Placodes: Difference between revisions
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* '''Review - Transcriptional regulation of cranial sensory placode development''' | * '''Review - Transcriptional regulation of cranial sensory placode development'''{{#pmid:25662264|PMID25662264}} "Cranial sensory placodes derive from discrete patches of the head ectoderm and give rise to numerous sensory structures. During gastrulation, a specialized "neural border zone" forms around the neural plate in response to interactions between the neural and nonneural ectoderm and signals from adjacent mesodermal and/or endodermal tissues. This zone subsequently gives rise to two distinct precursor populations of the peripheral nervous system: the neural crest and the preplacodal ectoderm (PPE). The PPE is a common field from which all cranial sensory placodes arise (adenohypophyseal, olfactory, lens, trigeminal, epibranchial, otic). Members of the Six family of transcription factors are major regulators of PPE specification, in partnership with cofactor proteins such as Eya. Six gene activity also maintains tissue boundaries between the PPE, neural crest, and epidermis by repressing genes that specify the fates of those adjacent ectodermally derived domains. As the embryo acquires anterior-posterior identity, the PPE becomes transcriptionally regionalized, and it subsequently becomes subdivided into specific placodes with distinct developmental fates in response to signaling from adjacent tissues. Each placode is characterized by a unique transcriptional program that leads to the differentiation of highly specialized cells, such as neurosecretory cells, sensory receptor cells, chemosensory neurons, peripheral glia, and supporting cells. In this review, we summarize the transcriptional and signaling factors that regulate key steps of placode development, influence subsequent sensory neuron specification, and discuss what is known about mutations in some of the essential PPE genes that underlie human congenital syndromes." | ||
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* '''Setting appropriate boundaries: Fate, patterning and competence at the neural plate border''' | * '''Setting appropriate boundaries: Fate, patterning and competence at the neural plate border'''{{#pmid:24321819|PMID24321819}} "The neural crest and craniofacial placodes are two distinct progenitor populations that arise at the border of the vertebrate neural plate. This border region develops through a series of inductive interactions that begins before gastrulation and progressively divide embryonic ectoderm into neural and non-neural regions, followed by the emergence of neural crest and placodal progenitors. In this review, we describe how a limited repertoire of inductive signals-principally FGFs, Wnts and BMPs-set up domains of transcription factors in the border region which establish these progenitor territories by both cross-inhibitory and cross-autoregulatory interactions." | ||
* '''Graded levels of Pax2a and Pax8 regulate cell differentiation during sensory placode formation''' | |||
* '''Mutual repression between Gbx2 and Otx2 in sensory placodes reveals a general mechanism for ectodermal patterning''' | * '''Graded levels of Pax2a and Pax8 regulate cell differentiation during sensory placode formation'''{{#pmid:22745314|PMID22745314}} "Pax gene haploinsufficiency causes a variety of congenital defects. Renal-coloboma syndrome, resulting from mutations in Pax2, is characterized by kidney hypoplasia, optic nerve malformation, and hearing loss. ..We sho.w that differential levels of zebrafish Pax2a and Pax8 modulate commitment and behavior in cells that eventually contribute to the otic vesicle and epibranchial placodes." | ||
* '''An effective assay for high cellular resolution time-lapse imaging of sensory placode formation and morphogenesis''' | |||
* '''Epibranchial Placodes''' | * '''Mutual repression between Gbx2 and Otx2 in sensory placodes reveals a general mechanism for ectodermal patterning'''{{#pmid:22564795|PMID22564795}} "In the vertebrate head, central and peripheral components of the sensory nervous system have different embryonic origins, the neural plate and sensory placodes. This raises the question of how they develop in register to form functional sense organs and sensory circuits. Here we show that mutual repression between the homeobox transcription factors Gbx2 and Otx2 patterns the placode territory by influencing regional identity and by segregating inner ear and trigeminal progenitors. Activation of Otx2 targets is necessary for anterior olfactory, lens and trigeminal character, while Gbx2 function is required for the formation of the posterior otic placode. Thus, like in the neural plate antagonistic interaction between Otx2 and Gbx2 establishes positional information thus providing a general mechanism for rostro-caudal patterning of the ectoderm." | ||
