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排序方式: 共有1275条查询结果,搜索用时 279 毫秒
991.
Marianna Sadagurski Taylor Landeryou Gillian Cady John J. Kopchick Edward O. List Darlene E. Berryman Andrzej Bartke Richard A. Miller 《Aging cell》2015,14(6):1045-1054
Mice in which the genes for growth hormone (GH) or GH receptor (GHR?/?) are disrupted from conception are dwarfs, possess low levels of IGF‐1 and insulin, have low rates of cancer and diabetes, and are extremely long‐lived. Median longevity is also increased in mice with deletion of hypothalamic GH‐releasing hormone (GHRH), which leads to isolated GH deficiency. The remarkable extension of longevity in hypopituitary Ames dwarf mice can be reversed by a 6‐week course of GH injections started at the age of 2 weeks. Here, we demonstrate that mutations that interfere with GH production or response, in the Snell dwarf, Ames dwarf, or GHR?/? mice lead to reduced formation of both orexigenic agouti‐related peptide (AgRP) and anorexigenic proopiomelanocortin (POMC) projections to the main hypothalamic projection areas: the arcuate nucleus (ARH), paraventricular nucleus (PVH), and dorsomedial nucleus (DMH). These mutations also reduce hypothalamic inflammation in 18‐month‐old mice. GH injections, between 2 and 8 weeks of age, reversed both effects in Ames dwarf mice. Disruption of GHR specifically in liver (LiGHRKO), a mutation that reduces circulating IGF‐1 but does not lead to lifespan extension, had no effect on hypothalamic projections or inflammation, suggesting an effect of GH, rather than peripheral IGF‐1, on hypothalamic development. Hypothalamic leptin signaling, as monitored by induction of pStat3, is not impaired by GHR deficiency. Together, these results suggest that early‐life disruption of GH signaling produces long‐term hypothalamic changes that may contribute to the longevity of GH‐deficient and GH‐resistant mice. 相似文献
992.
Foster JT Woodworth BL Eggert LE Hart PJ Palmer D Duffy DC Fleischer RC 《Molecular ecology》2007,16(22):4738-4746
Infectious diseases now threaten wildlife populations worldwide but population recovery following local extinction has rarely been observed. In such a case, do resistant individuals recolonize from a central remnant population, or do they spread from small, perhaps overlooked, populations of resistant individuals? Introduced avian malaria (Plasmodium relictum) has devastated low‐elevation populations of native birds in Hawaii, but at least one species (Hawaii amakihi, Hemignathus virens) that was greatly reduced at elevations below about 1000 m tolerates malaria and has initiated a remarkable and rapid recovery. We assessed mitochondrial and nuclear DNA markers from amakihi and two other Hawaiian honeycreepers, apapane (Himatione sanguinea) and iiwi (Vestiaria coccinea), at nine primary study sites from 2001 to 2003 to determine the source of re‐establishing birds. In addition, we obtained sequences from tissue from amakihi museum study skins (1898 and 1948–49) to assess temporal changes in allele distributions. We found that amakihi in lowland areas are, and have historically been, differentiated from birds at high elevations and had unique alleles retained through time; that is, their genetic signature was not a subset of the genetic variation at higher elevations. We suggest that high disease pressure rapidly selected for resistance to malaria at low elevation, leaving small pockets of resistant birds, and this resistance spread outward from the scattered remnant populations. Low‐elevation amakihi are currently isolated from higher elevations (> 1000 m) where disease emergence and transmission rates appear to vary seasonally and annually. In contrast to results from amakihi, no genetic differentiation between elevations was found in apapane and iiwi, indicating that slight variation in genetic or life‐history attributes can determine disease resistance and population recovery. Determining the conditions that allow for the development of resistance to disease is essential to understanding how species evolve resistance across a landscape of varying disease pressures. 相似文献
993.
