DNA Vaccine Against Malaria: A Long Way To Go

Vaccination is the attempt to mimic certain aspects of an infection for the purpose of causing an immune response that will protect the individual from that infection. Malaria, a disease responsible for immense human suffering, is caused by infection with Plasmodium spp. parasites, which have a very complex life cycle — antigenically unique stages infect different tissues of the body. It is a parasitic disease for which no successful vaccine has been developed so far, despite considerable efforts to develop a subunit vaccine that offers protective immunity. Due to the spread of drug-resistant malaria, efforts to develop an effective vaccine have become increasingly critical. DNA vaccination provides a stable and long-lived source of protein vaccine capable of inducing both antibody- and cell-mediated immune responses to a wide variety of antigens. Injected DNA enters the cells of the host and makes the protein, which triggers the immune response. According to present needs, the flexibility of DNA vaccine technology permits the combination of multiple antigens from both the preerythrocytic and erythrocytic stages of malaria parasite. DNA vaccines with genes coding for different antigenic parts of malaria proteins have been created and presently some of these are undergoing field trials. The results from these trials will help to determine the likelihood of success of this technology in humans. This review presents an update of the studies carried out in malaria using DNA vaccine approach, the challenges, and the future prospects.     

Making a Little Affinity Go a Long Way: A Topological View of LFA-1 Regulation

Lymphocytes utilize adhesion to navigate in the body and to transiently interact with a variety of potential antigen presenting cells. Interactions of adhesion molecules are governed by the law of mass action and the less understood rules of apposed biological membranes. Biochemical parameters such as adhesion molecule affinity only tell part of the story. Factors such as lateral mobility, membrane alignment and cytoskeletal interactions are equally important in determining the final outcome. Therefore it is important to determine mechanisms by which the properties of cell membranes and the cytoskeleton reinforce or hinder adhesion molecule interactions. Work from my lab has shown that one mechanism by which lymphocyte adhesion molecules cooperate is to align adhering membranes with nanometer precision. Here, I discuss a model for LFA-1 regulation that is dependent on three independent processes: LFA-1 lateral mobility, ligand induced generation of a small amount of high affinity LFA-1 and local membrane alignment. I propose that coordination of these processes allows rapid interconversion between stable adhesion and detachment.     

植物离体组织染色体加倍诱导同源四倍体

随着生物技术的迅速发展,通过植物离体组织人工诱导多倍体已经成为获得多倍体植株的有效途径。本文就植物离体组织染色体加倍诱导同源四倍体的研究进展做一介绍,详细评述了植物离体组织细胞加倍的途径、影响植物离体组织加倍的因素、利用不同诱导剂进行处理效果比较及离体组织材料的早期倍性鉴定技术等,并展望了植物离体诱导同源四倍体的前景。     

高等植物细胞壁中纤维素的合成

植物细胞壁主要由纤维素、半纤维素、木质素和果胶质等构成.近年来,在细胞壁形成,如纤维素合成方面的研究取得了一系列非常令人鼓舞的进展.本文就高等植物细胞壁中纤维素合成机制的研究进展作一介绍.     

植物细胞壁中纤维素合成的研究进展

纤维素是植物细胞壁的主要成分,是植物细胞壁执行生理功能的基础,也是人类生产和生活中必不可少的一类物质。本文对纤维素合成、合成中所需要的酶以及纤维素沉积中微纤丝的作用等方面进行了综述和探讨, 并对纤维素合成的深入研究进行了展望。     

Gas Exchange of In Vitro and Ex Vitro Grown Grapevine Plants

Net photosynthetic rate (P _N) and dark respiration rate (R _D) were measured in Vitis vinifera L. cvs. Dimiat 4/24 (23^rd subculture), Dimiat 4/38 (22^nd subculture), and Italian Riesling 3/47 (22^nd subculture) on days 3, 2, and 1 (1^st series) before transfer from the in vitro culture and on days 14, 15, 16 (2^nd series) and 28, 29, 30 (3^rd series) after the transfer. P _N of in vitro and ex vitro plants was strongly affected by irradiance. P _N and R _D of in vitro plantlets were lower and transpiration rate (E) was higher compared to those of ex vitro plantlets. P _N, R _D, and E changed in the course of acclimation.     

Leaf Senescence in Plants:From Model Plants to Crops,Still so Many Unknowns

Senescence is a developmental process in the life cycle of a plant or a plant organ which has an intrinsic link with longevity.In human and animal sciences, the question of what controlsthe length of life is a fundamental biological query which has been puzzling scientists for centuries.     

