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PubMed1993

Statistical analysis of neural organization.

1. The responses of 32 taste neurons in the solitary nucleus of the rat to 12 stimuli were analyzed with multidimensional scaling (MDS) and cluster analysis (CA) procedures. These analyses of empirical taste data were compared with similar analyses of two model data sets of known configuration to help clarify the implications of these methods commonly used in forming conclusions about the organization of the taste system. 2. To relate to possible conclusions about groupings in taste, both model data sets were chosen as the best possible examples of ungrouped data, the first being completely regular (in the form of a checkerboard) across the taste space, the second randomly arranged. The analysis of the present empirical data appear to be similar to the present ungrouped models, more so the random than the regular model, in the sense that all are amenable to grouping. 3. Because of the similarity of these model MDS and CA solutions to the present empirical solutions and to most published analyses of this sort, the idea is suggested that the appearance of the plots per se for empirical data does not support the conclusion of grouping. And, technically, MDS and CA do not have the statistical power to provide conclusions about issues of neural organization. 4. MDS and CA analyses have two very powerful roles relating to their ability to disclose the hidden organization of complex data sets; they may lend support for or refute theories about the data sets developed from other considerations, and may help generate theories for further consideration. The question of groupings is only one of many such issues. 5. Because data in the present and other reports are quite adequately accounted by MDS solutions of low dimensionality, it is suggested that their organization is characterized as continuous (i.e., rather than belonging to several disjoint spaces). 6. The use of correlations as distance measures in MDS and CA procedures distorts the spatial solutions, making analysis by visual inspection misleading. For example, using correlations, the true or natural spatial arrangements of data sets are probably less circular or spherical than shown in published MDS solutions. Also they are probably more evenly distributed across the space in the sense that the points are actually more concentrated toward the centers of the spaces; this may have strong influences on interpretations of the general form of the solutions. CA solutions can be influenced in analogous fashion. These problems of distortion of the solutions can be avoided with use of direct, linear estimates of distances. (ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1994

Responses of single hamster parabrachial neurons to binary taste mixtures of NaCl with sucrose or QHCl.

1. Although human psychophysical responses to taste mixtures have been investigated extensively, there have been few reports on the neurophysiological coding of taste mixtures in the mammalian gustatory system. In recent studies we have investigated the responses of single third-order neurons in the hamster parabrachial nucleus (PbN) to anterior tongue stimulation with binary mixtures of heterogenous taste stimuli including sucrose+QHCl, sucrose+citric acid, and NaCl+citric acid. Some of these stimulus combinations evoked mixture suppression, or response frequencies that were less than that evoked by the more effective component (MEC) presented alone, which is analogous to the mixture suppression reported in human psychophysical studies of similar taste mixtures. In the current report we extend our investigation to include NaCl+QHCl and NaCl+sucrose mixtures. 2. The action potentials of single PbN neurons were recorded extracellularly. Four concentrations of each stimulus were employed: NaCl and sucrose at 0.001, 0.01, 0.1, and 1.0 M; QHCl at 0.00032, 0.0032, 0.032, and 0.1 M. All stimuli were tested alone and in mixture; the NaCl+sucrose and NaCl+QHCl mixtures were formed by pairing the four concentrations of each stimulus with the strongest concentration of the other stimulus. 3. For both NaCl+sucrose and NaCl+QHCl mixtures, the response frequencies evoked by the mixtures did not differ from those evoked by the MEC presented alone, whether averaged across all neurons or across subgroups of NaCl- or sucrose-best cells. Furthermore, the across-neuron patterns (ANPs) of mixture responses were similar to those of the MECs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Gustatory neural coding in the monkey cortex: the quality of saltiness.

