Developmental Stage Age Groups and African Population Structure: The Kusasi of the West African Savanna

African population structures based on censuses exhibit a distinctive pattern of distortion. It is often assumed that the cause for this distortion is systematic biases in age estimates by census enumerators and respondents influenced by perceptions of social and biological development. African developmental stage age groups are the cultural codification of such perceptions. I describe developmental stage age groups among the Kusasi of Bawku District in northeast Ghana, and analyze their age and sex structure for a sample of 1,132 individuals from the village of Zorse. I show that differences between men and women reflect differences in biological and social development, and that cultural concepts of developmental stages could influence age estimates to produce the pattern of distortions typical of those found in African population structures based on censuses. This is supported by a comparison of Bawku District population structure based on the Ghana census and an ethnographic sample census in Zorse which eliminated most age estimate biases.     

Evidence for Rosettes as an Unrecognized Stage in the Life Cycle of Leishmania Parasites

ABSTRACT. Leishmania parasites, which afflict 12 million people in 88 countries, exist as promastigotes transmitted by insect vectors and as amastigotes residing in mammalian macrophages. Promastigote cells arranged in rosettes have also been described but universally disregarded as a distinct stage in the life cycle. We present evidence that only rosettes of Leishmania major promastigotes express cell surface poly‐α2,8 N‐acetyl neuraminic acid (PSA) and PSA containing de‐N‐acetyl neuraminic acid (NeuPSA). Expression of rosette‐specific PSA antigens was mosaic, with individual promastigotes expressing PSA, NeuPSA or both. A 50 kDa protein was detected by Western blot analysis of a detergent‐insoluble cell fraction with both PSA and NeuPSA‐reactive antibodies. Frequencies of rosette formation as well as cell surface PSA/NeuPSA expression were temperature dependent. Rosettes also engaged in an unusual swarming behavior, congregating into extended clusters. Distinct structures resembling cellular fusion bodies were formed in and released from rosettes. The results indicate that rosettes are an unrecognized stage in the life cycle of Leishmania. We hypothesize that rosettes initiate mating in Leishmania during which PSA/NeuPSA expression plays an important role. Recognizing rosettes as a distinct form of the Leishmania life cycle opens new possibilities for treatment or prevention of disease and, possibly, in vitro genetic recombination without passage of cells through insect vectors.     

无核荔枝胚胎发育时期蛋白质图谱分析

通过二维聚丙烯酰胺凝胶电泳(2DE)以及计算机辅助的图像分析技术,对荔枝开花后20d的正常与败育胚蛋白质图谱进行了初步分析。结果表明,正常胚总蛋白质斑点数为129,败育胚总蛋白质斑点数为130,其中24个蛋白质点在两种胚中的表达丰度没有明显变化,35个蛋白质点在表达丰度上有明显差异,55%的蛋白则发生了蛋白质缺失、增加以及位置改变等变化。这两种蛋白质组的表达差异说明了胚内蛋白质成分在其败育过程中发生了变化,这些蛋白可能参与了胚败育的调节和控制。     

Glutathione Reductase-null Malaria Parasites Have Normal Blood Stage Growth but Arrest during Development in the Mosquito

Malaria parasites contain a complete glutathione (GSH) redox system, and several enzymes of this system are considered potential targets for antimalarial drugs. Through generation of a γ-glutamylcysteine synthetase (γ-GCS)-null mutant of the rodent parasite Plasmodium berghei, we previously showed that de novo GSH synthesis is not critical for blood stage multiplication but is essential for oocyst development. In this study, phenotype analyses of mutant parasites lacking expression of glutathione reductase (GR) confirmed that GSH metabolism is critical for the mosquito oocyst stage. Similar to what was found for γ-GCS, GR is not essential for blood stage growth. GR-null parasites showed the same sensitivity to methylene blue and eosin B as wild type parasites, demonstrating that these compounds target molecules other than GR in Plasmodium. Attempts to generate parasites lacking both GR and γ-GCS by simultaneous disruption of gr and γ-gcs were unsuccessful. This demonstrates that the maintenance of total GSH levels required for blood stage survival is dependent on either de novo GSH synthesis or glutathione disulfide (GSSG) reduction by Plasmodium GR. Our studies provide new insights into the role of the GSH system in malaria parasites with implications for the development of drugs targeting GSH metabolism.     

Characterizing the Community Structure of Complex Networks

Background

Community structure is one of the key properties of complex networks and plays a crucial role in their topology and function. While an impressive amount of work has been done on the issue of community detection, very little attention has been so far devoted to the investigation of communities in real networks.

Methodology/Principal Findings

We present a systematic empirical analysis of the statistical properties of communities in large information, communication, technological, biological, and social networks. We find that the mesoscopic organization of networks of the same category is remarkably similar. This is reflected in several characteristics of community structure, which can be used as “fingerprints” of specific network categories. While community size distributions are always broad, certain categories of networks consist mainly of tree-like communities, while others have denser modules. Average path lengths within communities initially grow logarithmically with community size, but the growth saturates or slows down for communities larger than a characteristic size. This behaviour is related to the presence of hubs within communities, whose roles differ across categories. Also the community embeddedness of nodes, measured in terms of the fraction of links within their communities, has a characteristic distribution for each category.

