EXTRUSION OF NUCLEOLI FROM PRONUCLEI OF THE RAT

Electron microscope observations of osmium tetroxide-fixed rat eggs indicate that small nucleoli are extruded from pronuclei in a sharply demarcated time period after sperm penetration. Approximately 4½ hours after sperm penetration, fine fibrous material aggregated in distinct loci along the inner surface of the nuclear envelope and condensed into small, dense bodies. The term tertiary nucleolus or extrusion body is used to designate the forming bodies. The small tertiary nucleoli form distinct protrusions from the pronuclei during the following developmental period and finally bud off into the cytoplasm, carrying with them a small portion of the double nuclear envelope. The extrusion bodies can be observed only in the vicinity of the pronuclei and have not been seen near the cell membrane. The fate of the tertiary nucleoli is not known; apparently they transform or disappear after they have passed into the cytoplasm. Eleven hours after sperm penetration, tertiary nucleoli are not present near the nuclear membrane and the extrusion activity has apparently ceased. Large and small nucleoli react similarly to cytochemical reagents: they are Feulgen negative; they are positive to the Millon, Sakaguchi, brom-phenol blue, and PAS reactions. Azure B stain combined with nuclease extraction indicates the presence of small amounts of RNA in the nucleoli.     

Phenotypic variation during micropropagation of the chimeralRhododendron ‘President Roosevelt’

The putative periclinal chimeraRhododendron xlimbatum President Roosevelt was used to study the origin of shoots in vitro. Genotypic segregation readily occurred in vitro. Numerous phenotypes were observed, although most shoots were either entirely green or maintained the original variegation pattern. Derivatives of the third apical layer were rarely involved in shoot formation. A reversed chimeral form was isolated. Adventitious shoots were usually miniaturized and rapidly proliferating, but axillary shoots had thicker stems, larger leaves and proliferated more slowly. Corolla tissue produced stunted, leafy shoots; no variegated shoots were produced from floret explants. In shoot tip cultures the addition of 40M 2iP without IBA resulted in the greatest number of shoots. Explant choice was the most critical factor for maintenance of foliar variegation.     

Phylogenetic systematic evaluation of a classification of the Zoogonidae Odhner, 1902 (Cercomeria: Trematoda: Digenea: Plagiorchiiformes)

A recent systematic study of the digenean family Zoogonidae presented a series of cladograms, which are the product of phylogenetic systematic, or cladistic, analysis. However, one of the two subfamilies and nine of the 21 genera recognised in that study lacked putative synapomorphies, a requirement for phylogenetic systematic studies. This study presents a re-analysis of the database for the zoogonids, based on rigorous application of phylogenetic systematic methods. A new phylogenetic tree is presented, which better fits the original data than the published tree (with a consistency index of 52.3% vs. 46.3%). Four subfamilies, three monophyletic and one of uncertain status, and 10 genera could be recognised phylogenetically. This would affect the nomenclatorial status of one-third (26) of the species in the family. However, it is recommended that another analysis, based on more characters, be carried out before nomenclatorial changes are proposed.     

Induction and ionic basis of slow wave potentials in seedlings of Pisum sativum L.

Slow wave potentials (SWPs) are transient depolarizations which propagate substantial distances from their point of origin. They were induced in the epidermal cells of pea epicotyls by injurious methods such as root excision and heat treatment, as well as by externally applied defined steps in xylem pressure (Px) in the absence of wounding. The common principle of induction was a rapid increase in Px. Such a stimulus appeared under natural conditions after (i) bending of the epicotyl, (ii) wounding of the epidermis, (iii) rewatering of dehydrated roots, and (iv) embolism. The induced depolarization was not associated with a change in cell input resistance. This result and the ineffectiveness of ion channel blockers point to H(+)-pumps rather than ion channels as the ionic basis of the SWP. Stimuli such as excision, heat treatment and pressure steps, which generate SWPs, caused a transient increase in the fluorescence intensity of epicotyls loaded with the pH-indicator DM-NERF, a 2',7'-dimethyl derivative of rhodol, but not of those loaded with the pH indicator 2',7'bis(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF). Matching kinetics of depolarization and pH response identify a transient inactivation of proton pumps in the plasma membrane as the causal mechanism of the SWP. Feeding pump inhibitors to the cut surface of excised epicotyls failed to chemically simulate a SWP; cyanide, azide and 2,4-dinitrophenol caused sustained, local depolarizations which did not propagate. Of all tested substances, only sodium cholate caused a transient and propagating depolarization whose arrival in the growing region of the epicotyl coincided with a transient growth rate reduction.     

