基于选择基因型对数量性状进行关联分析

数量性状的遗传分析可以通过＂选择基因型＂的方式完成。本文提出了一个利用极端样本来对数量性状位点（QTL）进行关联分析的统计量T。统计量T比较上极端群体样本中具有纯合子标记的性状值差异。通过计算机模拟考察了无关联情形时T的分布和Ⅰ型错误率,结果表明,在各种样本选择策略下,T的分布近似于χ^2-分布,Ⅰ型错误率接近设定的显著性水平。同时,考察了各种遗传模型下不同遗传率,不同样本大小,及不同样本选择阈值对T的统计功效的影响,结果表明,T的功效随着标记和QTL间连锁不平衡程度的增强及遗传率和样本大小的增大而增大,当样本选择阈值更严格时,功效也越大。     

The contribution of conservation biological control to integrated control of Bemisia tabaci in cotton

Integrated control systems are based on the complimentary contribution of chemical and biological control fostered by conservation of natural enemies. Yet, in the 50 years since the integrated control concept [ICC] [Stern, V.M., Smith, R.F., van den Bosch, R., Hagen, K.S., 1959. The integrated control concept. Hilgardia 29, 81–101] was introduced there are few operational programs and even fewer attempts to analyze the mechanisms that allow chemical and biological control to act in concert. The dearth of demonstrable evidence for the ICC has eroded the credibility of biological control and its usage in operational IPM plans. We used in situ life tables within an experimental design to measure and compare the contribution and interaction of biological control and insecticides as tactical components within three pest management systems for Bemisia tabaci (Gennadius) in cotton. Insecticides were the key factor immediately following applications of broad-spectrum materials or one of two selective insect growth regulators (IGRs), and this mortality replaced that provided by natural enemies. Two to six weeks later, however, mortality from natural enemies, primarily predation, in the IGR regimes rebounded to the high levels observed in untreated controls and became the key factor. Mortality from natural enemies remained depressed in the broad-spectrum insecticide regime. Single IGR applications were sufficient to suppress B. tabaci populations throughout the season, while up to five broad-spectrum applications were needed to achieve comparable control. The chemical residual of IGRs was limited to several weeks, demonstrating a key role for mortality from conserved natural enemies that extended the control interval. This “bioresidual” allows for long-term, commercially-acceptable pest suppression following the use of selective insecticides. We provide a rare experimental illustration of integrated control, where chemical and biological controls “augment one another”. Our approach and methodology could be applied to demonstrate and validate integrated control in many other systems, addressing a critical need for implementation of biological control in practicing IPM systems.     

A positively charged amino acid at position 129 in nitrilase from Rhodococcus rhodochrous ATCC 33278 is an essential residue for the activity with meta-substituted benzonitriles

A positively charged amino acid (Arg, Lys, or His) at position 129 in Rhodococcus rhodochrous ATCC 33278 nitrilase is essential for the activity of aromatic nitriles. The wild-type enzyme containing Arg129 was active only for meta- and para-substituted benzonitriles with a methyl or amino group, but the R129K and R129H mutant enzymes were active only for meta-substituted benzonitriles. The lack of activity of the mutants for para-substituted benzonitriles may be attributable to steric hindrance between the para-substituent and the side chain of Lys or His.     

The Cvt pathway as a model for selective autophagy

Autophagy is a highly conserved, ubiquitous process that is responsible for the degradation of cytosolic components in response to starvation. Autophagy is generally considered to be non-selective; however, there are selective types of autophagy that use receptor and adaptor proteins to specifically isolate a cargo. One type of selective autophagy in yeast is the cytoplasm to vacuole targeting (Cvt) pathway. The Cvt pathway is responsible for the delivery of the hydrolase aminopeptidase I to the vacuole; as such, it is the only known biosynthetic pathway that utilizes the core machinery of autophagy. Nonetheless, it serves as a model for the study of selective autophagy in other organisms.     

A new approach to understanding the molecular mechanisms through which estrogens affect cognition

Traditional approaches to the study of hormones and cognition have been primarily observational or correlational in nature. Because this work does not permit causal relationships to be identified, very little is known about the specific molecules and cellular events through which hormones affect cognitive function. In this review, we propose a new approach to study hormones and memory, where the systematic blocking of cellular events can reveal which such events are necessary for hormones to influence memory consolidation. The discussion will focus on the modulation of the hippocampus and hippocampal memory by estrogens, given the extensive literature on this subject, and will illustrate how the application of this approach is beginning to reveal important new information about the molecular mechanisms through which estrogens modulate memory consolidation. The clinical relevance of this work will also be discussed.     

