Genome evolution in yeasts

Identifying the mechanisms of eukaryotic genome evolution by comparative genomics is often complicated by the multiplicity of events that have taken place throughout the history of individual lineages, leaving only distorted and superimposed traces in the genome of each living organism. The hemiascomycete yeasts, with their compact genomes, similar lifestyle and distinct sexual and physiological properties, provide a unique opportunity to explore such mechanisms. We present here the complete, assembled genome sequences of four yeast species, selected to represent a broad evolutionary range within a single eukaryotic phylum, that after analysis proved to be molecularly as diverse as the entire phylum of chordates. A total of approximately 24,200 novel genes were identified, the translation products of which were classified together with Saccharomyces cerevisiae proteins into about 4,700 families, forming the basis for interspecific comparisons. Analysis of chromosome maps and genome redundancies reveal that the different yeast lineages have evolved through a marked interplay between several distinct molecular mechanisms, including tandem gene repeat formation, segmental duplication, a massive genome duplication and extensive gene loss.     

Apolipoprotein L-I is the trypanosome lytic factor of human serum

Human sleeping sickness in east Africa is caused by the parasite Trypanosoma brucei rhodesiense. The basis of this pathology is the resistance of these parasites to lysis by normal human serum (NHS). Resistance to NHS is conferred by a gene that encodes a truncated form of the variant surface glycoprotein termed serum resistance associated protein (SRA). We show that SRA is a lysosomal protein, and that the amino-terminal alpha-helix of SRA is responsible for resistance to NHS. This domain interacts strongly with a carboxy-terminal alpha-helix of the human-specific serum protein apolipoprotein L-I (apoL-I). Depleting NHS of apoL-I, by incubation with SRA or anti-apoL-I, led to the complete loss of trypanolytic activity. Addition of native or recombinant apoL-I either to apoL-I-depleted NHS or to fetal calf serum induced lysis of NHS-sensitive, but not NHS-resistant, trypanosomes. Confocal microscopy demonstrated that apoL-I is taken up through the endocytic pathway into the lysosome. We propose that apoL-I is the trypanosome lytic factor of NHS, and that SRA confers resistance to lysis by interaction with apoL-I in the lysosome.     

Field evidence for surface-wave-induced instability of sand dunes

Field studies of barchans--crescent-shaped dunes that propagate over solid ground under conditions of unidirectional wind--have long focused on the investigation of an equilibrium between sand transport by wind and the control of air flow by dune topography, which are thought to control dune morphology and kinematics. Because of the long timescale involved, however, the underlying dynamic processes responsible for the evolution of dune fields remain poorly understood. Here we combine data from a three-year field study in the Moroccan Sahara with a model study to show that barchans are fundamentally unstable and do not necessarily behave like stable solitary waves, as suggested previously. We find that dune collisions and changes in wind direction destabilize the dunes and generate surface waves on the barchans. Because the resulting surface waves propagate at a higher speed than the dunes themselves, they can produce a series of new barchans of elementary size by breaking the horns of large dunes. The creation of these new dunes provides a mechanism for sand loss that prevents dune fields from merging into a single giant dune and therefore plays a fundamental role in the control of size selection and the development of dune patterns.     

一种新的中空纤维液流场流分离装置及其对葡聚糖保留行为的研究

中空纤维液流场流分离法对高分子和小粒子分离效果好,但目前因所使用的中空纤维均为各实验室自制且分子量阻断值不够小,使该技术的推广应用受到限制.设计了一种新的中空纤维液流场流分离装置,该装置的优越性在于其中空纤维分子量阻断值小,可以用于分离较小分子量的分子;并且中空纤维为商业购买,使得该技术的推广成为可能;该装置易于安装,操作简便.应用它获得了高分子物质葡聚糖的保留,并探讨了液流交汇时间、外场强度、流速和进样量对葡聚糖保留行为的影响.研究结果表明,给予足够的液流交汇时间,足够强的外场,葡聚糖能得到很好的保留.超量进样时,被测葡聚糖的保留时间不变,峰的对称性良好,结果重现性好.     

光学异常透射的微观理论

本文介绍了作者最近在《自然》杂志（Nature,2008,452：728-31）发表的一项解释光学异常透射的微观理论。该理论建立了描述异常透射的一个金属表面等离子体（surface plasmon polariton,SPP）模型,通过比较模型预言的结果和严格求解Maxwell方程组全矢量方法的数值计算结果,发现在可见光及近红外波段,该模型能够定量给出异常透射的所有主要特征,从而验证了该模型的有效性。由于模型中仅保留了SPP而忽略了其它金属表面波,因此能够单独考察SPP在异常透射中的贡献,有助于调和之前不同观点间的争论。同时,由于该模型将二维孔阵列分解为一维孔链的周期组合,然后综合考虑各孔链处SPP的激发及散射过程。因此能够从微观层面分析形成异常透射的物理原因,解释了传统模式展开方法中表面Bloch模式的物理根源,同时能够为相关器件的设计提供理论指导。     

Geology and palaeontology of the Upper Miocene Toros-Menalla hominid locality,Chad

All six known specimens of the early hominid Sahelanthropus tchadensis come from Toros-Menalla site 266 (TM 266), a single locality in the Djurab Desert, northern Chad, central Africa. Here we present a preliminary analysis of the palaeontological and palaeoecological context of these finds. The rich fauna from TM 266 includes a significant aquatic component such as fish, crocodiles and amphibious mammals, alongside animals associated with gallery forest and savannah, such as primates, rodents, elephants, equids and bovids. The fauna suggests a biochronological age between 6 and 7 million years. Taken together with the sedimentological evidence, the fauna suggests that S. tchadensis lived close to a lake, but not far from a sandy desert, perhaps the oldest record of desert conditions in the Neogene of northern central Africa.     

Implications of the polymorphism of HLA-G on its function,regulation, evolution and disease association

The HLA-G gene displays several peculiarities that are distinct from those of classical HLA class I genes. The unique structure of the HLA-G molecule permits a restricted peptide presentation and allows the modulation of the cells of the immune system. Although polymorphic sites may potentially influence all biological functions of HLA-G, those present at the promoter and 3′ untranslated regions have been particularly studied in experimental and pathological conditions. The relatively low polymorphism observed in the MHC-G coding region both in humans and apes may represent a strong selective pressure for invariance, whereas, in regulatory regions several lines of evidence support the role of balancing selection. Since HLA-G has immunomodulatory properties, the understanding of gene regulation and the role of polymorphic sites on gene function may permit an individualized approach for the future use of HLA-G for therapeutic purposes.