PAIRS

English
 
Yonatan Herzig and Dr. Maya Schuldiner
                  

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Imagine sorting a pile of thousands of unmatched socks into pairs. Now imagine those pairs are microscopic. That begins to approach the challenge faced by Dr. Maya Schuldiner of the Molecular Genetics Department and her colleagues and students when they set out to identify pairs of proteins – proteins that get transported out of a cellular organelle coupled with the proteins that escort them to their rides. But Schuldiner and her team had some help: They adapted the robotic equipment in her lab to develop a system they call PAIRS, which prepares and sifts through thousands of samples to identify matches.
socks
Scientists have been searching for such pairs for the past 20 years, with only partial success. But the issue is vital: The proteins that the escorts match up with are hormones, growth factors and various other signaling molecules that are produced for export to other cells or organs, and their activities are implicated in many diseases, from autoimmune syndromes to cancer. A better understanding of the escorts’ functions could point to possible drug targets for treating these diseases.

The first way station for all proteins that need to either make it out of the cell or end up displayed on the cell’s outer surface is the endoplasmic reticulum (ER) – a maze-like organelle composed of folded internal membranes. The proteins entering the ER must get folded into shape as well as undergo quality-control testing before exiting the maze. But leaving for the next way station – the Golgi apparatus – for final sorting and routing is a much more complex affair than entering. The now functional, folded protein must be enclosed in a bubble of membrane that buds off from the ER, creating a vesicle – a sort of private taxi that delivers its passenger to the Golgi apparatus without letting it come in contact with the cell’s interior. This is where the escorts come into play. They sort and package the proteins – ensuring that only mature proteins leave the ER, and in the right vesicles.
 
Until now, identifying escorts and finding their matches had been something like trying to sort through all those socks by hand, one at a time. That is why only 10 escorts had been identified, and these had been matched to only a handful of proteins. And that, says Schuldiner, is not enough to begin to understand the rules of protein trafficking.
"Liquid Handling" robotic setup performs experiments in 96 wells in parallel

 
 
To remedy the situation, she and her team – including research student Yonatan Herzig and Dr. Yael Elbaz, together with Prof. Sean Munro and Hayley Sharpe of the MRC Laboratory of Molecular Biology, Cambridge, UK – decided a more systematic approach was called for. In the PAIRS method they developed, a lab robot prepared and cultured yeast cells. The samples – grown in rows of tiny wells – each contained a yeast strain that had been genetically engineered so that one of 400 different proteins would glow fluorescent green, while one of the 10 known escorts was rendered inactive. Producing all the possible combinations – just finding matches for the known escorts – required 4,000 different samples. Then, a second robot automatically scanned images of the cells, looking for the tell-tale green glow showing that a particular protein was building up in the cell rather than being exported – a sure sign of a match.
 
 
For each escort, new passenger proteins were identified. At that point, says Schuldiner, the team could begin to formulate some rules about the ER transport system. For instance, the scientists found that the escorts worked mainly with relatively small sets of proteins, each commited to using that particular escort. In some cases, the group of proteins tied to and escort had similar functions; in others, a shared chemical “password” gave them access.

Even more interesting was the one escort protein that seemed to be an exception to the rule: The scientists noted that Erv14 paired up with an unusually large number of proteins that apparently had nothing in common. After a series of experiments ruled out all sorts of possible factors, the team hit upon the one thing they all shared – an extra-long domain that is required for them to be displayed on the outer plasma membrane of the cell.
 
"Colony Arrayer" robot enables the production of tailor-made yeast libraries for screening
 
Because versions of this escort are found in everything from yeast to fruit flies to mammals, the same rule should apply to human Erv14 and the proteins it pairs with. One of those using the Erv14 escort is EGF receptor protein, a protein required for proper embryonic development that also plays a well-studied role in cancer growth. A better understanding of the requirements for EGF receptor trafficking is essential for developing models of both development and tumor progression.

In addition to the matches the researchers managed to identify, there were many proteins that didn’t pair with any of the known escorts. Do these forgo the help, or do they use other, as-yet-undiscovered escorts? Schuldiner and her team plan to continue investigating. Their eventual goal is to produce a “traffickome” that will map out transportation systems for all the proteins in the cell.
 
Dr. Maya Schuldiner's research is supported by the European Research Council; the Minna James Heineman Stiftung; the Enoch Foundation; Roberto and Renata Ruhman, Brazil; the Karen Siem Fellowship for Women in Science; Miel de Botton, UK; James  and Ilene Nathan, Beverly Hills, CA; and the Kahn Family Research Center for Systems Biology of the Human Cell.
 
