Mirror neurons control erection response to porn

Does anyone find this surprising? Isn't it exactly the effect one would expect mirror neurons to have? (Past discussion here.) However, it is welcome to note basic research that has practical applications...

Mirror neurons control erection response to porn (6/16/08)

You don't have to be a scientist to observe that pornographic images lead to erections in men. But you would have to be one to show those images to volunteers while meticulously measuring the volume of response in the brain and penis.

Harold Mouras, at University of Picardie Jules Verne in Amiens, France, and his colleagues wanted to understand the cerebral underpinnings of visually-induced erections.

They suspected there might be a role for mirror neurons, a special class of brain cell that fires both when people perform an action and when they observe it being performed.

Not a terribly difficult guess to make. So what did they find?

While the volunteers watched the movies, the researchers watched their brains using functional magnetic resonance imaging (fMRI).

They also kept tabs on the tumescence of the other target organ, using a hand-crafted "penile plethysmograph" – essentially an airtight tube in which the enlarging penis causes measurable pressure changes.

As expected, all the subjects got erections and many parts of the brain lit up.

Interestingly, the volume of the erections correlated with the strength of activation in a part of the brain called the pars opercularis, which is known to display mirror neuron activity. Even more intriguing, the brain activation, say the researchers, precedes the penile response.

Tags: mirror neurons

Bdelloid rotifers

The bdelloid rotifers are certainly in the news a lot recently.

They may not be into sex very much, but it turns out they are world-class gene snarfers.

No sex, but plenty of gene transfer

Where do you get your genes? If you are an animal, you inherit them from your parents at the moment of conception, and that's about it. No later incorporation of environmental DNA for you, unless you become host to a parasite or an endosymbiont that somehow transfers bits of its genome into yours (which is a rarely documented event). Unless you are a bdelloid rotifer, that is.

This odd, microscopic, freshwater animal is making news once again, this time for the startling discovery of numerous chunks of foreign DNA in its genome. In a paper published this week in Science, evidence for massive horizontal gene transfer—from bacteria, fungi, even from plants—into the bdelloid rotifer genome is presented by Irina Arkhipova and Matthew Meselson. ...

While horizontal gene transfer is common in bacterial species, it was unheard of in the animal kingdom on such a massive scale – until this study.

"It is quite amazing that bdelloids are able to recruit foreign genes, which were acquired from remarkably diverse sources, to function in the new host," says Arkhipova. "Bdelloids may have the capacity for tapping into the entire environmental gene pool, which may be of (evolutionarily) adaptive significance during expansion into new ecological niches, and may even contribute to bdelloid speciation," she says.

So the first question one has is, how have all these genes from totally different species gotten into the bdelloid genome? The most likely answer is: as a direct consequence of how bdelloids are able to survive such traumatic events as complete dessication or levels of radiation deadly to almost all other species.

Apparently bdelloids are able to do this because of a nearly unique ability to reconstitute and repair heavily damaged DNA. Evidently, in the process, they sometimes incorporate foreign DNA from other creatures they have eaten, or which may simply be lying around. And since some of this reconstituted bdelloid DNA is included in bdelloid egg cells, which eventually become separate individual animals, it is passed on to subsequent generations.

(Something similar to this process, but on a much smaller scale, occurs in "higher" animals too, such as humans. Our genome is full of remnants of the DNA ("exogenous DNA") of viruses that infected our ancestors unknown millions of years ago.)

How bdelloids have been able to gobble up such a variety of genes from their environment and incorporate it into their genome is a good question. Typically in animals, the germ line–the heritable egg and sperm cells–are protected from environmental assaults, such as intrusion of foreign DNA, by the rest of the body cells, which are not heritable and serve to "sequester" the germ line. Ideas on why the bdelloids' germ line is so exposed to environmental exchange, Arkhipova says, "are all speculative. But we talk about this a lot!"

One clue is the unusual ability of bdelloids to survive total desiccation (drying out), which is fatal for most organisms. When water disappears from their environment, bdelloids enter a kind of suspended, dehydrated state, and can stay there for months or even years. But once water returns, they spring back to action, move around, eat things, and start reproducing again.

During the desiccation phase, Arkhipova says, "you would imagine there is potential for membrane damage and DNA damage in the rotifer. And not only the rotifer desiccates, but also everything it just consumed." If the DNA of both the rotifer and its food are broken up during desiccation, "this would provide an opportunity for the (foreign) DNA to enter the rotifer's germ line. During rehydration, the DNA breakage is somehow repaired, and the foreign DNA may get incorporated," she says.

From the details mentioned so far, there may be some other things you could be wondering about.

For instance, do any of these foreign genes actually work like normal genes once they've become part of the bdelloid genome? Generally, they do not. But there is evidence that a few foreign genes are sufficiently intact that they are transcribed into messenger RNA. And some of this RNA may even be used to make proteins, such as enzymes to catalyze basic metabolic processes.

Interestingly enough, some bacterial genes that have entered the bdelloid genome now have embedded introns, which is normal for eukaryotic genes, but unheard of in prokaryotic (bacterial) genes. (The introns are like punctuation marks that separate distinct segments of a gene, called exons. This makes it possible to construct a number of different proteins from a single gene, by the process of "alternative splicing".)

Another more general question that might occur to you is: why do asexual animals such as bdelloids have egg cells, like more normal sexual creatures? And how, exactly, do they reproduce, anyhow? The answer is probably that at some time back in the evolutionary history of bdelloids (estimated at 50 to 100 million years ago), bdelloids diverged from a rotifer ancestor species that was sexual, as are many species of rotifers today.

