Podcast Transcript

Neuronal Trip Switch

Scientists have discovered that brain cells have an in-built electrical trip system to prevent themselves from becoming overloaded. Nerve cells respond to chemical signals called neurotransmitters, which lock onto specialised docking sites, called receptors, that are dotted across the cell surface. The binding of a neurotransmitter to its receptor triggers pore-like channels in the cell membrane to open, allowing different chemicals to flow into and out of the cell, altering its activity. One very potent substance that behaves in this way is calcium, which in too large-a-dose could destroy the cell. But now, writing in the Journal of Cell Biology, Stanford researcher Fuminori Tsuruta and colleagues have found that nerve cells protect themselves from this kind of damage by effectively "tripping out".

The team have discovered that, rather like pulling players off a football field, when a neurone senses that it is becoming over-excited, a signal is issued that leads to the removal of the neurotransmitter receptors and the calcium channels from the cell surface. This is achieved by wrapping the receptors and channels up into oily bags called endosomes, inside the cell where another another chemical messager, called PIKfyve (short for phosphatidyl inositol (3,5) bisphosphate), causes them to be broken down. The process isn't fool-proof, however, and some diseases, including stroke and Alzheimer's, can nonetheless bypass these safeguards and lead to cell damage. That's why, say the scientists, the discovery of this new pathway opens up a host of fresh avenues for exploring ways to reduce the damage done to the brain by various diseases.

25th Oct 2009

Painful to listen to

We've probably all had cause to use the phrase "painful to listen to", but now scientists in the US have discovered why. Writing in Nature, Johns Hopkins researcher Paul Fuchs and his colleagues show that a small group of nerve cells in the ear respond to sounds that would best be described as "traumatic". The ear converts sound waves into brain waves using a specialised structure called the cochlea. Here, vibrations of the eardrum are transferred to a group of cells called hair cells. The information from these hair cells is then transmitted to the brain by a family of nerve cells. 95% of these nerves are known as type I fibres and respond very strongly to even the quietest sounds. But the other 5%, which are known as type II neurones, have remained something of an enigma, because, in previous attempts to study them, they didn't seem to respond to sounds at all.

Now, the Johns Hopkins team have shed some light on the mystery by managing to record, in young rats, the electrical activity from inside some of these unusual nerve cells. They also labelled some of the cells with a dye so that they could study their structure and how they were wired up to the cochlea. What this has revealed is that the cells are activated by an excitatory nerve transmitter chemical, called glutamate, which is released from the sound-sensing hair cells. But the recordings suggest that the sounds have to be very loud indeed to trigger any response, meaning that the cells might be there to help to process and discriminate different types of very loud sound. The team also found that the nerve fibres respond to another nerve chemical called ATP, which is often associated with tissue damage, so they could also be providing the brain with a way to monitor the health and function of the of auditory system. This means that they might help us to better understand and even treat hearing problems like tinnitus, which causes sufferers to experience distracting high-frequency buzzing noises.

According to Fuchs, "no one thought recording them was even possible," he said. "We knew the type II neurons were there are now at lest we know something about what they do and how they do it."

25th Oct 2009

World’s biggest web-spinning spider

Halloween is approaching, and what better story to get us in the spooky mood that the discovery of the world’s largest web-spinning spider.

The record breaker, named Nephila komaci, is a type of golden orb weaver spider from Africa and Madagascar. The female have bodies up to around 4cm long (1.5 inches) and their legs reach to 12cm: so she would stretch out across the palm of your hand. The males are much tinier, about 5 times smaller than the giant females.

Tarantulas still hold the title of king of the spiders. The Goliath bird eating tarantula from South America has a leg span of 30cm and inch-long fangs! But they don’t make webs.

This giant web-spinner is the discovery of Matjaz Kuntner from the Slovenian Academy of Sciences and Arts and Jonathan Coddington from the Smithsonian National Museum of Natural History in Washington DC, publishing in the online journal Plos One.

