Discussion

The attempt to produce cardia bifida in chicken embryos was successful, providing strong support to the hypothesis that the heart is an organ that undergoes regulative development. Our results suggest that the two heart primordia do not require interactions with each other in order to form beating hearts at the loop stage, because they form two beating hearts even when migration is prevented. Each primordium therefore appears to have the ability to compensate for the lack of the other. In this experiment, migration and fusion were physically prevented by the incision along the ventral midline, but two beating hearts still formed. The signals from the anterior and lateral endoderm therefore appear to be sufficient for inducing heart cell specification and differentiation. If the other heart primordium is not present, a complete heart tube nevertheless forms and loops. Thus, it is likely that if cardia bifida occurred in vivo, the organism would develop two beating hearts, much as the embryos did in culture.

This experiment could be improved with practice and an increased sample size. Over the course of the experiment, only 54.6% of the chicken embryos available were killed or lost during the transfer from the eggs to the culture dishes. Such a high attrition rate could, in large part, be attributed to methodical difficulties like breaking the egg yolk during the transfer. This was most likely due to inexperience in manipulating such young and fragile chicken embryos. Hence, any attempts to reproduce this experiment should anticipate a high attrition rate. In addition, it would be useful to carry out post-operative observations at standardized time periods. However, given the diversity of stages in the 1-day old eggs, the most feasible ways to address this concern would be with a very large sample size of eggs or a large number of observers who could make the necessary observations as each egg reached the standardized stages.

The data collected during this experiment, then, illustrates that it is possible to induce cardia bifida in chicks. The two migrating heart primordia appear to be specified as heart tissue early during organogenesis and undergo regulative development thereafter. This, in turn, implies that in cases where one heart primordium is naturally or experimentally damaged or removed, the remaining tissue is capable of compensating for the loss. These findings are interesting for their potential in medical and technological fields. Heart regeneration and the culturing of cardiac tissue for transplantation are two such areas.

©Cebra-Thomas, 2000

Last Modified: May 2nd 2004

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