Placodes: Difference between revisions
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* '''Nasal and otic placode specific regulation of Sox2 involves both activation by Sox-Sall4 synergism and multiple repression mechanisms'''{{#pmid:29137924|PMID29137924}} "Transcription factor gene Sox2 is expressed throughout sensory development, but the enhancers that regulate the gene vary depending on the developmental stages and tissues. To gain new insights into the gene regulatory network in sensory placode specification, regulation of the nasal-otic bispecific NOP1 enhancer of {{Sox}}2 was investigated in chicken embryos. Deletion and mutational analyses using electroporation showed that transcriptional repression mechanisms in combination with activation mechanisms determine placodal specificity. Activation of the NOP1 enhancer involves synergistic action by Sall4 and SoxB1/SoxE factors that bind to the adjacent sites. Deletion of repressive elements resulted in widening of the tissue area for enhancer activity to a region where the expression of Sall4 and SoxB1/E overlaps, e.g., the CNS and neural crest. Among multiple repressive elements that contribute to the placodal confinement of the NOP1 enhancer activity, CACCT/CACCTG motifs bound by Zeb/Snail family repressors play important roles. Overexpression of δEF1 (Zeb1) or Snail2 (Slug) strongly inhibited NOP1 activity. These data indicate that both activation by Sall4-Sox synergism and multiple repression mechanisms involving Zeb/Snail factors are essential for Sox2 regulation to be confined to the nasal and otic placodes." | |||
* '''Anosmin-1 is essential for neural crest and cranial placodes formation in Xenopus'''{{#pmid:29277616|PMID29277616}} "During embryogenesis vertebrates develop a complex craniofacial skeleton associated with sensory organs. These structures are primarily derived from two embryonic cell populations the neural crest and cranial placodes, respectively. ...Anos1 was identified as a target of Pax3 and Zic1, two transcription factors necessary and sufficient to generate neural crest and cranial placodes. Anos1 is expressed in cranial neural crest progenitors at early neurula stage and in cranial placode derivatives later in development. We show that Anos1 function is required for neural crest and sensory organs development in Xenopus, consistent with the defects observed in Kallmann syndrome patients carrying a mutation in ANOS1." [[Frog Development]] | * '''Anosmin-1 is essential for neural crest and cranial placodes formation in Xenopus'''{{#pmid:29277616|PMID29277616}} "During embryogenesis vertebrates develop a complex craniofacial skeleton associated with sensory organs. These structures are primarily derived from two embryonic cell populations the neural crest and cranial placodes, respectively. ...Anos1 was identified as a target of Pax3 and Zic1, two transcription factors necessary and sufficient to generate neural crest and cranial placodes. Anos1 is expressed in cranial neural crest progenitors at early neurula stage and in cranial placode derivatives later in development. We show that Anos1 function is required for neural crest and sensory organs development in Xenopus, consistent with the defects observed in Kallmann syndrome patients carrying a mutation in ANOS1." [[Frog Development]] | ||
Revision as of 13:34, 12 May 2019
Embryology - 18 Apr 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.[12] 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 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[15]
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 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, April 18) Embryology Placodes. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Placodes
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