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
|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)|
Some Recent Findings
Preplacodal development model
|Late Blastula Stage
||Late Gastrula Stage (9–10 hpf)
Experiments carried out in zebrafish.
(Above text from figure legend)
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.
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.
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.
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).
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.
Drosophila and mouse placode similarity
- Links: Pituitary Development
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.
| Senses Links: Introduction | Placodes | Hearing and Balance | Vision | Smell | Taste | Touch | Stage 22 | Category:Senses | original Sensory page
- ↑ Matthew N McCarroll, Zachary R Lewis, Maya Deza Culbertson, Benjamin L Martin, David Kimelman, Alex V Nechiporuk Graded levels of Pax2a and Pax8 regulate cell differentiation during sensory placode formation. Development: 2012, 139(15);2740-50 PMID:22745314
- ↑ Ben Steventon, Roberto Mayor, Andrea Streit Mutual repression between Gbx2 and Otx2 in sensory placodes reveals a general mechanism for ectodermal patterning. Dev. Biol.: 2012, 367(1);55-65 PMID:22564795
- ↑ A Tehindrazanarivelo, H Massiou, M G Bousser [What is new in the treatment of migraine?]. Rev Prat: 1990, 40(5);407-10 PMID:2155472 | BMC Neurosci.
- ↑ Raj K Ladher, Paul O'Neill, Jo Begbie From shared lineage to distinct functions: the development of the inner ear and epibranchial placodes. Development: 2010, 137(11);1777-85 PMID:20460364
- ↑ Lisa D Urness, Christian N Paxton, Xiaofen Wang, Gary C Schoenwolf, Suzanne L Mansour FGF signaling regulates otic placode induction and refinement by controlling both ectodermal target genes and hindbrain Wnt8a. Dev. Biol.: 2010, 340(2);595-604 PMID:20171206
- ↑ Andres F Sarrazin, Viviana A Nuñez, Dora Sapède, Valériane Tassin, Christine Dambly-Chaudière, Alain Ghysen Origin and early development of the posterior lateral line system of zebrafish. J. Neurosci.: 2010, 30(24);8234-44 PMID:20554875
- ↑ 7.0 7.1 Hye-Joo Kwon, Neha Bhat, Elly M Sweet, Robert A Cornell, Bruce B Riley Identification of early requirements for preplacodal ectoderm and sensory organ development. PLoS Genet.: 2010, 6(9); PMID:20885782 | PLoS Genet.
- ↑ Hillery Metz, Susan Wray Use of mutant mouse lines to investigate origin of gonadotropin-releasing hormone-1 neurons: lineage independent of the adenohypophysis. Endocrinology: 2010, 151(2);766-73 PMID:20008041
- ↑ Shu Wang, Natalia Tulina, Daniel L Carlin, Eric J Rulifson The origin of islet-like cells in Drosophila identifies parallels to the vertebrate endocrine axis. Proc. Natl. Acad. Sci. U.S.A.: 2007, 104(50);19873-8 PMID:18056636 | PMC2148390
- 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
Gerhard Schlosser Making senses development of vertebrate cranial placodes. Int Rev Cell Mol Biol: 2010, 283();129-234 PMID:20801420
Raj K Ladher, Paul O'Neill, Jo Begbie From shared lineage to distinct functions: the development of the inner ear and epibranchial placodes. Development: 2010, 137(11);1777-85 PMID:20460364
J Begbie, J F Brunet, J L Rubenstein, A Graham Induction of the epibranchial placodes. Development: 1999, 126(5);895-902 PMID:9927591
17205191 15380243 10906460
June 2010 "placode development" All (852) Review (90) Free Full Text (285)
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.
- 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
- Dr Mark Hill 2013, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G