1. We analyzed the activity of single neurons in the insularopercular cortex of four alert cynomolgus monkeys in response to the oral application of four basic taste stimuli (glucose, NaCl, HCl, and quinine HCl) and fruit juice and to a range of 17 sodium and lithium salts with a variety of anions. 2. Neurons responsive to gustatory stimulation were encountered in an area of 34.5 mm3 (2.0 mm A-P x 2.5 mm M-L x 6.9 mm D-V). Taste cells composed 46 (4.5%) of the 1,028 neurons whose sensitivities were tested. Nongustatory cells included those responsive to mouth movements (20.4%), tactile stimulation in the mouth (3.4%), and visual approach of the stimulus (0.7%). The functions of the remaining 71.0% could not be determined. 3. The mean spontaneous discharge rate of these cortical taste cells was 4.4 spikes/s (range, 0.1-23.8 spikes/s). The mean breadth-of-tuning coefficient was a moderate 0.72 (range, 0.15-1.00). Inhibitory responses were nearly nonexistent. 4. There was no evidence that taste cells with similar functional characteristics were clustered within the cortex, i.e., there was no apparent topographic organization of taste qualities. 5. The 46 taste cells were divisible into three functional types, based on their response profiles to the four basic stimuli used here. The types could be characterized as sweet-, salt-, and quinine-oriented. 6. A taste space was generated from correlations among the response profiles evoked by the stimulus array. The 17 salts formed a coherent group from which the other basic stimuli were separated. Glucose was closest to the salt group, followed by quinine and HCl. 7. Within the salt group, the four halides (NaCl, LiCl, NaBr, LiBr) formed a tight cluster; the 11 stimuli with acetate, citrate, phosphate, sulfate, and tartrate anions joined with monosodium glutamate and Na bicarbonate to form two closely related clusters; Na succinate was somewhat distinct from the others, and Na carbonate was most separate. 8. The relative qualities of the salts did not relate systematically to anionic size, promotion of sodium transport, or molar conductivity. 9. The configuration of stimuli in this taste space was compared with that in a space derived from human descriptions of the relative similarities of many of these same stimuli. Using the position of NaCl as a reference, the distances to all other stimuli common to the two studies was measured.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1996

Responses of primate cortical neurons to unitary and binary taste stimuli.

1. The responses of 126 neurons in primary gustatory cortices of two rhesus monkeys were recorded during sapid stimulation of the tongue with 18 taste stimuli. Ten of these stimuli were dissolved in distilled water (DW): 1.0 M sucrose (Suc), 0.1 M and 0.03 M sodium chloride (NaCl), 0.003 M hydrochloric acid (HCl), 0.001 M quinine hydrochloride (QHCl), 0.03 M monosodium glutamate (MSG), 0.03 M polycose, 0.3 M glycine, 0.1 M proline, and 0.1 M malic acid. Seven other stimuli were dissolved in 0.03 M MSG; the last stimulus was a mixture of 1.0 M Suc and 0.03 M NaCl. 2. The average spontaneous rate (2.2 +/- 0.2 spikes/s, mean +/- SE) and response to DW (2.5 +/- 0.2) of these 126 neurons was low but within the range previously reported for neurons in primate taste cortex. Suc was the most effective stimulus for 24.1% of the neurons tested followed by NaCl (15.7%), QHCl (14.8%), HCl (11.1%), MSG (10.2%), and other miscellaneous unitary gustatory stimuli (8.3%). Binary taste mixtures were the most effective stimuli for 15.7% of the sample. The net responses (corrected for DW, in spikes/s) for Suc-best (3.3), NaCl-best (4.3), HCl-best (3.4), QHCl-best (2.3), and MSG-best (4.1) were sluggish, but comparable with that reported previously. 3. The response breadth of the 82 neurons that responded best to either Suc, NaCl, HCl, or QHCl measured with the entropy coefficient indicated a moderate response breadth for these neurons (mean = 0.79; range = 0.30-0.98). According to the response criteria adopted in this experiment (water response +/- 1.96 SD), however, 81 of these 82 neurons (98.1%) responded to only one or two of the four basic taste stimuli. The disparity between the entropy- and criterion-based measures of response derive from the nature of the two statistics. Adjustments that would make the entropy statistic less inclusive and the definition of a response according to statistical criteria less exclusive would increase their concordance. 4. Three multivariate statistics (cluster, principal axis factor, and multidimensional analysis) were used to analyze the data. Cluster analysis enabled us to divide the 82 taste neurons into groups on the basis of response similarity. Each of the four largest groups was dominated by neurons that responded best to one of the four basic taste stimuli: Suc, NaCl, QHCl, and HCl (ranked in descending order); the fifth largest cluster contained neurons that responded best to MSG. Principal axis factor analysis demonstrated that 80.8% of the total variance could be accounted for by three factors. Neurons responding best to Suc, NaCl, and QHCl each were closely associated with one of those three factors, but the loadings of the HCl-best neurons were evenly distributed across all three factors. The communality coefficient of these three factors was > 80% for the Suc-, NaCl-, HCl-, and QHCl-best neurons; the MSG-best neurons, by comparison, had very few high loadings on any of these three factors and a correspondingly low communality coefficient of 40.4%, a difference that was statistically significant from the other four groups. Thus the three factors related to Suc-, NaCl-, HCl-, and QHCl-best neurons are not relevant to MSG-best neurons. We used multidimensional analysis to arrange the neurons that responded best to Suc, NaCl, HCl, QHCl, and MSG into five loosely arranged and partially overlapping clusters. A multidimensional space based on stimulus similarity showed that MSG was as different from the four basic taste stimuli as they were from one another. 5. Mixture suppression, a common observation in human psychophysical experiments, was examined at the neurophysiological level by including binary tastants in the stimulus battery. The average response of 19 Suc-best neurons to 1.0 M Suc (4.1 spikes/s) decreased to near 0 when the solvent was changed from DW to either 0.03 M MSG or 0.03 M NaCl. Similar decrements were observed in NaCl- and MSG-best neurons tested with Suc/NaCl mixtures.

