The Role of Actin in Cardiac Looping in the Chick Embryo

Camille Edelen, Biomedical Engineering Lab of Dr. Larry Taber, Washington University in St. Louis.

Cardiac looping is the process by which the embryonic heart develops from a straight heart tube into a four-chambered heart. This process merits further investigation because the heart is not only the first organ to function, but it also establishes left-right asymmetry in the embryo. Although much is known about cardiac looping and its role in heart development, little is known about the mechanisms that drive looping. Throughout the years, several hypotheses regarding these mechanisms have been proposed, although none have been supported by the literature. Cardiac looping can be divided into two phases: c-looping and s-looping. Cardiac c-looping can be subdivided into two primary deformation components: ventral bending and dextral rotation. This study of cardiac looping investigated the role of actin in ventral bending. Actin in both the dorsal and ventral sides of the heart was studied to determine the relative contribution of each side to the overall force required to bend the tube. Silica gel beads infused with latrunculin A were used to disrupt actin polymerization. Latrunculin A binds to and sequesters actin monomers, and thus inhibits actin polymerization. Beads infused with dimethyl sulfoxide were used as a vehicle control. Photographs were taken after 24 hours of development to quantify the amount of looping progression. Results from these experiments indicated that disruption of actin on either the dorsal or ventral side of the straight tube decreased the amount of looping. Therefore, the data collected from these experiments suggest that actin, on both the dorsal and ventral surfaces of the heart, is required for normal looping progression