Cellular power outage
Mitochondria are small 'organelles' that reside within cells and have one of the most important roles in cellular function: they are the power generators, producing the all-important energy molecule ATP. Mitochondria contain their own DNA, from which they make some of the products necessary for ATP production, but they rely on the genes in the cell nucleus-where the vast majority are located-to supply most of the components.
So what happens when there's a mitochondrial blackout? One clinical symptom of impaired mitochondrial function is impaired function and weakness of muscles - not a surprise, as that's where energy is generally the most needed. One such syndrome, progressive external ophthalmoplegia (PEO), is characterized by lack of eye movements and exercise intolerance. Within the mitochondria of individuals afflicted with PEO, large pieces of the DNA are missing - without which the mitochondria cannot function properly.
New results from two independent groups indicate why the mitochondrial DNA deletions may be present in PEO (Nature Genetics, Vol. 28, No. 3, 01 July 2001). In a large group of individuals with PEO, Johannes Spelbrink (of Tampere University Hospital) and colleagues found one gene whose protein, Twinkle, is similar to proteins that unwind and reconfigure DNA. A second group, led by Christine Van Broeckhoven (of the Flanders Interuniversity Institute for Biotechnology), identified another factor - DNA polymerase gamma (POLG), a protein that replicates DNA - that is mutated in other individuals afflicted with PEO. Both of these types of proteins are essential for propagation of DNA, providing a very good basis for understanding why these defects could lead to PEO.
As indicated in an accompanying News & Views article by Carlos Moraes (of the University of Miami School of Medicine), "these reports confirm…that the mitochondrial DNA repair/replication machinery is involved in at least some cases of PEO" and are "a significant step towards understanding [these] disorders."
Dr. Johannes Spelbrink
Tampere University Hospital
University of Tampere, Finland
Telephone: +358 32-15-85-98
Fax: +358 32-15-77-10
Dr. Christine Van Broeckhoven
University of Antwerp
Telephone: +32 3-820-2601
Fax: +32 3-820-2541
Dr. Carlos Moraes
University of Miami School of Medicine
Miami, Florida, USA.
Telephone: +1 (305) 243-5858
Fax: +1 (305) 243-3814
(C) Nature Genetics press release.
Message posted by: Trevor M. D'Souza