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41.
Cultured rat schwann cells grown in association with sensory neurons when labeled with [(3)H]leucinem, [(3)H]glucosamine, or [(35)S]methionine release labeled polypeptides into the culture medium. Analysis by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) of the culture medium reveals a reproducible pattern of more than 20 polypeptides with molecular weights ranging from 15,000 to more than 250,000. Five major polypeptides (apparent molecular weights 225,000, 210,000, 90,000, 66,000, 50,000, and 40,000) account for approximately 40 percent of the leucine or methionine radioactivity in medium polypeptide. Schwann cells grown in a serum-free defined medium, in which schwann cells do not relate normally to axons, release approximately four times less labeled medium polypeptides tha cultures grown in medium supplemented with serum and chick embryo extract. In addition, there is a qualitative difference in the pattern of medium polypeptides resolved by SDS-PAGE, so that a single polypeptide (mol wt 40,000) accounts for nearly all of the label in medium polypeptides. Switching of cultures grown in defined medium to supplemented medium for 2 d results in a fourfold increase in the amount of labeled polypeptides appearing in the culture medium, and a return to the normal pattern of medium polypeptides appearing in the culture medium, and a return to the normal pattern of medium polypeptides as resolved by SDS-PAGE. This change in the pattern of polypeptides release by schwann cells is accompanied by changes in the association between schwann cells and axons. An early step in the establishment of normal axon-schwann cell relations appears to be an inward migration of schwann cells into axonal bundles and spreading of schwann cells along neurites. These changes are evident within 48 h after medium shift. Our results thus suggest that the release of proteins by schwann cells may be important for the development of normal axonal ensheathment. 相似文献
42.
Steven G Thomas Simon DJ Calaminus Jocelyn M Auger Stephen P Watson Laura M Machesky 《BMC cell biology》2007,8(1):46
Background
The platelet cytoskeleton mediates the dramatic change in platelet morphology that takes place upon activation and stabilizes thrombus formation. The Arp2/3 complex plays a vital role in these processes, providing the protrusive force for lamellipodia formation. The Arp2/3 complex is highly regulated by a number of actin-binding proteins including the haematopoietic-specific protein HS1 and its homologue cortactin. The present study investigates the role of HS1 in platelets using HS1-/- mice. 相似文献43.
WS Watkins R Thara BJ Mowry Y Zhang DJ Witherspoon W Tolpinrud MJ Bamshad S Tirupati R Padmavati H Smith D Nancarrow C Filippich LB Jorde 《BMC genetics》2008,9(1):1-17
Background
Major population movements, social structure, and caste endogamy have influenced the genetic structure of Indian populations. An understanding of these influences is increasingly important as gene mapping and case-control studies are initiated in South Indian populations.Results
We report new data on 155 individuals from four Tamil caste populations of South India and perform comparative analyses with caste populations from the neighboring state of Andhra Pradesh. Genetic differentiation among Tamil castes is low (RST = 0.96% for 45 autosomal short tandem repeat (STR) markers), reflecting a largely common origin. Nonetheless, caste- and continent-specific patterns are evident. For 32 lineage-defining Y-chromosome SNPs, Tamil castes show higher affinity to Europeans than to eastern Asians, and genetic distance estimates to the Europeans are ordered by caste rank. For 32 lineage-defining mitochondrial SNPs and hypervariable sequence (HVS) 1, Tamil castes have higher affinity to eastern Asians than to Europeans. For 45 autosomal STRs, upper and middle rank castes show higher affinity to Europeans than do lower rank castes from either Tamil Nadu or Andhra Pradesh. Local between-caste variation (Tamil Nadu RST = 0.96%, Andhra Pradesh RST = 0.77%) exceeds the estimate of variation between these geographically separated groups (RST = 0.12%). Low, but statistically significant, correlations between caste rank distance and genetic distance are demonstrated for Tamil castes using Y-chromosome, mtDNA, and autosomal data.Conclusion
Genetic data from Y-chromosome, mtDNA, and autosomal STRs are in accord with historical accounts of northwest to southeast population movements in India. The influence of ancient and historical population movements and caste social structure can be detected and replicated in South Indian caste populations from two different geographic regions. 相似文献44.
