These notes introduce the development of the sense of taste which can divided into five basic tastes: bitter, salty, sweet, umami (savoury) and sour.
The human tounge and taste: a, Taste buds (left) are composed of 50–150 taste-receptor cells (TRCs) depending on the species, distributed across different papillae. b, Recent molecular and functional data shown there is no tongue 'map' modalities are present in all areas of the tongue. (Image reprinted by permission from Macmillan Publishers Ltd: Nature 444, 288-294 16 November 2006 | Reference)
These notes cover development of taste, not the muscular tongue. (More? Head and Neck Development - Tongue)
Page Links: Introduction | Some Recent Findings | stage 13/14 embryo | stage 22 embryo | Reading | Computer Activities | Objectives | Development Timing | Development Overview | Adult Taste Bud Cells | Gustatory Anatomy | Taste Receptors | Taste Pathway | Developmental Genes | References | WWW Links | Glossary
Fate mapping of mammalian embryonic taste bud progenitors. Thirumangalathu S, Harlow DE, Driskell AL, Krimm RF, Barlow LA. Development. 2009 May;136(9):1519-28. PMID: 19363153
"Taste buds differentiate at birth within epithelial appendages, termed taste papillae, which arise at mid-gestation as epithelial thickenings or placodes. However, the embryonic relationship between placodes, papillae and adult taste buds has not been defined. Here, using an inducible Cre-lox fate mapping approach with the ShhcreER(T2) mouse line, we demonstrate that Shh-expressing embryonic taste placodes are taste bud progenitors, which give rise to at least two different adult taste cell types, but do not contribute to taste papillae. Strikingly, placodally descendant taste cells disappear early in adult life."
Epithelial-derived brain-derived neurotrophic factor is required for gustatory neuron targeting during a critical developmental period. Ma L, Lopez GF, Krimm RF. J Neurosci. 2009 Mar 18;29(11):3354-64. PMID: 19295142
Human taste: peripheral anatomy, taste transduction, and coding. Breslin PA, Huang L. Adv Otorhinolaryngol. 2006;63:152-90.
There are no Stage 13/14 sections which relate to development of taste. (More? Head and Neck Development - Tongue)
Section (B4) through head showing tongue and head structures.
Molecular Biology of the Cell (4th ed.) Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter. New York: Garland Publishing; 2002. Sensory Epithelia
Neuroscience (2nd ed.) Purves, Dale; Augustine, George.J.; Fitzpatrick, David; Katz, Lawrence.C.; LaMantia, Anthony-Samuel.; McNamara, James.O.; Williams, S. Mark, editors. Sunderland (MA): Sinauer Associates, Inc. 2001 Taste Receptors and the Transduction of Taste Signals |
Embryo Images Unit: Embryo Images Online
Week 6 - gustatory papilla, caudal midline near the foramen caecum
Week 6-7 - nerve fibers approach the lingual epithelium
Week 8 - nerves penetrate epitheilai basal lamina and synapse with undifferentiated, elongated, epithelial cells (taste bud progenitor cell)
Week 10 - shallow grooves above the taste bud primordium
Week 12 - first differentiated epithelial cells (Type II and III)
Week 12 -13 - maximum synapses between cells and afferent nerve fibers
Week 14-15 - taste pores develop, mucous
Week 18 - substance P detected in dermal papillae, not in taste bud primordia
3rd Trimester -
(These are Human embryonic timings, not clinical which is based on last menstral period +2 weeks)
Electron Microscope Characterization
Type I cells, characterized by apically located dense secretory granules.
Type II cells, electron-dark cells with well developed endoplasmic reticulum and many apical mitochondria, with foot-like processes containingdense-cored vesicles (120-200 nm in diameter)
Type III cells, electron-dense cells containing large numbers of dense-cored vesicles (80-150 nm in diameter).
Sources: Witt M, Reutter K., 1996
Two opposing views of how taste qualities are encoded in the periphery.
a, In the labelled-line model, receptor cells are tuned to respond to single taste modalities — sweet, bitter, sour, salty or umami — and are innervated by individually tuned nerve fibres. In this case, each taste quality is specified by the activity of non-overlapping cells and fibres.
b,c, Two contrasting models of what is known as the 'across-fibre pattern'. This states that either individual TRCs are tuned to multiple taste qualities (indicated by various tones of grey and multicoloured stippled nuclei), and consequently the same afferent fibre carries information for more than one taste modality (b), or that TRCs are still tuned to single taste qualities but the same afferent fibre carries information for more than one taste modality (c). In these two models, the specification of any one taste quality is embedded in a complex pattern of activity across various lines. Recent molecular and functional studies in mice have demonstrated that different TRCs define the different taste modalities, and that activation of a single type of TRC is sufficient to encode taste quality, strongly supporting the labelled-line model.
Umami historical Japanese word describing the taste in seaweed, used to describe the taste of "savoury".
An overview of the basic neuroanatomy of the gustatory system.
A cartoon of geniculate neurons innervating the tongue (red) and the palate (green) and petrosal neurons innervating the tongue (blue) are shown innervating peripheral taste bud containing regions and the rostral nucleus of the solitary tract (NST). On the tongue, taste buds are located in fungiform papillae, foliate papillae, and circumvallate papillae (CV). The palate has taste buds on the nasoincisor papilla/ducts (NID) and on the soft palate (circles).
Photomicrographs of innervation patterns in the tongue and in the palate at E16.5 are shown next to the appropriate regions. An overlay image of two geniculate ganglia (E14.5) is also shown; one ganglia following DiI-label to the palate was pseudo-colored green, the other following DiI-labeling of the tongue remains red.
These two ganglia images were anatomically aligned and superimposed using Adobe Photoshop. E = embryonic day, rodent
Anterior 2/3 tongue - Cranial nerve VII
Posterior 1/3 tongue - Cranial nerve IX
Epiglottis - Cranial nerve X
Brainstem - Solitary Nucleus
Thalamus - Ventral Posterior Medial (VPM) Nucleus
Reward - dopamine in the nucleus accumbens?
sonic hedgehog Iwatsuki K, Liu HX, Grunder A, Singer MA, Lane TF, Grosschedl R, Mistretta CM, Margolskee RF. Wnt signaling interacts with Shh to regulate taste papilla development. Proc Natl Acad Sci U S A. 2007 Feb 6
Wnt Iwatsuki K, Liu HX, Grunder A, Singer MA, Lane TF, Grosschedl R, Mistretta CM, Margolskee RF. Wnt signaling interacts with Shh to regulate taste papilla development. Proc Natl Acad Sci U S A. 2007 Feb 6
Sox2 Tadashi Okubo, Larysa H. Pevny, and Brigid L.M. Hogan Sox2 is required for development of taste bud sensory cells. Genes Dev. 2006;20 2654-2659 "Sox2 is expressed in basal epithelial cells of the tongue, with high levels in taste bud placodes, fungiform papillae, and mature taste cells, and low levels in filiform papillae." (More? OMIM Sox2)