Neuronal delivery of Hedgehog directs spatial patterning of taste organ regeneration

How organs maintain and restore functional integrity during ordinary tissue turnover or following injury represents a central biological problem. The maintenance of taste sensory organs in the tongue was shown 140 years ago to depend on innervation from distant ganglion neurons, but the underlying mechanism has remained unknown. Here, we show that Sonic hedgehog (Shh), which encodes a secreted protein signal, is expressed in these sensory neurons, and that experimental ablation of neuronal Shh expression causes loss of taste receptor cells (TRCs). TRCs are also lost upon pharmacologic blockade of Hedgehog pathway response, accounting for the loss of taste sensation experienced by cancer patients undergoing Hedgehog inhibitor treatment. We find that TRC regeneration following such pharmacologic ablation requires neuronal expression of Shh and can be substantially enhanced by pharmacologic activation of Hedgehog response. Such pharmacologic enhancement of Hedgehog response, however, results in additional TRC formation at many ectopic sites, unlike the site-restricted regeneration specified by the projection pattern of Shh-expressing neurons. Stable regeneration of TRCs thus requires neuronal Shh, illustrating the principle that neuronal delivery of cues such as the Shh signal can pattern distant cellular responses to assure functional integrity during tissue maintenance and regeneration.

Involvement of PI3K and PKA pathways in mouse tongue epithelial differentiation

In mice, tongue epithelial differentiation is mainly regulated by the interactions among various signalling molecules including Fgf signalling pathways. However, the subsequent signalling modulations for epithelial maturation, initiated by Fgf signalling, remain to be elucidated. Therefore, we employed an in vitro tongue organ cultivation system along with the applications of various pharmacological inhibitors against the intracellular signalling molecules of Fgf signalling pathways, including H89, LY294002, PD98059, and U0126. Following treatments with LY294002 and H89, inhibitors for PI3K and PKA, respectively, the decreased thickness of the tongue epithelium was observed along with the alteration in cell proliferative and apoptotic patterns. Meanwhile, cultivated tongues treated with MEK inhibitor U0126 or PD98059 showed significantly decreased cell proliferation in the tongue epithelium and the mesenchyme. Based on these results, we suggest that the tongue epithelium is differentiated into multiple epithelial cell layers via the PI3K and PKA pathways in tissue-specific manner during the epithelial-mesenchymal interactions.

Tracking endogenous amelogenin and ameloblastin in vivo

Research on enamel matrix proteins (EMPs) is centered on understanding their role in enamel biomineralization and their bioactivity for tissue engineering. While therapeutic application of EMPs has been widely documented, their expression and biological function in non-enamel tissues is unclear. Our first aim was to screen for amelogenin (AMELX) and ameloblastin (AMBN) gene expression in mandibular bones and soft tissues isolated from adult mice (15 weeks old). Using RT-PCR, we showed mRNA expression of AMELX and AMBN in mandibular alveolar and basal bones and, at low levels, in several soft tissues; eyes and ovaries were RNA-positive for AMELX and eyes, tongues and testicles for AMBN. Moreover, in mandibular tissues AMELX and AMBN mRNA levels varied according to two parameters: 1) ontogenic stage (decreasing with age), and 2) tissue-type (e.g. higher level in dental epithelial cells and alveolar bone when compared to basal bone and dental mesenchymal cells in 1 week old mice). In situ hybridization and immunohistodetection were performed in mandibular tissues using AMELX KO mice as controls. We identified AMELX-producing (RNA-positive) cells lining the adjacent alveolar bone and AMBN and AMELX proteins in the microenvironment surrounding EMPs-producing cells. Western blotting of proteins extracted by non-dissociative means revealed that AMELX and AMBN are not exclusive to mineralized matrix; they are present to some degree in a solubilized state in mandibular bone and presumably have some capacity to diffuse. Our data support the notion that AMELX and AMBN may function as growth factor-like molecules solubilized in the aqueous microenvironment. In jaws, they might play some role in bone physiology through autocrine/paracrine pathways, particularly during development and stress-induced remodeling.

Spatial and temporal lingual coarticulation and motor control in preadolescents

PURPOSE In this study, the authors compared coarticulation and lingual kinematics in preadolescents and adults in order to establish whether preadolescents had a greater degree of random variability in tongue posture and whether their patterns of lingual coarticulation differed from those of adults. METHOD High-speed ultrasound tongue contour data synchronized with the acoustic signal were recorded from 15 children (ages 10-12 years) and 15 adults. Tongue shape contours were analyzed at 9 normalized time points during the fricative phase of schwa-fricative-/a/ and schwa-fricative-/i/ sequences with the consonants /s/ and /ʃ/. RESULTS There was no significant age-related difference in random variability. Where a significant vowel effect occurred, the amount of coarticulation was similar in the 2 groups. However, the onset of the coarticulatory effect on preadolescent /ʃ/ was significantly later than on preadolescent /s/, and also later than on adult /s/ and /ʃ/. CONCLUSIONS Preadolescents have adult-like precision of tongue control and adult-like anticipatory lingual coarticulation with respect to spatial characteristics of tongue posture. However, there remains some immaturity in the motor programming of certain complex tongue movements.

[Expressions of microtubule-associated protein 2 and nestin in the development of human embryo and fetal tongue muscles]

OBJECTIVE

To explore the role of microtubule-associated protein 2 (MAP-2) and nestin in the development of tongue muscles of human embryos and fetuses.

METHODS

PV immunohistochemistry was used to detect the expressions of MAP-2 and nestin proteins in the tongue tissues of human embryos and fetuses at the second, third and fourth months of gestation.

RESULTS

MAP-2 and nestin positivity was detected in the tongue muscles of human embryos at 2 to 4 months of gestation. In the embryos at the second month of gestation, no obvious MAP-2 positive cells were found in the tongue muscles; at 3 and 4 months, the number of MAP-2-positive cells in the tongue muscles was 24.14∓8.28 and 15.86∓3.89, with the expression intensity of 109.42∓11.62 and 124.27∓8.73, respectively. At 2, 3 and 4 months of gestation, the number of nestin-positive cells in the tongue muscles was 12.50∓3.17, 19.00∓7.63, and 22.80∓6.91, with expression intensity of 119.99∓24.02, 102.20∓11.76, and 98.24∓10.66, respectively. As the gestational age increased, the number of MAP-2-positive cell number continued to decline following a transient increase but the expression intensity kept increasing; nestin-positive cells increased continuously but the expression intensity kept decreasing in the embryonic or fetal tongue muscles.

CONCLUSION

MAP-2 and nestin proteins are involved in the regulation of the development of tongue muscles in human embryos and fetuses.

Developmental changes in the variability of tongue and lip movements during speech from childhood to adulthood: an EMA study

This study investigated the developmental variability of lip and tongue movement in 48 children and adults. Motion of the tongue-tip, tongue-body and lower lip was recorded using electromagnetic articulography during productions of sentences containing /t/, /s/, /l/, /k/ and /p/. Four groups of speakers participated in the study: (1) aged 6-7 years; (2) 8-11 years; (3) 12-17 years; and (4) adults. The variation in distance, duration, speed, acceleration and deceleration of the articulators during single open-close speech movements was analysed, and the stability of multiple movement sequences was examined using the spatiotemporal index. The experimental findings revealed a gradual developmental progression from 6 years to adulthood. At adolescence, speakers continued to exhibit significantly more variable speech motor output compared to adult speakers. The observed developmental pattern suggests that attenuated, but important, changes in the speech motor system occurs from mid-childhood, through adolescence, to adulthood.

