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101.
A flexural model of four-point bending fatigue that has been experimentally validated for human cortical bone under load control was used to determine how load and displacement control testing affects the fatigue behavior of human cortical bone in three-point and symmetric four-point bending. Under load control, it was predicted that three-point bending produced no significant differences in fatigue life when compared to four-point bending. However, three-point bending produced less stiffness loss with increasing cycles than four-point bending. In four-point bending, displacement control was predicted to produce about one and a half orders of magnitude greater fatigue life when compared to load control. This prediction agrees with experimental observations of equine cannon bone tested in load and displacement control (Gibson et al., 1998). Displacement controlled three-point bending was found to produce approximately a 25% greater fatigue life when compared to load control. The prediction of longer fatigue life under displacement control may have clinical relevance for the repair of damaged bone. The model can also be adapted to other geometric configurations, including modeling of whole long bones, and with appropriate fatigue data, other cortical bone types. 相似文献
102.
Characteristics and transferability of new apple EST-derived SSRs to other Rosaceae species 总被引:1,自引:0,他引:1
Ksenija Gasic Yuepeng Han Sunee Kertbundit Vladimir Shulaev Amy F. Iezzoni Ed W. Stover Richard L. Bell Michael E. Wisniewski Schuyler S. Korban 《Molecular breeding : new strategies in plant improvement》2009,23(3):397-411
Genic microsatellites or simple sequence repeat markers derived from expressed sequence tags (ESTs), referred to as EST–SSRs,
are inexpensive to develop, represent transcribed genes, and often have assigned putative function. The large apple (Malus × domestica) EST database (over 300,000 sequences) provides a valuable resource for developing well-characterized DNA molecular markers.
In this study, we have investigated the level of transferability of 68 apple EST–SSRs in 50 individual members of the Rosaceae
family, representing three genera and 14 species. These representatives included pear (Pyrus communis), apricot (Prunus armeniaca), European plum (P. domestica), Japanese plum (P. salicina), almond (P. dulcis), peach (P. persica), sour cherry (P. cerasus), sweet cherry (P. avium), strawberry (Fragaria vesca, F. moschata, F. virginiana, F. nipponica, and F. pentaphylla), and rose (Rosa hybrida). All 68 primer pairs gave an amplification product when tested on eight apple cultivars, and for most, the genomic DNA-derived
amplification product matched the expected size based on EST (in silico) data. When tested across members of the Rosaceae, 75% of these primer pairs produced amplification products. Transferability
of apple EST–SSRs across the Rosaceae ranged from 25% in apricot to 59% in the closely related pear. Besides pear, the highest
transferability of these apple EST–SSRs, at the genus level, was observed for strawberry and peach/almond, 49 and 38%, respectively.
Three markers amplified in at least one genotype within all tested species, while eight additional markers amplified in all
species, except for cherry. These 11 markers are deemed good candidates for a widely transferable Rosaceae marker set provided
their level of polymorphism is adequate. Overall, these findings suggest that transferability of apple EST–SSRs across Rosaceae
is varied, yet valuable, thereby providing additional markers for comparative mapping and for carrying out evolutionary studies. 相似文献
103.
Aulus EAD Barbosa Érika VS Albuquerque Maria CM Silva Djair SL Souza Osmundo B Oliveira-Neto Arnubio Valencia Thales L Rocha Maria F Grossi-de-Sa 《BMC biotechnology》2010,10(1):44
Background
Coffee is an important crop and is crucial to the economy of many developing countries, generating around US70 billion per year. There are 115 species in the < i > Coffea < /i > genus, but only two, < i > C. arabica < /i > and < i > C. canephora < /i > , are commercially cultivated. Coffee plants are attacked by many pathogens and insect-pests, which affect not only the production of coffee but also its grain quality, reducing the commercial value of the product. The main insect-pest, the coffee berry borer ( < i > Hypotheneumus hampei < /i > ), is responsible for worldwide annual losses of around US70 billion per year. There are 115 species in the Coffea genus, but only two, C. arabica and C. canephora, are commercially cultivated. Coffee plants are attacked by many pathogens and insect-pests, which affect not only the production of coffee but also its grain quality, reducing the commercial value of the product. The main insect-pest, the coffee berry borer (Hypotheneumus hampei), is responsible for worldwide annual losses of around US500 million. The coffee berry borer exclusively damages the coffee berries, and it is mainly controlled by organochlorine insecticides that are both toxic and carcinogenic. Unfortunately, natural resistance in the genus Coffea to H. hampei has not been documented. To overcome these problems, biotechnological strategies can be used to introduce an α-amylase inhibitor gene (α-AI1), which confers resistance against the coffee berry borer insect-pest, into C. arabica plants. 相似文献104.
