Water,Water Compartments and Water Regulation in Some Nematodes Parasitic in Vertebrates

While nematodes are sometimes regarded as osmoconformers, at least one species is capable of short-term osmoregulation over a wide range of osmotic environments, and the principal site of osmoregulation is the body wall. This general osmoregulation is important to the life of the nematode not only in confronting variations in the environment, but also in maintaining its hydrostatic skeleton. There is also evidence suggesting that compartments exist in some nematodes and that water exchange between the compartments is limited and slow. The ability to regulate the internal movements of water is important in molting and in the infective process. Hormones may be the mediators of osmotic control.     

Production, crystallization, and preliminary X-ray analysis of rabbit skeletal muscle troponin complex consisting of troponin C and fragment (1-47) of troponin I.

Troponin is a ternary protein complex consisting of subunits TnC. TnI, and TnT, and plays a key role in calcium regulation of the skeletal and cardiac muscle contraction. In the present study, a partial complex (CI47) was prepared from Escherichia coli-expressed rabbit skeletal muscle TnC and fragment 1-47 of TnI, which is obtained by chemical cleavage of an E. coli-expressed mutant of rabbit skeletal muscle TnI. Within the ternary troponin complex, CI47 is thought to form a core that is resistant to proteolytic digestion, and the interaction within CI47 likely maintains the integrity of the troponin complex. Complex CI47 was crystallized in the presence of sodium citrate. The addition of trehalose improved the diffraction pattern of the crystals substantially. The crystal lattice belongs to the space group P3(1)(2)21, with unit cell dimensions a = b = 48.2 A, c = 162 A. The asymmetric unit presumably contains one CI47 complex. Soaking with p-chloromercuribenzenesulfonate (PCMBS) resulted in loss of isomorphism, but enhanced the quality of the crystals. The crystals diffracted up to 2.3 A resolution, with completeness of 91% and R(merge) = 6.4%. The crystals of PCMBS-derivative should be suitable for X-ray studies using the multiple-wavelength anomalous diffraction technique. This is the first step for elucidating the structure of the full troponin complex.     

miRNA参与肿瘤基因表达调控研究进展

调查表明,我国城乡居民恶性肿瘤死亡率属于世界较高水平,而且呈持续的增长趋势。近年来的研究发现在肿瘤的发生与发展过程中涉及到多种因素,其中mi RNA可能扮演了重要的作用。mi RNA是一种长度约为22 nt的非编码短序列RNA,通过介导特异性的基因沉默导致靶m RNA降解,促使相应蛋白质的转译受阻而失去原有编码蛋白质的功能。mi RNA在细胞分裂周期中影响着基因的表达调控,在此过程中基因表达的失控就可能导致疾病的发生。而肿瘤的发生是以细胞恶变为基础,细胞恶变则是与细胞周期调控因素失衡相关,由此提示了一些mi RNA可能参与了肿瘤的发生、发展过程并在其中发挥了重要作用。随着研究的深入,mi RNA逐渐成为肿瘤诊治的新研究方向。本文主要讨论mi RNA在肿瘤基因表达调控方面的研究进展。     

Role of interferons in the regulation of cell proliferation,differentiation, and development

There now appears to be evidence to support the view that the type I IFNs are naturally produced negative regulators of growth that also modify cell differentiation. Consistent with this, it appears that the ability to produce and respond to IFN is suppressed in early embryonic development when cell proliferation and differentiation are essential. In the later stages of fetal development, IFN production is de-repressed, and cells show increased sensitivity to IFN, which may be important in regulating cell proliferation and/or differentiation processes or the interaction between fetal and maternal tissues. Interestingly, the IFN system can also be suppressed in disease states such as the development of tumours or in the establishment of a (chronic) viral infection. Therefore, understanding the developmental regulation of the IFN system may be important to understanding and controlling the IFN system in disease. More extensive studies of the developmental stage and tissue-specific expression of type I IFNs and their receptors are necessary, as well as more direct in vivo experiments to further elucidate the role of the IFN system in reproduction and development. © 1994 Wiley-Liss, Inc.     

Environmental conditions differentially affect vir gene induction in different Agrobacterium strains. Role of the VirA sensor protein

The induction of vir gene expression in different types of Agrobacterium strains shows different pH sensitivity profiles. The pH sensitivity pattern demonstrated by octopine Ti strains was similar to that of a supervirulent leucinopine Ti strain, whereas this was different from that shown by nopaline Ti strains and agropine Ri strains. Data are given which indicate that these differences are due to different properties of the virA genes of these wild types. An exceptional case was formed by strains with the limited-host-range plasmid pTiAG57 which showed AS-dependent vir induction only if reduced inoculum sizes were used and the temperature was 28°C or below.     

Fatness and fitness: exposing the logic of evolutionary explanations for obesity

To explore the logic of evolutionary explanations of obesity we modelled food consumption in an animal that minimizes mortality (starvation plus predation) by switching between activities that differ in energy gain and predation. We show that if switching does not incur extra predation risk, the animal should have a single threshold level of reserves above which it performs the safe activity and below which it performs the dangerous activity. The value of the threshold is determined by the environmental conditions, implying that animals should have variable ‘set points’. Selection pressure to prevent energy stores exceeding the optimal level is usually weak, suggesting that immediate rewards might easily overcome the controls against becoming overweight. The risk of starvation can have a strong influence on the strategy even when starvation is extremely uncommon, so the incidence of mortality during famine in human history may be unimportant for explanations for obesity. If there is an extra risk of switching between activities, the animal should have two distinct thresholds: one to initiate weight gain and one to initiate weight loss. Contrary to the dual intervention point model, these thresholds will be inter-dependent, such that altering the predation risk alters the location of both thresholds; a result that undermines the evolutionary basis of the drifty genes hypothesis. Our work implies that understanding the causes of obesity can benefit from a better understanding of how evolution shapes the mechanisms that control body weight.     

Cloning and characterization of the rpoH gene of Rhodobacter capsulatus

By using an oligonucleotide mixture corresponding to a region highly conserved among alternative sigma factors we identified a new σ factor gene (rpoH) from Rhodobacter capsulatus. This gene encodes a protein of 34 kDa with strong similarity to the RpoH (σ ³²) factors from other bacterial species. It was not possible to inactivate the R. capsulatusrpoH gene by introducing a resistance cassette, implying that it is essential for growth. The 5′ ends of the mRNAs were mapped to two sequences with similarity to an rpoH- and an rpoD-dependent promoter, respectively. The amounts of both these mRNAs increased after heat shock, but were unaffected by a decrease in oxygen tension. Western analysis using a σ factor-specific antibody revealed the accumulation of a protein of about 34 kDa after heat shock, and an increase in the amounts of a protein with the same size after reduction of oxygen tension in R. capsulatus cultures. Received: 16 March 1998 / Accepted: 28 July 1998