Male mitochondrial DNA found to self-destruct after arrival in embryo

via wanderinginthestacks.wordpress.com

"A team of researchers with members from Taiwan, the U.S., China and Japan has found that mitochondrial DNA from sperm that makes its way into an embryo begins to self-destruct before autophagosomes in the cytoplasm can reach it. In their paper published in the journal Science, the researchers describe their study involving the close monitoring of male mitochondrial DNA activity immediately after an embryo has been fertilized and as it is subsequently destroyed—they also offer some theories regarding why this occurs.

Over the past half-century, scientists have learned that some amount of DNA exists outside of the cell nucleus and inside mitochondria. They have also found that only the mitochondrial DNA from the mother is passed on to the child during reproduction—the mitochondrial DNA from the father is destroyed before it can have an impact. These discoveries have led to other studies looking to better understand why this occurs.

In this new effort, the researchers used electron microscopy to watch the process in a type of roundworm. In so doing, they discovered that the male mitochondria in sperm actually began to break down before being cut up by autophagosomes in the cytoplasm—an extra guarantee, it seemed, to ensure that the male DNA would not be allowed to become part of the embryo's DNA. 

Looking more closely, the researchers found that the existence of the cps-6 gene caused expression of an enzyme that initiated the self-destruction process—they also found that the enzyme was able to both break down the membrane protecting the DNA and then to cause the DNA itself to break down..."

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http://medicalxpress.com/news/2016-06-male-mitochondrial-dna-self-destruct-embryo.html

Scientists find that our cells' power plants run on timers

"When one eats may be as important as what one eats. New research at the Weizmann Institute of Science and in Germany, which recently appeared in the Proceedings of the National Academy of Sciences (PNAS), suggests that the cells' power plants - the mitochondria - are highly regulated by the body's biological, or circadian, clocks. This may help explain why people who sleep and eat out of phase with their circadian clocks are at higher risk of developing obesity, diabetes and metabolic syndrome.

Dr. Gad Asher of the Weizmann Institute's Biomolecular Sciences Department, who led the study, explains that circadian clocks, which are found in living things from bacteria to flies and humans, control our rhythms of sleep, activity, eating and metabolism. "In a sense," he says, "it's like a daily calendar, telling the body what to expect, so it can prepare for the future and operate optimally."

Dr. Adi Neufeld-Cohen, of Asher's group, in collaboration with Dr. Maria S. Robles and Prof. Matthias Mann of the Max Planck Institute of Biochemistry in Germany, looked for circadian changes in the mitochondria that, by creating peaks and dips in the cells' energy levels, would also help regulate their day-night cycles. The group identified and quantified hundreds of mitochondrial proteins, finding that the quantities of a whopping 40% peak once a day. 

Further research identified the proteins making up the mitochondrial circadian clock that regulates these activities. Surprisingly, most of the circadian proteins in the mitochondria peaked four hours into the daylight part of the cycle (in mice, which are active at night)..."

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http://medicalxpress.com/news/2016-03-scientists-cells-power-timers.html

What role do mitochondria play in embryo development?

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"Embryos require adequate amounts of energy so that they can successfully progress through each of their cell divisions.

Mitochondria have a key function during early development, as they are the main energy providers of embryos. They are also involved in the regulation of other key cellular processes, such as apoptosis, amino acid and protein synthesis.

Up until now, why has little been known about the biological and clinical implications of mitochondrial variation between embryos prior to implantation?

Until recently the technical tools necessary for such studies were not available. The development of methods such as next generation sequencing (NGS) have made the detailed analysis (quantity and sequence) of the mitochondrial genome (mtDNA) of human embryos possible..."

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