Category: Biology

Exposure to environmental poisons is suspected of disturbing the secondary sex ratio, i.e. the difference in numbers of girls and boys born as opposed to the ratio of girls and boys conceived. Indeed, several countries, including Canada, Denmark, England and Wales, Germany, The Netherlands, and the USA, have seen the secondary sex ratio shift during the last hundred years or so that the number of girls among live-births has risen significantly. One of the more significant declines is seen in Mexico, although some countries, Ireland, in particular, have seen the reverse, with more boys.

You can read the complete story in my news story on SpectroscopyNOW.com

A gene associated with disease might vary from a healthy gene in one individual DNA base pair – a so-called point mutation. Investigating point mutations and diagnosing genetic disease would benefit from a simple, cost-effective and rapid sequencing technique.

Now, Japanese researchers have developed a new approach for a miniaturized system that detects small differences in DNA sequences with high sensitivity. In contrast to other methods, this technique works without labeling the bases and exploits a field effect transistor (FET) to detect changes in the charge on DNA molecules.

According to Toshiya Sakata and Yuji Miyahara multiple FETs can feel electrical fields and react to changes by changing the current that flows through their conducting channels. The researchers loaded the surface of an FET with short, single-stranded pieces of DNA. These probes are the exact counterparts to the sequence at the beginning of the DNA segment being investigated. If a sample containing the target DNA comes into contact with the surface, the target DNA binds to the probes. The polymerase chain reaction (PCR) is then used to reconstruct the complete target DNA strand. Cleverly, the team do not use all four DNA building blocks at once but dip the FET into four different solutions, each containing only one of the building blocks, one after the other. After each dip, the electrical characteristics of the FET are measured. If and only if a component has been added to the end of the chain, a change is registered. This occurs because each building block brings with it a negative charge, which changes the electrical field on the surface of the FET. In this way, DNA chains of a length up to about ten components can be precisely sequenced. Missing, extra, or changed nucleotides can be rapidly and unambiguously identified.

You can read more details in Angew Chem Int Edn, 2006, 45, 2225

Mammalian paleobiologists must be a cynical lot. How else to explain their presumably ironic use of the term Lazarus Effect in piecing together the very evidence for evolution that must by its nature preclude much of what is discussed in the same context as Lazarus? Moreover, this particular piece of evidence is one that plugs a gap in the fossil record and helps bring continuity to the theory of evolution, something that is often considered a fatal flaw by those who’d dispossess it. You could say they’ve brought it back to life…

Anyway, a new type of rodent discovered last year in Laos is a survivor of a group believed to
have been extinct for 11 million years, according to a new study published today in Science. Mary Dawson and colleagues compared skeletal remains of the squirrel-like animal with those of a little understood extinct group of Southeast Asian rodents and confirmed that it is actually a living member of this long-gone family. When the new species was discovered in early 2005, it drew wide acclaim because it was thought to be a member of an entirely new family of living mammals. Instead, according to the researchers, the rodent represents a striking example of the ‘Lazarus effect’ in which an organism suddenly reappears after a long gap in its fossil record. That such a phenomenon has only rarely been documented among mammals and other vertebrates shows that Southeast Asia’s prehistoric ‘zoo’ can offer invaluable insights regarding past and present
biodiversity, the researchers write.

The missing piece in the biochemistry of haem (heme) is reported in this week’s spectroscopyNOW. Japanese researchers have used x-ray diffraction to determine the crystal structure of the enzyme human indoleamine 2,3-dioxygenase (IDO). This crucial enzyme splits the pyrrole ring of the amino acid L-tryptophan and incorporates both atoms of a molecule of oxygen, an essential step in dozens of metabolic reactions. The discovery could have implications for other studies involving this enzyme and medical problems with which it is associated.

David Bradley reports in this week’s SpectroscopyNow on how scientists in Israel are using UV-Vis spectroscopy to track the underlying logic of enzyme systems that compute.

The research could lead ultimately to implantable enzyme-based computers that respond to metabolic changes in the body and allow complex drug therapies to be monitored and controlled.

TL:DR – Short news article from 2006 about salamanders. The headline alludes to a lyric from a song by the band Genesis, The Carpet Crawlers.

---

Salamanders can transform from an aquatic juvenile form into their terrestrial, adult form only if the stream bed on which they develop is of the right nature. A study published today in the journal BMC Biology reveals that the Oklahoma salamander Eurycea tynerensis metamorphoses into a terrestrial adult form in streambeds composed of fine, tightly packed gravel but stays in the juvenile form in loosely packed streambeds composed of large particles.

The study by Ronald Bonett and Paul Chippindale from the University of Texas at Arlington, Texas, USA, exemplifies how small habitat differences can influence developmental patterns and morphology, they also suggest that such microstructure changes could influence a species’ evolution too.

Bonett and Chippindale explain that large gravel creates porous streambeds with large spaces between particles, where aquatic paedomorphic salamanders can access sub-surface water during dry months. However, if these spaces are filled in by small particles, metamorphosis is the only way they can survive when surface streams dry-up.

Hunger for protein and salt, and a fear of cannibalism, drives the
mass migration of Mormon crickets across western North America, says Stephen Simpson of the University of Sydney, Australia. Mormon cricket swarms, sometimes millions strong covering more than 50 miles in a season. They destroy vegetation in their path and are a severe hazard to drivers.

