Depleting neuronal PrP in prion infection prevents disease and reverses spongiosis

The mechanisms involved in prion neurotoxicity are unclear, and therapies preventing accumulation of PrPSc, the disease-associated form of prion protein (PrP), do not significantly prolong survival in mice with central nervous system prion infection. We found that depleting endogenous neuronal PrPc in mice with established neuroinvasive prion infection reversed early spongiform change and prevented neuronal loss and progression to clinical disease. This occurred despite the accumulation of extraneuronal PrPSc to levels seen in terminally ill wild-type animals. Thus, the propagation of nonneuronal PrPSc is not pathogenic, but arresting the continued conversion of PrPc to PrPSc within neurons during scrapie infection prevents prion neurotoxicity.     

Reversible conversion of monomeric human prion protein between native and fibrilogenic conformations

Prion propagation involves the conversion of cellular prion protein (PrPC) into a disease-specific isomer, PrPSc, shifting from a predominantly alpha-helical to beta-sheet structure. Here, conditions were established in which recombinant human PrP could switch between the native alpha conformation, characteristic of PrPC, and a compact, highly soluble, monomeric form rich in beta structure. The soluble beta form (beta-PrP) exhibited partial resistance to proteinase K digestion, characteristic of PrPSc, and was a direct precursor of fibrillar structures closely similar to those isolated from diseased brains. The conversion of PrPC to beta-PrP in suitable cellular compartments, and its subsequent stabilization by intermolecular association, provide a molecular mechanism for prion propagation.     

Human prion protein with valine 129 prevents expression of variant CJD phenotype

Variant Creutzfeldt-Jakob disease (vCJD) is a unique and highly distinctive clinicopathological and molecular phenotype of human prion disease associated with infection with bovine spongiform encephalopathy (BSE)-like prions. Here, we found that generation of this phenotype in transgenic mice required expression of human prion protein (PrP) with methionine 129. Expression of human PrP with valine 129 resulted in a distinct phenotype and, remarkably, persistence of a barrier to transmission of BSE-derived prions on subpassage. Polymorphic residue 129 of human PrP dictated propagation of distinct prion strains after BSE prion infection. Thus, primary and secondary human infection with BSE-derived prions may result in sporadic CJD-like or novel phenotypes in addition to vCJD, depending on the genotype of the prion source and the recipient.     

Evolution of mechanisms controlling mating behavior

The proximate mechanisms underlying mating behavior in naturally occurring species can be fundamentally different from those in more commonly studied laboratory and domesticated forms. In naturally occurring species, reproductive strategies are much more diverse, and mechanisms controlling behavior are correspondingly diverse. A variety of hormonal, environmental, and social cues can be used to activate mating behavior. Which cues are used by particular species depends on differences in environmental and physiological constraints imposed by particular reproductive strategies. Study of this diversity of mechanisms promises to identify specific selective forces that have shaped their evolution. This evolutionary perspective leads to widely applicable generalizations and provides a useful context within which to conceptualize differences between species, populations, and individuals.     

浙江省野生动物驯养繁殖业现状分析

为促进浙江省野生动物驯养繁殖产业的发展,于2006年4月至2007年3月,对全省野生动物驯养繁殖单位现状进行了调查。结果表明,全省现有野生动物驯养繁殖单位276家,驯养繁殖野生动物物种360种321．1万只（头、条）,其中观赏类驯养繁殖单位18家,囊括了全省所有的驯养繁殖物种;食用类驯养繁殖单位257家,驯养繁殖野生动物物种不到1／3;杭州、宁波和金华占全省养殖单位总量的54．34％;单物种存栏数在万只以上的有15个物种,主要是中华草龟Chinemys reevesii,虎纹蛙Rana tigrina rugulosa,棘胸蛙Rana spinosa,梅花鹿Cervus nippon等。浙江省野生动物驯养繁殖业具有很大的发展空间,应及时增补驯养繁殖技术成熟的陆生野生动物种类,对现有野生动物驯养繁殖单位加强监管并正确引导,对欠发达地区进行野生动物驯养繁殖技术推广。图3表2参12     

