Shh and ROCK1 modulate the dynamic epithelial morphogenesis in circumvallate papilla development

In rodents, a circumvallate papilla (CVP) develops with dynamic changes in epithelial morphogenesis during early tongue development. Molecular and cellular studies of CVP development revealed that there would be two different mechanisms in the apex and the trench wall forming regions with specific expression patterns of Wnt11 and Shh. Molecular interactions were examined using in vitro organ culture with over-expression of Shh, important signalling molecules and various inhibitors revealed that there are two significant different mechanisms in CVP formation by Wnt11 and Shh expressions. Wnt, a well known key molecule to initiate taste papillae, would govern Rho activation and cytoskeleton formation in the apex epithelium of CVP. In contrast, Shh regulates the cell proliferation to differentiate taste buds and to invaginate the epithelium for development of von Ebner's gland (VEG). Based on these results, we suggest that these different molecular signalling cascades of Wnt11 and Shh would play crucial roles in specific morphogenesis and pattern formation of CVP during early mouse embryo development.     

Calbindin D28k-like immunoreactivity in the developing and regenerating circumvallate papilla of the rat

The distribution of calbindin D28k (CB)-like immunoreactivity (-LI) in the circumvallate papilla (CVP) was examined during development and regeneration following bilateral crush injury to the glossopharyngeal nerve in the rat. In the adult CVP, CB-like immunoreactive (-IR) nerve fibers were observed in the subgemmal region and some penetrated into the taste buds. CB-LI was also detected in the cytoplasm of the spindle-shaped gustatory cells in the lower half of the trench epithelium, which contained numerous synaptic vesicles and bundles of intermediate filaments. These CB-IR gustatory cells made synapse-like contacts with CB-IR nerve terminals. Some CB-IR nerve terminals made contacts with the gustatory cells negative for CB-LI. At least three developmental stages were defined with regard to the developmental changes in the distribution of CB-LI: (1) Stage I (embryonic day (E) 18–postnatal day (P)5): CB-IR nerve fibers appeared in the lamina propria just beneath the newly-formed CVP at E18, but the gustatory epithelium of the CVP contained no CB-IR structures. Taste buds with taste pores appeared at P1. (2) Stage II (P5–10): thin CB-IR nerve fibers began entering the trench epithelium, but no CB-IR cells were observed. (3) Stage III (P10–adult): in addition to the intragemmal and perigemmal CB-IR nerve fibers, very few CB-IR cells appeared in the taste buds around P10, and their numbers increased progressively. The changes in the distribution of taste buds and CB-LI following glossopharyngeal nerve injury were similar to those observed during development. On post-operative day (PO) 4, the taste buds and CB-IR cells decreased markedly in number. These CB-IR cells became round in shape, and the number of CB-IR nerve fibers decreased markedly. On PO8, both taste buds and CB-IR cells disappeared completely. The regenerated taste buds were first observed on PO12, increased rapidly in number by PO20, and increased slowly thereafter. CB-IR nerve fibers accumulated at the subgemmal region and began penetrating into the trench wall epithelium around PO16. CB-IR cells appeared between PO20 and PO24, and their numbers increased progressively and reached the normal level on PO40. The topographical localizations of the taste buds and CB-IR cells during development and regeneration were comparable to those of normal animals. The delay of the time courses for appearance of CB-IR nerve fibers and CB-IR cells compared to the appearance of taste buds during development and regeneration suggests that CB in the gustatory epithelium may participate in the survival of the taste bud cells rather than in the induction of the taste buds.     

Observations on the ultrastructure of ganglion cells in the circumvallate papilla of rat and mouse

Ganglion cells in the circumvallate papilla of adult rodents are described as typical autonomic neurons. Some neurons are aggregated to form a discrete structure in the base of the papilla; others are scattered through the core, along the nerve bundles, and particularly near the dome. The term "circumvallate ganglion" is applied to the entire population. Satellite cells completely ensheathe each neuron. Preganglionic fibers, containing clear vesicles, synapse on the soma and stumpy dendrites of the neurons. Axons, containing dense-cored vesicles, are observed in close proximity to the neurons. However, these fibers do not establish true morphological synaptic contacts with the neurons. We have not observed serial or reciprocal synapses on or in the vicinity of the ganglion cells. The hypothesis that the axons of the circumvallate ganglion neurons act as parasympathetic vasodilators is indicated by the proximity of the two structures and by nerve terminations on the arteriole muscle cells. Direct modulation of taste transduction by these neurons is ruled out.     

