February 17, 2011

Getting left-right asymmetry right

The protein Nodal has been found to hold the keys to vertebrate asymmetry.

(iStock photo) (iStock photo)
(iStock photo)
(iStock photo)

Human beings – like all vertebrates – are asymmetric inside. Organs are on the left or right side of the body, and even the sides of the brain have important physical and functional differences.

During embryonic development, the left-sided expression of a protein called Nodal is the main regulator of this asymmetric patterning of the body. Disruptions in Nodal signaling may underlie defects in organ placement and structure, such as congenital heart defects.

Lindsay Marjoram and Chris Wright explored the movement of the proteins Nodal and Lefty (Nodal induces Lefty’s expression) in frog embryos. They report in the Feb. 1 issue of Development that Nodal and Lefty move long distances in the embryo along the extracellular matrix (ECM), and that sulfated proteoglycans in the ECM facilitate Nodal movement. They also showed that Lefty can move from the left side of the embryo to the right, an important finding related to its function in preventing Nodal from being improperly expressed on the right side.