105.
Graham JR Ray LJ Stover SK Salmen JJ Gardiner CS 《Journal of reproduction and fertility》1999,117(1):35-40
The effects of nutrient intake and insemination of gilts at first versus third oestrus on the in vitro development of preimplantation pig embryos were investigated. Standard swine management involves ad libitum feeding of gilts at first oestrus and restricted feeding of gilts at third oestrus. According to previous research, gilts inseminated at first oestrus demonstrate greater embryonic mortality than gilts inseminated at third oestrus, and it is possible that differences in nutrient intake between gilts inseminated at first versus third oestrus affect the viability of eggs or embryos. In the present study, experimental gilts were assigned to three treatments: animals designated 1A were inseminated at first oestrus and fed ad libitum; animals designated 3R were inseminated at third oestrus and were fed a restricted diet; and 3A animals were inseminated at third oestrus and fed ad libitum. Embryos collected from each treatment group were cultured in vitro, and data were evaluated according to cell stage at collection. Comparison of treatments 1A and 3R supported the contention of increased embryo mortality in gilts inseminated at first oestrus under normal management conditions. When cultures were initiated at the one- to two-cell or two- to four-cell stages, the percentage of 1A embryos developing to the morula stage (50.9%, 68.0%) was significantly lower than that of 3R embryos (88.9%, 90.9%; P < 0.05). Comparison of treatments 1A and 3A addressed effects due to the number of oestrous cycles. Significantly more two- to four-cell embryos from gilts inseminated at third oestrus and fed ad libitum reached the morula and expanded blastocyst stages of development (87.0%, 41.3%) compared with embryos from gilts inseminated at first oestrus and fed ad libitum (68.0%, 20.3%; P < 0.05). Finally, the effects of ad libitum feeding were determined by comparing treatments 3A and 3R. These data were inconclusive, as both positive and negative effects were observed. More one- to two-cell embryos from treatment 3R developed to the morula stage (88.9%) compared with 3A embryos collected at the same stage (64.7%), whereas a greater number of 3A embryos in the two- to four-cell category reached the expanded blastocyst stage (41.3%) than 3R embryos (21.2%; P < 0.05). These results support the hypothesis of lower in vitro developmental capacity for embryos collected from gilts inseminated at first oestrus. Furthermore, the findings indicate that differences in embryo viability between gilts inseminated at first versus third oestrus are related to the number of oestrous cycles and possibly to differential nutrition. 相似文献
106.
CM Galmarini A Kertesz R Oliva J Porta F C Galmarini 《Cancer immunology, immunotherapy : CII》1998,15(4):282-285
Bone metastasis in the hand is rare. The etiology is quite different from that of metastasis to other bones; bronchogenic
carcinoma is by far the most frequent case. Distal phalanges are mainly involved with irregular osteolysis and cortical destruction.
Differential diagnosis of phalangeal metastasis includes osteomyelitis, rheumatoid arthritis and gout. The prognosis is always
that of metastatic bronchial cancer with an average survival of three months. Treatment may involve distal digital amputation
or antalgic radiotherapy. A case of bronchogenic carcinoma with metastasis to the thumb is presented. The metastasis was located
in the distal phalanx of the left thumb. The primary tumor was located in the lung. Treatment consisted of amputation. The
overall survival was five months. 相似文献
107.
Fort DJ Propst TL Stover EL Strong PL Murray FJ 《Biological trace element research》1998,66(1-3):237-259
Frog embryo teratogenesis assay—Xenopus (FETAX) was utilized as a model system to evaluate the effects on embryo-larval development at various low boron (B) exposure
levels in the culture media. Concentrations tested ranged from <1 to 5000 μg B/L. A statistically significant (P < 0.05) increase
in malformations was observed at ≤ 3 μg B/L, but not at the greater concentrations. Abnormal development of the gut, craniofacial
region and eye, visceral edema, and kinking of the tail musculature (abnormal myotome development) and notochord were observed.
In subsequent studies, adult frogs were maintained for 28 d on two diets: (1) low B (LB, 62 μg B/kg) or (2) boric acid supplemented
(BA, 1851 μg B/kg); the frogs were subsequently mated, and their offspring were cultured in media containing various levels
of B. Results of the 28-d depletion studies indicated that frogs maintained under LB conditions produced a greater proportion
of (1) necrotic eggs and (2) fertilized embryos, which abnormally gastrulated at a greater rate and were substantially less
viable than embryos from frogs fed the BA diet. Malformations similar to those seen in the initial study were observed in
embryos from the B-depleted adults maintained in an LB environment; 28 d on the LB diet enhanced the incidence of malformations
associated with the LB culture media. These abnormalities were not observed in embryos cultured in ≥4 μg B/L from adults cultured
on the BA diet. These studies showed that insufficient B reproducibly interfered with normalXenopus laevis development during organogenesis, substantially impaired normal reproductive function in adult frogs, and thus represent
the first studies demonstrating the nutritional essentiality of B in an amphibian species. 相似文献
108.