Synthesis of the psbA Gene Product in Euglena: In Organello and In Vitro

To identify the psbA gene product of Euglena gracilis, we compared products translated in organello and in vitro. The most prominently labeled membrane protein of isolated Euglena plastids migrates as a band at 28 kilodaltons. An apparent precursor appears at 30 kilodaltons under conditions which inhibit the synthesis of cytoplasmically synthesized proteins. Translation of the 14S mRNA selected by hybridization with the Sephacryl S-500-immobilized psbA gene, however, yields products of ~37- and 41-kilodaltons. In organello, no significant label migrates to this region of the gel. We interpret these data to indicate that the primary translation product of Euglena psbA gene is larger than that of higher plants, but the mature, processed polypeptide is smaller.     

beta]-Glucan Synthesis in the Cotton Fiber (IV. In Vitro Assembly of the Cellulose I Allomorph)

In vitro assembly of cellulose from plasma membrane extracts of the cotton (Gossypium hirsutum) fiber was enriched by a combination of 3-(N-morpholino)propanesulfonic acid extraction buffer and two independent digitonin solubilization steps consisting of 0.05% digitonin (SE1) followed by 1% digitonin (SE2). Glucan synthase activity assays revealed that, although the SE2 fraction possessed higher activity, only 8.6% of the in vitro product survived acetic/nitric acid treatment. On the other hand, the SE1 fraction was less active, but 32.1% of the total glucan in vitro product was resistant to acetic/nitric acid. In vitro products synthesized from the SE1 fraction contained [beta]-1,3-glucan and fibrillar cellulose I, whereas the SE2 fraction produced [beta]-1,3-glucan and cellulose II. Both celluloses assembled in vitro were labeled with cellobiohydrolase I-gold complex, and the electron diffraction patterns of both products from SE1 and SE2 revealed cellulose I and cellulose II, respectively. Contamination of native cellulose was ruled out by extensive evidence from autoradiography of the ethanol-insoluble and acetic/nitric acid-insoluble materials, including three different controls.     

In Vitro Synthesis of Adenovirus Core Proteins

mRNA extracted from polysomes of KB cells at late stages of productive infection with adenovirus type 2 was translated in a cell-free system derived from Krebs II ascites cells. Two of the polypeptides obtained in this reaction corresponded to the adenovirus core protein V and the precursor to core protein VII. The following criteria were used to establish identity between the in vitro products and the virion proteins: comigration during sodium dodecyl sulfatepolyacrylamide gel electrophoresis, cochromatography in sodium dodecyl sulfate-hydroxyapatite, specific immunoprecipitation of the precursor to core protein VII, and tryptic peptide analysis.     

Isolation of Plants Able to Grow in Air Lacking In Vitro Ferredoxin-Dependent Glutamate Synthase Activity

Revertants of Arabidopsis thaliana have been selected in theferredoxin-dependent glutamate synthase deficient genetic backgroundwhich now grow in air. Further they have a near normal photosyntheticCO₂ exchange plot against light intensity in contrast to theoriginal mutant. (Received February 1, 1989; Accepted April 24, 1989)     

In Vitro Synthesis of the Myelin Basic Proteins: Subcellular Site of Synthesis

Abstract: Brains of 3-week-old C57BL/6J mice were homogenized and fractionated into several subcellular components, each of which was examined for ability to synthesize the myelin basic proteins (MBPs) in vitro. Myelin basic proteins were purified from incubation mixtures by conventional means. That the products of synthesis were the myelin basic proteins was established by solubility at pH 3, co-chromatography with authentic proteins on carboxymethylcellulose and co-migration with standards in two different polyacrylamide gel electrophoretic systems. The fractions examined for their ability to synthesize MBPs were the whole homogenate, postnuclear supernatant, postmitochondrial supernatant, crude mitochondrial pellet, free ribosomes and bound ribosomes. Although there was no requirement for exogenous energy sources for protein synthesis in the whole homogenate, as the homogenate was fractionated an increasing requirement emerged. Most of the label in the MBP preparations from whole homogenate and postnuclear supernatant incubations migrated with the large (L) and small (S) MBPs on gel electrophoresis; however, as the homogenate was subfractionated and incubated, a greater percentage of the label migrated more slowly than L and S on acetic acid-urea gels. To show synthesis of the MBPs the L and S bands were cut out of these gels and rerun on sodium dodecylsulfate gels. Alternatively, MBP preparations were subjected directly to two-dimensional gel electrophoresis and the bands corresponding to L and S were excised and counted. With this method only the whole homogenate, postnuclear supernatant, postmitochondrial supernatant and free ribosomes were observed to synthesize the MBPs in vitro. The "bound" ribosomes were not observed to synthesize significant amounts of the MBPs, incubated either intact or released from the membrane. It was concluded that the free ribosomes are the principal site of synthesis of the myelin basic proteins in the brain.     

