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Snapshots of Life

A Ray of Molecular Beauty from Cryo-EM

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Credit: Subramaniam Lab, National Cancer Institute, NIH

Walk into a dark room, and it takes a minute to make out the objects, from the wallet on the table to the sleeping dog on the floor. But after a few seconds, our eyes are able to adjust and see in the near-dark, thanks to a protein called rhodopsin found at the surface of certain specialized cells in the retina, the thin, vision-initiating tissue that lines the back of the eye.

This illustration shows light-activating rhodopsin (orange). The light photons cause the activated form of rhodopsin to bind to its protein partner, transducin, made up of three subunits (green, yellow, and purple). The binding amplifies the visual signal, which then streams onward through the optic nerve for further processing in the brain—and the ability to avoid tripping over the dog.

A Lean, Mean DNA Packaging Machine

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Three views of bacteriophage T4

Credit: Victor Padilla-Sanchez, The Catholic University of America, Washington, D.C.

All plants and animals are susceptible to viral infections. But did you know that’s also true for bacteria? They get nailed by viruses called bacteriophages, and there are thousands of them in nature including this one that resembles a lunar lander: bacteriophage T4 (left panel). It’s a popular model organism that researchers have studied for nearly a century, helping them over the years to learn more about biochemistry, genetics, and molecular biology [1].

The bacteriophage T4 infects the bacterium Escherichia coli, which normally inhabits the gastrointestinal tract of humans. T4’s invasion starts by touching down on the bacterial cell wall and injecting viral DNA through its tube-like tail (purple) into the cell. A DNA “packaging machine” (middle and right panels) between the bacteriophage’s “head” and “tail” (green, yellow, blue spikes) keeps the double-stranded DNA (middle panel, red) at the ready. All the vivid colors you see in the images help to distinguish between the various proteins or protein subunits that make up the intricate structure of the bacteriophage and its DNA packaging machine.

Unlocking the Brain’s Memory Retrieval System

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Memory Trace in Mouse Hippocampus

Credit:Sahay Lab, Massachusetts General Hospital, Boston

Play the first few bars of any widely known piece of music, be it The Star-Spangled Banner, Beethoven’s Fifth, or The Rolling Stones’ (I Can’t Get No) Satisfaction, and you’ll find that many folks can’t resist filling in the rest of the melody. That’s because the human brain thrives on completing familiar patterns. But, as we grow older, our pattern completion skills often become more error prone.

This image shows some of the neural wiring that controls pattern completion in the mammalian brain. Specifically, you’re looking at a cross-section of a mouse hippocampus that’s packed with dentate granule neurons and their signal-transmitting arms, called axons, (light green). Note how the axons’ short, finger-like projections, called filopodia (bright green), are interacting with a neuron (red) to form a “memory trace” network. Functioning much like an online search engine, memory traces use bits of incoming information, like the first few notes of a song, to locate and pull up more detailed information, like the complete song, from the brain’s repository of memories in the cerebral cortex.

Lens Crafting

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Credit: Salma Muhammad Al Saai, Salil Lachke, University of Delaware, Newark

Live long enough, and there’s a good chance that you will develop a cataract, a clouding of the eye’s lens that impairs vision. Currently, U.S. eye surgeons perform about 3 million operations a year to swap out those clouded lenses with clear, artificial ones [1]. But wouldn’t it be great if we could develop non-surgical ways of preventing, slowing, or even reversing the growth of cataracts?  This image, from the lab of NIH-grantee Salil Lachke at the University of Delaware, Newark, is part of an effort to do just that.

Here you can see the process of lens development at work in a tissue cross-section from an adult mouse. In mice, as in people, a single layer of stem-like epithelial cells (far left, blue/green) gives rise to specialized lens cells (middle, blue/green) throughout life. The new cells initially resemble their progenitor cells, displaying nuclei (blue) and the cytoskeletal protein actin (green). But soon these cells will produce vast amounts of water-soluble proteins, called crystallins, to enhance their transparency, while gradually degrading their nuclei to eliminate light-scattering bulk. What remains are fully differentiated, enucleated, non-replicating lens fiber cells (right, green), which refract light onto the retina at the back of the eye.

The Science of Saliva

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Artificial salivary glands

Credit: Swati Pradhan-Bhatt, Christiana Care Health System, Newark, DE

Whether it’s salmon sizzling on the grill or pizza fresh from the oven, you probably have a favorite food that makes your mouth water. But what if your mouth couldn’t water—couldn’t make enough saliva? When salivary glands stop working and the mouth becomes dry, either from disease or as a side effect of medical treatment, the once-routine act of eating can become a major challenge.

To help such people, researchers are now trying to engineer replacement salivary glands. While the research is still in the early stages, this image captures a crucial first step in the process: generating 3D structures of saliva-secreting cells (yellow). When grown on a scaffold of biocompatible polymers infused with factors to encourage development, these cells cluster into spherical structures similar to those seen in salivary glands. And they don’t just look like salivary cells, they act like them, producing the distinctive enzyme in saliva, alpha amylase (blue).

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