Secretions of von Ebner's glands influence responses from taste buds in rat circumvallate papilla

The influence of secretions from von Ebner's lingual salivaryglands on gustatory function was studied in the rat. Neurophysiologicaltaste responses elicited by chemical stimulation of the circumvallatepapilla were recorded from the glossopharyngeal nerve whileinitiating salivary secretion in the same papilla. Salivarysecretion from von Ebner's glands significantly reduced tasteresponses to stimulation of the circumvallate papilla with variouschemicals. However, the magnitude of the reduction in responsediffered depending on the taste stimulus used. The reductionin response due to salivary secretion was blocked by prior administrationof the parasympathetic antagonist, atropine. These results demonstratea direct effect of salivary secretion on taste responses andillustrate the close relationship between taste function andthe secretion of von Ebner's glands.     

Influence of innervation on the levels of noradrenaline and serotonin in the circumvallate papilla of the rat

The levels and the distribution of monoamines within the rat circumvallate papilla have been studied. Noradrenaline was found in the connective tissue underlying the taste buds, whereas serotonin was located in the basal area of the gustatory epithelium but not inside the taste buds. Following denervation, noradrenaline levels decreased and serotonin levels increased. These results suggest that both neurotransmitters may have some mutual interaction in modulating transmission at the papilla.     

Developmental patterning in the Caenorhabditis elegans hindgut

Developmental pattern formation allows cells within a tissue or organ to coordinate their development and establish cell types in relationship to one another. To better characterize the developmental patterning events within one organ, the C. elegans hindgut, we have analyzed the expression pattern of several genes using green fluorescent protein-based reporter transgenes. In wild-type animals, these genes are expressed in subsets of hindgut cells rather than in individual cell types. In mutant animals, we find that some, but not all, genes expressed in cells with altered development exhibit a corresponding alteration of gene expression. The results are consistent with a model where a combination of factors contribute to each cell's fate, and address how developmental information converges to specify cell types.     

The reversible effect of colchicine on the taste bud cells of the central circumvallate papilla in the rat

Summary It is believed that differentiation and maintenance of taste buds in vertebrates is dependent on the trophic function of their sensory nerve supply. In the present work colchicine was injected into the circumvallate papilla of the rat. This produced a reversible blockade of neuroplasmic transport and disappearance of taste buds. Colchicine inhibited the further differentiation of bud cells, but apparently did not change the life cycle of the cells present already at the time of injection. It is speculated that the neurotrophic factors in this particular cell system are effective to induce cell differentiation only.This work was supported by CAIT Grant No 1776     

Developmental patterning deciphered in avian chimeras

I started my scientific carer by investigating the development of the digestive tract in the laboratory of a well-known embryologist, Etienne Wolff, then professor at the Collège de France. My animal model was the chick embryo. The investigations that I pursued on liver development together with serendipity, led me to devise a cell-marking technique based on the construction of chimeric embryos between two closely related species of birds, the Japanese quail ( Coturnix coturnix japonica ) and the chick ( Gallus gallus ).
The possibility to follow the migration and fate of the cells throughout development from early embryonic stages up to hatching and even after birth, was a breakthrough in developmental biology of higher vertebrates.
This article describes some of scientific achievements based on the use of this technique in my laboratory during the last 38 years.     

Immunohistochemical observation of growth-associated protein 43 (GAP-43) in the developing circumvallate papilla of the rat

The distribution and development of growth-associated protein 43 (GAP-43)-like immunoreactivity (-LI) in the rat circumvallate papilla (CVP) were compared to those of protein gene product 9.5 (PGP 9.5)-LI. In the adult, thick GAP-43-like immunoreactive (-IR) structures gathered densely in the subgemmal region. Some of these further penetrated the apical epithelium and trench wall epithelium. At least two types of GAP-43-IR structures were recognized; taste bud-related and non-gustatory GAP-43-IR neural elements. Immunoelectron microscopy revealed that GAP-43-LI was localized predominantly in the Schwann cells, and a few axons displayed GAP-43-LI in the lamina propria. In the trench epithelium, GAP-43-LI was detected in the cytoplasmic side of the axonal membrane. Some intragemmal GAP-43-IR axons made synaptic-like contacts with taste bud cells. At least four developmental stages were defined on the basis of the changes in distribution of GAP-43-LI. In stage I [embryonic day (E) 16–17] GAP-43-IR structures accumulated at the lamina propria just beneath the newly-formed circumvallate papilla. In stage II (E18–19) GAP-43-IR nerve fibers began to penetrate the apical epithelium. In stage III [E20-postnatal day (P) 0] GAP-43-IR nerve fibers first appeared in the trench wall epithelium. Penetration of GAP-IR nerve fibers occurred in the inner trench wall epithelium first, and then in the outer trench wall epithelium. In stage IV (P1-) the distribution of GAP-43-LI was similar to that observed in the adult; but the density of GAP-43-LI was much higher than in adults. PGP 9.5-LI showed a similar distribution pattern to that of GAP-43-LI, except for round-shaped cells in the apical epithelium at the late embryonic stages, and in taste bud cells and intralingual ganglionic cells which lacked GAP-43-LI. The similarities in distribution patterns of GAP-43-LI and PGP 9.5-LI during the development and mature circumvallate papilla suggest that GAP-43 may be a key neuronal molecule for induction and maintenance of the taste buds.     

