Influence of ionic environment on intestinal oxygen consumption

Summary The oxygen consumption of rat small intestine in vitro is influenced by the anions, chloride and bicarbonate, as well as by sodium.USPHS support: Grant number AM13240 and Award number AM70199.     

A fundamental avian wing-stroke provides a new perspective on the evolution of flight

The evolution of avian flight remains one of biology's major controversies, with a long history of functional interpretations of fossil forms given as evidence for either an arboreal or cursorial origin of flight. Despite repeated emphasis on the 'wing-stroke' as a necessary avenue of investigation for addressing the evolution of flight, no empirical data exist on wing-stroke dynamics in an experimental evolutionary context. Here we present the first comparison of wing-stroke kinematics of the primary locomotor modes (descending flight and incline flap-running) that lead to level-flapping flight in juvenile ground birds throughout development. We offer results that are contrary both to popular perception and inferences from other studies. Starting shortly after hatching and continuing through adulthood, ground birds use a wing-stroke confined to a narrow range of less than 20 degrees , when referenced to gravity, that directs aerodynamic forces about 40 degrees above horizontal, permitting a 180 degrees range in the direction of travel. Based on our results, we put forth an ontogenetic-transitional wing hypothesis that posits that the incremental adaptive stages leading to the evolution of avian flight correspond behaviourally and morphologically to transitional stages observed in ontogenetic forms.     

The genome of the simian and human malaria parasite Plasmodium knowlesi

Plasmodium knowlesi is an intracellular malaria parasite whose natural vertebrate host is Macaca fascicularis (the 'kra' monkey); however, it is now increasingly recognized as a significant cause of human malaria, particularly in southeast Asia. Plasmodium knowlesi was the first malaria parasite species in which antigenic variation was demonstrated, and it has a close phylogenetic relationship to Plasmodium vivax, the second most important species of human malaria parasite (reviewed in ref. 4). Despite their relatedness, there are important phenotypic differences between them, such as host blood cell preference, absence of a dormant liver stage or 'hypnozoite' in P. knowlesi, and length of the asexual cycle (reviewed in ref. 4). Here we present an analysis of the P. knowlesi (H strain, Pk1(A+) clone) nuclear genome sequence. This is the first monkey malaria parasite genome to be described, and it provides an opportunity for comparison with the recently completed P. vivax genome and other sequenced Plasmodium genomes. In contrast to other Plasmodium genomes, putative variant antigen families are dispersed throughout the genome and are associated with intrachromosomal telomere repeats. One of these families, the KIRs, contains sequences that collectively match over one-half of the host CD99 extracellular domain, which may represent an unusual form of molecular mimicry.     

Evolutionary origin and development of snake fangs

Many advanced snakes use fangs-specialized teeth associated with a venom gland-to introduce venom into prey or attacker. Various front- and rear-fanged groups are recognized, according to whether their fangs are positioned anterior (for example cobras and vipers) or posterior (for example grass snakes) in the upper jaw. A fundamental controversy in snake evolution is whether or not front and rear fangs share the same evolutionary and developmental origin. Resolving this controversy could identify a major evolutionary transition underlying the massive radiation of advanced snakes, and the associated developmental events. Here we examine this issue by visualizing the tooth-forming epithelium in the upper jaw of 96 snake embryos, covering eight species. We use the sonic hedgehog gene as a marker, and three-dimensionally reconstruct the development in 41 of the embryos. We show that front fangs develop from the posterior end of the upper jaw, and are strikingly similar in morphogenesis to rear fangs. This is consistent with their being homologous. In front-fanged snakes, the anterior part of the upper jaw lacks sonic hedgehog expression, and ontogenetic allometry displaces the fang from its posterior developmental origin to its adult front position-consistent with an ancestral posterior position of the front fang. In rear-fanged snakes, the fangs develop from an independent posterior dental lamina and retain their posterior position. In light of our findings, we put forward a new model for the evolution of snake fangs: a posterior subregion of the tooth-forming epithelium became developmentally uncoupled from the remaining dentition, which allowed the posterior teeth to evolve independently and in close association with the venom gland, becoming highly modified in different lineages. This developmental event could have facilitated the massive radiation of advanced snakes in the Cenozoic era, resulting in the spectacular diversity of snakes seen today.     

