Research reveals how a cell mixes its mitochondria before it divides

In a landmark study, a team led by researchers at the Perelman School of Medicine has discovered—and filmed—the molecular details of how a cell, just before it divides in two, shuffles important internal components called mitochondria to distribute them evenly to its two daughter cells.

molecules showing the cyclic assembly and disassembly of actin (in orange) on mitochondria (in blue) in dividing HeLa cells
Time-lapse imaging reveals the cyclic assembly and disassembly of actin (in orange) on mitochondria (in blue) in dividing HeLa cells. In the merged movie on the left, or in the two individual channels in the center and right panels, you can see that actin assembly moves as a wave around the mitotic spindle at the cell center. This wave leads to the localized mixing of mitochondria, shown in blue in the right panel. (Image: Penn Medicine News)

The finding, published in Nature, is principally a feat of basic cell biology, but this line of research may one day help scientists understand a host of mitochondrial and cell division-related diseases, from cancer to Alzheimer’s and Parkinson’s.

Mitochondria are tiny oxygen reactors that are crucial for energy production in cells. The Penn Medicine team found in the study that a protein called actin, which is known to assemble into filaments that play a variety of structural roles in cells, also has the important task of ensuring an even distribution of mitochondria prior to cell division. Thanks to this system, the two new cells formed by the division will end up with approximately the same mass and quality of these critical energy producers.

“We were able to observe and film distinct processes by which actin filaments mix mitochondria—the strangest one involved the rapid formation of actin ‘comet tails’ on some mitochondria, which propel them randomly around the cell interior,” says study senior author Erika Holzbaur, the William Maul Measey Professor of Physiology at Penn Medicine.

Cell division, also called mitosis, is one of the basic features of living things, but involves a delicate and complex set of maneuvers. The dividing cell—the “mother cell”—must ensure that it has two identical copies of its genome, one for each daughter cell. It must also apportion other key cellular contents evenly.

Mitochondria, which can number from a handful to tens of thousands per cell, depending on the cell type, are probably especially important to mix evenly. They are critical for the health of a cell, and contain their own small DNA genomes—new mitochondria can’t be produced in a cell except by the splitting of mitochondria inherited from the mother cell.

Read more at Penn Medicine News.