American Scientist

In this roundup, digital features editor Katie L. Burke summarizes notable recent developments in scientific research, selected from reports compiled in the free electronic newsletter Sigma Xi SmartBrief. Online: https://www.smartbrief.com/sigmaxi/index.jsp

Ninth Planet Proposed

Two Caltech astronomers have reported strong circumstantial evidence for an additional large planet in our Solar System—one that is perhaps 5,000 times the mass of Pluto and considerably further from the Sun. The planetary body has not been observed, but inferred from its gravitational effect: Six relatively small objects just beyond the Kuiper Belt have orbits whose shape and orientations suggest they have been perturbed by the pull of another, much more massive object. This potential ninth planet would follow a highly elliptical path taking it 30 billion to 200 billion kilometers from the Sun; completing one orbit would require 10,000 to 20,000 years. Astronomers are now attempting to confirm the reality of “Planet 9” by spotting it directly using the Subaru telescope in Hawaii.

Batygin, K., and M. E. Brown. Evidence for a distance giant planet in the Solar System. The Astronomical Journal 151:22 (January 20)

Germ Layers from Stem Cells

Most studies of induced pluripotent stem (IPS) cells, which are mature cells that have been reprogrammed to act like undifferentiated embryonic stem cells, have focused on differentiating them into a single type of cell, even though most tissues and organs are made up of several types of cells. Patrick Guye and his colleagues were able to differentiate IPS cells into all three germ layers—endoderm, mesoderm, and ectoderm—that go on to form the cells of the body, such as blood vessels, muscle, and skin. By genetically engineering the IPS cells to express a protein called GATA6, the cells developed into endoderm. Rather than immediately prompting the cells to develop into a particular tissue cell, the researchers waited to see what would happen next. In two weeks, they found all three germ layers present in the cell culture, so that all the precursors to a fetal liver were present. The differences in differentiation were based on variation in GATA6 production. In the long term, this technique could be refined to generate whole organs for transplant. But it can also immediately be used for growing different human tissues for drug testing in culture. Testing drugs and their interactions, specifically on an individual patient’s cells using an “organ-on-a-chip,” could be feasible.

Guye, P., et al. Genetically engineering self-organization of human pluripotent stem cells into a liver bud-like tissue using Gata6. Nature Communications 7:10243 (January 6)

One-Shot Machine Learning

For a limited set of image perception tasks, a new machine-learning computer vision program can outperform humans. The artificial intelligence program is able to learn handwritten characters after “seeing” a single example, for instance. Deep neural networks, a type of machine learning used for visual perception, need to be exposed to many examples to successfully detect objects in images or recognize human speech. Even though deep neural networks are modeled after human neuron behaviors, they fail to learn concepts quickly, the way humans do. This new approach, called Bayesian Program Learning, was used to classify and recreate handwritten characters from the world’s alphabets as well as generate new letters. Brendan Lake of New York University and his coauthors applied “visual Turing tests” indicating that their software has the ability for human-like creative generalization.

Lake, B. M., R. Salakhutdinov, and J. B. Tenenbaum. Human-level concept learning through probabilistic program induction. Science 350:1332–1338 (December 11)

Dinosaurs’ Rapid Evolution

Dinosaurs evolved from their reptilian predecessors over a period of about 5 million years, according to a new study; previously, most paleontologists thought dinosaurs took about 15 million years to diverge from their ancestors, the dinosauromorphs. Researchers used radioisotopic dating to more precisely date zircon crystals recovered from the Chañares Formation in Argentina, which preserves a quintessential group of early dinosauromorph fossils. The more precise dating method shows the fossils are younger than previously thought, and so the time gap between rock layers containing dinosauromorphs and those with true dinosaurs is correspondingly smaller. The study also shows that there was little compositional difference between the two layers, suggesting that the environment did not shift fundamentally as dinosaurs evolved. This new research will inform debates about how and why dinosaurs evolved.

Marsicano, C., R. B. Irmis, A. C. Mancuso, R. Mundil, and F. Chemale. The precise temporal calibration of dinosaur origins. Proceedings of the National Academy of Sciences of the U.S.A. 113:509-513 (January 19)

Frog Disease Treated in Wild

Spanish biologists have cleared wild populations of Majorcan midwife toads of an infectious disease that has caused alarming declines in amphibian species worldwide. This successful eradication is the first in the wild for the devastating fungal skin disease called chytridiomycosis. Researchers removed thousands of tadpoles from six ponds on the Spanish island Majorca, and then drained the ponds. They treated the tadpoles with antifungals and hoped Sun exposure would kill any chytrid fungus remaining in the environment. That first attempt failed, but the team tried again, this time treating half of the drained ponds with low concentrations of disinfectant. Treated tadpoles were returned to all ponds after a year. These three ponds remain free of the fungus three years later. Although this study is a proof of principle, the approach does not prevent re-infection, and such extreme measures are not possible in many environments where chytridiomycosis has been causing declines in frog and salamander species.

Bosch, J., et al. Successful elimination of a lethal wildlife infectious disease in nature. Biology Letters doi:10.1098/rsbl.2015.0874 (November 18)