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PubMed2003

Co-expression pattern of Shh with Prox1 and that of Nkx2.2 with Mash1 in mouse taste bud.

In mammals, taste buds are maintained by continuous turnover of cells, even in adulthood. Cell proliferation and differentiation continue to produce taste cells, which express various genes related to taste reception. We found the co-expression of Sonic hedgehog (Shh) with Prox1 and that of Nkx2.2 with Mash1 in adult mouse taste buds. Whereas Prox1was expressed strongly in cells in the basal region of mouse taste buds where Shh was co-expressed, it was expressed weakly in almost all taste bud cells lacking Shh expression. At 0.5 day after birth, when taste cells have not yet differentiated, the expressions of Shh and Prox1 completely overlapped in the epithelium of circumvallate papillae. Nkx2.2 was observed in cells expressing Mash1, but not in cells expressing genes related to taste reception, such as gustducin and T1R3. Almost all fusiform cells expressing Mash1 co-expressed Nkx2.2, while the majority of round cells expressing Mash1 in the basal region of taste buds lacked Nkx2.2 expression.

Animals↗

PubMed1973

Disc electrophoresis of extracts from the taste buds located in circumvallate papillae of rat tongues.

The epithelium of the circumvallate papillae of rat tongues was stripped off by treatment with 0.005% elastase in a state when many taste buds were present. The taste buds were isolated from the stripped epithelium by further treatment with 0.005% elastase and 0.08% trypsin. A protein which was thought to be characteristic of taste buds was found from semimicro disc polyacrylamide gel electrophoretic studies of the stripped epithelia with and without taste buds. This result was supported by micro disc polyacrylamide gel electrophoretic studies of isolated taste buds.

Animals↗

PubMed1994

Analysis of the embryonic lineage of vertebrate taste buds.

In all vertebrates, taste buds are the last sensory receptors to appear late in embryonic development. They are thought to arise locally from the oropharyngeal epithelium, although this hypothesis has not been tested experimentally. Alternatively, taste buds have been proposed to arise from neuroectodermal cells that migrate from peripheral neurogenic sources to the oropharyngeal epithelium and give rise to taste bud precursor cells. In order to determine the exact embryonic lineage of the cells of vertebrate taste buds, we have employed a combination of endogenous and exogenous cell marking techniques to follow neuroectodermal and endodermal cells through development. We find, in the ambystomatid salamander used in our studies, taste buds arise locally within the endodermally-derived epithelium lining the oropharyngeal cavity, and do not receive a contribution from neuroectodermal sources, i.e. ectodermal placodes or cephalic neural crest.

Animals↗

PubMed1988

Human taste bud density across adult age groups.

Some of the subjective variability attributed to taste experience could be related to wide variations of taste bud density. Studies of taste perception show a direct relationship between sensation and the number of receptors. Taste bud densities are quantified in this study using light microscopy to reconstruct two regions of 18 human cadaver tongues. Specimens came from male and female cadavers representing three age groups: young adults, middle-aged adults, and older adults. The results show a range of more than 100-fold in taste bud density that is evenly distributed among age groups and sexes. The disparity is not attributable to the state of health of the adults prior to death, and it is corroborated in the literature. Differences in taste bud density that extend across age groups probably confound some inferences about the effects of aging on taste sensitivity that are derived from cross-sectional studies of human populations. It is not clear from the data whether or not human taste bud density in individuals and in populations is stable or changing with time.

Adult↗

PubMed1998

Pattern formation in epithelial development: the vertebrate limb and feather bud spacing.

The ectoderm of the vertebrate limb and feather bud are epithelia that provide good models for epithelial patterning in vertebrate development. At the tip of chick and mouse limb buds is a thickening, the apical ectodermal ridge, which is essential for limb bud outgrowth. The signal from the ridge to the underlying mesoderm involves fibroblast growth factors. The non-ridge ectoderm specifies the dorsoventral pattern of the bud and Wnt7a is a dorsalizing signal. The development of the ridge involves an interaction between dorsal cells that express radical fringe and those that do not. There are striking similarities between the signals and genes involved in patterning the limb ectoderm and the epithelia of the Drosophila imaginal disc that gives rise to the wing. The spacing of feather buds involves signals from the epidermis to the underlying mesenchyme, which again include Wnt7a and fibroblast growth factors.

