Production of Lysine by Pyruvate Dehydrogenase Mutants of Brevibacterium flavum

Mutants with low pyruvate dehydrogenase (PD) activities were derived from a pyruvate kinase-deficient lysine-producing mutant of Brevibacterium flavum, No. 22. They were selected as prototrophic revertants of the acetate auxotrophs of strain No. 22. Among them strain KD-11 produced 55g/liter of lysine as its HCI salt when cultured for 72 hr in a medium containing lOOg/liter of glucose, soybean-meal hydrolysate and methionine. The lysine yield of strain KD-11 was the highest ever reported (55%). The mutant required a higher concentration of methionine for maximum production and gave a smaller amount of cell mass in cultivation than its parent. PD activity of strain No. 22 was stimulated by cysteine, stabilized by glycerol, and gave apparent Kms of 89, 22, 380, 83 μM for pyruvate, coenzyme A, 3-acetylpyridine adenine dinucleotide, and NAD, respectively, under standard conditions. The apparent Km for NAD of PD from strain KD-11 was 10-times higher than that from No. 22. When the concentration of NAD was low, the cell extracts of strain KD-11 showed low PD activity. The specific activity of phosphoenolpyruvate carboxylase of strain KD-11 was slightly higher than that of strain No. 22, while the inhibition by aspartate of the former enzyme was weaker than that of the latter.     

Statistical method for prediction of gait kinematics with Gaussian process regression

We propose a novel methodology for predicting human gait pattern kinematics based on a statistical and stochastic approach using a method called Gaussian process regression (GPR). We selected 14 body parameters that significantly affect the gait pattern and 14 joint motions that represent gait kinematics. The body parameter and gait kinematics data were recorded from 113 subjects by anthropometric measurements and a motion capture system. We generated a regression model with GPR for gait pattern prediction and built a stochastic function mapping from body parameters to gait kinematics based on the database and GPR, and validated the model with a cross validation method. The function can not only produce trajectories for the joint motions associated with gait kinematics, but can also estimate the associated uncertainties. Our approach results in a novel, low-cost and subject-specific method for predicting gait kinematics with only the subject's body parameters as the necessary input, and also enables a comprehensive understanding of the correlation and uncertainty between body parameters and gait kinematics.     

伊犁地区野生毛牛蒡和牛蒡的种群分布、生态和群落特性的研究

在充分踏察的基础上,选择具有代表性的样地,接线路调查法和样地调查法得出野生毛牛蒡和牛蒡种群的分布格局在伊犁地区总体上呈随机分布,占86．7％的调查样地;小范围内也有群聚分布的,占13．3％的调查样地;分布于喜光、低海拔、对土壤适应性高、生活力强等是牛蒡和毛牛蒡的生态习性;常与各类草本为伍,与菊科、禾本科、唇形科、藜科、蓼科、蒺藜科等常见科的植物均能共生于同一环境,是牛蒡和毛牛蒡的群落学特性;植被类型和人为因素是影响它们分布的环境因素。     

Molecular mechanisms of homeostatic plasticity in central pattern generator networks

Central pattern generator (CPG) networks rely on a balance of intrinsic and network properties to produce reliable, repeatable activity patterns. This balance is maintained by homeostatic plasticity where alterations in neuronal properties dynamically maintain appropriate neural output in the face of changing environmental conditions and perturbations. However, it remains unclear just how these neurons and networks can both monitor their ongoing activity and use this information to elicit homeostatic physiological responses to ensure robustness of output over time. Evidence exists that CPG networks use a mixed strategy of activity‐dependent, activity‐independent, modulator‐dependent, and synaptically regulated homeostatic plasticity to achieve this critical stability. In this review, we focus on some of the current understanding of the molecular pathways and mechanisms responsible for this homeostatic plasticity in the context of central pattern generator function, with a special emphasis on some of the smaller invertebrate networks that have allowed for extensive cellular‐level analyses that have brought recent insights to these questions.     

Caenorhabditis elegans anillin (ani-1) regulates neuroblast cytokinesis and epidermal morphogenesis during embryonic development

The formation of tissues is essential for metazoan development. During Caenorhabditis elegans embryogenesis, ventral epidermal cells migrate to encase the ventral surface of the embryo in a layer of epidermis by a process known as ventral enclosure. This process is regulated by guidance cues secreted by the underlying neuroblasts. However, since the cues and their receptors are differentially expressed in multiple cell types, the role of the neuroblasts in ventral enclosure is not fully understood. Furthermore, although F-actin is required for epidermal cell migration, it is not known if nonmuscle myosin is also required. Anillin (ANI-1) is an actin and myosin-binding protein that coordinates actin–myosin contractility in the early embryo. Here, we show that ANI-1 localizes to the cleavage furrows of dividing neuroblasts during mid-embryogenesis and is required for their division. Embryos depleted of ani-1 display a range of ventral enclosure phenotypes, where ventral epidermal cells migrate with similar speeds to control embryos, but contralateral neighbors often fail to meet and are misaligned. The ventral enclosure phenotypes in ani-1 RNAi embryos suggest that the position or shape of neuroblasts is important for directing ventral epidermal cell migration, although does not rule out an autonomous requirement for ani-1 in the epidermal cells. Furthermore, we show that rho-1 and other regulators of nonmuscle myosin activity are required for ventral epidermal cell migration. Interestingly, altering nonmuscle myosin contractility alleviates or strengthens ani-1's ventral enclosure phenotypes. Our findings suggest that ventral enclosure is a complex process that likely relies on inputs from multiple tissues.     

