Author: Diana Gitig

Mitochondria are “the powerhouse of the cell” (or so every fifth grade biology book will tell you) because they use aerobic respiration to generate ATP, the molecular form of energy that enables cellular processes to occur.

Structurally, mitochondria are unusual in that they have their own DNA. This is because they were initially bacterial cells that long ago got subsumed by other cells, relinquishing their independence for a safe harbor and giving their hosts an energy boost in exchange.

Mitochondrial DNA (mtDNA) encodes many of the proteins required for aerobic respiration—but not all of them. Respiration still requires many proteins that are encoded by the cell's regular chromosomes. A new study suggests that the right match between mtDNA genes and chromosomal genes could be key to an organism's health and that some mtDNA may actually be beneficial.

Despite the best efforts of Walt Disney and Elton John, it is the tree of life, not the circle, that remains the primary way that organisms are classified and by which their evolutionary relationships are depicted. The tree was initially made by categorizing life forms with similar features into groups; this method distinguished not only amphibians from reptiles but also protists from amoeba.

Genetic data expanded the tree by allowing us to use similarities in genetic sequences—we didn’t have to actually see anything in order to determine how everyone is related to each other. Now, genomic studies have expanded the tree still further, allowing us to place species we can’t even grow in the lab onto their proper branch.

It is hardly news that most life on Earth is unicellular. But the newest tree of life, published in Nature Microbiology, reveals that most of life's diversity is bacterial and that much of it belongs to a recently discovered branch of especially tiny bacteria that no one has ever grown or seen under a microscope. All we have is their DNA, mixed in with the DNA of everything else that inhabits the same ecosystem.

A nucleus is one of many membrane-bound compartments that distinguishes our eukaryotic cells from the prokaryotic cells of microorganisms like bacteria. Eukaryotic cells also possess energy-producing compartments we call mitochondria.

Because mitochondria look like prokaryotes, it's long been assumed that eukaryotic cells came into existence when one prokaryote swallowed another prokaryote. The subsumed prokaryote then set up shop inside the host prokaryote and evolved into a mitochondrion. A problem with this idea is that prokaryotic cells lack the ability to phagocytose—to swallow other cells. Eukaryotic cells can, but every eukaryote we know about has mitochondria. It's not clear which came first: the ability to swallow other cells, or the mitochondria.

But over time, researchers have made the case that the ancestor of all eukaryotes belonged to a group of organisms called archaea. And now, one team says it can point the finger at a specific organism.

In the popular fiction series, Jeeves eats a lot of fish; Bertie Wooster thinks that that’s why he’s so smart. In real life we should all probably be eating more fish given how healthy it is, but can we do that in a way that keeps fish populations healthy, too?

A visit to the fishmonger can be daunting, and Monterey Bay Aquarium’s Seafood Watch App doesn’t necessarily make it any easier. Fresh or frozen? Wild or farmed? Local or imported? What are the best options for your body, your wallet, the planet?

You and I are not the only ones to grapple with these issues; environmental scientists in New York and California did, too. Specifically, they wondered how reform would impact fisheries, which are defined as the wild and cultivated regions where fish are caught, as well as the act and occupation of catching fish. They modeled two types of reform—one that aimed to maximize the economic value of fisheries, and one that aimed to maximize their long term catch. They were interested in how these reforms would affect the fisheries’ profit, catch, and the biomass of all the fish in the sea by the year 2050. Turns out that if fisheries were better managed, all three variables would improve.

The Dengue virus comes in four distinct but related varieties called serotypes, and they're all bad. Rather than inducing tolerance for each other, infection with one Dengue serotype actually makes people more sensitive to the other three. Victims infected by a second serotype can develop hemorrhagic fevers, which can be fatal. Somewhere around 400 million people are infected with Dengue annually—more than any other mosquito-borne ailment. There is no cure.

Dengue is also in the same family as Zika and is spread by the same mosquitos, so learning more about one could have broad applications for the other. This week, researchers published a paper in Nature describing how the Dengue virus avoids one arm of our immune system.

