Sessions S K, Gardiner D M, Bryant S V
Developmental Biology Center, University of California, Irvine 92717.
Dev Biol. 1989 Feb;131(2):294-301. doi: 10.1016/s0012-1606(89)80002-8.
We have experimentally tested the similarity of limb pattern-forming mechanisms in urodeles and anurans. To determine whether the mechanisms of limb outgrowth are equivalent, we compared the results of two kinds of reciprocal limb bud grafts between Xenopus and axolotls: contralateral grafts to confront anterior and posterior positions of graft and host, and ipsilateral grafts to align equivalent circumferential positions. Axolotl limb buds grafted to Xenopus hosts are immunologically rejected at a relatively early stage. Prior to rejection, however, experimental (but not control) grafts form supernumerary digits. Xenopus limb buds grafted to axolotl hosts are not rejected within the time frame of the experiment and therefore can be used to test the ability of frog cells to elicit responses from axolotl tissue that are similar to those that are elicited by axolotl tissue itself. When Xenopus buds were grafted to axolotl limb stumps so as to align circumferential positions, the majority of limbs did not form any supernumerary digits. However, in experimental grafts, where anterior and posterior of host and graft were misaligned, supernumerary digits formed at positional discontinuities. These results suggest that Xenopus/axolotl cell interactions result in responses that are similar to axolotl/axolotl cell interactions. Furthermore, axolotl and Xenopus cells can cooperate to build recognizable skeletal elements, despite large differences in cell size and growth rate between the two species. We infer from these results that urodeles and anurans share the same limb pattern-forming mechanisms, including compatible positional signals that allow appropriate localized cellular interactions between the two species. Our results suggest an approach for understanding homology of the tetrapod limb based on experimental cellular interactions.
我们已经通过实验测试了有尾目动物和无尾目动物肢体模式形成机制的相似性。为了确定肢体生长机制是否相同，我们比较了非洲爪蟾和蝾螈之间两种相互肢体芽移植的结果：对侧移植以对比移植体和宿主的前后位置，同侧移植以对齐等效的圆周位置。移植到非洲爪蟾宿主的蝾螈肢体芽在相对早期就会被免疫排斥。然而，在排斥之前，实验性（而非对照性）移植会形成额外的指。移植到蝾螈宿主的非洲爪蟾肢体芽在实验时间范围内不会被排斥，因此可用于测试蛙细胞引发蝾螈组织产生与蝾螈组织自身引发的反应相似的反应的能力。当将非洲爪蟾芽移植到蝾螈肢体残端以对齐圆周位置时，大多数肢体不会形成任何额外的指。然而，在实验性移植中，宿主和移植体的前后位置未对齐，在位置不连续处形成了额外的指。这些结果表明，非洲爪蟾/蝾螈细胞间相互作用产生的反应与蝾螈/蝾螈细胞间相互作用相似。此外，尽管这两个物种的细胞大小和生长速度存在很大差异，但蝾螈和非洲爪蟾细胞可以合作构建可识别的骨骼元素。我们从这些结果推断，有尾目动物和无尾目动物共享相同的肢体模式形成机制，包括允许两个物种之间进行适当局部细胞相互作用的兼容位置信号。我们的结果提出了一种基于实验性细胞相互作用来理解四足动物肢体同源性的方法。
