quote:Newts' Ability To Regenerate Tissue Replicated In Mouse Cells By Stanford Scientists
STANFORD, Calif. — Tissue regeneration a la salamanders and newts seems like it should be the stuff of science fiction. But it happens routinely. Why can't we mammals just re-grow a limb or churn out a few new heart muscle cells as needed? New research suggests there might be a very good reason: Restricting our cells' ability to pop in and out of the cell cycle at will — a prerequisite for the cell division necessary to make new tissue — reduces the chances that they'll run amok and form potentially deadly cancers.
Now scientists at the Stanford University School of Medicine have taken a big step toward being able to confer this regenerative capacity on mammalian muscle cells; they accomplished this feat in experiments with laboratory mice in which they blocked the expression of just two tumor-suppressing proteins. The finding may move us closer to future regenerative therapies in humans — surprisingly, by sending us shimmying back down the evolutionary tree.
"Newts regenerate tissues very effectively," said Helen Blau, PhD, the Donald E. and Delia B. Baxter Professor and a member of Stanford's Institute for Stem Cell Biology and Regenerative Medicine. "In contrast, mammals are pathetic. We can regenerate our livers, and that's about it. Until now it's been a mystery as to how they do it."
Blau is the senior author of the research, which will be published in Cell Stem Cell on Aug. 6. Kostandin Pajcini, PhD, a former graduate student, and Jason Pomerantz, MD, a former postdoctoral scholar in Blau's laboratory, are primarily responsible for the work and are first author and co-senior author, respectively.
Although there's been a lot of discussion about using adult or embryonic stem cells to repair or revitalize tissues throughout the body, in this case the researchers weren't studying stem cells. Instead they were investigating whether myocytes, run-of-the mill muscle cells that normally don't divide, can be induced to re-enter the cell cycle and begin proliferating. This is important because most specialized, or differentiated, cells in mammals are locked into a steady state that does not allow cell division. And without cell division, it is not possible to get regeneration.
In contrast, the cells of some types of amphibians are able to replace lost or damaged tissue by entering the cell cycle to give rise to more muscle cells. While doing so, the cells maintain their muscle identity, which prevents them from straying from the beaten path and becoming other, less useful cell types.
Pomerantz and Blau wondered if it could be possible to coax mammalian cells to follow a similar path. To do so, though, they needed to pinpoint what was different between mammalian and salamander cells when it comes to cell cycle control. One aspect involves a class of proteins called tumor suppressors that block inappropriate cell division.
Previous research had shown that a tumor suppressor called retinoblastoma, or Rb, plays an important role in preventing many types of specialized mammalian cells, including those found in muscle, from dividing willy-nilly. But the effect of blocking the expression of Rb in mammalian cells has been inconsistent: In some cases it has allowed the cells to hop back into the cell cycle; in others, it hasn't.
The researchers employed some evolutionary detective work to figure out that another tumor suppressor called ARF might be involved. Like Rb, ARF works to throw the brakes on the cell cycle in response to internal signals. An examination of the evolutionary tree provided a key clue. They saw that ARF first arose in chickens. It is found in other birds and mammals, but not in animals like salamanders nestled on the lower branches. Tellingly, it's also missing in cell lines that begin cycling when Rb is lost, and it is expressed at lower-than-normal levels in mammalian livers — the only organ that we humans can regenerate.
Based on previous investigators' work with newts, Blau said it "seemed to us that they don't have the same limitations on growth. We hypothesized that maybe, during evolution, humans gained a tumor suppressor not present in lower animals at the expense of regeneration."
Sure enough, Pajcini and Pomerantz found that blocking the expression of both Rb and ARF allowed individual myocytes isolated from mouse muscle to dedifferentiate and begin dividing. When they put the cells back into the mice, they were able to merge with existing muscle fibers — as long as Rb expression was restored. Without Rb the transplanted cells proliferated excessively and disrupted the structure of the original muscle.
"These myocytes have reached the point of no return," said Blau. "They can't just start dividing again. But here we show that temporarily blocking the expression of just two proteins can restore an ancient ability to contribute to mammalian muscle."
