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121.
Intramuscular fat content and water-holding capacity are important traits in livestock as they influence meat quality, nutritive value of the muscle, and animal health. As a model for livestock, two inbred lines of the Berlin Muscle Mouse population, which had been long-term selected for high muscle mass, were used to identify genomic regions affecting intramuscular fat content and water-holding capacity. The intramuscular fat content of the Musculus longissimus was on average 1.4 times higher in BMMI806 than in BMMI816 mice. This was accompanied by a 1.5 times lower water-holding capacity of the Musculus quadriceps in BMMI816 mice. Linkage analyses with 332 G3 animals of reciprocal crosses between these two lines revealed quantitative trait loci for intramuscular fat content on chromosome 7 and for water-holding capacity on chromosome 2. In part, the identified loci coincide with syntenic regions in pigs in which genetic effects for the same traits were found. Therefore, these muscle-weight-selected mouse lines and the produced intercross populations are valuable genetic resources to identify genes that could also contribute to meat quality in other species.  相似文献   
122.
Postcopulatory sexual selection is widely accepted to underlie the extraordinary diversification of sperm morphology. However, why does it favour longer sperm in some taxa but shorter in others? Two recent hypotheses addressing this discrepancy offered contradictory explanations. Under the sperm dilution hypothesis, selection via sperm density in the female reproductive tract favours more but smaller sperm in large, but the reverse in small, species. Conversely, the metabolic constraint hypothesis maintains that ejaculates respond positively to selection in small endothermic animals with high metabolic rates, whereas low metabolic rates constrain their evolution in large species. Here, we resolve this debate by capitalizing on the substantial variation in mammalian body size and reproductive physiology. Evolutionary responses shifted from sperm length to number with increasing mammalian body size, thus supporting the sperm dilution hypothesis. Our findings demonstrate that body-size-mediated trade-offs between sperm size and number can explain the extreme diversification in sperm phenotypes.  相似文献   
123.
p24 proteins are assumed to play an important role in the transport of secreted and transmembrane proteins into membranes. However, only few cargo proteins are known that partially, but in no case completely require p24 proteins for membrane transport. Here, we show that two p24 proteins are essential for dorsoventral patterning of Drosophila melanogaster embryo. Mutations in the genes, eclair (eca) and baiser (bai), encoding two p24 proteins reduce signalling by the TGF-beta homologue, Dpp, in early embryos. This effect is strictly maternal and specific to early embryogenesis, as Dpp signalling in other contexts is not notably affected. We provide genetic evidence that in the absence of eca or bai function in the oocyte, the maternally expressed type I TGF-beta receptor Tkv is not active. We propose that during early embryogenesis eca and bai are specifically required for the activity of the maternal Tkv, while the zygotic Tkv is not affected in the mutant embryos. Mutations in either eca or bai are sufficient for the depletion of Tkv activity and no enhancement of the phenotypes was observed in embryos derived from oocytes mutant for both genes. The dependence of maternal Tkv protein on the products of p24 genes may serve as an in vivo model for studying p24 proteins.  相似文献   
124.
To elucidate the function of the two cytokine-binding modules (CBM) of the leukemia inhibitory factor receptor (LIFR), receptor chimeras of LIFR and the interleukin-6 receptor (IL-6R) were constructed. Either the NH(2)-terminal (chimera RILLIFdeltaI) or the COOH-terminal LIFR CBM (chimera RILLIFdeltaII) were replaced by the structurally related CBM of the IL-6R which does not bind LIF. Chimera RILLIFdeltaI is functionally inactive, whereas RILLIFdeltaII binds LIF and mediates signalling as efficiently as the wild-type LIFR. Deletion mutants of the LIFR revealed that both the NH(2)-terminal CBM and the Ig-like domain of the LIFR are involved in LIF binding, presumably via the LIF site III epitope. The main function of the COOH-terminal CBM of the LIFR is to position the NH(2)-terminal CBM and the Ig-like domain, so that these can bind to LIF. In analogy to a recently published model of the IL-6R complex, a model of the active LIFR complex is suggested which positions the COOH-terminal CBM at LIF site I and the NH(2)-terminal CBM and the Ig-like domain at site III. An additional contact is postulated between the Ig-like domain of gp130 and the NH(2)-terminal CBM of the LIFR.  相似文献   
125.
