Ustilago maydis Mating Hyphae Orient Their Growth toward Pheromone Sources

Snetselaar, K. M., Bolker, M., and Kahmann, R. 1996. Ustilago maydis mating hyphae orient their growth toward pheromone sources. Fungal Genetics and Biology 20, 299-312. When small drops of Ustilago maydis sporidia were placed 100-200 μm apart on agar surfaces and covered with paraffin oil, sporidia from one drop formed thin hyphae that grew in a zig-zag fashion toward the other drop if it contained sporidia making the appropriate pheromone. For example, a2b2 mating hyphae grew toward a1b1 and a1b2 mating hyphae, and the filaments eventually fused tip to tip. Time-lapse photography indicated that the mating hyphae can rapidly change orientation in response to nearby compatible sporidia. When exposed to pheromone produced by cells in an adjacent drop, haploid sporidia with the a2 allele began elongating before sporidia with the a1 allele. Sporidia without functional pheromone genes responded to pheromone although they did not induce a response, and sporidia without pheromone receptors induced formation of mating hyphae although they did not form mating hyphae. Diploid sporidia heterozygous at b but not at a formed straight, rigid, aerial filaments when exposed to pheromone produced by the appropriate haploid sporidia. Again, the a2a2b1b2 strain formed filaments more quickly than the a1a1b1b2 strain. Taken together, these results suggest that the a2 pheromone diffuses less readily or is degraded more quickly than the a1 pheromone.     

Hyperimmune hens as a novel source of anti-Cryptosporidium antibodies suitable for passive immune transfer.

Leghorn hens were subcutaneously immunized with 25 micrograms of Cryptosporidium parvum oocyst emulsified in Freund's complete adjuvant. A booster dose was injected 5 weeks later. Anti-Cryptosporidium activities of yolks and sera measured by an enzyme-linked immunosorbent assay (ELISA), demonstrated high levels in both sera and egg yolks which persisted for at least 17 wk. Preparations from yolks with high, medium and low anti-Cryptosporidium ELISA activities were used in a neonatal mouse model to assess their biological activities. A significant parasite reduction (P less than or equal to 0.001) was found between the high and all other groups. Hyperimmune eggs could be used as a source for passive immunity in cryptosporidiosis.     

Restriction fragment length polymorphism analysis of Cryptosporidium parvum isolates of bovine and human origin.

Cryptosporidium parvum oocysts isolated from different hosts and geographical areas were compared by restriction endonuclease analysis of repetitive DNA: Iowa (bovine), Florida (bovine), New York (bovine), Peru (human), Brazil (human), and Mexico (human). Southern blot hybridization analysis was performed using the restriction endonuclease enzyme Eco RI and the DNA probe pV47-2. The probe hybridized with 18 bands present in all the isolates. The Brazilian, Mexican, and Peruvian human isolates had an additional common band of 4.3 kbp that was absent in the bovine isolates. Two extra bands of 14 and 12 kbp were present in the Brazilian isolate whereas the Mexican isolate had an extra band of 14 kbp. When the Iowa and Peru C. parvum isolates were passed twice through calves, oocysts recovered from both passages showed identical banding patterns, suggesting that recombination of the repetitive sequences was not altered during sexual reproduction. The DNA digested with other restriction endonucleases were tested confirming differences between isolates. A genomic DNA library is currently being produced to better define isolate variation in C. parvum.     