Animals↗

PubMed2004

A paracrine signaling role for serotonin in rat taste buds: expression and localization of serotonin receptor subtypes.

Recent advances in peripheral taste physiology now suggest that the classic linear view of information processing within the taste bud is inadequate and that paracrine processing, although undemonstrated, may be an essential feature of peripheral gustatory transduction. Taste receptor cells (TRCs) express multiple neurotransmitters of unknown function that could potentially participate in a paracrine role. Serotonin is expressed in a subset of TRCs with afferent synapses; additionally, TRCs respond physiologically to serotonin. This study explored the expression and cellular localization of serotonin receptor subtypes in TRCs as a possible route of paracrine communication. RT-PCR was performed on RNA extracted from rat posterior taste buds with 14 prime sets representing 5-HT(1) through 5-HT(7) receptor subtype families. Data suggest that 5-HT(1A) and 5-HT(3) receptors are expressed in taste buds. Immunocytochemistry with a 5-HT(1A)-specific antibody demonstrated that subsets of TRCs were immunopositive for 5-HT(1A). With the use of double-labeling, serotonin- and 5-HT(1A)-immunopositive cells were observed exclusively in nonoverlapping populations. On the other hand, 5-HT(3)-immunopositive taste receptor cells were not observed. This observation, combined with other data, suggests 5-HT(3) is expressed in postsynaptic neural elements within the bud. We hypothesize that 5-HT release from TRCs activates postsynaptic 5-HT(3) receptors on afferent nerve fibers and, via a paracrine route, inhibits neighboring TRCs via 5-HT(1A) receptors. The ole of the 5-HT(1A)-expressing TRC within the taste bud remains to be explored.

Animals↗

PubMed2000

Distribution pattern of taste buds along hyoidal barbels of Mullus barbatus and M. surmuletus.

The external taste buds of bony fishes are differentiated and grouped throughout the body epithelium, concentrating in the buccopharyngeal cavity or in certain external organs such as the lips, barbels or fins. The family Mullidae (goatfishes) is characterized by having barbels covered with taste buds (TBs). However, It is not known how the TBs are distributed and how their characteristics vary along the barbels. To obtain answers to these questions, the morphological variability in taste bud density (deltaTB), pore area (A(P)) and taste bud area (A(TB)) was studied in Mullus barbatus (L., 1758) (red mullet) and M. surmuletus (L., 1758) (striped red mullet), for fish ranging in size from 58 to 227 and from 56 to 287 mm in total length (L(T)), respectively. Assuming that larger fish are older, in both species the pore area (A(P)) and taste bud area (A(TB)) increased with ontogenic development. Also, in both species clear differences were observed along the barbel. The delta(TB) increased from the basal area to the apical area, whereas both the A(P) and A(TB) had an inverse pattern.

Animals↗

PubMed1977

Effect of the length of the distal stump of transected nerve upon the rate of degeneration of taste buds.

The present work was carried out to study the effect of the length of the distal stump of transected nerve upon the rate of degeneration and the time course of disappearance of mammalian taste buds. Twelve adult rabbits were anaesthetized and the glossopharyngeal nerves of both sides were exposed and transected so as to leave a long distal stump on the right and a short one on the left side. The animals were sacrificed at different post-operative periods ranging from 2 to 14 days and the circumvallate and foliate papillae of both sides were examined. The taste buds on the side of the short distal stump always showed a greater decrease in number, size and cell contents than those of the side of the long distal stump. The taste buds on the side of the short distal stump disappeared earlier than those of the side of the long distal stump. Vallate taste buds disappeared earlier than the foliate: possible reasons for this were put forwards. The validity of the neurohumoral theory to the mammalian taste buds was discussed.

Animals↗

PubMed2003

Pitx1 and Pitx2 are required for development of hindlimb buds.

