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Apical ectodermal ridge
The apical ectodermal ridge is a region of thickened epithelium at the most distal end of the limb bud. The zone of polarising activity (ZPA) is at the posterior part of the limb bud.
Details
Identifiers
Latin
crista ectodermalis apicalis
TE
ectodermal ridge_by_E5.0.3.0.0.3.4 E5.0.3.0.0.3.4
Anatomical terminology
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The apical ectodermal ridge (AER) is a structure that forms from the ectodermal cells at the distal end of each limb bud and acts as a major signaling center to ensure proper development of a limb. After the limb bud induces AER formation, the AER and limb mesenchyme—including the zone of polarizing activity (ZPA)—continue to communicate with each other to direct further limb development.[1]
The position of the limb bud, and hence the AER, is specified by the expression boundaries of Hox genes in the embryonic trunk. At these positions, the induction of cell outgrowth is thought to be mediated by a positive feedback loop of fibroblast growth factors (FGFs) between the intermediate mesoderm, the lateral plate mesoderm and the surface ectoderm. FGF8 in the intermediate mesoderm signals to the lateral mesoderm, restricting the expression of FGF10 through intermediate Wnt signals. Then, FGF10 in the lateral plate mesoderm signals to the surface ectoderm to create the AER, which expresses FGF8.[2]
The AER is known to express FGF2, FGF4, FGF8, and FGF9, while the limb bud mesenchyme expresses FGF2 and FGF10. Embryo manipulation experiments have shown that some of these FGFs alone are sufficient for mimicking the AER.[3]
^Gilbert, Scott F. "Developmental Biology". 9th ed., 2010
^Ohuchi H, Nakagawa T, Yamamoto A, et al. (June 1997). "The mesenchymal factor, FGF10, initiates and maintains the outgrowth of the chick limb bud through interaction with FGF8, an apical ectodermal factor". Development. 124 (11): 2235–44. doi:10.1242/dev.124.11.2235. PMID 9187149.
^Martin GR (June 1998). "The roles of FGFs in the early development of vertebrate limbs". Genes Dev. 12 (11): 1571–86. doi:10.1101/gad.12.11.1571. PMID 9620845.
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lacrimal gland, tarsal glands, and the conjunctiva of the eye The apicalectodermalridge, which induces the development of the limb buds of the embryo List...
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parietal layer of lateral plate mesoderm. Ectodermal cells at the distal end of the buds form the apicalectodermalridge, which creates an area of rapidly proliferating...
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involves many signaling molecules such as FGF, BMP, SHH and WNT. The apicalectodermalridge is a structure found at the distal most tip which becomes a key...
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ectoderm to form an important organizing structure called the apicalectodermalridge (AER). The AER reciprocatively secretes FGF8 and FGF4 which maintains...
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similar protein is thought to be responsible for maintaining the apicalectodermalridge of developing limb buds; disruption of the mouse gene results in...
that zone of polarizing activity (ZPA) requires maintenance of apicalectodermalridge (AER). The dependence of ZPA on ARE indicates the linkage between...
the distal tip of the forming limb bud with an abundance in the apicalectodermalridge. In a knockout mouse model, mice manifest with severe limb malformations...
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