Muscle fibers are large cells that contain many nuclei. They begin, like all animal cells, as naive embryonic cells. These cells differentiate, producing intermediate cells called myoblasts that are now destined to become muscle. New myoblasts then seek out other myoblasts, and when they find each other, they stick together like best friends. In the final stage of muscle fiber development, the cell membranes of attached myoblasts open up and fuse together, forming one large, unified cell.
How myoblasts identify other myoblasts and how they cling together had been established, but the way that the cell membranes fuse into one has remained a mystery. Now, a study by Weizmann Institute scientists has shed light on this mystery. The study was carried out by research student Rada Massarwa and lab technician Shari Carmon under the guidance of Dr. Eyal Schejter and Prof. Ben-Zion Shilo of the Institute's Molecular Genetics Department, with help from Dr. Vera Shinder of the Electron Microscopy Unit. The cells' system for identifying other myoblasts and sticking to them consists of protein molecules that poke through the outer cell membrane one end pointing out and the other extending into the body of the cell. These recognition proteins anchor the cells together, but what makes myoblasts open their doors to each other and merge into one cell?
The scientists discovered that a protein called WIP, which attaches to the internal part of the myoblast recognition protein, plays a key role in muscle cell fusion. WIP communicates between the recognition protein and the cell's internal skeleton, which is made of tough, elastic fibers composed of a protein called actin. The skeletal actin applies force to the abutting cell membranes, opening and enlarging holes that allow the cells to merge. The Weizmann Institute team found that the WIP protein is activated by an external signal once myoblasts identify and attach to each other. Only when it receives this sig
Contact: Jennifer Manning
American Committee for the Weizmann Institute of Science