多色荧光原位杂交对昆明山海棠和丙烯酰胺诱发微核染色体组成的研究

采用着丝粒和端粒DNA探针多色荧光原位杂交,分析了昆明山海棠和丙烯酰胺诱导的 NIH3T3细胞微核的染色体组成。结果表明,昆明山海棠和丙烯酰胺诱导的由整条染色体组成的微核分别可达70.7％和65.9％,提示昆明山海棠和丙烯酰胺均有较强的非整倍体毒性。     

Participation of breast and leg muscles in shivering thermogenesis in young turkeys and guinea fowl

Turkey (Meleagris gallopavo) and guinea fowl (Numida meleagris) chicks (0–27 days posthatch) were exposed to decreasing or increasing ambient temperatures. Root mean square electromyographic activity of musculus pectoralis (m. pect.) and musculus iliotibialis (m. iliot.) was recorded simultaneously with O₂ consumption and CO₂ production. From both muscles, relative mass, water fraction and fibre type were determined. M. iliot. participated in shivering from hatching onwards. The relationship between its root mean square electromyographic activity and ambient temperature resembled that of metabolic rate and ambient temperature, and the shivering threshold temperature was indistinguishable from the lower critical temperature. This suggests that the leg muscles are major contributors to shivering thermogenesis. M. pect. participated in shivering only at days 6–20 in turkeys and at days 6–10 in guinea fowl. Both water fraction and histological analysis indicated that m. pect. was less developed than m. iliot. at hatching. We hypothesize that a minimal level of maturity is required before a muscle can participate in shivering, which is probably represented by a water fraction of about 0.85. Both species recruited the aerobic leg muscles first; the anaerobic breast muscle was recruited only when the rate of mass-specific heat loss was high. Accepted: 20 March 1997     

Alternative risk-taking styles: The case of time-budgeting strategies of terrestrial gastropods

The terrestrial slugs Arion ater, Limax maximus and Ariolimax columbianus have similar morphological designs but differ remarkably in their life history tactics and behavioural time budgets. The adaptive value of particular risk-taking styles was investigated using a comprehensive computer simulation model. The model allowed each species' success (growth rates, food acquisition) and costs (distance travelled, hydration deficits, injury from aggressive encounters) to be evaluated in various types of weather (benign, harsh and surprise). This was interpreted in terms of the species' life history design. In addition, each species was simulated with the behavioural strategy of the other two species substituted for its natural programming. The simulation experiments demonstrated how variations in a few simple rules could lead to divergent cost-benefit consequences. The model also illustrated that coarsely-tuned sensitivity to the environment may be better than finely-tuned responses, depending on the animal's ability to respond quickly and the degree of risk. The simulations suggested that competition has shaped the time-budgeting tactics of A. ater and L. maximus. Each species actually performed better in harsh weather, using the behavioural program of the other. L. maximus is an aggressive species with a narrow, nocturnal activity period. The concentrated activity of L. maximus may allow it to displace competitors more effectively, whereas the broader time span of A. ater's activity may be necessary to avoid L. maximus.     

Evaluation of statistical precision and design of efficient sampling for the population estimation based on frequency of occurrence

The binomial sampling to estimate population density of an organism based simply upon the frequency of its occurrence among sampled quadrats is a labour-saving technique which is potentially useful for small animals like insects and has actually been applied occasionally to studies of their populations. The present study provides a theoretical basis for this convenient technique, which makes it statistically reliable and tolerable for consistent use in intensive as well as preliminary population censuses. Firs, the magnitude of sampling error in relation to sample size is formulated mathematically for the estimate to be obtained by this indirect method of census, using either of the two popular models relating frequency of occurrence (p) to mean density (m), i.e. the negative binomial model, p=1−(1+m/k)^−k, and the empirical model, p=1−exp(−am^b). Then, the equations to calculate sample size and census cost that are necessary to attain a given desired level of precision in the estimation are derived for both models. A notable feature of the relationship of necessary sample size (or census cost) to mean density in the frequency method, in constrast to that in the ordinary census, is that it shows a concave curve which tends to rise sharply not only towards lower but also towards higher levels of density. These theoretical results make it also possible to design sequential estimation procedures based on this convenient census technique, which may enable us with the least necessary cost to get a series of population estimates with the desired precision level. Examples are presented to explain how to apply these programs to acutal censuses in the field.     

Translational selection on codon usage in the genus Aspergillus

Aspergillus is a genus of mold fungi that includes more than 200 described species. Many members of the group are relevant pathogens and other species are economically important. Only one species has been analyzed for codon usage, and this was performed with a small number of genes. In this paper, we report the codon usage patterns of eight completely sequenced genomes which belong to this genus. The results suggest that selection for translational efficiency and accuracy are the major factors shaping codon usage in all of the species studied so far, and therefore they were active in the last common ancestor of the group. Composition and molecular distances analyses show that highly expressed genes evolve slower at synonymous sites. We identified a conserved core of translationally optimal codons and study the tRNA gene pool in each genome. We found that the great majority of preferred triplets match the respective cognate tRNA with more copies in the respective genome. We discuss the possible scenarios that can explain the observed differences among the species analyzed. Finally we highlight the biotechnological application of this research regarding heterologous protein expression.     

