News & Views in 1999

The neurotrophins were named after their ability to regulate the survival and differentiation of nerve cells. But they are also thought to be involved in the processes that underlie neuronal plasticity, and a new report indicates that their function goes even further than this -- they not only modulate chemical transmission, but, like the more classical neurotransmitters, they mediate it.

The most intensively studied element of the immune system is the major histocompatibility complex, to which various gene families contribute. Two papers which provide complete nucleotide sequences of these complexes in the human and chicken allow more thorough comparison of them than ever before.

Arthur Cain -- naturalist and doughty Darwinian, who did seminal work in ecological genetics and was a standard bearer for the view that most evolutionary changes are not neutral in terms of natural selection.

From time to time the Earth's magnetic field reverses in polarity, and the record of such reversals is preserved in rocks magnetized at the time of their formation. The cause of reversals has usually been sought in the behaviour of the Earth's core, where the geomagnetic field is generated. But new simulations, which provide a good fit with part of the rock record, implicate mantle events in reversals.

The Laplace operator has had a central place in the development of large areas of the physical sciences, and remains a subject of investigation. The so-called 'hotspots conjecture' is important in the theory underlying the Laplace operator: applied to heat diffusion, it states that the hottest and coldest regions eventually lie on the boundary of any planar domain. This expected answer, however, is it seems wrong.

The decline of growth rate with increasing size and lifespan is one of the few universal laws in ecology. Now, a theoretical growth law for trees has been combined with field measurements to show that rainforest species with different ecological strategies can still attain the same optimal use of energy.

Although many mutations are harmful, some can help a population to adapt to environmental changes and enhance its chances of survival. Mutations have always been thought to be random, chance events, but the discovery of a set of enzymes known as mutases indicates that cells have mechanisms for generating them. The process needs to be tightly regulated, though, and is switched on only when the cell is under stress.

Cyclotrons are well known as the first useful particle accelerators. Less familiar is their use for high-precision measurements of fundamental constants, such as the electron magnetic moment. An experiment that records the fundamental quantum limit of a cyclotron opens the way to even better measurements of the electron magnetic moment.

Biochemical reactions are extremely rapid, yet the techniques for imaging the enzymes that catalyse them can be very slow. To get around this problem, structures can be determined at roughly the temperature of liquid nitrogen -- literally freezing an enzyme's movements in time. This has now been done for a protein called bacteriorhodopsin.

Hot springs on the sea floor pump out a potent cocktail of chemicals. Now mercury has been added to the mix, discovered at hydrothermal vents off the coast of New Zealand.

How do you stick your tongue into an ant's nest? The giant anteater does it by opening its mouth using the muscles that other mammals employ for the reverse operation.

To form the connections of the nervous system, axons must connect up with the areas that will be their final target. Intermediate targets are thought to act as signposts along the way, sending out guidance molecules that tell the axons which way to go. But a new study shows that these intermediate targets do much more than this, and that they are required to keep the migrating neurons alive.

What are the 'features' or 'parts' that our brains use to tell one thing from another? Several algorithms exist for learning object parts, and the development of the latest -- known as non-negative matrix factorization -- is now reported. This algorithm seems to decompose sets of faces into 'basis functions' that are different, and more part-like, than those found by conventional algorithms.

The development of methods for slowing and trapping gaseous species has led to a renaissance in atomic physics, which is now also progressing into molecular/chemical physics. The latest advances come from two groups who have devised techniques that, in principle, provide new approaches for trapping molecules and spectroscopically studying them.

New insights continue to emerge into fluid mixing -- a complex process that remains poorly understood. The latest progress comes from experimental investigations of a type of low-speed mixing called chaotic advection, which show that surprisingly stable spatial patterns can arise.

Since the discipline of space biology was launched over 40 years ago there have been many developments, some of which were reviewed and discussed at a workshop last month. The workshop was unusual in that it focused on the effects of microgravity above the cellular level -- in contrast to much of contemporary biology, which is concerned more with molecules.

The focus of drugs for treating HIV-1 infection has switched from protease and reverse-transcriptase inhibitors to compounds that prevent fusion of the virus with human cells. The target protein in this pathway is known as gp41, and, last year, a pocket was identified in gp41 that could act as the binding site for a fusion inhibitor. Peptide inhibitors that specifically bind this pocket have now been identified.

Benzodiazepine drugs -- such as Valium -- induce relaxation, but they also have unwelcome side effects. These drugs work by binding to the GABA_A receptor on nerve cells and damping down the electrical activity of these cells. Depending on where in the brain they are found, GABA_Areceptors have different actions, so the aim is to develop drugs that target only those receptors that produce the desired effects.