To test how differences in locomotor behaviors may be reflected in muscle fiber-type diversity within anurans, a comparison of hindlimb muscles between the powerful terrestrial hopper, Rana catesbeiana, and the tree frog, Litoria caerulea, was done. One postural muscle (tibialis posticus, TP) and one primary hopping muscle (plantaris longus, PL), were characterized to identify muscle fiber types using standard histochemical methods. In addition, spectophotometric analysis of activity levels of the oxidative enzyme citrate synthase (CS) and the glycolytic enzyme lactate dehydrogenase (LDH) were done in each muscle. In spite of presumed differences in behavior between the species, we found no significant differences in the proportions of the identified fiber types when the muscles were compared across species. In addition, there were no significant differences in the proportions of the different fiber types between the postural versus phasic muscles within species. Within Rana, the postural muscle (TP) had greater oxidative capacity (as measured by CS activity) than did the phasic muscle (PL). Both muscles had equivalent LDH activities. Within Litoria, PL and TP did not differ in either LDH or CS activities. Both PL and TP of Litoria had less LDH activity and greater CS activity than their homologs in Rana. Thus, in spite of the uniform populations of fiber types between muscles and species, the metabolic diversity based on enzyme activity is consistent with behavioral differences between the species. These results suggest that the range of functional diversity within fiber types may be very broad in anurans, and histochemical fiber typing alone is not a clear indicator of their metabolic or functional properties.  相似文献   
126.
Recent advances in chlorophyll biosynthesis and breakdown in higher plants   总被引:18,自引:0,他引:18  
Chlorophyll (Chl) has unique and essential roles in photosynthetic light-harvesting and energy transduction, but its biosynthesis, accumulation and degradation is also associated with chloroplast development, photomorphogenesis and chloroplast-nuclear signaling. Biochemical analyses of the enzymatic steps paved the way to the identification of their encoding genes. Thus, important progress has been made in the recent elucidation of almost all genes involved in Chl biosynthesis and breakdown. In addition, analysis of mutants mainly in Arabidopsis, genetically engineered plants and the application of photo-reactive herbicides contributed to the genetic and regulatory characterization of the formation and breakdown of Chl. This review highlights recent progress in Chl metabolism indicating highly regulated pathways from the synthesis of precursors to Chl and its degradation to intermediates, which are not longer photochemically active.  相似文献   
127.
The influence of adrenergic receptor blockers on the prolactin releasing effect of methysergide and cyproheptadine was examined in sexually mature female monkeys under ketamine anesthesia. Propranolol, a β-adrenergic blocker, at a dose of 1 mg/kg did not alter the prolactin releasing action of 0.1 mg/kg of methysergide but significantly potentiated (P < 0.025) the prolactin releasing action of 0.5 mg/kg of cyproheptadine. Phentolamine and phenoxybenzamine, both α-adrenergic blockers, at 1 mg/kg blunted the prolactin releasing effect of methysergide and cyproheptadine, but the pattern of prolactin blockade was different between the two putative antiserotonergic drugs. The prior administration of apomorphine, 4 mg/kg, a dopamine receptor stimulator, blocked the prolactin releasing effect of methysergide and cyproheptadine. Evidence presented here and from the literature indicate that the prolactin releasing action of methysergide and cyproheptadine is mediated by an antidopaminergic action directly on the pituitary.  相似文献   
128.
