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971.
Understanding regional variability in species richness is necessary for conservation efforts to succeed in the face of large-scale environmental deterioration. Several analyses of North American vertebrates have shown that climatic energy provides the best explanation of contemporary species richness patterns. The paucity of analyses of insect diversity patterns, however, remains a serious obstacle to a general hypothesis of spatial variation in diversity. We collected species distribution data on a North American beetle genus, Epicauta (Coleoptera: Meloidae) and tested several major diversity hypotheses. These beetles are generally grasshopper egg predators as larvae, and angiosperm herbivores as adults. Epicauta richness is highest in the hot, dry American southwest, and decreases north and east, consistent with the species richness-energy hypothesis. Potential evapotranspiration, which is also the best predictor of richness patterns among North American vertebrates, explains 80.2% of the variability in Epicauta species richness. Net primary productivity and variables measuring climatic heat energy only (such as PET) are not generally comparable, though they are sometimes treated as if they were equivalent. We conclude that the species richness-energy hypothesis currently provides a better overall explanation for Epicauta species richness patterns in North America than other major diversity hypotheses. The observed relationship between climatic energy and regional species richness may provide significant insight into the response of ecological communities to climate change. 相似文献
972.
A direct method for determination of Δ5 3β-hydroxysteroid dehydrogenase (3β-HSD) activity was employed in isolated Leydig cells (LC) derived from rats on fetal day 19 (F19) and postnatal (N) days 1,12,24, 34 and 45 and adults. The activity of 3β-HSD in the adult LC was 1.15 ± 0.02 (μmole/μg DNA/hr, mean ± SEM, n = 73). Activities in the other groups, expressed as a percentage of the respective adult control, were: F19-38%; N1-39%; N12-8%; N24-89%; N34-166%; and N45-118%. A good correlation was found between histochemical staining for 3β-HSD and the quantitive method employed. Using (3H)-DHA as a substrate, LC isolated from F19, n1 and N12 produced testosterone in appreciable amounts (41%, 55% and 20% of the toal products respectively) whereas at advanced stages of development (N24 to adulthood) the major product was androstenedione (93 ± 1%). These findings may be explained by the observed decrease in 17β-hydroxysteroid dehydrogenase (17β-HSD) activity, due to an insufficient supply of NADPH, in the older vs. earlier stages of development. This study indicates the presence of steroidogenic enzymatic activity in LC throughout development in the rat. It also provides a relatively simple in vitro model for studies of testicular regulation during development. 相似文献
973.
Alexander P Walker Haitian Fan Jeremy R Keown Michael L Knight Jonathan
M Grimes Ervin Fodor 《Nucleic acids research》2021,49(22):13019
SARS-CoV-2 is a positive-sense RNA virus responsible for the Coronavirus Disease 2019 (COVID-19) pandemic, which continues to cause significant morbidity, mortality and economic strain. SARS-CoV-2 can cause severe respiratory disease and death in humans, highlighting the need for effective antiviral therapies. The RNA synthesis machinery of SARS-CoV-2 is an ideal drug target and consists of non-structural protein 12 (nsp12), which is directly responsible for RNA synthesis, and numerous co-factors involved in RNA proofreading and 5′ capping of viral RNAs. The formation of the 5′ 7-methylguanosine (m7G) cap structure is known to require a guanylyltransferase (GTase) as well as a 5′ triphosphatase and methyltransferases; however, the mechanism of SARS-CoV-2 RNA capping remains poorly understood. Here we find that SARS-CoV-2 nsp12 is involved in viral RNA capping as a GTase, carrying out the addition of a GTP nucleotide to the 5′ end of viral RNA via a 5′ to 5′ triphosphate linkage. We further show that the nsp12 NiRAN (nidovirus RdRp-associated nucleotidyltransferase) domain performs this reaction, and can be inhibited by remdesivir triphosphate, the active form of the antiviral drug remdesivir. These findings improve understanding of coronavirus RNA synthesis and highlight a new target for novel or repurposed antiviral drugs against SARS-CoV-2. 相似文献
974.
975.