Locust plagues of Biblical proportions have been with mankind, since, well, Biblical times, at least(!) and usually these creatures swarm in response to a shortage of food. The precise nutritional triggers for the migrations of Mormon crickets though have remained a mystery. Now, field observations by Simpson and his colleagues offer an explanation.

It seems that total starvation is not the driving force, rather migratory crickets preferentially feed at experimental protein-rich and salt rich sources. In the field, crickets were frequently observed feeding on carrion and on each other. When the movement of crickets was experimentally impaired (immobilized by gluing and/or tethering), these insects became targets for cannibalism by neighbouring crickets. These results thus reveal a different model for collective motion, with the crickets’ migration in effect a forced march, the researchers say. The constant threat of cannibalism from the rear appears to push the crickets’ movement as much as the need to find protein and salt pulls it.

Simpson and his colleagues publish further details of their findings today in the online edition of PNAS.

According to The Register, levels of the “satisfaction” hormone prolactin do not reach as high a peak following manual stimulation in men as they do after purportedly procreational activity with a partner.

The original research published in Biological Psychology could explain what The Register describes subtly as a “niggling dissatisfaction” following the former approach to gratification. Needless to say, the remainder of their article is anything but subtle and the link above should only be followed if you’re feeling up to blatant sexual innuendo.

Differences in immune response between males and females appear at puberty, according to a study published today in the journal BMC Immunology.

The differences in the male and female immune responses, which make females more prone to autoimmune disease and males more subject to infection, are established during puberty, report US scientists who have identified one of the mechanisms responsible for the difference in immune response between male and female mice. They show that this sexual disparity is established during puberty and is influenced by sex hormones. These findings have implications for studies of autoimmunity, transplantation and vaccination.

Kanneboyina Nagaraju and Eric Hoffman’s groups from the Children’s National Medical Center, Washington DC, and colleagues elsewhere in the USA, used microarrays to study 12,000 genes expressed in the spleen of pre-pubertal, pubertal and post-pubertal male and female mice.

The results show that a number of genes are upregulated in both males and females during puberty. The authors found that genes involved in the innate immune response, which provides an immediate defence against pathogens and involves phagocytic cells such as macrophages, were significantly underexpressed in pubertal and post-pubertal females. Genes involved in the adaptive immune response, which provides a long-lasting protection and involves antibodies or ‘immunoglobulins’, were overexpressed in pubertal and post-pubertal females compared with males. This difference in expression was not found in pre-pubertal mice, indicating that the sexual disparity in immune system expression is established during puberty.

The researchers have also demonstrated that the differences in immunoglobulin expression between males and females are controlled by a gene signalling pathway called the Fas/FasL pathway, which is modulated by the female sex hormone estrogen.

SOURCE: BMC Immunology press release.

Our brains have a specific mechanism for recognising human faces that is separate from the mechanism that allows us to recognise objects like houses, cars, horses or even
parts of the body, according to Brad Duchaine of University College London. In a forthcoming paper in the journal Cognitive Neuropsychology, he shows how we recognise faces by analysing
one man, who cannot tell one face from another.

I assume he’s not generalising from this one case to the whole human race, but it’s an intriguing piece of work nevertheless.

Duchaine said: ‘There have been many theories about whether there is a part of the brain that deals specifically with faces or whether faces and other objects are handled by the same brain areas. We’ve found that there is a different, very separate, bit of the brain that lets you recognise faces. If those cells aren’t working, someone may not be able to tell two faces apart but they
will recognise two horses apart. This indicates that we go about looking at, analysing and recognising faces in a different way from how we recognise objects.

‘There are many theories out there about how we recognise faces and whether there is a separate social bit of the brain. So that we could draw firm conclusions to prove our facial recognition theory, we addressed all the alternatives in a single case study — Edward, a 53 year-old married man with a PhD in theology and physics, who happens to be unable to
recognise faces.’

For more than 35 years, researchers have debated whether face recognition is carried out by face-specific mechanisms or whether it involves more generic mechanisms that are also used for objects. Prosopagnosic patients (people who have difficulty recognising faces) have been some of the most powerful sources of evidence for there being face-specific mechanisms.

Scientists have put forward a number of different theories about why some people can’t recognise faces. One theory states that people with face recognition just have problems with objects that have a lot of curved surfaces (Curvature explanation); another theory states that it’s caused by problems with perceiving distances between parts such as judging the distance between eyes (Configural-processing explanation); another puts it down to a problem in recognising any individual item in a class — objects and faces (individuation explanation); another points to an inability to develop expertise with regularly encountered objects
(Expertise explanation).

But, for each case of prosopagnosia that has been scientifically tested there have always been several untested alternative explanations that could account for the inability to recognise faces. Each of these individuals has not been sufficiently tested to provide conclusive evidence for face-specific processes.

This study addresses all the existing theories that make a case against there being a specific mechanism in the brain that deals just with faces. Duchaine said: ‘We reject each in turn and eliminate all alternative accounts. The results show that face recognition uses mechanisms in the
brain that are different from those used in recognising anything else.’

The tests at UCL were done using a variety of types of objects — horses, guns, cars, greebles (novel objects). Edward performed just as well on as the test group people at differentiating between different objects but he just couldn’t tell faces apart.