Excretory-secretory products of Echinostoma paraensei sporocysts mediate interference with Biomphalaria glabrata hemocyte functions.

Miracidia of Echinostoma paraensei were cultured in medium containing 14C-labeled amino acids, allowed to transform into sporocysts, and their excretory/secretory products (E-S) were collected and characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis and autoradiography. Effects of E-S on hemocytes of Biomphalaria glabrata were also assessed. E-S collected during day 1 of culture (E-S1) contained several polypeptides, none of which were labeled, suggesting that E-S1 are largely preformed. E-S1 significantly depressed the ability of hemocytes to phagocytose sheep red blood cells (SRBC), but otherwise had little effect on hemocyte structure or behavior. E-S released by sporocysts in day-2 cultures (E-S2) and in older cultures generally were similar and also contained several polypeptides, many of which were labeled, indicating active synthesis of E-S in vitro. E-S2 strongly inhibited hemocyte uptake of SRBC. Also, hemocytes pretreated with E-S2 assumed a spherical shape and failed to spread normally. E-S obtained through 10 days of culture mediated this effect. Active components of E-S2 were greater than 100 kDa in their native configuration, were heat- and trypsin-labile, and were bound by anti-E-S antibodies. Both greater than 200- and 80-kDa bands were prominent in anti-E-S immunoprecipitates. Hemocytes derived from snails of the 13-16-R1 strain of B. glabrata (a strain resistant to infection with Schistosoma mansoni), when pretreated with E-S2, bound to sporocysts of S. mansoni but lost their ability to damage such sporocysts. E-S2 interfered with hemocyte functions in ways inferred from earlier classic in vivo studies of trematode-snail interactions.     

Sequential appearance of epidermal growth factor in plasma membrane-associated and intracellular vesicles during endocytosis

Receptor-mediated internalization of epidermal growth factor (EGF) occurs by a process involving initially clathrin-coated pits on the cell surface and the subsequent formation of ligand-containing endosomes. Using a modified acid wash technique, cell surface-bound EGF was removed. Utilizing sucrose density centrifugation, the residual cell-associated EGF was separated into plasma membrane-associated and intracellular vesicle-associated forms. Using these procedures we have identified a transient form of cell-associated EGF that is still attached to the plasma membrane but not accessible to the extracellular fluid. This form of EGF appears to be the precursor for endosomic EGF. We suggest that this intermediate form represents the receptor-ligand complex shown by electronmicroscopy to be located in narrow-necked plasma membrane invaginations (Willingham, M. C., and Pastan, I. (1980) Cell 21, 67-77).     

Amyloplasts are necessary for full gravitropic sensitivity in roots of Arabidopsis thaliana

The observation that a starchless mutant (TC7) of Arabidopsis thaliana (L.) Heynh. is gravitropic (T. Caspar and B.G. Pickard, 1989, Planta 177, 185–197) raises questions about the hypothesis that starch and amyloplasts play a role in gravity perception. We compared the kinetics of gravitropism in this starchless mutant and the wild-type (WT). Wild-type roots are more responsive to gravity than TC7 roots as judged by several parameters: (1) Vertically grown TC7 roots were not as oriented with respect to the gravity vector as WT roots. (2) In the time course of curvature after gravistimulation, curvature in TC7 roots was delayed and reduced compared to WT roots. (3) TC7 roots curved less than WT roots following a single, short (induction) period of gravistimulation, and WT, but not TC7, roots curved in response to a 1-min period of horizontal exposure. (4) Wild-type roots curved much more than TC7 roots in response to intermittent stimulation (repeated short periods of horizontal exposure); WT roots curved in response to 10 s of stimulation or less, but TC7 roots required 2 min of stimulation to produce a curvature. The growth rates were equal for both genotypes. We conclude that WT roots are more sensitive to gravity than TC7 roots. Starch is not required for gravity perception in TC7 roots, but is necessary for full sensitivity; thus it is likely that amyloplasts function as statoliths in WT Arabidopsis roots. Furthermore, since centrifugation studies using low gravitational forces indicated that starchless plastids are relatively dense and are the most movable component in TC7 columella cells, the starchless plastids may also function as statoliths.Abbreviations S2 story two - S3 story three - WT wild-type     

Cephalodiate Arten der GattungLecidea sensu lato (Ascomycetes lichenisati)

