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31.
32.
In autumn the vast majority of the North American population of Eared Grebes ( Podiceps nigricollis ) congregates for several months at Great Salt Lake, Utah, and Mono Lake, California. Because the lakes are so large, it has not been possible to monitor grebe migration with sufficient accuracy to determine when peak numbers are reached. To clarify migration phenology, we analyzed data from 2 isolated wetland areas in southwestern Wyoming where grebes land en route between breeding areas in the interior and Great Salt Lake. Occasional birds, probably nonbreeders or failed breeders, begin moving southward as early as mid-June. Migration of postbreeding birds starts in late July, peaks in late August and September, and is largely completed by the end of October, with very small numbers arriving into November. The pattern of migration and number of birds encountered varied annually, but 95% of the migration was usually completed by 15 October. As a result, censuses at the major staging lake made on or after 15 October but before the grebes depart for wintering areas can be used to study trends in size of the North American population. 相似文献
33.
Long stretches of sea and desert often interrupt the migration routes of small songbirds, whose fat reserves must be restored before these can be crossed as they provide no opportunity for refuelling. To investigate whether magnetic cues might enable inexperienced migratory birds to recognize a region where they need to replenish their body fat, we caught and held thrush nightingales (Luscinia luscinia) in Sweden just before their first migration and exposed them to a magnetic field simulating that at a migratory stopover in northern Egypt, before the Sahara Desert. We found that this magnetic field stimulated the birds to extend their fat-deposition period, indicating that magnetic cues may help small migratory birds to confront large ecological barriers. 相似文献
34.
Central nervous system stem cells in the embryo and adult 总被引:19,自引:0,他引:19
J. Frisén C. B. Johansson C. Lothian U. Lendahl 《Cellular and molecular life sciences : CMLS》1998,54(9):935-945
The central nervous system is generated from neural stem cells during embryonic development. These cells are multipotent
and generate neurons, astrocytes and oligodendrocytes. The last few years it has been found that there are populations of
stem cells also in the adult mammalian brain and spinal cord. In this paper, we review the recent development in the field
of embryonic and adult neural stem cells.
Received 26 March 1998; received after revision 27 April 1998; accepted 27 April 1998 相似文献
35.
Hundreds of variants clustered in genomic loci and biological pathways affect human height 总被引:2,自引:0,他引:2
Lango Allen H Estrada K Lettre G Berndt SI Weedon MN Rivadeneira F Willer CJ Jackson AU Vedantam S Raychaudhuri S Ferreira T Wood AR Weyant RJ Segrè AV Speliotes EK Wheeler E Soranzo N Park JH Yang J Gudbjartsson D Heard-Costa NL Randall JC Qi L Vernon Smith A Mägi R Pastinen T Liang L Heid IM Luan J Thorleifsson G Winkler TW Goddard ME Sin Lo K Palmer C Workalemahu T Aulchenko YS Johansson A Zillikens MC Feitosa MF Esko T Johnson T Ketkar S Kraft P Mangino M Prokopenko I Absher D Albrecht E 《Nature》2010,467(7317):832-838
Most common human traits and diseases have a polygenic pattern of inheritance: DNA sequence variants at many genetic loci influence the phenotype. Genome-wide association (GWA) studies have identified more than 600 variants associated with human traits, but these typically explain small fractions of phenotypic variation, raising questions about the use of further studies. Here, using 183,727 individuals, we show that hundreds of genetic variants, in at least 180 loci, influence adult height, a highly heritable and classic polygenic trait. The large number of loci reveals patterns with important implications for genetic studies of common human diseases and traits. First, the 180 loci are not random, but instead are enriched for genes that are connected in biological pathways (P = 0.016) and that underlie skeletal growth defects (P?0.001). Second, the likely causal gene is often located near the most strongly associated variant: in 13 of 21 loci containing a known skeletal growth gene, that gene was closest to the associated variant. Third, at least 19 loci have multiple independently associated variants, suggesting that allelic heterogeneity is a frequent feature of polygenic traits, that comprehensive explorations of already-discovered loci should discover additional variants and that an appreciable fraction of associated loci may have been identified. Fourth, associated variants are enriched for likely functional effects on genes, being over-represented among variants that alter amino-acid structure of proteins and expression levels of nearby genes. Our data explain approximately 10% of the phenotypic variation in height, and we estimate that unidentified common variants of similar effect sizes would increase this figure to approximately 16% of phenotypic variation (approximately 20% of heritable variation). Although additional approaches are needed to dissect the genetic architecture of polygenic human traits fully, our findings indicate that GWA studies can identify large numbers of loci that implicate biologically relevant genes and pathways. 相似文献
36.