* '''Otic Placode''' | |||
* '''Postotic Placode''' | * '''An effective assay for high cellular resolution time-lapse imaging of sensory placode formation and morphogenesis'''{{#pmid:2155472|PMID2155472}} "This new imaging assay provides a powerful method to analyze directly development of placode-derived sensory neurons and subsequent ganglia formation for the first time in amniotes. Viewing placode development in a head cross-section provides a vantage point from which it is possible to study comprehensive events in placode formation, from differentiation, cell ingression to ganglion assembly. Understanding how placodal neurons form may reveal a new mechanism of neurogenesis distinct from that in the central nervous system and provide new insight into how cells acquire motility from a stationary epithelial cell type." | ||
* '''Epibranchial Placodes'''{{#pmid:20460364|PMID20460364}} "The inner ear and the epibranchial ganglia constitute much of the sensory system in the caudal vertebrate head. ...However, recent studies indicate that both systems arise from a morphologically distinct common precursor domain: the posterior placodal area. This review summarises recent studies into the induction, morphogenesis and innervation of these systems and discusses lineage restriction and cell specification in the context of their common origin." | |||
* '''Otic Placode'''{{#pmid:20171206|PMID20171206}} "The inner ear epithelium, with its complex array of sensory, non-sensory, and neuronal cell types necessary for hearing and balance, is derived from a thickened patch of head ectoderm called the otic placode. ...Collectively, our results suggest that Wnt8a provides the link between FGF-induced formation of the pre-otic field and restriction of the otic placode to ectoderm adjacent to the hindbrain." | |||
* '''Postotic Placode'''{{#pmid:20554875|PMID20554875}} "The (zebrafish) embryonic line originates from a postotic placode that produces both a migrating sensory primordium and afferent neurons. Nothing is known about the origin and innervation of the larval lines. Here we show that a "secondary" placode can be detected at 24 h postfertilization (hpf), shortly after the primary placode has given rise to the embryonic primordium and ganglion." | |||
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==Movies== | ==Movies== | ||
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[[File:Preplacodal development model.jpg|600px]] | [[File:Preplacodal development model.jpg|600px]] | ||
'''Preplacodal development model''' | '''Preplacodal development model'''{{#pmid:20885782|PMID20885782}} | ||
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(Above text from figure legend | (Above text from figure legend{{#pmid:20885782|PMID20885782}}) | ||
==Otic Placode== | ==Otic Placode== | ||
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In the mouse, gonadotropin-releasing hormone-1 neurones control the release of gonadotropins from the anterior pituitary and were thought to originate from the adenohypophyseal placed. A recent study has shown that they are really associated early with the formation of the nasal placode. | In the mouse, gonadotropin-releasing hormone-1 neurones control the release of gonadotropins from the anterior pituitary and were thought to originate from the adenohypophyseal placed. A recent study has shown that they are really associated early with the formation of the nasal placode.{{#pmid:20008041|PMID20008041}} | ||
[[File:Drosophila and mouse placode similarity.jpg|200px]] | [[File:Drosophila and mouse placode similarity.jpg|200px]] | ||
Drosophila and mouse placode similarity | Drosophila and mouse placode similarity{{#pmid:18056636|PMID18056636}} | ||
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==Epibranchial Placodes== | ==Epibranchial Placodes== | ||
[[File:Zebrafish placode model.jpg|thumb|Zebrafish placode model | [[File:Zebrafish placode model.jpg|thumb|Zebrafish placode model{{#pmid:24358375|PMID24358375}}]] | ||
Epibranchial ganglia sensory neurons formed by the facial, glossopharyngeal, and vagal placodal regions. These ganglia neurons relay from the sensory organs such as gustatory taste buds, heart baroreceptors, gut sensory enteric nerves. | Epibranchial ganglia sensory neurons formed by the facial, glossopharyngeal, and vagal placodal regions. These ganglia neurons relay from the sensory organs such as gustatory taste buds, heart baroreceptors, gut sensory enteric nerves. | ||
Revision as of 12:49, 15 February 2018
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Introduction
Placodes are ectodermal thickenings which have important roles in development of special sensory systems.
In human development, during week 4 a series of thickened surface ectodermal patches form in pairs rostro-caudally in the head region.
