According to the endosymbiotic hypothesis, around 1500 million years ago, the mitochrondrion was a bacterium or prokaryotic cell phagocytosed by another to which it provided energy in the form of ATP; the host cell gave it a stable, nutrient medium. Over time, instead of integrating itself in the nucleus, this invader became specialised as an energy centre and reduced its DNA to the current 37 genes. “Why do we still have mitochondrial DNA?” asked Ben Williams of the Whitehead Institute for Biomedical Research in February this year in Cell Systems. “It’s like saying you have a central library with all your books in it, but we’re going to keep 10 of them off-site in a leaky shed”, protected from fire, flood or theft.
Despite this age-old coexistence in all multicellular organisms, the mitochondrion continues to hide mysteries. It is responsible for more than 150 diseases, many of which affect the musculoskeletal and central nervous system, and have no cure. Last year, Great Britain approved so-called mitochondrial replacement — which has still not been given the green light for use in medicine — from which three-parent embryos would result: paternal spermatozoa and maternal nuclear DNA without defective mitochondria, which is transferred to an enucleated donor egg with healthy mitochondria. There has been great bioethical and scientific discussion in recent months about a technique on which few tests have been carried out and which would alter the germ line.
This is something that, in addition, appears simple on paper but is not so straightforward in the laboratory.
The views, opinions and positions expressed by these authors and blogs are theirs and do not necessarily represent that of the Bioethics Research Library and Kennedy Institute of Ethics or Georgetown University.