(1) The ability to produce cephalodia is usually a genus-specific character in lichens. (2)Lecidea shushanii Thoms., is a member of the genusTephromela, closely related toT. aglaea. It is not clear, whether or not the cephalodia of this taxon are true cephalodia or colonies of epiphytic cyanobacteria and whether or notLecidea shushanii is an independent species. (3)Lecidea dovrensis Nyl., is, in contrast to the traditional concept, not conspecific withLecidea alpestris Sommerf., but an earlier name forLecidea pallida Th. Fr. (4)Lecidea dovrensis is described in some detail. Chemically the species is characterized by the presence of isousnic acid (previously unknown in lecideoid lichens). It is restricted to areas north of the 60th parallel with an oceanic climate. (5) In connection with the attempt to clarify the taxonomic relationships ofLecidea dovrensis, figures of ascus apical structures of the following species are given (marked by an asterisk are genera where we found discrepancies with published data):Austrolecia antarctica, Catillaria chalybeia, Lecidea alpestris, L. caesioatra, L. limosa, Lecidoma demissum, Koerberiella wimmeriana, Micarea assimilata, M. crassipes, M. melaenida, M. prasina, Pilophorus robustus, Placodiella olivacea, Placolecis opaca, Porpidia trullisata, Protoblastenia rupestris, Psilolechia lucida, Psorula rufonigra, Squamarina gypsacea, Xanthopsorella texana. (6) Among crustaceous lichens we find no groups related toLecidea dovrensis. We supportTimal's concept of including this species in the genusPilophorus. Pilophorus, as well asLecidea dovrensis is characterized by the same ascus type, by a similar structure of thallus, cephalodia, paraphyses, and ascocarp (although there is no pseudopodetium developed inLecidea dovrensis), and the presence of isousnic acid. In addition, both taxa are restricted to cool oceanic climates and non-calciferous substrates. The following combination is proposed:Pilophorus dovrensis (Nyl.)Timdal, Hertel & Rambold, comb. nova. (7) The species of theLecidea alpestris-group form an independent genus, probably near toAustrolecia Hertel.

Frau Prof. Dr.Elisabeth Tschermak-Woess zu ihrem 70. Geburtstag gewidmet.     

Structural organization of the beta-globin locus of B-haplotype sheep

Goats and some sheep synthesize a juvenile hemoglobin, Hb C (alpha 2 beta C2), at birth and produce this hemoglobin exclusively during severe anemia. Sheep that synthesize this juvenile hemoglobin are of the A haplotype. Other sheep, belonging to a separate group, the B haplotype, do not synthesize hemoglobin C and during anemia continue to produce their adult hemoglobin. To understand the basis for this difference we have determined the structural organization of the beta- globin locus of B-type sheep by constructing and isolating overlapping genomic clones. These clones have allowed us to establish the linkage map 5' epsilon I-epsilon II-psi beta I-beta B-epsilon III-epsilon IV- psi beta II-beta F3' in this haplotype. Thus, B sheep lack four genes, including the BC gene, and have only eight genes, compared with the 12 found in the goat globin locus. The goat beta-globin locus is as follows: 5' epsilon I-epsilon II-psi beta X-beta C-epsilon III-epsilon IV-psi beta Z-beta A-epsilon V-epsilon VI-psi beta Y-beta F3'. Southern blot analysis of A-type sheep reveals that these animals have a beta- globin locus similar to that of goat, i.e., 12 globin genes. Thus, the beta-globin locus of B-haplotype sheep resembles that of cows and may have retained the duplicated locus of the ancestor of cows and sheep. Alternatively, the B-sheep locus arrangement may be the result of a deletion of a four-gene set from the triplicated locus.      

Kinetic characterization of reduced pyridine nucleotide dehydrogenases (duroquinone-dependent) in cucurbita microsomes

Stomatal conductances of normally oriented and inverted leaves were measured as light levels (photosynthetic photon flux densities) were increased to determine whether abaxial stomata of Vicia faba leaves were more sensitive to light than adaxial stomata. Light levels were increased over uniform populations of leaves of plants grown in an environmental chamber. Adaxial stomata of inverted leaves reached maximum water vapor conductances at a light level of 60 micromoles per square meter per second, the same light level at which abaxial stomata of normally oriented leaves reached maximum conductances. Abaxial stomata of inverted leaves reached maximum conductances at a light level of 500 micromoles per square meter per second, the same light level at which adaxial stomata of normally oriented leaves reached maximum conductances. Maximum conductances in both normally oriented and inverted leaves were about 200 millimoles per square meter per second for adaxial stomata and 330 millimoles per square meter per second for abaxial stomata. Regardless of whether leaves were normally oriented or inverted, when light levels were increased to values high enough that upper leaf surfaces reached maximum conductances (about 500 micromoles per square meter per second), light levels incident on lower, shaded leaf surfaces were just sufficient (about 60 micromoles per square meter per second) for stomata of those surfaces to reach maximum conductances. This `coordinated' stomatal opening on the separate epidermes resulted in total leaf conductances for normally oriented and inverted leaves that were the same at any given light level. We conclude that stomata in abaxial epidermes of intact Vicia leaves are not more sensitive to light than those in adaxial epidermes, and that stomata in leaves of this plant do not respond to light alone. Additional factors in bulk leaf tissue probably produce coordinated stomatal opening on upper and lower leaf epidermes to optimally meet photosynthetic requirements of the whole leaf for CO₂.     