Recent research suggests that all sensory placodes arise from common panplacodal ectoderm (PPE) a horseshoe-shaped region of ectoderm surrounding the anterior neural plate and neural crest. Each placode then differentiates to eventually have different developmental fates. These sensory placodes will later contribute key components of each of our special senses (vision, hearing and smell). Note that their initial postion on the developing head is significantly different to their final position in the future sensory system.
- Adenohypophyseal placode
- Otic placodes - the first placodes visible on the surface of the embryo.
- Olfactory (Nasal) placodes - has 2 components (medial and lateral) and will form the nose olfactory epithelium.
- Optic (Lens) placodes - lies on the surface, adjacent to the outpocketing of the nervous system (which will for the retina) and will form the lens.
- Profundal/trigeminal placodes
Other species have a number of other placodes which form additional sensory structures (fish, lateral line receptor).
- Epibranchial placodes
- Lateral line placodes
- Hypobranchial placodes
Other Placodes? | |
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Note that a second, later developing, form of ectodermal placode development occurs with the development of hair follicles and other integumentary specialisations. This topic does not directly relate to the specialised placodes of the head region covered here. (More? Hair Development | Integumentary_System Development) |
Placode Links: placode | Week 4 | sensory | Otic Placode | Optic Placode | Nasal Placode | Category:Placode | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
Some Recent Findings
Movies
Preplacodal DevelopmentPreplacodal development model[9]
(Above text from figure legend[9]) Otic PlacodeThe otic placode is the first of the sensory placodes visible on the surface of the developing human embryo. This placode will differentiate to contribute almost entirely the components of the inner ear. The images below show the first appearance on the embryo surface during week 4 and the eventual disappearance from the surface by week 5. This is only the beginning of the complex development of this structure, influenced by the surrounding epidermis, neural tube and neural crest. Stage 11The scanning EM of the week 4 human embryo Carnegie stage 11 shown below is a superior dorsal view of the paired otic placodes sinking into the surface at the level of the hindbrain between day 24 and day 25. Stage 12By Carnegie stage 12 26 days, only a small opening of the developing otic vesicle (otocyst) remains visible on the embryo surface located behind the second pharyngeal arch. Stage 13By week 5 Carnegie stage 13 the otic vesicle (otocyst) is completely formed and is no longer visible on the embryo surface. Cross-sections of the embryo head at this stage show the otocyst now lies within the embryo as a hollow fluid-filled epithelial "ball", located between the epidermis and the neural tube (hindbrain).
Adenohypophyseal PlacodeThe hypophysis, or pituitary, is an endocrine gland that links the brain to peripheral endocrine organs and systems of the body through several specific hormones. The developmental origin of the hypophysis is unique, with epithelial origins from neural ectoderm (posterior) and from surface ectoderm (anterior) the adenohypophyseal placode.
Drosophila and mouse placode similarity[11]
Olfactory Placodes(Nasal) Optic PlacodesOptic placodes (Lens) lie on the embryo surface, adjacent to the out-pocketing of the nervous system (forms the retina) and will form the lens. surface ectoderm -> lens placode -> lens pit -> lens vesicle -> lens fibres -> lens capsule and embryonic/fetal nucleus.
Trigeminal Placodes(Profundal)
Epibranchial PlacodesEpibranchial ganglia sensory neurons formed by the facial, glossopharyngeal, and vagal placodal regions. These ganglia neurons relay from the sensory organs such as gustatory taste buds, heart baroreceptors, gut sensory enteric nerves.
Sensory System
References
Online Textbooks
Reviews<pubmed></pubmed> <pubmed>24491817</pubmed> <pubmed>24495912</pubmed> <pubmed>22512454</pubmed> <pubmed>20801420</pubmed> <pubmed>20460364</pubmed> <pubmed>9927591</pubmed> Articles<pubmed></pubmed> <pubmed></pubmed> <pubmed>26258298</pubmed> <pubmed>17205191</pubmed> <pubmed>15380243</pubmed> <pubmed>10906460</pubmed> Search PubmedJune 2010 "placode development" All (852) Review (90) Free Full Text (285) Search Pubmed placode development | otic placode development | optic placode development | nasal placode development |
adenohypophyseal placode development
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Glossary Links
Cite this page: Hill, M.A. (2024, April 19) Embryology Placodes. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Placodes
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