Animals↗
PubMed2000

Biophysical properties and responses to neurotransmitters of petrosal and geniculate ganglion neurons innervating the tongue.

The properties of afferent sensory neurons supplying taste receptors on the tongue were examined in vitro. Neurons in the geniculate (GG) and petrosal ganglia (PG) supplying the tongue were fluorescently labeled, acutely dissociated, and then analyzed using patch-clamp recording. Measurement of the dissociated neurons revealed that PG neurons were significantly larger than GG neurons. The active and passive membrane properties of these ganglion neurons were examined and compared with each other. There were significant differences between the properties of neurons in the PG and GG ganglia. The mean membrane time constant, spike threshold, action potential half-width, and action potential decay time of GG neurons was significantly less than those of PG neurons. Neurons in the PG had action potentials that had a fast rise and fall time (sharp action potentials) as well as action potentials with a deflection or hump on the falling phase (humped action potentials), whereas action potentials of GG neurons were all sharp. There were also significant differences in the response of PG and GG neurons to the application of acetylcholine (ACh), serotonin (5HT), substance P (SP), and GABA. Whereas PG neurons responded to ACh, 5HT, SP, and GABA, GG neurons only responded to SP and GABA. In addition, the properties of GG neurons were more homogeneous than those of the PG because all the GG neurons had sharp spikes and when responses to neurotransmitters occurred, either all or most of the neurons responded. These differences between neurons of the GG and PG may relate to the type of receptor innervated. PG ganglion neurons innervate a number of receptor types on the posterior tongue and have more heterogeneous properties, while GG neurons predominantly innervate taste buds and have more homogeneous properties.

Acetylcholine↗
PubMed2002

Distinctive neurophysiological properties of embryonic trigeminal and geniculate neurons in culture.