Two closely related homeobox transcription factors, Pitx1 and Pitx2, have been implicated in patterning of lateral plate mesoderm derivatives: Pitx1 for specification of hindlimb identity and Pitx2 for determination of laterality. We show that, together, Pitx1 and Pitx2 are required for formation of hindlimb buds and, when present in limited doses, for development of proximal (femur) and anterior (tibia and digit 1) hindlimb structures. Although Pitx1 is expressed throughout developing hindlimb buds, Pitx2 is not expressed in limb bud mesenchyme itself, but is co-expressed with Pitx1 in the presumptive hindlimb field before bud growth. Thus, Pitx1 and Pitx2 genes are required for sustained hindlimb bud growth and formation of hindlimbs.

Animals↗

PubMed2003

Tbx5 is required for forelimb bud formation and continued outgrowth.

Tbx5 is a T-box transcription factor expressed exclusively in the developing forelimb but not in the developing hindlimb of vertebrates. Tbx5 is first detected in the prospective forelimb mesenchyme prior to overt limb bud outgrowth and its expression is maintained throughout later limb development stages. Direct evidence for a role of Tbx5 in forelimb development was provided by the discovery that mutations in human TBX5 cause Holt-Oram Syndrome (HOS), a dominant disorder characterised predominantly by upper(fore) limb defects and heart abnormalities. Misexpression studies in the chick have demonstrated a role for this gene in limb-type specification. Using a conditional knockout strategy in the mouse to delete Tbx5 gene function in the developing forelimb, we demonstrate that this gene is also required at early limb bud stages for forelimb bud development. In addition, by misexpressing dominant-negative and dominant-activated forms of Tbx5 in the chick wing we provide evidence that this gene is also required at later stages of limb bud development for continued limb outgrowth. Our results provide a context to understand the defects observed in HOS caused by haploinsufficiency of TBX5 in human. Moreover, our results also demonstrate that limb bud outgrowth and specification of limb identity are linked by a requirement for Tbx5.

Animals↗

PubMed1996

BMP-2/-4 mediate programmed cell death in chicken limb buds.

During limb development, the mesenchymal cells in restricted areas of limb bud, anterior necrotic zone, posterior necrotic zone, opaque zone and interdigital necrotic zones, are eliminated by programmed cell death. The transcripts of bone morphogenetic protein (Bmp)-2 and -4 were first detected in the areas where cell death was observed, then showed overlapping expression with the programmed cell death zones except the opaque zone. To investigate the function of BMP-2 and BMP-4 during limb pattern formation, the dominant negative form of BMP receptor was overexpressed in chick leg bud via a replication-competent retrovirus to block the endogenous BMP-2/-4 signaling pathway. This resulted in excess web formation at the anterior and posterior regions of limb buds in addition to marked suppression of the regression of webbing at the interdigital regions. Significant reductions in the number of apoptotic cells in these three necrotic zones were found in the limb buds which received the virus carrying dominant negative BMP receptor. This indicates that extra tissue formation is due to suppression of programmed cell death in the three necrotic zones. Moreover, BMP-2/-4 protein induced apoptosis of mesenchymal cells isolated from the interdigital region in vitro. Other TGFbeta family proteins as TGFbeta1 and Activin did not show this effect. These results suggest that BMP-2 and BMP-4 are the apoptotic signal molecules of the programmed cell death process in the chick limb buds.

Animals↗

PubMed1997

Cell fate in the chick limb bud and relationship to gene expression.

