Effect of adrenergic amines on the membrane potential of guinea-pig liver parenchymal cells in short term tissue culture

Zusammenfassung Mit Hilfe der intrazellulären Mikroelektrodentechnik wirk gezeigt, dass Parenchymzellen der Meerschweinchenleber in der Gewebekultur hyperpolarisieren, wenn sympathomimetische Drogen ionophoretisch appliziert werden.     

Membrane response to 1-methyladenine requires the presence of the nucleus

Meiosis is re-initiated in starfish oocytes by the action of the hormone 1-methyladenine (1-MA). It is thought that the primary trigger is localised at the plasma membrane, and early changes reported are the activation of a Na+ pump and variation in membrane potential and conductance. We report here that external application of 1-MA results in an irreversible switching of the starfish oocyte membrane from one stable electrical state to another. This induced change requires the presence of the germinal vesicle.     

Atom-by-atom substitution of Mn in GaAs and visualization of their hole-mediated interactions

The discovery of ferromagnetism in Mn-doped GaAs has ignited interest in the development of semiconductor technologies based on electron spin and has led to several proof-of-concept spintronic devices. A major hurdle for realistic applications of Ga(1-x)Mn(x)As, or other dilute magnetic semiconductors, remains that their ferromagnetic transition temperature is below room temperature. Enhancing ferromagnetism in semiconductors requires us to understand the mechanisms for interaction between magnetic dopants, such as Mn, and identify the circumstances in which ferromagnetic interactions are maximized. Here we describe an atom-by-atom substitution technique using a scanning tunnelling microscope (STM) and apply it to perform a controlled study at the atomic scale of the interactions between isolated Mn acceptors, which are mediated by holes in GaAs. High-resolution STM measurements are used to visualize the GaAs electronic states that participate in the Mn-Mn interaction and to quantify the interaction strengths as a function of relative position and orientation. Our experimental findings, which can be explained using tight-binding model calculations, reveal a strong dependence of ferromagnetic interaction on crystallographic orientation. This anisotropic interaction can potentially be exploited by growing oriented Ga(1-x)Mn(x)As structures to enhance the ferromagnetic transition temperature beyond that achieved in randomly doped samples.     

Radiocarbon evidence of mid-Holocene mammoths stranded on an Alaskan Bering Sea island

Island colonization and subsequent dwarfing of Pleistocene proboscideans is one of the more dramatic evolutionary and ecological occurrences, especially in situations where island populations survived end-Pleistocene extinctions whereas those on the nearby mainland did not. For example, Holocene mammoths have been dated from Wrangel Island in northern Russia. In most of these cases, few details are available about the dynamics of how island colonization and extinction occurred. As part of a large radiocarbon dating project of Alaskan mammoth fossils, I addressed this question by including mammoth specimens from Bering Sea islands known to have formed during the end-Pleistocene sea transgression. One date of 7,908 +/- 100 yr bp (radiocarbon years before present) established the presence of Holocene mammoths on St Paul Island, a first Holocene island record for the Americas. Four lines of evidence--265 accelerator mass spectrometer (AMS) radiocarbon dates from Alaskan mainland mammoths, 13 new dates from Alaskan island mammoths, recent reconstructions of bathymetric plots and sea transgression rates from the Bering Sea--made it possible to reconstruct how mammoths became stranded in the Pribilofs and why this apparently did not happen on other Alaskan Bering Sea islands.     

Hedgehog signalling in prostate regeneration, neoplasia and metastasis

Metastatic cancers adopt certain properties of normal cells in developing or regenerating organs, such as the ability to proliferate and alter tissue organization. We find here that activity of the Hedgehog (Hh) signalling pathway, which has essential roles in developmental patterning, is required for regeneration of prostate epithelium, and that continuous pathway activation transforms prostate progenitor cells and renders them tumorigenic. Elevated pathway activity furthermore distinguishes metastatic from localized prostate cancer, and pathway manipulation can modulate invasiveness and metastasis. Pathway activity is triggered in response to endogenous expression of Hh ligands, and is dependent upon the expression of Smoothened, an essential Hh response component that is not expressed in benign prostate epithelial cells. Monitoring and manipulating Hh pathway activity may thus offer significant improvements in diagnosis and treatment of prostate cancers with metastatic potential.     