Ecology of insect host-parasitoid communities

Although conclusive evidence is lacking for its establishment, the thesis that complexity adds stability to communities is probably accepted by the majority of ecologists. I believe this attitude found its origins in the indisputable fact that there are latitudinal and altitudinal changes in community complexity. As one progresses northward or southward from the equator, or higher in altitude in most parts of the world, one cannot help but notice that communities tend to become simpler, that is, there are fewer species per community. At the same time, these communities appear to become less stable. But perhaps this change in stability is in appearance only; they appear to be less stable because of the relatively greater number of individuals comprising each species population in temperate areas. Each population, because of its greater numbers, is therefore conspicuous, and changes in these numbers are noticed. We are particularly aware of such changes because populations in these areas of the world have been comparatively well studied. Many of the most studied populations include species of economic importance where changes in population numbers are vital to agricultural or forestry practices. Equatorial populations, on the other hand, contain smaller numbers of individuals of each species because of the greater number of species present. Number changes are simply not as noticeable because the population itself is not as obvious among the other populations. It may be that when (if ever) we have as much data on equatorial populations as we have on those of temperate climates, we will find fluctuations of equal relative magnitude (but not of equal numbers, of course). If, on the other hand, we really do find a correlation between complexity and stability, the suggestion by May (12) that stability permits complexity may be well worth investigating. Because of its organization and physical setting, the Rhopalomyia community I have studied might be expected to have considerable stability. In fact, however, it does not. Each of the populations in the community fluctuates greatly and irregularly in both percentages and numbers, and these populations apparently become locally extinct occasionally, because they sometimes cannot be found even in extensive collections. After studying several of the more important parasitoid species, it is evident to me that there is little or nothing about their interactions that might induce greater community stability. Each species seems to have evolved into the community with no higher purpose than simply to usurp what it can from some other member, and it does this by concentrating its energies on better competitive mechanisms rather than higher reproductive capacities. There are never empty niches to be filled by organisms having the "correct specifications" because new niches are created out of parts of older, broader niches which were occupied by other, more r-selected organisms. Thus, perhaps we have read too much into community organization. Perhaps the "ifiling of niches" is essentially nothing more than the haphazard result of competitive jostling among species; and that as communities develop, they are not necessarily programmed for such things as greater stability or better energy utilizationthe species merely become more closely packed.     

Facilitated cross-species transmission of prions in extraneural tissue

Prions are infectious pathogens essentially composed of PrP(Sc), an abnormally folded form of the host-encoded prion protein PrP(C). Constrained steric interactions between PrP(Sc) and PrP(C) are thought to provide prions with species specificity and to control cross-species transmission into other host populations, including humans. We compared the ability of brain and lymphoid tissues from ovine and human PrP transgenic mice to replicate foreign, inefficiently transmitted prions. Lymphoid tissue was consistently more permissive than the brain to prions such as those causing chronic wasting disease and bovine spongiform encephalopathy. Furthermore, when the transmission barrier was overcome through strain shifting in the brain, a distinct agent propagated in the spleen, which retained the ability to infect the original host. Thus, prion cross-species transmission efficacy can exhibit a marked tissue dependence.     

3种白蜡嫩枝扦插繁殖试验研究

[目的]筛选适合白蜡嫩枝扦插繁殖的最优条件。[方法]以‘京绿’绒毛白蜡(Franxinus velutina‘Jinglü’)、‘雷舞’窄叶白蜡(F.angustifolia‘Raywood’)和‘京黄’洋白蜡(F.platyphylla‘Jinghuang’)3个品种的当年生枝条为试验材料,采用正交试验设计,研究树种、激素种类、处理浓度和浸泡时间4个因素对插穗生根的影响。[结果]树种是影响白蜡插穗生根率、生根量、根长和总根长的主导因子,白蜡嫩枝扦插的最佳组合为A_1B_3C_3D_3,即‘京绿’绒毛白蜡+ABT_1+200 mg/L+浸泡60 min。[结论]该研究可为白蜡的快速繁殖提供科学依据。     