We have produced detailed fate maps for mesenchyme and apical ridge of a stage 20 chick wing bud. The fate maps of the mesenchyme show that most of the wing arises from the posterior half of the bud. Subapical mesenchyme gives rise to digits. Cell populations beneath the ridge in the mid apical region fan out into the anterior tip of the handplate, while posterior cell populations extend right along the posterior margin. Subapical mesenchyme of the leg bud behaves similarly. The absence of anterior bending of posterior cell populations has implications when considering models of vertebrate limb evolution. The fatemaps of the apical ridge show that there is also a marked anterior expansion and cells that were in anterior apical ridge later become incorporated into non-ridge ectoderm along the margin of the bud. Mesenchyme and apical ridge do not expand in concert--the apical ridge extends more anteriorly. We used the fatemaps to investigate the relationship between cell lineage and elaboration of Hoxd-13 and Fgf-4 domains. Hoxd-13 and Fgf-4 are initially expressed posteriorly until about the mid-point of the early wing bud in mesenchyme and apical ridge respectively. Later in development, the genes come to be expressed throughout most of the handplate and apical ridge respectively. We found that at the proximal edge of the Hoxd-13 domain, cell populations stopped expressing the gene as development proceeded and found no evidence that the changes in extent of the domains were due to initiation of gene expression in anterior cells. Instead the changes in extent of expression fit with the fate maps and can be attributed to expansion and fanning out of cell populations initially expressing the genes.

Animals↗

PubMed1998

Sonic hedgehog is not required for polarising activity in the Doublefoot mutant mouse limb bud.

The mouse mutant Doublefoot (Dbf) shows preaxial polydactyly of all four limbs. We have analysed limb development in this mutant with respect to morphogenesis, gene expression patterns and ectopic polarising activity. The results reveal a gain-of-function mutation at a locus that mediates pattern formation in the developing limb. Shh expression is identical with that of wild-type embryos, i.e. there is no ectopic expression. However, mesenchyme from the anterior aspects of Dbf/+ mutant limb buds, when transplanted to the anterior side of chick wing buds, induces duplication of the distal skeletal elements. Mid-distal mesenchymal transplants from early, but not later, Dbf/+ limb buds are also able to induce duplication. This demonstration of polarising activity in the absence of Shh expression identifies the gene at the Dbf locus as a new genetic component of the Shh signalling pathway, which (at least in its mutated form) is able to activate signal transduction independently of Shh. The mutant gene product is sufficient to fulfil the signalling properties of Shh including upregulation of the direct Shh target genes Ptc and Gli, and induction of the downstream target genes Bmp2, Fgf4 and Hoxd13. The expression domains of all these genes extend from their normal posterior domains into the anterior part of the limb bud without being focused on a discrete ectopic site. These observations dissociate polarising activity from Shh gene expression in the Dbf/+ limb bud. We suggest that the product of the normal Dbf gene is a key active constituent of the polarising region, possibly acting in the extracellular compartment.

Animals↗

PubMed1988

Immunocytochemical localizations of neuron-specific proteins in the taste bud of the guinea pig.

The taste buds and their nerves in the guinea pig were immunocytochemically investigated with regard to the localization of spot 35 protein, neuron-specific enolase (NSE), neurofilament protein (NFP), and S-100 protein. The spot 35 protein-like immunoreactivity was confined to slender cells comprising half the number of taste bud cells. NSE-like immunoreactivity was recognized in some taste bud cells as well as nerve fibers both within the taste bud and in the subepithelial connective tissue. The NSE-immunoreactive cells were divided into two cell populations: one weakly and the other intensely immunoreactive. The former cells proved to be spot 35 protein-immunoreactive. Moreover, the cells immunoreactive for both spot 35 protein and NSE were frequently associated with nerve fibers immunostained intensely for NSE. The NFP- and S-100 protein-like immunoreactivities were found in none of cells in the taste bud, but exclusively in the subepithelial neural elements.

Animals↗

PubMed2005

Immunohistochemical detection of neurotrophin-3 and -4, and their receptors in mouse taste bud cells.

