Journal of Undergraduate Research


elucidation, embryonic chicken limbs, limb growth, morphogenetic paradigm


Life Sciences


Physiology and Developmental Biology


As established by John Saunders 60 years ago, the AER is required for limb growth and patterning. However, the mechanisms whereby the AER regulates these processes remain poorly understood. My professor and I propose that one of the primary roles of the AER is to regulate directional growth of the adjacent limb mesenchyme. Over time, the AER extends along the anteroposterior (AP) and thins along the dorsoventral (DV) axes. These results highlight a morphogenetic paradigm: the dimensions of recruitment signaling centers ultimately shape organs. This model also provides mechanistic insight for evolutionary change. We also show that sonic hedgehog (Shh) protein, excreted by the zone of polarizing activity (ZPA), directly regulates AER viability. The ZPA regulates AER viability through Shh signaling in the posterior AER. Surgical removal of the posterior AER and implantation of a Shh-soaked bead in the anterior mesenchyme maintains anterior AER.

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