Accumulation and degradation of scar tissue in fibrotic liver disease occur slowly, typically over many years. Direct measurement of fibrogenesis, the rate of scar tissue deposition, may provide valuable therapeutic and prognostic information. We describe here results from a pilot study utilizing in vivo metabolic labeling to measure the turnover rate of hepatic collagen and collagen-associated proteins in plasma for the first time in human subjects. Eight subjects with chronic liver disease were labeled with daily oral doses of 2H2O for up to 8 weeks prior to diagnostic liver biopsy and plasma collection. Tandem mass spectrometry was used to measure the abundance and fractional synthesis rate (FSR) of proteins in liver and blood. Relative protein abundance and FSR data in liver revealed marked differences among subjects. FSRs of hepatic type I and III collagen ranged from 0.2–0.6% per day (half-lives of 4 months to a year) and correlated significantly with worsening histologic fibrosis. Analysis of plasma protein turnover revealed two collagen-associated proteins, lumican and transforming growth factor beta-induced-protein (TGFBI), exhibiting FSRs that correlated significantly with FSRs of hepatic collagen. In summary, this is the first direct measurement of liver collagen turnover in vivo in humans and suggests a high rate of collagen remodeling in advanced fibrosis. In addition, the FSRs of collagen-associated proteins in plasma are measurable and may provide a novel strategy for monitoring hepatic fibrogenesis rates.  相似文献   
129.
Evidence for specific and direct bacterial product recognition through toll-like receptors (TLRs) has been emphasized recently. We analyzed lipopeptide analogues and enterobacterial lipopolysaccharide (eLPS) for their potential to activate cells through TLR2 and TLR4. Whereas bacterial protein palmitoylated at its N-terminal cysteine and N-terminal peptides derived thereof are known to induce TLR2-mediated cell activation, a synthetic acylhexapeptide mimicking a bacterial lipoprotein subpopulation for which N-terminal trimyristoylation is characteristic (Myr(3)CSK(4)) activated cells not only through TLR2 but also through TLR4. Conversely, highly purified eLPS triggered cell activation through overexpressed TLR2 in the absence of TLR4 expression if CD14 was coexpressed. Accordingly, TLR2(-/-) macrophages prepared upon gene targeting responded to Myr(3)CSK(4) challenge, whereas TLR2(-/-)/TLR4(d/d) cells were unresponsive. Through interferon-gamma (IFNgamma) priming, macrophages lacking expression of functional TLR4 and/or MD-2 acquired sensitivity to eLPS, whereas TLR2/TLR4 double deficient cells did not. Not only TLR2(-/-) mice but also TLR4(-/-) mice were resistant to Myr(3)CSK(4) challenge-induced fatal shock. d-Galactosamine-sensitized mice expressing defective TLR4 or lacking TLR4 expression acquired susceptibility to eLPS-driven toxemia upon IFNgamma priming, whereas double deficient mice did not. Immunization toward ovalbumin using Myr(3)CSK(4) as adjuvant was ineffective in TLR2(-/-)/TLR4(-/-) mice yet effective in wild-type, TLR2(-/-), or TLR4(-/-) mice as shown by analysis of ovalbumin-specific serum Ig concentration. A compound such as Myr(3)CSK(4) whose stimulatory activity is mediated by both TLR2 and TLR4 might constitute a preferable adjuvant. On the other hand, simultaneous blockage of both of the two TLRs might effectively inhibit infection-induced pathology.  相似文献   
130.
Ligand binding to the extracellular domain of the thrombopoietin receptor (TpoR) imparts a specific orientation on the transmembrane (TM) and intracellular domains of the receptors that is required for physiologic activation via receptor dimerization. To map the inactive and active dimeric orientations of the TM helices, we performed asparagine (Asn)-scanning mutagenesis of the TM domains of the murine and human TpoR. Substitution of Asn at only one position (S505N) activated the human receptor, whereas Asn substitutions at several positions activated the murine receptor. Second site mutational studies indicate that His499 near the N terminus of the TM domain is responsible for protecting the human receptor from activation by Asn mutations. Structural studies reveal that the sequence preceding His499 is helical in the murine receptor but non-helical in peptides corresponding to the TM domain of the inactive human receptor. The activating S505N mutation and the small molecule agonist eltrombopag both induce helix in this region of the TM domain and are associated with dimerization and activation of the human receptor. Thus, His499 regulates the activation of human TpoR and provides additional protection against activating mutations, such as oncogenic Asn mutations in the TM domain.  相似文献   
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