Taxonomic status of putative Verticillum alboatrum isolates

Two fungal isolates, formerly classified as Verticillium alboatrum and proposed as forming the basis of a new sub-group (`Group 2') within the species, have been shown to be non-pathogenic to known hosts of V. alboatrum and, on the basis of molecular evidence, to be closely related to Verticillium psalliotae and Verticillium fungicola. We propose that the taxon V. alboatrum be confined to those closely related isolates, usually plant pathogenic and usually producing dark resting mycelium, referred to by other authors as Group 1. The only sub-specific groupings which appear valid (based on pathological and molecular evidence) comprise: (1) host-adapted isolates from lucerne; and (2) all other isolates.     

Inhibition of the Cardiac Na+ Channel Nav1.5 by Carbon Monoxide

Sublethal carbon monoxide (CO) exposure is frequently associated with myocardial arrhythmias, and our recent studies have demonstrated that these may be attributable to modulation of cardiac Na⁺ channels, causing an increase in the late current and an inhibition of the peak current. Using a recombinant expression system, we demonstrate that CO inhibits peak human Nav1.5 current amplitude without activation of the late Na⁺ current observed in native tissue. Inhibition was associated with a hyperpolarizing shift in the steady-state inactivation properties of the channels and was unaffected by modification of channel gating induced by anemone toxin (rATX-II). Systematic pharmacological assessment indicated that no recognized CO-sensitive intracellular signaling pathways appeared to mediate CO inhibition of Nav1.5. Inhibition was, however, markedly suppressed by inhibition of NO formation, but NO donors did not mimic or occlude channel inhibition by CO, indicating that NO alone did not account for the actions of CO. Exposure of cells to DTT immediately before CO exposure also dramatically reduced the magnitude of current inhibition. Similarly, l-cysteine and N-ethylmaleimide significantly attenuated the inhibition caused by CO. In the presence of DTT and the NO inhibitor N^ω-nitro-l-arginine methyl ester hydrochloride, the ability of CO to inhibit Nav1.5 was almost fully prevented. Our data indicate that inhibition of peak Na⁺ current (which can lead to Brugada syndrome-like arrhythmias) occurs via a mechanism distinct from induction of the late current, requires NO formation, and is dependent on channel redox state.     

Protein Tyrosine Phosphatase PTP1B Is Involved in Hippocampal Synapse Formation and Learning

ER-bound PTP1B is expressed in hippocampal neurons, and accumulates among neurite contacts. PTP1B dephosphorylates ß-catenin in N-cadherin complexes ensuring cell-cell adhesion. Here we show that endogenous PTP1B, as well as expressed GFP-PTP1B, are present in dendritic spines of hippocampal neurons in culture. GFP-PTP1B overexpression does not affect filopodial density or length. In contrast, impairment of PTP1B function or genetic PTP1B-deficiency leads to increased filopodia-like dendritic spines and a reduction in mushroom-like spines, while spine density is unaffected. These morphological alterations are accompanied by a disorganization of pre- and post-synapses, as judged by decreased clustering of synapsin-1 and PSD-95, and suggest a dynamic synaptic phenotype. Notably, levels of ß-catenin-Tyr-654 phosphorylation increased ∼5-fold in the hippocampus of adult PTP1B^−/− (KO) mice compared to wild type (WT) mice and this was accompanied by a reduction in the amount of ß-catenin associated with N-cadherin. To determine whether PTP1B-deficiency alters learning and memory, we generated mice lacking PTP1B in the hippocampus and cortex (PTP1B^fl/fl–Emx1-Cre). PTP1B^fl/fl–Emx1-Cre mice displayed improved performance in the Barnes maze (decreased time to find and enter target hole), utilized a more efficient strategy (cued), and had better recall compared to WT controls. Our results implicate PTP1B in structural plasticity within the hippocampus, likely through modulation of N-cadherin function by ensuring dephosphorylation of ß-catenin on Tyr-654. Disruption of hippocampal PTP1B function or expression leads to elongation of dendritic filopodia and improved learning and memory, demonstrating an exciting novel role for this phosphatase.     

