Three groups report crystal structures of the plant stress hormone abscisic acid (ABA) unbound and in various complexes with its receptors: a fourth paper reports the reconstitution of the ABA signalling pathway in vitro — a first for plant hormones. The cover image shows a desert primrose coping with drought. Picture credit: Alan Kearney/Getty Images.
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Research Highlights
Nature 462, 546 (3 December 2009) | doi:10.1038/462546b; Published online 2 December 2009
Immunology: Timely defence
Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0906361106 (2009)
Many activities of the immune system follow rhythmic daily cycles. Now researchers have found that some immune cells have their own circadian clocks.
Achim Kramer of the Charité Medical University in Berlin and his colleagues took immune cells and tissues from mice at regular intervals throughout the day. They found that macrophages — cells that form part of the immune system’s first line of defence against bacterial infections — from the spleen, lymph nodes and abdominal area express circadian clock genes. In addition, they showed that about 8% of macrophage genes are expressed rhythmically.
The authors also report that the secretion of immune modulators by spleen macrophages in response to bacterial toxins follows circadian rhythms.
Biology: Beetle-juice antifreeze
S. SHARMA
Proc. Natl Acad. Sci. USA 106, 20210–20215 (2009)
Many animals survive extreme cold by producing ‘antifreeze’ compounds that inhibit ice growth. The compounds described so far have all been proteins.
Kent Walters at the University of Notre Dame in Indiana and his colleagues have now characterized the first animal antifreeze that contains little or no protein.
They isolated the compound from the darkling beetle Upis ceramboides (pictured), which can withstand temperatures as low as -60° C, allowing it to live in harsh climates like that of Alaska. Analysis showed it to comprise a xylomannan saccharide with a fatty acid component.
Genetics: One on one
Human cells, with their two sets of chromosomes, do not lend themselves to large-scale genetic screens as simple model organisms such as yeast have so profitably done.
Thijn Brummelkamp at the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, and his colleagues have devised a way around the problem. Using a cell line with only one copy of most human chromosomes, they inactivated various genes using a method called insertional mutagenesis. The researchers then screened cells that were resistant to particular pathogens to see which genes invaders might rely on to attack.
Using the technique, the team identified two host genes used by the influenza H1N1 virus to infect cells, as well as genes exploited by other bacterial toxins to kill host cells. The authors say the method could help in developing new antiviral therapies.
Neuroscience: Brain’s immune connection
Connections between neurons strengthen or break during brain development. Unexpectedly, key cell-surface proteins involved in immunity seem to regulate some of this plasticity.
Carla Shatz of Stanford University in Palo Alto, California, and her colleagues found that two members of the family of major histocompatibility complex class I (MHC I) proteins limit the ‘tuning up’ of circuitry involved in visual processing. Mice in which the genes for these two proteins had been deleted performed better in a visual task involving the blocking of one eye than did normal mice. The MHC I proteins curb the retuning of circuitry that enables the functioning eye to compensate for the blocked one, the authors say.
Genetics: Immune impediment
Nature Genet. 41, 1341–1344 (2009)
Transplanted bone marrow cells commonly attack the recipient’s cells, even though key proteins on the surface of the donor’s and recipient’s cells match. To find out what might be the cause of this ‘graft-versus-host disease’, Steven McCarroll of Harvard Medical School in Boston, Massachusetts, and his colleagues analysed gene deletions in the genomes of 1,345 pairs of patients and immune-matched siblings from whom bone-marrow transplants were made.
They found that the immune attack was more likely to occur when the donor — but not the recipient — had deletions in both copies of the gene UGT2B17. The donor’s immune cells seem to respond to the gene’s protein as ‘foreign’ in the recipient.
Neuroscience: Rude awakening
ElSEVIER
Fruitflies recruit distinct neural circuits when undergoing different forms of arousal — either waking from sleep, or being disturbed by puffs of air.
David Anderson at the California Institute of Technology in Pasadena and his colleagues found that flies with loss-of-function mutations in the dopamine receptor were more easily startled by air puffs than were flies without the mutation, but seemed less easily roused from sleep, as they slept longer.
When the researchers restored normal functionality to the dopamine receptor in a brain area called the central complex (pictured, dopamine receptors labelled green), the puff-induced arousal dropped to normal levels but sleep arousal remained unchanged.
标签：自然杂志
