Archive for October 14th, 2011

October 14, 2011

Researchers Take the Temperature of Mars’ Past

Suppose you were told that it was possible to determine the surface temperature and presence of water on some planet other than Earth – at at time more than 4 billion years in the past? Sounds a little far-fetched, no? In fact, the deduction actually seems quite plausible, if you consider the reasoning.

The specific finding is that about 4 billion years ago, there was a spot on Mars that was wet and enjoying essentially shirt-sleeve weather – actually a bit warmer than a typical summer day on the beach at San Francisco.

How could anyone figure that out? Well, in the first place, a piece of Mars landed on Earth about 13,000 years ago in the form of a meteorite known as ALH84001. Standard methods of isotopic analysis established that minerals in the rock crystallized about 4 billion years ago.

But that’s only the beginning of the story. Carbonates in the minerals (which must have formed somewhat before the minerals themselves crystallized) contained rare isotopes of carbon and oxygen (carbon-13 and oxygen-18). The exact ratio of these two isotopes depends on the temperature at which the carbonates originally formed. That temperature must have been around 18° C. And the only way that carbonates could have formed at that temperature was by precipitation from liquid water. Voilà.

If this conclusion holds up, it will be the first time that we have good evidence the surface of Mars was once considerably warmer than it is now.

Wet and Mild: Caltech Researchers Take the Temperature of Mars’s Past

Researchers at the California Institute of Technology (Caltech) have directly determined the surface temperature of early Mars for the first time, providing evidence that’s consistent with a warmer and wetter Martian past.

By analyzing carbonate minerals in a four-billion-year-old meteorite that originated near the surface of Mars, the scientists determined that the minerals formed at about 18 degrees Celsius (64 degrees Fahrenheit). “The thing that’s really cool is that 18 degrees is not particularly cold nor particularly hot,” says Woody Fischer, assistant professor of geobiology and coauthor of the paper.

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October 14, 2011

Researchers demonstrate that iPS stem cells may be used for gene therapy

Gene therapy sounds good, in principle, as a means of treating diseases that result from genetic defects. But there have been at least two major practical problems in making use of gene therapy in the clinic. First, it’s very important for the safety of the procedure to make changes only to the defective gene (or even just the critical part of the gene) and no other portion of the DNA. Second, there needs to be an effective way to deliver the therapy, in whatever form it takes, to exactly the right tissues in the body that are affected by the defective gene.

Solving these two problems simultaneously is especially difficult. There are a variety of techniques for modifying DNA in specific ways, using a number of specialized enzymes. But these techniques are actually usable only in a test tube. Simply setting the enzymes loose in a patient’s body doesn’t work. The usual way to get around this is by preparing the appropriate modified DNA segments and incorporating them into “vectors”, such as some sort of virus, and introducing the vector into a patient’s body, in the hope that it will reach the right tissues to deliver the DNA, without causing any other problems. That hasn’t worked very well, so far, despite a large number of attempts.

What about taking some cells from the patient, modifying their DNA in vitro and then putting them back in the body? The problem there is being able to produce enough cells with good DNA, either before or after reintroduction to the patient’s body, to make a significant difference. Most human cells just don’t reproduce very prolifically outside the body, or even inside for that matter.

At this point you should be thinking, “stem cells!” They are specialized to reproduce quickly, when needed. Up until now, there have been practical problems here, too. Adult stem cells capable of differentiating into the specific type of cell needed in a given tissue may be difficult or impossible to find in useful quantities. And embryonic stem cells, well, even any other problems aside, there’s the problem of avoiding rejection by the patient’s immune system.

The potential solution: induced pluripotent stem cells (iPSCs), made from any convenient cell type of the actual patient. It’s only been five years since iPSCs were first produced. Various practical problems have arisen along the way since then. Some have been mostly overcome; some haven’t. But progress seems to be occurring steadily – including very recently. The application to gene therapy involves making appropriate corrections to the DNA, producing a sufficient number of differentiated cells of the required type from the “fixed” iPSCs, and finally reintroducing them into the patient.

Alpha 1-antitrypsin deficiency is a genetic disorder caused by a point mutation that results in inadequate production of the alpha 1-antitrypsin (A1AT) enzyme in liver cells. The disease affects functioning of the lungs, as well as the liver. Research just published has shown that gene therapy to correct the mutation, applied to iPSCs, is successful at treating the condition in a mouse model.