Effect of testosterone on serotonin and noradrenaline concentrations and taste bud cell number of rat circumvallate papilla

Intramuscular administration of testosterone (T) to male orfemale rats produced a significant increase in the rate of developmentof the intermediate type of taste bud cells. T treatment produceda similar effect in rats previously submitted to the in-blockor selective removal of the main salivary glands. 5-Hydroxytryptamine(5-HT) and noradrenaline (NA) concentrations in the vallatepapilla of normal rats were sensitive to T. The concentrationof 5-HT decreased significantly and the concentration of NAincreased slightly, both with respect to the controls.     

Developmental evolution: Axial patterning in insects.

The Drosophila bicoid gene is well known for encoding a protein that forms a morphogenetic gradient with a key role in anterior patterning of the fruitfly embryo. Recent results suggest the evolution of bicoid might have involved dramatic changes in function - essentially the invention of a new regulatory protein.     

Developmental biology: hippo promotes posterior patterning by preventing proliferation

The Hippo pathway is a potent regulator of tissue growth. Two recent studies report a new function of the pathway in the differentiation of the follicular epithelium during Drosophila oogenesis.     

Developmental mechanisms underlying tooth patterning in continuously replacing osteichthyan dentitions

The dentition of osteichthyans presents an astonishing diversity with regard to the distribution of teeth in the oral cavity, tooth numbers, arrangements, shapes, and sizes. Taking examples from three unrelated teleosts--the most speciose group of osteichthyans--and from the literature, this study explores how the initial tooth pattern is set up, and how this relates to the establishment and maintenance (or modification) of the tooth replacement pattern. In teleosts, first-generation teeth (the very first teeth in ontogeny to develop at a particular locus) are commonly initiated in adjacent or in alternate (odd and even) positions. The mechanisms responsible for these divergent developmental patterns remain to be elucidated, in particular, whether they reflect a field or local type of control. However, patterns of adjacent or alternate tooth initiation, set up by the first-generation teeth, can easily turn into replacement patterns where new teeth are initiated simultaneously every second, or even every third position, by synchronizing the formation of new first-generation teeth to the formation of replacement teeth at older loci. Our observations suggest that, once established, the replacement pattern appears to be maintained, as a kind of "default" state. Variations and modifications in this pattern are nevertheless common and suggest that tooth replacement is under local control, exerted at the level of the initiation of replacement teeth. Further studies are needed to test the hypothesis that regular replacement patterns are more frequent in association with the plesiomorphic condition of extramedullary replacement (replacement on the surface of the dentigerous bone) and more rare in the derived condition of intramedullary replacement (replacement within the medullary cavity of the dentigerous bone).     

Developmental patterning of the carbohydrate antigen FC10.2 during early embryogenesis in the chick

An oligosaccharide antigen (FC10.2), formerly described only in mammalian cells and secreted glycoproteins, has been detected and found to display striking temporal and spatial patterning in the chick during early embryonic development. This antigen is expressed on type 1 chains, which are isomers of oligosaccharides of the poly-N-acetyllactosamine series (type 2 chains). Immunoreactivities before and after neuraminidase treatment of serial sections of chick embryos during the first 17 stages of development indicate that the FC10.2 structure occurs predominantly in the sialylated form (S-FC10.2). The FC10.2 and S-FC10.2 antigens are prominent markers of the primordial germ cells, being strongly expressed by these cells from the pre-primitive streak stage onwards. S-FC10.2 is also a clear marker of the pronephric duct from its first appearance. Initially present over the entire apical surface of the ectoderm, antigenicity diminishes in an antero-posterior direction as neurulation proceeds. A unique pattern for a carbohydrate antigen is displayed by cells of the primitive streak; antigenicity is lost with de-epithelialisation and ingression, but is regained in a pericellular distribution on the mesoderm cells that emerge from the primitive streak. Thereafter, successive changes in expression and distribution of FC10.2 and S-FC10.2 are features of mesodermal tissues, particularly during somitogenesis. These antigens are prominent components of the extracellular matrix around the notochord and sclerotome cells. They are also prominent posteriorly in the subectodermal region, ceasing abruptly at the lateral limits of the embryo proper. Although no absolute correlations can yet be made, several features of the distribution of these antigens suggest that they may be integral components of, or ligands for, cell adhesion molecules.