Stimulation of Melatonin Synthesis in Ovine Pineals In Vitro

Static and superfused pineal slices (750 micron) have been used to study the control of melatonin synthesis by ovine pineals. Static incubates show a time-dependent accumulation of melatonin in the medium; this is significantly increased by stimulation with norepinephrine (NE) (10(-5) M), reaching 300% above control levels after 4 h. Perifused pineal slices show a rapid rise in melatonin release within 12-18 min in response to NE stimulation. This reaches a 3.5-4.5-fold increase in melatonin released within 30 min. Withdrawal of NE is associated with a rapid return to prestimulated levels within 12-18 min. These time-course characteristics compare favorably to those changes seen in vivo. The formation of [14C]melatonin from [14C]-tryptophan shows a linear increase with time. In the presence of NE (10(-5) M), the rate of synthesis is increased, albeit after an initial time lag of at least 30 min. The latter may reflect an N-acetyltransferase-independent mechanism of synthesis and release. In static incubations, propranolol (10(-5) M) inhibited NE-induced melatonin production by about 60%, but prazosin (10(-5) M) had no effect. As dibutyryl cyclic AMP (10(-3) M) stimulated melatonin production, it is concluded that beta-receptors are of primary importance to the control of melatonin production, as in the rat. The role of alpha 1-receptors is less clear, but the stimulatory action of phorbol 12-myristate 13-acetate on melatonin release implicates a receptor linked to phosphatidylinositol turnover.     

Programs for Cell Death: Apoptosis is Only One Way to Go

Cell death programs are major players in tissue homeostasis, development and cellular stress responses. A prominent cause of malignant transformation is the cumulative genetic alterations in pathways that regulate cellular growth and death. The processes that govern cell death following genotoxic stress are a major focus of basic research and are also very relevant to translational research in clinical oncology: understanding cell death following cancer therapy is essential for designing new treatment modalities. Cell death is usually, and sometimes automatically, linked with one of its major programs, apoptosis. Recent advances have led, however, to the emergence of additional, non-apoptotic cell death pathways, each with its triggers and readouts. Genotoxic stress appears to induce several cell death pathways, only part of which fall within the classical definition of apoptosis. Accordingly, solid tumor cells that are refractive to apoptosis were shown to die via non-apoptotic mechanisms. Recently we demonstrated that mitotic cell death induced by DNA damage in cells with defective G2/M checkpoint is mechanistically distinct from apoptosis. This review outlines recent advances in the understanding of molecular networks operative in apoptotic and non-apoptotic cell death mechanisms and their cross-talks.     

In Vitro Reconstitution of Light-harvesting Complexes of Plants and Green Algae

In plants and green algae, light is captured by the light-harvesting complexes (LHCs), a family of integral membrane proteins that coordinate chlorophylls and carotenoids. In vivo, these proteins are folded with pigments to form complexes which are inserted in the thylakoid membrane of the chloroplast. The high similarity in the chemical and physical properties of the members of the family, together with the fact that they can easily lose pigments during isolation, makes their purification in a native state challenging. An alternative approach to obtain homogeneous preparations of LHCs was developed by Plumley and Schmidt in 1987¹, who showed that it was possible to reconstitute these complexes in vitro starting from purified pigments and unfolded apoproteins, resulting in complexes with properties very similar to that of native complexes. This opened the way to the use of bacterial expressed recombinant proteins for in vitro reconstitution. The reconstitution method is powerful for various reasons: (1) pure preparations of individual complexes can be obtained, (2) pigment composition can be controlled to assess their contribution to structure and function, (3) recombinant proteins can be mutated to study the functional role of the individual residues (e.g., pigment binding sites) or protein domain (e.g., protein-protein interaction, folding). This method has been optimized in several laboratories and applied to most of the light-harvesting complexes. The protocol described here details the method of reconstituting light-harvesting complexes in vitro currently used in our laboratory,and examples describing applications of the method are provided.     

The In Vitro Action of Griseofulvin against Pathogenic Fungi of Plants

The action of griseofulvin in vitro against forty economicallyimportant fungal pathogens of plants has been examined. Thepathogens were assigned to one of four groups, according tothe severity of the morphological symptoms observed. It wasconcluded that griseofulvin has considerable potential valuefor the protection of plants against a wide range of fungaldiseases.