Discussion
Discussion
In this experiment, it was predicted that exposure to cyclopamine and ethanol would induce developmental malformations in the axolotl embryos, and that increased dosages of these teratogens would produce more severe defects. These predictions were made based on existing information that cyclopamine is known to block the Shh signaling pathway in some higher vertebrates (Gilbert, 2003).
The results of the experiment support the prediction that exposing embryos to cyclopamine causes defects in areas that depend on Shh during development. In particular, the 100 uM cyclopamine experimental group suffered severe body and tail truncation, which is closely associated with Shh inhibition. This sugests that axolotols share the same Shh signaling pathway with other higher vertebrates, such as birds and mammals, and establishes an evolutionary connection between these groups.
It was not predicted that the 50 uM cyclopamine group, as well as both ethanol experimental groups, would experience a 100% fatality rate. These results are especially confounding when the 100% survival rate of the 100 uM cyclopamine experimental group is taken into consideration. It is possible that the 100 uM group randomly consisted of hardier embryos, or that the 50 uM group and the ethanol groups randomly consisted of embryos that were more susceptible to teratogenic agents. It is also possible that most of the dead embryos suffered mechanical harm during the de-jellying process, which contributed to their early demise. However, this aspect of the experiment must remain inconclusive until further experiments using cyclopamine and ethanol on axolotls can be performed. Repetition of this experiment is the only way to be sure that random error did not play a role in skewing these data. It may also be worthwhile to expose axolotl embryos to amounts of ethanol less than 30 uL in order to determine the horizon of ethanol tolerance in this species.
Based on these data, it can be inferred that axolotls share a common signaling pathway with some birds and mammals. Does this mean that Shh exists in all vertebrates? Cyclopmine testing in a wider array of animals may help address this question. Also,is it possible to determine if evolution has consistently selected to conserve this trait in vertebrates? Answering these questions will help the scientific community gain greater insight into animal genetic history and the evolution.
Acknowledgements
The author would like to thank Judy Cebra-Thomas and William Gresh for their assistance both in and out of lab. Without their help, this paper would not have been possible.