Experimental infection of house finches with Mycoplasma gallisepticum

Mycoplasma gallisepticum (MG) has caused an endemic upper respiratory and ocular infection in the eastern house finch (Carpodacus mexicanus) after the epidemic first described in 1994. The disease has been studied by a number of investigators at a population level and reports describe experimental infection in group-housed MG-free house finches. Because detailed observation and evaluation of individual birds in group-housed passerines is problematic, we studied individually housed house finches that were experimentally inoculated with the finch strain of MG in a controlled environment. To accomplish this, a study was conducted spanning the period of November 2001-April 2002 with 20 MG-free (confirmed by the rapid plate agglutination assay and polymerase chain reaction [PCR] assay) eastern house finches captured in the Cayuga Basin area of central New York (USA) in the summer of 2001. After a period of acclimatization and observation (12 wk), 20 finches were inoculated with a 0.05-ml aliquot of MG (3.24 x 10(5) colony-forming units/ml) via bilateral conjunctival sac instillations. Two additional finches acted as controls and were inoculated in the same manner with preservative-free sterile saline solution. After inoculation, all finches except the controls exhibited clinical signs of conjunctivitis within 2-6 days. The progression of the disease was evaluated by several methods, including PCR, behavioral observations, and physical examination including eye scoring, body weight, and body condition index. Over a period of 21 wk, MG-infected finches developed signs of disease and recovered (80%), developed signs of disease and progressed to become chronically infected (15%), or died (5%). We hypothesize that the high survival rate and recovery of these finches after infection was associated with the use of controlled environmental conditions, acclimatization, a high plane of nutrition, and low stocking (housing) density, all of which are factors documented to be important in the outcome of MG infections in domestic poultry and other species.     

Competition between lithium and magnesium ions for the G-protein transducin in the guanosine 5'-diphosphate bound conformation

Li(+) is the most effective drug used to treat bipolar disorder; however, its exact mechanism of action has yet to be elucidated. One hypothesis is that Li(+) competes with Mg2+ for the Mg2+ binding sites on guanine-nucleotide binding proteins (G-proteins). Using 7Li T1 relaxation measurements and fluorescence spectroscopy with the Mg2+ fluorophore furaptra, we detected Li(+)/Mg(2+) competition in three preparations: the purified G-protein transducin (Gt), stripped rod outer segment membranes (SROS), and SROS with purified Gt reattached (ROS-T). When purified ROS-T, SROS or transducin were titrated with Li+ in the presence of fixed amounts of Mg(2+), the apparent Li(+) binding constant decreased due to Li(+)/Mg(2+) competition. Whereas for SROS the competition mechanism was monophasic, for G(t), the competition was biphasic, suggesting that in G(t), Li(+)/Mg(2+) competition occurred with different affinities for Mg(2+) in two types of Mg(2+) binding sites. Moreover, as [Li(+)] increased, the fluorescence excitation spectra of both ROS-T and G(t) were blue shifted, indicating an increase in free [Mg(2+)] compatible with Li(+) displacement of Mg(2+) from two low affinity Mg(2+) binding sites of G(t). G(t) release from ROS-T membrane was also inhibited by Li(+) addition. In summary, we found evidence of Li(+)/Mg(2+) competition in G(t)-containing preparations.     

Sympatric natural Saccharomyces cerevisiae and S. paradoxus populations have different thermal growth profiles

Saccharomyces cerevisiae and its close congener S. paradoxus are typically indistinguishable by the phenotypic criteria of classical yeast taxonomy, but they are evolutionarily distinct as indicated by hybrid spore inviability and genomic sequence divergence. Previous work has shown that these two species coexist in oak-associated microhabitats at natural woodland sites in North America. Here, we show that sympatric populations of S. cerevisiae and S. paradoxus from a single natural site are phenotypically differentiated in their growth rate responses to temperature. Our main finding is that the S. cerevisiae population exhibits a markedly higher growth rate at 37 degrees C than the S. paradoxus population; we also find possible differences in growth rate between these populations at two lower temperatures. We discuss the implications of our results for the coexistence of these yeasts in natural environments, and we suggest that thermal growth response may be an evolutionarily labile feature of these organisms that could be analyzed using genomic approaches.     

A method for rapidly screening functionality of actin mutants and tagged actins

Recombinant production and biochemical analysis of actin mutants has been hampered by the fact that actin has an absolute requirement for the eukaryotic chaperone CCT to reach its native state. We therefore have developed a method to rapidly screen the folding capacity and functionality of actin variants, by combining in vitro expression of labelled actin with analysis on native gels, band shift assays or copolymerization tests. Additionally, we monitor, using immuno-fluorescence, incorporation of actin variants in cytoskeletal structures in transfected cells. We illustrate the method by two examples. In one we show that tagged versions of actin do not always behave native-like and in the other we study some of the molecular defects of three β-actin mutants that have been associated with diseases. Published: October 25, 2004.     

Arsenobetaine in Atlantic salmon (Salmo salar L.): influence of seawater adaptation

Glycine betaine has been suggested to improve the maintenance of ionic and osmotic homeostasis during seawater adaptation in teleost fish. Arsenobetaine may also behave as an osmolyte, due to its structural similarity to glycine betaine. The influence of seawater adaptation on intestinal uptake and muscle accumulation of arsenobetaine in the teleost Atlantic salmon (Salmo salar L.) was investigated. Atlantic salmon (freshwater and seawater adapted) were given a single oral dose of arsenobetaine, which was absorbed over the intestine within 6 h after exposure. Seawater adapted Atlantic salmon had significantly higher levels of accumulated arsenobetaine in blood compared to the freshwater adapted salmon. However, seawater adaptation had no effect on the levels of accumulated arsenobetaine in muscle tissue. Similar retention of the administered dose was found in muscle tissue in both freshwater and seawater adapted salmon, with 49+/-6% and 50+/-10% retention after 144 h, respectively. Results indicate that muscle retention was not influenced by salinity in seawater adapting teleosts.     

Vertebrate organogenesis: getting the heart into shape

Recent mutant analysis in zebrafish points to an important role for oriented cell division in cardiac chamber formation and reveals its molecular control by a novel signal from the heart's interior.     

A putative polyketide synthase/peptide synthetase from Magnaporthe grisea signals pathogen attack to resistant rice

Isolates of the rice blast fungus Magnaporthe grisea that carry the gene encoding Avirulence Conferring Enzyme1 (ACE1) are specifically recognized by rice (Oryza sativa) cultivars carrying the resistance gene Pi33. This recognition enables resistant plants to activate a defense response. ACE1 was isolated by map-based cloning and encodes a putative hybrid between a polyketide synthase and a nonribosomal peptide synthetase, enzymes involved in microbial secondary metabolism. ACE1 is expressed exclusively during fungal penetration of host leaves, the time point at which plant defense reactions are triggered. Ace1 appears to be localized in the cytoplasm of the appressorium. Mutation of the putative catalytic site of the beta-ketoacyl synthase domain of Ace1 abolishes recognition of the fungus by resistant rice. This suggests that Ace1 biosynthetic activity is required for avirulence. Our results are consistent with the hypothesis that the fungal signal recognized by resistant rice plants is the secondary metabolite whose synthesis depends on Ace1.     

Motor physiology: a brain of two halves

Brain changes after stroke suggest that undamaged areas may 'take over' the function of damaged regions. Recent studies using magnetic stimulation to disrupt the healthy human brain shed new light on the potential for dynamic compensation across the motor system.