 
 
 
socks
Life Sciences
English
  • Endoplasmic reticulum
  • Maya Schuldiner
  • Molecular Genetics
  • Protein
  • Robot›Robotic lab

Micro Control for Insulin

English
(l-r) Standing: Sharon Kredo, Dr. Tali Melkman Zehavi, Roni Oren. Sitting: Dr. Eran Hornstein, Natali Rivkin, Amitai Mandelbaum

 
 
The water came and extinguished the fire that burned the stick that beat the dog that bit the cat that ate the goat that father bought for two zuzim. – Had Gadya (from the Passover Haggada)



 
According to Dr. Eran Hornstein of the Molecular Genetics Department, a Had-Gadya-like scenario takes place daily in the pancreas, and it goes something like this: The microRNA slew the negative transcription factor that inhibited the gene that codes for insulin that regulates sugar in the body.
 
The focus of Hornstein’s research is on one of those players: microRNAs – short bits of genetic material that don’t code for proteins. Nonetheless, these tiny sequences of code perform all sorts of regulatory functions in the cells, and they may be involved in a number of complex diseases. In a series of experiments over the past four years, Hornstein and his research team have been examining the role of microRNAs in the pancreatic beta cells – the producers of insulin. Their findings not only shed new light on the way that insulin production is controlled – they may aid, in the future, in the diagnosis and treatment of diabetes.
 

The team included Dr. Tali Melkman Zehavi, students Roni Oren, Sharon Kredo, Amitai Mandelbaum and Tirosh Shapira, and lab technician Natali Rivkin. To begin, the researchers first checked to see whether microRNAs were involved in any way in pancreatic function. Using advanced genetic techniques to prevent microRNA from forming in the pancreases of mice, they came up with a clear answer: Without microRNA, the mice did not produce insulin, and they soon developed the symptoms of diabetes.
 

Next, as the team probed further, they identified the step in the gene-to-protein process that is dependent on microRNA control. That step is transcription – the stage in which the information encoded in the genes is copied out for use in protein production. But this finding left them with further questions. “It’s not obvious that microRNAs would be involved in the control of insulin transcription, as they are more often known to regulate post-transcriptional events in the cell,” says Hornstein. “We had to sit down and come up with a hypothesis that would include another intermediate – a so-called negative transcription factor.”
 

All cells carry the genetic information needed to produce insulin, but only beta cells actually do so. One of the reasons for this is that other cells actively repress insulin production; negative transcription factors keep the genetic information from ever getting transcribed. Beta cells, in contrast, normally maintain a profusion of the transcription factors that bind to genes and initiate insulin production, and very few of the negative factors that inhibit this process. Further testing showed that microRNA affects only the negative transcription factors in beta cells, squelching them so that insulin production can proceed.
 

Finally, Hornstein and his team identified four specific microRNA genes that appear to promote insulin synthesis.
 

This research recently appeared in the EMBO Journal. By showing how microRNA affects insulin production, Hornstein and his team have added a new layer to our understanding of the mechanisms involved in diabetes. Their findings may pave the way, in the future, to better tools for diagnosing the disease and eventually to better treatment.

 
Dr. Eran Hornstein's research is supported by the Nella and Leon Benoziyo Center for Neurological Diseases; the Women's Health Research Center funded by the Bennett-Pritzker Endowment Fund, the Marvelle Koffler Program for Breast Cancer Research, the Harry and Jeanette Weinberg Women's Health Research Endowment, and the Oprah Winfrey Biomedical Research Fund;the Nathan, Shirley, Philip and Charlene Vener New Scientist Fund; the Legacy Heritage Fund; and the Wolfson Family Charitable Trust. Dr. Hornstein is the incumbent of the Helen and Milton A. Kimmelman Career Development Chair.
 

 
(l-r) Standing: Sharon Kredo, Dr. Tali Melkman Zehavi, Roni Oren. Sitting: Dr. Eran Hornstein, Natali Rivkin, Amitai Mandelbaum
Life Sciences
English
  • Diabetes
  • Eran Hornstein
  • Insulin
  • Molecular Genetics
  • RNA

Reversing Malignancy

English
 
Prof. Leo Sachs
 
Prof. Leo Sachs was the first to show that cancer cells – in tissue cultures and in living organisms – can be made to revert to normal behavior.
 

Application

 
Sachs' studies on reversing malignancy led to the development of a new treatment, differentiation therapy. This approach is now being used clinically in human promyelocytic leukemia and is being tested in other types of cancer.
 
Prof. Leo Sachs
Life Sciences
English
  • Leo Sachs

Boosting Production of White Blood Cells

English
Prof. Leo Sachs
 
In the 1960s, Prof. Leo Sachs developed the first ever procedure to grow, clone and induce the development of different types of normal blood cells in a laboratory dish. Using this process he discovered and identified a family of proteins, among them colony-stimulating factors, that control blood cell production in its various stages.
 