Mariann M. Gabrawy Reyhan Westbrook Austin King Nick Khosravian Neeraj Ochaney Tagide DeCarvalho Qinchuan Wang Yuqiong Yu Qiao Huang Adam Said Michael Abadir Cissy Zhang Pratik Khare Jennifer E. Fairman Anne Le Ginger L. Milne Fernando J. Vonhoff Jeremy D. Walston Peter M. Abadir 《Aging cell》2024,23(4):e14102
Tryptophan catabolism is highly conserved and generates important bioactive metabolites, including kynurenines, and in some animals, NAD+. Aging and inflammation are associated with increased levels of kynurenine pathway (KP) metabolites and depleted NAD+, factors which are implicated as contributors to frailty and morbidity. Contrastingly, KP suppression and NAD+ supplementation are associated with increased life span in some animals. Here, we used DGRP_229 Drosophila to elucidate the effects of KP elevation, KP suppression, and NAD+ supplementation on physical performance and survivorship. Flies were chronically fed kynurenines, KP inhibitors, NAD+ precursors, or a combination of KP inhibitors with NAD+ precursors. Flies with elevated kynurenines had reduced climbing speed, endurance, and life span. Treatment with a combination of KP inhibitors and NAD+ precursors preserved physical function and synergistically increased maximum life span. We conclude that KP flux can regulate health span and life span in Drosophila and that targeting KP and NAD+ metabolism can synergistically increase life span. 相似文献
976.
Jeremy N. Skepper 《BioEssays : news and reviews in molecular, cellular and developmental biology》1999,21(9):802-802
Biological Specimen Preparation for Transmission Electron Microscopy (1998). A.M. Glauert, P.R. Lewis. In: A.M. Glauert (Ed). Practical Methods in Electron Microscopy, Vol 17. London: Portland Press, 326 pp. £39.50 paperback; ISBN 1 85578 060 7 相似文献
977.
978.
979.
The spider tree of life: phylogeny of Araneae based on target‐gene analyses from an extensive taxon sampling
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Ward C. Wheeler Jonathan A. Coddington Louise M. Crowley Dimitar Dimitrov Pablo A. Goloboff Charles E. Griswold Gustavo Hormiga Lorenzo Prendini Martín J. Ramírez Petra Sierwald Lina Almeida‐Silva Fernando Alvarez‐Padilla Miquel A. Arnedo Ligia R. Benavides Silva Suresh P. Benjamin Jason E. Bond Cristian J. Grismado Emile Hasan Marshal Hedin Matías A. Izquierdo Facundo M. Labarque Joel Ledford Lara Lopardo Wayne P. Maddison Jeremy A. Miller Luis N. Piacentini Norman I. Platnick Daniele Polotow Diana Silva‐Dávila Nikolaj Scharff Tamás Szűts Darrell Ubick Cor J. Vink Hannah M. Wood Junxia Zhang 《Cladistics : the international journal of the Willi Hennig Society》2017,33(6):574-616
980.
Organismal dispersal through mountain passes should be more constrained by temperature‐related differences between lowland and highland sites in montane environments. This may lead to higher rates of diversification through isolation of existing lineages toward the tropics. This mechanism, proposed by Janzen, could influence broad‐scale patterns of biodiversity across mountainous regions and more broadly across latitudinal gradients. We constructed two complementary analyses to test this hypothesis. First, we measured topographically‐derived thermal gradients using recently‐developed climatic data across the Americas, reviewing the main expectations from Janzen's climatic model. Then, we evaluated whether thermal barriers predict assemblage similarity for amphibians and mammals along elevational gradients across most of their latitudinal extent in the Americas. Thermal barriers between low and high elevation areas, initially proposed to be unique to tropical environments, are comparably strong in some temperate regions, particularly along the western slopes of North American dividing ranges. Biotic similarity for both mammals and amphibians decreases between sites that are separated by elevation‐related thermal barriers. That is, the stronger the thermal barrier separating pairs of sites across the latitudinal gradient, the lower the similarity of their species assemblages. Thermal barriers explain 10–35% of the variation in latitudinal gradients of biotic similarity, effects that were stronger in comparisons of sites at high elevations. Mammals' stronger dispersal capacities and homeothermy may explain weaker effects of thermal barriers on gradients of assemblage similarity than among amphibians. Understanding how temperature gradients have shaped gradients of montane biological diversity in the past will improve understanding of how changing environments may affect them in the future. 相似文献