M Kale R Ramsey-Goldman S Bernatsky MB Urowitz D Gladman PR Fortin M Petri E Yelin S Manzi S Edworthy O Nived S-C Bae D Isenberg A Rahman JG Hanly C Gordon S Jacobsen E Ginzler DJ Wallace GS Alarcón MA Dooley L Gottesman K Steinsson A Zoma J-L Senécal S Barr G Sturfelt L Dreyer L Criswell J Sibley JL Lee AE Clarke 《Arthritis research & therapy》2012,14(Z3):A15
45.
46.
Pairwise likelihood methods for inference in image models 总被引:3,自引:0,他引:3
47.
48.
MOTIVATION: Searching a protein sequence database for homologs is a
powerful tool for discovering the structure and function of a sequence. Two
new methods for searching sequence databases have recently been described:
Probabilistic Smith-Waterman (PSW), which is based on Hidden Markov models
for a single sequence using a standard scoring matrix, and a new version of
BLAST (WU-BLAST2), which uses Sum statistics for gapped alignments.
RESULTS: This paper compares and contrasts the effectiveness of these
methods with three older methods (Smith- Waterman: SSEARCH, FASTA and
BLASTP). The analysis indicates that the new methods are useful, and often
offer improved accuracy. These tools are compared using a curated (by Bill
Pearson) version of the annotated portion of PIR 39. Three different
statistical criteria are utilized: equivalence number, minimum errors and
the receiver operating characteristic. For complete-length protein query
sequences from large families, PSW's accuracy is superior to that of the
other methods, but its accuracy is poor when used with partial-length query
sequences. False negatives are twice as common as false positives
irrespective of the search methods if a family-specific threshold score
that minimizes the total number of errors (i.e. the most favorable
threshold score possible) is used. Thus, sensitivity, not selectivity, is
the major problem. Among the analyzed methods using default parameters, the
best accuracy was obtained from SSEARCH and PSW for complete-length
proteins, and the two BLAST programs, plus SSEARCH, for partial-length
proteins.
相似文献
49.
Recent horizontal transfer of a mariner transposable element among and between Diptera and Neuroptera 总被引:11,自引:4,他引:7
Transposable elements of the mariner family are widespread among insects
and other invertebrates, and initial analyses of their relationships
indicated frequent occurrence of horizontal transfers between hosts. A
specific PCR assay was used to screen for additional members of the
irritans subfamily of mariners in more than 400 arthropod species.
Phylogenetic analysis of cloned PCR fragments indicated that relatively
recent horizontal transfers had occurred into the lineages of a fruit fly
Drosophila ananassae, the horn fly Haematobia irritans, the African malaria
vector mosquito Anopheles gambiae, and a green lacewing Chrysoperla
plorabunda. Genomic dot-blot analysis revealed that the copy number in
these species varies widely, from about 17,000 copies in the horn fly to
three copies in D. ananassae. Multiple copies were sequenced from genomic
clones from each of these species and four others with related elements.
These sequences confirmed the PCR results, revealing extremely similar
elements in each of these four species (greater than 88% DNA and 95% amino
acid identity). In particular, the consensus sequence of the transposase
gene of the horn fly elements differs by just two base pairs out of 1,044
from that of the lacewing elements. The mosquito lineage has diverged from
the other Diptera for over 200 Myr, and the neuropteran last shared a
common ancestor with them more than 265 Myr ago, so this high similarity
implies that these transposons recently transferred horizontally into each
lineage. Their presence in only the closest relatives in at least the
lacewing lineage supports this hypothesis. Such horizontal transfers
provide an explanation for the evolutionary persistence and widespread
distribution of mariner transposons. We propose that the ability to
transfer horizontally to new hosts before extinction by mutation in the
current host constitutes the primary selective constraint maintaining the
sequence conservation of mariners and perhaps other DNA-mediated elements.
相似文献
50.
The effects of 18-crown-6 on the synthesis of peptides catalyzed by alpha-chymotrypsin are reported. Lyophilization of the enzyme in the presence of 50 equivalents of 18-crown-6 results in a 425-fold enhanced activity when the reaction between the 2-chloroethylester of N-acetyl-L-phenylalanine and L-phenylalaninamide is carried out in acetonitrile. Addition of crown ether renders the dipeptide synthesis in nonaqueous solvents catalyzed by alpha-chymotrypsin possible on a preparative scale. The acceleration is observed in different solvents and for various peptide precursors. Copyright 1998 John Wiley & Sons, Inc. 相似文献