AdaptivSearch: A Novel Iterative Algorithm for the Generation of n-dimensional Hypersurfaces Using an Adaptive Numerical Strategy

AdaptivSearch is the first adaptive strategy based algorithm for the rational and economical construction of n-dimensional hypersurfaces. AdaptivSearch works iteratively: At each step it parcels out the definition range into several triangles, evaluates the worst according to a built-in error criterion, and refines the approximation to the unknown function by choosing the barycenter of this partial area as the node to be calculated next. Based upon the error criterion, AdaptivSearch selectively approaches those parts of the hypersurface in which the curvature exhibits the strongest changes. Some examples of AdaptivSearch applications for both analytical functions and chemical model surfaces are given in order to demonstrate the behavior of the algorithm. These show its broad applicability and the usefulness, especially for chemical problems.     

Cell surface adhesion receptors

Several new structural motifs found in cell surface adhesion receptors have been described in the past few years. Also, several two-domain structures of extracellular portions of cell surface proteins have been reported. Structural models for complexes between receptors and counter-receptors have been proposed. The first reports on carbohydrate conformation in intact glycoprotein domains have recently appeared. These new data are presented within a more general review of the field of cell adhesion receptors.     

Alzheimer's disease-like phosphorylation of the microtubule-associated protein tau by glycogen synthase kinase-3 in transfected mammalian cells

Background: Paired helical filaments (PHFs) are a characteristic pathological feature of Alzheimer's disease; their principal component is the microtubule-associated protein tau. The tau in PHFs (PHF-tau) is hyperphosphorylated, but the cellular mechanisms responsible for this hyperphosphorylation have yet to be elucidated. A number of kinases, including mitogen-activated protein (MAP) kinase, glycogen synthase kinase (GSK)-3α, GSK-3β and cyclin-dependent kinase-5, phosphorylate recombinant tau in vitro so that it resembles PHF-tau as judged by its reactivity with a panel of antibodies capable of discriminating between normal tau and PHF-tau, and by a reduced electrophoretic mobility that is characteristic of PHF-tau. To determine whether MAP kinase, GSK-3α and GSK-3β can also induce Alzheimer's disease-like phosphorylation of tau in mammalian cells, we studied the phosphorylation status of tau in primary neuronal cultures and transfected COS cells following changes in the activities of MAP kinase and GSK-3.Results Activating MAP kinase in cultures of primary neurons or transfected COS cells expressing tau isoforms did not increase the level of phosphorylation for any PHF-tau epitope investigated. But elevating GSK-3 activity in the COS cells by co-transfection with GSK-3α or GSK-3β decreased the electrophoretic mobility of tau so that it resembled that of PHF-tau, and induced reactivity with eight PHF-tau-selective monoclonal antibodies.Conclusion Our data indicate that GSK-3α and/or GSK-3β, but not MAP kinase, are good candidates for generating PHF-type phosphorylation of tau in Alzheimer's disease. The involvement of other kinases in the generation of PHFs cannot, however, be eliminated. Our results suggest that aberrant regulation of GSK-3 may be a pathogenic mechanism in Alzheimer's disease.     

Optimization of transverse alternating field electrophoresis for strain identification of Leuconostoc oenos

Genomic DNA of several strains oof oenological lactic bacteria belonging to the species Lactobacillus plantarum, Leuconostoc oenos and Pediococcus pentosaceus was digested by the rare-cutting endonucleases ApaI and SmaI. The restriction products were separated by transverse alternating field electrophoresis (TAFE). The size of the genome of L. oenos estimated by adding the molecular size of the ApaI fragments was on average 1320 kb. A strong polymorphism was observed between the strains, which could be easily differentiated except for two industrial strains of L. oenos. A simple modification of the TAFE apparatus is proposed to improve the separation of the DNA fragments. Correspondence to: J.-N. Hallet