Salt transport organelle in Artemia salenis (brine shrimp)

The branchiae of Artemia adapted to triple-strength sea water (105 per mil salinity) were studied with the electron microscope. The epithelial lining of the metepipodite segment possesses organelles composed of stacks of disc-shaped mitochondria interlaced with flattened extensions of a canalicular system that in turn communicates with the plasma-bound surface of the cells. The distance between the canalicular and mitochondrial membranes is small and quite constant. The marked similarity to "mitochondrial pumps" in the anal papillae of tosquito larvae suggests that the organelle is concerned with salt transport.     

Fluid transport: concentration of the intercellular compartment

Intercellular spaces of Periplaneta rectal pads are visible at a magnification of x 100 and distend during fluid uptake. Samples (0.025 to 0.1 nanoliter) obtained by micropuncture from the spaces were consistently more concentrated than the fluid in the rectal lumen. This observation supports the hypothesis of "local" osmosis in epithelial fluid transport.     

Fluid transport and tubular intercellular spaces in reptilian kidneys

Renal tubules of crocodiles, lizards, snakes, and turtles have intercellular spaces similar in type to those observed in the mammalian gall bladder, but different from those of mammalian renal tubules. The fluid movements across renal tubules of reptiles are correlated with the width of the tubular intercellular spaces. In the proximal tubules, where transport is always isosmotic, the spaces are open whenever the tubular epithelium is tranporting, but closed when no transport is taking place. In distal tubules, intercellular spaces are wide open when the osmolality of the urine is close to that of the blood, that is, when the fluid resorbed is almost isosmotic to the tubular fluid. The apical two-thirds of the intercellular spaces are closed when the urine is hypoosmotic. They are also closed when the tubules are not transporting, as in collapsed tubules or tubules poisoned with ouabain. Thus, as in the gall bladder, the open intercellular spaces appear to be found whenever there is fluid transport across the epithelium.     

Microtubule-severing activity of Shigella is pivotal for intercellular spreading

Some pathogenic bacteria actually invade the cytoplasm of their target host cells. Invasive bacteria acquire the propulsive force to move by recruiting actin and inducing its polymerization. Here we show that Shigella movement within the cytoplasm was severely hindered by microtubules and that the bacteria destroyed surrounding microtubules by secreting VirA by means of the type III secretion system. Degradation of microtubules by VirA was dependent on its alpha-tubulin-specific cysteine protease-like activity. virA mutants did not move within the host cytoplasm and failed to move into adjacent cells.     

Peroxisomal membrane ghosts in Zellweger syndrome--aberrant organelle assembly

Peroxisomes are apparently missing in Zellweger syndrome; nevertheless, some of the integral membrane proteins of the organelle are present. Their distribution was studied by immunofluorescence microscopy. In control fibroblasts, peroxisomes appeared as small dots. In Zellweger fibroblasts, the peroxisomal membrane proteins were located in unusual empty membrane structures of larger size. These results suggest that the primary defect in this disease may be in the mechanism for import of matrix proteins.     

Mitochondrion of yeast: ultrastructural evidence for one giant, branched organelle per cell

Three-dimensional models constructed from 80 to 150 consecutive serial sections of entire yeast cells showed that all the separate mitochondrial profiles were cross sections through a single, branching, tubular structure about 50 to 60 micrometers in length and 200 to 600 nanometers in diameter. The data are contrary to conventional notions of mitochondrial size, form, and number per cell and should lead to a reassessment of mitochondrial genetics and biogenesis.     

Mutation pressure and the evolution of organelle genomic architecture

The nuclear genomes of multicellular animals and plants contain large amounts of noncoding DNA, the disadvantages of which can be too weak to be effectively countered by selection in lineages with reduced effective population sizes. In contrast, the organelle genomes of these two lineages evolved to opposite ends of the spectrum of genomic complexity, despite similar effective population sizes. This pattern and other puzzling aspects of organelle evolution appear to be consequences of differences in organelle mutation rates. These observations provide support for the hypothesis that the fundamental features of genome evolution are largely defined by the relative power of two nonadaptive forces: random genetic drift and mutation pressure.     

Toad urinary bladder: intercellular spaces

Vasopressin causes dilation of the intercellular spaces of the mucosal epithelium in toad bladder, an effect previously thought to result from enhanced net transepithelial water transport. Under conditions of zero net fluid transport, vasopressin exerted the same effect in seven tissues, which indicates that the width of the intercellular spaces cannot be taken as a reliable index of net transepithelial fluid transport.     

无膜细胞器与细胞应激反应关系的研究进展

无膜细胞器是缺乏分隔膜的细胞区室。无膜细胞器在多个生物学过程中发挥着关键作用,包括基因转录、RNA 代谢、翻译、蛋白质修饰和信号转导等。细胞在受到外界刺激时,会产生应激反应,维持细胞稳态。而由液–液相分离 (Liquid-liquid phase separation) 驱动而形成的无膜细胞器具有类液体特性,可以快速响应压力,在细胞应激反应中发挥重要作用。本文以应激颗粒、P–小体、核仁和卡哈尔体为无膜细胞器代表,总结了无膜细胞器与应激反应的关系,以及无膜细胞器与疾病的联系。     

Direct visualization of organelle movement along actin filaments dissociated from characean algae

A system has been developed in which organelle transport can be studied without the influence of an organized cellular cytoplasm. Binding and continuous unidirectional movement of organelles along isolated cellular transport cables were directly visualized by video light microscopy after the dissociation of the cytoplasm of characean algae cells in a Ca2+-free buffer containing adenosine triphosphate. Individual organelles had more than one attachment site and moved at mean rates of 11.2 or 62.1 micrometers per second along multiple parallel pathways on each cable. Electron microscopy of these cables after direct freezing demonstrated that they consist of compact bundles of actin filaments. Under these conditions, characteristics of organelle movement should reflect directly the underlying molecular processes of binding and force generation.     

