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51.
52.
A new genus of Platycopioida is described from a boxcore sample taken at a depth of 534 m in the ArcticBarents Sea. This is the deepest record ofPlatycopioida so far. Sarsicopia gen. n. is thesistergroup of a taxon comprising Platycopia and Nanocopia; the sistergroup ofthese is Antrisocopia. Sarsicopia gen. n.is the only platycopioid to retain 2 inner setae onthe second endopod segment P2–P4, and 8 setae in thethird endopod segment of P2. The male antennnule isremarkable in having a geniculation located betweenancestral segments XX and XXI. It is suggested thatthis flexure zone was already present in thegroundpattern of Copepoda. Platycopia and Nanocopia have secondarily lost thisgeniculation. 相似文献
53.
Pedro J.I. Salas Marcelo L. Rodriguez Ana L. Viciana Dora E. Vega-Salas Hans-Peter Hauri 《The Journal of cell biology》1997,137(2):359-375
In a previous publication (Rodriguez, M.L., M. Brignoni, and P.J.I. Salas. 1994. J. Cell Sci. 107: 3145–3151), we described the existence of a terminal web-like structure in nonbrush border cells, which comprises a specifically apical cytokeratin, presumably cytokeratin 19. In the present study we confirmed the apical distribution of cytokeratin 19 and expanded that observation to other epithelial cells in tissue culture and in vivo. In tissue culture, subconfluent cell stocks under continuous treatment with two different 21-mer phosphorothioate oligodeoxy nucleotides that targeted cytokeratin 19 mRNA enabled us to obtain confluent monolayers with a partial (40–70%) and transitory reduction in this protein. The expression of other cytoskeletal proteins was undisturbed. This downregulation of cytokeratin 19 resulted in (a) decrease in the number of microvilli; (b) disorganization of the apical (but not lateral or basal) filamentous actin and abnormal apical microtubules; and (c) depletion or redistribution of apical membrane proteins as determined by differential apical–basolateral biotinylation. In fact, a subset of detergent-insoluble proteins was not expressed on the cell surface in cells with lower levels of cytokeratin 19. Apical proteins purified in the detergent phase of Triton X-114 (typically integral membrane proteins) and those differentially extracted in Triton X-100 at 37°C or in n-octyl-β-d-glycoside at 4°C (representative of GPIanchored proteins), appeared partially redistributed to the basolateral domain. A transmembrane apical protein, sucrase isomaltase, was found mispolarized in a subpopulation of the cells treated with antisense oligonucleotides, while the basolateral polarity of Na+– K+ATPase was not affected. Both sucrase isomaltase and alkaline phosphatase (a GPI-anchored protein) appeared partially depolarized in A19 treated CACO-2 monolayers as determined by differential biotinylation, affinity purification, and immunoblot. These results suggest that an apical submembrane cytoskeleton of intermediate filaments is expressed in a number of epithelia, including those without a brush border, although it may not be universal. In addition, these data indicate that this structure is involved in the organization of the apical region of the cytoplasm and the apical membrane.Cell polarity (asymmetry) is a broadly distributed and highly conserved feature of many different cell types, from prokaryotes to higher eukaryotes (Nelson, 1992). In multicellular organisms it is more conspicuous in, but not restricted to, neurons and epithelial cells. In the latter, the plasma membrane is organized in two different domains, apical and basolateral. This characteristic enables epithelia to accomplish their most specialized roles including absorption and secretion and, in general, to perform the functions of organs with an epithelial parenchyma such as the kidney, liver, intestine, stomach, exocrine glands, etc. (Simons and Fuller, 1985; Rodriguez-Boulan and Nelson, 1989).The acquisition and maintenance of epithelial polarity is based on multiple interrelated mechanisms that may work in parallel. Although the origin of polarization depends on the sorting of apical and basolateral membrane proteins at the trans-Golgi network (Simons and Wandinger-Ness, 1990), the mechanisms involved in the transport of apical or basolateral carrier vesicles, the specific fusion of such vesicles to the appropriate domain, and the retention of membrane proteins in their correct positions are also important (Wollner and Nelson, 1992). Various components of the cytoskeleton seem to be especially involved in these mechanisms (Mays et al., 1994). Among them, the microtubules, characteristically oriented in the apical–basal axis with their minus ends facing toward the apical domain, appear in a strategic position to transport carrier vesicles (Bacallao et al., 1989). This orientation is largely expected because of the apical distribution of centrioles and microtubule organizing centers in epithelial cells (Buendia et al., 1990). The molecular interactions responsible for that localization, however, are unknown.Actin is a widespread component of the membrane skeleton found under apical, lateral, and basal membranes in a nonpolarized fashion (Drenckhahn and Dermietzel, 1988; Vega-Salas et al., 1988). Actin bundling into microvillus cores in the presence of villin/fimbrin, on the other hand, is highly polarized to the apical domain (Ezzell et al., 1989; Louvard et al., 1992). In fact, different isoforms of plastins determine microvillus shape in a tissue-specific manner (Arpin et al., 1994b