The inductive role of Wnt-β-Catenin signaling in the formation of oral apparatus

Proper patterning and growth of oral structures including teeth, tongue, and palate rely on epithelial-mesenchymal interactions involving coordinated regulation of signal transduction. Understanding molecular mechanisms underpinning oral-facial development will provide novel insights into the etiology of common congenital defects such as cleft palate. In this study, we report that ablating Wnt signaling in the oral epithelium blocks the formation of palatal rugae, which are a set of specialized ectodermal appendages serving as Shh signaling centers during development and niches for sensory cells and possibly neural crest related stem cells in adults. Lack of rugae is also associated with retarded anteroposterior extension of the hard palate and precocious mid-line fusion. These data implicate an obligatory role for canonical Wnt signaling in rugae development. Based on this complex phenotype, we propose that the sequential addition of rugae and its morphogen Shh, is intrinsically coupled to the elongation of the hard palate, and is critical for modulating the growth orientation of palatal shelves. In addition, we observe a unique cleft palate phenotype at the anterior end of the secondary palate, which is likely caused by the severely underdeveloped primary palate in these mutants. Last but not least, we also discover that both Wnt and Shh signalings are essential for tongue development. We provide genetic evidence that disruption of either signaling pathway results in severe microglossia. Altogether, we demonstrate a dynamic role for Wnt-β-Catenin signaling in the development of the oral apparatus.

Fluorescence immunohistochemistry in combination with differential interference contrast microscopy for studies of semi-ultrathin specimens of epoxy resin-embedded samples

We have developed a technique, using a combination of immunofluorescent staining of semi-ultrathin sections of epoxy resin-embedded samples and the corresponding differential interference contrast (DIC) images obtained by light microscopy that provides detailed information about the immuno-localization of histological and cellular structures. To demonstrate the effectiveness of our method, we examined the immunofluorescence of immuno-stained keratin 13 (K13) and type III collagen (CIII) and the corresponding DIC images during the morphogenesis of filiform papillae on the rat tongue. Immunoreactivity specific for K13 and CIII was detected on the lingual epithelium of juveniles on postnatal days 7 and 14 (P7 and P14). The immunoreactivity specific for K13 was clearly located in the intermediate-layer cells of the interpapillary cell columns, while that specific for CIII was also distinct in the connective-tissue fibers between the lingual epithelium and the lingual muscle. The DIC images revealed the keratinization of the stratified squamous cells of the lingual epithelium and, also, myogenesis beneath the connective tissue. In addition, immunoreactivity specific for CIII was also recognizable in the endomysium and perimysium around the lingual muscle. Thus, our method demonstrated changes in patterns of immunoreactivity of K13 and of CIII during the morphogenesis of the rat tongue.

Producing American English vowels during vocal tract growth: a perceptual categorization study of synthesized vowels

PURPOSE

To consider interactions of vocal tract change with growth and perceived output patterns across development, the influence of nonuniform vocal tract growth on the ability to reach acoustic-perceptual targets for English vowels was studied.

METHOD

Thirty-seven American English speakers participated in a perceptual categorization experiment. For the experiment, an articulatory-to-acoustic model was used to synthesize 342 five-formant vowels, covering maximal vowel spaces for speakers at 5 growth stages (from 6 months old to adult).

RESULTS

Results indicate that the 3 vowels /i u ae/ can be correctly perceived by adult listeners when produced by speakers with a 6-month-old vocal tract. Articulatory-to-acoustic relationships for these 3 vowels differ across growth stages. For a given perceived vowel category, the infant's tongue position is more fronted than the adult's. Furthermore, nonuniform vocal tract growth influences degree of interarticulator coupling for a given perceived vowel, leading to a reduced correlation between jaw height and tongue body position in infantlike compared with adult vocal tracts.

CONCLUSION

Findings suggest that nonuniform vocal tract growth does not prevent the speaker from producing acoustic-auditory targets related to American English vowels. However, the relationships between articulatory configurations and perceptual targets change from birth to adulthood.

Claudin immunolocalization in neonatal mouse epithelial tissues

Emerging evidence supports the notion that claudins (Cldns) are dynamically regulated under normal conditions to respond to the selective permeability requirements of various tissues, and that their expression is developmentally controlled. We describe the localization of those Cldns that we have previously demonstrated to be functionally important in epidermal differentiation and the formation of the epidermal permeability barrier, e.g., Cldn1, Cldn6, Cldn11, and Cldn18, and the presence of Cldn3 and Cldn5 in various neonatal mouse epithelia including the epidermis, nail, oral mucosa, tongue, and stomach. Cldn1 is localized in the differentiated and/or undifferentiated compartments of the epidermis and nail and in the dorsal surface of the tongue and glandular compartment of the stomach but is absent from the oral mucosa and the keratinized compartment of the stomach. Cldn3 is present in the basal cells of the nail matrix and both compartments of the murine stomach but not in the epidermis, oral mucosa, or tongue. Cldn5 is found in the glandular compartment of the stomach but not in the epidermis, nail unit, oral mucosa, forestomach, and tongue. Cldn6, Cldn11, and Cldn18 occur in the differentiating suprabasal compartment of the epidermis, nail, and oral mucosa and in the dorsal and ventral surfaces of the tongue and the keratinized squamous epithelium of the stomach. The simple columnar epithelium of the glandular stomach stains for Cldn18 and reveals a non-membranous pattern for Cldn6 and Cldn11 expression. Our results demonstrate differential Cldn protein profiles in various epithelial tissues and their differentiation stages. Although the molecular mechanisms regulating Cldn expression are unknown, elucidation of their differential localization patterns in tissues with diverse permeability requirements should provide a better understanding of the role of tight junctions in tissue function.

Physiologic development of tongue-jaw coordination from childhood to adulthood

PURPOSE

This investigation aimed to examine the development of tongue-jaw coordination during speech from childhood to adolescence.

METHOD

Electromagnetic articulography was used to track tongue and jaw motion in 48 children and adults (aged 6-38 years) during productions of /t/ and /k/ embedded in sentences.

RESULTS

The coordinative organization of the tongue and jaw exhibited changes until the age of 8-11 years and continued to undergo refinement into late adolescence. The tongue-tip and tongue-body were observed to develop unique kinematic relations with the jaw. While tongue-tip movement became increasingly synchronized with jaw movement, tongue-body and jaw retained movement independence but developed a more consistent kinematic relation.

CONCLUSION

The present results support the notion that speech motor development is nonuniform, with a refinement period from mid-childhood to late adolescence.

Development of fungiform papillae: patterned lingual gustatory organs

The fungiform papilla is a gustatory organ that provides a specific tissue residence for taste buds on the anterior tongue. Thus, during development there must be a progressive differentiation to acquire papilla epithelium, then taste cell progenitor epithelium, and finally taste cells within the papilla apex. Arranged in rows, the patterned distribution of fungiform papillae requires molecular regulation not only to induce papillae, but also to suppress papilla formation in the between-papilla tissue. Intact sensory innervation is not required to initiate papilla development or pattern. However, members of several molecular families have now been identified with specific localization in developing papillae. These may participate in papilla development and pattern formation, and subsequently in taste progenitor and taste cell differentiation. This review focuses on development of fungiform papillae in embryonic rat and mouse. Basic morphology, cell biology and molecular phenotypes of developing papillae are reviewed. Regulatory roles for molecules in several families are presented, and a broad schema is proposed for progressive epithelial differentiation to form taste cell progenitors in parallel with the temporal course, and participation of lingual sensory innervation.

