Evolution at work: Even yeast mothers sacrifice all for their babies

Nov 08, 2012
Evolution at work: Even yeast mothers sacrifice all for their babies
This is a computer-generated image of mitochondrial networks in yeast cells. Network structures are extracted computationally and represented by balls (nodes) and rods (edges). Credit: UCSF

A mother's willingness to sacrifice her own health and safety for the sake of her children is a common narrative across cultures – and by no means unique to humans alone. Female polar bears starve, dolphin mothers stop sleeping and some spider moms give themselves as lunch for their crawly babies' first meal.

Now an unexpected discovery at the University of California, San Francisco (UCSF) shows that even "mothers" do it, giving all to their offspring – even at the cost of their own lives.

As described this week in the journal Science, the UCSF scientists found that the yeast ensures the health of its budding offspring by pushing essential internal structures known as mitochondria into them.

Mitochondria are the mini powerhouses of living cells, supplying the all yeast and higher life forms need to survive. Like all , yeast need these structures to survive. In the new paper, the UCSF team describes how ferry just the right amount of mitochondria along a network of protein tracks and molecular motors into the young yeastlings, which bud off their mother like mini-me's.

But what surprised the researchers, led by Wallace Marshall, PhD, UCSF associate professor of biochemistry and biophysics and UCSF postdoc Susanne Rafelski, PhD, was how yeast mothers continued to give generous amounts of their mitochondria to their offspring even when it meant hastening their own death.

"The mom will pump in as many as [the bud] needs," said Marshall. "The bud gets more and more as it grows, and mom doesn't get any more."

UCSF, which includes a top-ranked medical center providing patient care and many ongoing clinical studies, also is one of the world's leading institutions pursuing fundamental research in basic biomedical fields, including , biochemistry, physiology, biophysics and genetics – work that offers insight into the ways normal cells function and what sometimes goes wrong in diseases such as cancer, AIDS, diabetes, multiple sclerosis and Alzheimer's.

How Cells Divide

The classic picture of cell division – a process known as mitosis – is an even splitting whereby one cell gives birth to two identical copies. Scientists have always reasoned that during this classic division, the mitochondria were likewise evenly split – the same way that both sides of a pepperoni pizza cut in two would have half the toppings.

But not all cells divide evenly. Human stem cells, for instance, often divide into two cells that look and behave very differently. Some cancer cells do this as well. There is a growing sense in the biomedical field, Marshall said, that understanding how a cell moves its mitochondria around during such uneven divisions may hold some of the clues to understanding aspects of stem cell or cancer biology.

Working with yeast, the UCSF team developed sophisticated microscope and computer techniques that allowed them to track the movement of mitochondria within . If these structures had divided randomly, they would expect to find fewer in the bud than in the mother (since the buds are smaller than the mother).

What they found instead was that the yeast mothers gave a consistent amount of mitochondria to their offspring at each generation, and so over time they had fewer and fewer of the organelles themselves. The price they paid to ensure their offspring was healthy was steep: The yeast mothers would eventually give away too many of the mitochondria to survive and begin to die off after 10 generations. By 20 generations, most of the mothers had died.

Mutant forms of yeast, which were much more stingy in giving up their , lived much longer.

Explore further: Adventurous bacteria

More information: The article, Mitochondrial Network Size Scaling in Budding Yeast" by Susanne M. Rafelski, Matheus P. Viana, Yi Zhang, Yee-Hung M. Chan, Kurt S. Thorn, Phoebe Yam, Jennifer C. Fung, Hao Li, Luciano da F. Costa, and Wallace F. Marshall appears in the November 9, 2012 issue of Science.

Related Stories

New insight in how cells' powerhouse divides

Sep 02, 2011

New research from the University of California, Davis, and the University of Colorado at Boulder puts an unexpected twist on how mitochondria, the energy-generating structures within cells, divide. The work, ...

New mitochondria mechanism identified

Sep 27, 2011

A team of researchers led by the University of Freiburg in Germany has identified a novel mechanism that plays a key role in the architecture and functioning of mitochondria - the power plants of the cell, ...

Cell death pathway linked to mitochondrial fusion

Jan 24, 2011

New research led by UC Davis scientists provides insight into why some body organs are more susceptible to cell death than others and could eventually lead to advances in treating or preventing heart attack or stroke.

Recommended for you

For cells, internal stress leads to unique shapes

2 hours ago

From far away, the top of a leaf looks like one seamless surface; however, up close, that smooth exterior is actually made up of a patchwork of cells in a variety of shapes and sizes. Interested in how these ...

Adventurous bacteria

3 hours ago

To reproduce or to conquer the world? Surprisingly, bacteria also face this problem. Theoretical biophysicists at Ludwig-Maximilians-Universitaet (LMU) in Munich have now shown how these organisms should ...

Revealing camouflaged bacteria

6 hours ago

A research team at the Biozentrum of the University of Basel has discovered an protein family that plays a central role in the fight against the bacterial pathogen Salmonella within the cells. The so cal ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

JVK
2 / 5 (2) Nov 13, 2012
The Science magazine article makes it clearer that mitochondrial- to-cell size ratio is relatively constant in HeLa cells and in two yeast species during germ tube formation. This links reproduction by fission in yeasts to the advent of sexual reproduction via the same nutrient chemical-dependent molecular mechanisms that are important to cancer research (e.g., glucose-dependent and social regulation of mammalian gonadotropin releasing hormone and its downstream effects on.... everything else in species from microbes to man). Of course, "everything" includes sex differences in different cancer types and in different incidence rates of genetically predisposed epigenetically-effected neurodevelopmental disorders.

More news stories

Chimpanzees prefer firm, stable beds

Chimpanzees may select a certain type of wood, Ugandan Ironwood, over other options for its firm, stable, and resilient properties to make their bed, according to a study published April 16, 2014 in the open-access ...

For cells, internal stress leads to unique shapes

From far away, the top of a leaf looks like one seamless surface; however, up close, that smooth exterior is actually made up of a patchwork of cells in a variety of shapes and sizes. Interested in how these ...

Down's chromosome cause genome-wide disruption

The extra copy of Chromosome 21 that causes Down's syndrome throws a spanner into the workings of all the other chromosomes as well, said a study published Wednesday that surprised its authors.

Ebola virus in Africa outbreak is a new strain

The Ebola virus that has killed scores of people in Guinea this year is a new strain—evidence that the disease did not spread there from outbreaks in some other African nations, scientists report.