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1.
Carbon and nitrogen stable isotope analyses have improved our understanding of food webs and movement patterns of aquatic
organisms. These techniques have recently been applied to diet studies of elasmobranch fishes, but isotope turnover rates
and isotope diet–tissue discrimination are still poorly understood for this group. We performed a diet switch experiment on
captive sandbar sharks (Carcharhinus plumbeus) as a model shark species to determine tissue turnover rates for liver, whole blood, and white muscle. In a second experiment,
we subjected captive coastal skates (Leucoraja spp.) to serial salinity reductions to measure possible impacts of tissue urea content on nitrogen stable isotope values.
We extracted urea from spiny dogfish (Squalus acanthias) white muscle to test for effects on nitrogen stable isotopes. Isotope turnover was slow for shark tissues and similar to
previously published estimates for stingrays and teleost fishes with low growth rates. Muscle isotope data would likely fail
to capture seasonal migrations or diet switches in sharks, while liver and whole blood would more closely reflect shorter
term movement or shifts in diet. Nitrogen stable isotope values of skate blood and skate and dogfish white muscle were not
affected by tissue urea content, suggesting that available diet–tissue discrimination estimates for teleost fishes with similar
physiologies would provide accurate estimates for elasmobranchs. 相似文献
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Combining experimental evolution with whole‐genome resequencing is a promising new strategy for investigating the dynamics of evolutionary change. Published studies that have resequenced laboratory‐selected populations of sexual organisms have typically focused on populations sampled at the end of an evolution experiment. These studies have attempted to associate particular alleles with phenotypic change and attempted to distinguish between different theoretical models of adaptation. However, neither the population used to initiate the experiment nor multiple time points sampled during the evolutionary trajectory are generally available for examination. In this issue of Molecular Ecology, Orozco‐terWengel et al. (2012) take a significant step forward by estimating genome‐wide allele frequencies at the start, 15 generations into and at the end of a 37‐generation Drosophila experimental evolution study. The authors identify regions of the genome that have responded to laboratory selection and describe the temporal dynamics of allele frequency change. They identify two common trajectories for putatively adaptive alleles: alleles either gradually increase in frequency throughout the entire 37 generations or alleles plateau at a new frequency by generation 15. The identification of complex trajectories of alleles under selection contributes to a growing body of literature suggesting that simple models of adaptation, whereby beneficial alleles arise and increase in frequency unimpeded until they become fixed, may not adequately describe short‐term response to selection. 相似文献
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Kathryn S. Evans Janneke Wit Lewis Stevens Steffen R. Hahnel Briana Rodriguez Grace Park Mostafa Zamanian Shannon C. Brady Ellen Chao Katherine Introcaso Robyn E. Tanny Erik C. Andersen 《PLoS pathogens》2021,17(3)
Parasitic nematodes cause a massive worldwide burden on human health along with a loss of livestock and agriculture productivity. Anthelmintics have been widely successful in treating parasitic nematodes. However, resistance is increasing, and little is known about the molecular and genetic causes of resistance for most of these drugs. The free-living roundworm Caenorhabditis elegans provides a tractable model to identify genes that underlie resistance. Unlike parasitic nematodes, C. elegans is easy to maintain in the laboratory, has a complete and well annotated genome, and has many genetic tools. Using a combination of wild isolates and a panel of recombinant inbred lines constructed from crosses of two genetically and phenotypically divergent strains, we identified three genomic regions on chromosome V that underlie natural differences in response to the macrocyclic lactone (ML) abamectin. One locus was identified previously and encodes an alpha subunit of a glutamate-gated chloride channel (glc-1). Here, we validate and narrow two novel loci using near-isogenic lines. Additionally, we generate a list of prioritized candidate genes identified in C. elegans and in the parasite Haemonchus contortus by comparison of ML resistance loci. These genes could represent previously unidentified resistance genes shared across nematode species and should be evaluated in the future. Our work highlights the advantages of using C. elegans as a model to better understand ML resistance in parasitic nematodes. 相似文献
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Nerve growth factor treatment or cAMP elevation reduces Ca2+/calmodulin-dependent protein kinase III activity in PC12 cells 总被引:3,自引:0,他引:3
A C Nairn R A Nichols M J Brady H C Palfrey 《The Journal of biological chemistry》1987,262(29):14265-14272
Ca2+/calmodulin-dependent protein kinase III (Ca2+/CaM kinase III) phosphorylates a protein of Mr = 100,000 (the 100-kDa protein), a major substrate for Ca2+/CaM-dependent protein phosphorylation found in many mammalian tissues and cell lines (Nairn, A.C., Baghat, B., and Palfrey, H.C. (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 7939-7943). Treatment of PC12 cells with nerve growth factor (NGF) or forskolin resulted in a decrease in the depolarization-dependent phosphorylation of the 100-kDa protein in intact cells and in a decrease in the Ca2+/CaM-dependent phosphorylation of the 100-kDa protein in cytosolic extracts. In experiments using cytosolic extracts, the initial effect of NGF on the phosphorylation of the 100-kDa protein was observed in less than 1 h, was maximal (70% decrease) after 12 h, and began to recover after 24 h. The effect of forskolin was more rapid and the maximal effect was greater (90-95% decrease). Decreased Ca2+/CaM kinase III activity was also found in PC12 cells treated with epidermal growth factor, 2-chloroadenosine plus isobutylmethylxanthine, or dibutyryl cAMP. The effect of forskolin did not reverse unless it was removed. Cycloheximide blocked the recovery of Ca2+/CaM kinase III activity observed following the removal of forskolin but did not affect the ability of forskolin to reduce kinase activity. Short-term treatment with phorbol ester had little effect on Ca2+/CaM kinase III activity; long-term treatment with phorbol ester, which results in the disappearance of enzymatically detectable protein kinase C, had no effect on the ability of NGF or 2-chloroadenosine to reduce Ca2+/CaM kinase III activity. The level of the 100-kDa protein as determined by immunological techniques was not changed by any treatment. These results suggested that the effect of treatment of PC12 cells with NGF or forskolin was to reduce the level of Ca2+/CaM kinase III per se. 相似文献
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Identification of a novel sequence that governs both polyadenylation and alternative splicing in region E3 of adenovirus. 总被引:13,自引:0,他引:13 下载免费PDF全文
Region E3 encodes four major overlapping mRNAs with different splicing patterns. There are two poly(A) sites, an upstream site called E3A and a downstream site called E3B. We have analyzed virus mutants with deletions or insertions in E3 in order to identify sequences that function in the alternative processing of E3 pre-mRNAs, and to understand what determines which poly(A) sites and which splice sites are used. In previous studies we established that the 5' boundary of the E3A poly(A) signal is at an ATTAAA sequence. We now show, using viable virus mutants, that the 3' boundary of the E3A signal is located within 47-62 nucleotides (nt) downstream of the ATTAAA (17-32 nt downstream of the last microheterogenous poly(A) addition site). Our data further suggest that the spacing between the ATTAAA, the cleavage sites, and the essential downstream sequences may be important in E3A 3' end formation. Of particular interest, these mutants suggest a novel mechanism for the control of alternative pre-mRNA processing. Mutants which are almost completely defective in E3A 3' end formation display greatly increased use of a 3' splice site located 4 nt upstream of the ATTAAA. The mRNA that uses this 3' splice site is polyadenylated at the E3B poly(A) site. We suggest, for this particular case, that alternative pre-mRNA processing could be determined by a competition between trans-acting factors that function in E3A 3' end formation or in splicing. These factors could compete for overlapping sequences in pre-mRNA. 相似文献