In the caves of Slovenia and Croatia lives an animal that’s a cross between Peter Pan and Gollum. It’s the olm, a blind, cave-dwelling salamander, also called the proteus and the “human fish”, for its pale, pinkish skin. It has spent so long adapting to life in caves that it’s mostly blind, hunting instead with various supersenses including the ability to sense electricity. It never grows up, retaining the red, feathery gills of its larval form even when it becomes sexually mature at sweet sixteen. It stays this way for the rest of its remarkably long life, and it can live past 100.
The olm was once described as a baby dragon on account of its small, snake-like body. It’s fully aquatic, swimming with a serpentine wriggle, while foraging for insects, snails and crabs. It can’t see its prey for as it grows up, its eyes stop developing and are eventually covered by layers of skin. It’s essentially blind although its hidden eyes and even parts of its skin can still detect the presence of light. It also has an array of supersenses, including heightened smell and hearing and possibly even the ability to sense electric and magnetic fields.
Imagine trying to rewind the clock and start your life anew, perhaps by moving to a new country or starting a new career. You would still be constrained by your past experiences and your existing biases, skills and knowledge. History is difficult to shake off, and lost potential is not easily regained. This is a lesson that applies not just to our life choices, but to stem cell research too.
Over the last four years, scientists have made great advances in reprogramming specialised adult cells into stem-like ones, giving them the potential to produce any of the various cells in the human body. It’s the equivalent of erasing a person’s past and having them start life again.
But a large group of American scientists led by Kitai Kim have found a big catch. Working in mice, they showed that these reprogrammed cells, formally known as “induced pluripotent stem cells” or iPSCs, still retain a memory of their past specialities. A blood cell, for example, can be reverted back into a stem cell, but it carries a record of its history that constrains its future. It would be easier to turn this converted stem cell back into a blood cell than, say, a brain cell.
The history of iPSCs is written in molecular marks that annotate its DNA. These ‘epigenetic’ changes can alter the way a gene behaves even though its DNA sequence is still the same. It’s the equivalent of sticking Post-It notes in a book to tell a reader which parts to read or ignore, without actually editing the underlying text. Epigenetic marks separate different types of cells from one another, influencing which genes are switched on and which are inactivated. And according to Kim, they’re not easy to remove, even when the cell has apparently been reprogrammed into a stem-like state.
The Benguela region, off the coast of Namibia, is a shadow of its former self. In the first half of the 20th century, it was one of the world’s most productive ocean areas and supported a thriving fishing community. Today, the plentiful stocks of sardines and anchovies, and the industries that overexploited them, are gone. The water is choked of oxygen and swarming with jellyfish. Plumes of toxic gas frequently erupt from the ocean floor. But one fish, the bearded goby, is positively thriving in this inhospitable ecosystem. It’s a critical link in a food web that’s on the verge of collapse.
Walk among the Arctic ice and you’ll sometimes encounter distinctive patches of red snow. They’re caused by a species of bacteria called Colwellia psycherythraea. It’s a cold specialist – a cryophile – that can swim and grow in extreme subzero temperatures where most other bacteria would struggle to survive. Colwellia’s cold-tolerating genes allow it to thrive in the Arctic, but Barry Duplantis from the University of Victoria wants to use them in human medicine, as the basis of the next generation of anti-bacterial vaccines.
Colwellia’s fondness for cold comes at a price – it dies at temperatures that most other bacteria cope with easily. By shoving Colwellia genes into bacteria that cause human diseases, Duplantis managed to transfer this temperature sensitivity, creating strains that died at human body temperature. When he injected these heat-sensitive bacteria into mice, they perished, but not before alerting the immune system and triggering a defensive response that protected the mice against later assaults. The Colwellia genes transformed another species of bacteria from a cause of disease into a vaccine against it.
In humans, two chromosomes – X and Y – determine whether we are male or female. Of the two, Y tends to get more attention because of its small, degenerate size. Both X and Y probably evolved from a pair of ordinary chromosomes that have nothing to do with sex (also known as autosomes). The story goes that one of these autosomes developed a gene that immediately caused its bearer to become male, and eventually became the Y chromosome of today. The other one became X.
Throughout its history, Y has been a hotbed of genetic change, gaining, losing and remodelling its genes at breakneck pace, and shrinking by 97%. Its partner – X – has allegedly had a less eventful past, and should faithfully represent the ancestral autosome. This history of X and Y was first proposed in 1914 by Herman Muller, and ever since, his assumptions about X’s stability have gone untested. Now, it seems that Muller was wrong. Daniel Bellott from the Howard Hughes Medical Institute had uncovered the secret history of X, which turns out to be no less storied than Y’s tale.
Animals must wage a never-ending war against parasites, constantly evolving new ways of resisting these threats. Resistance comes in many forms, including genes that allow their owners to shrug off infections. But one species of fly has developed a far more radical solution – it has formed a partnership with a bacterium that lives in its body and defends it against a parasitic worm. So successful is this microscopic bodyguard that it’s spreading like wildfire across America’s besieged flies.
The fly Drosophila neotestacea is plagued by a nematode worm called Howardula. Around a quarter of adults are infected and they don’t fare well. The worm produces thousands of young in the body of its hapless host, and the little worms make their way into the outside world via the fly’s ovaries. Not only does this severely slash the fly’s lifespan, it also always sterilises her. But according to John Jaenike from the University of Rochester, the fly is fighting back.