Sequential activation of HOX2 homeobox genes by retinoic acid in human embryonal carcinoma cells

RETINOIC acid had been implicated as a natural morphogen in chicken and frog embryogenesis, and is presumed to act through the gene regulatory activity of a family of nuclear receptors. Homeobox genes, which specify positional information in Drosophila and possibly in vertebrate embryogenesis, are among the candidate responsive genes. We previously reported that retinoic acid specifically induces human homeobox gene (HOX) expression in the embryonal carcinoma cell line NT2/D1. We now show that the nine genes of the HOX2 cluster are differentially activated in NT2/D1 cells exposed to retinoic acid concentrations ranging from 10(-8) to 10(-5) M. Genes located in the 3' half of the cluster are induced at peak levels by 10(-8) M retinoic acid, whereas a concentration of 10(-6) to 10(-5) M is required to fully activate 5' genes. At both high and low retinoic acid concentrations, HOX2 genes are sequentially activated in embryonal carcinoma cells in the 3' to 5' direction.     

The synthetic genetic interaction spectrum of essential genes

The nature of synthetic genetic interactions involving essential genes (those required for viability) has not been previously examined in a broad and unbiased manner. We crossed yeast strains carrying promoter-replacement alleles for more than half of all essential yeast genes to a panel of 30 different mutants with defects in diverse cellular processes. The resulting genetic network is biased toward interactions between functionally related genes, enabling identification of a previously uncharacterized essential gene (PGA1) required for specific functions of the endoplasmic reticulum. But there are also many interactions between genes with dissimilar functions, suggesting that individual essential genes are required for buffering many cellular processes. The most notable feature of the essential synthetic genetic network is that it has an interaction density five times that of nonessential synthetic genetic networks, indicating that most yeast genetic interactions involve at least one essential gene.     

基于广义能量法的曲面光顺

提出了同时考虑曲面几何及物理等多项光顺准则的基于广义能量法的曲面整体光顺思路，建立了包含曲面截线族粗光顺、曲面粗光顺两个步骤的曲面光顺方法，论述了曲面精光顺中广义能量表达式和约束条件的建立，实践证明，这种方法对于提高曲面的整体光顺性能具有良好的效果。     

Positional cloning of zebrafish ferroportin1 identifies a conserved vertebrate iron exporter

Defects in iron absorption and utilization lead to iron deficiency and overload disorders. Adult mammals absorb iron through the duodenum, whereas embryos obtain iron through placental transport. Iron uptake from the intestinal lumen through the apical surface of polarized duodenal enterocytes is mediated by the divalent metal transporter, DMTi. A second transporter has been postulated to export iron across the basolateral surface to the circulation. Here we have used positional cloning to identify the gene responsible for the hypochromic anaemia of the zebrafish mutant weissherbst. The gene, ferroportin1, encodes a multiple-transmembrane domain protein, expressed in the yolk sac, that is a candidate for the elusive iron exporter. Zebrafish ferroportin1 is required for the transport of iron from maternally derived yolk stores to the circulation and functions as an iron exporter when expressed in Xenopus oocytes. Human Ferroportin1 is found at the basal surface of placental syncytiotrophoblasts, suggesting that it also transports iron from mother to embryo. Mammalian Ferroportin1 is expressed at the basolateral surface of duodenal enterocytes and could export cellular iron into the circulation. We propose that Ferroportin1 function may be perturbed in mammalian disorders of iron deficiency or overload.     

一种基于事务冲突图的并发控制方法

提出了一种基于事务冲突图的并发控制方法．事务在执行前要提交其读集和写集，系统根据事务的读集和写集构造出一无圈的事务冲突图，并根据事务冲突图进行并发控制．这种并发控制方法具有对数据库无结构要求、无死锁、非两阶段等优点．讨论了其集中式并发控制方法和分布式并发控制方法．     

分布式选举算法

提出了一种基于任意网络拓扑的分布式选举领导人算法。每一处理机既不知道系统的网络拓扑，也不知道系统中处理机的台数。对于由ｎ台处理机组成的分布式系统，算法的消息复杂度最好为３＃Ｅ，最坏不超过＃Ｅ（２Ｎ＋１）－Ｎ＋ｎ；对于同步分布式系统，其时间复杂度最好不超过３（ｎ－１）△ｔ，最坏不超过４（ｎ－１）△ｔ。     

Evolution and environment in the Hominoidea.

Between 10 and 20 million years ago, a variety of hominoid primates lived in Africa, Europe and Asia. The question of which of these, if any, lie closest to the ancestries of humans and modern apes remains a lively source of debate. Recent fossil discoveries, though, shed light on the environments in which the various groups of hominoid emerged and, it is hoped, on their evolution. But the lack of a hominid fossil record before about 5 million years ago--and any fossil record for the African apes--is still a frustrating barrier.