Researchers demonstrate that iPS stem cells may be used for gene therapy

Researchers from the University of Cambridge, directed by Ludovic Vallier and David Lomas, and from the Sanger Institute, coordinated by Allan Bradley, began by sampling patients’ skin cells, which were then cultured in vitro for “differentiation” before applying the properties of the pluripotent stem cells: this is the “iPS cells” stage. Through genetic engineering, scientists were then able to correct the mutation responsible for the disease. They then engaged the now “healthy” stem cells in the maturation process, leading them to differentiate to liver cells.

Scientists from the Institut Pasteur and Inserm, led by H-l-ne Strick-Marchand in the mixed Institut Pasteur/Inserm Innate Immunity unit (directed by James Di Santo), then tested new human hepatic cells thus produced on an animal model afflicted with liver failure. Their research showed that the cells were entirely functional and suited to integration in existing tissue and that they may contribute to liver regeneration in the mice treated.

Further reading:

Liver-disease mutation corrected in human stem cells

Spell-Checked Stem Cells Show Promise Against Liver Disease

Targeted gene correction of α1-antitrypsin deficiency in induced pluripotent stem cells

October 14, 2011

Seeking superior stem cells

The first research reporting the productions of induced pluripotent stem cells (iPSCs) was announced five years ago. Since then, the field has made significant progress, encouraging high hopes that iPSCs could be so similar to embryonic stem cells (ESCs) that they could eventually replace ESCs in research and therapeutic applications.

However, as with almost any new technology, there have been various problems along the way. These include incomplete reproduction of all important characteristics of ESCs, alterations of cell DNA that might cause cancer, and susceptibility of iPSCs to rejection by the immune system even of the donor of the reprogrammed cells.

Further progress depends on being able to deal with these problems. In addition, depending on the method used to produce iPSCs, the process may be too slow and inefficient for practical use. The latest research demonstrates what appears to be an effective technique to significantly improve speed and efficiency of reprogramming.

Seeking superior stem cells – Wellcome Trust Sanger Institute

Researchers from the Wellcome Trust Sanger Institute have today (10/10/2011) announced a new technique to reprogramme human cells, such as skin cells, into stem cells. Their process increases the efficiency of cell reprogramming by one hundred-fold and generates cells of a higher quality at a faster rate.

Until now cells have been reprogrammed using four specific regulatory proteins. By adding two further regulatory factors, Liu and co-workers brought about a dramatic improvement in the efficiency of reprogramming and the robustness of stem cell development. The new streamlined process produces cells that can grow more easily.

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October 14, 2011

Suspects in the quenching of star formation exonerated

Active galactic nuclei (AGN) – produced by matter swept violently into the vortex around a supermassive black hole that may have billions of times as much mass as our Sun – can put on some of the most spectacular fireworks in the universe, over periods as long as 100 million years.

Astrophysicists have sometimes speculated that AGN may be so energetically active that they diminish or even extinguish formation of new stars in the host galaxy.

Recently published research, making use of the PRIMUS faint galaxy spectroscopic redshift survey, suggests that the speculations are wrong, and that AGN can be found even in galaxies in which very active star formation is occurring. The research gives some answers to the larger question of what special characteristics, if any, the host galaxies of AGN may have.

Suspects in the quenching of star formation exonerated

Because astronomers had seen these objects primarily in the oldest, most massive galaxies that glow with the red light of aging stars, many thought active galactic nuclei might help to bring an end to the formation of new stars, though the evidence was always circumstantial.

That idea has now been overturned by a new survey of the sky that found active galactic nuclei in all kinds and sizes of galaxies, including young, blue, star-making factories.

“The misconception was simply due to observational biases in the data,” said Alison Coil, assistant professor of physics at the University of California, San Diego and an author of the new report, which will be published in The Astrophysical Journal.

“Before this study, people found active galactic nuclei predominantly at the centers of the most massive galaxies, which are also the oldest and are making no new stars,” said James Aird, a postdoc at the University of California, San Diego’s Center for Astrophysics and Space Sciences, who led the study.

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