Staley AM Blanco JM Dufty AM Wildt DE Monfort SL 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2007,177(6):609-622
We examined the efficacy of noninvasive monitoring of endocrine function via fecal steroid immunoassays in the golden eagle
and peregrine falcon. High-pressure liquid chromatography analyses of fecal glucocorticoid metabolites (fGCM) revealed that
minor percentages of immunoreactive fGCM co-eluted with [3H]corticosterone in both sexes of the eagle (2.5–2.7%) and falcon (7.5–11.9%). In contrast, most fecal estrogen metabolites
in eagle and falcon females co-eluted with radiolabeled estradiol-17β ([3H]; 57.6, 64.6%, respectively) or estrone ([3H]; 26.9, 4.1%, respectively). Most fecal progestin metabolite immunoreactivity in the female eagle (24.8%) and falcon (21.7%)
co-eluted with progesterone ([14C]). Most fecal androgen metabolite immunoreactivity in eagle (55.8%) and falcon (63.7%) males co-eluted with testosterone
([14C]). Exogenous adrenocorticotropin hormone induced increased fGCM excretion above pre-treatment in both species, but only
significantly (P < 0.05) in the eagle. Both species showed increased fGCM after saline administration, suggesting the detection of ‘handling
stress.’ Both species exhibited enterohepatic and renal recirculation of administered steroids as demonstrated by biphasic
and triphasic excretion patterns. Thus, noninvasive fecal hormone monitoring is a valid and promising tool for assessing gonadal
and adrenal status in rare and threatened birds-of-prey. 相似文献
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996.
目的:经抗原表位预测和同源性比较,禽流感M1蛋白位于58-66序列的九肽是A型流感病毒中保守并具有很强免疫原性的T细胞表位,鉴于鼠伤寒沙门氏菌LT2的SEF17菌毛基因agfA作为疫苗载体的优势,在其上构建引起机体细胞免疫的沙门氏茵口服活体重组疫苗,以求在人类对抗禽流感过程中发挥作用。方法:利用两步重叠延伸PCR和基因置换,将外源表位插入LT2茵毛,并利用抗生素抗性,温度敏感质粒,及茵毛的刚果红吸附能力筛选菌毛上插有外源抗原表位的重组菌,并通过测序进一步验证外源基因的插入。结果:两步重叠延伸PCR产物AB,CD,AD长度与理论大小530bp,423bp,932bp一致。两次转化PCR鉴定,产物长度与理论大小932bp,634bp一致。刚果红吸附测定,菌毛上插入有外源肽的菌落因吸附刚果红能力减弱呈粉色,对筛选出的KmS型粉色茵落的PCR鉴定,产物长度与理论大小417bp一致,测序结果也显示agfA中外源表位基因的插入。结论:禽流感M1蛋白位于58-66序列的T细胞表位成功插入沙门氏茵SEF17菌毛基因agfA。 相似文献
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999.
Rubolini D Ambrosini R Caffi M Brichetti P Armiraglio S Saino N 《International journal of biometeorology》2007,51(6):553-563
Climate change is affecting the phenology of seasonal events in Europe and the Northern Hemisphere, as shown by several studies
of birds’ timing of migration and reproduction. Here, we analyse the long-term (1982–2006) trends of first arrival dates of
four long-distance migratory birds [swift (Apus apus), nightingale (Luscinia megarhynchos), barn swallow (Hirundo rustica), and house martin (Delichon urbicum)] and first egg laying dates of two migrant (swift, barn swallow) and two resident species [starling (Sturnus vulgaris), Italian sparrow (Passer italiae)] at a study site in northern Italy. We also addressed the effects of local weather (temperature and precipitation) and a
climate index (the North Atlantic Oscillation, NAO) on the interannual variability of phenological events. We found that the
swift and the barn swallow significantly advanced both arrival and laying dates, whereas all other species did not show any
significant temporal trend in either arrival or laying date. The earlier arrival of swifts was explained by increasing local
temperatures in April, whereas this was not the case for arrival dates of swallows and first egg laying dates of both species.
In addition, arrival dates of house martins were earlier following high NAO winters, while nightingale arrival was earlier
when local spring rainfall was greater. Finally, Italian sparrow onset of reproduction was anticipated by greater spring rainfall,
but delayed by high spring NAO anomalies, and swift’s onset of reproduction was anticipated by abundant rainfall prior to
reproduction. There were no significant temporal trends in the interval between onset of laying and arrival in either the
swift or the barn swallow. Our findings therefore indicate that birds may show idiosyncratic responses to climate variability
at different spatial scales, though some species may be adjusting their calendar to rapidly changing climatic conditions. 相似文献
1000.