It was long established that vertebrate development is a one-way path. Like time’s arrow, cells differentiate by losing their old “pluripotency” (multiple possible fates). There were glimmers of the opposite, such as the partial loss of differentiation observed in cancer cells. But such phenomena always involved really bad results, such as uncontrolled growth. Fate maps such as this one could predict where embryonic cells would go, and what their differentiation would form. In certain organisms, such as the worm Caenorhabditis, nearly every cell of the early embryo has a predestined fate.
But in recent years, reports of “adult stem cells” suggest that a surprisingly small number of genes in the cells of a mature organism could direct a reversal of differentiation, restoring an at least partly pluripotent state. Now, it is startling to hear that something as simple as an acid shock can convert an adult cell into a cell with embryonic potential. Acid shock is something that my students study all the time in bacteria–that is our business, acid-shocking E. coli, and observing it adapt. The acid shocking of the mouse cells to form “stem cells” looks surprisingly similar.
In this case, apparently pH 5.7 is enought of an acid shock to do the trick. How this works is unknown, although not entirely unprecedented; for example, fertilization of sea urchin eggs involved an acid change. And viral infections, such as the uptake of influenza virus, involve acid-mediated fusion events to get the virus into the cytoplasm. More interestingly, a neural transformation event in salamanders has been triggered by acid treatment.
What is amazing in Obogata’s work is that the acid-induced cells could actually be put into a mouse embryo and observed to form all different parts of the new embryonic mouse (see above). The introduced cells could be observed because their genes express GFP (green fluorescent protein)–a molecule that Kenyon students use to track pH of single E. coli cells. The acid-shocked cells appear pluripotent, to the point of forming placental tissue as well as embryo tissues.
What does all this mean for our concepts of the embryo and adult? Perhaps the fertilized egg and embryo become less special, if any adult cell can become an embryo? Or do we have to treat every human cell as a potential human being?
It’s time to make your plans for Boskone, my favorite science fiction convention.
This year I’m back on all my favorite science themes–climate disaster, space-beamed solar, plagues and parasites, and of course 3D printing. To top it off, I get to play R2D2 — the Shakespeare version, directed by Laurie Mann.
Joan’s Schedule at Boskone
Rising Tides Fri 18:00 – 18:50, Carlton
Stay Near the Fire: The New Solar System Science Fiction Sat 10:00 – 10:50, Harbor III
Killer Plagues Sat 11:00 – 11:50, Harbor III
The Potential of 3D Printing Sat 15:00 – 15:50, Harbor III
The Pleasures of Parasites Sat 16:00 – 16:50, Harbor III
Kaffeeklatsche with Joan Slonczewski Sat 17:00 – 17:50, Galleria-Kaffeeklatsch 2
R2D2 in Shakespeare Star Wars Reading Sat 21:15 – 22:45, Harbor II+III
If a car drives itself, what does it see? How does it compare with you?
Ford and MIT are teaming up to help the car do better. A big challenge: How to see around an obstacle, to see what other obstacles lie ahead. My first thought is, the human driver may see more distractions, like the reflections on the hood and the shadows on the ground. On the other hand, the driverless car might miss “potential” hazards farther off. What do you think?
No, these are not the “pure spirits” from the tropical trees of Avatar. They are anemones, growing beneath 250 meters of ice–off Antarctica.
About an inch long, with two dozen tentacles, each anemone seeks its tiny dinner to strangle; in subfreezing temperatures, with no light (until the exporers came.) Marymegan Daly and colleagues found these tiny denizens of the dark by drilling a hole through all those meters of ice, in the Ross ice shelf. While blizzards rage above, these tiny creatures grow and multiply. One of the simplest of the animals, these creatures do come female and male; and the females bear eggs. And they react–when the remote camera approached, the tentacles drew back. The animals didn’t want to warm up; they clung fast to their ice. Life adapts, even to this remote niche so forbidding to most other forms.
Ever since I can remember, scientists have been trying to figure out photosynthesis–and do it ourselves. In elementary school, back mid-twentieth century, we were shown a film (the kind you feed through a projector, and hope it doesn’t break) where a little cartoon creature labeled “photosynthesis” says, “And I’m NOT going to tell you!” Outside immunology, bacterial and plant photosynthesis is the most complex topic in my textbook–the one that took three editions to get straight (almost).
Yet the fundamental aim of photosynthesis is surprisingly simple. You absorb light, split water, and store the energy in chemical bonds. Plants mainly store it in sugar, amino acids, vitamins–messy molecules useful to them. But some bacteria, for unaccountable reasons, store much of their energy in hydrogen–and get rid of it.
