Regulative Development in Axolotl Embryos; Splitting the Heart Field

Katy Lewis, Swarthmore College Biology dept., 2004

Objective

This experiment will seek to demonstrate regulative development in Ambystoma mexicanum embryos. Specifically, we will split the morphogenetic field that is responsible for heart formation using grafted tissue from the gill area, and attempt to form two hearts – one on either side of the grafted tissue.

Background

Organisms that use regulative development rely on cell-cell interactions to determine what develops where, rather than having fixed cell fates (as in mosaic development). Because of this, embryos that undergo regulative development are able to compensate for missing or damaged parts (Gilbert, 2003). This sort of compensation is particularly seen in regions known as morphogenetic fields. These regions of cells are each committed to form a certain organ, but made up of individual cells that are not yet committed to form a specific part of that organ. Damage to these fields can be compensated for by the other cells in the field (Gilbert 2003).

In the axolotl salamander (Ambystoma mexicanum), the heart forms through the fusion of two regions of heart forming tissue -- the heart primordia (Hamburger, 1973). In order for the axolotl to have one fully formed heart, these two regions must communicate with each other so that they can "decide" when and how to come together. Theoretically, if this communication were interrupted by damage to the tissue (or a barrier placed between the primordia tissue), the heart primordia would be unable to fuse into one. This communication and subsequent ability to compensate for damage, is a prime example of regulative development.

This experiment will take advantage of the morphogenetic field of the axolotl heart. The fact that two hearts form is not only amazing to behold, but demonstrates that the cells, when prevented from communicating with each other, will go on to form two separate organs. This is a direct result of regulative development.