Placodes: Difference between revisions
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===Stage 11=== | ===Stage 11=== | ||
The scanning EM of the week 4 human embryo | The scanning EM of the week 4 human embryo Carnegie stage {{CS11}} 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. | ||
[[File:Stage11_sem13.jpg|300px]] [[File:Stage11_sem20.jpg|300px]] | [[File:Stage11_sem13.jpg|300px]] [[File:Stage11_sem20.jpg|300px]] | ||
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===Stage 12=== | ===Stage 12=== | ||
By | By Carnegie stage {{CS12}} 26 days, only a small opening of the developing otic vesicle (otocyst) remains visible on the embryo surface located behind the second pharyngeal arch. | ||
[[File:Stage12 sem4.jpg|300px]] [[File:Stage12 sem5.jpg|300px]] | [[File:Stage12 sem4.jpg|300px]] [[File:Stage12 sem5.jpg|300px]] | ||
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===Stage 13=== | ===Stage 13=== | ||
By week 5 | By week 5 Carnegie stage {{CS13}} the otic vesicle (otocyst) is completely formed and is no longer visible on the embryo surface. | ||
[[File:Stage13_sem1.jpg|300px]] | [[File:Stage13_sem1.jpg|300px]] | ||
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{| | {| | ||
! colspan=4|''' | ! colspan=4|'''Carnegie stage {{CS13}} - serial sections''' ''serial labeled images'' | ||
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| [[File:Stage 13 image 051.jpg|180px]] | | [[File:Stage 13 image 051.jpg|180px]] | ||
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:'''Links:''' | :'''Links:''' {{Inner ear}} | {{Hearing}} | {{Balance}} | ||
==Adenohypophyseal Placode== | ==Adenohypophyseal Placode== | ||
[[File:Mouse-pituitary development.jpg|thumb|Pituitary Development]] | |||
Adenohypophysis placodal precursors arise within the midline rostral preplacodal cranial ectoderm.{{#pmid:28974641|PMID28974641}} This placode is unique, in being unpaired (only single placode) and also generating a structure endocrine endocrine character. | |||
The hypophysis, or '''{{pituitary}}''', is an endocrine gland that links the brain to peripheral endocrine organs and systems of the body through several specific hormones. There is a dual developmental origin of the hypophysis, with epithelial origins from neural ectoderm (posterior) and from surface ectoderm (anterior) the adenohypophyseal placode. | |||
The hypophysis, or '''pituitary''', is an endocrine gland that links the brain to peripheral endocrine organs and systems of the body through several specific hormones. | |||
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[[File:Drosophila and mouse placode similarity.jpg|200px]] | [[File:Drosophila and mouse placode similarity.jpg|200px]] | ||
Drosophila and mouse placode similarity{{#pmid:18056636|PMID18056636}} | Drosophila and mouse placode similarity.{{#pmid:18056636|PMID18056636}} | ||
:'''Links:''' | :'''Links:''' {{Pituitary}} | ||
==Olfactory Placodes== | ==Olfactory Placodes== | ||
(Nasal) | (Nasal) | ||
The olfactory epithelium develops from the paired nasal placodes, each develop initially with two components, a medial and lateral region. | |||
{| | |||
! colspan=4|'''Carnegie stage {{CS13}} - serial sections''' ''nasal placodes'' | |||
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| [[File:Stage 13 image 059.jpg|200px]] | |||
| [[File:Stage 13 image 060.jpg|200px]] | |||
| [[File:Stage 13 image 061.jpg|200px]] | |||
| [[File:Stage 13 image 062.jpg|200px]] | |||
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| [[File:Stage 13 image 063.jpg|200px]] | |||
| [[File:Stage 13 image 064.jpg|200px]] | |||
| [[File:Stage 13 image 065.jpg|200px]] | |||
| [[File:Stage 13 image 066.jpg|200px]] | |||
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{| | |||
| Nasal Placode - Human Embryo stage {{CS14}} | |||
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| [[File:Stage14 sem2b-limb.jpg|300px]] | |||
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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 the real origin is associated with the formation of the nasal placode.{{#pmid:20008041|PMID20008041}} | |||
:'''Links:''' {{nasal placode}} | {{smell} | |||
==Optic Placodes== | ==Optic Placodes== |
Latest revision as of 11:40, 31 July 2019
Embryology - 11 May 2024 Expand to Translate |
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Introduction
The term placode refers to ectoderm thickenings in the cranial region that have important roles in development of special sensory and other systems. There are also integumentary placodes that are involved with hair follicle development covered on a separate content page.