And for a long while they thought this spider that was first found in 1978 must be extinct, or perhaps a hybrid of two other species, because only that single specimen was known. Together these two researchers went on expeditions to South Africa but they failed to find a living specimen of this giant spider. And even searching through 2500 more specimens from 37 museums, still another one didn’t show up.

Then eventually, another specimen turned up from Madagascar, and three more were found in South Africa, confirming that this is indeed a new species.

That adds another name to the list of around 41,000 spider species that are currently known to science (every year another 400 or 500 are added).

While obviously being an important discovery for spider biodiversity, these spiders also shed light on how and why some female animals evolve to be much bigger than their male partners. In their paper, the spider sleuths build a family tree of the known species of Nephila spiders, showing that there is a branch of African spiders in which the females evolved to be bigger and bigger over time.

The discoverers of this fantastic new species are urging others to go and try and find more of these spiders, because they are obviously extremely rare and they want to know more about them. The only place they are definitely known to live is in the sand forests of Tembe Elephant Park in KwaZulu-Natal in South Africa.

A rare wonder indeed and a treat for Halloween...

25th Oct 2009

Why Mantis shrimp eyes work better than DVDs

The most sophisticated eyes in the animal kingdom belong to mantis shrimps a group of extraordinary species that live on coral reefs around the world. In a brand new paper just out, a team of scientists examine just what lies behind these complex eyes and they’ve uncovered some tricks of nature that could find applications in the cutting edge of modern technology, perhaps spawning a new generation of DVDs and CDs.

Last year, a paper in the journal Current Biology announced the discovery that mantis shrimp can see both linear polarized and circular polarized light. Now a team led by Nicholas Roberts from the University of Bristol have discovered that mantis shrimp eyes do this using special light-sensitive cells that act as a device known as a quarter-wave plate. Essentially these plates convert circular polarized light into linear polarised light. Manmade quarter wave plates are vital components of DVD players and some camera filters, but they don’t work nearly as well as the ones that have evolved in the eyes of mantis shrimps.

Normal light behaves like a wave that can vibrate in any direction. In contrast, linear polarized light only vibrates in only one plane. We usually don’t see polarized light, although we are aware of it, for example the light that reflects off glass or the surface of a pool of water (putting on polarizing sunglasses cuts out those polarising rays and lets you see through the water).

Circular polarized light behaves like a spiral or a helix. The remarkable mantis shrimps can even tell the difference between circular polarized light spins to the left or to the right.

Not only that, but unlike manmade quarter wave plates that only work well in one colour, mantis shrimp eyes work almost perfectly across the whole visual spectrum from near ultra violet to infra-red.

Leading on from their earlier work, the research team discovered that the receptors that detect circular polarized light are located in a central band across the mantis shrimp eye – their eyes are divided into 3 distinct regions, giving them trinocular vision in each eye and are packed with light-detecting units called omatidia, similar to other invertebrates including insects. They did this essentially by shining polarized light of different types through thin sections of parts of the eye and measuring how well those cells absorbed the light.

Part of the reason why these biological structures work so much better than manmade structures is because they are so tiny – on the nano scale – with components that are smaller than the wavelength of even ultra violet light (10-400nm). That is very challenging to create in manmade structures.

The big question is why on earth do mantis shrimps need such incredibly complex eyes?

There is lots of polarized light bouncing around the clear shallow waters of coral reefs where most mantis shrimps live. Their favourite prey includes small slivery fish whose scales polarize light.

Scientists also think that mantis shrimps might use circular polarized light as a way of secretly communicating with each other. Parts of their bodies reflect circular polarized light, and we so far don’t know that any other animal can detect this type of light. So perhaps they send out signals – flashing mating colours maybe - without any fear of being detected by anyone else except another mantis shrimp.

So when it comes to solving technical problems like how to see well in a bright watery world, natural selection has come up with an elegant and simple solution. And perhaps the mantis shrimp will teach us a thing or two about how to build the optical devices of the future.

25th Oct 2009

Engineering Spider Glue

Chris -   Well also in the news this week, scientists at the University of Wyoming have identified what it is that can make spider webs so sticky and the genes that spiders use to actually make them.  And knowing this could bring us a step closer, maybe even a spider step, I don't know, to making our own spider-based glues.  And to tell us a bit more about how they're doing this is Dr. Randy Lewis who’s at the University of Wyoming.  Hello, Randy.