). Why this arrangement is not found in other actin-rich regions of the cell is unclear (Louvard et al., 1992; Fath and Burgess, 1995).Fodrin, the nonerythroid form of spectrin, underlies the basolateral domain (Nelson and Veshnock, 1987a
,b) and is known to participate in the anchoring/retention of basolateral proteins (Drenckhahn et al., 1985; Nelson and Hammerton, 1989). Although different groups have found specific cytoskeletal anchoring of apical membrane proteins at the “correct” domain (Ojakian and Schwimmer, 1988; Salas et al., 1988; Parry et al., 1990), no specific apical counterpart of the basolateral fodrin cytoskeleton is known. This is especially puzzling since we showed that MDCK cells can maintain apical polarity in the absence of tight junctions, an indication that intradomain retention mechanisms are operational for apical membrane proteins (Vega-Salas et al., 1987a
).It is known that a network of intermediate filament (IF)1, the major component of the terminal web, bridges the desmosomes under the apical membrane in brush border cells (Franke et al., 1979; Hull and Staehelin, 1979; Mooseker, 1985), although no specific protein has been identified with this structure. The observation of a remarkable resistance to extractions of apical proteins anchored to cytoskeletal preparations (Salas et al., 1988) comparable to that of intermediate filaments, led us to the study of cytokeratins in polarized cells. We developed an antibody against a 53-kD intermediate filament protein in MDCK cells. This protein was found to be distributed exclusively to the apical domain and to form large (2,900 S) multi-protein complexes with apical plasma membrane proteins. Internal microsequencing of the 53-kD protein showed very high (95– 100%) homology with two polypeptides in the rod domain of cytokeratin 19 (CK19; Moll et al., 1982) a highly conserved and peculiar intermediate filament protein (Bader et al., 1986). A complete identification however, could not be achieved (Rodriguez et al., 1994). The present study was undertaken to establish that identity and to determine the possible functions of this apical membrane skeleton. Because cytokeratins have been poorly characterized in canine cells, and no cytokeratin sequences are available in this species, we decided to switch from MDCK cells to two human epithelial cell lines, CACO-2, an extensively studied model of epithelial polarization that differentiates in culture to form brush border containing cells (Pinto et al., 1983), and MCF-10A (Tait et al., 1990), a nontumorigenic cell line derived from normal mammary epithelia, as a model of nonbrush border cells.To assess possible functions of cytokeratin 19, we chose to selectively reduce its synthesis using anti-sense phosphorothioate oligodeoxy nucleotides, an extensively used approach in recent years (e.g., Ferreira et al., 1992 ; Hubber et al., 1993; Takeuchi et al., 1994). Although we could not achieve a complete knock out, the steady-state levels of cytokeratin 19 were decreased to an extent that enabled us to detect significant changes in the phenotype of CACO-2 and MCF-10A cells. 相似文献
54.
55.
A Genetic Polymorphism in Coumarin 7-Hydroxylation: Sequence of the Human CYP2A Gnes and Identification of Variant CYP2A6 Alleles
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Pedro Fernandez-Salguero Susan M. G. Hoffman Suzanne Cholerton Harvey Mohrenweiser Hannu Raunio Arja Rautio Olavi Pelkonen Jin-ding Huang William E. Evans Jeffrey R. Idle Frank J. Gonzalez 《American journal of human genetics》1995,57(3):651-660
A group of human cytochrome P450 genes encompassing the CYP2A, CYP2B, and CYP2F subfamilies were cloned and assembled into a 350-kb contig localized on the long arm of chromosome 19. Three complete CYP2A genes—CYP2A6, CYP2A7, and CYP2A13—plus two pseudogenes truncated after exon 5, were identified and sequenced. A variant CYP2A6 allele that differed from the corresponding CYP2A6 and CYP2A7 cDNAs previously sequenced was found and was designated CYP2A6ν2. Sequence differences in the CYP2A6ν2 gene are restricted to regions encompassing exons 3, 6, and 8, which bear sequence relatedness with the corresponding exons of the CYP2A7 gene, located downstream and centromeric of CYP2A6ν2, suggesting recent gene-conversion events. The sequencing of all the CYP2A genes allowed the design of a PCR diagnostic test for the normal CYP2A6 allele, the CYP2A6ν2 allele, and a variant—designated CYP2A6ν1—that encodes an enzyme with a single inactivating amino acid change. These variant alleles were found in individuals who were deficient in their ability to metabolize the CYP2A6 probe drug coumarin. The allelic frequencies of CYP2A6ν1 and CYP2A6ν2 differed significantly between Caucasian, Asian, and African-American populations. These studies establish the existence of a new cytochrome P450 genetic polymorphism. 相似文献
56.
A newZornia species from Cuba, the endemicZornia arenicola sp. nova, is described. It was found on moving sand dunes between the town of Guane and the village of Cortes (Pinar del Rio province). 相似文献
57.