Cytochrome c oxidase: evolution of control via nuclear subunit addition

According to theory, present eukaryotic cells originated from a beneficial association between two free-living cells. Due to this endosymbiotic event the pre-eukaryotic cell gained access to oxidative phosphorylation (OXPHOS), which produces more than 15 times as much ATP as glycolysis. Because cellular ATP needs fluctuate and OXPHOS both requires and produces entities that can be toxic for eukaryotic cells such as ROS or NADH, we propose that the success of endosymbiosis has largely depended on the regulation of endosymbiont OXPHOS. Several studies have presented cytochrome c oxidase as a key regulator of OXPHOS; for example, COX is the only complex of mammalian OXPHOS with known tissue-specific isoforms of nuclear encoded subunits. We here discuss current knowledge about the origin of nuclear encoded subunits and the appearance of different isozymes promoted by tissue and cellular environments such as hypoxia. We also review evidence for recent selective pressure acting on COX among vertebrates, particularly in primate lineages, and discuss the unique pattern of co-evolution between the nuclear and mitochondrial genomes. Finally, even though the addition of nuclear encoded subunits was a major event in eukaryotic COX evolution, this does not lead to emergence of a more efficient COX, as might be expected from an anthropocentric point of view, for the "higher" organism possessing large brains and muscles. The main function of these subunits appears to be "only" to control the activity of the mitochondrial subunits. We propose that this control function is an as yet under appreciated key point of evolution. Moreover, the importance of regulating energy supply may have caused the addition of subunits encoded by the nucleus in a process comparable to a "domestication scenario" such that the host tends to control more and more tightly the ancestral activity of COX performed by the mtDNA encoded subunits.     

The enzymatic synthesis of amyrin glucoside

Label appeared in several cell fractions isolated from the cotyledons of pea seeds germinated for 48 hr with mevalonate-[2-¹⁴C]. The major radioactive metabolite in each fraction was amyrin. In a similar experiment, a fraction sedimenting between 1000 and 25 000 g and a microsomal pellet were labeled with 3H from mevalonate-[2-³H]. Each of these tritiated fractions on incubation with UDP-glucose-[U-¹⁴C] yielded CHCl₃-MeOH-soluble material bearing ¹⁴C and ³H. TLC of the extracts gave a compound chromatographically identical with a glucoside and bearing the two isotopes. Acid hydrolysis of this compound gave an ether-soluble material carrying ³H alone. On TLC it co-chromatographed with amyrin. Of the two tritiated cotyledon fractions, the microsomal pellet had the lower glucosyltransferase activity. The labeled amyrin residing in this fraction served as an acceptor for glucose from UDP-glucose in the presence of a glucosyltransferase from pea seedling axis tissue. In such a mixed preparation, the axis tissue transferase suffers a marked inhibition by the cotyledon preparation.     

Selective loss of mitochondrial genome can be caused by certain unsaturated fatty acids

Various unsaturated fatty acids had different effectiveness for maintaining the continued replication of functional mitochondria in an unsaturated fatty acid auxotroph of Saccharomyces cerevisiae (KD115). Certain isomers of octadecenoic acid (i.e., cis-9) and eicosatrienoic acid (i.e.,cis-8,11,14) permitted continued replication of mitochondria and provided cultures that contained only 4 to 5% cells that formed petite colonies. On the other hand, cultures grown with cis-12- or cis-13-octadecenoic acid or cis-11,14,17-eicosatrienoic acid, produced a 12- to 16-fold greater frequency of petite mutants (50-60%) after 8 to 10 generations of growth. The production of the petite mutants occurred despite adequate incorporation of these unsaturated fatty acids into cellular phospholipids and an apparently normal ability to undergo the initial steps in the induction of cellular respiration. The evidence suggests that some cellular processes necessary for continued mitochondrial replication depend on the structural features of the fatty acyl chains as well as the overall content of unsaturated fatty acids in membrane phospholipids. Impairment of that process by certain inadequate fatty acids or by an inadequate supply of a suitable fatty acid leads to a permanent loss of the mitochondrial genome from the cells of subsequent generations.     

Golgi duplication in Trypanosoma brucei

Duplication of the single Golgi apparatus in the protozoan parasite Trypanosoma brucei has been followed by tagging a putative Golgi enzyme and a matrix protein with variants of GFP. Video microscopy shows that the new Golgi appears de novo, near to the old Golgi, about two hours into the cell cycle and grows over a two-hour period until it is the same size as the old Golgi. Duplication of the endoplasmic reticulum (ER) export site follows exactly the same time course. Photobleaching experiments show that the new Golgi is not the exclusive product of the new ER export site. Rather, it is supplied, at least in part, by material directly from the old Golgi. Pharmacological experiments show that the site of the new Golgi and ER export is determined by the location of the new basal body.