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Trabecular bone is modeled as a cellular material with an idealized periodic structure made of open cubic cells, which is effectively orthotropic. We evaluate apparent couple-stress moduli of such a periodic material; apparent moduli refer to the moduli obtained using a domain smaller than a Representative Volume Element and they depend on boundary conditions. We conduct this analysis computationally (using ANSYS) by subjecting a unit cell of this periodic cellular material to either displacement or traction boundary conditions. Cell walls, representing bone tissue, and void space, representing bone marrow, are both modeled and they are assumed to be linear elastic. The applied loadings include a uniaxial extension (or uniaxial stress), a hydrostatic deformation (or hydrostatic stress) and a shear deformation (or shear stress) to evaluate the first stiffness (or compliance) tensor, and an applied curvature (or bending moment), a uniaxial twist (or torsion), and a triaxial twist (or triaxial torsion) to evaluate the second couple-stress stiffness (or compliance) tensor. Apparent couple-stress moduli are computed by equating the total strain energy stored in the unit cell with the energy of an equivalent homogeneous orthotropic couple-stress material for each applied loading. The moduli computed using displacement boundary conditions give upper bound, while those obtained using traction boundary conditions give lower bound on effective couple-stress moduli. These bounds are very wide due to a large mismatch in elastic moduli of bone tissue and bone marrow. These results are in agreement with our studies on composite materials with very stiff or very compliant inclusions. 相似文献
124.
The molecular chaperone Hsp90α is required for meiotic progression of spermatocytes beyond pachytene in the mouse 总被引:1,自引:0,他引:1
Grad I Cederroth CR Walicki J Grey C Barluenga S Winssinger N De Massy B Nef S Picard D 《PloS one》2010,5(12):e15770
The molecular chaperone Hsp90 has been found to be essential for viability in all tested eukaryotes, from the budding yeast to Drosophila. In mammals, two genes encode the two highly similar and functionally largely redundant isoforms Hsp90α and Hsp90β. Although they are co-expressed in most if not all cells, their relative levels vary between tissues and during development. Since mouse embryos lacking Hsp90β die at implantation, and despite the fact that Hsp90 inhibitors being tested as anti-cancer agents are relatively well tolerated, the organismic functions of Hsp90 in mammals remain largely unknown. We have generated mouse lines carrying gene trap insertions in the Hsp90α gene to investigate the global functions of this isoform. Surprisingly, mice without Hsp90α are apparently normal, with one major exception. Mutant male mice, whose Hsp90β levels are unchanged, are sterile because of a complete failure to produce sperm. While the development of the male reproductive system appears to be normal, spermatogenesis arrests specifically at the pachytene stage of meiosis I. Over time, the number of spermatocytes and the levels of the meiotic regulators and Hsp90 interactors Hsp70-2, NASP and Cdc2 are reduced. We speculate that Hsp90α may be required to maintain and to activate these regulators and/or to disassemble the synaptonemal complex that holds homologous chromosomes together. The link between fertility and Hsp90 is further supported by our finding that an Hsp90 inhibitor that can cross the blood-testis barrier can partially phenocopy the genetic defects. 相似文献
125.
