By Marissa SteplerCommonly known as the “powerhouses” of the cell, mitochondria provide the vast majority of energy required for cells to function, grow, move, and thrive. Mitochondria self-replicate and have their own DNA, but only 37 of the approximately 3000 genes needed for mitochondrial function are found in mitochondrial DNA. The majority of genes contributing to mitochondrial energy generation, nucleotide synthesis, hormone production, and the many other functions of the mitochondria are located in the nuclear chromosomal DNA of each cell.
When the “powerhouses” of the cell fail, cellular health and function can be drastically decreased, often leading to cell dysfunction and death across numerous different cell types and tissues. In mitochondrial disease, this dysfunction occurs due to inherited or spontaneous mutations in nuclear genes encoding proteins involved in mitochondrial function or mitochondrial DNA. Mutations in nuclear genes can be inherited from either parent. However, because, in a fertilized embryo, all cytoplasm and mitochondria are provided by the egg, mutations in the mitochondrial DNA of a child are inherited solely from his mother. Furthermore, a mother’s mitochondrial DNA mutation may occur in a small enough percentage of her total mitochondria that she remains unaffected, yet the mutation may be lethal when passed on to her children. So if a mother knows she carries a mitochondrial DNA mutation, how can she prevent the transmission of the mutation to her children? Recently, researchers have addressed this problem through a new variation on in vitro fertilization (IVF) called three-parent IVF. In this procedure, instead of using an egg from a single female donor and sperm from a single male donor, eggs from two female donors – one from the mother and one from a female donor lacking mitochondrial DNA mutations – are used. When a cell, such as an egg cell, undergoes DNA replication, the dividing chromosomes are pulled apart by microtubule spindles before being separated into two daughter nuclei. In three-parent IVF, a technique called spindle transfer is used to extract the spindles and their attached chromosomes, which are then injected into the healthy donor egg from which the spindles have been removed. This new combined egg is then fertilized with the father’s sperm, resulting in an embryo which has maternal and parental nuclear DNA but healthy donor mitochondrial DNA. While this IVF method has been previously tested in primates and mammals, it was not attempted in humans until recently, when the procedure was used by a mother who had a mitochondrial gene mutation which results in Leigh syndrome, a lethal neurological disorder. After two of her previous children inherited the disease, the mother underwent spindle transfer three-parent IVF, which resulted in a successful pregnancy and birth of a healthy baby boy. Although considered controversial in some circles, three-parent IVF seems to be a powerful and effective method for preventing some inherited human mitochondrial diseases. As technology continues to advance, this procedure may be used to prevent other inherited disorders related to mitochondria and organelle dysfunction. Currently, this breakthrough procedure offers hope for parents carrying mutations in mitochondrial disease-related genes and for scientists researching organelle-related diseases. Sources: [1] https://www.sciencenews.org/article/three-parent-babies-explained [2]http://www.umdf.org/site/c.8qKOJ0MvF7LUG/b.7934627/k.3711/What_is_Mitochondrial_Disease.htm [3]http://whut.pbslearningmedia.org/resource/tdc02.sci.life.cell.mitochondria/the-powerhouse-of-the-cell/
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AuthorsThe authors of these blog posts are staff writers of The Triple Helix at Georgetown University. Archives
November 2016
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