Functional redundancy of NSCL-1 and NeuroD during development of the petrosal and vestibulocochlear ganglia

To study the role of different members of the bHLH gene family for sensory organ development we have generated NSCL-1 and NeuroD compound-mutant mice. Double homozygous animals were characterized by a more severe reduction of the petrosal and vestibulocochlear ganglia than NeuroD-knockout mice. The more severe reduction of the petrosal and vestibulocochlear ganglia in double-knockout mice indicates overlapping functions of the two genes during neuronal development. Interestingly, we also found that the two genes are jointly regulated by thyroid hormone during sensory hair cell development. We further present a detailed expression analysis of NSCL-1 and NSCL-2 during sensory neuron development. NSCL-1 expression was detected in all developing cranial ganglia including the petrosal and vestibulocochlear ganglion, in inner and outer hair cells of the organ of Corti and in hair cells of the vestibular system. Expression domains in other sensory structures include the retina, Merkel cells of the developing skin and sensory cells of the tongue. The expression of NSCL-2 was restricted to developing cranial ganglia, the retina and the vestibular nerve. Both NSCL-1 and NSCL-2 genes are active only in postmitotic neurons, indicating a role for neuronal cell migration and/or differentiation within the sensory system.

Long-term evaluation of orofacial function in children with Down syndrome after treatment with a stimulating plate according to Castillo Morales

The aim of this investigation was to evaluate the long-term orofacial development of Down children who received plate therapy according to Castillo Morales in their early childhood. The orofacial development of 27 Down children was documented before and after plate therapy and at a follow-up examination 13 years +/- 6 months after initiation of therapy. The orofacial appearance significantly improved during therapy (p = 0.00). During the follow-up, mouth posture remained stable (p = 0.259), whereas tongue position further improved (p = 0.034). A better long-term development was documented in children with initial severe orofacial dysfunctions.

Myosin heavy chain composition of tongue muscle in microphthalmic (mi/mi) mice before and after weaning

To elucidate the effects of teeth on muscle fibers in the tongue during the developmental process, we examined the expression of muscle contractile proteins and the genes for those proteins in normal mice and microphthalmic (mi/mi) mice with impaired tooth eruption. The mice were observed during the growth period, including weaning, which is when feeding movements undergo major changes. Expression of the myosin heavy chain (MyHC)-2a protein, whose contraction speed is relatively slow, disappeared after weaning in normal mice, while it remained in high concentrations even after weaning in mi/mi mice. The presence of MyHC-2a after weaning in mice with no tooth eruption was attributed to a compensation for lack of proper masticatory function and sucking-like movements, as MyHC-2a is necessary for these movements.

Epithelial overexpression of BDNF and NT4 produces distinct gustatory axon morphologies that disrupt initial targeting

Most fungiform taste buds fail to become innervated when BDNF or NT4 is overexpressed in the basal layer of tongue epithelium. Here, we examined when and how overexpression of BDNF and NT4 disrupt innervation to fungiform papillae. Overexpression of either factor disrupted chorda tympani innervation patterns either before or during the initial innervation of fungiform papillae. NT4 and BDNF overexpression each disrupted initial innervation by producing different gustatory axon morphologies that emerge at distinct times (E12.5 and E14.5, respectively). Chorda tympani nerve branching was reduced in NT4 overexpressing mice, and neuronal fibers in these mice were fasciculated and remained below the epithelial surface, as if repelled by NT4 overexpression. In contrast, many chorda tympani nerve branches were observed near the epithelial surface in mice overexpressing BDNF, and most were attracted to and invaded non-taste filiform papillae instead of gustatory papillae. These results suggest that BDNF, but not NT4, normally functions as a chemoattractant that allows chorda tympani fibers to distinguish their fungiform papillae targets from non-gustatory epithelium. Since BDNF and NT4 both signal through the p75 and TrkB receptors, trophin-specific activation of different internal signaling pathways must regulate the development of the distinct gustatory axon morphologies in neurotrophin-overexpressing mice.

Runx3 expression during mouse tongue and palate development

Studies of molecular mechanisms underlying the development of the mammalian oral mucosa have revealed a major involvement of transforming growth factor beta (TGF-beta) and bone morphologic protein (BMP) signaling pathways. Here, we examined the expression of a downstream target of TGF-beta and BMPs, Runx3, in oral mucosa. Runx3 is a runt-related transcription factor that acts as a gastric tumor suppressor and regulator of growth and differentiation in mammalian gastric epithelial cells. Another member of the Runx family in C. elegans, run, is involved in the development of a functional hypodermis and gut. In this report, we examined Runx3 expression using reverse transcription-polymerase chain reaction, immnunohistochemistry, and in situ hybridization and found that Runx3 is expressed in the tongue and palate epithelium of mouse embryos from embryonic day 12.5 to 16.5. The functional relationship between Runx3 and TGF-beta/BMPs signaling in tongue and palate development is discussed.

Embryonic and postnatal development of masticatory and tongue muscles

This review summarizes findings concerning the unique developmental characteristics of mouse head muscles (mainly the masticatory and tongue muscles) and compares their characteristics with those of other muscles. The developmental origin of the masticatory muscles is the somitomeres, whereas the tongue and other muscles, such as the trunk (deep muscles of the back, body wall muscles) and limb muscles, originate from the somites. The program controlling the early stages of masticatory myogenesis, such as the specification and migration of muscle progenitor cells, is distinctly different from those in trunk and limb myogenesis. Tongue myogenesis follows a similar regulatory program to that for limb myogenesis. Myogenesis and synaptogenesis in the masticatory muscles are delayed in comparison with other muscles and are not complete even at birth, whereas the development of tongue muscles proceeds faster than those of other muscles and ends at around birth. The regulatory programs for masticatory and tongue myogenesis seem to depend on the developmental origins of the muscles, i.e., the origin being either a somite or somitomere, whereas myogenesis and synaptogenesis seem to progress to serve the functional requirements of the masticatory and tongue muscles.

Distribution of tenascin-C and -X and expression of tenascin-C and X mRNA in the postnatal rat tongue

Different distributions of tenascin-C and -X are found in various organs. However, the role of the tenascin family in the process of formation in the papillae epithelium during development is poorly understood. In order to find more information an tenascin-C and -X distributions during tongue development, immunohistocheminical studies have been carried out to demonstrate these distributions. The number of PCNA positive cells gradually increased from 5- to 15-days, and decreased on 21-days in the intercellular space of the epithelal layer in the postnatal development of rat tongue (150 specimens of Wistar male rats (0-, 5-, 10-, 15-, and 21-days). The reaction of tenascin-C was found mainly in the intercellular space of the epithelial layer on contrast to that of tenascin-X which was mainly found an the epithelial layer under a confocal laser scanning microscope. The level of mRNA of tenascin-C (600bp) and tenascin-X (588bp) gradually decreased from 5-days using RT-PCR methods. The different distribution of these extracellular matrices and weakly-regulated expressions may be related to the replication process of the epithelium in the tongue during development.

Pax9 is required for filiform papilla development and suppresses skin-specific differentiation of the mammalian tongue epithelium

The epidermis is a derivative of the surface ectoderm. It forms a protective barrier and specific appendages including hair, nails, and different eccrine glands. The surface ectoderm also forms the epithelium of the oral cavity and tongue, which develop a slightly different barrier and form different appendages such as teeth, filiform papillae, taste papillae, and salivary glands. How this region-specific differentiation is genetically controlled is largely unknown. We show here that Pax9, which is expressed in the epithelium of the tongue but not in skin, regulates several aspects of tongue-specific epithelial differentiation. In Pax9-deficient mice filiform papillae lack the anterior-posterior polarity, a defect that is associated with temporal-spatial changes in Hoxc13 expression. Barrier formation is disturbed in the mutant tongue and genome-wide expression profiling revealed that the expression of specific keratins (Krt), keratin-associated proteins, and members of the epidermal differentiation complex is significantly down-regulated. In situ hybridization demonstrated that several 'hard' keratins, Krt1-5, Krt1-24, and Krt2-16, are not expressed in the absence of Pax9. Notably, specific 'soft' keratins, Krt2-1 and Krt2-17, normally weakly expressed in the tongue but present at high levels in skin and in orthokeratinized oral dysplasia are up-regulated in the mutant tongue epithelium. This result indicates a partial trans-differentiation to an epithelium with skin-specific characteristics. Together, our findings show that Pax9 regulates appendage formation in the mammalian tongue and identify Pax9 as an important factor for the region-specific differentiation of the surface ectoderm.