Krzysztof Mikołajczak Anetta Kuczyńska Paweł Krajewski Aneta Sawikowska Maria Surma Piotr Ogrodowicz Tadeusz Adamski Karolina Krystkowiak Andrzej G. Górny Michał Kempa Iwona Szarejko Justyna Guzy-Wróbelska Kornelia Gudyś 《Journal of applied genetics》2017,58(1):23-35
High-yielding capacity of the modern barley varieties is mostly dependent on the sources of semi-dwarfness associated with the sdw1/denso locus. The objective of the study was to identify quantitative trait loci (QTLs) associated with the plant height and yield potential of barley recombinant inbred lines (RILs) grown under various soil moisture regimes. The plant material was developed from a hybrid between the Maresi (European cv.) and CamB (Syrian cv.). A total of 103 QTLs affecting analysed traits were detected and 36 of them showed stable effects over environments. In total, ten QTLs were found to be significant only under water shortage conditions. Nine QTLs affecting the length of main stem were detected on 2H-6H chromosomes. In four of the detected QTLs, alleles contributed by Maresi had negative effects on that trait, the most significant being the QLSt-3H.1-1 in the 3H.1 linkage group. The close linkage between QTLs identified around the sdw1/denso locus, with positive alleles contributed by Maresi, indicates that the semi-dwarf cv. Maresi could serve as a donor of favourable traits resulting in grain yield improvement, also under water scarcity. Molecular analyses revealed that the Syrian cv. also contributed alleles which increased the yield potential. Available barley resources of genomic annotations were employed to the biological interpretation of detected QTLs. This approach revealed 26 over-represented Gene Ontology terms. In the projected support intervals of QGWSl-5H.3-2 and QLSt-5H.3 on the chromosome 5H, four genes annotated to ‘response to stress’ were found. It suggests that these QTL-regions may be involved in a response of plant to a wide range of environmental disturbances. 相似文献
126.
Lipopolysaccharides of seven Bradyrhizobium strains and three whole-cell fatty acid preparations from bacteria isolated from nodules of Sarothamnus scoparius (common broom) were studied for the presence of very long chain (ω-1)-hydroxy fatty acids. Several such fatty acids were identified. Among them, straight-chain as well as mono- and dimethyl branched acids with chains in the range from 26 to 34 carbon atoms were found. Pyrrolidides and 4,4-dimethyloxazoline derivatives were used to determine the branching position. Carbons at the (ω-10) and/or (ω-11) positions in alkyl chains were points of attachment of methyl groups. These data complete the structure of bradyrhizobial lipid A with important details. The obtained results can be applied in the chemotaxonomy of Bradyrhizobium. 相似文献
127.
Although the human nonclassical class Ib major histocompatibility complex (Mhc) locus, HLA-G, is known to act as an immune suppressor in immune-privileged sites, little is currently known regarding participation of
the rodent class Ib Mhc in similar pathways. Here, we investigated the expression properties of the mouse nonclassical Mhc H2-Q5
k
gene, previously detected in tumors and tissues associated with pregnancy. We find that H2-Q5
k
is alternatively spliced into multiple novel isoforms in a wide panel of C3H tissues. Unlike other known class I MHC, it
is most highly transcribed in the brain, where the classical class Ia Mhc products are scarce. The truncated isoforms are selectively enriched in sites of immune privilege and are translated into
cell surface proteins in neural crest-derived transfected cells. Furthermore, we present data supporting a model whereby Q5k isoforms serve an immune-protective role by donating their Qdm leader peptide to Qa-1, in a pathway homologous to the HLA-G
leader fragment binding HLA-E and inhibiting CD94/NKG2A-positive cytotoxic cells. In addition, we report a previously unknown
homolog of H2-Q5
k
in the C57BL/6 mouse, which encodes Qdm, but is transcribed solely into noncanonical isoforms. Collectively, these studies
demonstrate that H2-Q5
k
, and its homologous class I-like H2
b
gene may play tissue-specific roles in regulating immune surveillance. 相似文献
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Glycotypes, particularly those that terminate with sialic acid and fucose are known to play a fundamental role in human development, during implantation, growth and differentiation of fetal tissues. The present review describes changes in the exposition of terminal sialic acid and fucose isoforms in the amniotic fluid glycoconjugates, α1-acid glycoprotein and fibronectin during critical stages of pregnancy, i.e. second and third trimester, perinatal period, delivery and post-date pregnancy. The distinct amniotic glycoforms are suggested to be implicated in regulatory processes to ensure homoeostasis during pregnancy and to protect the fetus. These may have the potential of becoming additional laboratory makers in obstetrics to monitor pregnancy. 相似文献