The key word here is "temporarily." As is clear from the mouse experiments, blocking the expression of tumor suppressors in mammalian cells can be a tricky gambit. Permanently removing these proteins can lead to uncontrolled cell division. But, a temporary and well-controlled loss — as the researchers devised here — could be a useful therapeutic tool.
The research required some sophisticated technology to separate individual myocytes from one another for study. To do so, Pajcini traveled to Munich to learn how to optimize a technique normally used on cryopreserved and fixed tissue sections — "laser micro-dissection catapulting" — for use with living cells. But the effort paid off when he was able to prove conclusively that once the expression of the two proteins was blocked, individual live cells were, in fact, dividing in culture.
Next, the researchers would like to see if the technique works in other cell types, like those of the pancreas or the heart, and whether they can induce it to happen in tissue at sites of injury. If so, it may be possible to trigger temporary cell proliferation as a means of therapy for a variety of ailments.
In addition to Blau, Pajcini and Pomerantz, other Stanford researchers involved in the study include senior research scientist Stephane Corbel, PhD, and assistant professor of pediatrics and genetics Julien Sage, PhD. Pajcini is now at the University of Pennsylvania, and Pomerantz is an assistant professor of surgery at the University of California-San Francisco.
Jazekerquote:Op maandag 16 augustus 2010 09:26 schreef SpecialK het volgende:
Heb je toevallig een directe link naar dat artikel? Ik ben wel benieuwd naar de bloemlezingen?
http://arstechnica.com/sc(...)from-social-cues.arsquote:Migratory species get wanderlust mostly from social cues
By Casey Johnston | Last updated about 18 hours ago
Birds and other migrating species may be as dependent on social networks as we are, according to a study released by PNAS on Monday. By studying migration simulations of everything from bison to bacteria, a team of researchers found that very few individuals in a group migrate because of environmental cues. Most are just following the leader, which may be the reason many species eventually stop migrating as their habitable areas become more distant and fragmented.
Modeling the migration process of a few different species suggested to the authors that an impulse to migrate can be motivated by two things. One is termed a "gradient," and consists of whatever factors we normally think spurs a flock or herd of animals to migrate: a drop or rise in temperature, diminishing of food sources, and so on.
The second motivation was much larger, and unexpected by the authors. It seemed many organisms had little or no sense of the first type of motivator, the gradients. Instead, they relied on social interaction to tell them when wanderlust was the prevailing sentiment in the herd or flock. They deferred to the few members of the group that were sensitive to gradients, and followed the ad-hoc leaders to their new habitat.
While humans are intimately familiar with the follower-leader relationship, the phenomenon may be relatively new in migratory animal behavior. The authors think the mix of social and gradient factors may explain the issue of habitat fragmentation, where animals that have to travel increasing distances eventually stop migrating altogether.
The problem may be that the group leaders, who are a small minority in migratory groups, are eventually unable to rise to the occasion. They no longer detect gradients and are loath to risk leading their peers to increasingly distant areas. With no leaders to latch on to, the group becomes locked down to one area.
Loss of migratory ability is often long-lived or permanent, and can change the evolutionary path of many organisms. Considering both this social reliance on leaders with increased habitat destruction and habitat fragmentation, the authors expect declines in migratory species.
Bronquote:'Evolutietheorie van Darwin klopt niet'
Uitgegeven: 24 augustus 2010 11:26
Laatst gewijzigd: 24 augustus 2010 11:26
AMSTERDAM - De bedenker van de evolutietheorie Charles Darwin had het mis toen hij beweerde dat competitie de belangrijkste drijfveer achter het evolutieproces was. Dat beweren Britse wetenschappers in een nieuwe studie.
Volgens onderzoekers van de Universiteit van Bristol is niet de competitie tussen de soorten doorslaggevend voor het evolutieproces, maar de leefruimte die een soort heeft. De juistheid van de beroemde term ‘survival of the fittest’ van Charles Darwin wordt daarmee in twijfel getrokken.
De wetenschappers komen tot hun opmerkelijke conclusies in het wetenschappelijk tijdschrift Biology Letters. Ze hebben voor hun onderzoek evolutionaire patronen bestudeerd in de afgelopen 400 miljoen jaar op basis van fossielen.