Application

 
One of the proteins that Sachs identified, the granulocyte colony-stimulating factor, is now used to boost the production of disease-fighting white blood cells in cancer patients undergoing chemotherapy.
 
Prof. Leo Sachs
Life Sciences
English
  • Leo Sachs

p53 Turns Thirty

English
 
 
(l-r) Dr. Perry Stambolsky and Profs. Varda Rotter and Moshe Oren
 
In 1979, disco was reaching  its height, Egypt and Israel were negotiating a peace treaty, and cancer researchers were in the midst of the revelation that genes can promote cancer. Certain viruses, for instance those that insert their DNA into the genes of their host cells and others that “borrow” host genes and manipulate them, were found to cause cancer. Almost accidentally, several research groups noted the existence of a gene that seemed to play a role in the cell’s switch to malignancy after becoming infected with  cancer-causing viruses.

Two young Israeli researchers working in the US became involved with the new gene, called p53. (The number refers to the molecular weight. It has since been corrected to 43.7, but the name has stuck.) Moshe Oren was in the Princeton lab of Prof. Arnold Levine – one of those labs that first published the discovery of p53. Meanwhile, Varda Rotter, under the guidance of Nobel laureate Prof. David Baltimore, identified the p53 gene in a different type of virus-caused tumor.
 
That early research seemed to indicate that p53 was an oncogene – a cancer-causing gene. Rotter’s research in Baltimore’s lab revealed high levels of the p53 protein in many types of cancer cells (including those not infected with a virus), but almost none in non-cancerous ones.
 
Oren and Rotter both returned to Israel in 1981, soon setting up independent labs in what would become the Weizmann Institute’s Molecular Cell Biology Department, and they began to study the gene in earnest. Quantities of DNA were needed for experiments, and this meant that the gene had to be cloned – a procedure that in those days required, says Oren, “a lot of improvisation, ingenuity and (not least) good luck.” Oren, beginning his work in the lab of Prof. David Givol and continuing to collaborate with Levine, was the first to clone the p53 gene, in 1983. Givol has since joined the circle of p53 researchers, with numerous contributions of his own. Rotter, continuing the work she started in the US, developed new methods for detecting p53 in cells – methods that are in use today in hundreds of labs around the world. In 1983, she suggested that the p53 protein can be regarded as a “tumor-specific marker.”
 
The two scientists enjoyed a sort of “friendly, constructive competition.” In that first decade p53 research began to take some interesting twists and turns. Sometimes the gene clearly played a role in cancer, but in other cancer cells it was inactivated, and results from different clones didn’t always match. In 1989, Oren, Rotter and others compared the various p53 clones and discovered they were all different; what they had thought were oncogenes were in fact mutated versions of a gene that in healthy cells normally plays an entirely different role.
 
It soon became apparent that unmutated, healthy p53 is the opposite of a cancer gene – it’s a tumor suppressor that prevents renegade genes from driving the cell toward cancer. Sir David Lane, one of p53’s codiscoverers, dubbed it “the guardian of the genome.” Just as significant were discoveries that p53 is mutated in about half of all cancers and its actions stymied in many others. With that, p53 research took off. But just when it seemed that this one gene might hold the answer to how cancer develops, scientists began to discover how many complex roles that gene can play. To date, over 50,000 scientific papers have been published on p53, and the flow of new discoveries has by no means abated.
 
While the research of Profs. Oren and Rotter diverged – he turned more to unraveling the role of unmutated p53 in healthy cellular function, she to investigating mutated p53 in cancer – they also began to collaborate. To date, they have published 15 joint papers (see box). They have received numerous awards for their pioneering work, and each of them was recently honored with an invitation to contribute to a special issue of Nature Reviews: Cancer, commemorating 30 years of p53 research.
 
Was it worthwhile for one small institute to support two groups conducting cutting-edge studies on the same gene? Oren and Rotter say the synergy between them has generated a critical mass that has put the Weizmann Institute and Israel at the forefront of p53 research. They emphasize that at least 20 Weizmann research teams are involved in p53-related research; and the younger generation of scientists is using new methods to address as yet unanswered questions. Indeed, there is hardly a cancer researcher around who hasn’t investigated p53 in one way or another.
 
Prof. Moshe Oren’s research is supported by the M.D. Moross Institute for Cancer Research.
 
Prof. Varda Rotter’s research is supported by the Leir Charitable Foundations; the Centre Leon Berard Lyon; the Lombroso Prize for Cancer Research; the Jeanne and Joseph Nissim Family Foundation for Life Sciences; the estate of John M. Lang; and Donald Schwarz, Sherman Oaks, CA. Prof. Rotter is the incumbent of the Norman and Helen Asher Chair of Cancer Research.
 

