Frontiers news briefs: July 4

July 04, 2013

Frontiers in Computational Neuroscience

Large-scale network organisation in the avian forebrain

Birds have been evolving separately from mammals for around 300 million years. So it's hardly surprising that under a microscope, the brain of a bird looks quite different to that of a mammal. Nevertheless, birds have been shown to be remarkably intelligent. They can use tools, make plans, and solve unfamiliar puzzles. How is it that both kinds of brain are capable of these things? A new study published in Frontiers in Computational Neuroscience presents the first large-scale wiring diagram for the brain of a prototypical bird (a pigeon). Using mathematical tools from the theory of networks, a team of researchers show that the way the connections are organised in a pigeon's brain is remarkably similar to the way they are organised in mammals, including cats, monkeys, and humans. In particular, both types of brain can be thought of as comprising a number of modules. And both types of brain contain "hub nodes", which can be thought of as regions with widespread, global connections (like major airports in a transport network). Most remarkably, the major hub nodes in the bird brain have analogous functional roles to those in the mammalian brain, and in both animals they include the most important regions for high-level cognition.

Researcher contact:

Prof. Murray Shanahan
Department of Computing
Imperial College London, UK


Frontiers in Microbiology

Toxoplasma gondii inhibits mast cell degranulation by suppressing phospholipase Cy-mediated Ca2+ mobilization

An estimated one-third of people around the world are infected by the parasite Toxoplasma gondii, a distant relative of the malaria parasite, although normally only persons with a weakened immune response show any symptoms. But how does T. gondii subvert immune defenses, enabling it to survive inside cells of its bird and mammal hosts? With new methods for the real-time imaging of single cells, David Holowka and his team from Cornell University, USA, obtained results that help to explain this trick: when T. gondii is about to enter a host cell, it releases a factor that dampens a key signal within the host's white blood cells, namely the release of calcium from within-cell stores into the cytoplasm, necessary to relay the message that an invader has been detected outside the cell. Holowka and colleagues suggest that T. gondii could use the same mechanism to suppress other immune responses, for example the production of cytokines, signaling molecules that promote inflammation.

Researcher contact:

Dr. David Holowka
Department of Chemistry and Chemical Biology
Cornell University, USA


Frontiers in Plant Science

Plant growth in Arabidopsis is assisted by compost soil-derived microbial communities

Plant growth has been doubled by adding soil microbes. Plants and soil microbes are constantly interacting in natural and agricultural environments and many examples of one-to-one interactions have been studied. However, the effect of mixed microbial populations on the growth and gene expression of plants still remained largely unknown. This study evaluated the growth of leaves and roots of the model plant Arabidopsis thaliana in the presence or absence (i.e. in sterilized soil) of microbes extracted from compost soil. Surprisingly, leaf growth was doubled in the presence of microbes. Chemical analyses and high-throughput analysis of gene expression within plant tissues and soil surrounding roots revealed that the added microorganisms facilitated iron acquisition by plants. Soil microbes also affected other plant processes, including acquisition of nitrogen, production of free radicals, and defense against diseases. In conclusion, this study showed the main underlying processes occurring in plants during interactions with soil microbial populations and emphasized the important role of soil microbes for plant growth.

Researcher contact:

Prof. Peer Schenk
School of Agriculture and Food Sciences
University of Queensland


Frontiers in Neuroscience

Dopamine imbalance in Huntington's disease: a mechanism for the lack of behavioral flexibility

Huntington's disease is a hereditary neurodegenerative disease that is caused by a mutation in the human huntingtin gene. It is characterized by uncontrollable dance-like movements (chorea) in the early stages of the disease and loss of voluntary movement (behavioral inflexibility) in the later stages. Huntington's disease leads to massive cell death in the striatum, a part of the brain involved in voluntary motor movement, as well as to degenerative changes in the brain's cortex. Since many cells in the striatum use dopamine as a chemical signal for communication, changes in dopamine neurotransmission may hinder cell-to-cell communication in the brain, which leads to dysfunction and ultimately cell death. In this article, researchers discuss the function of dopamine in the striatum as affected during Huntington's disease. Based on studies of human patients and genetically modified mice, they show that changes in dopamine function could contribute to some of the symptoms of Huntington's disease. Specifically, they propose that increases in dopamine levels may be involved in the initial onset of chorea whereas decreases in dopamine are part of the late-stage symptoms of this disease. According to the researchers, effective treatments for Huntington's disease should be tailored to these time-dependent changes in dopamine levels.

Researcher contact:

Dr. Michael S. Levine
Intellectual and Developmental Disabilities Research Center, Semel Institute for Neuroscience and Human Behavior,
and the Brain Research Institute
University of California, USA


Frontiers in Plant Science

Electrical signalling along the phloem and its physiological responses in the maize leaf

Electrical phenomena in plants have attracted scientists since the eighteenth century. Similar to animal cells, also plant cells possess the ability to become excited under the influence of certain environmental factors and to generate rapid electrical signals propagating over long distances. The reason why plants have developed pathways for fast signal transmission presumably lies in the necessity to rapidly respond to environmental stress factors. Jörg Fromm and colleagues from the University of Hamburg here show that maize plants generate electrical signals in the phloem, that is, the inner layer of the bark, after cold shock as well as wounding of a leaf tip. Interestingly, the signal induced by cold shock travels rapidly with up to 3 cm per second towards the middle of the leaf to reduce assimilate transport within the phloem and the neighbouring leaf cells, and to trigger the synthesis of carbohydrates like starch and callose. In contrast, wound-induced signals have a different shape, a speed of only 0.5 cm per second, and do not inhibit assimilate translocation but reduce photosynthesis and the amount of almost all metabolites in the leaf. Fromm and colleagues conclude that different environmental factors such as cold shock and wounding incite characteristic electrical signals, each with a specific influence on photosynthesis, assimilate transport and biochemistry.

Researcher contact:

Prof. Jörg Fromm
Institute for Wood Biology
University of Hamburg, Germany


Frontiers in Microbiology

Nitrate ammonification by Nautilia profundicola AmH: experimental evidence consistent with a free hydroxylamine intermediate

Many microbes use nitrate in the environment for growth. Nitrate can be converted to ammonium and used in molecules such as proteins, or used as a terminal electron acceptor to make energy. A new report in Frontiers in Microbiology sheds light on how the deep-sea hydrothermal vent bacterium Nautilia profundicola strain AmH carries out these functions. Normally, genes encoding the enzymes required for nitrate reduction to ammonium are easily recognized in complete genome sequences. The genome of N. profundicola does not encode any recognizable nitrite reductases, enzymes that are necessary for the second step in the reduction of nitrate to ammonium. Three research groups from the USA predicted and then experimentally tested a new pathway for nitrate reduction to ammonium. The novel aspect of this pathway is that hydroxylamine, a potent mutagen, appears to be a free intermediate between nitrite and ammonium. The key module in the pathway is a quinone-reactive protein coupled to a hydroxylamine dehydrogenase enzyme that works in reverse. Hydroxylamine dehydrogenase shares ancestry with certain nitrite reductases and the nitrite-reducing type may represent an evolutionary precursor of the variants that oxidize hydroxylamine to nitrite. This enzyme complex is also found in other ε-proteobacteria, including some pathogenic Campylobacteria.

Researcher contact:

Prof. Barbara Campbell
Department of Biological Sciences
Clemson University, USA

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