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Size dependence during the development of the amphibian foot. Colchicine-induced digital loss and reduction.
Alberch P
,
Gale EA
.
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Localized treatment of the limb buds of the frog, Xenopus laevis, and the salamander, Ambystoma mexicanum, with the mitotic inhibitor colchicine results in limbs that, when compared with the contralateral control, are smaller in size and have lost skeletal elements. There is a very well defined pattern in terms of what elements are most likely to be lost. For example, frogs that have lost a toe always lose the first toe, while salamanders always lose the fifth. These differences correspond to qualitative differences in developmental sequence of digital differentiation in anurans as compared to urodeles. We propose a hypothesis in which the digital pattern is indirectly affected by reduction in the number of mesenchymal cells in the embryonic field.
Fig. 1. Stage-52 Xenopus laevis limb bud. No chondrogenetic condensations have occurred yet. Bar equal to 0-1 mm.
Fig. 2. Cleared and stained axolotl digital ontogeny: A) two-digit stage, the metatarsals of digits 1 and 2 have differentiated; B) three-digit stage; C) four-digit stage.
Note the clearly asynchronous development of the toes. In Figs C and D the peculiar 'splitting' of the cartilaginous rod to form phalanges 2 and 3 can be observed in the fourth toe. Bar equal to 1 mm
Fig. 4. Detail of limb bud treated with colchicine (A). Cells exhibit a rounded morphology and are more closely packed together than in the normal limb bud (B). Also some cell death and extracellular debris can be observed. Bar equal to 0-05 mm
Fig. 5. Summary of the loss of skeletal elements in colchicine-treated animals. Numbers within the boxes indicate the percentage of specimens that have lost the given element. Columns represent digit number, while rows are: MT- metatarsal; PH1-4- phalanges one to four.
Fig. 6. Cleared and stained (A) control right foot and (B) treated left foot of
Xenopus laevis (specimen No. X-29). Note the smaller size of the treated foot
Fig. 7. Cleared and stained (A) treated left foot and (B) control right foot of Ambystoma mexicanum (specimen No. A-5). Note the smaller size of the treated foot.
