Immunoelectron microscopic localization of dystrophin in myofibres

Duchenne muscular dystrophy, a common X-linked recessive human disease, has recently been shown to be caused by the deficiency of a large, low abundance protein called 'dystrophin'. Biochemical techniques have shown dystrophin to be membrane-associated in skeletal muscle, with enrichment of dystrophin in the t-tubules of 'triads'. Other studies using immunohistochemistry on thick (10 micron) sections have shown dystrophin to be located at the periphery of muscle fibres, possibly at the plasma membrane. These results have been interpreted as being either consistent and complementary, or contradictory. To localize dystrophin more precisely relative to these membrane systems we have employed highly sensitive and spatially accurate immuno-gold electron microscopy of ultra-thin (70-100 nm) cryosections. The major distribution of dystrophin was on the cytoplasmic face of the plasma membrane of muscle fibres, and possibly on the contiguous t-tubule membranes. The presented data, taken together with recently accumulated information regarding the primary structure of dystrophin, suggests that dystrophin is a component of the membrane cytoskeleton in myogenic cells. Thus, myofibre necrosis in patients affected with Duchenne muscular dystrophy is likely the result of plasma membrane instability.     

A protein of the endoplasmic reticulum involved early in polypeptide translocation.

To identify components of the mammalian endoplasmic reticulum involved in the translocation of secretory proteins, crosslinking and reconstitution methods were combined. A multispanning abundant membrane glycoprotein was found which is in proximity to nascent chains early in translocation. In reconstituted proteoliposomes, this protein is stimulatory or required for the translocation of secretory proteins.     

Importance of stirring in the development of an iron-fertilized phytoplankton bloom

The growth of populations is known to be influenced by dispersal, which has often been described as purely diffusive. In the open ocean, however, the tendrils and filaments of phytoplankton populations provide evidence for dispersal by stirring. Despite the apparent importance of horizontal stirring for plankton ecology, this process remains poorly characterized. Here we investigate the development of a discrete phytoplankton bloom, which was initiated by the iron fertilization of a patch of water (7 km in diameter) in the Southern Ocean. Satellite images show a striking, 150-km-long bloom near the experimental site, six weeks after the initial fertilization. We argue that the ribbon-like bloom was produced from the fertilized patch through stirring, growth and diffusion, and we derive an estimate of the stirring rate. In this case, stirring acts as an important control on bloom development, mixing phytoplankton and iron out of the patch, but also entraining silicate. This may have prevented the onset of silicate limitation, and so allowed the bloom to continue for as long as there was sufficient iron. Stirring in the ocean is likely to be variable, so blooms that are initially similar may develop very differently.     

石棉对N，N－二甲基苯胺的吸附和氧化作用

研究了青石棉、温石棉、直闪石和铁石棉与不同浓度Ｎ，Ｎ－二甲基苯胺（ＤＭＡ）在１１０℃的吸附氧化反应，测定了产物的紫外可见光谱、红外光谱、元素分析和热分析数据．结果表明，四种石棉均能使ＤＭＡ氧化为甲基紫．质子可以提高石棉的氧化能力．此外，反应过程还生成一种紫外可见光最大吸收为３４０ｎｍ的物质，其结构有待进一步鉴定．     

柴油机连杆轴颈磨损量组合预测模型及应用

为了得到更合理、准确的柴油机的磨损预测结果,基于已有的柴油机连杆轴颈磨损数据,结合现代新的预测理论技术,提出一种指数回归灰色理论相结合的组合预测模型.实际应用情况表明,指数回归灰色理论相结合的组合预测模型在4个预测步长内,组合预测的相对误差在1.0%内,比单个预测的精度要高得多.     

Molecular mechanisms in male determination and germ cell differentiation

Sex determination and gametogenesis are key processes in human reproduction, and any defect can lead to infertility. We describe here the molecular mechanisms of male sex determination and testis formation; defects in sex determination lead to a female phenotype despite the presence of a Y chromosome, more rarely to a male phenotype with XX chromosomes, or to intersex phenotypes. Interestingly, these phenotypes are often associated with other developmental malformations. In testis, spermatozoa are produced from renewable stem cells in a complex differentiation process called spermatogenesis. Gene expression during spermatogenesis differs to a surprising degree from gene expression in somatic cells, and we discuss here mechanistic differences and their effect on the differentiation process and male fertility.Received 23 January 2004; received after revision 30 March 2004; accepted 6 April 2004     

Effect of X-537A on the phosphorylated protein in sarcoplasmic reticulum vesicles

Summary The effect of the antibiotic X-537A on the phosphorylated ATPase (EP) was investigated. The results show that X-537A depresses the level of EP which is dependent on the Ca²⁺ gradient, while the Ca²⁺-independent EP is not affected. Acknowledgments. This work was supported by grants from the Instituto de Alta Cultura of the Portuguese Ministry of Education (No. CB/2) and the Calouste Gulbenkian Foundation.