松嫩平原破碎化羊草草甸退化演替系列植物多样性的空间格局

物种多样性格局是国际生物多样性科学前沿领域热点问题.本文以松嫩平原破碎化羊草草甸退化演替系列(6种植物群落、144个斑块)为研究对象,系统地探讨了其α、β和γ多样性空间格局及其机理.结果表明:在羊草草甸退化演替系列中共发现87种植物,但没有一种能分布于所有斑块;羊草+鸡儿肠群落或羊草群落的α、β和γ多样性较高,多稀有种和特有种;碱地肤群落最低,少稀有种,无特有种;γ多样性与α多样性显著正相关,但与β多样性无相关性.各植物群落的α多样性与单个斑块面积呈显著幂函数关系,β多样性(相似性指数Sjk)仅羊草+鸡儿肠群落呈显著幂函数关系;斑块平均面积和总面积与α、γ多样性呈显著正相关,与β多样性无相关性.群落的物种丰富度越高,稀有种和特有种就越多,物种在局域斑块上灭绝的可能性越大;β多样性在物种多样性格局中的重要性与生境破碎化程度有关.     

基于复合叶片特征的计算机植物识别方法

该文探讨如何根据植物的叶片特征,利用图像处理和机器学习的方法对植物进行分类。鉴于现有的叶片分类系统多采用单一的特征,如几何和纹理等,仅能在小规模数据库上得到较好的结果。然而,随着样本种类的增多,单一特征在不同种类叶片之间的相似性非常明显,致使分类正确率降低。该研究使用多种复合特征,并提出了原创的预处理方法以及宽度、叶缘频率特征,较传统的几何特征更为详尽。研究结果显示,复合特征可以有效避免算法过拟合问题,使之适用于更大的数据库。通过提取21类植物的叶片宽度、颜色、叶缘和纹理共292维特征,对1 915张数字图像进行了分类,正确率达到93%,并分析了各类特征对分类结果的影响。研究结果表明,在不影响分类正确率前提下,可将特征减少到约100维。     

青海湖裸鲤寄生舌状绦虫的空间格局研究

舌状绦虫裂头蚴只寄生在体长小于２２０ｍｍ的青海湖裸鲤中,其种群在宿主种群中呈聚集分布。其聚集分布的强度随寄生虫种群平均密度的增加而降低。由于舌状绦虫在宿主体腔生长,产生明显的空间拥挤效应,可能导致宿主死亡或被食鱼鸟类捕食而转移到终末宿主中。在体长小于１２０ｍｍ的宿主中,密度依赖的死亡过程可能是使聚集强度降低的原因;而体长１４０－２００ｍｍ的鱼中,则是非密度依赖的全死过程使聚集强度增加．     

Analysis of sequence patterns proximal to the stop codons in Oryza sativa

Abstract

A comprehensive analysis of sequence patterns around the stop codons was performed, by using more than 26,000 rice full-length cDNA sequences. Here it is shown that the bias was most outstanding at the position immediately before the stop codons (?1 codon), where the AAC codon was strongly preferred among ANC codons. Compared with other positions, the codon immediately after the stop codons (+1 codon) also displayed an apparent difference, and had a strong consensus for base A at the first, C at the second, and A at the third letters, respectively. Notably, the base biases at the positions directly downstream of the stop codons, such as the +4, +5 and +6 positions, were much stronger than other positions in the 3′-UTR region, suggesting that those base positions might act as an extended stop signal in the process of protein synthesis. Examination of the relationship between sequence pattern and gene expression level, assessed by CAI values and EST counting, revealed a tendency towards bigger base biases for highly expressed genes. It could be inferred that the translation stop signal is possibly involved in many sequence recognition elements other than the stop codons; highly expressed genes should hold strong sequence consensus around the stop codons for efficient translation termination.     

The evolution and genetics of sexually dimorphic ‘dual’ mimicry in the butterfly Elymnias hypermnestra

Sexual dimorphism is a major component of morphological variation across the tree of life, but the mechanisms underlying phenotypic differences between sexes of a single species are poorly understood. We examined the population genomics and biogeography of the common palmfly Elymnias hypermnestra, a dual mimic in which female wing colour patterns are either dark brown (melanic) or bright orange, mimicking toxic Euploea and Danaus species, respectively. As males always have a melanic wing colour pattern, this makes E. hypermnestra a fascinating model organism in which populations vary in sexual dimorphism. Population structure analysis revealed that there were three genetically distinct E. hypermnestra populations, which we further validated by creating a phylogenomic species tree and inferring historical barriers to gene flow. This species tree demonstrated that multiple lineages with orange females do not form a monophyletic group, and the same is true of clades with melanic females. We identified two single nucleotide polymorphisms (SNPs) near the colour patterning gene WntA that were significantly associated with the female colour pattern polymorphism, suggesting that this gene affects sexual dimorphism. Given WntA''s role in colour patterning across Nymphalidae, E. hypermnestra females demonstrate the repeatability of the evolution of sexual dimorphism.