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991.
The reproductive toxicity of dimethyl methyl phosphonate (DMMP) was studied in the male B6C3F1 mouse. Male mice were treated with 0, 250, 500, 1000, and 2000 mg/kg DMMP by gavage 5 days per week for 13 weeks. After 4, 8 and 12 weeks of treatment the male mice were mated to untreated CD-1 female mice. At the two highest doses (1000 and 2000 mg/kg) the chemical caused a dominant lethal effect (early resorptions). Groups of male mice (at 1000 and 2000 mg/kg), mated after a 15-week recovery period without chemical dosing, had a resorption rate comparable to the control group. After 13 weeks of dosing, the male mice showed no histopathologic changes of the reproductive organs, no abnormalities in sperm concentration or sperm morphology, no evidence for hormone imbalance, no signs of general toxicity, and no effects on the fertilization rate. The male B6C3F1 mouse was less responsive than the male Fischer 344/N rat to the reproductive toxic effects of DMMP. 相似文献
992.
David D. Eckels Thomas W. Sell Sandra Rosen Bronson Armead H. Johnson Robert J. Hartzman Jonathan R. Lamb 《Immunogenetics》1984,19(5):409-423
Human T-lymphocyte clones (TLCs) were generated against the hemagglutinin (HA) of A/Texas/1/77 influenza virus by limiting dilution. TLCs were then screened for antigen specificity on chemically synthesized peptides representing the HA1 molecule. It has been hypothesized that different T cells that recognize the identical antigenic determinant are controlled by (restricted by) the same class II epitope. Two TLCs, HA1.4 and HA1.7, both recognized the same HA peptide and in proliferation studies exhibited identical restriction patterns. Two other clones, HA 1.9 and HA 2.43, recognized different HA determinants and also had distinct restriction patterns. Proliferation inhibition studies with monoclonal antibodies against human class II molecules demonstrated three unique patterns of blocking with the clones, suggesting that clones may be restricted to a unique class II epitope depending on the HA determinant recognized. These data can be interpreted as supporting the argument that human immune responses to influenza hemagglutinin are under Ir gene control exerted at the level of the viral antigenic determinant recognized in association with particular D-region restricting elements. The determinant selection and clonal deletion theories are compared for their capacity to best explain these findings.Abbreviations used in this paper
3HTdR
tritiated methyl thymidine
- MHC
major histocompatibility complex
- HLA
human MHC
- PBLs
peripheral blood lymphocytes
- APCs
antigen-presenting cells
- TLCs
T-lymphocyte clones
- TCGF
T-cell growth factor
- MoAbs
monoclonal antibodies 相似文献
993.
994.
Variations in the foliar concentrations of macro and micro elements in a fast-growing tropical eucalypt 总被引:1,自引:1,他引:0
D. Lamb 《Plant and Soil》1976,45(2):477-492
Summary The concentrations of N, P, K, Ca, Mg, Zn, Cu, Mn, Fe and B were measured in leaves of various ages in upper, mid and lower crown positions in Eucalyptus deglupta Blume during both wet and dry seasons. Based on coefficients of variation, the number of samples trees necessary for different levels of precision were calculated for each crown position.Least variation was found during the wet season for all elements except K. For all elements except Ca, fewest trees were needed when foliar material was collected from upper crown branches.The rate of leaf production in the upper crown was constant and it was possible to sample leaves of the same age by collecting from similar sampling positions; in contrast, that in the lower crowns was erratic and it was difficult to collect leaves of comparable age.The patterns of distribution and variation of foliar nutrients in the crown of E. deglupta are discussed. re]19750521 相似文献
995.
SOME OBSERVATIONS ON THE MALPIGHIAN TUBULES AND OVARIOLES IN MYRMECIA DISPAR (CLARK) (HYMENOPTERA: FORMICIDAE) 总被引:1,自引:1,他引:0
i
Myrmecia dispar (Clark) workers have a variable number of malpighian tubules; the number counted ranged from 21 to 29. The larger workers tend to have more tubules than smaller workers. Two male specimens had 16 tubules and 3 queen specimens had 23, 23 and 26 tubules respectively. Workers collected in winter and summer had 10 well developed polytrophic ovarioles while the queens had 18 ovarioles. 相似文献
Myrmecia dispar (Clark) workers have a variable number of malpighian tubules; the number counted ranged from 21 to 29. The larger workers tend to have more tubules than smaller workers. Two male specimens had 16 tubules and 3 queen specimens had 23, 23 and 26 tubules respectively. Workers collected in winter and summer had 10 well developed polytrophic ovarioles while the queens had 18 ovarioles. 相似文献
996.
Inhibition of cAMP-dependent protein kinase plays a key role in the induction of mitosis and nuclear envelope breakdown in mammalian cells. 总被引:15,自引:3,他引:12 下载免费PDF全文
Inhibiting cAMP-dependent protein kinase (A-kinase) in mammalian fibroblasts through microinjection of a modified specific inhibitor peptide, PKi(m) or the purified inhibitor protein, PKI, resulted in rapid and pronounced chromatin condensation at all phases of the cell cycle. Together with these changes in chromatin, a marked reorganization of microtubule network occurred, accompanied in G2 cells by extensive alterations in cell shape which have many similarities to the premitotic phenotype previously observed after activation of p34cdc2 kinase, including the lack of spindle formation and the persistence of a nuclear envelope. In order to examine whether A-kinase inhibition and p34cdc2 kinase form part of the same or different inductive pathways, PKI and p34cdc2 kinase were injected together. Co-injection of both components resulted in nuclear envelope disassembly, an event not observed with injection of either component alone. This result implies that p34cdc2 and A-kinase inhibition have complementary and additive effects on the process of nuclear envelope breakdown in living fibroblasts, a conclusion further supported by our observation of a pronounced dephosphorylation of lamins A and C in cells after injection of PKi(m). Taken together, these data suggest that down-regulation of A-kinase is a distinct and essential event in the induction of mammalian cell mitosis which co-operates with the p34cdc2 pathway. 相似文献
997.