There are two arms to our immune system. Adaptive immunity generates antibodies and T cell receptors to combat unique aspects of a specific pathogen. After the fight is over, these antibodies and receptors stick around to remember and attack that pathogen should we encounter it again. Antibodies and T cell receptors form the molecular premise upon which vaccines are based.

Almost all autism spectrum disorders (ASD) risk factors that we know about are found in the unaffected, general population. (That’s what makes them risk factors, rather than genetic determinants.) And in that general population, there is a very wide range of social awareness, engagement in relationships, and communication styles.

The relationships among ASD genetic risk factors, normal variability in social functioning, and neuropsychiatric disorders (like ASD) have not been carefully examined. So a bunch of geneticists, psychiatrists, epidemiologists, and bioinformaticists decided it was time to examine it.

Genetic links to ASD—not causes of autism, but links to it—have been identified through genome wide-association studies. In these studies, the genetic variants present in people with ASD are compared to those of controls to see which variants might be associated with risk. This is the method by which genetic links to other psychiatric disorders have been identified, and it has been effective; over a hundred ASD associated mutations have been found this way.

A mouse feels panicky. It freezes; its little nose twitches. Something is in the air, and it doesn’t like the smell of it. Not one… little… bit.

In mice, the scent of predators causes a surge of stress hormones to course through the blood and induces behavioral changes. Quite a lot is known about olfaction in mice—Richard Axel and Linda Buck split the Nobel Prize in 2004 for elucidating the organization of the thousand or so unique odorant receptors expressed by the sensory neurons in those little noses.

But the neural circuits that transmit a threatening scent from the nose to the hypothalamus, where the stress hormones are released, were not known. Until now.

Alzheimer’s disease leads to tragic memory deficits, but it's not clear whether those memories are actually lost. It's also not clear whether this is a problem with memory formation and storage or a problem in memory retrieval. This is clinically relevant, since memory retrieval could potentially be restored by targeted brain stimulation.

New work using mouse models of early Alzheimer’s disease just showed that the problem at least starts with memory retrieval. Strikingly, it can also be reversed provided the correct set of neurons is activated. (The results are published in Nature.)

Engrams are the traces of the paths that memories leave as they settle in the brain. They are present both in our psyches and in biochemical alterations present in our neurons. Molecular, genetic, and optogenetic methods have been used to try to identify the population of neurons that hold onto these engrams.

In vitro fertilization (IVF) accounts for up to five percent of babies born in developed countries, and the technique has yielded some five million people ever since Louise Brown was born in the UK on July 25, 1978. And that’s just humans; the technology has been a huge boon in breeding farm animals. Yet there are hints that the procedure can have some unwanted effects on the resultant embryos. One such indication is a skewed sex ratio.

The sex ratio of a population should be roughly fifty-fifty. That ratio is sensitive, and possibly adaptive, to a number of environmental factors like maternal nutrition and population density. It's thus viewed as an indicator of reproductive health.

But in 1991, it was noted that IVF generates more bulls than heifers; the same skewing towards males has since been seen in pigs, mice—and, yes, people. A new paper in PNAS offers an explanation of what is going on and how to fix it.

Cataracts—the clouding of the lens in our eyes—are the leading cause of blindness in the world. Though we often associate them with the elderly, they're also a major cause of vision loss in infants, especially in the developing world. In either case, they are dealt with surgically, by removing the entire lens and replacing it with either a transplanted lens or an artificial one.

More than twenty million people undergo this surgery annually, but it often comes with a host of complications, and children in particular usually still need glasses afterward. But now some researchers have shown that it's possible to skip the replacement lens and get stem cells to repair the damage, a procedure that results in fewer complications.

Researchers in China noticed that the eye contains lens epithelial stem/progenitor cells (LECs) that continue to divide, even in forty-year-old adults. Injury can stimulate them to grow into three-dimensional, transparent, light refracting, lens-like structures. Rather than using artificial lenses, these researchers thought, maybe they could get infants to regrow their own new lenses.