TEDx on Excellence in Science and Science Education at the Weizmann Institute; Where Have all the Mitochondria Gone?; This Bump Means “Start”

TEDx on Excellence in Science and Science Education at the Weizmann Institute

TEDx Weizmann Institute, a conference on excellence in science and science education, will be held on May 20 at the Weizmann Institute of Science. The Institute has been working for the past 50 years to advance science education in Israel. The conference will be led by the Davidson Institute of Science Education, the educational arm of the Weizmann Institute, together with scientists and staff of the Weizmann Institute and with the support of the Trump Foundation, which promotes the advancement of science and math education.

The conference will include 10 short talks by top scientists, leaders in the field of science education, and science teachers with unique teaching strategies, as well as students who will share their inspiring experiences in learning science. The speakers will impart their own perspectives on science and science teaching, as well as their thoughts on motivating students, teachers, and the general public to take an interest in science.

TEDx events are local, independently organized conferences in the spirit of the original TED talks, which aim to stimulate discussion and ideas. The TEDx Weizmann Institute talks will be given in English, and they will be broadcast live online, on Tuesday, May 20th, from 4:30 pm to 9:30 pm, Israel time, on the event website: http://www.tedxweizmanninstitute.com.

The Weizmann Institute speakers will be Prof. Oded Aharonson, Department of Earth and Planetary Sciences; Dr. Maya Schuldiner, Department of Molecular Genetics; and Dr. Ron Milo, Department of Plant Sciences. The other speakers include two winners of the Trump Master Teacher Award: chemistry teacher Dr. Abir Abed and physics teacher Kobi Shvarzbord; Dr. Rachel Knoll, a physics teacher who instituted a robotics program in Yeruham, and Rotem Stahl, a student who participated in the program and is now an assistant for the program; Noam Ottolenghi, a student who won an Intel ISEF prize for his thesis; Dr. Efrat Furst, a neurobiologist who is involved in science education, and Mickey Choma, who teaches juggling, dancing, and fencing; Dr. Ran Peleg, a chemical engineer, educator, and actor; and Dr. Ayelet Baram-Tsabari, head of the biology and science communications groups in the Science and Technology Education Department of the Technion.

Where Have all the Mitochondria Gone?

Weizmann Institute researchers shed light on a crucial step in fertilization

It’s common knowledge that all organisms inherit their mitochondria – the cell’s “power plants” – from their mothers. But what happens to all the father’s mitochondria? Surprisingly, how – and why – paternal mitochondria are prevented from getting passed on after fertilization is still shrouded in mystery; the only thing that’s certain is that there must be a compelling reason, as this phenomenon has been conserved throughout evolution.

Studying female fruit flies, Dr. Eli Arama and a team in the Weizmann Institute’s Department of Molecular Genetics have now discovered special cellular vesicles (small cavities) that originate in the eggs and, upon fertilization, actively seek out and destroy the father’s mitochondria.

This study, recently published in Development Cell, may help shed light on the prevailing theories. One theory holds that it is an active process in which paternal mitochondria are selectively degraded by a “self-eating” system known as autophagy, in which vesicles called autophagosomes engulf the cell’s unwanted structures. But the autophagy study was conducted on worms (C. elegans), whose sperm are quite different from the long, flagellated “head” and “tail” structures of both mammalian and fruit-fly sperm. The tail comprises the mitochondria: a long tube attached to, or coiled around, the tail’s skeletal structure. How would the tiny autophagosome engulf such a large structure – about 2 mm long in the fruit fly?

A second theory, based mainly on mouse models, states that the absence of paternal mitochondria is due to a passive process of dilution in the sea of maternal mitochondria. But that could not explain why certain genetic markers related to autophagy were still detected on the paternal mitochondria after fertilization.

Enter the egg’s special cellular vesicles. The Weizmann team, led by PhD students Liron Gal and Yoav Politi in Dr. Arama’s group, together with former senior intern Yossi Kalifa and former PhD student Liat Ravid, and with the assistance of Prof. Zvulun Elazar of the Department of Biological Chemistry, found that as soon as the sperm enters the egg, the cellular vesicles – already present in the fruit fly egg – are immediately attracted, magnet-like, to the sperm. The vesicles then proceed to disintegrate the sperm’s outer membrane and separate the mitochondria from the tail section, which is subsequently cut into smaller pieces that are “devoured” by conventional selective autophagy.