Microsatellite variation in Drosophila melanogaster and Drosophila simulans: a reciprocal test of the ascertainment bias hypothesis 总被引:2,自引:1,他引:1
Interspecific comparisons of microsatellite loci have repeatedly shown that
the loci are longer and more variable in the species from which they are
derived (the focal species) than are homologous loci in other (nonfocal)
species. There is debate as to whether this is due to directional evolution
or to an ascertainment bias during the cloning and locus selection
processes. This study tests these hypotheses by performing a reciprocal
study. Eighteen perfect dinucleotide microsatellite loci identified from a
Drosophila simulans library screen and 18 previously identified in an
identical Drosophila melanogaster library screen were used to survey
natural populations of each species. No difference between focal and
nonfocal species was observed for mean PCR fragment length. However,
heterozygosity and number of alleles were significantly higher in the focal
species than in the nonfocal species. The most common allele in the
Zimbabwe population of both species was sequenced for 31 of the 36 loci.
The length of the longest stretch of perfect repeat units is, on average,
longer in the focal species than in the non-focal species. There is a
positive correlation between the length of the longest stretch of perfect
repeats and heterozygosity. The difference in heterozygosity can thus be
explained by a reduction in the length of the longest stretch of perfect
repeats in the nonfocal species. Furthermore, flanking-sequence length
difference was noted between the two species at 58% of the loci sequenced.
These data do not support the predictions of the directional-evolution
hypothesis; however, consistent with the ascertainment bias hypothesis, the
lower variability in nonfocal species is an artifact of the microsatellite
cloning and isolation process. Our results also suggest that the magnitude
of ascertainment bias for repeat unit length is a function of the
microsatellite size distribution in the genomes of different species.
相似文献
109.
Staphylococcus aureus genetic loci impacting growth and survival in multiple infection environments 总被引:6,自引:2,他引:4
Silvija N. Coulter William R. Schwan Eva Y. W. Ng Michael H. Langhorne Heather D. Ritchie Shannon Westbrock-Wadman Wendy O. Hufnagle Kim R. Folger Arnold S. Bayer & C. Kendall Stover 《Molecular microbiology》1998,30(2):393-404
The Gram-positive bacterium Staphylococcus aureus infects diverse tissues and causes a wide spectrum of diseases, suggesting that it possesses a repertoire of distinct molecular mechanisms promoting bacterial survival in disparate in vivo environments. Signature-tag transposon mutagenesis screening of a 1520-member library identified numerous S. aureus genetic loci affecting growth and survival in four complementary animal infection models including mouse abscess, bacteraemia and wound and rabbit endocarditis. Of a total of 237 in vivo attenuated mutants identified by the murine models, less than 10% showed attenuation in all three models, emphasizing the advantage of screening in diverse disease environments. The largest gene class identified by these analyses encoded peptide and amino acid transporters, some of which were important for S. aureus survival in all animal infection models tested. The identification of staphylococcal loci affecting growth, persistence and virulence in multiple tissue environments provides insight into the complexities of human infection and on the molecular mechanisms that could be targeted by new antibacterial therapies. 相似文献
110.
Prospects for estimating nucleotide divergence with RAPDs 总被引:11,自引:0,他引:11
The technique of random amplification of polymorphic DNA (RAPD), which is
simply polymerase chain reaction (PCR) amplification of genomic DNA by a
single short oligonucleotide primer, produces complex patterns of anonymous
polymorphic DNA fragments. The information provided by these banding
patterns has proved to be of great utility for mapping and for verification
of identity of bacterial strains. Here we consider whether the degree of
similarity of the banding patterns can be used to estimate nucleotide
diversity and nucleotide divergence. With haploid data, fragments generated
by RAPD-PCR can be treated in a fashion very similar to that for
restriction-fragment data. Amplification of diploid samples, on the other
hand, requires consideration of the fact that presence of a band is
dominant to absence of the band. After describing a method for estimating
nucleotide divergence on the basis of diploid samples, we summarize the
restrictions and criteria that must be met when RAPD data are used for
estimating population genetic parameters.
相似文献