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Researchers at the National Institutes of Health (NIH) have identified proteins that allow muscle cells in mice to form from the fusion of the early stage cells that give rise to the muscle cells.

The findings have implications for understanding how to repair and rehabilitate muscle tissue and to understanding other processes involving cell fusion, such as when a sperm fertilizes an egg, when viruses infect cells, or when specialized cells called osteoclasts dissolve and assimilate bone tissue in order to repair and maintain bones.

The findings were published online January 7 in the Journal of Cell Biology.

"Through a process that starts with these progenitor cells, the body forms tissue that accounts for about one-third of its total weight," said the study's senior author, Leonid V. Chernomordik, PhD. "Our study provides the first look at the very early stages of this fusion process."

Muscle cells originate from precursor cells known as myoblasts. Myoblasts fuse to form a single long tubular cell called a myocyte (a muscle fiber). Muscle tissue is composed of large collections of these fibers. The fusion of myoblasts into muscle fibers takes place early in fetal development. With exercise and throughout a person's life, the process is repeated to form new muscle mass and repair old or damaged muscle.

It takes many hours for cells to prepare for fusion, but the fusion process itself is very rapid. To study myoblast fusion, the researchers first blocked the start of the fusion process with a chemical. Ordinarily, the mouse myoblasts the researchers worked with fuse at varied intervals. By blocking fusion, and then lifting the block, the researchers were able to synchronize fusion in a large number of cells, making the process easier to study.

The researchers identified the 2 distinct stages of cell fusion and the essential proteins that facilitate these stages.

In the first stage, 2 myoblasts meet, and proteins on cell surface membranes cause the membranes to meld. In the second stage, a pore opens between the cells and their contents merge. This second step is guided by proteins inside the cells. (See graphic provided by NIH.)

The work identifies 2 cell surface proteins that act at the start of myoblast fusion. These proteins belong to a large family of proteins called annexins. Annexins also are known to play a role in membrane repair and in inflammation.

The researchers identified the protein dynamin, found inside the cell, as essential to the second stage of the cell fusion process.

"Dynamin also has an unexplained link to certain rare and poorly understood myopathies—disorders characterized by underdeveloped muscles," said Chernomordik. "We hope that further examination of the role of dynamin in cell fusion will lead to a greater understanding of these conditions."

Lisa K. Saladin, PT, PhD, has been appointed by the APTA Board of Directors to fill the unexpired term of director David Pariser, PT, PhD, who died unexpectedly January 14. Saladin's term will begin immediately and run through June 2014.

"Today, we honor our friend and colleague Dave Pariser by continuing the important work of the association he loved so dearly in appointing Lisa Saladin to fill his unexpired term," said APTA President Paul A Rockar Jr, PT, DPT, MS. "Lisa's previous experience as a member of APTA's Board of Directors and her in-depth knowledge of the issues currently facing the association will help the Board retain continuity while moving the association forward, as Dave would certainly have wanted."

A member of APTA's Board from 2008-2011, Saladin, serves as professor and dean of the College of Health Professions at the Medical University of South Carolina, where she has been a full-time faculty member since 1990. She served on APTA's Government Affairs Committee for 3 years, including 1 year as chair, and as chief delegate and delegate from South Carolina for 8 years. She also has served as president of the South Carolina Chapter, where she was known as a strong advocate for student membership and active participation in professional service. In 2004, she received APTA's Dorothy Baethke-Eleanor J. Carlin Award for Excellence in Academic Teaching.

Saladin has been instrumental in advancing the body of knowledge in the areas of community-based service learning, health disparities, and neuropathology/neurological rehabilitation. In 2001, she was awarded the Neurology Section's Golden Synapse Award for best journal publication in recognition of her efforts in this area.

Saladin has been recognized by her peers and students with numerous teaching awards, including 3 University Teaching Excellence Awards and the South Carolina Governor's Distinguished Professor Award.