Neurons in trigeminal and geniculate ganglia extend neurites that share contiguous target tissue fields in the fungiform papillae and taste buds of the mammalian tongue and thereby have principal roles in lingual somatosensation and gustation. Although functional differentiation of these neurons is central to formation of lingual sensory circuits, there is little known about electrophysiological properties of developing trigeminal and geniculate ganglia or the extrinsic factors that might regulate neural development. We used whole cell recordings from embryonic day 16 rat ganglia, maintained in culture as explants for 3-10 days with neurotrophin support to characterize basic properties of trigeminal and geniculate neurons over time in vitro and in comparison to each other. Each ganglion was cultured with the neurotrophin that supports maximal neuron survival and that would be encountered by growing neurites at highest concentration in target fields. Resting membrane potential and time constant did not alter over days in culture, whereas membrane resistance decreased and capacitance increased in association with small increases in trigeminal and geniculate soma size. Small gradual differences in action potential properties were observed for both ganglion types, including an increase in threshold current to elicit an action potential and a decrease in duration and increase in rise and fall slopes so that action potentials became shorter and sharper with time in culture. Using a period of 5-8 days in culture when neural properties are generally stable, we compared trigeminal and geniculate ganglia and revealed major differences between these embryonic ganglia in passive membrane and action potential characteristics. Geniculate neurons had lower resting membrane potential and higher input resistance and smaller, shorter, and sharper action potentials with lower thresholds than trigeminal neurons. Whereas all trigeminal neurons produced a single action potential at threshold depolarization, 35% of geniculate neurons fired repetitively. Furthermore, all trigeminal neurons produced TTX-resistant action potentials, but geniculate action potentials were abolished in the presence of low concentrations of TTX. Both trigeminal and geniculate neurons had inflections on the falling phase of the action potential that were reduced in the presence of various pharmacological blockers of calcium channel activation. Use of nifedipine, omega-conotoxin-MVIIA and GVIA, and omega-agatoxin-TK indicated that currents through L-, N-, and P/Q- type calcium channels participate in the action potential inflection in embryonic trigeminal and geniculate neurons. The data on passive membrane, action potential, and ion channel characteristics demonstrate clear differences between trigeminal and geniculate ganglion neurons at an embryonic stage when target tissues are innervated but receptor organs have not developed or are still immature. Therefore these electrophysiological distinctions between embryonic ganglia are present before neural activity from differentiated receptive fields can influence functional phenotype.

Action Potentials↗
PubMed1997

Epithelial sodium channels: function, structure, and regulation.

The apical (outward-facing) membranes of high-resistance epithelia contain Na+ channels, traditionally identified by their sensitivity to block by the K(+)-sparing diuretic amiloride. Such channels have been characterized in amphibian skin and urinary bladder, renal collecting duct, distal colon, sweat and salivary glands, lung, and taste buds. They mediate the first step of active Na+ reabsorption and play a major role in the maintenance of electrolyte and water homeostasis in all vertebrates. In the past, these channels were classified according to their biophysical and pharmacological properties. The recent cloning of the three homologous channel subunits denoted alpha-, beta-, and gamma-epithelial Na+ channels (ENaC) has provided a molecular definition of at least one class of amiloride-blockable channels. Subsequent studies have established that ENaC is a major Na(+)-conducting pathway in both absorbing and secretory epithelia and is related to one type of channel involved in mechanosensation. This review summarizes the biophysical characteristics, molecular properties, and regulatory mechanisms of epithelial amiloride-blockable Na+ channels. Special emphasis is given to recent studies utilizing cloned ENaC subunits and purified amiloride-binding proteins.

Animals↗
PubMed2004

Immunolocalization of Alk8 during replacement tooth development in zebrafish.

The novel type I transforming growth factor-beta (TGF-beta) family member receptor Alk8 was previously identified in a degenerate RT-PCR screen for zebrafish type I and II TGF-beta family member receptors. Functional analyses revealed that Alk8 acts through Bmp signaling pathways in early embryonic dorsoventral patterning, in neural crest cell specification, and in patterning and differentiation of neural crest cell-derived pharyngeal arch cartilages. In addition, Alk8 forms active signaling complexes with TGF-beta1 and the TGF-beta RII receptor, suggesting that Alk8 mediates cross talk between Bmp and TGF-beta subfamily members. In this study, immunohistochemical analysis was performed on zebrafish aged 2 days postfertilization to 1 year, revealing immunolocalization of Alk8 to tissues of the tooth-bearing ceratobranchial 5 (cb5) arch including dental epithelial and mesenchymal tooth tissues of developing primary and replacement teeth, mucous-producing crypt epithelium, keratinized bite plate, and developing taste buds. These results suggest roles for Alk8 in patterning tooth-bearing pharyngeal epithelium, in the initiation of tooth development, in odontoblast and ameloblast differentiation, and in osteoblast maturation. The ability for zebrafish to continuously form teeth throughout their lives allows for the comparison of Alk8 expression in both primary and replacement tooth development, revealing identical Alk8 expression profiles. This study advances our current understanding of the functions of Alk8, particularly with respect to primary and replacement tooth formation, reveals additional roles for Alk8 in dental epithelial patterning and in odontoblast, ameloblast and osteoblast differentiation, and demonstrates the utility of the zebrafish as a model for primary and replacement tooth development.