When to Skip the Vitamins

Vitamin D may have cancer-prevention properties. But can it help if a person is already ill? Clinical trials examining the effects of vitamin D on patients receiving chemotherapy have not yet answered this question. But Profs. Oren and Rotter’s latest collaborative effort, conducted with former student Perry Stambolsky, began from a different angle altogether: Two unrelated experiments in their labs seemed to point to a connection between p53 and the molecular machinery mediating the cell’s response to vitamin D. Probing further, they found out exactly how this machinery interacts with p53, providing a sort of booster that reinforces its actions. That’s good news when the p53 is a non-mutated tumor suppressor: Vitamin D can assist in destroying the tumor. It might, however, be a reason for concern when p53 is mutated. Oren: “When healthy, p53 prevents cancer. But mutations are like sticks jamming the machinery that keeps cancer at bay, and vitamin D may wedge those ‘sticks’ into the works a little tighter.” Rotter: “When deciding whether to prescribe vitamin D, it might be important to know not just whether the p53 is mutated, but the nature of those mutations.”
 
 
(l-r) Dr. Perry Stambolsky and Profs. Varda Rotter and Moshe Oren
Life Sciences
English
  • Cancer genetics
  • Molecular Cell Biology
  • Moshe Oren
  • Varda Rotter
  • p53

Outside Influences

English

The whole is more than the sum of its parts

– Aristotle, Metaphysics

Zelzer and his team investigate joint development

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The body is a sort of self-contained society, governed by the coordinated efforts of its individual organs and components. But what about the individual organs themselves? Are they “self-governing” – able to develop independently of the whole – or do they rely on outside influences to develop and function? In other words, do different growing tissues interact, helping to sculpt one another as they take shape?
 
In two recently published papers, Dr. Elazar Zelzer and his colleagues in the Weizmann Institute’s Molecular Genetics Department present mounting evidence that tissue interactions are a fairly influential factor in the shaping of organs.
 
In the formation of joints, for example, the different tissues develop from a pool of uncommitted cells called progenitor cells which, as they “grow up,” turn into the various cell types that constitute the mature joint. So, for instance, the fate of some cells in the “joint pool” is to grow into tough cartilage, while others become soft synovium (joint capsule) tissue. Keeping progenitor cells committed to their designated fate is a prerequisite for correct organ development; how they are kept on course is a key question. The answer, Zelzer believes, lies in outside influences.
 
One hint comes from the kicks and prods that expectant mothers experience during pregnancy: It’s long been recognized that their babies are not merely practicing to become the next Bruce Lee; but in fact, such movements play a fundamental role in normal development. When fetal movement is restricted, as in fetal akinesia deformation sequence (FADS), the result is various disorders, among them arthrogryposis multiplex congenita (AMC), which is characterized by multiple joint abnormalities. However, the exact relationship between muscular movement and joint formation remained unknown.
 
To shed light on the matter, former postdoctoral fellow Dr. Joy Kahan, who initiated the study, and M.Sc. student Yulia Schwartz started working backwards to try to identify the developmental checkpoint at which joint malfunctions first occur. They took four mutant strains of mice – three that don’t form any muscle in the limbs whatsoever and one that forms muscle, but is paralyzed. They genetically labeled the various progenitor cells so they could trace the events.
 
The team found, as they reported in Developmental Cell, that in all four scenarios, the ability to form functional joints was lost. Why should missing or paralyzed muscle affect joint development? Upon further analysis, they discovered that in the absence of muscle contractions, the joint progenitor cells’ critical “puberty” stage is disrupted: Instead of maturing into the joint-forming cells they were destined to become, these cells experience a sort of “identity crisis” and grow up to be cartilage cells
.
“Through our findings that muscular contraction ultimately regulates joint cell fate and formation, we have provided, for the first time, in vivo evidence highlighting the important connection between embryonic movement and organ development, showing that it’s not solely dependent on intrinsic factors,” says Zelzer.
 
Another example of tissue interaction can be seen in the developing vascular system. Since blood vessels supply all the other organs with all their oxygen and nutrient needs, it’s vital that their development be synchronized. The question is, does the developing organ regulate blood vessel growth or vice versa? Or are they all innately programmed to develop independently? Zelzer’s Ph.D. student Idit Eshkar-Oren turned to the skeletal system to try to provide some answers.
 
