Smooth Muscle Differentiation Controls Spiraling in the Intestine of L. erinacea

The digestive systems of animals have evolved to optimize the efficiency of nutrient absorption, and adapt to different diets and habitats. While most vertebrates contain long, coiling intestines, the Leucoraja erinacea (little skate), like all basal fishes, has a short intestine with many internal spirals similar to the thread of a screw. This unique intestinal morphology allows cartilaginous fish to fit an intestine with a high surface area for absorption into a narrow body cavity. How the spiral intestine develops still remains a mystery. Research has found that smooth muscle differentiation is a key player in intestinal villi formation, leading us to hypothesize that smooth muscle may play a role in spiral intestine formation. To examine the role of smooth muscle differentiation during spiral formation, skate embryos were injected with muscle inhibitors AG1295 and FK506 prior to and after initiation of the spiral fold during development. Treated spiral intestines were visualized on a microCT, and 3D renderings of the lumens were generated on Amira. Preliminary results indicate that in the absence of muscle differentiation, the spiral intestine has a decreased number of expected turns, as well as changes in pitch length and perimeter to circumference ratios. These results indicate that smooth muscle differentiation likely plays a role in later spiraling of the intestinal fold, but not initiation of the spiral. As the spiral intestine is a precursor to the winding intestines of vertebrates, understanding how the spiral intestine forms may help us to uncover the evolutionary origins of our long coiled intestines.