Eating too much salt seems to impair body’s ability to fight bacteria

By Michael Le Page

Eating too much salt may impair the body’s ability to fight bacterial infections, according to studies in mice and in 10 human volunteers.

Christian Kurts at the University Hospital of Bonn in Germany and his team first showed that mice given a high salt diet were less able to fight kidney infections caused by E. coli and body-wide infections caused by Listeria monocytogenes, a common cause of food poisoning.

“The bacteria caused more damage before the immune system got rid them,” says Kurts.

Next, the team gave 10 healthy women and men who were 20 to 50 years old an extra 6 grams of salt a day on top of their normal diet, in the form of three tablets a day. After a week, some of their immune cells, called neutrophils, had a greatly impaired ability to engulf and kill bacteria compared with the same tests done on each individual before they took extra salt.

The team didn’t examine the effect of high salt intake on the body’s ability to fight viral infections.

The World Health Organization recommends that people eat no more than 5 grams of salt a day to avoid high blood pressure, which can cause strokes and heart disease. In the UK, people eat 8 grams on average, suggesting many consume as much or more than the volunteers in the study.

The team thinks two mechanisms are involved. First, when we eat lots of salt, hormones are released to make the body excrete more salt. These include glucocorticoids that have the side effect of suppressing the immune system throughout the body.

Second, there is a local effect in the kidney. Kurts found that urea accumulates in the kidney when salt levels are high, and that urea suppresses neutrophils.

Journal reference: Science Translational Medicine, DOI: 10.1126/scitranslmed.aay3850

Pig-Monkey Hybrid Engineered in China

This piglet had some cells from a monkey but died within a week of birth
Tang Hai

By Michael Le Page

Pig-primate chimeras have been born live for the first time but died within a week. The two piglets, created by a team in China, looked normal although a small proportion of their cells were derived from cynomolgus monkeys.

“This is the first report of full-term pig-monkey chimeras,” says Tang Hai at the State Key Laboratory of Stem Cell and Reproductive Biology in Beijing.

The ultimate aim of the work is to grow human organs in animals for transplantation. But the results show there is still a long way to go to achieve this, the team says.

Hai and his colleagues genetically modified cynomolgus monkey cells growing in culture so they produced a fluorescent protein called GFP. This enabled the researchers to track the cells and their descendents. They then derived embryonic stem cells from the modified cells and injected them into pig embryos five days after fertilisation.

More than 4000 embryos were implanted in sows. Ten piglets were born as a result, of which two were chimeras. All died within a week. In the chimeric piglets, multiple tissues – including in the heart, liver, spleen, lung and skin – partly consisted of monkey cells, but the proportion was low: between one in 1000 and one in 10,000.

It is unclear why the piglets died, says Hai, but because the non-chimeric pigs died as well, the team suspects it is to do with the IVF process rather than the chimerism. IVF doesn’t work nearly as well in pigs as it does in humans and some other animals.

The team is now trying to create healthy animals with a higher proportion of monkey cells, says Hai. If that is successful, the next step would be to try to create pigs in which one organ is composed almost entirely of primate cells.

Something like this has already been achieved in rodents. In 2010, Hiromitsu Nakauchi, now at Stanford University in California, created mice with rat pancreases by genetically modifying the mice so their own cells couldn’t develop into a pancreas.

Pig-human chimeras

In 2017, Juan Carlos Izpisua Belmonte’s team at the Salk Institute in California created pig-human chimeras, but only around one in 100,000 cells were human and, for ethical reasons, the embryos were only allowed to develop for a month. The concern is that a chimera’s brain could be partly human.

This is why Hai and his team used monkey rather than human cells. But while the proportion of monkey cells in their chimeras is higher than the proportion of human cells in Belmonte’s chimeras, it is still very low.

“Given the extremely low chimeric efficiency and the deaths of all the animals, I actually see this as fairly discouraging,” says stem cell biologist Paul Knoepfler at the University of California, Davis.

He isn’t convinced that it will ever be possible to grow organs suitable for transplantation by creating animal-human chimeras. However, it makes sense to continue researching this approach along with others such as tissue engineering, he says.

According to a July report in the Spanish newspaper El País, Belmonte’s team has now created human-monkey chimeras, in work carried out in China. The results have not yet been published.