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
Animal studies have shown that programmed cell death (apoptosis) appears regulate precursor cells of some of the early developing placodes and leads to the regression of epibranchial placodes.[1]
Other Placodes? | |
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Note that a second, later developing, form of ectodermal placode development occurs with the development of hair, gland, feather (other species), follicles associated with integumentary specialisations. This topic does not directly relate to the specialised placodes of the head region covered here. (More? hair | integumentary) |
Placode Links: placode | Week 4 | sensory | Otic Placode | Optic Placode | Nasal Placode | Category:Placode | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Some Recent Findings
Movies
Preplacodal DevelopmentThe neural plate and mesoderm together release fibroblast growth factors (FGFs) that, together with local down-regulation of BMPs and Wnts, act to induce the "pre-placodal" region.[13] This initial original ectodermal thickenings arising from the anterior neural plate border area.
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 PlacodeAdenohypophysis placodal precursors arise within the midline rostral preplacodal cranial ectoderm.[15] This placode is unique, in being unpaired (only single placode) and also generating a structure endocrine endocrine character.
Drosophila and mouse placode similarity.[17]
Olfactory Placodes(Nasal) The olfactory epithelium develops from the paired nasal placodes, each develop initially with two components, a medial and lateral region.
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 Placodes
Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9
Paratympanic Organ PlacodeThe paratympanic organ is a mechanoreceptive sense organ in the middle ear of birds and other tetrapods. It develops from the paratympanic organ placode that is probably developmentally independent of the ventrally adjacent first epibranchial (or 'geniculate') placode. References
Online Textbooks
ReviewsStreit A. (2018). Specification of sensory placode progenitors: signals and transcription factor networks. Int. J. Dev. Biol. , 62, 195-205. PMID: 29616729 DOI. Adameyko I & Fried K. (2016). The Nervous System Orchestrates and Integrates Craniofacial Development: A Review. Front Physiol , 7, 49. PMID: 26924989 DOI. Schlosser G, Patthey C & Shimeld SM. (2014). The evolutionary history of vertebrate cranial placodes II. Evolution of ectodermal patterning. Dev. Biol. , 389, 98-119. PMID: 24491817 DOI. Patthey C, Schlosser G & Shimeld SM. (2014). The evolutionary history of vertebrate cranial placodes--I: cell type evolution. Dev. Biol. , 389, 82-97. PMID: 24495912 DOI. Graham A & Shimeld SM. (2013). The origin and evolution of the ectodermal placodes. J. Anat. , 222, 32-40. PMID: 22512454 DOI. Schlosser G. (2010). Making senses development of vertebrate cranial placodes. Int Rev Cell Mol Biol , 283, 129-234. PMID: 20801420 DOI. Ladher RK, O'Neill P & Begbie J. (2010). From shared lineage to distinct functions: the development of the inner ear and epibranchial placodes. Development , 137, 1777-85. PMID: 20460364 DOI. Schlosser G. (2006). Induction and specification of cranial placodes. Dev. Biol. , 294, 303-51. PMID: 16677629 DOI. Begbie J, Brunet JF, Rubenstein JL & Graham A. (1999). Induction of the epibranchial placodes. Development , 126, 895-902. PMID: 9927591 ArticlesWashausen S & Knabe W. (2018). Lateral line placodes of aquatic vertebrates are evolutionarily conserved in mammals. Biol Open , 7, . PMID: 29848488 DOI. Abitua PB, Gainous TB, Kaczmarczyk AN, Winchell CJ, Hudson C, Kamata K, Nakagawa M, Tsuda M, Kusakabe TG & Levine M. (2015). The pre-vertebrate origins of neurogenic placodes. Nature , 524, 462-5. PMID: 26258298 DOI. Mazet F. (2006). The evolution of sensory placodes. ScientificWorldJournal , 6, 1841-50. PMID: 17205191 DOI. Bhattacharyya S & Bronner-Fraser M. (2004). Hierarchy of regulatory events in sensory placode development. Curr. Opin. Genet. Dev. , 14, 520-6. PMID: 15380243 DOI. Köster RW, Kühnlein RP & Wittbrodt J. (2000). Ectopic Sox3 activity elicits sensory placode formation. Mech. Dev. , 95, 175-87. PMID: 10906460 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 External LinksExternal Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name. Links to any external commercial sites are provided for information purposes only and should never be considered an endorsement. UNSW Embryology is provided as an educational resource with no clinical information or commercial affiliation.
Glossary Links
Cite this page: Hill, M.A. (2024, May 11) Embryology Placodes. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Placodes
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