The mutator phenotype theory can explain the complex morphology and behaviour of cancers

Almost all solid malignancies exhibit complex cytological and architectural abnormalities, which vary from cell to cell and area to area within the same tumour, and between tumours of the same type. The degrees of these abnormalities do not correlate perfectly with the biological behaviour (especially growth rate and metastatic potential) among the various tumour types. These features of tumours have long been considered to invalidate simple mutational or 'abnormal gene expression' (epigenetic) theories of carcinogenesis. The 'mutator phenotype/clonal selection' hypothesis is based on the now well-established phenomenon of genetic instability of cancer cells, and proposes that this instability is an essential requirement for the development of tumours, and not an irrelevant side-effect of some other process. This paper argues that this hypothesis can provide a satisfactory explanation for the diverse histological and biological features of solid malignancies. Further, because virtually all solid tumours are histologically abnormal, genetic instability is likely to be essential for the malignant process. The concepts of mutator phenotype and clonal selection are therefore supported. Received 8 April 2002; accepted 25 April 2002     

The functions of mucosal T cells in containing the indigenous commensal flora of the intestine

There is an immense load of non-pathogenic commensal bacteria in the distal small intestine and the colon of mammals. The physical barrier that prevents penetration (translocation) of these organisms into the body is a simple epithelium comprised of the single enterocyte/colonocyte cell layer with its overlying mucus. In this review, we discuss the roles of intestinal T cells in initiating and regulating innate and adaptive mucosal immune responses of the mucosal immune system that avoid or limit penetration of the commensal intestinal bacteria. Received 9 August 2002; accepted 9 September 2002 RID="*" ID="*"Corresponding author.     

下一代通信网络技术的演进和发展

研究了建立在不同的传输技术基础上通信网络的特点,分析了通信网络的发展历程以及下一代通信网络的发展趋势和结构特点。     

坚持和发展劳动价值论——对当前政治经济学研究中几个问题的看法

在我国建立社会主义市场经济体制的过程中,随着科学技术水平的提高,科学技术等生产要素在物质生产过程中的作用越来越大,“科学技术是第一生产力”、“按劳分配和按生产要素分配相结合”等观点的提出突出了生产要素的巨大作用。在这种情况下,人们产生了“科学技术等生产要素是否也创造价值”的疑惑。另外,人们把第三产业劳动是否创造价值与第三产业是否有其存在的合理性混在一起,从而对坚持和发展马克思劳动价值论产生了一定的不良影响。本文拟通过对这几个问题进行分析,以达到廓清是非的目的:科学技术作为生产要素在生产过程中并不创造价值;第三产业是否创造价值不能一概而论;劳动价值论并没有过时,不能用要素价值论取代它。     

CD1d and natural T cells: how their properties jump-start the immune system

Cellular and humoral immune mechanisms recruited to defend the host from infectious agents depend upon the early immune events triggered by antigen. The cytokine milieu within which the immune response matures is the most important of many factors that govern the nature of the immune response. Natural T cells, whose function is controlled by CD1d molecules, are an early source of cytokines that can bestow type 1 or type 2 differentiative potential upon helper T lymphocytes. This review attempts to illuminate the glycolipid antigen presentation properties of CD1d, how CD1d controls the function of natural T cells and how CD1d and natural T cells interact to jump start the immune system. CD1d is postulated to function as a sensor, sensing alterations in cellular lipid content by virtue of its affinity for such ligands. The presentation of a neo-self glycolipid, presumably by infectious assault of antigen-presenting cells, activates natural T cells, which promptly release pro-inflammatory and anti-inflammatory cytokines and jumpstart the immune system. Received 10 July 2000; received after revision 16 October 2000, accepted 16 November 2000     

Culture in low levels of oxygen enhances in vitro proliferation potential of satellite cells from old skeletal muscles