While interspecies chimerism doesn’t occur naturally, the bodies of animals including people can consist of a mix of cells. Mothers have cells from their children growing in many of their organs, for instance, a phenomenon called microchimerism.

Journal reference: Protein & Cell, DOI: 10.1007/s13238-019-00676-8

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Crypt-keeper wasps can control the minds of 7 other species of wasp

By Michael Le Page

A recently discovered parasitic wasp appears to have extraordinary mind-controlling abilities – it can alter the behaviour of at least seven other species.

Many parasites manipulate the behaviour of their victims in extraordinary ways. For instance, sacculina barnacles invade crabs and make them care for barnacle larvae as if they were their own offspring. If the host crab is male, the parasite turns them female.

It was thought each species of parasite could manipulate the behaviour of only one host, or least only very closely related species. But the crypt-keeper wasp Euderus set is more versatile.

It parasitises other wasps called gall wasps. Gall wasps lay their eggs in plants, triggering abnormal growths – galls – inside which the wasp larvae feed and grow. Adult gall wasps chew their way out of the gall and fly off.

The crypt-keeper wasp seeks out oak galls and lays an egg inside them. The crypt-keeper larva then attacks the gall wasp larva. Infected gall wasps still start chewing their way out of the gall, but they stop chewing when the hole is still small and then remain where they are with their head blocking the exit and thus protecting the larva growing inside them – “keeping the crypt”.

How the crypt-keeper larva makes the gall wasp stop chewing at such a precise point is not clear. “I’d love to know how they do it,” says Anna Ward of the University of Iowa.

When the crypt-keeper larva turns into an adult wasp after a few days, it then chews through the head of the gall wasp to get out of the gall.

The crypt-keeper wasp, which was only described in 2017, was thought to parasitise just one species. But when Ward’s team collected 23,000 galls from 10 kinds of oak trees as part of a bigger study, they found at least 7 of the 100 species of gall wasp they collected were parasitised by the same crypt-keeper wasp. “What we found is that it is attacking different hosts that don’t seem to be closely related,” says Ward.

And there are likely many more extraordinary parasites out there. Ward thinks there are more species of parasitic wasps – most yet to be discovered – than there are species of beetle. So far 350,000 species of beetle have been described, the most of any group of animals. Parasitic wasps are small and hard to find, and hardly anyone looks for them, she says.

Journal reference: Biology Letters, DOI: 10.1098/rsbl.2019.0428

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Bluehead wrasse fish switch from female to male in just 20 days

By Michael Le Page

For many fish, changing sex is a normal part of life. For the first time, we have found out exactly how one of these species – a small cleaner fish called the bluehead wrasse – does it.

Erica Todd at the University of Otago in New Zealand and her colleagues removed some male bluehead wrasse from a few sites on reefs off Key Largo in Florida. This triggers females to change sex. They then caught changing females at regular intervals and looked at what was happening in their bodies down to the level of which genes were turning on or off.

They found that the loss of males makes some females stressed. They become more aggressive and start performing male courtship behaviours.

In individuals that become dominant in a social group, the genes associated with female hormones shut down in a day or two, and their colours begin to change – females of the species are yellow and brown (see above), while the males are green and blue.

At the same time, the egg-producing tissues in their ovaries start to shrink and begin to be replaced by sperm-producing tissues. In just 8 to 10 days, the mature ovaries are transformed into testes, and the fish can mate with females and sire offspring.

Read more: Zoologger: Shrimp plays chicken with its sex change
After around 20 days, the fish have the full male colours and the process is complete. “The bluehead is certainly remarkable for its speed,” says Todd. “Other species do take much longer.”

However, as the fish only live around two or three years, those 20 days are a fair chunk of their lifespan, equivalent to 2 years of a human lifetime.

Around 500 species of fish can change sex, a fact long known to biologists but which got wider attention recently when the Blue Planet II documentary narrated by David Attenborough showed Asian sheepshead wrasse changing sex. It is most common for female fish to turn into males but in some species including clownfish the males turn into females.

In at least one species, the hawkfish found around southern Japan, the females can not only turn into males but also turn back into females again if circumstances require it. For one species of shrimp, there is no need to change back. It starts out male but becomes an hermaphrodite – a phenomenon known as protandric simultaneous hermaphroditism.

Journal reference: Science Advances, DOI: 10.1126/sciadv.aaw7006