Role of vocal tract morphology in speech development: perceptual targets and sensorimotor maps for synthesized French vowels from birth to adulthood

The development of speech from infancy to adulthood results from the interaction of neurocognitive factors, by which phonological representations and motor control abilities are gradually acquired, and physical factors, involving the complex changes in the morphology of the articulatory system. In this article, an articulatory-to-acoustic model, integrating nonuniform vocal tract growth, is used to describe the effect of morphology in the acoustic and perceptual domains. While simulating mature control abilities of the articulators (freezing neurocognitive factors), the size and shape of the vocal apparatus are varied, to represent typical values of speakers from birth to adulthood. The results show that anatomy does not prevent even the youngest speaker from producing vowels perceived as the 10 French oral vowels /i y u e phi o epsilon oe [symbol: see text] a/. However, the specific configuration of the vocal tract for the newborn seems to favor the production of those vowels perceived as low and front. An examination of the acoustic effects of articulatory variation for different growth stages led to the proposed variable sensorimotor maps for newbornlike, childlike, and adultlike vocal tracts. These maps could be used by transcribers of infant speech, to complete existing systems and to provide some hints about underlying articulatory gestures recruited during growth to reach perceptual vowel targets in French.

Neuronal intermediate filaments in the developing tongue of the frog Rana esculenta

The expression of several neuronal intermediate filament (NIF) proteins was investigated in the tongue of metamorphosing tadpoles (stage 38-45 of Gosner) and in adult individuals of the frog, Rana esculenta by means of immunohistochemistry. Results showed that nerve fibres at early stages of tongue development expressed peripherin (a NIF protein usually found in differentiating neurones) as well as the light- and medium molecular weight NIF polypeptide subunits (NF-L and NF-M, respectively); in the adult frog, peripherin was still found in nerve fibres reaching the fungiform papilla together with NF-M, but NF-L immunoreactivity was absent therein. Clusters of epithelial cells expressing peripherin were found in the early developing tongue before differentiation of taste organs, and NF-L and NF-H immunoreactivities were present in basal (Merkel) cells of the adult frog taste disc. Results indicate that neurones innervating the adult frog's taste disc maintain a certain plasticity in their cytoskeleton and that neuronal-like cells are present in the undifferentiated and differentiated tongue epithelium possibly playing a role in the developing and mature taste organ.

Comparison of tongue functions between mature and tongue-thrust swallowing--an ultrasound investigation

Many studies have proved that tongue thrusting plays a significant role in the etiology of some orofacial deformities. To learn more about the relationship between tongue function and the form of orofacial structures, it is important to recognize patients with abnormal swallowing patterns. A cushion scanning technique in combination with M-mode ultrasound was applied to measure and compare tongue movements between mature swallowing and tongue-thrust swallowing. Forty subjects with a mature swallowing pattern (23 female, 17 male, aged 21.8 +/- 6.1 years) and 15 subjects with a tongue-thrust swallowing pattern (8 female, 7 male, aged 13.6 +/- 6.6 years) were included in this study. Duration, range, speed, and reproducibility for each of the swallowing subphases were calculated and compared. Tongue-thrust swallowers had a longer late transport phase than mature swallowers (P <.0009), and the tongue speed was faster in the early final phase (P <.05) compared with mature swallowers. Distinctly different movements can be positively differentiated with the method used.

Development of the orohypopharyngeal cavity in normal infants and young children

OBJECTIVE

To study the growth of the oropharynx and hypopharynx in infants and young children by measuring the lengths of the segments between nasopharyngeal valve and tongue base, tongue base and arytenoids, and arytenoids and upper esophageal sphincter. These measurements will be used as references for developing manofluoroscopy to study deglutition in infants and young children.

PATIENTS AND METHODS

Twenty-three children (14 boys, 9 girls) between birth and 4 years of age were prospectively studied. All children had near normal growth parameters and were free of medical illnesses or other major medical conditions that are known to influence the pharyngeal cavity. Lateral videofluoroscopy was used to assess the pharyngeal structures during breathing. All images were digitally recorded and analyzed using a computer program designed specifically for this study.

RESULTS AND CONCLUSIONS

Statistically significant correlations were found between the age or height of the patient and the distance from velopharyngeal valve to tongue base and the distance from tongue base to arytenoids, showing a linear increase of the length of the oro- and hypopharynx with age and patient height. There was no significant difference in the pharyngeal distances between boys and girls. On the basis of these results, a linear regression comparison could be established to define the length of each pharyngeal segment for any age until 4 years and for the 50th percentile of height.

Development of the tongue and taste disks in Pelobates fuscus

In the tadpole of Pelobates fuscus the process of tongue formation starts at the 32nd developmental stage. In more advanced stages (older than 38th) fast anterior and faucial growth of the tongue fold has been observed. This process is accompanied by the development of the gustatory organs. The dorsal surface of the tongue fold, smooth at the beginning, in older tadpoles (developmental stages 36-39th) forms protrusions in which gustatory organs of the taste disk type (TDs) develop. In the 41 st tadpole developmental stage anlages of TDs are formed by elongated cells, located more or less perpendicularly to the surface of the tongue. The diameter of the sensory area of a TD at the 45th developmental stage amounts to 94 microm, while in metamorphosed individuals it reaches 130-140 microm. At the base of a TD the presence of basal cell morphologically similar to that of Merkel cell was observed at the 42nd developmental stage of a tadpole. Fully developed afferent synaptic connections in the sensory epithelium of a TD were found starting from the 44th developmental stage. Single synaptic vesicles with an electron-dense core were observed in gustatory cells as early as at the 41 st developmental stage of the tadpole. From the observations reported here it can be inferred that in Pelobates fuscus development of both the tongue and TDs is similar to that already described in the representatives of the Rana genus.

Immunohistochemical detection of the expression of keratin 14 in the lingual epithelium of rats during the morphogenesis of filiform papillae

An immunofluorescence study of the expression of keratin 14 (K14) during the formation of filiform papillae was performed and the progress of keratinization of the epithelium of the rat tongue was monitored on semi-ultrathin sections by laser-scanning microscopy. Differential interference contrast (DIC) images were also examined to provide details of histology and cell morphology. No cells with immunoreactivity specific for K14 were detected on the lingual epithelium of foetuses on embryonic days 12 and 16 (E12 and E16), when the lingual epithelium was composed of a single layer or several layers of cuboidal cells. Immunoreactivity specific for K14 was detected first on basal and suprabasal keratinocytes of the dorsal epithelium of the tongue of new-borns on postnatal day 0 (P0) and was conspicuous in juveniles on P14. The immunoreactivity was particularly strong on the basal and suprabasal keratinocytes along the connective tissue papillae. The immunoreactivity extended over the entire cytoplasm but was not detected in the nucleus. The lingual epithelium was composed of stratified squamous cells and the rounded rudiments of filiform papillae were compactly arranged at equal intervals, for the most part, and the spaces between them were narrow and indistinct. Immunostaining of K14 was distinct on basal and suprabasal keratinocytes of the filiform papillar area of tongues of juveniles on P21, when the filiform papillae were conical. The spaces between them were relatively wide and, as a result, interpapillar cell columns were clearly visible. Immunoreactivity specific for K14 in the basal and suprabasal keratinocytes of the interpapillar cell columns was recognizable but was weaker than that in cells of papillar cell columns. The thickness of the epithelium in papillar and interpapillar areas increased gradually with the development of filiform papillae. However, sizes of basal and suprabasal keratinocytes remained almost unchanged during this process. These results suggest that the basal and suprabasal keratinocytes of the filiform papillar area proliferate with the initiation of the morphogenesis of filiform papillae and the keratinization of the epithelium. In addition, it appears that, after P14, the basal and suprabasal keratinocytes of the interpapillar area proliferate to supply the keratinocytes of the expanding interpapillar regions.