Neurotoxicity and neurodegeneration when PrP accumulates in the cytosol

Changes in prion protein (PrP) folding are associated with fatal neurodegenerative disorders, but the neurotoxic species is unknown. Like other proteins that traffic through the endoplasmic reticulum, misfolded PrP is retrograde transported to the cytosol for degradation by proteasomes. Accumulation of even small amounts of cytosolic PrP was strongly neurotoxic in cultured cells and transgenic mice. Mice developed normally but acquired severe ataxia, with cerebellar degeneration and gliosis. This establishes a mechanism for converting wild-type PrP to a highly neurotoxic species that is distinct from the self-propagating PrP(Sc) isoform and suggests a potential common framework for seemingly diverse PrP neurodegenerative disorders.     

离体培养高山杜鹃增殖的影响因子研究

[目的]培养基种类以及激素TDZ、NAA对高山杜鹃组培苗增殖的影响.[方法]应用正交试验设计拟定试验方案,以增殖系数为测定指标,筛选适合高山杜鹃组培苗增殖的最优培养基.[结果]经直观分析、方差分析和多重比较进行综合评价,高山杜鹃增殖的最优培养基为WPM培养基+NAA 0.01 mg/L+TDZ1 mg/L,其中培养基种类和激素TDZ对其影响最大,通过方差分析达到了极显著水平.[结论]用组织培养方法进行杜鹃的快速繁殖生产,为工厂化育苗提供了科学依据.     

Prevention of scrapie pathogenesis by transgenic expression of anti-prion protein antibodies

Variant Creutzfeldt-Jakob disease and bovine spongiform encephalopathy are initiated by extracerebral exposure to prions. Although prion transmission from extracerebral sites to the brain represents a potential target for prophylaxis, attempts at vaccination have been limited by the poor immunogenicity of prion proteins. To circumvent this, we expressed an anti-prion protein (anti-PrP) mu chain in Prnp(o/o) mice. Transgenic mice developed sustained anti-PrP titers, which were not suppressed by introduction of Prnp+ alleles. Transgene expression prevented pathogenesis of prions introduced by intraperitoneal injection in the spleen and brain. Expression of endogenous PrP (PrP(C)) in the spleen and brain was unaffected, suggesting that immunity was responsible for protection. This indicates the feasibility of immunological inhibition of prion disease in vivo.     

Convergent morphological evolution detected by studying proteins of tree frogs in the Hyla eximia species group

Protein studies have uncovered an apparent case of convergent evolution among North American tree frogs. The species Hyla eximia and Hyla regilla are so similar in external morphology that the "wrightorum" subspecies is assigned by some authorities to H. eximia and by others to H. regilla. Yet microcomplement fixation experiments show that "wrightorum" albumin, though virtually indistinguishable from authentic H. eximia albumin, differs as much from H. regilla albumin as from albumins of species outside the genus Hyla, such as Acris crepitans. The morphological resemblance of "wrightorum" to H. regilla is thus probably due to convergence.     

A size threshold limits prion transmission and establishes phenotypic diversity

According to the prion hypothesis, atypical phenotypes arise when a prion protein adopts an alternative conformation and persist when that form assembles into self-replicating aggregates. Amyloid formation in vitro provides a model for this protein-misfolding pathway, but the mechanism by which this process interacts with the cellular environment to produce transmissible phenotypes is poorly understood. Using the yeast prion Sup35/[PSI(+)], we found that protein conformation determined the size distribution of aggregates through its interactions with a molecular chaperone. Shifts in this range created variations in aggregate abundance among cells because of a size threshold for transmission, and this heterogeneity, along with aggregate growth and fragmentation, induced age-dependent fluctuations in phenotype. Thus, prion conformations may specify phenotypes as population averages in a dynamic system.     

