Results
Ten transplants were sucessfully completed using portions of albino embryos inserted into regularly pigmented embryos (Figure 3). Of these ten transplants, nine continued to develop twenty-four hours post surgery. However, after forty eight hours, once the process of diluting the HBSt solution was begun, development of all remaining embryos failed due to developmental abnormalities unrelated to the transfer region of the embryo (Figure 4). Cells lost their cohesiveness and failed to divide within the expected patterns, resulting in fatal delamination and abnormal extensions of mesoderm. These abnormailites resulted in the termination of development.
Discussion
Termination of development was caused by the abnormal cell growth of region of the embryos not directly affected by the transplant. These growths may have been caused by insufficient cadherin expression between cells (Gilbert, 2000), given that the protective and somewhat shape sustaining membrane had been removed. Once the membrane was removed from the embryo, there may not have been sufficient structural constrictions to maintain proper form and direction of growth. Furthermore, the agar plates used as operating dishes in this experiment had depressions in order to facilitate the surgery, and to hold the embryos stable post-surgery. Post surgery, however, the embryos lost their shape and mesodermal and endodermal cells extended into the depressions. The changes in shape most likely were sufficient to destroy the embryos.
However, with the exception of one embryo, all transplants were sucessful up to twenty four hours after surgery (Figure 5). In the failed embryo, the transplant may have been inserted into the transplant incision incorectly, that is, the cells that were fated to become ectoderm were aligned with the endo derm of the recipient embryo. Grafts transplanted in this manner would fail to heal because the ectodermal cells would express different cadherins than would the endodermal cells (Gilbert, 2000). Experimental errors such as this may be avoidable if the transplant was taken from a pigmented donor and grafted to an albino recipient because in pigmented specimens, the ectoderm is easily distinguishable from the endoderm, and inversions of the grafts would not occur.
In the remaining nine embryos, however, the grafts began to heal, indicating that, had other unrelated problems not arisen, the transplants would have resulted in fully developed Axolotl embryos displaying albino regions on their dorsal side. In the future, dilutions of the HBSt solution should be made more gradually, and the embryos should be transferred to a petri dish without depressions as soon after the transplant as possible.