Expression of BDNF and TrkB in mouse taste buds after denervation and in circumvallate papillae during development

BDNF (brain-derived neurotrophic factor) is a member of the neurotrophin family which affects the proliferation and survival of neurons. Using an immunocytochemical method, we examined the expression of BDNF and its receptor, TrkB, in the taste bud cells of the circumvallate papillae of normal mice and of mice after transection of the glossopharyngeal nerves. We additionally observed the expression of BDNF and TrkB in the developing circumvallate papillae of late prenatal and early postnatal mice. In normal untreated mice, BDNF was expressed in most of the taste bud cells; TrkB was detected in the plasma membrane of taste bud cells and in the nerve fibers. Double-labeling studies showed that BDNF and NCAM (neural cell adhesion molecule) or TrkB and NCAM colocalized in some of the taste bud cells, but that most taste bud cells were immunopositive for only BDNF or TrkB. NCAM-immunoreactive cells are known to be type-III cells, which have afferent synaptic contacts with the nerve terminals. Five days after denervation, the number of taste buds and nerve fibers markedly decreased; however, the remaining taste bud cells still expressed BDNF and TrkB. By 10 days after denervation, most of the taste buds had disappeared, and there were a few TrkB-immunoreactive nerve fibers in the connective tissue core. By 4 weeks after denervation, numerous TrkB-immunoreactive nerve fibers had invaded the papillae, and a few taste buds expressing BDNF and TrkB had regenerated. At E (embryonic day) 15 during development, the circumvallate papillae appeared, and then TrkB-immunoreactive nerve fibers entered the connective tissue core, and some of these fibers further invaded among the dorsal epithelial cells of the papillae. TrkB-immunoreactive oval-shaped cells were occasionally found in the dorsal epithelium. Such TrkB-immunoreactive nerve fibers and cells were also observed at E16-18. However, BDNF was not expressed in the papillae through the late prenatal days of E15 to E18. At P (postnatal day) 0, a cluster of BDNF-and TrkB-immunoreactive cells appeared in the dorsal epithelium of the papillae, and was presumed to be primitive taste buds. We conclude that TrkB-immunoreactive nerve fibers are necessary for papillary and taste bud formation during development and for the regeneration of taste buds after denervation. BDNF in the taste bud cells may act as a neurotrophic factor for innervating sensory neurons--through TrkB receptors of the axons of those neurons, and also may exert autocrine and paracrine trophic actions on neighboring taste bud cells by binding to their TrkB receptors.

A quantitative study of fungiform papillae and taste pore density in adults and children

Male children (8-9 years) are reported to have a higher sensitivity than male adults to the sweet tastant sucrose when small regions of the anterior tongue are stimulated. The present study investigated the hypothesis that the higher sensitivity was due to a greater density of fungiform papillae and taste pores (buds), since it has been reported in adults that increased densities of these two structures correlates with increased taste suprathreshold sensitivity [Physiol. Behav. 47 (1990) 1213]. Quantitative measures of the number and size of papillae and pores in two areas of the tongue that had been shown to have a higher sensitivity for sucrose were achieved in 20 male children 8-9 years of age and 20 adults 18-30 years of age, using videomicroscopy and NIH Image software. Customized templates and a red food dye were used to define the equivalent tongue locations across the 40 subjects and taste pores were stained with methylene blue. Children were found to have substantially smaller papillae than adults but significantly higher papilla densities in both areas. Similar numbers of taste pores per papilla were found for both groups, resulting in children having much higher taste pore densities in each area than adults. Other differences included smaller taste pore diameters in children compared to adults, and the papillae tended to be rounder in children. Overall, the results support the hypothesis that the higher densities of fungiform papillae and taste pores in children underlie their greater sensitivity for sucrose in the two areas. In addition, the anatomical differences between adults and children indicate the sense of taste is in a state of development during mid-childhood.

Angioarchitectural characteristics of the anterodorsal surface of aging and young rabbit tongue: scanning electron microscopy study

The three-dimensional angioarchitecture of young and aging rabbit tongues were studied using a vascular corrosion cast method. The vascular network of different lingual papillae were observed by scanning electron microscope (SEM). Young animals showed filiform papillae distributed all over considered area, with fungiform ones among them. In comparison to developed specimens, young rabbits demonstrated dense and higher organization of microvascular network.

Taste development: differential growth rates of tongue regions in humans

There is a paucity of information about the anatomical and functional development of the human gustatory system. Although the anatomical development of the taste-sensitive fungiform, circumvallate and foliate papillae in the respective anterior, posterior and latero-posterior regions of the dorsal surface of the tongue has been well documented in the fetus, there is limited information about how these regions grow and when they exhibit adult function. The present study is concerned with determining when the growth of one of these taste-sensitive regions becomes adult in size, namely, the anterior region, and how this growth compares with that of the remaining posterior region. Two-hundred and thirty-two living subjects aged between 4 and 32 years participated. Following the identification and marking of a series of landmarks on the dorsal surface of the tongue with blue food dye, five measurements of the width and length of various parts of the tongue allowed calculation of the growth of the anterior and posterior regions. The results indicate that the fungiform papillae-rich anterior region attains adult-size by 8-10 years of age whilst the posterior region continues to grow until 15-16 years. Interestingly, this early development is not matched by achievement of adult function [Dev. Brain Res. 82 (1994) 286] or adult size papillae or taste pores [Dev. Brain Res., submitted]. Finally, the findings of the present study will allow studies of the development of taste function in humans to be conducted using equivalent tongue areas in subjects of different ages.

Morphometrically observable aging changes in the human tongue

Like the outside parts of the nose and the ear but unlike most other organs, the tongue continues to grow at advanced age. Therefore, internal morphological aging processes must also proceed in a specific way. We used sectioned specimens of the radix linguae from 111 humans. The specimens were fixed in 4% formalin solution, embedded in paraffin, then cut at a thickness of 5 microm and stained with hematoxylin-eosin. The structures of interest were measured with an automatic image analyzing system (SIS, Münster, Germany). The statistical analysis package SPSS was used for correlation and regression analysis and testing of the resulting coefficients. The mean cross-sectional area of the muscle fibers increases sharply during youth, but remains at a high level into old age. After the age of seventy, it increases again. With muscles of the locomotor apparatus, this same parameter decreases after the fifth decade. We have demonstrated the process of adipose tissue formation in muscles and serous glands. Gender differences in the aging process could be clearly shown. Numerous oncocytes were visible in ducts from elder persons.

Syndecan-1 expression during postnatal tooth and oral mucosa development in rats aged from two days to six weeks

Syndecans are a family of heparan sulphate proteoglycans that regulate cell-matrix interactions that influence cell growth, proliferation and morphology. The aim of this study was to observe changes in the expression of Syndecan-1 in the developing epithelium of the rat oral mucosa and in the epithelial cell rests of Malassez in the developing periodontium of normal rat molars, from late crown development through to early eruption. Immuno-histochemistry (Syndecan-1 N-18) and histochemistry (Alcec Bluel were used to observe changes in the expression of Syndecon-1 in rats aged two to 42 days. Results indicated that during normal tooth development in the rat, labelling or staining of variable intensity for Syndecan-1 was demonstrated in the stratified oral epithelium above the stratum basale in the rat tongue and palate, and in ameloblasts of the developing molar in rats aged two to 14 days. Histochemical staining of the predentine and dentine layers was consistent in all specimens. Labelling or staining for Syndecan-1 was negative in the rat periodontal ligament, which may suggest that either Syndecan-1 was not expressed during normal molar root development or that continued work is required for identification of a suitable label in rats.