During the initial stages of embryonic development, the limbs are populated with blood vessels throughout. As development proceeds, the skeleton secretes anti-growth factors, causing the blood vessels to regress and making way for the growth of cartilage, which is, in turn, later replaced by bone. It would make sense, then, to find fewer new blood vessels near the skeleton and more farther away, where the anti-growth signals are weaker. Yet, this is not the case: Flanking the bony growth are areas rich in blood vessels. What regulates this unlikely patterning? Surprisingly, both processes – vessel growth and vessel regression – are governed by the skeleton. In research published in Development, the team showed that not only does the skeleton secrete negative growth factors, but it also secretes a well-known factor (VEGF) that encourages blood vessel growth. In this way, the scientists believe, the skeleton compensates for the blood vessel retreat, ensuring a sufficient supply of nutrients and oxygen nearby, even as the bones themselves are disconnected from the blood system.
Zelzer: “The evidence we have accrued from our studies clearly suggests that tissue interactions are an important factor governing embryonic organ development. Because the skeletal system is a central organ system associated with a large variety of congenital diseases and malformations, shedding more light on its embryonic development may hopefully improve our ability to treat and prevent such conditions.”
 
 
Dr. Elazar Zelzer’s research is supported by the Helen and Martin Kimmel Institute for Stem Cell Research; the Kirk Center for Childhood Cancer and Immunological Disorders; the David and Fela Shapell Family Center for Genetic Disorders Research; and the estate of Rubin Feryszka. Dr. Zelzer is the incumbent of the Martha S. Sagon Career Development Chair.
 
Mouse embryo skeleton showing sites of initial bone formation (stained red) and cartilage (green and blue), which will later be replaced by bone
 

 

 

 

 
Mouse embryo skeleton showing sites of initial bone formation (stained red) and cartilage (green and blue), which will later be replaced by bone
Life Sciences
English
  • Elazar Zelzer
  • Embryonic development
  • Molecular Genetics
  • Muscle tissue
  • Musculoskeletal system

Tending the Brain’s Garden

English
 
Dr. Oren Schuldiner. Remodeling in the developing brain
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The developing brain resembles a well-tended garden. Budding neurons sprout bushy extensions; but with time, unneeded extensions are “pruned,” as if by an invisible gardener. Entire segments are eliminated and connections between neurons are erased. Many of the neurons then grow new extensions, which wire up the adult brain with amazing precision.
 
This fascinating “garden design,” essential for sculpting the mature brain and nervous system, is being investigated in the lab of Dr. Oren Schuldiner, who recently joined the Weizmann faculty. Schuldiner seeks to reveal the molecular mechanisms that govern neuronal remodeling: What commands instruct segments of neuronal extensions (axons) to become fragmented and disappear? How do the axons know exactly at which spot to begin disintegrating? How does the axon begin to regrow? And what roles do various brain cells play in these remodeling processes?
 
Though it seems wasteful to wire up a developing brain by pruning, the seemingly excessive axonal growth in early development probably serves a purpose – one that scientists have yet to discover. It might, for instance, be simply easier to generate exuberant growth and later refine the brain circuits by trimming branches here and there, rather than immediately generating the correct connectivity. Whatever the reason, axonal pruning is obviously an evolutionary success story: It exists in living beings from worms to mammals, most certainly including humans.
 
Schuldiner was attracted to research into axonal pruning by the novelty of this important and challenging field. In his new lab in the Institute’s Molecular Cell Biology Department, he investigates this process in fruit flies, which can help clarify brain remodeling in humans. Fruit flies have long been considered an excellent model for genetic studies as they are small, cheap and reach maturity within 10 days. And, since each fly’s life cycle involves major transformations, from a larva to an adult fly, its brain undergoes massive pruning and remodeling.
 
During his postdoctoral studies at Stanford University, Schuldiner designed an approach that dramatically speeds up the screening of fruit fly genes. In such screening, scientists reveal the function of a gene by creating a mutation and observing its consequences; they then map the location of the mutated gene in the genome. To optimize this process, Schuldiner designed a technique for producing just the kinds of mutations that can be examined by MARCM, the pioneering method for viewing individually mutated neurons in the fruit fly brain that was developed by his postdoctoral supervisor Prof. Liqun Luo. As a result, the time it takes to map a fruit fly gene has been shortened from at least a year to just two days. Schuldiner and colleagues used the approach to create some 2,500 types of fruit fly, each with a unique mutated gene. These mutations, covering about 20% of the fly’s genome, provide researchers worldwide with a valuable resource for investigating individual fly genes.
 
With the help of this powerful method, Schuldiner identified a dozen genes involved in axonal pruning – about twice the number of all previously known pruning genes. At the Weizmann Institute, he is studying the function of these genes and searching for additional molecules and mechanisms that control the remodeling of the nervous system during development. Employing sophisticated genetic techniques and confocal microscopy, he is able to visualize single nerve cells within a whole brain while creating specific mutations in individual neurons.
 
