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排序方式: 共有1335条查询结果,搜索用时 15 毫秒
101.
Aida Z. Kebede Baldev S. Dhillon Wolfgang Schipprack Jose L. Araus Marianne Bänziger Kassa Semagn Gregorio Alvarado Albrecht E. Melchinger 《Euphytica》2011,180(2):219-226
For in vivo production of doubled haploid (DH) lines in maize, the rate of haploid induction is of crucial importance. Maternal
haploid induction depends primarily on the inducer used as a pollinator. However, the source germplasm used as a maternal
parent and the environmental conditions for induction may also influence haploid induction and these aspects have not been
examined in tropical maize so far. The objectives of our study were to (i) monitor the variation for haploid induction rate
(HIR) among diverse source germplasm in tropical maize, (ii) determine the relative importance of general (GCA) and specific
(SCA) combining abilities for HIR, and (iii) investigate the influence of summer and winter seasons and genotype × season
interactions on this trait. Ten inbreds were mated in a half diallel design. The resulting 45 F1 single crosses were pollinated with the haploid inducer hybrid RWS × UH400 during the summer 2008 and winter 2009 seasons
in a lowland tropical environment in Mexico. HIR of the single crosses averaged over seasons ranged from 2.90 to 9.66% with
an overall mean of 6.74%. Mean HIR was significantly (P < 0.01) higher during the winter (7.37%) than summer season (6.11%). Significant (P < 0.01) variation was observed due to GCA effects of parental inbreds of single crosses but not for SCA, GCA × season and
SCA × season interactions. Our study underpins that a higher HIR in tropical maize can be obtained by selecting appropriate
source germplasm and undertaking pollination under favorable environmental conditions. 相似文献
102.
Revenue risk management, risk aversion and the use of Livestock Gross Margin for Dairy Cattle insurance 总被引:1,自引:0,他引:1
Mayuri Valvekar Jean P. Chavas Brian W. Gould Victor E. Cabrera 《Agricultural Systems》2011,104(9):671-678
The Livestock Gross Margin Insurance for Dairy Cattle is a federally reinsured insurance program that enables US dairy producers to establish minimum levels of milk income net of feed cost. Given the structure of this program there are an infinite number of possible contract designs based on the choice of deductible level and proportion of production insured. Adding to this complexity, producers vary in their risk preferences, which affect the incentive to insure their margin. It is unclear as to how producers may adopt this program for revenue risk management. This paper investigates the interplay between producer risk preferences, contract design and the subsidization of premium in determining program coverage. We undertook this analysis within an expected utility framework. Optimal contracts under different rates of constant relative rate of risk aversion and subsidies were analyzed using a nonlinear optimization model. We found that total optimal coverage increased significantly with the level of risk of aversion at lower deductibles but as deductible level increased, the level of risk aversion had a lesser impact on total optimal coverages. As expected, at the same deductible and risk aversion levels, inclusion of a premium subsidy increased the total optimal coverage. 相似文献
103.
Muegge BD Kuczynski J Knights D Clemente JC González A Fontana L Henrissat B Knight R Gordon JI 《Science (New York, N.Y.)》2011,332(6032):970-974
Coevolution of mammals and their gut microbiota has profoundly affected their radiation into myriad habitats. We used shotgun sequencing of microbial community DNA and targeted sequencing of bacterial 16S ribosomal RNA genes to gain an understanding of how microbial communities adapt to extremes of diet. We sampled fecal DNA from 33 mammalian species and 18 humans who kept detailed diet records, and we found that the adaptation of the microbiota to diet is similar across different mammalian lineages. Functional repertoires of microbiome genes, such as those encoding carbohydrate-active enzymes and proteases, can be predicted from bacterial species assemblages. These results illustrate the value of characterizing vertebrate gut microbiomes to understand host evolutionary histories at a supraorganismal level. 相似文献
104.
Gu Y Filippi MD Cancelas JA Siefring JE Williams EP Jasti AC Harris CE Lee AW Prabhakar R Atkinson SJ Kwiatkowski DJ Williams DA 《Science (New York, N.Y.)》2003,302(5644):445-449
The Rho guanosine triphosphatases (GTPases) Rac1 and Rac2 are critical signaling regulators in mammalian cells. The deletion of both Rac1 and Rac2 murine alleles leads to a massive egress of hematopoietic stem/progenitor cells (HSC/Ps) into the blood from the marrow, whereas Rac1-/- but not Rac2-/- HSC/Ps fail to engraft in the bone marrow of irradiated recipient mice. In contrast, Rac2, but not Rac1, regulates superoxide production and directed migration in neutrophils, and in each cell type, the two GTPases play distinct roles in actin organization, cell survival, and proliferation. Thus, Rac1 and Rac2 regulate unique aspects of hematopoietic development and function. 相似文献
105.
Tadokoro S Shattil SJ Eto K Tai V Liddington RC de Pereda JM Ginsberg MH Calderwood DA 《Science (New York, N.Y.)》2003,302(5642):103-106
Control of integrin affinity for ligands (integrin activation) is essential for normal cell adhesion, migration, and assembly of an extracellular matrix. Integrin activation is usually mediated through the integrin beta subunit cytoplasmic tail and can be regulated by many different biochemical signaling pathways. We report that specific binding of the cytoskeletal protein talin to integrin beta subunit cytoplasmic tails leads to the conformational rearrangements of integrin extracellular domains that increase their affinity. Thus, regulated binding of talin to integrin beta tails is a final common element of cellular signaling cascades that control integrin activation. 相似文献
106.