In vitro synthesis of peptidoglycan by spheroplasts of Proteus mirabilis grown in the presence of penicillin

Spheroplasts of the unstable l-form of Proteus mirabilis with fragile, shape defective cell walls grown in medium containing 120 mg/l penicillin G and then killed and permeabilized by ether treatment, were capable of in vitro synthesis of peptidoglycan from the precursors UDP-GlcNAc and UDP-MurNAc-l-Ala-d-Glu(ms-A₂pm-d-Ala-d-Ala). The in vitro peptidoglycan was extensively peptide-crosslinked, indicating a continuing function of peptidoglycan transpeptidase in the spheroplasts. The seven penicillin-binding proteins (PBPs) of P. mirabilis with their functions as multiple peptidoglycan transpeptidases were shown to be saturated in the spheroplasts and thereby functionally inactivated by the penicillin of the growth medium to a very different degree. Complete or almost complete saturation occurred with the PBPs 1A, 1B, and 3, for which functions as indispensible transpeptidases in Escherichia coli have been postulated. In contrast, PBPs 5 and 6 were not saturated in the l-form spheroplasts. Transpeptidase function has been described previously in PBP 5 of P. mirabilis. The working hypothesis is proposed that synthesis of the functionally defective peptidoglycan of l-form spheroplasts in the presence of penicillin takes place with transpeptidase function of PBP 5.Dedicated to Professor Dr. H.-G. Schlegel on the occasion of his 60th birthday     

择伐强度对中亚热带天然针阔混交林林分空间结构的影响

利用混交度、大小比数和角尺度3个结构参数,研究4种不同择伐强度（弱度13.0%、中度29.1%、强度45.8%、极强度67.1%）对中亚热带天然针阔混交林林分空间结构的影响。结果表明：弱度择伐后林木的平均混交度最大,中度择伐次之,极强度择伐林木单种聚集的比例最高;不同择伐强度对林木的大小分化程度影响不大,但各主要树种的地位都有一定程度变化;择伐并未改变林木的空间分布格局,各样地林分整体和主要树种均为聚集分布,极强度择伐林木多呈团状分布,而弱度、中度择伐树种大多处于不均匀和随机分布。总的来说,弱度和中度择伐有利于林分空间结构的优化。     

Realized heritability and genetic gains of three generation for superior growth in the pearl oyster Pinctada martensii

The pearl oyster Pinctada martensii is an important economic shellfish species and mainly cultured in the southern provinces of China. The species is cultured for marine pearl production. However, pearl quality has recently decreased because the cultured stocks had slow growth and mass mortalities caused by inbreeding depression. We have initiated a selective breeding program to improve the cultivated stocks since 2002. In 2004, a base population was developed by collecting the breeders from Beibuwan and Liushagang stocks. During the period of 2005–2007, a two successive generation selection for shell length in the base population was carried out to produce the second generation selected and unselected lines. In May of 2008, three types of lines were produced by selecting the breeders from the second generation selected and unselected lines. The three types of lines were designated as SS (Selected for three generations), SC (selected for the two generations) and CC (unselected for three generations). Realized heritability for the third generation, cumulative (over three generation) and current (for the third generation) genetic gains were evaluated by comparing the growth performance of three types of lines at days 8, 16, 45, 75, 180 and 360. It was found that the SS lines had significant larger mean shell length and shell height than the SC and CC lines at all sampling ages (P < 0.05). The realized heritability estimate for adult shell length for the third generation was 0.41, similar with those detected for the first and second generation. The cumulative and current genetic gains for adult shell length were 20.94% and 13.27%, respectively. The present results indicate that there exists a high genetic variation in the population and mass selection is potential to improve pearl oyster stocks.     

Selective consumption of acorns by the Japanese wood mouse according to tannin content: a behavioral countermeasure against plant secondary metabolites

We examined the presence of selective consumption against tannins in acorns as a pre-ingestive countermeasure to plant secondary metabolites by using the Japanese wood mouse (Apodemus speciosus) and acorns of Quercus serrata, which contained ca. 6.4% tannins on a dry weight basis. In addition, the presence of selective consumption against proteins was also examined. In the acorn-feeding experiment, 18 wood mice were allocated to two groups: the experienced group (N = 9), which had previous experience in feeding on acorns, and the inexperienced group (N = 9), which had no experience. Mice of both groups were fed only acorns for 3 nights. Selectivity against tannins (an index estimated from the tannin content in control, remaining, and ingested acorns) was significantly positive in the experienced group, indicating the presence of selective consumption against tannins. In contrast, mice in the inexperienced group did not show significant selectivity against tannins. Comparing the selectivity indices directly between two groups, however, they did not differ significantly. Selective consumption against proteins rather than that for proteins also occurred in the experienced group, but it was thought to be a byproduct resulted from the selectivity against tannins. Selective consumption against tannins can mitigate the negative effects of tannins by decreasing tannin intake.     

Mean-field analysis of selective persistent activity in presence of short-term synaptic depression

Mean-Field theory is extended to recurrent networks of spiking neurons endowed with short-term depression (STD) of synaptic transmission. The extension involves the use of the distribution of interspike intervals of an integrate-and-fire neuron receiving a Gaussian current, with a given mean and variance, in input. This, in turn, is used to obtain an accurate estimate of the resulting postsynaptic current in presence of STD. The stationary states of the network are obtained requiring self-consistency for the currents—those driving the emission processes and those generated by the emitted spikes. The model network stores in the distribution of two-state efficacies of excitatory-to-excitatory synapses, a randomly composed set of external stimuli. The resulting synaptic structure allows the network to exhibit selective persistent activity for each stimulus in the set. Theory predicts the onset of selective persistent, or working memory (WM) activity upon varying the constitutive parameters (e.g. potentiated/depressed long-term efficacy ratio, parameters associated with STD), and provides the average emission rates in the various steady states. Theoretical estimates are in remarkably good agreement with data “recorded” in computer simulations of the microscopic model. Action Editor: Karen Sigvardt