Activin Receptors, Type I↗
PubMed2004

Sensory systems in amphioxus: a window on the ancestral chordate condition.

Amphioxus has an assortment of cells and organs for sensing light and mechanical stimuli. Vertebrate counterparts of these structures are not always apparent, and a strong case can be made for homology in only a few instances. For example, amphioxus has anatomically simple but plausible homologs of both the pineal and paired eyes of vertebrates. Placodal and neural crest derivatives are, however, more problematic: the evidence for an olfactory system in amphioxus is only circumstantial and, despite the variety of secondary sensory cell types that occur on the body surface in amphioxus, none are obvious homologs of vertebrate taste buds, neuromasts or acoustic hair cells. A useful perspective can nevertheless be gained by examining differences in amphioxus and vertebrate development, specifically how each specifies and positions sensory precursors, controls their proliferation, and deploys them through the body. The much larger size of vertebrate embryos and the need to cope developmentally with increased scale and cell numbers may account for some key vertebrate innovations, including placodes and neural crest. The presence or absence of specific structural adaptations, like the latter, is therefore less useful for judging homology between amphioxus and vertebrates than shared features of specific cell types. It is also clear that the duration of embryogenesis in vertebrates has been significantly extended in comparison with ancestral chordates so as to incorporate events that would originally have occurred during the post-embryonic growth period, including events of neurogenesis. Consequently, no scenario for the origin of vertebrates can be considered complete unless it deals explicitly with the whole of the life history and changes to it.

Animals↗
PubMed1994

Brain morphogenesis of the red sea bream, Pagrus major (teleostei).

Post-embryonic morphogenesis and regional volumetric growth of the brain in larval and juvenile red sea bream, Pagrus major, were analyzed by employing a computer-aided three-dimensional reconstruction of serial sections of the head. The relative volume of the optic tectum rapidly increases after hatching until day 8, implying the importance of the visual sense for the first feeding, which begins on day 4. The differentiation and outgrowth of the primary gustatory center in the medulla after day 43 may reflect the increasing number of taste buds, suggesting a relationship to the onset of benthic feeding as juveniles. The rather rapid increases in the relative volumes of the corpus and valvula cerebelli after day 28 and their progressive morphogenesis may be correlated with improved motor performance. The relative volumes of the octaval-lateral line centers, including the eminentia granularis and the crista cerebellaris, and the relative volume of the torus longitudinalis, increase in parallel with those of the corpus and valvula cerebelli.

Animals↗
PubMed1982

Morphological observations on the papillae of the opossum tongue.

The dorsum of the opossum tongue shows filiform, fungiform, conical and three vallate papillae. An additional type, the compound filiform papilla, is characteristic of most marsupials, including the opossum. These are unique structures in which the epithelium forms fringe-like, keratinized projections around the apical borders of the papillae. The covering epithelium is an extensively keratinized, stratified squamous type with a well-developed stratum granulosum containing numerous keratohyalin granules. Large, heavily cornified conical papillae occur in a patch near the anterior end of the tongue and the apex of each papilla is directed posteriorly. Taste buds are associated with only the three vallate papillae which form a triangle near the base of the tongue. They are not present on the fungiform papillae or in the posterolateral mucosal folds which appear to replace the foliate papillae of other species.

Animals↗
PubMed1990

Blood vascular architecture of the rat lingual papillae with special reference to their relations to the connective tissue papillae and surface structures: a light and scanning electron microscope study.