Some behavioral and physical defenses of Lymantria dispar (L.) pupae are described. It was found that the layer of webbing surrounding pupae significantly reduced oviposition rates in the pupal parasitoid Brachymeria intermedia (Nees) (Hymenoptera, Chalcididae). The reasons for this reduction and consequent parasitoid responses were investigated. The role of these behaviors in this host parasitoid relationship are discussed.
Résumé Le comportement défensif des chrysalides de Lymantria dispar L. consiste en cambrage et en tournoiement. Les chrysalides encoconées étaient plus sensibles aux stimuli tactiles que celles qui ont été extraites des cocons. Brachymeria intermedia Nees avait moint de succès dans l'insertion complète de la tarière dans des chrysalides encoconées qu'extraites, car elles devenaient empêtrées dans le cocon quand la chrysalide se défendait. Il y avait différentes réponses du parasitoïde à l'empêtrement. Elles comprenaient l'abandon de l'attaque par un départ, la remise en selle sur l'hôte, la morsure à travers les fils du cocon, l'attaque d'un hôte voisin, le repos ou la toilette. Les taux d'insertion de la tarière pouvaient être augmentés par l'élimination artificielle de quelques fils. La durée des opérations était plus courte sur les chrysalides plus petites. La discussion a porté sur l'importance de ces comportements sur les relations de ces parasitoïdes avec leurs hôtes.相似文献
58.
An attempt was made to use 3,3'-dipropylthiacarbocyanine as a membrane potential probe in yeast by following both its fluorescence changes and its uptake by the cells under different conditions. It was found that the uptake of the dye into the cytoplasmic compartment was translated into an increased fluorescence, and the uptake by the mitochondria produced a quenching of the fluorescence. The experiments to measure uptake showed that a large amount of the dye was taken up by the cells under "deenergized" conditions. The uptake of the cyanine, however, was significantly reduced by the omission of the substrate, by deenergization of the mitochondria, or by the addition of K+, but not by Na+. This cyanine seems to be a good, qualitative indicator of the potential of the plasma membrane and of the mitochondria of the cells, with a faster response than those probes used before in yeast. 相似文献
59.
The blue light dependent utilization of nitrate by green algae under common air and high irradiances, besides its assimilatory nature, is associated with the release of NO2
– and NH4
+ to the culture medium. If the CO2 content of the sparging air was increased up to 2%, previously excreted NO2
– and NH4
+ were rapidly assimilated. When under air and high irradiances the cell density in the culture reached values corresponding to 25 g Ch 1.ml-1, no further growth was observed and the highest values of NO3
– consumption and NO2
– and NH4
+ release were attained. Besides low CO2 tensions, increasing NO3
– concentrations in the medium stimulated the release of NO3
– and NH4
+. Under CO2-free air the consumption of NO3
– and the release of NO2
– and NH4
+ on a total N bases were almost stoichiometric and their rates saturated at much lower irradiances than under air. Under CO2-free air high rates of NO2
– release were only observed under the blue radiations that were effectively absorbed by photosynthetically active pigments, i.e. 460 nm, but not under 404 and 630 nm radiations. However, the simultaneous illumination of the cells with 404 and 630 nm monochromatic light showed a remarkable synergistic effect on NO2
– release.The results are discussed in terms of the close relationship between C and N metabolism, the photosynthetic reducing power required to convert NO
inf3
sup±
-N into R – NH2-N and the blue light activation of nitrate reductase. 相似文献
60.
Temperature Dependence of Photosynthesis in Agropyron smithii Rydb. : III. Responses of Protoplasts and Intact Chloroplasts
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Protoplasts and intact chloroplasts isolated from Agropyron smithii Rybd. were utilized in an effort to determine the limiting factor(s) for photosynthesis at supraoptimal temperatures. Saturated CO2-dependent O2 evolution had a temperature optimum of 35°C for both protoplasts and intact chloroplasts. A sharp decline in activity was observed as assay temperature was increased above 35°C, and at 45°C only 20% of the maximal rate remained. The temperature optimum for 3-phosphoglycerate reduction by intact chloroplasts was 35°C. Above this temperature, 3-phosphoglycerate reduction was more stable than CO2-dependent O2 evolution. Reduction of nitrite in coupled intact chloroplasts had a temperature optimum of 40°C with only slight variation in activity between 35°C and 45°C. Reduction of nitrite in uncoupled chloroplasts had a temperature optimum of 40°C, but increasing the assay temperature to 45°C resulted in a complete loss of activity. Reduction of p-benzoquinone by protoplasts and intact chloroplasts had a temperature optimum of 32°C when measured in the presence of dibromothymoquinone. This photosystem II activity exhibited a strong inhibition of O2 evolution as assay temperature increased above the optimum. It is concluded that, below the temperature optimum, ATP and reductant were not limiting photosynthesis in these systems or intact leaves. Above the temperature optimum, photosynthesis in these systems is limited in part by the phosphorylation potential of the stromal compartment and not by the available reductant. 相似文献