But whatever the reasons, for a long time that difference obscured the role of mitochondria in stem cells, says Mireille Khacho, a cell biologist at the University of Ottawa. Why the cells differ in this way is not known: It may have something to do with the rate or byproducts of each process. Drivers of Stem Cell Fateįor stem cells, the primary means of producing energy is glycolysis, a process that generates ATP in the cytoplasm, rather than oxidative phosphorylation, the mitochondria-dependent method preferred by most mature, specialized cells. One crucial role that has emerged is in promoting the differentiation of various types of stem cell, including those for blood and fat cells - and, most recently, for neurons. Since then, Chandel and others have shown that mitochondrial ROS signaling is important in diverse processes. Under oxygen-deficient conditions, they observed, mitochondria produced higher levels of ROS, and the excess molecules exited into the cytoplasm, where they would aid in the expression of proteins that helped the cells survive. Those investigations led to a discovery a couple of years later involving the reactive oxygen species (ROS) - unstable molecules containing oxygen, such as peroxides, singlet oxygen and hydroxyl radicals - that mitochondria release while making ATP. The study propelled Chandel, then at the University of Chicago, and his colleagues to examine whether mitochondria could release other signals as well. Their work also indicated that, at least in principle, mitochondria might be able to trigger cell death by releasing the cytochrome c they housed into the surrounding cytoplasm.Īccording to Navdeep Chandel, a professor of biochemistry and molecular biology at Northwestern University, this was an aha! moment for mitochondrial biology, because it suggested that the organelles could generate signals to control other cellular processes. They found that cytochrome c - a protein essential to ATP production - was crucial to this process. In one early study, researchers at Emory University and the University of Minnesota investigated apoptosis, the process of programmed cell death that eliminates cells from tissues as a normal part of growth and development. The first hints that mitochondria had a broader repertoire emerged in the mid-1990s. In making this discovery, the scientists have pieced together a connection between the organelle’s shape transitions and how it carries out its signaling functions. Now scientists at the University of Ottawa in Canada have provided evidence that the morphing shapes of mitochondria powerfully influence neurogenesis, the development of neurons. In the past few years, research has revealed that one of their key roles is in controlling the development and ultimate role of stem cells. Recently, it has become clear that mitochondria also perform signaling and regulatory functions that are only indirectly related to their job as energy providers. They form highly dynamic, short-lived tubular networks threading throughout a cell. Mitochondria may look static and uniform in textbooks, but as researchers recognized early on, in reality the organelles change shape constantly through cycles of fusion (in which they combine and elongate) and fission (in which they split and shrink). For more than a century, biologists believed that energy production was their only role.īut that simple picture of mitochondria is turning out to be shockingly incomplete. Mitochondria are familiar as bean-shaped structures floating in the cytoplasm, and they are almost inevitably referred to as “powerhouses” of the cell because they generate adenosine triphosphate (ATP), the fuel for most metabolic processes. Of all the organelles to be found inside eukaryotic cells, the DNA-sheltering nuclei might be the best-known, but the mitochondria are surely not far behind.
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