Mobile genetic elements are big players in mammalian genomes. Some of my previous Snippets have visited wildly selfish elements and our cells’ efforts to fight them, so I think it’s time to look at some of their positive (ish) contributions to mammalian evolution. In this case, “they” are the abundant LINE-1 elements that alone make up 1/6 of the human genome. LINE-1 retrotransposons are so-called transposable elements (TEs), capable of hopping around inside of a genome using their own machinery.…

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Recently, I’ve been reading about sickness behaviours – the behavioural changes we often experience when we’re ill (e.g., see my previous snippet on sickness-induced sleep). These are generally thought to be host-adaptive, meaning that they help us get better. However, there are some examples of infection-induced behavioural changes that clearly benefit the invading pathogen rather than the host. The most famous example is rabies: infected animals become more aggressive and therefore more likely to spread the virus through bites or…

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Did you know that all of us harbor human cells that are not our own? I didn’t, until I saw a recent book review in Nature. Hidden Guests, by Lise Barnéoud, is the first popular science book about microchimerism, a phenomenon whereby cells from our biological relatives can persist in our bodies for decades. Microchimerism occurs because cells can pass between mother and fetus during pregnancy or between twins sharing a uterus. Although rare, these cells have been found in…

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A good brain somehow balances plasticity (the ability to change) with stability (the need to maintain information and structure). Our brains famously lose some of their plasticity when we become adults, and we more seasoned adults sometimes lament the reduced plasticity that accompanies our hard-earned wisdom. We also wonder how the whole dance is controlled. A new paper in Nature, in a technical tour de force, shows that astrocytes (those long-neglected, oft-forgotten glial cells) are central players in the dance…

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We mammals have some nice features (temperature regulation, big brains that seem too seldom used, etc), but we’re unremarkable when it comes to vision. I assumed this was a standard evolutionary trade-off but the story is weirder than that, as I learned this week when reading a new paper about mammalian retinas. Recall that rods are basically night-vision photoreceptors, able to detect small amounts of light, and cones are the cells that are less sensitive but respond to color. A…

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Last week I wrote about some deviously selfish genetic elements (toxin-antidote systems) and how they evolve. The vast majority of selfish genetic elements, however, are mobile elements we’ll call TEs: tiny modules of DNA that hop around in genomes (including our genomes). These things make up vast tracts of our genomes (more than half, in humans), so it seems that we and our fellow animals are stuck with some kind of truce or coexistence. Animals use elaborate silencing systems to…

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Selfish genes are very interesting phenomena, if too often misunderstood. (They are not “genes for selfishness.”) Animal genomes are overflowing with selfish mobile elements and their debris, but for pure devious self-interest, it’s hard to top toxin-antidote systems. These systems deliver a deadly genetically-encoded toxin to offspring, along with the antidote. The result is a system that ensures its own propagation, because whenever the toxin gene gets separated from the antidote gene*… you know the rest. How can such a…

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Complex cognitive tasks, such as value-based decision-making, can be influenced by sex and by sex steroids, but surprisingly little is known about the nature of these influences or how they happen. This is due, at least in part, to the fact that decades of research looked only at male subjects. In addition, however, there are formidable challenges facing experimenters who aim to explore the effects of sex steroids (such as estrogens) in the brain and behavior. In the case of…

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Human pathogens are diverse (bacteria, viruses, parasites) and destructive. Controlling and killing them is a major goal of humanity, hindered by (among other things) the sophisticated arsenals that pathogens have acquired over millions of years of evolutionary arms races with us. So it follows that we are keen to learn more about pathogen weaponry. A fascinating new preprint presents a powerful new resource in this struggle, with this added angle: the authors seek to not only block pathogenic weapons, but…

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