Apical ectodermal ridge

Apical Ectodermal Ridge (AER) is a critical structure in vertebrate embryonic development. It is a thickened area of ectoderm at the most distal part of the developing limb bud. The AER plays a crucial role in the process of limb development, guiding the growth and patterning of the limb along the anterior-posterior axis.

Function

The AER is responsible for the production of several important growth factors, including Fibroblast Growth Factor (FGF). These growth factors stimulate the proliferation of underlying mesodermal cells, allowing for the elongation of the limb bud. The AER also plays a role in the patterning of the limb, with different regions of the AER corresponding to different parts of the mature limb.

Formation

The AER forms from the ectoderm, one of the three primary germ layers in the early embryo. The formation of the AER is induced by signals from the underlying mesoderm, particularly the region known as the Progress Zone (PZ). The PZ produces FGFs, which induce the overlying ectoderm to thicken and form the AER.

Role in Disease

Abnormalities in the AER can lead to a variety of congenital limb defects, such as polydactyly (extra digits), syndactyly (fused digits), and limb reduction defects (shortened or missing limbs). These defects can occur as a result of mutations in the genes that regulate AER formation and function, or due to environmental factors that disrupt AER activity.

See Also

• Limb development
• Ectoderm
• Fibroblast Growth Factor
• Congenital limb defects