AER- apical ectodermal ridge AEC- apical epidermal cap How are the AER and the A
ID: 179282 • Letter: A
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AER- apical ectodermal ridge
AEC- apical epidermal cap
How are the AER and the AEC similar and how are they different? Replacement of the AEC by the progress zone of a developing axolotl limb allows regeneration to occur (see figure, left). However, if the progress zone form the opposite side of the body is used, you get a structure like the one on the right. What does this tell you about limb growth and regeneration? Come up with another experiment that you think would investigate some aspect of the regeneration process. What would you expect the experiment to show you?Explanation / Answer
The AEC is uniformly smooth and thickly covers the entire limb-tip, unlike the AER, which is a protruding ridge covering only the dorsoventral boundary. Ther are functinally similar.
They both differs in size and shape.
The two processes by which the limb is produced through development and regeneration are likely to use biochemical and developmental pathways. Some of these limb features are also likely to be conserved across vertebrate families. AEC may be subdivided into separate functional compartments. We used hematoxylin and eosin staining as well as in situ hybridization to examine the basal layer of the AEC, the layer that lies immediately over the distal limb mesenchyme. In late-stage regenerates, this basal layer expresses fibronectin message very strongly in a stripe of cells along the dorso-ventral boundary. H+E staining also reveals the unique shape of basal cells in this area. The stripe of cells in the basal AEC also contains the notch/groove structure previously seen in avian and reptilian AERs. In addition, AEC expression of FN message in the cells around the groove correlates with previous amniote AER localization of FN protein inside the groove. The structural and biochemical analyses presented here suggest that there is a specialized ridge-like compartment in the basal AEC in late-stage regenerates. The data also suggest that this compartment may be homologous to the AER of the developing amniote limb. Thus, the external differences between amniote limb development and urodele limb regeneration may be outweighed by internal similarities, which enable both processes to produce morphologically complete limbs. In addition, we propose that this basal layer of the AEC is uniquely responsible for AEC functions in regeneration, such as secreting molecules to promote mesenchymal cell cycling and dictating the direction of limb outgrowth. Finally, we include here a clarification of existing nomenclature to facilitate further discussion of the AEC and its basal layer.
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