Placodes: Difference between revisions
mNo edit summary |
mNo edit summary |
||
Line 32: | Line 32: | ||
|-bgcolor="F5FAFF" | |-bgcolor="F5FAFF" | ||
| | | | ||
* '''Setting appropriate boundaries: Fate, patterning and competence at the neural plate border'''<ref name=PMID24321819><pubmed>24321819</pubmed></ref> "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'''<ref name=PMID22745314><pubmed>22745314</pubmed></ref> "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." | * '''Graded levels of Pax2a and Pax8 regulate cell differentiation during sensory placode formation'''<ref name=PMID22745314><pubmed>22745314</pubmed></ref> "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." | ||
* '''Mutual repression between Gbx2 and Otx2 in sensory placodes reveals a general mechanism for ectodermal patterning'''<ref><pubmed>22564795</pubmed></ref> "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." | * '''Mutual repression between Gbx2 and Otx2 in sensory placodes reveals a general mechanism for ectodermal patterning'''<ref><pubmed>22564795</pubmed></ref> "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." |
Revision as of 00:16, 27 December 2013
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 may arise from common panplacodal primordium origin around the neural plate, and then differentiate 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? | ||
---|---|---|
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) |
- Links: Week 4 | Otic Placode | Optic Placode | Nasal Placode | Sensory System Development
Some Recent Findings
|
More recent papers |
---|
This table allows an automated computer search of the external PubMed database using the listed "Search term" text link.
More? References | Discussion Page | Journal Searches | 2019 References | 2020 References Search term: Placode <pubmed limit=5>Placode</pubmed> |
Preplacodal Development
Preplacodal development model[8]
Late Blastula Stage
|
Late Gastrula Stage (9–10 hpf)
Experiments carried out in zebrafish. |
(Above text from figure legend[8])
Otic Placode
The 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 11
The 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 12
By 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 13
By 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).
A2L | A3L | A4L | A5L |
- Links: Inner Ear | Hearing and Balance Development
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. The developmental origin of the hypophysis is unique, with epithelial origins from neural ectoderm (posterior) and from surface ectoderm (anterior) the adenohypophyseal 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.[9]
Drosophila and mouse placode similarity[10]
- Links: Pituitary Development
Olfactory Placodes
(Nasal)
Optic Placodes
Optic 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.
- Links: Lens Development | Vision Development
Trigeminal Placodes
(Profundal)
Epibranchial Placodes
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.
Sensory System
Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9
- Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline
References
- ↑ <pubmed>24321819</pubmed>
- ↑ <pubmed>22745314</pubmed>
- ↑ <pubmed>22564795</pubmed>
- ↑ <pubmed>2155472</pubmed>| BMC Neurosci.
- ↑ <pubmed>20460364</pubmed>
- ↑ <pubmed>20171206</pubmed>
- ↑ <pubmed>20554875</pubmed>
- ↑ 8.0 8.1 <pubmed>20885782</pubmed>| PLoS Genet.
- ↑ <pubmed>20008041</pubmed>
- ↑ <pubmed>18056636</pubmed>| PMC2148390
Online Textbooks
- Colloquium Series on Developmental Biology Induction and Segregation of the Vertebrate Cranial Placodes Park BY, Saint-Jeannet JP. San Rafael (CA): Morgan & Claypool Life Sciences; 2010.
- Developmental Biology (6th ed.) Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000. Chick embryo rhombomere neural crest cells | Some derivatives of the pharyngeal arches | Tissue Architecture of the Central Nervous System | Neuronal Types | Snapshot Summary: Central Nervous System and Epidermis
- Neuroscience Purves, Dale; Augustine, George J.; Fitzpatrick, David; Katz, Lawrence C.; LaMantia, Anthony-Samuel; McNamara, James O.; Williams, S. Mark. Sunderland (MA): Sinauer Associates, Inc. ; c2001 The Auditory System | The Inner Ear | Early Brain Development
- Clinical Methods 63. Cranial Nerves IX and X: The Glossopharyngeal and Vagus Nerves | The Tongue | 126. The Ear and Auditory System | An Overview of the Head and Neck - Ears and Hearing | Audiometry
- Eurekah Bioscience Collection Cranial Neural Crest and Development of the Head Skeleton
Search Bookshelf placode development
Reviews
<pubmed>20801420</pubmed> <pubmed>20460364</pubmed> <pubmed>9927591</pubmed>
Articles
17205191 15380243 10906460
Search Pubmed
June 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 Links
External 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
- Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link
Cite this page: Hill, M.A. (2024, April 26) Embryology Placodes. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Placodes
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G