Pericytes regulate the blood-brain barrier 总被引:2,自引:0,他引:2
Armulik A Genové G Mäe M Nisancioglu MH Wallgard E Niaudet C He L Norlin J Lindblom P Strittmatter K Johansson BR Betsholtz C 《Nature》2010,468(7323):557-561
The blood-brain barrier (BBB) consists of specific physical barriers, enzymes and transporters, which together maintain the necessary extracellular environment of the central nervous system (CNS). The main physical barrier is found in the CNS endothelial cell, and depends on continuous complexes of tight junctions combined with reduced vesicular transport. Other possible constituents of the BBB include extracellular matrix, astrocytes and pericytes, but the relative contribution of these different components to the BBB remains largely unknown. Here we demonstrate a direct role of pericytes at the BBB in vivo. Using a set of adult viable pericyte-deficient mouse mutants we show that pericyte deficiency increases the permeability of the BBB to water and a range of low-molecular-mass and high-molecular-mass tracers. The increased permeability occurs by endothelial transcytosis, a process that is rapidly arrested by the drug imatinib. Furthermore, we show that pericytes function at the BBB in at least two ways: by regulating BBB-specific gene expression patterns in endothelial cells, and by inducing polarization of astrocyte end-feet surrounding CNS blood vessels. Our results indicate a novel and critical role for pericytes in the integration of endothelial and astrocyte functions at the neurovascular unit, and in the regulation of the BBB. 相似文献
37.
Proinsulin C-peptide and its analogues induce intracellular Ca2+ increases in human renal tubular cells 总被引:3,自引:0,他引:3
Shafqat J Juntti-Berggren L Zhong Z Ekberg K Köhler M Berggren PO Johansson J Wahren J Jörnvall H 《Cellular and molecular life sciences : CMLS》2002,59(7):1185-1189
Based on the findings that proinsulin C-peptide binds specifically to cell membranes, we investigated the effects of C-peptide
and related molecules on the intracellular Ca2+ concentration ([Ca2+]i) in human renal tubular cells using the indicator fura-2/AM. The results show that human C-peptide and its C-terminal pentapeptide
(positions 27–31, EGSLQ), but not the des (27–31) C-peptide or randomly scrambled C-peptide, elicit a transient increase in
[Ca2+]i. Rat C-peptide and rat C-terminal pentapeptide also induce a [Ca2+]i response in human tubular cells, while a human pentapeptide analogue with Ala at position 1 gives no [Ca2+]i response, and those with Ala at positions 2–5 induce responses with different amplitudes. These results define a species
cross-reactivity for C-peptide and demonstrate the importance of Glu at position 1 of the pentapeptide. Preincubation of cells
with pertussis toxin abolishes the effect on [Ca2+]i by both C-peptide and the pentapeptide. These results are compatible with previous data on C-peptide binding to cells and
activation of Na+,K+ATPase. Combined, all data show that C-peptide is a bioactive peptide and suggest that it elicits changes in [Ca2+]i via G-protein-coupled pathways, giving downstream enzyme effects.
Received 13 May 2002; accepted 16 May 2002 相似文献
38.