Vliegen
Als bewijs voor de nieuwe theorie over het belang van leefruimte wordt de evolutie van vogels genoemd. Volgens de Britse wetenschappers kwam de ontwikkeling van die soort pas echt op gang toen de dieren vleugels ontwikkelden en in de lucht gingen leven.
“Een ander voorbeeld is het feit dat zoogdieren 60 miljoen jaar lang naast dinosaurussen leefden. Zij waren zeker niet in staat om de competitie te winnen van deze dominante reptielen”, verklaart onderzoeker Mike Benton op BBC News. “Maar toen de dinosaurussen uitstierven, hebben zoogdieren wel snel de lege plaatsen ingenomen en vandaag de dag domineren zij het land.”
Competitie
Toch is het volgens andere wetenschappers maar de vraag of de nieuwe theorie ook daadwerkelijk daadwerkelijk bewijst dat competitie tussen verschillende soorten niet doorslaggevend is bij evolutie.
“Waarom zouden soorten nieuwe stukken land innemen”, vraagt evolutiewetenschapper Stephen Stearns zich af. “Is de reden daarvan niet gewoon dat ze competitie proberen te vermijden met de soorten die op de stukken land leven die al bezet zijn?”
Dat stukje geeft vooral aan hoe weinig de schrijver van nu.nl begrijpt van de materie.quote:Op dinsdag 24 augustus 2010 16:42 schreef Semisane het volgende:
Persoonlijk ben ik niet echt onder de indruk van de onderstaande argumenten die men gebruikt, maar kan ook het originele artikel in Biology letters vinden waarin wellicht de argumenten beter zijn onderbouwd.
[..]
Bron
Nou ja oké dat is waar, ik wil eigenlijk wel het originele artikel lezen, maar kan het niet vinden.quote:Op dinsdag 24 augustus 2010 16:51 schreef Monolith het volgende:
[..]
Dat stukje geeft vooral aan hoe weinig de schrijver van nu.nl begrijpt van de materie.
quote:Op woensdag 25 augustus 2010 13:33 schreef Semisane het volgende:
[..]
Nou ja oké dat is waar, ik wil eigenlijk wel het originele artikel lezen, maar kan het niet vinden.
bronquote:Sahney, S. et al. (2010) Links between global taxonomic diversity, ecological diversity and the expansion of vertebrates on land. Biology Letters, 6, 544-547.
Tetrapod biodiversity today is great; over the past 400 Myr since vertebrates moved onto land, global tetrapod diversity has risen exponentially, punctuated by losses during major extinctions. There are links between the total global diversity of tetrapods and the diversity of their ecological roles, yet no one fully understands the interplay of these two aspects of biodiversity and a numerical analysis of this relationship has not so far been undertaken. Here we show that the global taxonomic and ecological diversity of tetrapods are closely linked. Throughout geological time, patterns of global diversity of tetrapod families show 97 per cent correlation with ecological modes. Global taxonomic and ecological diversity of this group correlates closely with the dominant classes of tetrapods (amphibians in the Palaeozoic, reptiles in the Mesozoic, birds and mammals in the Cenozoic). These groups have driven ecological diversity by expansion and contraction of occupied ecospace, rather than by direct competition within existing ecospace and each group has used ecospace at a greater rate than their predecessors.
Thanks!quote:
Interessant, ook even doorlezen dan.quote:Een uitbreidende of krimpende ecoruimte heeft natuurlijk een enorme impact op het zogenaamde fitnesslandscape. Daardoor kan er opeens wel degelijk sprake zijn van sterke selectiedruk op eigenschappen die daarvoor praktisch een neutraal effect hadden. Deze publicatie heeft m.i. ook wel raakvlakken met de zogenaamde 'facilitated variation' van Kirschner.
http://arstechnica.com/sc(...)-goes-a-long-way.arsquote:For crows, a little tool use goes a long way
By Kate Shaw | Last updated about 3 hours ago
Evolutionarily, animals that use tools have an leg up on their competition: they can access hard-to-get food items, learn more about their environment, and better protect and defend themselves. But exactly how much of an evolutionary edge does tool use provide? In a new article in Science, a group of researchers set out to answer this question, and were surprised at how much of an advantage tool use can provide.