But what were these vesicles? Close observation revealed they did not resemble an autophagosome, but rather a different type of vesicle that is usually involved in a distinct pathway. Yet these vesicles carried autophagy markers. Says Dr. Arama, “We were not witnessing classic autophagy machinery; these structures were too large and morphologically distinct to be typical autophagosomes.” The team’s findings suggest that the egg’s special cellular vesicles represent a new type of system that is a unique combination of three separate biological processes whose pathways may have diverged from their classic functions.

These new discoveries, which the scientists believe hold true for other organisms with flagellated sperm, including humans, may lead, among other things, toward an understanding of why only a quarter of IVF pregnancies carry to term. It may be that this invasive procedure somehow abrogates the ability of the egg to destroy the paternal mitochondria. Dr. Arama and team hope that further research will help shed new light on a variety of issues pertaining to paternal mitochondria, with the ultimate goal of understanding mitochondrial turnover and male fertility.

Dr. Eli Arama’s research is supported by the Yeda-Sela Center for Basic Research; the Fritz Thyssen Stiftung; and the late Rudolfine Steindling. Dr. Arama is the incumbent of the Corinne S. Koshland Career Development Chair in Perpetuity.

This Bump Means “Start”

Scientists decode “notation” in the folds of RNA strands that may help the cellular machinery read the gene code

The DNA strands in our genomes can pair up comfortably in double-helix fashion, but what about the lonely, single-stranded RNA that is copied from the DNA? The “letters” in the RNA sequence, nucleotides, are chemically built like those in the DNA to seek a mate – sometimes even with another letter on the strand – causing the strand to curl and bend over on itself into irregular hairpin-shaped configurations. A new study performed by Weizmann Institute and Stanford University scientists and published in Nature suggests that these shapes seem to act as a sort of “notation” on top of the gene code, helping the cell’s machinery to read out that code.

In possibly one of the broadest studies done on RNA structure in human cells, Prof. Eran Segal and research student Ohad Manor in the Weizmann Institute’s Department of Computer Science and Applied Mathematics and Department of Molecular Cell Biology, joined up with the research team of Prof. Howard Chang of Stanford to map the total set of RNA configurations in one type of cell, in three individuals. Using a technique Prof. Segal and his group developed and patented in 2010, they created a scorecard for each sequence of RNA in order to locate the points where the segments doubled up and where they remained unattached. Analyzing over 160 million RNA fragments from each individual – all together, thousands of RNAs – enabled them to produce sort of a panoramic, topographical map of the RNA landscape.

“Some things immediately stood out when we looked at the pairing scores,” says Prof. Segal. “For example, we can see very clearly the sharp dips at the ‘start’ and ‘stop’ points of the gene that demarcate its functional region.” Those dips – unpaired regions in the folded strand – are the hairpin-like curves and bulges in the structure. This nearly braille-like notation, says Prof. Segal, may be a handy way for such machinery as the ribosome, which produces proteins according to the RNA sequence, to find its place on the strand without having to perform a search for the right group of letters. In fact, the code hidden within the shapes may extend to the readouts for individual amino acids, each of which is encoded in a three-letter sequence known as a codon. The score showed a pattern of extra-close pairing every three letters that may signal the beginning of a new codon.

The three individuals were parents and child, a setup that enabled the researchers to ask some questions about the RNA landscape and heredity. They looked at short segments of the RNA where alterations in a one or two letters are known to occur frequently, so the child would likely have inherited two different versions. What difference does a single letter substitution make? Comparing the pairing scores from mother, father, and child showed that the shapes of around 15% of the RNAs containing these sequences were significantly altered – enough to substantially affect the function of the protein. The team named these configurations RiboSNitches.

The team then flagged the RiboSNitches they identified on the RNA map. The sites of these suggested to them that such RiboSNitches could play a crucial role in regulating the process in which the gene code is translated into protein. Their positions on the map even hint that some RiboSNitches may be involved in such diseases as multiple sclerosis, asthma, and Parkinson’s.

Prof. Eran Segal’s research is supported by the Kahn Family Research Center for Systems Biology of the Human Cell; the Carolito Stiftung; the Cecil and Hilda Lewis Charitable Trust; and the European Research Council.