Crystal structure of RecBCD enzyme reveals a machine for processing DNA breaks

RecBCD is a multi-functional enzyme complex that processes DNA ends resulting from a double-strand break. RecBCD is a bipolar helicase that splits the duplex into its component strands and digests them until encountering a recombinational hotspot (Chi site). The nuclease activity is then attenuated and RecBCD loads RecA onto the 3' tail of the DNA. Here we present the crystal structure of RecBCD bound to a DNA substrate. In this initiation complex, the DNA duplex has been split across the RecC subunit to create a fork with the separated strands each heading towards different helicase motor subunits. The strands pass along tunnels within the complex, both emerging adjacent to the nuclease domain of RecB. Passage of the 3' tail through one of these tunnels provides a mechanism for the recognition of a Chi sequence by RecC within the context of double-stranded DNA. Gating of this tunnel suggests how nuclease activity might be regulated.     

Inhibitory neurones of a motor pattern generator in Xenopus revealed by antibodies to glycine

Glycine and gamma-aminobutyric acid (GABA) are inhibitory transmitters of major importance. Whereas neurones using GABA as the transmitter can be visualized by immunocytochemical methods for glutamate decarboxylase (GAD) or GABA, no comparable techniques have been available for the selective visualization of glycinergic neurones. We have now produced polyclonal antibodies which specifically recognize glycine in glutaraldehyde-fixed tissue. We used these antibodies to investigate the distribution of glycine in the simple central nervous system (CNS) of the Xenopus embryo, which contains an anatomically and physiologically defined class of reciprocal inhibitory interneurones, the commissural interneurones. These interneurones have an important role in the generation of the swimming motor pattern and are thought to be glycinergic. The glycine antibodies specifically stain these interneurones, revealing their distribution and number in the embryo CNS. This is the first demonstration of the selective localization of glycine-like immunoreactivity in a putative glycinergic class of neurone that has been characterized physiologically, pharmacologically and anatomically.     

Lithium and phorbol ester modify the activating capacity of ascidian spermatozoa

In this paper we have shown, using the whole-cell voltage clamp technique, that two parameters of the fertilization current in ascidian eggs may be modified by exposing spermatozoa to lithium or to phorbol ester. When spermatozoa were pre-treated in 250 mM lithium sea water for up to 30 min there was a significant increase in the mean initial slope of the fertilization current, from 116±90 to 169±84 pA/s (p<0.05). The peak current increased from 1371±1079 to 1719±1052 pA (p>0.05). Pre-treatment in 200–600 nM phorbol 12-myristate 13-acetate also increased the activating capacity of ascidian sperm, as monitored by a significant increase in the initial slope current in control eggs; however, there was no increase in peak current. Furthermore, we have shown, using NH₄Cl, that an increase in intracellular pH alone is insufficient to change the activating capacity of spermatozoa. This is the first report showing that the kinetics of an egg activation event depend upon the physiological status of the spermatozoon.     

A proteomic view of the Plasmodium falciparum life cycle

The completion of the Plasmodium falciparum clone 3D7 genome provides a basis on which to conduct comparative proteomics studies of this human pathogen. Here, we applied a high-throughput proteomics approach to identify new potential drug and vaccine targets and to better understand the biology of this complex protozoan parasite. We characterized four stages of the parasite life cycle (sporozoites, merozoites, trophozoites and gametocytes) by multidimensional protein identification technology. Functional profiling of over 2,400 proteins agreed with the physiology of each stage. Unexpectedly, the antigenically variant proteins of var and rif genes, defined as molecules on the surface of infected erythrocytes, were also largely expressed in sporozoites. The detection of chromosomal clusters encoding co-expressed proteins suggested a potential mechanism for controlling gene expression.