Variations in collagen fibril structure in tendons

Variation of collagen fibril structure in tendon was investigated by x-ray diffraction. Anatomically distinct tendons from single species, as well as tendons from different species, were examined to determine the variations that exist in both the axial and lateral structure of the collagen fibrils. The meridional diffraction is derived from the axial collagen fibril structure. Anatomically distinct tendons of a particular species give meridional patterns that are indistinguishable within experimental error. The meridional diffraction patterns from tendons of different mammals are similar but show small species-specific variations, most noticeably in the 14th–18th orders. Tendons of birds also give meridional patterns that are similar to each other, but the avian patterns differ considerably from the mammalian ones. Avian tendons give stronger odd and weaker even low orders, a feature consistent with a reduced gap:overlap ratio, and have a distinctive intensity pattern for the higher meridional orders. Interpretation of these differences has been approached using biochemical data, diffraction by reconsituted fibers of purified collagen, and Fourier transform analysis. From these methods, it appears that the variations observed in the lower orders (2nd–8th) and in the higher orders (29th–52nd) are probably related to differences in the primary structure of the Type I collagen found in the different species. The variations observed in the 14th–18th orders appear not to be related to features within the triple-helical domain of the molecule. Equatorial diffraction yields information on the lateral packing of collagen molecules in the fibrils, and considerable variation was seen in different tendons. Rat tail tendon gives sharp Bragg reflections, demonstrating the presence of a crystalline lateral arrangement of molecules in the fibril. For the first time, sharp lattice reflections similar to those in rat tail tendon have been observed in nontail tendons, including rat achilles tendon, rabbit leg tendon, and wing and leg tendons of quail. In the rabbit and quail tendons, one of the strong equatorial reflections characteristic of the rat tendon pattern, at 1.26 nm, was absent. The positions of the equatorial maxima, which are a measure of intermolecular spacing, varied considerably, being smallest in the specimens displaying crystalline packing. The intermolecular distance in chiken and turkey leg tendons is longer than that found in mammalian tendons, or in avian wing tendons, which supports the hypothesis that a larger intermolecular spacing is characteristic of tendons that calcify. Thus, x-ray diffraction indicates there are reproducible differences in both the axial and lateral structure of collagen fibrils among different tendons. This work on tendon, a tissue containing almost exclusively Type I collagen as its major component, should serve as a basis for analyzing the structure of other connective tissues, which contain different genetic types of collagen and larger amounts of noncollagenous components.     

Effect of Chronic Lead Ingestion by Rats on Glucose Metabolism and Acetylcholine Synthesis in Cerebral Cortex Slices

Abstract: The effect of chronic low-level lead (Pb²⁺) ingestion on the metabolic pathways leading to the acetyl moiety of acetylcholine (ACh) was examined. Cerebral cortex slices, prepared from untreated or Pb²⁺-exposed rats (600 ppm lead acetate in the drinking water for 20 days), were incubated in Krebs-Ringer bicarbonate buffer with 10 m M glucose and tracer amounts of [6-³H]glucose and either [6-¹⁴C]glucose or [3-¹⁴C] β -hydroxybutyrate. Altering the concentration of Pb²⁺ in the drinking water produced a dose-related increase in blood and brain lead levels. When tissue from Pb²⁺-exposed rats was incubated with mixed-labeled glucose, incorporation into lacate, citrate, and ACh was considerably decreased, although no changes occurred in the ³H/¹⁴C ratios. Similar effects of Pb²⁺ were found when ¹⁴C-labeled β -hydroxy-butyrate was substituted for the [¹⁴C]glucose. It appears from these data that Pb²⁺ exerts a generalized effect on energy metabolism and not on a specific step in glucose metabolism. The impairment of glucose metabolism may explain partially the Pb²⁺-induced changes observed in cholinergic function.     

Enzymatic resolution of racemic amines in a continuous reactor in organic solvents

An enzymatic process has been developed for the continuous production of the pharmaceutically important intermediate (R)-1-aminoindan and of the chiral resolving agent (R)-1-(1-naphthyl)ethylamine. The process consists of the subtilisin catalyzed stereoselective aminolysis of the racemic primary amine with an active ester in organic solvent. The competing nonenzymatic reaction has been suppressed by appropriate choice of solvent and reactant's concentration and by minimizing the time of contact between the amine and the active ester. Subtilisin was immobilized on glass beads and the reaction carried out in a continuous-flow column bioreactor. By using a 450-mL column bioreactor containing 5.7 g of subtilisin immobilized on 570 g of glass beads, 1.6 kg of racemic 1-(1-naphthyl)ethylamine was resolved after 320 h of continuous operation with only a slight loss of the enzymatic activity. During the whole process, the optical purity of the chiral amine eluting from the column was higher than 90%. A facile procedure was developed for separating the unreacted (R)-amine from the (S)-amide and for the recycling of the solvent 3-methyl-3-pentanol and the active ester 2,2,2-trifluoroethyl butyrate. (c) 1992 John Wiley & Sons, Inc.     