One of the genes Schuldiner discovered serves as the first known molecular switch that triggers the regrowth of axons after pruning. He intends to find out whether this gene also triggers regrowth after nerve injury and whether it can be manipulated to help induce such regrowth, with a view to potential future therapies.
 
Because the fragmentation of axons after injury and in certain pathological conditions –
including Alzheimer’s disease and certain other neurodegenerative disorders – is similar to the fragmentation that occurs during developmental axon pruning, Schuldiner’s research on the developing fruit fly brain
could provide valuable new insights into nerve injury and various diseases of the nervous system.
 
 
Axon pruning in normal fuit fly brain
 
Unpruned axons in mutant fruit fly brain
 
 
 
 
 
 
 
 

From Sinai to Rehovot


Born in Tel Aviv, Israel, Dr. Oren Schuldiner conducted his undergraduate and graduate studies at the Hebrew University of Jerusalem. After earning a Ph.D. in genetics in 2002, he performed postgraduate research at Stanford University for five years. He joined the Weizmann faculty as a senior scientist in 2008. Schuldiner is married to Maya, a senior scientist in Weizmann’s Molecular Genetics Department, and has two sons: Daniel, seven, and Noam, four. While a student, he worked as a tour guide in Sinai and later wrote and edited the life science column in the Hebrew-language popular science monthly Galileo.
He enjoys hiking, mostly in the desert, as well as scuba diving, photographing people and scenery, and listening to jazz.
 

Dr. Oren Schuldiner’s research is supported by the Women’s Health Research Center funded by the Bennett-Pritzker Endowment Fund, the Marvelle Koffler Program for Breast Cancer Research, the Harry and Jeanette Weinberg Women’s Health Research Endowment and the Oprah Winfrey Biomedical Research Fund; the Adelis Foundation; and the estate of Lela London.

 
 
 
 
Dr. Oren Schuldiner. Early pruning for proper growth
Life Sciences
English
  • Alzheimer's
  • Axon
  • Molecular Cell Biology
  • Mutation
  • Neural pathway
  • Oren Schuldiner

The Organ Underground

English

R’ada Massarwa, Ben-Zion Shilo, Eyal Schejter. transporting substances in the cell

 

 
The London Tube is the city’s lifeline, transporting people to every corner and back. Similarly, the body relies on networks of tubes – tubular organs such as the gut, windpipe and glands – to transport such bodily substances as solutes, hormones, nutrients, oxygen and waste products.
 
The inner lining of the tubular organ is composed of a layer of specialized epithelial, or “outer,” cells, which, among other things, control the secretion of useful substances into the organ’s “tunnel.” To enter the tunnel, these substances must first make their way to the exposed edge of the epithelial cells. Special proteins within the cells lead the substances in the right direction, but how they do this is not exactly clear.
 
An epithelial cell’s tunnel-facing edge is always rich in “cables” made from a common protein called filamentous actin. “Who” makes these actin cables? How do they become localized only in the cell’s tunnel-facing edge? What is their function there? New research recently published in Developmental Cell by Prof. Ben-Zion Shilo, together with (then) research student Dr. R’ada Massarwa and Dr. Eyal Schejter of the Weizmann Institute’s Molecular Genetics Department, has provided, for the first time, possible answers to these questions
.
Working with fruit fly embryos, the team discovered that a protein called Dia was responsible for the specialized actin structures. When the scientists removed the gene for Dia production, they found signs of filament production along other parts of the cell, but no cable structures were being formed along its tunnel-facing edge. Further experiments revealed that in order for Dia to carry out its function, it first has to be activated by other types of proteins. These Dia-activating proteins are bound to the tunnel-facing side of the epithelial cell, thus ensuring the cables’ polarized distribution.
 
How exactly are the actin cables used? The scientists noted that in cells where cables weren’t produced, no substances were secreted into the organ’s tunnel. In other words, the actin cables seem to be the “route” the substances need to travel to arrive at the tunnel. The team discovered that the substances are “shuttled” on a type of “cable car” – a motor protein called myosin V – which transports them along the actin cable and drops them off at the tunnel entrance, from which they eventually get secreted.
 
“Our research shows that this mechanism for secretion in the fruit fly embryo is employed in different tubular organs, regardless of their size and function,” said Shilo. “For our next study, we plan to check whether the same mechanism is found in mammalian species, including humans. We hope that these insights will help us gain a better understanding of the mechanisms involved in secretion by tubular organs and, on a practical level, to improve doctors’ ability to deal with pathological situations that are caused by a failure of the secretion process.”
 
