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Journal of Undergraduate Research

Keywords

limb formation, tetra pods, AER, apical ectodermal ridge, proximal to distal, PD

College

Life Sciences

Department

Physiology and Developmental Biology

Abstract

Limb formation in tetra pods, animals with four legs, starts with the outgrowth of lateral plate mesoderm at the level of both forelimb and hind limb. A ridge of ectodermal tissue located at the distal margin, named the apical ectodermal ridge (AER), plays an essential role for the outgrowth and patterning of limbs. Patterning is defined as molecular or morphological differences that are established along an axis. The limb is patterned along each of its three axes: along the proximal to distal (PD) axis, the nature of the limb changes from humerus/femur (stylopod) to radius, ulna/tibia, fibula (zeugopod), to hand/foot (autopod). Anterior posterior (AP) axis patterning in the fore limb is defined as radius and thumb anteriorly and pinky and ulna posteriorly. Finally, the limb is patterned along the dorsoventral (DV) axis with the palm of the hand being ventral and the back of the hand being dorsal. The embryonic precursor to the vertebrate limb is the limb bud. The limb bud is composed of loosely organized cells that will give rise to the limb skeleton known as the limb mesenchyme. These cells are jacketed by overlying surface ectoderm which will later form the epidermis that covers the limb.

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