998.
Mitochondrial DNA evolution at a turtle's pace: evidence for low genetic variability and reduced microevolutionary rate in the Testudines. 总被引:16,自引:0,他引:16
J C Avise B W Bowen T Lamb A B Meylan E Bermingham 《Molecular biology and evolution》1992,9(3):457-473
Evidence is compiled suggesting a slowdown in mean microevolutionary rate for turtle mitochondrial DNA (mtDNA). Within each of six species or species complexes of Testudines, representing six genera and three taxonomic families, sequence divergence estimates derived from restriction assays are consistently lower than expectations based on either (a) the dates of particular geographic barriers with which significant mtDNA genetic clades appear associated or (b) the magnitudes of sequence divergence between mtDNA clades in nonturtle species that otherwise exhibit striking phylogeographic concordance with the genetic partitions in turtles. Magnitudes of the inferred rate slowdowns average eightfold relative to the "conventional" mtDNA clock calibration of 2%/Myr sequence divergence between higher animal lineages. Reasons for the postulated deceleration remain unknown, but two intriguing correlates are (a) the exceptionally long generation length most turtles and (b) turtles' low metabolic rate. Both factors have been suspected of influencing evolutionary rates in the DNA sequences of some other vertebrate groups. Uncertainities about the dates of cladogenetic events in these Testudines leave room for alternatives to the slowdown interpretation, but consistency in the direction of the inferred pattern, across several turtle species and evolutionary settings, suggests the need for caution in acceptance of a universal mtDNA-clock calibration for higher animals. 相似文献
999.
J R Strahler N Hailat B J Lamb K P Rogers J A Underhill R F Melhem D R Keim X Zhu R D Kuick D A Fox 《Journal of immunology (Baltimore, Md. : 1950)》1992,149(4):1191-1198
Op18 is a highly conserved major cytosolic phosphoprotein that has been implicated in signal transduction in a wide variety of cell types. Freshly isolated peripheral blood lymphocytes (PBL) constitutively express low levels of mostly unphosphorylated Op18. After mitogenic stimulation of PBL, Op18 synthesis is induced at a time when cells are entering S-phase. In this study, we have examined the phosphorylation of Op18 in freshly isolated PBL after activation of the T cell receptor by OKT3. Quantitative analysis of Op18 phosphorylation was undertaken by metabolic labeling with 32Pi and PhosphorImager analysis of two-dimensional gels. After 10 or 15 min of activation by OKT3, one of the three major phosphorylated forms of Op18, designated Op18c, increased approximately 10-fold, which represented a most pronounced change among a large number of phosphoproteins analyzed. In time course experiments, increased Op18 phosphorylation to yield Op18c was observed as early as 2 min. Continued OKT3-induced activation for 20 to 72 h resulted in a further increase in phosphorylated Op18 forms, which paralleled new Op18 synthesis and occurred at a time when cells were entering S-phase, as determined by [3H]-thymidine incorporation. Inhibitors of lymphoid proliferation, cyclosporin A and RPM, had no effect on early (less than 15 min) phosphorylation. Addition of calphostin C, a specific inhibitor of protein kinase C, 1 min prior to stimulation of resting T cells with OKT3 completely inhibited further phosphorylation of Op18. Incubation of PBL with calphostin C for 75 min decreased constitutive levels of phosphorylated Op18. In contrast, inhibition of cyclic nucleotide-dependent protein kinases with HA1004 had no effect on Op18 phosphorylation. Activation of cAMP-dependent protein kinase with Forskolin or 8Br-cAMP did not increase Op18 phosphorylation. Our results suggest that Op18 phosphorylation is mediated by protein kinase C activation as an early event in T cell activation through the T cell receptor. 相似文献
1000.
Expression of the influenza A virus M2 protein is restricted to apical surfaces of polarized epithelial cells. 下载免费PDF全文
The M2 protein of influenza A virus is a small, nonglycosylated transmembrane protein that is expressed on surfaces of virus-infected cells. A monoclonal antibody specific for the M2 protein was used to investigate its expression in polarized epithelial cells infected with influenza virus or a recombinant vaccinia virus that expresses M2. The expression of M2 on the surfaces of influenza virus-infected cells was found to be restricted to the apical surface, closely paralleling that of the influenza virus hemagglutinin (HA). Membrane domain-specific immunoprecipitation indicated that the M2 protein was inserted directly into the apical membrane with transport kinetics similar to those of HA. In polarized cells infected with a recombinant vaccinia virus that expresses M2, we found that 86 to 93% of surface M2 was restricted to the apical domain compared with 88 to 90% of HA in a similar assay. These results indicate that the M2 protein undergoes directional transport in the absence of other influenza virus proteins and that M2 contains the structural features required for apical transport in polarized epithelial cells. The ultrastructural localization of the M2 protein in influenza virus-infected MDCK cells was investigated by immunoelectron microscopy using M2 antibody and a gold conjugate. In cells in which extensive virus budding was occurring, the apical cell membrane was labeled with gold particles evenly distributed between microvilli and the surrounding membrane. In addition, a significant fraction of the M2 label was apparently associated with virions. A monoclonal antibody specific for HA demonstrated a similar labeling pattern. These results indicate that M2 is localized in close proximity to budding and assembled virions. 相似文献