The scientists studied New Caledonian crows, a bird species that is particularly well known for its tool use. These crows often use sticks to find and extract beetle larvae from holes, much like chimpanzees use sticks to “fish” for termites. This is a very specialized task, because the crows fish for just one beetle species (the wood boring longhorn beetle) in the trunk of a single species of tree (the candlenut tree).
Learning to use these stick tools is costly, since it takes young crows a considerable amount of time and effort for to become proficient at fishing for the larvae; in fact, even experienced adults take a relatively long time to catch each larvae. However, the slow learning curve and long handling time are worthwhile because the grubs that the crows catch in this way are extremely nutritious. The study's authors wanted to determine exactly how advantageous tool use is for these crows.
Since the birds are extremely shy and live in a heavily-forested habitat, New Caledonian crows are notoriously hard to observe, so the scientists had to figure out another way to answer their question. The team captured wild crows and took both feather and blood samples. By analyzing the stable isotope profiles of these samples, they could figure out how much of the omnivorous crows’ diet came from beetle larvae, and how much came from other sources such as lizards, carrion, nuts, and fruit.
The larvae constituted about as much of the birds’ protein as the other food sources; however, the grubs provided far more fat than the other foods did, providing nearly 50 percent of the crows’ total lipid intake. Clearly, spending a little extra time and energy on tool use provides a large nutritional benefit.
The researchers took the question one step further and, using the average nutritional value of the beetle larvae, calculated how many larvae a crow would need to catch to satisfy its total daily nutritional needs. Surprisingly, they found that catching merely three larvae would provide a crow with more than enough energy for an entire day. With this kind of nutritional advantage, it's no wonder tool use spread through the population at some point in the past and is still maintained today.
The authors close the paper with an interesting idea: since these nutritionally-rich beetle larvae come from a single tree species that was introduced to New Caledonia by humans, it’s possible that tool use in these crows is actually at least partly due to anthropogenic influence.
sorry, ik zie nu pas dat deze dubbel gepostisquote:Op woensdag 15 september 2010 09:29 schreef Semisane het volgende:
Mexicaanse vis evolueert door religieus ritueel.
AMSTERDAM –Een plaatselijke vissoort uit Mexico is geëvolueerd onder invloed van een religieus ritueel dat elk jaar wordt uigevoerd door inwoners van het gebied. Dat hebben Amerikaanse wetenschappers vastgesteld.
[ afbeelding ]
De vissen van de soort Poecilia mexicana hebben in de loop der tijd een resistentie ontwikkeld tegen het gif van een tropische plant die wordt gebruikt bij een godsdienstig ritueel van de Zoque, een lokale stam. De dieren kunnen veel beter tegen het gif dan hun soortgenoten die op andere plaatsen leven.
Dat melden Amerikaanse onderzoekers van de A&M Universiteit van Texas in het wetenschappelijk tijdschrift Biology Letters.
Regen
De stamleden van de Zoque verzamelen zich al eeuwenlang elk jaar in de grot Cueva del Azufre en verdoven de vissen in het water dan met een mengsel waarin giftige bladeren van de tropische plant Lonchocarpus urucu zijn verwerkt. Met het ritueel vraagt het volk de goden om regen.
Volgens de wetenschappers heeft de ceremonie invloed gehad op de evolutie van de vissen. “Ons onderzoek suggereert dat de vissen zich hebben aangepast aan de Zoque tradities”, verklaart hoofdonderzoeker Mark Tobler in het Britse tijdschrift New Scientist.
Lokale cultuur
De wetenschappers kwamen tot hun ontdekking door vissen uit de grot samen met soortgenoten uit andere gebieden aan een experiment te onderwerpen. De dieren werden allemaal blootgesteld aan het gif van de tropische plant. Al snel bleek dat de vissen uit de grot veel minder snel verdoofd raakten door het goedje dan de vissen die afkomstig waren uit andere gebieden.
Het onderzoek toont aan dat menselijke activiteit grote invloed kan hebben op de evolutie van andere soorten. “Er is hier een intieme band bestaan tussen natuur en lokale cultuur”, aldus Tobler.
nu.nl
Zie je wel dat evolutie en religie prima samen gaan.
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