7. [PMID: 11999434 DOI: 10.1271/bbb.66.484] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Cell morphology and cell-to-cell adhesion of taste bud cells were significantly altered by extracellular Ca2+ during in vitro culture. Under high Ca2+ condition (above 0.5 mM), the cells were tightly associated with each other and formed packed aggregates. Under low Ca2+ condition (below 0.1 mM), the cells were dispersed and had an elongated shape. These two forms were reversible and specifically dependent on Ca2+. The results indicate that extracellular Ca2+ regulates cell shape and cell-to-cell adhesion of taste bud cells.
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Affiliation(s)
- Mikiya Kishi
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Japan
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Ishimaru Y, Yasuoka A, Asano-Miyoshi M, Abe K, Emori Y. An actin-binding protein, CAP, is expressed in a subset of rat taste bud cells. Neuroreport 2001; 12:233-5. [PMID: 11209926 DOI: 10.1097/00001756-200102120-00011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Single cell cDNA libraries were constructed from taste bud cells of rat circumvallate papillae. Using three steps of screening, including differential hybridization, sequence analyses and in situ hybridization, a clone encoding a rat homolog of yeast adenylyl cyclase-associated protein (CAP) was identified to be highly expressed in a subset of taste bud cells.
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Affiliation(s)
- Y Ishimaru
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Japan
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