Development of anterior gustatory epithelia in the palate and tongue requires epidermal growth factor receptor

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.

Linear dimensions of the upper airway structure during development: assessment by magnetic resonance imaging

The upper airway undergoes progressive changes during childhood. Using magnetic resonance imaging (MRI), we studied the growth relationships of the tissues surrounding the upper airway (bone and soft tissues) in 92 normal children (47% males; range, 1 to 11 yr) who underwent brain MRI. None had symptoms of sleep-disordered breathing or conditions that impacted on their upper airway. MRI was performed under sedation. Sequential T1-weighted spin echo sagittal and axial sections were obtained and analyzed on a computer. We measured lower face skeletal growth along the midsagittal and axial oropharyngeal planes. In the midsagittal plane the mental spine-clivus distance related linearly to age (r = 0.86, p < 0.001). Along this axis, the dimensions of tongue, soft palate, nasopharyngeal airway, and adenoid increased with age and maintained constant proportion to the mental spine-clivus distance. Similarly, a linear relationship was noted for mandibular growth measured along the intermandibular line on the axial plane and age (r = 0.78, p < 0.001). In addition, the intertonsillar, tonsils, parapharyngeal fat pads, and pterygoids widths maintained constant proportion to intermandibular width with age. We conclude that the lower face skeleton grows linearly along the sagittal and axial planes from the first to the eleventh year. Our data indicate that soft tissues, including tonsils and adenoid, surrounding the upper airway grow proportionally to the skeletal structures during the same time period.

Morphological differentiation of taste organs in the ontogeny of Salamandra salamandra

Morphological studies presented here provide additional cytological evidence that in the postnatal development of Salamandra salamandra there are two successive generations of taste organs: premetamorphic taste buds (TBs) in larval forms and taste disks (TDs) in postmetamorphic animals. The TBs have been found in the epithelium of the whole oropharyngeal cavity of larval forms, while in adults TDs appear only at the end of metamorphosis. The TDs can be papillary (or fungiform) on the soft (secondary) tongue and non-papillary outside the tongue. Two main cyto-morphological criteria distinguishing TDs from TBs have been established: (1) high differentiation of "nonsensory" components of a taste organ into several kinds of cells (often named "associate cells")--at least mucous cells and, separating them, wing cells; (2) a considerably larger area of the sensory epithelium than that in TBs, as the consequence of the large size of the mucous cells. In contrast to TDs each TB consists of longitudinally elongated supporting cells and taste cells, as well as of horizontally oriented basal cells, adjacent to the basement membrane. The sensory area in TBs measures 10-12 microm in diameter, while that in TDs has diameter of 45-90 microm. The anlage of the secondary tongue appears as a small folding of the floor epithelium just in front to the tip of the primary tongue in larvae 3 cm long, and is definitely formed in an animal with body length of about 6 cm.

Epithelial overexpression of BDNF or NT4 disrupts targeting of taste neurons that innervate the anterior tongue

Brain-derived neurotrophic factor (BDNF) and neurotrophin-4 (NT4) are essential for the survival of geniculate ganglion neurons, which provide the sensory afferents for taste buds of the anterior tongue and palate. To determine how these target-derived growth factors regulate gustatory development, the taste system was examined in transgenic mice that overexpress BDNF (BDNF-OE) or NT4 (NT4-OE) in basal epithelial cells of the tongue. Overexpression of BDNF or NT4 caused a 93 and 140% increase, respectively, in the number of geniculate ganglion neurons. Surprisingly, both transgenic lines had severe reduction in fungiform papillae and taste bud number, primarily in the dorsal midregion and ventral tip of the tongue. No alterations were observed in taste buds of circumvallate or incisal papillae. Fungiform papillae were initially present on tongues of newborn BDNF-OE animals, but many were small, poorly innervated, and lost postnatally. To explain the loss of nerve innervation to fungiform papillae, the facial nerve of developing animals was labeled with the lipophilic tracer DiI. In contrast to control mice, in which taste neurons innervated only fungiform papillae, taste neurons in BDNF-OE and NT4-OE mice innervated few fungiform papillae. Instead, some fibers approached but did not penetrate the epithelium and aberrant innervation to filiform papillae was observed. In addition, some papillae that formed in transgenic mice had two taste buds (instead of one) and were frequently arranged in clusters of two or three papillae. These results indicate that target-derived BDNF and NT4 are not only survival factors for geniculate ganglion neurons, but also have important roles in regulating the development and spatial patterning of fungiform papilla and targeting of taste neurons to these sensory structures.

The secondary tongue of Salamandra salamandra: histochemical and ultrastructural aspects of the developing lingual epithelium

The development of the lingual epithelium of Salamandra salamandra was investigated with emphasis on histochemical and ultrastructural aspects. The temporal and spatial occurrence and the typical appearance of various cell types; i.e. pavement cells, replacement pavement cells, basal cells, mitochondria rich cells, goblet cells and glandular cells have been analysed and documented in detail from the young larval stage up to the metamorphosed animal (2 months after metamorphosis). It is shown that anatomical re- and de novo-constructions related to the formation of the secretory tongue led to distinct changes in the cellular equipment of the epithelium of the tongue, including various histochemical properties. Finally, functional aspects of the morphological characteristics are discussed in detail and compared with respective findings in other species.

Embryonic, fetal, and neonatal tongue myoblasts exhibit molecular heterogeneity in vitro

Variable gene expression patterns have been shown to exist between embryonic, fetal, and neonatal lineages of limb skeletal myoblasts in vitro and in vivo. In this study, we examined the molecular phenotype of embryonic, fetal, and neonatal tongue myoblasts in primary culture for comparison with in vivo developmental tongue myoblasts. Myogenic regulatory factor (MRF) and myosin heavy chain (MHC) gene expression were determined in culture during both growth and differentiation conditions by PCR, immunoblotting, and immunohistochemistry. Unlike their in vivo tongue myoblast equivalents, developmental tongue myoblast cultures featured the expression of MyoD when kept in growth conditions. Differentiation conditions in vitro induced myogenic tongue lineages to maintain characteristics of their in vivo morphologic and contractile gene phenotype. Both in vivo and in vitro, embryonic tongue lineages predominantly expressed MHC-embryonic isoforms, while fetal and neonatal tongue lineages predominantly expressed fast and perinatal isoforms of contractile genes. A notable difference from the in vivo condition that was observed in differentiated tongue myotubes in vitro was the presence of the MHC-slow protein. It was previously demonstrated that MHC-slow protein was undetectable during the in vivo development of the tongue musculature despite the abundance of slow isoform transcripts. The present characterization of primary tongue myogenic cultures indicates that murine myoblast heterogeneity exists primarily between developmental lineages at the level of contractile gene expression. Outside their native surroundings, developmental myogenic tongue populations are unable to recapitulate the determination and differentiation molecular profiles that occur in vivo.