Randy -   Hello.

Chris -   Welcome to The Naked Scientists.  Tell us.  So how are you first of all, identifying these genes that spiders use to make their web so sticky?

Randy -   Well we took webs, about 100 of them actually and washed the glue off of those webs then we separated the proteins that make up that glue, and using some chemical tricks, we were able to get some evidence of the proteins that were in there.  And then we did a mass spectrometry study of all the peptides to find those and then used that information to go back to the spider itself and identify which were the genes that were involved in making these spider silk proteins.

Chris -   I see.  So because we know the genetic code, we can basically – so we know what the protein sequence is that’s in the spider stickiness that we’ve washed off the web.  So we can work out what gene sequence is probably went into making those proteins.  So if we then go back to the spider, spinneret I guess, the structure that makes a silk and ask, “Can we find any genes like what the sequence would be in there?” then you got a chance of finding them.

Randy -   Right.  And especially in this case because all the glue comes from a specialized gland.  So you can actually just go directly to that gland and not worry about other kinds of genes because the predominant genes that are being made or being used in that gland are going to be for the spider silk glue.

Chris -   And presumably, the glue isn’t just one particular protein.  It must be a cocktail.

Randy -   In this case, we believe it’s two proteins actually and one of them looks more like a silk protein, the regular silk protein.  The other one actually looks like what we call a mucin protein which makes up slime and snot.  So, our combination is, is that it’s really a silk and snot protein and the two of them together provide both strength and stickiness.

Chris -   I think spiders will probably be mortified if they realize that you were calling their web stickiness as snotty.  But is it possible to do what the spider does in its backend, in a test tube?  In other words, can you borrow from biology?  Can you copy this effectively?

Randy -   We’re in the process of defining whether we can do that or not, but we believe we can because the proteins are actually very simple and we need to find a system that can reproduce that.  And we believe that if we can get those genes into some insect cells that grow in culture, that those cells should be able to produce the proteins with the sticky parts on them.  The key here is, is that one of the proteins in particular has a whole lot of sugars put on it and you need to be able to have those sugars, we’re fairly sure, in order to be able to get the stickiness.  So we believe that using something like insect cells to start with, we can reproduce what the spider has and then actually test the material and see how well it performs.

Chris -   And that’s presumably because insect cells, evolutionary speaking are much closer to a spider than say, one of our cells would be.  And so therefore, they're likely to have the right chemistry going on in the cell to add those sticky sugar molecules.

Randy -   Right.  And also, it turns out that insect cells are fairly easy to work with.  So, we think that in inserting the genetic code from the spiders, also probably will fit better with the insect cells.

Chris -   And if you are successful in making this happen, what will you be able to do with this glue?

Randy -   Well, right now, we’re not exactly sure, but we think that there certainly are possibilities for some biomedical applications, for closing on sutures, things like that, other places you might be able to use glue.  We’re also hopeful, and that remains to be seen, that you can use it in something like Epoxy and that is, put the two components separately won't be – won't give you that the real stickiness and that when we put the two together, you’ll have a glue, and that’s also very useful in a number of applications.  And so, you can basically put it together and then have it be sticky and separately, they're just fine.

Chris -   And lastly Randy, I understand that you are currently heading across Canada to rescue some goats.  What’s that all about?

Randy -   Basically, a company we worked with, NECSI Biotechnologies, developed some transgenic goats that make the spider silk proteins in the milk and the company has – for all intent and purposes, gone under.  And so, we’re right now about 20 miles from the farm and this afternoon, we’re going to go and prepare the goats.  We’ll pick them up tomorrow morning and bring them back to Wyoming, so we can preserve the genetics of those goats that have been made, because the company can't afford to keep them anymore.  And we’re going to move them down to Wyoming and keep the genes going and actually, use the milk to produce protein now or we can really get serious about looking at various kinds of products from it.

October 2009