Dubrovinsky L Dubrovinskaia N Langenhorst F Dobson D Rubie D Gessmann C Abrikosov IA Johansson B Baykov VI Vitos L Le Bihan T Crichton WA Dmitriev V Weber HP 《Nature》2003,422(6927):58-61
The boundary between the Earth's metallic core and its silicate mantle is characterized by strong lateral heterogeneity and sharp changes in density, seismic wave velocities, electrical conductivity and chemical composition. To investigate the composition and properties of the lowermost mantle, an understanding of the chemical reactions that take place between liquid iron and the complex Mg-Fe-Si-Al-oxides of the Earth's lower mantle is first required. Here we present a study of the interaction between iron and silica (SiO2) in electrically and laser-heated diamond anvil cells. In a multianvil apparatus at pressures up to 140 GPa and temperatures over 3,800 K we simulate conditions down to the core-mantle boundary. At high temperature and pressures below 40 GPa, iron and silica react to form iron oxide and an iron-silicon alloy, with up to 5 wt% silicon. At pressures of 85-140 GPa, however, iron and SiO2 do not react and iron-silicon alloys dissociate into almost pure iron and a CsCl-structured (B2) FeSi compound. Our experiments suggest that a metallic silicon-rich B2 phase, produced at the core-mantle boundary (owing to reactions between iron and silicate), could accumulate at the boundary between the mantle and core and explain the anomalously high electrical conductivity of this region. 相似文献
39.
Johansson S Gullbo J Lindholm P Ek B Thunberg E Samuelsson G Larsson R Bohlin L Claeson P 《Cellular and molecular life sciences : CMLS》2003,60(1):165-175
Four novel proteins (phoratoxins C–F) have been isolated from the North American mistletoe Phoradendron tomentosum. The amino acid sequences of these phoratoxins were determined unambiguously using a combination of Edman degradation and
trypsin enzymatic digestion, and by electrospray ionization tandem mass spectrometry sequencing. Phoratoxins C, E and F consist
of 46 amino acid residues; and phoratoxin D of 41. All proteins had six cysteines, similar to the earlier described phoratoxins
A and B, which are thionins. The cytotoxicity of each protein was evaluated in a human cell line panel that represented several
cytotoxic drug-resistance mechanisms. For the half-maximal inhibitory concentrations (IC50 values) of the different cell lines in the panel, correlation with those of standard drugs was low. The most potent cytotoxic
phoratoxin C was further tested on primary cultures of human tumor cells from patients. The solid tumor samples from breast
cancer cells were 18 times more sensitive to phoratoxin C than the tested hematological tumor samples.
Received 30 September 2002; received after revision 28 October 2002; accepted 7 November 2002
RID="*"
ID="*"Corresponding author. 相似文献
40.
Unordered structured of proinsulin C-peptide in aqueous solution and in the presence of lipid vesicles 总被引:2,自引:0,他引:2
Henriksson M Shafqat J Liepinsh E Tally M Wahren J Jörnvall H Johansson J 《Cellular and molecular life sciences : CMLS》2000,57(2):337-342
Proinsulin C-peptide ameliorates renal and autonomic nerve function and increases skeletal muscle blood flow, oxygen uptake and glucose transport in patients with insulin-dependent diabetes mellitus. These effects have in part been ascribed to the stimulatory influence of C-peptide on Na+,K+-ATPase and endothelial nitric oxide synthase. To evaluate the capacity of C-peptide to insert into lipid bilayers and form ion channels, C-peptide secondary structure and membrane interactions were studied with circular dichroism spectroscopy and size exclusion chromatography. C-peptide is shown to lack a stable secondary structure, both when part of proinsulin and when free in aqueous solution, although the N-terminal third of the peptide exhibits an alpha-helical conformation in trifluoroethanol. Moreover, C-peptide remains disordered in the aqueous solvent in the presence of lipid vesicles, regardless of vesicle composition. In conclusion, C-peptide is unlikely to elicit physiological effects through stable conformation-dependent interactions with lipid membranes. 相似文献