Prof. Ben-Zion Shilo’s research is supported by the Jeanne and Joseph Nissim Foundation for Life Sciences Research; the Mary Ralph Designated Philanthropic Fund; the Carolito Stiftung; La Fondation Raphael et Regina Levy; and the estate of Georg Galai. Prof. Shilo is the incumbent of the Hilda and Cecil Lewis Professorial Chair of Molecular Genetics.
(l-r) Dr. R’ada Massarwa, Prof. Ben-Zion Shilo and Dr. Eyal Schejter. On the secreting edge
Life Sciences
English
  • Ben-Zion Shilo
  • Fruit fly
  • Hormone
  • Molecular Genetics

Cell Detective

English
 
 

Dr. Guy Shakhar and his research team. Where do immune cells go?

 

 

 

 

 

 

 

 

 

 

 

 

 

Our immune systems are hugely complex cellular networks that depend on each member carrying out its task. Dr. Guy Shakhar of the Immunology Department is a sort of immune system sleuth, staking out immune system cells and tailing them to find out where they go, how they get there and who they talk to. His surveillance equipment consists of a sophisticated imaging microscope (see box) that enables him to observe these cells both in their normal daily routines and in the act of abetting disease.

 
One group of cells that Shakhar and his team track is dendritic cells. These cells hang around in organs like the gut, skin and lungs – places where pathogens like to enter the body. Dendritic cells sample any foreign matter they find and, if further action is called for, whisk their sample – a bit of protein from the pathogen called an antigen – off to the nearest lymph node to present it to other cells of the immune system. These are primarily T cells that can kick-start an immune response, kill dangerous cells and recruit other immune cells – such as the B cells that produce disease-fighting antibodies. Shakhar is investigating how dendritic cells mobilize, traveling from the skin or gut through the lymph ducts and into the lymph nodes. It's known that these cells don't travel well if their surface receptors for two molecules – one that allows them to sense their target and another that helps them adhere – are blocked. Shakhar is trying to find out exactly when these molecules come into play – whether they help the immune cells leave their patrol sites, steer them to their destinations or enable them to enter the lymph nodes.
 
But sometimes the pathogen invasion is more of a sneak attack: For instance, just a few malaria parasites in a mosquito's bite are enough to cause disease. If these parasites are unfamiliar to the immune system, only a few out of the billions of patrolling T cells may have surface molecules that can identify the new antigens. A race begins between pathogens and immune system, and this small number of cells must convince the immune system to launch a full-scale attack on short notice. The team's evidence suggests that the T cells and dendritic cells combine forces, the dendritic cells forming networks that coordinate their presentation. The T cells can then navigate these networks to find the most informative antigen-presenting dendritic cells. The team is currently exploring how this coordination is carried out.
 
Shakhar is also on the trail of a network of cells involved in a family of lower digestive system disorders that includes Crohn's disease. Evidence suggests these autoimmune diseases are rooted in the faulty regulation of immune responses to the normal population of microbes living in the intestines. This network involves three-way interactions between the inflammation-causing immune system cells, regulatory T cells, which damp down immune responses, and dendritic cells. He and his team are imaging the intestines of mice into which they have introduced both bacteria with specific antigens and immune system T cells that recognize and respond only to these antigens. They believe the dendritic cells are key players in this network, and the team's efforts to pin down their role might provide new targets for treating these diseases.  
 

True to Life
 

When Robert Hooke first observed a slice of cork under a microscope in the 17th century, he named the tiny empty compartments he saw "cells." In the ensuing years, microscopes have become much more powerful, revealing the world of cells in infinitely greater detail. But until recently, whenever researchers wanted to visualize cells inside complex tissues, they had to fix them firmly in place – as dead as those in Hooke's cork.
 
In the last few years, new kinds of microscopes have enabled scientists to observe living, moving cells deep inside live animals.
 
Dr. Guy Shakhar uses one called a two-photon microscope to track immune cells in anesthetized mice. Based on a physical phenomenon in which two infrared photons striking fluorescent molecules in rapid succession cause them to emit a flash of visible light, the method produces 3-D images of cells and tissues by shining ultra-quick pulses of highly focused infrared laser light. The infrared beam can penetrate tissue to a depth of several hundred microns, allowing Shakhar to observe the organization of the tissue without slicing into it and to follow the activities of cells over time.
 

Image of a Scientist
 

Dr. Guy Shakhar was born in Jerusalem and grew up in Givatayim, near Tel Aviv. After serving in the IDF, he enrolled in Tel Aviv University, receiving an M.Sc. in interdisciplinary studies and a Ph.D. in neuroscience, in which he researched interactions between the immune system and the nervous system. In his postdoctoral work with Prof. Michael Dustin at NYU School of Medicine, Shakhar turned to imaging immune cells to investigate their activities. In 2006, Shakhar joined the Weizmann Institute as a senior scientist.
 