A comparison of catecholamine-induced internalization of beta-adrenergic receptors and receptor-mediated endocytosis of epidermal growth factor in human astrocytoma cells. Inhibition by phenylarsine oxide

The ligand-induced internalization of beta-adrenergic receptors and the receptor-mediated internalization of epidermal growth factor were blocked, under similar conditions, by phenylarsine oxide (PAO) in human astrocytoma cells (1321N1). The inhibition was not prevented or reversed by monofunctional sulfhydryl agents such as 2-mercaptoethanol or glutathione; however, the inhibitory action of PAO was blocked and reversed by bifunctional thiols such as 2,3-dimercaptoethanol or dithiothreitol. The results are consistent with the interaction of PAO with vicinal sulfhydryl groups to form a stabile ring structure. PAO did not prevent isoproterenol-induced uncoupling (desensitization) of beta-adrenergic receptors even though receptor internalization was completely blocked. The effects of PAO on receptor internalization could not be explained by any action of the trivalent arsenical to lower ATP levels. Ligand binding to both receptors was not detectably altered by PAO under conditions selective for inhibition for endocytosis. The results suggest a common mechanism for internalization of beta-adrenergic receptors and epidermal growth factor by a process that involves vicinal sulfhydryl groups.     

Eimeria species (Apicomplexa: Eimeriidae) infecting Peromyscus rodents in the southwestern United States and northern Mexico with description of a new species

Of 198 deermice (Peromyscus spp) collected from various localities in the southwestern United States and northern Mexico, 106 (54%) had eimerian oocysts in their feces when examined. These included 50 of 106 (47%) Peromyscus truei, 34 of 54 (63%) Peromyscus maniculatus, 4 of 17 (24%) Peromyscus leucopus, and 18 of 21 (86%) Peromyscus eremicus. The following Eimeria were identified from infected mice: Eimeria arizonensis and Eimeria langebarteli from P. truei; E. arizonensis, Eimeria peromysci, and Eimeria delicata from P. maniculatus; E. arizonensis and Eimeria lachrymalis n. sp. from P. eremicus; and E. langebarteli from P. leucopus. Of the 106 Peromyscus found positive for Eimeria, 97 (91.5%) harbored only a single eimerian species at the time of examination. Sporulated oocysts of E. lachrymalis n. sp. were ellipsoid, 27-35 X 17-21 (30.8 +/- 1.7 X 19.1-0.9) micron, possessed a smooth wall and one polar granule, but lacked a micropyle and an oocyst residuum. Sporocysts were teardrop-shaped, 9-13 X 6-10 (10.9 +/- 0.9 X 7.9 +/- 0.5) micron, and had a Stieda body and sporocyst residuum, but no substieda body. Prepatent periods in experimental infections were 3-6 days after inoculation (DAI) for E. arizonensis (hosts: P. eremicus, P. maniculatus, P. truei); 4-5 DAI for E. peromysci (host: P. maniculatus); 6-9 DAI for E. langebarteli (hosts: P. truei, P. leucopus); and 8-10 DAI for E. lachrymalis (host: P. eremicus). Patency in these infections lasted 6-11 days for E. arizonensis, 5-10 days for E. peromysci, 14-40+ days for E. langebarteli, and 19-50+ days for E. lachrymalis. Eimeria lachrymalis appears to produce occult infections in P. eremicus that can be reactivated upon inoculation of the host with E. arizonensis.     

Spectral sensitivity of photoreceptors in insect compound eyes: Comparison of species and methods

Summary Three different methods were used to determine the spectral sensitivity of retinula cells in the compound eyes of three species of hymenopteran insects (Apis mellifera, Melipona quadrifasciata, Osmia rufa). The conventional flash method gives the least reliable results. Sensitivity is extremely sensitive to small fluctuations of the resting potential and long lasting changes induced by preceding test flashes. The ramp method, which speeds up a spectral scan to about 1 min and keeps effective illumination constant at every flash, determines S() much more reliably. The best results are obtained with the spectral scan method, which provides the experimenter with aS() function of high spectral resolution within 20 s. Using this method we demonstrate that the high observed variability inS() of individual receptors is the result of the inadequacy of the flash method, which was the only method used in earlier studies.Double microelectrode experiments and variations of the stimulus conditions reveal that field potentials and return flow of electric current produced by activated neighboring cells have no effect in the bee eye. We conclude that the model of Shaw (1975, 1981) of current flow in the locust and fly eye does not apply to the bee eye. Very rare recordings (about 1%) of UV receptors with hyperpolarizing responses to long wavelength light are interpreted as having a synaptic inhibitory connection to green receptors.The improvement of spectral measurements of single receptors allows us for the first time to model the spectral input to a color-coding network with great precision.     

Evidence for the appearance of an uncoupled form of the beta-adrenergic receptor distinct from the internalized receptor

Agonist treatment of C6-glioma cells induces two altered states in beta-adrenergic receptors, a low affinity for the hydrophilic antagonist CGP-12177 and a low affinity for agonists like isoproterenol. We present evidence that, in cells not treated to inhibit receptor internalization, the two properties occur with a different time course, the low affinity for isoproterenol preceding that for CGP-12177. In that the low affinity for CGP-12177 is due to the internalization of the receptor, the results indicate that uncoupling of the receptor, indicated by the low affinity for isoproterenol, occurs while the receptor is still located on the cell surface. Removal of the agonist leads to reappearance of the receptor to the plasma membrane followed by loss of the uncoupled state.