Resistance to plant toxins in milkweed butterflies is linked to toxin storage for defense

A monarch caterpillar feeding on milkweed (Credit: OakleyOriginals. CC BY 2.0)
A monarch caterpillar feeding on milkweed (Credit: OakleyOriginals. CC BY 2.0)

When your only food source also contains a deadly poison, your options are pretty limited: either find a new food source or find some way of making the poison less toxic. This is exactly the situation that many plant-eating insects find themselves in, particularly those that eat milkweed.

Milkweeds produce a class of chemical toxins named cardenolides. These compounds specifically bind and inhibit the sodium potassium pumps found in heart muscle cells. Without working pumps sodium levels in the cell rise, setting off a chain of events that ultimately disrupt muscle contraction in cardiac tissue. At a high enough dose, these heart-stimulating effects can be lethal to insects, humans and animals in between. How then do insects that depend on milkweed as their main food source cope with this hidden poison? Continue reading

Saving brains: malaria in pregnancy leads to cognitive deficits in offspring

The malaria clinic at Nalufenya Children’s Hospital in Jinja, Uganda (Credit: Chloe McDonald)

In the global effort to eradicate malaria, the focus has often been on the number of lives saved—through insecticide-treated bed nets, artemisinin-based therapies, vector control and other strategies. Equally important in this fight is the concept of saving brains, particularly in young children.

Malaria is caused by an infection with the parasite Plasmodium falciparum and can manifest as either an uncomplicated or severe disease. The most severe neurological complication is cerebral malaria, a disease that disproportionally affects young children because they have not yet developed immunity against Plasmodium parasites. More than 785,000 children under the age of nine living in sub-Saharan Africa are affected by cerebral malaria each year. The idea of saving brains becomes especially relevant in this population because cerebral malaria can have long-lasting effects on the cognitive function of these children. An early study found that children who developed cerebral malaria were roughly three and a half times more likely to have a cognitive deficit than children who did not have malaria. Importantly, researchers observed this difference two years after the initial episode of cerebral malaria and long after the disease itself had been treated.

If exposure to malaria at a young age could have long-lasting effects on the cognitive abilities of children, what happened when that exposure happened much earlier? Like during pregnancy? In a new study published in PLoS Pathogens, a team of researchers led by Dr. Chloë McDonald and Dr. Kevin Kain showed that malaria in pregnancy leads to cognitive impairments in the offspring that persist into adulthood. Continue reading

Phages fight back: how anti-CRISPRs interfere with the bacterial immune system

A transmission electron micrograph of phage JBD93, which contains an anti-CRISPR gene. (Credit: Joe Bondy-Denomy)
A transmission electron micrograph of phage JBD93, which contains an anti-CRISPR gene. (Credit: Joe Bondy-Denomy)

So nat’ralists observe, a flea
Hath smaller fleas that on him prey;
And these have smaller fleas to bite ‘em.
And so proceeds Ad infinitum.

Jonathan Swift, 1733

When the Anglo-Irish satirist wrote these words nearly two centuries ago, he could not have known just how far down the tree of life his observations would hold true. These predator-prey relationships exist beyond the plains of Africa or the jungles of Borneo. They extend to the realm of microscopic organisms and to the world of bacteria and the teeny tiny, itsy bitsy viruses that prey on them. These viruses are called bacteriophages, or phages for short.

Like human and other animal viruses, phages rely completely on their host for reproduction. They enter a bacterial cell and hijack the cellular machinery to make new phages until the cell is literally bursting with viral cargo. A torrent of phages is unleashed that go on to infect more bacteria and continue the cycle.

But bacteria are not helpless victims in this story. They have a large arsenal of anti-phage weapons to keep phages out and prevent them from taking over. Perhaps the coolest of these weapons is the CRISPR-Cas system. First discovered in 2007, the CRISPR-Cas system functions as the bacteria’s immune system. It is both a memory keeper and a hitman. Every time a bacteria survives a phage infection (which doesn’t happen often), the CRISPR-Cas complex takes a small piece of phage DNA and adds it to the bacteria’s own DNA, gradually building a database of unique DNA fingerprints from every phage that has ever tried to kill it. In other words, bacteria with CRISPR-Cas systems are able to “learn” from their previous phage encounters and acquire immunological memory based on those experiences—a trait that was previously thought to be unique to animals.

“It’s the first example of a single cell, simple [bacteria] having an adaptive immune system,” says Dr. Joseph Bondy-Denomy, a faculty fellow at the University of California, San Francisco. “The adaptability of CRISPR is very, very rapid. I think that’s why it’s so exciting.” Continue reading