Silva JM Marran K Parker JS Silva J Golding M Schlabach MR Elledge SJ Hannon GJ Chang K 《Science (New York, N.Y.)》2008,319(5863):617-620
By virtue of their accumulated genetic alterations, tumor cells may acquire vulnerabilities that create opportunities for therapeutic intervention. We have devised a massively parallel strategy for screening short hairpin RNA (shRNA) collections for stable loss-of-function phenotypes. We assayed from 6000 to 20,000 shRNAs simultaneously to identify genes important for the proliferation and survival of five cell lines derived from human mammary tissue. Lethal shRNAs common to these cell lines targeted many known cell-cycle regulatory networks. Cell line-specific sensitivities to suppression of protein complexes and biological pathways also emerged, and these could be validated by RNA interference (RNAi) and pharmacologically. These studies establish a practical platform for genome-scale screening of complex phenotypes in mammalian cells and demonstrate that RNAi can be used to expose genotype-specific sensitivities. 相似文献
107.
Hwang WS Ryu YJ Park JH Park ES Lee EG Koo JM Jeon HY Lee BC Kang SK Kim SJ Ahn C Hwang JH Park KY Cibelli JB Moon SY 《Science (New York, N.Y.)》2004,303(5664):1669-1674
Somatic cell nuclear transfer (SCNT) technology has recently been used to generate animals with a common genetic composition. In this study, we report the derivation of a pluripotent embryonic stem (ES) cell line (SCNT-hES-1) from a cloned human blastocyst. The SCNT-hES-1 cells displayed typical ES cell morphology and cell surface markers and were capable of differentiating into embryoid bodies in vitro and of forming teratomas in vivo containing cell derivatives from all three embryonic germ layers in severe combined immunodeficient mice. After continuous proliferation for more than 70 passages, SCNT-hES-1 cells maintained normal karyotypes and were genetically identical to the somatic nuclear donor cells. Although we cannot completely exclude the possibility that the cells had a parthenogenetic origin, imprinting analyses support a SCNT origin of the derived human ES cells. 相似文献
108.
Large RNA molecules, such as ribozymes, fold with well-defined tertiary structures that are important for their activity. There are many instances of ribozymes with identical function but differences in their secondary structures, suggesting alternative tertiary folds. Here, we report a crystal structure of the 161-nucleotide specificity domain of an A-type ribonuclease P that differs in secondary and tertiary structure from the specificity domain of a B-type molecule. Despite the differences, the cores of the domains have similar three-dimensional structure. Remarkably, the similar geometry of the cores is stabilized by a different set of interactions involving distinct auxiliary elements. 相似文献
109.
El-Sayed NM Myler PJ Blandin G Berriman M Crabtree J Aggarwal G Caler E Renauld H Worthey EA Hertz-Fowler C Ghedin E Peacock C Bartholomeu DC Haas BJ Tran AN Wortman JR Alsmark UC Angiuoli S Anupama A Badger J Bringaud F Cadag E Carlton JM Cerqueira GC Creasy T Delcher AL Djikeng A Embley TM Hauser C Ivens AC Kummerfeld SK Pereira-Leal JB Nilsson D Peterson J Salzberg SL Shallom J Silva JC Sundaram J Westenberger S White O Melville SE Donelson JE Andersson B Stuart KD Hall N 《Science (New York, N.Y.)》2005,309(5733):404-409
A comparison of gene content and genome architecture of Trypanosoma brucei, Trypanosoma cruzi, and Leishmania major, three related pathogens with different life cycles and disease pathology, revealed a conserved core proteome of about 6200 genes in large syntenic polycistronic gene clusters. Many species-specific genes, especially large surface antigen families, occur at nonsyntenic chromosome-internal and subtelomeric regions. Retroelements, structural RNAs, and gene family expansion are often associated with syntenic discontinuities that-along with gene divergence, acquisition and loss, and rearrangement within the syntenic regions-have shaped the genomes of each parasite. Contrary to recent reports, our analyses reveal no evidence that these species are descended from an ancestor that contained a photosynthetic endosymbiont. 相似文献
110.
Garcia-Mira MM Sadqi M Fischer N Sanchez-Ruiz JM Muñoz V 《Science (New York, N.Y.)》2002,298(5601):2191-2195
Theory predicts the existence of barrierless protein folding. Without barriers, folding should be noncooperative and the degree of native structure should be coupled to overall protein stability. We investigated the thermal unfolding of the peripheral subunit binding domain from Escherichia coli's 2-oxoglutarate dehydrogenase multienzyme complex (termed BBL) with a combination of spectroscopic techniques and calorimetry. Each technique probed a different feature of protein structure. BBL has a defined three-dimensional structure at low temperatures. However, each technique showed a distinct unfolding transition. Global analysis with a statistical mechanical model identified BBL as a downhill-folding protein. Because of BBL's biological function, we propose that downhill folders may be molecular rheostats, in which effects could be modulated by altering the distribution of an ensemble of structures. 相似文献