Neurotrophin-3 (NT3) and neurotrophin-4 (NT4) affect the survival and maintenance of central and peripheral neurons. Using an immunohistochemical method, we examined whether the taste bud cells in the circumvallate papillae of normal mice expressed NT3, NT4, and their respective receptors TrkC and TrkB, and if so, what type of cells in the taste buds expressed them. Double immunostaining for either of them and PGP 9.5, NCAM, or gustducin was used to determine which cell types expressed which neurotrophins and receptors. Normal taste bud cells expressed NT3, NT4, and the TrkB receptor, but not TrkC. The percentage of NT3-immunoreactive cells among all taste bud cells was 89.0%, that of NT4-immunoreactive cells, 58.6%, and that of TrkB-immunoreactive cells, 80.8%. Almost none of the NT4-immunoreactive cells were reactive with anti-PGP 9.5 or the anti-NCAM antibody, but they could be stained with anti-gustducin, revealing that NT4-immunoreactive cells were contained only in the type-II--and possibly type-I--cell population. On the other hand, NT3-, and TrkB-immunoreactive cells included type-III cells, together with type-II, -I, and basal cells, because they were positive for PGP 9.5 and gustducin. We conclude that NT4 may exert trophic actions on all types of taste bud cells by binding to their TrkB receptors, and NT3 may also have a similar, though negligible role.

Animals↗

PubMed2006

The bHLH transcription factors, Hes6 and Mash1, are expressed in distinct subsets of cells within adult mouse taste buds.

Taste buds are multicellular receptor organs embedded in the lingual epithelium of vertebrates. Taste cells within these buds are modified epithelial cells as they lack axons and turnover rapidly throughout life, yet have neuronal properties enabling them to transduce taste stimuli and transmit this information to the nervous system. Taste cells are heterogeneous, comprising types I, II, III and basal cells, and are continually replaced during adult life, raising the question of how these different cells are generated. The molecular mechanisms governing taste cell differentiation are unknown, but the Notch signaling system has been implicated in this process based upon recent gene expression data. Here we investigate the expression in mature taste buds of Notch related transcription factors, Hes6 and Mash1, which are among the first genes expressed in embryonic taste buds. We further compare these patterns with those of immunocytochemical markers of discrete taste cell types. We find that Hes6 is expressed in a subset of basally located, possibly progenitor cells, yet is rarely coexpressed with taste cell markers. In contrast, Mash1 is detected in some basal cells and in the majority of differentiated type III taste cells, but never in type II cells. These data suggest a role for Notch signaling in taste cell differentiation in adult taste buds.

Animals↗

PubMed1976

An electron microscopic study on the innervation in the taste buds of the mouse circumvallate papillae.

Taste buds of the mouse circumvallate papillae were studied by electron microscopy to elucidate the innervation involving the adrenergic nerve supply. Typical afferent synaptic contacts, with increased density of the membranes and aggregations of synaptic vesicles in the cytoplasm adjacent to the nerve endings, were demonstrated between the type III cells and the nerve endings. Along the regions of contact between the type II cells and the nerve endings, cisternae of endoplasmic reticulum were often seen beneath the cell membrane, and the nerve endings contained relatively many synaptic-sized vesicles. Such an innervation seems to be efferent in nature. For the detection of the adrenergic nerve supply, 5-hydroxydopamine (5-OH-DA) was injected after pretreatment with L-DOPA and nialamide. The mice showed numerous adrenergic nerve fibers in the connective tissue underlying the taste buds. On very few occasions, the adrenergic nerves penetrated the basal lamina of the taste buds and came into contact with the bud cells. Some adrenergic nerves were distributed among the epithelial cells around the taste buds. The reaction product from acetylcholine esterase activity was found around the adrenergic nerve fibers labeled with 5-OH-DA.

Acetylcholinesterase↗

PubMed1978

Taste buds in the vallate papillae of the rat studied with freeze-fracture preparation.

The taste bud of the vallate papillae of the rat has been examined in the electron microscope by using the freeze-fracture technique. Tight junctions as a junctional complex are located at the taste pore, and form a seal between the oral environment and the taste buds. Tight junctions are not only within the taste buds, but also are demonstrated in the granular cell layers of the surrounding lingual epithelium. The present finding suggests that tight junctions of the taste pore link with those of the lingual epithelium. Desmosomes are observed in the buds, but they are smaller in size than in the surrounding lingual epithelium. Besides these junctions, within the buds, gap junctions containing particle-free zones are demonstrated which are called a subcompartment type.

Animals↗