Sonic hedgehog signaling pathway in vertebrate epithelial appendage morphogenesis: perspectives in development and evolution

Vertebrate epithelial appendages are elaborate topological transformations of flat epithelia into complex organs that either protrude out of external (integument) and internal (oral cavity, gut) epithelia, or invaginate into the surrounding mesenchyme. Although they have specific structures and diverse functions, most epithelial appendages share similar developmental stages, including induction, morphogenesis, differentiation and cycling. The roles of the SHH pathway are analyzed in exemplary organs including feather, hair, tooth, tongue papilla, lung and foregut. SHH is not essential for induction and differentiation, but is involved heavily in morphogenetic processes including cell proliferation (size regulation), branching morphogenesis, mesenchymal condensation, fate determination (segmentation), polarizing activities and so on. Through differential activation of these processes by SHH in a spatiotemporal-specific fashion, organs of different shape and size are laid down. During evolution, new links of developmental pathways may occur and novel forms of epithelial appendages may emerge, upon which evolutionary selections can act. Sites of major variations have progressed from the body plan to the limb plan to the epithelial appendage plan. With its powerful morphogenetic activities, the SHH pathway would likely continue to play a major role in the evolution of novel epithelial appendages.

Neonatal chorda tympani transection permanently disrupts fungiform taste bud and papilla structure in the rat

The present report examined the morphology of fungiform papillae in adult rats that received bilateral chorda tympani transection at 10 days of age. Tongue tissue was examined using surface-structure analysis. Counts were made of fungiform papillae with a pore, fungiform papillae with no pore and fungiform papillae with a keratinized conical surface; a feature referred to as "filiform-like. " Neonatal chorda tympani nerve transection resulted not only in a loss of taste buds but also in a permanent loss in numbers of fungiform papillae. Compared with an average of 152 fungiform papillae in sham-operated control rats, there was an average of only 54 fungiform papillae after neonatal chorda tympani transection. Nearly 80% of these fungiform papillae in neonatal chorda tympani transected rats were filiform-like. No filiform-like papillae were noted in sham-operated rats. These results suggest that the chorda tympani nerve is necessary during an early postnatal period of development to maintain normal fungiform papillae morphology.

Comparative angioarchitectural formation seen in microvascular cast specimens of the fungiform papillae in the weaning period and adult rat tongue

The purpose of this study was an attempt to identify the functional and comparative angioarchitectural differences between the sexes, and the developmental processes seen in microvascular cast specimens (MVCS) of the formation of the fungiform papillae (FuP) geometrically and regularly distributed on the anterodorsal surface in the weaning period and in the adult rat tongue. The basic microvascular structure seen in the MVCS of FuP of both the weaning and adult rat tongue consisted of several ascending (As. b) and descending branches (Ds. b) and a loop structure (L. st), and the cylindrical network structure of the L. st made up of the open-hole formation of the C form of the upper and lower microvascular structures. In the lateral view, the MVCS of FuP has a bamboo basket-like shape, and by means of the three-dimensional expansion of the surface area, effectively plays an assistant functional role in receiving the taste of foods and liquids. There were obviously no sex and morphological differences in the developmental process as to shape, but there was some difference between the weaning period and the adult rat in size in the MVCS of FuP.

Neuron/target matching between chorda tympani neurons and taste buds during postnatal rat development

During postnatal development, a relationship is established between the size of individual taste buds and number of innervating neurons. To determine whether rearrangement of neurons that innervate taste buds establishes this relationship, we labeled single taste buds at postnatal day 10 (P10) and again at either P15, P20, or P40 with retrograde fluorescent neuronal tracers. The number of single- and double-labeled geniculate ganglion cells was counted, and the respective taste bud volumes were measured for the three groups of rats. The current study replicates findings from an earlier report demonstrating that the larger the taste bud, the more geniculate ganglion cells that innervate it. This relationship between taste bud size and number of innervating neurons is not apparent until P40, when taste bud size reaches maturity. These findings are extended here by demonstrating that the number of neurons that innervate taste buds at P10, when taste bud size is small and relatively homogeneous, predicts the size that the respective taste bud will become at maturity. Moreover, while there is some neural rearrangement of taste bud innervation from P10 to P40, rearrangement does not impact the relationship between taste bud size and innervating neurons. That is, the neurons that maintain contact with taste buds from P10 through P40 accurately predict the mature taste bud size. Therefore, the size of the mature taste bud is determined by P10 and relates to the number of sensory neurons that innervate it at that age and the number of neurons that maintain contact with it throughout the first 40 days of postnatal development.

Lbx1 is required for muscle precursor migration along a lateral pathway into the limb

In mammalian embryos, myogenic precursor cells emigrate from the ventral lip of the dermomyotome and colonize the limbs, tongue and diaphragm where they differentiate and form skeletal muscle. Previous studies have shown that Pax3, together with the c-Met receptor tyrosine kinase and its ligand Scatter Factor (SF) are necessary for the migration of hypaxial muscle precursors in mice. Lbx1 and Pax3 are co-expressed in all migrating hypaxial muscle precursors, raising the possibility that Lbx1 regulates their migration. To examine the function of Lbx1 in muscle development, we inactivated the Lbx1 gene by homologous recombination. Mice lacking Lbx1 exhibit an extensive loss of limb muscles, although some forelimb and hindlimb muscles are still present. The pattern of muscle loss suggests that Lbx1 is not required for the specification of particular limb muscles, and the muscle defects that occur in Lbx1(−/−) mice can be solely attributed to changes in muscle precursor migration. c-Met is expressed in Lbx1 mutant mice and limb muscle precursors delaminate from the ventral dermomyotome but fail to migrate laterally into the limb. Muscle precursors still migrate ventrally and give rise to tongue, diaphragm and some limb muscles, demonstrating Lbx1 is necessary for the lateral, but not ventral, migration of hypaxial muscle precursors. These results suggest that Lbx1 regulates responsiveness to a lateral migration signal which emanates from the developing limb.

The epithelium of the tongue of Ambystoma mexicanum. Ultrastructural and histochemical aspects

The distribution pattern of taste buds and goblet cells and histochemical and ultrastructural aspects of the tongue epithelium of Ambystoma mexicanum are here described. This study is also concerned with the developmental stages and origins of the epithelial cells. Pavement cells and goblet cells of the stratum superficiale are replaced by basal cells of the stratum germinativum in larvae and neotenous adults. The pavement cells of the larvae are characterized by a marginal layer of mucin grana. Decompaction of the mucins occurs immediately before extrusion in the adult. The larval goblet cell type (type I), which is also present in the adult, contains unfused grana of irregular shape. At the tip of the tongue, a further type (type II) of goblet cells is found. In the type II cells the intracellular secretory grana fuse to a single homogeneous mass. Leydig cells of the tongue epithelium are discerned by light microscopy first in the semi-adult, apparently correlated with partial metamorphosis. In the course of ontogenesis and induced metamorphosis the secretion changes to neutral glycoconjugates. The mucins of the pavement cells change first followed by those of the goblet cells. The glands of the secondary tongue show a dorso-ventral pattern of varying secretory qualities. Taste buds are found at the anterior margin of the tongue and along the base of the gill clasps in the early larva. They are already distributed all over the tongue at the end of the early larval phase.

Compensatory defects associated with mutations in Hoxa1 restore normal palatogenesis to Hoxa2 mutants

The rhombencephalic neural crest play several roles in craniofacial development. They give rise to the cranial sensory ganglia and much of the craniofacial skeleton, and are vital for patterning of the craniofacial muscles. The loss of Hoxa1 or Hoxa2 function affects the development of multiple neural crest-derived structures. To understand how these two genes function together in craniofacial development, an allele was generated that disrupts both of these linked genes. Some of the craniofacial defects observed in the double mutants were additive combinations of those that exist in each of the single mutants, indicating that each gene functions independently in the formation of these structures. Other defects were found only in the double mutants demonstrating overlapping or synergistic functions. We also uncovered multiple defects in the attachments and trajectories of the extrinsic tongue and hyoid muscles in Hoxa2 mutants. Interestingly, the abnormal trajectory of two of these muscles, the styloglossus and the stylohyoideus, blocked the attachment of the hyoglossus to the greater horn of the hyoid, which in turn correlated exactly with the presence of cleft palate in Hoxa2 mutants. We suggest that the hyoglossus, whose function is to depress the lateral edges of the tongue, when unable to make its proper attachment to the greater horn of the hyoid, forces the tongue to adopt an abnormal posture which blocks closure of the palatal shelves. Unexpectedly, in Hoxa1/Hoxa2 double mutants, the penetrance of cleft palate is dramatically reduced. We show that two compensatory defects, associated with the loss of Hoxa1 function, restore normal attachment of the hyoglossus to the greater horn thereby allowing the palatal shelves to lift and fuse above the flattened tongue.