Why do the bacteria give up hydrogen, losing some of their energy for sugar, amino acids, etc.? New-age evolutionists would suggest that the hydrogen help out their fellow microbes somehow, down in the muck of the bogs where these purple bacteria live, and that overall their fitness is enhanced–well, read the book for details. Or check out Carrie Harwood’s research.
Tom Meyer and colleagues try to imitate plants and bacteria. They’ve made a chromophore (did you find the structure on the internet? I don’t see it, surprise.) that specifically splits water and stores almost all the energy as H2 (supposedly; I don’t see the details published). The idea of such a chromophore is to imitate what chlorophylls have done for at least three billion years. Chlorophylls are amazingly beautiful and intricate molecules that absorb a photon, store it in a chain of conjugated double bonds, and apply it to a precise reaction such as splitting water. And releasing hydrogen fuel–the kind we’ve been saying could drive your next car, and maybe store at night as formate. In fact the next target of Meyer’s group is “to reduce carbon dioxide, a greenhouse gas, to a carbon-based fuel such as formate.”
Could we actually use solar to get rid of some of our excess CO2?
The gospel lesson of the “widow’s mite” tells how the poorest person, a widow (no SSI in those days) offered two mites, the smallest coins in circulation, for the religious community–and was praised for giving proportionally more than the wealthy. So what do we say of Prochlorococcus–among the smallest known bacteria, half a millionth of a meter–donating buckets of its cytoplasm to surrounding marine life? On top of giving us half our atmosphere’s oxygen?
In the micrograph, you can see the tiny cells and the tinier little balloon-like vesicle that emerge from them. Each vesicle contains carbon- and nitrogen-rich food molecules.
To appreciate this more, we have to understand that these one-celled green life forms are extraordinarily competitive. Their entire existence consists of photosynthesis–growing and dividing as fast as they can, making the most of the light they absorb, to outnumber their fellow microbes. Whoever makes the most offspring is the winner.
The problem is that to make more offspring faster, it helps to have a tiny genome–to exclude any kind of genes you don’t need. So Prochlorococcus has jettisoned all kinds of genes, such as those that detoxify the hydrogen peroxide byproducts of oxygen production. (Yes, oxygen and its intermediates are toxic–among the most toxic wastes known.) How does it get away with this? By depending on its neighbors: heterotrophic (organic food eaters) bacteria that “breathe” the cyanos’ oxygen to eat their food. The neighbors produce the enzyme catalase that gets rid of H2O2. Thus the cyanos depend on their non-photosynthetic neighbors, as much as the heterotrophs depend on cyanos’ oxygen production. The basis of this dependence was discovered by Kenyon graduate Erik Zinser and students.
But why would Prochlorococcus give up so much of its hard-earned cytoplasm? As Sallie Chisholm and colleagues point out, one possibility is the need to feed the heterotrophic bacteria that swim over to breathe the oxygen. Marine water is extremely sparse, a nutrient desert. Without organic food, the heterotrophs cannot use the oxygen, and cannot make enzymes to convert hydrogen peroxide to harmless water.
We don’t yet know if that’s the real reason. Another, very different possibility is that the Prochlorococcus bacteria send out vesicle decoys for viruses. Marine viruses are even more numerous than bacteria; and they are actually the main predators on photosynthetic bacteria. But viruses require highly specific host receptors, found on given species. The same receptors would be on the vesicle decoys, which would absorb the viruses harmlessly away from the growing cells.
Whatever the reason, the relationship between these tiny green life forms and their bacterial neighbors is full of intricate details. There is competition, and much more, a social fabric in which many individuals depend upon each other.
Is true artificial intelligence just around the corner? The journal Nature thinks so.
It’s called deep learning–essentially, teaching a machine to learn the way a three year-old does. That’s how a Google supercomputer discovered a recurring phenomenon on the internet–cats.
Deep learning involves neural networks that change in response to experience. That’s how a toddler learns–by seeing an event, responding, and seeing what happens again. The game “peekaboo” is an example. In effect, we are teaching supercomputers to play peek-a-boo. So they grow up to be R2D2.
Facial recognition is a major goal, apparently achieving leaps and bounds. To get there, the computer progresses through four layers: (1) telling light from dark pixels; (2) recognizing edges and circles; (3) more complex shapes such as an eye; (4) defining a face.
What is deep learning good for? Translating foreign languages, and testing drug candidates. Forensic identification, no doubt.
Now we’re giving our toddler computer “a stack of scanned textbooks” to “pass standardized elementary-school science tests (ramping up eventually to pre-university exams).” R2D2 goes to college.
BTW, we’ll hear more from R2D2 at Boskone this year.