3d rendering of a Mitochondrium – microbiology illustration

Mitochondrion is the powerhouse of the cell, but who really powers the transmission of this amazing organelle?

Taosheng Huan (a geneticist from the USA) recently identified a case that has changed the way we look at mitochondrial inheritance: a four-year-old boy that carries mitochondrial DNA both from the mother, as well as from the father.

Until know, scientists thought that mitochondrial DNA is inherited

almost exclusively from the mother. The reason for this exclusiveness is unknown, but one theory suggests that the mitochondria found in sperm are more prone to mutation than their counterpart in the egg. Moreover, certain molecular mechanisms found in the egg can destroy the mitochondria if they manage to “leak” from the male gamete. If these mechanisms fail, then the paternal mitochondria will be passed on to the egg.

Following this discovery, Huang and his team went further and found 17 individuals from three unrelated families, who inherited mitochondrial DNA from their fathers. They concluded that both the maternal and paternal DNA was synchronized during fertilization which resulted in children with mixed mitochondria.

Researchers have also found one interesting aspect: children who possessed mitochondrial DNA from their grandfathers. This fascinating pattern of inheritance is explained as it follows: the mother inherited DNA from her grandfather and passed it on to the child, with no implications from the biological father. Preliminary results show that 1 in every 5000 people presents mixed mitochondrial DNA, making this anomaly more frequent than we thought.

This discovery opens up the possibility of various treatments and applications in the medical field, such as assisted reproductive technology. Huang’s team was part of the “three-parent” baby project in 2016 in which nuclear DNA from a mother with mitochondrial disease was transferred to an egg with healthy mitochondria which was then fertilized. Instead of using a foreign egg, paternal mitochondria could replace the affected maternal mitochondria. However, given the fact that mitochondria from the sperm can mutate more easily, multiple problems can appear in the evolution of the embryo. Alongside the biological difficulties, the ethics of these artificial procedures lead to various debates. While there is still a lot to be known about this process, it has already changed the way we describe mitochondria and its inheritance.

This topic is too big to be covered in just a few words, so I invite you to satisfy your thirst of knowledge by accessing this link: https://www.pnas.org/content/115/51/13039 .

Karim Cherry – SOMS Wisp of Science

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