Married to Keren, Shakhar is the father of two children – Amit, aged four and Gal, aged six. He enjoys mountain biking and playing the Asian board game Go.
 
Dr. Guy Shakhar's research is supported by the Kirk Center for Childhood Cancer and Immunological Disorders; the Crown Endowment Fund for Immunological Research; the Linda Tallen and David Paul Kane Educational and Research Foundation; the Philip M. Klutznick Fund for Research; the Wolfson Family Charitable Trust; and the estate of David Turner.
 
(l-r) Top: Julia Farache, Dr. Tali Feferman, Dr. Guy Shakhar and Ira Gurevich. Bottom: Orna Tal and Idan Milo. Intercepting a sneak attack
Life Sciences
English
  • Autoimmune
  • Guy Shakhar
  • Immune cells
  • Immunology

Passport Please

English
 
Prof. rony Seger. A code to enter through the membrane

 

 

 

 

 

 

 

 

 

 

Border controls are the way a country regulates who and what crosses into its territory. Living cells also have "border controls" – membranes that surround the whole cell or especially sensitive or important parts of it. One of the cell's organelles – the nucleus – is even enclosed in a double membrane that serves to protect its highly valuable contents – the organism's genetic material. This membrane regulates the flow of molecules into and out of the nucleus via "border gates" – referred to as membrane-bound pores – helping to prevent erroneous DNA activation.

Those molecules authorized to enter the nucleus and carry out legitimate activities usually possess a special "localization code" – a specific amino acid sequence harbored within a particular region of the molecule. This code is recognized by special carrier proteins (importins), which then facilitate the transport of these molecules into the nucleus.

Scientists have only recently begun to notice that some molecules entering the nucleus lack the localization code. So how do they pass through the border? In a research article recently published in Molecular Cell, Prof. Rony Seger and Ph.D. student Dana Chuderland, with help from postdoctoral fellow Dr. Alexander Konson, all of the Weizmann Institute's Biological Regulation Department, identified a previously unknown mechanism that grants permission to some of these molecules to enter. Because certain molecules that cross over into the nucleus are overactive in such diseases as cancer, this new mechanism may present an effective means of "stopping them at the border."

Seger's team focused on signaling proteins named ERK. These proteins, which function mainly within the nucleus, are involved in such cellular activities as gene expression (the production of proteins) as well as cell proliferation and differentiation. Seger's group discovered, through experiments and bioinformatics analyses, that these signaling proteins do possess a localization code after all – but its sequence is different from that of the commonly recognized one. As opposed to the molecules possessing the regular localization code, molecules bearing the newly identified code do not have an automatic free pass; the team identified further entry criteria they need to meet. ERK proteins are usually held in "customs" – anchored to other proteins in the cell's cytoplasm – and can only get released upon extracellular stimulation of the cells with growth factors and hormones. Once this occurs, their particular entry code needs to get "stamped" with a phosphate group. (The addition or removal of a phosphate is an important regulatory mechanism of cellular activity.) Only then can these proteins bind to the particular carrier protein that helps them localize to the nucleus, where they can carry out their assignment.

When the newly discovered entry code was removed from these proteins or the addition of the phosphate groups was prevented, the ERK proteins remained stranded outside the nuclear membrane, thus confirming that both are necessary for crossing the border. The scientists noted that these events inhibited cellular proliferation, hinting that the new code might be useful for fighting cancer, in which cell reproduction goes out of control.

It turns out that ERK is not the only type of protein to use this mechanism; a bioinformatics search revealed that about 40 proteins can translocate to the nucleus by the same route. In other words, Seger's group seems to have identified a unique general mechanism shared by these proteins.

 
Extracellular activation gets ERK proteins into the nucleus
 

These findings may have important implications for the development of new therapies: Inappropriate activation of ERK proteins and ensuing cell proliferation is common in human cancers. Because these proteins are important in so many other processes, however, existing treatments that target all ERK proteins lead to undesirable side effects. A drug that could selectively target the newly identified entry code might act mainly to prevent proliferation, resulting in a more effective anti-cancer drug with fewer adverse reactions.   

 

Prof. Rony Seger's research is supported by the M.D. Moross Institute for Cancer Research; and the Phyllis and Joseph Gurwin Fund for Scientific Advancement. Prof. Seger is the incumbent of the Yale S. Lewine and Ella Miller Lewine Professorial Chair for Cancer Research.

 
Prof. Rony Seger. Going through customs
Life Sciences
English
  • Biological Regulation
  • Cell
  • Rony Seger
  • Signaling molecule

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