Flow control among microvessels coordinated by intercellular conduction

Optimal distribution of blood flow requires coordination of vasodilation among resistance vessels. During hyperemia, blood vessels dilate upstream from the initiating stimulus. Spreading vasodilation independent of flow changes has not been previously demonstrated. In the present study, iontophoresis of acetylcholine adjacent to single hamster cheek pouch arterioles in situ (diameter, 20 to 37 micrometers) induced a rapid bidirectional dilation that was not attenuated when blood flow was eliminated with vascular occlusion. This finding indicates that a vasodilatory stimulus is conducted along the arteriole and demonstrates the existence of a mechanism of intercellular communication that is capable of coordinating diameter changes among resistance vessels.     

Intervacuole exchange in the yeast zygote: a new pathway in organelle communication

A new pathway of vesicle traffic between organelles has been identified. The vacuoles (lysosomes) of Saccharomyces cerevisiae zygotes rapidly exchange their contents at a specific point in the cell cycle. With the use of fluorescence microscopy, "tracks" were observed that connect the original parental vacuoles to the newly forming bud vacuoles. These observations suggest that vacuole-derived vesicles rapidly move along the tracks in both directions, equilibrating vacuole contents. This rapid vesicle movement may be responsible for vacuole formation in newly developing cells.     

外来入侵植物假臭草在海口各级公路分布的初步研究

为了研究外来入侵植物假臭草在海口市公路沿线的入侵情况,在海口市高速公路、国道、省道、县道四级公路沿线选取12个样地,共计108个样方进行了调查.对假臭草在不同等级道路和垂直于道路的不同距离上的分布进行了研究,结果显示各类植物91种,分属于38科.在海口市四级公路中,假臭草在高速公路和国道分布较多,在省道和县道分布较少;在同级道路垂直公路不同距离下,假臭草在垂直道路距离5m处分布较多,在l m和15 m处分布较少.但是,假臭草在海口市各级公路沿线的群落特征差异均未达到显著水平.     

The primary cilium as the cell's antenna: signaling at a sensory organelle

Almost every vertebrate cell has a specialized cell surface projection called a primary cilium. Although these structures were first described more than a century ago, the full scope of their functions remains poorly understood. Here, we review emerging evidence that in addition to their well-established roles in sight, smell, and mechanosensation, primary cilia are key participants in intercellular signaling. This new appreciation of primary cilia as cellular antennae that sense a wide variety of signals could help explain why ciliary defects underlie such a wide range of human disorders, including retinal degeneration, polycystic kidney disease, Bardet-Biedl syndrome, and neural tube defects.     

Mycoplasma pneumoniae infection: role of a surface protein in the attachment organelle

Attachment of Mycoplasma pneumoniae to host cell by means of a specialized terminus initiates infection. Monoclonal antibodies to a surface protein (Pl) inhibit this process, and react with a region of the tip covered with peplomer-like particles. Since antibodies against the Pl protein are generated by natural and experimental infection and by immunization, the substance may be an important determinant of protective immunity.     

Composition and formation of intercellular junctions in epithelial cells

The polarized nature of epithelial cells is manifested by the nonrandom partitioning of organelles within the cells, the concentration of intercellular junctions at one pole, and the asymmetric distribution of proteins and lipids within the plasma membrane. These features allow epithelia to fulfill their specific tasks, such as targeted uptake and secretion of molecules and the segregation of different tissue compartments. The accessibility of Drosophila melanogaster and Caenorhabditis elegans to genetic and cell biological analyses, combined with the study of mammalian cells in culture, provides an ideal basis for understanding the mechanisms that control the establishment and maintenance of epithelial cell polarity and tissue integrity. Here, we focus on some of the best-studied junctions and membrane-associated protein complexes and their relation to cell polarity. Comparisons between fly, worm, and vertebrate epithelia reveal marked similarities with respect to the molecules used, and pronounced differences in the organization of the junctions themselves.     

The Pex16p homolog SSE1 and storage organelle formation in Arabidopsis seeds

Mature Arabidopsis seeds are enriched in storage proteins and lipids, but lack starch. In the shrunken seed 1 (sse1) mutant, however, starch is favored over proteins and lipids as the major storage compound. SSE1 has 26 percent identity with Pex16p in Yarrowia lipolytica and complements pex16 mutants defective in the formation of peroxisomes and the transportation of plasma membrane- and cell wall-associated proteins. In Arabidopsis maturing seeds, SSE1 is required for protein and oil body biogenesis, both of which are endoplasmic reticulum-dependent. Starch accumulation in sse1 suggests that starch formation is a default storage deposition pathway.     

Carcinoma of the cervix: deficiency of nexus intercellular junctions

Intercellar junctions where cell membranes are in intimate contact (nexuses) are very abundant in the epithelium of normal human cervix. Squamous carcinoma cells are deficient in nexuses although a rare nexus is seen. Nexuses may be involved in normal growth regulation, while a deficiency of nexuses may be related to the invasive property of malignant growth.