Subepithelial blood vessels of the rat lingual papillae and their spatial relations to the connective tissue papillae and surface structures were demonstrated by light and scanning electron microscopy. In the rat, four types of papillae were distinguished on the dorsal surface of the tongue, i.e. the filiform, fungiform, foliate and circumvallate papillae. Vascular beds of various appearance were found in all four types of lingual papillae: a simple or twisted capillary loop in the filiform papilla; a basket- or petal-like network in the fungiform papilla; a ring-like network in the foliate papilla, and a conglomerated network surrounded by double heart-shaped capillary networks in the circumvallate papilla. These characteristic vascular beds corresponded to the shape of the connective tissue papillae and surface structures. The vascular bed beneath the gustatory epithelium in the fungiform, foliate and circumvallate papilla consisted of fine capillary networks next to the taste buds.

Animals↗
PubMedDate not supplied

Hypogeusia, dysgeusia, hyposmia, and dysosmia following influenza-like infection.

Hypogeusia, with or without dysgenusia, and hyposmia, with or without dysosmia, followed an influenzal-like infection in 87 of 143 consecutive patients who presented at the Taste and Smell Clinic at the NIH with taste and smell abnormalities. Findings in this disease included pale nasal mucous membranes with marked patency of the nasal airway, a postive Rudolph sign, elevated detection and recognition thresholds for several tastants and odorants, disruption of the pore region of the tast dub observed on electron microscopy and infiltration of the upper lamina propria of the nasal mucous membrane wih chronic inflammatory cells observed on light microscopy. These findings, taken together, are relatively specific for the diagnosis of this surprisingly common disorder.

Adult↗
PubMed1987

Sensory nerve endings in the mucosa of the epiglottis--morphologic investigations with silver impregnation, immunohistochemistry, and electron microscopy.

This study was conducted in order to investigate the structure of sensory nerve endings of the human epiglottis and substance P immunoreactive nerve fibers of the canine epiglottis in relationship to physiologic functions of the larynx. The human epiglottis was observed by light microscopy (silver impregnation) and electron microscopy, and the canine epiglottis was studied by peroxidase-anti-peroxidase (PAP) immunohistochemistry. The results are summarized as follows: (1) In the membranes of the epiglottis, we observed free endings of simple or complex tree shape, corpuscle endings with glomerular patterns, and taste-bud-like structures, and (2) electron microscopic studies revealed varicosity of the terminal axon with processes that contained small, clear and large, dense cored vesicles. Substance P was observed in these structures, and it was suggested that substance P was related to perception in the larynx.

Animals↗
PubMed1989

Growth, development, and aging of orofacial tissues: neural aspects.

Neural factors influence post-natal growth, development, and aging throughout the body. This influence may be mediated through sensory or motor effects interacting with endocrine and immunological factors. Growth effects may be expressed directly by sensory or motor nerves on the tissue or indirectly by motor function. Direct neutrotrophic effects have been well-documented in the development of striated muscle, the taste bud, and the amphibian limb. Evidence for a trigeminal neurotrophic effect on tooth development and facial development is lacking. Growth disturbances of the jaws consequent to lesioning of the trigeminal nerve are due most likely to functional disturbances rather than neutrotrophism. Examples of function impact on orofacial growth are abundant. Oral and facial target tissues, like those elsewhere in the body, determine the nature of the target tissue innervation and its central organization. Central effects consequent to tooth loss or dental pulp entirpation are well-documented. Inflammation and pain may exert growth effects through release of "wound hormones" or secondarily to somatic and autonomic effects. There is evidence that vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP) elaborated from sympathetic and parasympathetic neurons may have a modulatory role in growth. While the effects of longstanding motor pathologies on skeletal growth are well-known, concomitant sensory deficits and soft tissue disturbances have not been examined. However, the pathological models beg the question of normal regulation. While muscle develops in the absence of innervation, neurotrophic effects are clearly identified. Little is known about the interaction of simple and complex motor behavior on growth. Regulation of growth is frequently visualized within a form-function paradigm. For example, anterior open bites have been seen as the consequence of tongue thrusting or tongue thrusting as a consequence of open bites. Low tonic forces in posture are thought to be more important in the development of both the face and the dental alveolar complex than the higher intermittent forces in mastication and swallowing. The need for an active (reflex) contribution to growth at the TMJ is in dispute.(ABSTRACT TRUNCATED AT 400 WORDS)

Face↗
PubMed2004

Genetics of human taste perception.