Alpha-gustducin-immunoreactive solitary chemosensory cells in the developing chemoreceptorial epithelium of the rat vallate papilla

The presence of solitary chemosensory cells was studied in rat vallate papillae during the first week of post-natal life by alpha-gustducin immunocytochemistry. In 1- to 3-day-old rats, isolated alpha-gustducin-immunoreactive cells were found within the epithelium of the vallate papilla. These cells, mainly located in the basal layer, were scattered among keratocytes and wrapped in alpha-gustducin-negative epithelial cells in a glia-like fashion. The alpha-gustducin-immunoreactive cells were usually round and some of them gave rise to short, large processes directed towards the lumen of the oral cavity or the basal lamina. Rarely, some cells showed an evident bipolar shape. Small taste buds containing either alpha-gustducin-immunoreactive or alpha-gustducin-negative cells appeared in the vallate papillae of 4-day-old rats in which isolated, bipolar-shaped alpha-gustducin-immunoreactive cells were also found. After the first week of post-natal life, the taste buds appeared basically similar to those of adult animals. In conclusion, the present study demonstrates that the presence of epithelial cells with characteristics of solitary chemosensory cells precedes the development of the taste buds.

Alterations in size, number, and morphology of gustatory papillae and taste buds in BDNF null mutant mice demonstrate neural dependence of developing taste organs

Sensory ganglia that innervate taste buds and gustatory papillae (geniculate and petrosal) are reduced in volume by about 40% in mice with a targeted deletion of the gene for brain-derived neurotrophic factor (BDNF). In contrast, the trigeminal ganglion, which innervates papillae but not taste buds on the anterior tongue, is reduced by only about 18%. These specific alterations in ganglia that innervate taste organs make possible a test for roles of lingual innervation in the development of appropriate number, morphology, and spatial pattern of fungiform and circumvallate papillae and associated taste buds. We studied tongues of BDNF null mutant and wild-type littermates and made quantitative analyses of all fungiform papillae on the anterior tongue, the single circumvallate papilla on the posterior tongue, and all taste buds in both papilla types. Fungiform papillae and taste buds were reduced in number by about 60% and were substantially smaller in diameter in mutant mice 15-25 days postnatal. Remaining fungiform papillae were selectively concentrated in the tongue tip region. The circumvallate papilla was reduced in diameter and length by about 40%, and papilla morphology was disrupted. Taste bud number in the circumvallate was reduced by about 70% in mutant tongues, and the remaining taste buds were smaller than those on wild-type tongues. Our results demonstrate a selective dependence of taste organs on a full complement of appropriate innervation for normal growth and morphogenesis. Effects on papillae are not random but are more pronounced in specific lingual regions. Although the geniculate and petrosal ganglia sustain at least half of their normal complement of cell number in BDNF -/- mice, remaining ganglion cells do not substitute for lost neurons to rescue taste organs at control numbers. Whereas gustatory ganglia and the taste papillae initially form independently, our results suggest interdependence in later development because ganglia derive BDNF support from target organs and papillae require sensory innervation for morphogenesis.

G2 restriction point within populations of hepatocytes and tongue keratinocytes in young, growing mice

The authors studied the effect of either extracts from liver (LE) or the malignant tumour ES2 (TE) or plasma from intact mice (PI) or tumour-bearing animals (PT) on the mitotic activity of the hepatocytes and tongue keratinocytes in young, growing C3H/s male mice (28+/-1 days old). Animals standardized for periodicity analysis were injected intraperitoneally with either TE, LE, PI, PT, or saline (S) at 16:00 h with 0.01 ml of sample/g of body weight and were then killed at (time of day/h post-injection) 20:00/04, 00:00/08, and 04:00/12. Colchicine (2 microg/g) was injected 4 h before death. Samples of the liver and tongue from each animal were processed for histology and assessment of mitotic index. The results were expressed as colchicine-arrested metaphases/1000 nuclei. The TE and LE stimulated the mitotic activity of hepatocytes and tongue keratinocytes. Taking into account the time elapsed between the injections and the measurements made in these light-dark synchronized animals, we conclude that the increase in mitotic index observed in those tissues stemmed from a reinitiation of cell-cycle traverse in a subpopulation of G2-arrested, noncycling cells.

Merkel cells are responsible for the initiation of taste organ morphogenesis in the frog

Taste organs in the frog have a distinctive cell type located exclusively in the basal portion. In the same fashion as type III cells in mammalian taste buds, these basal cells show immunoreactivity for serotonin antibody. Further, these cells are morphologically similar to epidermal Merkel cells. To determine the significance of these serotonergic basal cells, we examined the early development of taste organs during metamorphosis of the frog by focusing on the origin and possible roles of serotonergic basal cells. For convenience of description, five stages of development (metamorphic stage to climax stages A-D) are defined. In the metamorphic stage, a few noninnervated Merkel cells appear at the upper layer of the lingual epithelium. No neuronal elements are seen in the epithelium at this stage. At climax stages A-B, immature fungiform papillae become discernible in the dorsal surface of the tongue, where the Merkel cells are located. Merkel cells then move downward and extend their cytoplasmic processes toward the basal lamina. These cells are identified by their intense immunoreactivity for serotonin. During the later stages, many nerve fibers in the subepithelial connective tissue approach the epithelium containing Merkel cells. At climax stages C-D, Merkel cells extend cytoplasmic processes along the basal lamina toward the center of the newly forming fungiform papillae. The morphology of these Merkel cells exactly coincides with that of serotonergic basal cells in adult taste organs. Profuse exocytotic release of dense-cored granules of Merkel cells toward the nerve fibers through the basal lamina is frequently seen in these stages. The present study indicates that serotonergic basal cells are derived from intraepithelial Merkel cells, which act as target sites for growing nerves and may be responsible for the initiation of taste organ morphogenesis.

Changes of the lingual epithelium in Ambystoma mexicanum

Changes in the lingual epithelium during ontogenesis and after induced metamorphosis in Ambystoma mexicanum are described as observed by light microscopy and scanning electron microscopy. The epithelium of the tongue is always multilayered in the larva as well as in the adult. It consists of a stratum germinativum with little differentiated basal cells and a stratum superficiale (superficial layer) with specialized superficial cells and goblet cells. Usually, there are more than two layers because of a stratum intermedium consisting of replacement cells. The apical cell membrane of the superficial cells is perforated by fine pores. Its most typical feature are microridges. Maturing superficial cells possess microvilli. Goblet cells occur in early larvae primarily in the centre of the tongue. They spread throughout the dorsal face of the tongue as their numbers increase during ontogenesis. The small apices of the goblet cells are intercalated in the wedges between the superficial cells. Leydig cells are not found on the larval tongue but on that of adults. Due to metamorphosis, the epithelium of the tongue changes. It is furrowed in its anterior part. The furrows house the openings of the lingual glands. The surface is further modulated by ridges which are densely coated by microvilli and which bear the taste buds. The villi of the tongue which lack extrusion pores show cilia and microvilli but lack microridges. The Leydig cells disappear during metamorphosis. In addition to the two types of goblet cells found in different regions of the glandular tubules, goblet cells occur in the caudal part. They secrete directly into the cavity of the mouth. The posterior part is characterised by a dense coat of cilia.