Investigations into the pathway of electron transport to the nitrogenase from nodule bacteroids

Summary A series of investigations were conducted with the objective of elucidating natural pathways of electron transport from respiratory processes to the site of N₂ fixation in nodule bacteroids. A survey of dehydrogenase activities in a crude extract of soybean nodule bacteroids revealed relatively high activities of NAD-specific β-hydroxybutyrate and glyceraldehyde-3-phosphate dehydrogenases. Moderate activities of NADP-specific isocitrate and glucose-6-phosphate dehydrogenases were observed. By use of the ATP-dependent acetylene reduction reaction catalyzed by soybean bacteroid nitrogenase, and enzymes and cofactors from bacteroids and other sources, the following sequences of electron transport to bacteroid nitrogenase were demonstrated: (1) H₂ to bacteroid nitrogenase in presence of a nitrogenase-free extract ofC. pasteurianum; (2) β-hydroxybutyrate to bacteroid nitrogenase in a reaction containing β-hydroxybutyrate dehydrogenase, NADH dehydrogenase, NAD and benzyl viologen; (3) β-hydroxybutyrate dehydrogenase, to nitrogenase in reaction containing NADH dehydrogenase, NAD and either FMN or FAD; (4) light-dependent transfer of electrons from ascorbate to bacteroid nitrogenase in a reaction containing photosystem I from spinach chloroplasts, 2,6-dichlorophenolindophenol, and either azotoflavin from Azotobacter or non-heme iron protein from bacteroids; (5) glucose-6-phosphate to bacteroid nitrogenase in a system that included glucose-6-phosphate dehydrogenase, NADP, NADP-ferredoxin reductase from spinach, azotoflavin from Azotobacter and bacteroid non-heme iron protein. The electron transport factors, azotoflavin and bacteroid non-heme iron protein, failed to function in the transfer of electrons from an NADH-generating system to bacteroid nitrogenase. When FMN or FAD were added to systems containing azotoflavin and bacteroid non-heme iron protein, electrons apparently were transferred to the flavin-nucleotides and then nitrogenase without involvement of azotoflavin and bacteroid non-heme iron protein. Evidence is available indicating that nodule bacteroids contain flavoproteins analogous to Azotobacter, azotoflavin, and spinach ferredoxin-NADP reductase. It is concluded that physiologically important systems involved in transport of electrons from dehydrogenases to nitrogenase in bacteroids very likely will include relatively specific electron transport proteins such as bacteroid non-heme iron protein and a flavoprotein from bacteroids that is analogous to azotoflavin.     

The distribution of nuclear progesterone receptor in the hypothalamus and forebrain of the domestic hen

Summary Cell nuclei containing progesterone receptor were identified immunohistochemically in the hypothalamus and forebrain of the domestic hen using an antiserum to the steroid binding B subunit (110 kDa) of chicken oviduct progesterone receptor and the avidin-biotin complex procedure. Cell nuclei containing progesterone receptor were widely distributed in the anterior, medial and basal hypothalamus with the highest density occurring in the lamina terminalis and the preoptic area. Abundant, though less intensely reacting progesterone receptor was present in cell nuclei in the tuberal infundibular area and in the internal zone of the median eminence. A large group of cell nuclei containing progesterone receptor occurred in the dorsal anterior hypothalamus between the anterior commissure and the lateral ventricle. This group of nuclei extended anteriorly into the telencephalon. A small number of cell nuclei containing progesterone receptor was also found in the ventral telencephalon in the region of the nucleus accumbens.     

TAXONOMIC IMPLICATIONS OF EXTERNAL POLLEN MORPHOLOGY TO VERNONIA (COMPOSITAE) IN THE WEST INDIES

External pollen morphology of 39 species of West Indian Vernonias was examined by light and scanning electron microscopy in conjunction with a systematic revision of these species. There were three distinct types of pollen: Type A: subechinolophate, tricolporate grains with prominent spines; Type B: echinolophate, tricolporate with expanded germinal furrows and coincident polar muri; Type C: echinolophate, tricolporate grains with prominent polar lacunae. Pollen grains intermediate between the major types were found in several species. These same species had very distinct and atypical megamorphologies. In general, pollen types were found to correlate well with classification based on megamorphological characters, particularly at the infrageneric level, and to provide confirmation of subsectional assignments in the genus.