菊花茎尖克隆体外繁殖研究

[目的]研究不同因子对菊花芽苗体外繁殖的影响。[方法]以秋菊品种＂绣球＂和＂妃子笑＂的顶芽或半木质化茎段为外植体,研究不同激素及组合对菊花芽苗体外繁殖的影响。[结果]在MS＋BA 0.5 mg/L＋IBA 0.1 mg/L的诱导培养基上两品种均能诱导分化出芽。在芽的生长增殖阶段,接种到MS＋BA 1.5 mg/L＋IBA 0.5 mg/L＋GA 0.1 mg/L的增殖培养基上,＂红绣球＂和＂妃子笑＂的增殖系数分别可达6.8和6.4,芽苗生长速度快,生长健壮。在1/2 MS＋IBA 0.5 mg/L的生根培养基上,生根所用时间短,根系数量大且粗细始终,移栽成活率较高。[结论]该研究为＂绣球＂和＂妃子笑＂菊花品种的组培快繁提供了理论与技术支持。     

朊病毒增殖机制的研究现状

朊病毒为一不含核酸的蛋白感染因子，能引起哺乳动物中枢神经组织病变，它是由正常形式的蛋白（PrPC)错误折叠成致病蛋白（PrPSc)而组成的，两种结构异型蛋白来源于同一基因，朊病毒抚养殖是通过PrPC构象转变成为PrPSc而实现的。     

Mad cow disease. New recruits for French prion research

As panic over "mad cow disease" engulfs France and threatens to spread to other countries in Western Europe, French research minister Roger-Gérard Schwartzenberg last week unveiled detailed plans for spending $27 million the government has earmarked for prion disease research in 2001. Next year's budget for studying prions--infectious, abnormal proteins linked to bovine spongiform encephalopathy and its human form, variant Creutzfeldt-Jakob disease--will triple France's current prion research spending.     

Balancing selection at the prion protein gene consistent with prehistoric kurulike epidemics

Kuru is an acquired prion disease largely restricted to the Fore linguistic group of the Papua New Guinea Highlands, which was transmitted during endocannibalistic feasts. Heterozygosity for a common polymorphism in the human prion protein gene (PRNP) confers relative resistance to prion diseases. Elderly survivors of the kuru epidemic, who had multiple exposures at mortuary feasts, are, in marked contrast to younger unexposed Fore, predominantly PRNP 129 heterozygotes. Kuru imposed strong balancing selection on the Fore, essentially eliminating PRNP 129 homozygotes. Worldwide PRNP haplotype diversity and coding allele frequencies suggest that strong balancing selection at this locus occurred during the evolution of modern humans.     

PrP antibodies do not trigger mouse hippocampal neuron apoptosis

Intraperitoneal administration of ICSM18 and 35, monoclonal antibodies against prion protein (PrP), has been shown to significantly delay the onset of prion disease in mice, and humanized versions are candidate therapeutics for prion and Alzheimer's diseases. However, a previous report of severe and widespread apoptosis after intracerebral injection of anti-PrP monoclonal antibodies raised concerns about such therapy and led to an influential model of prion neurotoxicity via cross-linking of cell surface PrP by disease-related PrP aggregates. In extensive studies including ICSM18 and 35, fully humanized ICSM18, and the previously reported proapoptotic antibodies, we found no evidence of apoptosis, thereby questioning this model of prion neurotoxicity.     

A yeast prion, Mod5, promotes acquired drug resistance and cell survival under environmental stress

Prion conversion from a soluble protein to an aggregated state may be involved in the cellular adaptation of yeast to the environment. However, it remains unclear whether and how cells actively use prion conversion to acquire a fitness advantage in response to environmental stress. We identified Mod5, a yeast transfer RNA isopentenyltransferase lacking glutamine/asparagine-rich domains, as a yeast prion protein and found that its prion conversion in yeast regulated the sterol biosynthetic pathway for acquired cellular resistance against antifungal agents. Furthermore, selective pressure by antifungal drugs on yeast facilitated the de novo appearance of Mod5 prion states for cell survival. Thus, phenotypic changes caused by active prion conversion under environmental selection may contribute to cellular adaptation in living organisms.