Placodes: Difference between revisions
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==Introduction== | ==Introduction== | ||
[[File:Stage14 sem2b-limb.jpg|thumb|Human Embryo stage 14 sensory placodes]] | [[File:Stage14 sem2b-limb.jpg|thumb|Human Embryo stage 14 sensory placodes]] | ||
Placodes are ectodermal thickenings which have important roles in development of special sensory systems. | Placodes are [[Ectoderm|ectodermal]] thickenings which have important roles in development of special sensory systems. | ||
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* '''Epibranchial Placodes'''<ref><pubmed>20460364</pubmed></ref> "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." | * '''Epibranchial Placodes'''<ref><pubmed>20460364</pubmed></ref> "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'''<ref><pubmed>20171206</pubmed></ref> "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." | * '''Otic Placode'''<ref><pubmed>20171206</pubmed></ref> "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'''<ref><pubmed>20554875</pubmed></ref> "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." | * '''Postotic Placode'''<ref><pubmed>20554875</pubmed></ref> "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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Revision as of 16:02, 10 April 2017
Embryology - 29 Mar 2024 Expand to Translate |
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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, March 29) Embryology Placodes. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Placodes
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