Why can creatures like starfish and some reptiles regenerate a lost limb or tail while humans cannot? That question has been the target of considerable study, but the answers are far from clear, according to EuroStemCell, a European organisation that tracks stem cell research.
People can regenerate some tissues, notably liver and skin. Many animals can regenerate complex body parts with many kinds of tissue using a variety of mechanisms, but most of the replacement mechanisms rely on special stem cells that collect at the injury site and then multiply and differentiate into the necessary kinds of tissue.
These special stem cells come in 2 varieties: pluripotent cells, which can give rise to all tissue products, and multipotent tissue-specific cells, which can give rise only to certain kinds of tissue. In one extreme case, scientists recently discovered that a single cell could be made to create a new flatworm.
That research was reported in the journal Science in May 2013. The scientists concluded that such stem cells, called adult pluripotent neoblasts, were not derived from the embryo but were present in adult flatworms and were behind the remarkable regenerative ability of the relatively simple animal.
In more complex animals, multipotent, tissue-specific stem cells can regenerate an entire limb in a frog or salamander, but it is not yet known why similar cells in humans cannot do so. Scientists are studying the process to determine if some kind of internal map assigning new cells to a specific place has been lost in mammals.
Another kind of regeneration relies on cells that have stopped dividing but are induced after injury to divide once more and develop into useful tissue. This process is seen in zebra fish and newborn mice, which can regenerate heart tissue. Again, scientists are studying the mechanism to find out why it does not happen in humans.
C Claiborne Ray
Cellphone screens, sharper and brighter
Tiny crystals called quantum dots could make television or cellphone screens sharper and brighter, but the manufacturing process can be toxic to the environment.
Chemical engineers at Lehigh University, USA may have found an environmentally friendly alternative: Feed metal to a single bacterial enzyme.
The vials are filled with the results, tiny crystals that can generate electricity and coloured light. Under UV lights, they glow like plastic pegs on a Lite-Brite screen.
Bryan Berger stumbled across the enzyme while studying a superbug spreading on metal surfaces in a hospital in Pennsylvania: Stenotrophomonas maltophila. The microbe appeared to be taking in electrical charges, he found, and spitting out clusters of metallic particles — quantum dots. Understandably leery of working with an infectious superbug, he and his colleagues went on to isolate the enzyme responsible for the alchemy. “As an engineer, it’s extremely exciting,” Bryan said. “But as a medical scientist, it’s extremely scary.”
Where can a PhD take you? Back to school, usually
Doctoral students in the sciences are more like the rest of us than previously thought: They don’t know what they want to do with their lives, either. When deciding what to do with newly minted doctorates, they tend to keep marching in a straight path, pursuing postdoctoral research positions.
In a study published in Science, researchers tried to figure out why, given the relatively low odds of landing a full-time faculty position, traditionally the goal of such work.
Their results were somewhat inconclusive. But the authors did find evidence that many students pursued postdocs as a default option after graduate school, or as part of a “holding pattern” until the job they wanted was available. The authors, who did not receive postdoctoral degrees themselves, conclusively demonstrated the need for more career planning among graduate students, and that graduate students should consider their career paths before they even begin a PhD programme.
“It’s probably not a controversial conclusion,” said Henry Sauermann, an associate professor at Georgia Tech and an author of the report. “But what might be a little different here is thinking about whether the PhD is the right path in the first place.”
One lesson may be to not get a PhD until you know what you want to do with it. But this may require further study.
The New York Times