So bdelloids still have egg cells, with paired chromosomes that carry two separate copies of the genome, just as "normal" sexual animals do. However, bdelloid eggs do not undergo the process of meiosis, in which egg cells divide, and the paired chromosomes are separated, to be later combined with chromosomes from another individual during fertilization.

Instead, bdelloid eggs are eventually expelled from the mother's body, and go on to develop into a new individual by parthenogenesis, which also occurs occasionally in a few other species capable of asexual reproduction, such as some insects, fish, snakes, and lizards. (Or even sharks and komodo dragons.)

In case you enjoy thinking about sex, you probably have many other questions about what's up with bdelloids. Answers to a lot of these questions can be found in the following.

Further reading:

Common Aquatic Animal's Genome Can Capture Foreign DNA – another 5/29/08 press release about the research

Water creatures caught stealing DNA – 5/30/08 ABC/Reuters news story on the research

Who needs sex when you can steal DNA? – 5/29/08 Reuters news story

Scientists find promiscuous genes in an asexual animal – informative 5/29/08 article from Science News

Massive Horizontal Gene Transfer in Bdelloid Rotifers – 5/30/08 research article in Science (sub. rqd.)

The Weird Sisters – very informative 6/3/08 New York Times blog article, by Olivia Judson

An Evolutionary Scandal – 11/2000 Harvard Magazine article on bdelloid rotifers

Who Needs Sex (or Males) Anyway? – 3/20/07 PLOS Biology article on bdelloids

Tags: bdelloids, bdelloid rotifers

Is DNA Repair A Substitute For Sex?

Yeah, it's a trick question. The answer is clearly "no" – unless you're a bdelloid rotifer.

What's interesting, of course, about these minute but multi-cellular animals is that they are completely asexual, and apparently have been for millions of years. There are no males, and females reproduce entirely by parthenogenesis. Although that might seem to imply a rather joyless existence, it hasn't stopped the bdelloids from persisting, and even diversifying into more than 370 species.

The conventional evolutionary reason for the invention and predominance of sexual reproduction – apart from the recreational aspect – is that it provides a mechanism for a species to cope with the inevitability of sustaining damage to its DNA. So why do the bdelloids seem to think they have a better way?

Is DNA Repair A Substitute For Sex?

These hardy creatures somehow escape the usual drawback of asexuality – extinction – and the MBL’s David Mark Welch, Matthew Meselson, and their colleagues are finding out how.

In two related papers published recently in Proceedings of the National Academy of Sciences (PNAS), the team proposes an interesting hypothesis: Bdelloid rotifers have been able to give up sex and survive because they have evolved an extraordinary efficient mechanism for repairing harmful mutations to their DNA. ...

In animals that do have sex, DNA repair is accomplished during meiosis, when chromosomes pair up (one from the father, one from the mother) and “fit” genes on one chromosome can serve as templates to repair damaged genes on the other chromosome. The bdelloid, though, always seems to reproduce asexually, by making a clone of itself. How then, does it cope with deleterious mutations?

Before we come to the hypothesized answer, it must be noted that the bdelloids' ability to repair their DNA is not merely adequate. It's spectacularly good:

MBL adjunct scientist Matthew Meselson and Eugene Gladyshev, both of Harvard University, demonstrate the enormous DNA repair capacity of bdelloid rotifers by zapping them with ionizing radiation (gamma rays), which has the effect of shattering its DNA into many pieces. “We kept exposing them to more and more radiation, and they didn’t die and they didn’t die and they didn’t die,” says Mark Welch. Even at five times the levels of radiation that all other animals are known to endure, the bdelloids were able to continue reproducing.

“Because there is no source of such intense ionizing radiation on Earth, except if we make it, there is no way these organisms could have evolved to be radiation resistant,” says Mark Welch. Instead, they propose that bdelloids’ DNA repair capacity evolved due to a different environmental adaptation – tolerance of extreme dryness.

Bdelloids, which live in ephemeral aquatic habitats such as temporary freshwater pools and on mosses, are able to survive complete desiccation (drying out) at any stage of their life cycle. They just curl up and go dormant for weeks, months, or years, and when water becomes available, they spring back to life. Mark Welch and his colleagues showed that desiccation, like ionizing radiation, breaks up the rotifers’ DNA into many pieces. Presumably, the same mechanisms they use to survive desiccation as part of their life cycle also protect them from ionizing radiation.

Hmmmm. That sounds oddly familiar. Where have we heard about that sort of thing before? Oh yes, this is apparently exactly the same thing found in a bacterium (Deinococcus radiodurans), as discussed here. And in the closely related bacterial species, Deinococcus geothermalis, as discussed here.

But what the bdelloids do is much more impressive, since they are multicellular eukaryotes, not simple prokaryotic bacteria. In any case, what't the trick for bdelloids?

One feature that may confer exceptional DNA repair capacity on the bdelloids is described in the team’s second PNAS paper. Here, they give evidence that the bdelloid rotifer, like most animals, originally had two copies of each chromosome. But at some point in its evolution, it underwent a “whole-genome duplication,” giving it four copies of each chromosome and hence of each gene. Normally, lineages that undergo whole-genome duplication lose the duplicate genes over time. The bdelloid, though, has kept most of its duplicate genes throughout its evolutionary history.

“We believe they have kept most of their duplicate genes because they are serving as templates for DNA repair,” says Mark Welch.