Apical epithelial cap morphology and fibronectin gene expression in regenerating axolotl limbs

Autor: Randolph N. Christensen, Roy A. Tassava
Rok vydání: 2000
Předmět:
Zdroj: Developmental Dynamics. 217:216-224
ISSN: 1097-0177
1058-8388
DOI: 10.1002/(sici)1097-0177(200002)217:2<216::aid-dvdy8>3.0.co;2-8
Popis: Urodele amphibians (salaman- ders) are unique among adult vertebrates in their ability to regenerate limbs. The regener- ated structure is often indistinguishable from the developmentally produced original. Thus, the two processes by which the limb is produced — development and regeneration — are likely to use many conserved biochemical and develop- mental pathways. Some of these limb features are also likely to be conserved across vertebrate families. The apical ectodermal ridge (AER) of the developing amniote limb and the larger api- cal epithelial cap (AEC) of the regenerating urodele limb are both found at the limb's distal- most tip and have been suggested to be function- ally similar even though their morphology is quite different. Both structures are necessary for limb outgrowth. However, the AEC is uniformly smooth and thickly covers the entire limb-tip, unlike the AER, which is a protruding ridge cov- ering only the dorsoventral boundary. Previous data from our laboratory suggest the multilay- ered AEC may be subdivided into separate func- tional compartments. We used hematoxylin and eosin (H1E) staining as well as in situ hybridiza- tion 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 (FN) message very strongly in a stripe of cells along the dorso- ventral boundary. H1E 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 localiza- tion of FN protein inside the groove. The struc- tural and biochemical analyses presented here suggest that there is a specialized ridge-like com- partment in the basal AEC in late-stage regener- ates. The data also suggest that this compart- ment may be homologous to the AER of the developing amniote limb. Thus, the external dif- ferences between amniote limb development and urodele limb regeneration may be outweighed by internal similarities, which enable both pro- cesses 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 mol- ecules to promote mesenchymal cell cycling and dictating the direction of limb outgrowth. Fi- nally, we include here a clarification of existing nomenclature to facilitate further discussion of the AEC and its basal layer. Dev Dyn 2000;217: 216 -224. © 2000 Wiley-Liss, Inc.
Databáze: OpenAIRE
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