John Huang
How are Morphological Position Landmarks Established in Regenerating Tissues?
Mentor:  Dr. Stephen Johnson, Department of Genetics, Washington University School of Medicine 

My lab work focuses on the study of regenerative growth, specifically where and how regenerating tissues determine the placement of anatomical landmarks in a limb. By using the zebrafish as my model organism, I am trying to discover what sorts of growth mechanisms control the placement and formation of structures such as joints found in the zebrafish caudal fin.

The caudal fin of the zebrafish is a simple appendage that is ideal for investigating morphological positioning because of its easy visibility and quick regeneration time. By amputating the caudal fin and allowing the fin to grow back, I can observe where new joints form after the amputation plane and what type of factors affect this placement.

I am particularly interested in what kinds of conditions (environmental, genetic, etc.) determine where the 1^st regenerative joint is placed after the amputation plane. By measuring the lengths of segments surrounding the amputation plane, I have discovered that the position of amputation on the fin has a noticeable effect on the length of the 1^st regenerative segment. Using this data I was able to create a constant ratio, which I called the Regenerative Segment Index (RSI), and compare it with data from a variety of conditions.  None of the ratios of these different conditions I tested differed significantly from my control RSI. However, by analyzing the RSI value of the short fin mutant, I found that the length of post-amputation segments was in proportion to those of pre-amputation segments.  Thus, I was able to conclude that regenerative segment length is also determined by the natural segment length of the fish.

In conclusion, the study of morphological landmarks in regenerating tissues of the zebrafish caudal fin will help us better understand the properties of regenerative growth in other organisms, namely humans.