Prediction of shape and internal structure of the proximal femur using a modified level set method for structural topology optimisation

A computational framework was developed to simulate the bone remodelling process as a structural topology optimisation problem. The mathematical formulation of the Level Set technique was extended and then implemented into a coronal plane model of the proximal femur to simulate the remodelling of internal structure and external geometry of bone into the optimal state. Results indicated that the proposed approach could reasonably mimic the major geometrical and material features of the natural bone. Simulation of the internal bone remodelling on the typical gross shape of the proximal femur, resulted in a density distribution pattern with good consistency with that of the natural bone. When both external and internal bone remodelling were simulated simultaneously, the initial rectangular design domain with a regularly distributed mass reduced gradually to an optimal state with external shape and internal structure similar to those of the natural proximal femur.     

Simulating complex tumor dynamics from avascular to vascular growth using a general level-set method

A comprehensive continuum model of solid tumor evolution and development is investigated in detail numerically, both under the assumption of spherical symmetry and for arbitrary two-dimensional growth. The level set approach is used to obtain solutions for a recently developed multi-cell transport model formulated as a moving boundary problem for the evolution of the tumor. The model represents both the avascular and the vascular phase of growth, and is able to simulate when the transition occurs; progressive formation of a necrotic core and a rim structure in the tumor during the avascular phase are also captured. In terms of transport processes, the interaction of the tumor with the surrounding tissue is realistically incorporated. The two-dimensional simulation results are presented for different initial configurations. The computational framework, based on a Cartesian mesh/narrow band level-set method, can be applied to similar models that require the solution of coupled advection-diffusion equations with a moving boundary inside a fixed domain. The solution algorithm is designed so that extension to three-dimensional simulations is straightforward.     

Bam HI DNA甲基化酶酶学性质的研究

以Lineweave-Burk plot双倒数作图法测得该酶对底物S-腺苷酰甲硫氨酸(SAM)的K_m=7.69×10~(-6)mol/L,在1mmol/LS-腺苷酰高半胱氨酸(SAH)存在下,Ki=7.33×10~(-4)mol/L,两条直线相交于纵轴,证明SAH是该酶的竞争性抑制剂。该酶最适pH为7.8,对热不稳定。同时还测定了该酶对不同DNA底物的专一性及盐浓度、代谢相关物’两价阳离子、某些酸根等对该酶调节性质的影响。以碘代乙酰胺修饰该酶的SH基’及用二硫苏糖醇(DTT)和巯基乙醇(MSH)保护该酶SH基所作的实验表明SH基是该酶活性中心所必需的,用高效液相色谱(HPLC)法证明该酶所甲基化的碱基为刘氏小球菌(M·L、DNA)分子中的胞嘧啶,且求得甲基化30min后所得甲基化水平为2.39％。同时也证明当用该酶将λDNA甲基化后,可使BamHI限制性核酸内切酶对甲基化后的λDNA丧失切割作用。     

Statistical optimization of enzymatic degradation process for oil palm empty fruit bunch (OPEFB) in rotary drum bioreactor using crude cellulase produced from Aspergillus niger EFB1

Oil palm empty fruit bunch (OPEFB) was pretreated with 2% (v/v) HNO₃ and degraded by Aspergillus niger EFB1 crude cellulase. Through 2 Level Factorial Design (2LFD), it was found that OPEFB concentration, temperature, incubation time, concentration of Tween 80 and agitation speed have significant effect in reducing sugar production. A standard Response Surface Methodology (RSM) design known as Central Composite Design (CCD) was used to optimize the enzymatic degradation condition of OPEFB in rotary drum bioreactor. Reducing sugar level of 1.183 g/L was obtained with the following optimized degradation conditions: 1.95% (w/v) OPEFB, 0.5% (v/v) Tween 80, 55 °C, 87.5 rpm in the incubation period of 3 days and 16 h. The optimal degradation condition improved reducing sugar production by 1.07 fold compared to that before optimization in shake flasks culture. The optimization strategy of enzymatic degradation of OPEFB inside rotary drum bioreactor led to increase in glucose, xylose, arabinose, galactose and mannose production by 3, 2.5, 1.64, 19.37 and 22.52 fold, respectively. The improvement in reducing sugar and polyoses production were comparable with the reduction in OPEFB cellulose and hemicellulose content by 89.32% and 48.17% respectively after enzymatic degradation in optimized condition.