Haematopoietic stem cells do not asymmetrically segregate chromosomes or retain BrdU

Stem cells are proposed to segregate chromosomes asymmetrically during self-renewing divisions so that older ('immortal') DNA strands are retained in daughter stem cells whereas newly synthesized strands segregate to differentiating cells. Stem cells are also proposed to retain DNA labels, such as 5-bromo-2-deoxyuridine (BrdU), either because they segregate chromosomes asymmetrically or because they divide slowly. However, the purity of stem cells among BrdU-label-retaining cells has not been documented in any tissue, and the 'immortal strand hypothesis' has not been tested in a system with definitive stem cell markers. Here we tested these hypotheses in haematopoietic stem cells (HSCs), which can be highly purified using well characterized markers. We administered BrdU to newborn mice, mice treated with cyclophosphamide and granulocyte colony-stimulating factor, and normal adult mice for 4 to 10 days, followed by 70 days without BrdU. In each case, less than 6% of HSCs retained BrdU and less than 0.5% of all BrdU-retaining haematopoietic cells were HSCs, revealing that BrdU has poor specificity and poor sensitivity as an HSC marker. Sequential administration of 5-chloro-2-deoxyuridine and 5-iodo-2-deoxyuridine indicated that all HSCs segregate their chromosomes randomly. Division of individual HSCs in culture revealed no asymmetric segregation of the label. Thus, HSCs cannot be identified on the basis of BrdU-label retention and do not retain older DNA strands during division, indicating that these are not general properties of stem cells.     

一种实用监控系统的人脸检测定位算法

对基于监控系统中彩色图像的人脸检测与定位方法进行了探讨,利用颜色对方向的不敏感来减少人脸区域的搜索范围,将颜色空间与Hough变换相结合实现人脸定位.首先在颜色空间YCbCr上建立肤色模型,并对肤色区域进行初步检测,然后利用自适应模糊Hough变换检测瞳孔所在的圆心,从而实现对人脸区域的精确定位.在Georgia Tech彩色人脸数据库上的实验结果表明:该方法能够较好地检测肤色偏黄的人脸,并且在人眼的定位阶段平均用时为0.1秒,满足数字监控中实时性的要求.     

硅灰石粒径对PP/PP-g-MMA/W复合体系非等温结晶的影响

以甲基丙烯酸甲酯接枝聚丙烯(PP-g-MMA)为硅灰石(W)填充聚丙烯(PP)复合材料(PP/W)的界面相容剂,研究了W粒径对聚丙烯/硅灰石(PP/PP-g-MMA/W)复合体系力学性能和非等温结晶行为的影响.用Avrami方程、Ozawa、Mo、和Kissinger方法分析了复合材料非等温结晶曲线,得到n、Kc、α、F(T)、TP、T1/2和△E等参数.结果表明,W粒径对n和α影响不大;在W异相成核、W粒径和增容荆共同作用下,W粒径为400目和800目的试样,K较大,F(T)、t1/2较小,TP较高,形成的晶粒较完善、细小,提高了复合材料的塑性和韧性,特别是800目的试样塑性和韧性最好.     

A 4000-year record of woodland vegetation from Wind River Canyon, central Wyoming

Plant macrofossil analyses of 16 radiocarbon-dated woodrat middens spanning the past 4000 years from the Wind River Canyon region in central Wyoming provide information concerning late Holocene development of juniper woodlands. The study sites are currently dominated by Juniperus osteosperma , with J. scopulorum present locally. Woodlands in the region were dominated by J. scopulorum from ca 4000 yr BP until at least 2800 yr BP. Juniperus osteosperma invaded and expanded before 2000 yr BP. This expansion fits a regional pattern of J. osteosperma colonization and expansion in north central Wyoming during a relatively dry period between 2800 and 1000 yr BP. At the time the Wind River Canyon region was colonized by J. osteosperma , the species had populations 50-100 km to both the north and south. Long-distance seed dispersal was required for establishment in the study area. Genetic studies are necessary to identify source populations and regions.     

Non-canonical activation of Notch signaling/target genes in vertebrates

Evolutionarily conserved Notch signaling orchestrates diverse physiological mechanisms during metazoan development and homeostasis. Classically, ligand-activated Notch receptors transduce the signaling cascade through the interaction of DNA-bound CBF1-co-repressor complex. However, recent reports have demonstrated execution of a CBF1-independent Notch pathway through signaling cross-talks in various cells/tissues. Here, we have tried to congregate the reports that describe the non-canonical/CBF1-independent Notch signaling and target gene activation in vertebrates with specific emphasis on their functional relevance.