The proliferation ability of satellite cells (considered the 'stem cells' of mature myofibers) declines with increasing age when cultured under standard cell culture conditions of 21% oxygen. However, actual oxygen levels in the intact myofiber in vivo are an order of magnitude lower. No studies to date have addressed the issue of whether culturing satellite cells from old muscles under more 'physiologic' conditions would enhance their proliferation and/or differentiation ability. Therefore, we analyzed satellite cells derived from 31-month-old rats in standard cultures with 21% O₂ and in lowered (∼3%) O₂. Under the lowered O₂ conditions, we noted a remarkable increase in the percentage of large-sized colonies, activation of cell cycle progression factors, phosphorylation of Akt, and downregulation of the cell cycle inhibitor p27^Kip1. These data suggest that lower O₂ levels provide a milieu that stimulates proliferation by allowing continued cell cycle progression, to result ultimately in the enhanced in vitro replicative life span of the old satellite cells. Such a method therefore provides an improved means for the ex vivo generation of progenitor satellite cell populations for potential therapeutic stem cell transplantation. Received 20 April 2001; received after revision 28 May 2001; accepted 31 May 2001     

Phylogeography of crossbills, bullfinches, grosbeaks, and rosefinches

Mitochondrial cytochrome b (cyt b) from 24 Carduelini species including crossbills, bullfinches, grosbeaks, rosefinches, and other related, but not conclusively classified species, was sequenced. These sequences were also compared with all the available sequences from the genera Carduelis, Serinus, and Passer. Phylogenetic analyses consistently gave the same groups of finches and the calculated divergence times suggest that speciation of the studied species occurred between 14 and 3 million years ago (Miocene-Pliocene), appearing before the Passer, Carduelis, and Serinus genera. Pleistocene glaciations may have been important in sub-speciation. Crossbills are integrated within the genus Carduelis, and within redpolls; the common crossbill shows subspeciation with Loxia japonica in the Pleistocene epoch. Pinicola enucleator groups together with bullfinches and is probably the ancestor of the group. Hawfinch is only distantly related to the studied groups, and might either represent an isolated genus or be related to the New World genus Hesperiphona. The grosbeak genera Eophona and Mycerobas are clearly sister groups, and species belonging to the former might have given rise to Mycerobas species. The isolated (in classification) Uragus sibiricus and Haematospiza sipahi are included within the genus Carpodacus (rosefinches); Carpodacus nipalensis is outside the genus Carpodacus in the molecular analyses and might be an isolated species or related to the genus Montifringilla.     

Melanocortin receptors: their functions and regulation by physiological agonists and antagonists

The melanocortins are a family of bioactive peptides derived from proopiomelanocortin, and share significant structural similarity. Those peptides are best known for their stimulatory effects on pigmentation and steroidogenesis. Melanocortins are synthesized in various sites in the central nervous system and in peripheral tissues, and participate in regulating multiple physiological functions. Research during the past decade has provided evidence that melanocortins elicit their diverse biological effects by binding to a distinct family of G protein-coupled receptors with seven transmembrane domains. To date, five melanocortin receptor genes have been cloned and characterized. Those receptors differ in their tissue distribution and in their ability to recognize the various melanocortins and the physiological antagonists, agouti signaling protein and agouti-related protein. These advances have opened new horizons for exploring the significance of melanocortins, their antagonists, and their receptors in a variety of important physiological functions. Received 5 October 2000; accepted 10 November 2000     

The neurotrophic factors in non-neuronal tissues

Although neurotrophic factors are defined as molecules that maintain neuronal cells, they possess a range of functions outside the nervous system. For example, glial cell line-derived neurotrophic factor is essential for ureteric branching in kidney morphogenesis and for regulating the fate of stem cells during spermatogenesis. Leukemia inhibitory factor, a member of the interleukin-6 (IL-6) ciliary neurotrophic factor family, inhibits differentiation of embryonic stem cells, induces tubulogenesis in the embryonic kidney, and regulates sperm differentiation. Other IL-6 family members are important in cardiac differentiation and they have pleiotropic functions in the hematopoietic and immune systems. Although neurotrophin receptors have been found on a number of non-neuronal tissues, they represent mostly truncated receptor isoforms that are incapable of signal transduction and may have scavenger or dominant negative functions. However, several examples can be presented of essential non-neuronal functions played by neurotrophins in e.g., cardiac, hair follicle, and vascular differentiation, and the maintenance of immune cells.     

TVOD系统设计

VOD即"按需服务电视".介绍了国外的相关研究工作,指出电视系统不应停留在数字化技术上,而应以此为基础向智能化与Web集成的方向发展.从电视业务级别的划分入手,定义了TVOD的概念,并区别了TVOD与VOD的技术思路和应用范畴.详细讨论了TVOD概念系统的结构和关键技术.