Die Morphologie der apikalen Epidermis w�hrend der fr�hen Extremit�tenentwicklung bei Anuren

Abstract

1. The hindlimb buds of AnuraAlytes obstetricans, Bombina variegata, Rana temporaria, Ranma esculenta, Bufo bufo andBufo calamita were investigated for the presence of an apical ectodermal ridge using histological techniques and dry preparations. 2. In all six Anura species an apical ectodermal ridge was found to be present. The ridge ofAlytes obstetricans, in particular, is comparable with that of Amniota. 3. InAlytes obstetricans, Rana temporaria andRana esculenta an increase in cell layers and development of basal columnar cells leads to the formation of the apical ectodermal ridge, while as inBufo bufo, Bufo calamita andBombina variegata the development of the basal columnar cells alone forms the ridge. 4. The apical ectodermal ridge exists from the stage when the limb buds are approximately the same length as breadth until the beginning of the digit formation. 5. With the exception ofBufo calamita the apical ectodermal ridge extends asymetrically over the apex of the limb bud being longer on the preaxial side. 6. The marginal vein is only visible after the ridge development has begun. It underlies the ridge in the mesenchyme one or more cell layers beneath the basal membrane. 7. InRana temporaria andAlytes obstetricans an increased percentage of pycnotic cells is found within the ridge during a particular period.

Morphological Variation in Anuran Limbs: Constraints and Novelties

“…In anurans, the few descriptions of the apical epidermis of the limb bud reveal some degree of variation in the number and configuration of its layers (Tarin and Sturdee, ; Stebler, ; Sturdee and Connock, ). Its thickening appears later, and it is less pronounced than in amniotes (Tarin and Sturdee, ; Stebler, ; Sturdee and Connock, ; Todt and Fallon, ; Raynaud, ; Davis et al., ). At least one anuran, the direct developing Eleutherodactylus coqui , has no distinct AER, but signal functions are carried out by distal ectoderm cells forming a thickened cap (Richardson et al., ).…”

“…However, the forelimb apical thickness is less pronounced than in the hind limb. Following the terms in the literature (Tarin and Sturdee, ; Stebler, ; Sturdee and Connock, ), we characterized the AER (Fig. ) as (1) low (two cuboidal external layers with a taller inner layer) in Ceratophrys cranwelli, Chacophrys pierottii, Dermatonotus muelleri, Elachistocleis bicolor, Lepidobatrachus llanensis, Leptodactylus chaquensis, L. latinasus, Physalaemus biligonigerus ; (2) moderate (two cuboidal external layers with a pseudostratified inner layer) in Hypsiboas andinus, Phyllomedusa sauvagii, Scinax acuminatus, S. fuscovarius ; and (3) well developed (an inner columnar layer covered by two external layers) as in Pseudis paradoxa .…”

“…It is a major signaling center for the developing appendage (Saunders, ; Gilbert, ). In anurans, the few descriptions of the apical epidermis of the limb bud reveal some degree of variation in the number and configuration of its layers (Tarin and Sturdee, ; Stebler, ; Sturdee and Connock, ). Its thickening appears later, and it is less pronounced than in amniotes (Tarin and Sturdee, ; Stebler, ; Sturdee and Connock, ; Todt and Fallon, ; Raynaud, ; Davis et al., ).…”