Floating around in almost all living cells, mitochondria vary in number from dozens to several thousand. Muscle cells, for example, have large numbers of mitochondria because of their high energy needs. New mitochondria are created when cells signal the need for more energy. Mitochondria also carry a small amount of DNA material passed down maternally.

Mitochondria are important for a host of reasons. They generate energy in cells, they can play a role in longevity and they are crucial for blood sugar maintenance and fat loss. Damaged mitochondria can cause problems in cells of the brain, liver, heart, skeletal muscles and respiratory systems.

A new study shows for the first time the final stages of how mitochondria, the sausage-shaped, power-generating organelles found in nearly all living cells, regularly divide and propagate.

In 2011 researchers surprisingly found that endoplasmic reticulum (ER), another cell organelle, branches through cytoplasm like a spider web, wrapping around other organelles including mitochondria. They discovered that once an ER tentacle touches a single mitochondrion and initiates constriction, a cell protein called a dynamin-related protein, or Drp1, is recruited to further constrict the mitochondria at the spot of ER contact.

Here is the new twist: the team has now shown that once the squeeze is on the mitochondria by the Drp1 protein, a second protein - called Dynamin-2, or Dyn2 - is recruited to finish the job in a process called fission, splitting the organelle in two. Shaped like tiny springs, the dynamin proteins encircle the mitochondria and squeeze, somewhat like a person squeezing and twisting an elongated balloon into two halves.

Both proteins are required for mitochondrial fission to occur since Drp1 is only strong enough to squeeze the mitochondria down to a certain size, and Dyn2 can only finish what Drp1 started after the constriction band is sufficiently shrunk.

A paper on the subject was published in Nature.

http://www.colorado.edu/today/2016/10/31/putting-squeeze-mitochondria-final-cut

http://www.nature.com/nature/journal/vaap/ncurrent/full/nature20555.html