Genetic approaches are rapidly yielding new information about our sense of taste. This information comes from both molecular studies of genes encoding taste receptors and other taste-signaling components, and from studies of inherited variation in taste abilities. Our understanding of bitter taste has advanced by combined information from discovery and study of the TAS2R family of taste receptor genes, hand in hand with genetic linkage and positional cloning studies, notably on the ability to taste phenylthiocarbamide (PTC). Sweet and umami tastes, mediated by TAS1R receptors, are becoming well-characterized at the molecular genetic level, and these taste classes are now targets for linkage, positional cloning, and genetic association strategies. Salty and sour tastes are still poorly characterized in genetic terms, and represent opportunities for the future.

Animals↗
PubMed1991

Diversity of expression of engrailed-like antigens in zebrafish.

We have studied developmental expression of zebrafish engrailed-like (Eng) antigens. Many cell types are reproducibly labeled by two antibodies that recognize the Eng homeodomain, but other cells are labeled by only one or the other, suggesting a hitherto unrecognized complexity of Eng proteins. Expression patterns vary remarkably according to cell type and location. In the undifferentiated primordia of the brain and of each myotome, expression by a stripe of cells spatially subdivides the primordium at a location where a morphological boundary forms later, suggesting expression may be required for development of the boundaries. Supporting this hypothesis, trunk myotomal cells that express Eng are absent in spt-1 mutant embryos, just where the myotomal boundaries fail to form. Another pattern is present in rhombomeres, pharyngeal arches, and the pectoral girdle. In each of these cases, cells (neuron, muscle, cartilage) generating a subset of a series of repeated elements selectively express Eng. These subsets then form specialized derivatives, suggesting Eng homeoproteins are involved in determining the specializations. Epidermal expression is present in the ventral half of the pectoral fin rudiment, precisely 'compartmentalizing' the fin. Neuronal cells at a certain dorsoventral level in each hindbrain and spinal cord segment selectively express Eng, suggesting segmental control of neuronal identity. Specific expression patterns are observed in taste buds, otic vesicles and teeth. Thus we propose that eng genes function in diverse cell types in zebrafish, but play selector roles that can be classified into a few basic types.

Animals↗
PubMed2000

Establishing neuronal identity in vertebrate neurogenic placodes.

The trigeminal and epibranchial placodes of vertebrate embryos form different types of sensory neurons. The trigeminal placodes form cutaneous sensory neurons that innervate the face and jaws, while the epibranchial placodes (geniculate, petrosal and nodose) form visceral sensory neurons that innervate taste buds and visceral organs. In the chick embryo, the ophthalmic trigeminal (opV) placode expresses the paired homeodomain transcription factor Pax3 from very early stages, while the epibranchial placodes express Pax2. Here, we show that Pax3 expression in explanted opV placode ectoderm correlates at the single cell level with neuronal specification and with commitment to an opV fate. When opV (trigeminal) ectoderm is grafted in place of the nodose (epibranchial) placode, Pax3-expressing cells form Pax3-positive neurons on the same schedule as in the opV placode. In contrast, Pax3-negative cells in the grafted ectoderm are induced to express the epibranchial placode marker Pax2 and form neurons in the nodose ganglion that express the epibranchial neuron marker Phox2a on the same schedule as host nodose neurons. They also project neurites along central and peripheral nodose neurite pathways and survive until well after the main period of cell death in the nodose ganglion. The older the opV ectoderm is at the time of grafting, the more Pax3-positive cells it contains and the more committed it is to an opV fate. Our results suggest that, within the neurogenic placodes, there does not appear to be a two-step induction of 'generic' neurons followed by specification of the neuron to a particular fate. Instead, there seems to be a one-step induction in which neuronal subtype identity is coupled to neuronal differentiation.

Animals↗