New & Noteworthy

Mixing Mitochondria Makes Magic

May 31, 2018

In the Harry Potter universe, there are two materials that make up a wand: the wood, which comes from trees like cedar and holly, and the core, which is a magical substance such as the feather of a phoenix or a unicorn hair.

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A variety of wizarding wands. From Flickr.

Every wand has unique properties that depend mainly on the combination of its wood and core. Different wood-core pairings give different characteristics that can either antagonize or synergize with the wizard using it. When a wand meets up with its ideal owner, it will begin to learn from and teach its human partner. Such auspicious pairings can continuously improve the wizard’s spell-casting, helping the wizard perform better and better under ever more varied circumstances. However, a poor pairing between a wand and a wizard can be devastating, enfeebling the wizard’s magic or even causing it to backfire.

And just like wizards and wands, it turns out that mitochondrial DNA and nuclear DNA in a cell need to be properly paired to perform the “magic” of running a cell in the most efficient way.

Mitochondria are dynamic structures inside eukaryotic cells that provide much of the energy to keep a cell humming along.

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A mitochondrion. These sub-cellular organelles produce much of the energy for a cell in the form of ATP. From Wikimedia Commons.

Mitochondria contain their own DNA, encoding genes necessary for the organelle to do its work. Although mitochondrial DNA is physically separate from nuclear DNA, it turns out that the two need to work together if the cell is to make functioning mitochondria.

Like the wand-wizard pairing in Harry Potter’s world, the combination of a specific mitochondrial genome (the wand) with a particular nuclear genome (the wizard) is important for making a healthy mitochondrion. Some mitochondrial-nuclear combinations work well and others not so much, but not a lot is known about where different mitochondrial DNAs come from and how they end up paired with their favored nuclear genomes.

Knowing more about this may help us understand how mitochondrial genomes evolve during interspecific hybridizations, such as in lager beer yeast and certain other fermentation yeasts.

A new study in GENETICS from Wolters et al. shows that when S. cerevisiae yeast cells go through the mating process, there is often mixing of mitochondrial genomes to give new combinations of mitochondrial genes — almost as if lots of new wood-core combinations of wands were being created.

How do these new mitochondrial combinations arise? When two haploid yeast cells mate, they merge to form a single diploid cell that contains mitochondria from both of its parents. Sometimes, these mitochondria exchange pieces of DNA, mixing-and-matching genes in a process known as mitochondrial recombination.

The authors found that a surprising proportion of mated yeast cells (~40%) had recombinant mitochondrial DNA. And in many cases, the recombined mitochondrial genomes work even better with the nuclear genome to make a super healthy cell. Often these optimal pairings allowed the cells to develop new powers, tolerating higher temperatures and more oxygen-stressed conditions than the original parent cells — in other words, the cell has found its optimal “wand”!

But other pairing combinations were inauspicious, giving sickly or dead mitochondria that can harm the cell, especially when it is growing under stressful conditions. For instance, when the authors swapped the mitochondrial-nuclear pairing for two different but very fit cell types, these new pairings gave unhealthy cells, meaning that the original fit cells had already found their perfect “wand”.

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Harry Potter first meeting his perfectly-paired wand. From harrypotter.wikia.com.

So just like when Harry Potter was in Ollivander’s wand shop and finally found his holly-phoenix feather wand and felt unified with its amazing magic, yeast cells can acquire new super powers when their nuclear and mitochondrial genomes are perfectly paired!

by Barbara Dunn, Ph.D. and Kevin MacPherson, M.S.

…and we wish a fond farewell to Barry Starr, Ph.D. who has left the Stanford Department of Genetics for new horizons. We miss you Barry and wish you well!

Categories: Research Spotlight

Tags: recombination , mitochondria , environmental stress