Conclusions/Significance

Our findings, verified by the use of two fundamentally different community detection methods, allow for a classification of real networks and pave the way to a realistic modelling of networks'' evolution.     

Developmental Self-Construction and -Configuration of Functional Neocortical Neuronal Networks

The prenatal development of neural circuits must provide sufficient configuration to support at least a set of core postnatal behaviors. Although knowledge of various genetic and cellular aspects of development is accumulating rapidly, there is less systematic understanding of how these various processes play together in order to construct such functional networks. Here we make some steps toward such understanding by demonstrating through detailed simulations how a competitive co-operative (‘winner-take-all’, WTA) network architecture can arise by development from a single precursor cell. This precursor is granted a simplified gene regulatory network that directs cell mitosis, differentiation, migration, neurite outgrowth and synaptogenesis. Once initial axonal connection patterns are established, their synaptic weights undergo homeostatic unsupervised learning that is shaped by wave-like input patterns. We demonstrate how this autonomous genetically directed developmental sequence can give rise to self-calibrated WTA networks, and compare our simulation results with biological data.     

Can Models of Soft-Sediment Community Structure Be Complete Without Parasites?

Most of the organisms that live in marine, soft-sediment environmentsare hosts for parasites. Rates of infection by micro- or macroparasitescan be quite high, but vary in space and time. Despite the prevalenceof parasites, their potential influence on soft-sediment communitiesis poorly understood. None of the conceptual models of soft-sedimentcommunity structure or dynamics published to date considersthe impact of parasitism. A variety of potential direct andindirect effects of parasites on host populations and communitiesare discussed. The greatest challenge for future research inthis area is the development of experimental methods for manipulatingthe abundance of parasites under field conditions.     

水稻胚胎发育时期的特异性蛋白质

对不同发育时期的水稻胚蛋白质,进行了单向SDS聚丙烯酰胺凝胶电泳和双向凝胶电泳分析。单向电泳图中存在20kD左右、胚分化完成期以后特有的蛋白质。根据双向电泳图谱,稻胚总蛋白按其在胚胎发育过程中的动态可分为7类,其中组成性的蛋白质约占85％,在不同发育时期基本不变;具有发育时期特异性的蛋白质约占15％。以分化期胚蛋白质的抗体,对各时期的胚蛋白质进行交叉免疫电泳,所得图谱总体上是相似的,但不同时期的图谱之间出现沉淀峰的峰形、位置和数目的差异。交叉免疫电泳图谱的这种变化可能反映了稻胚发育过程中某些分化期蛋白质发生的变化。     

PfVPS45 Is Required for Host Cell Cytosol Uptake by Malaria Blood Stage Parasites

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Raman Micro-Spectroscopy Can Be Used to Investigate the Developmental Stage of the Mouse Oocyte

In recent years, the uptake of assisted reproductive techniques such as in vitro fertilisation has risen exponentially. However, there is much that is still not fully understood about the biochemical modifications that take place during the development and maturation of the oocyte. As such, it is essential to further the understanding of how oocyte manipulation during these procedures ultimately affects its developmental potential; yet, there are few methods currently available which are capable of providing a quantitative measure of oocyte quality. Raman spectroscopy enables investigation of the global biochemical profile of intact cells without the need for labelling. Here, Raman spectra were acquired from the ooplasm of mouse oocytes at various stages of development, from late pre-antral follicles, collected after in vitro maturation within their ovarian follicles and from unstimulated and stimulated ovulatory cycles. Using a combination of univariate and multivariate statistical methods, it was found that ooplasm lipid content could be used to discriminate between different stages of oocyte development. Furthermore, the spectral profiles of mature oocytes revealed that oocytes which have developed in vitro are protein-deficient when compared to in vivo grown oocytes. Finally, the ratio of two Raman peak intensities, namely 1605∶1447 cm⁻¹, used as a proxy for the protein-to-lipid ratio of the ooplasm, was shown to be indicative of the oocyte’s quality. Together, results indicate that Raman spectroscopy may present an alternative analytical tool for investigating the biochemistry of oocyte developmental stage and quality.     

Toward the Structure of Dynamic Membrane-Anchored Actin Networks

In the cortex of a motile cell, membrane-anchored actin filaments assemble into structures of varying shape and function. Filopodia are distinguished by a core of bundled actin filaments within finger-like extensions of the membrane. In a recent paper by Medalia et al.[1] cryo-electron tomography has been used to reconstruct, from filopodia of Dictyostelium cells, the 3-dimensional organization of actin filaments in connection with the plasma membrane. A special arrangement of short filaments converging toward the filopod's tip has been called a "terminal cone". In this region force is applied for protrusion of the membrane. Here we discuss actin organization in the filopodia of Dictyostelium in the light of current views on forces that are generated by polymerizing actin filaments, and on the resistance of membranes against deformation that counteracts these forces.     

Estimating the Stochastic Bifurcation Structure of Cellular Networks

High throughput measurement of gene expression at single-cell resolution, combined with systematic perturbation of environmental or cellular variables, provides information that can be used to generate novel insight into the properties of gene regulatory networks by linking cellular responses to external parameters. In dynamical systems theory, this information is the subject of bifurcation analysis, which establishes how system-level behaviour changes as a function of parameter values within a given deterministic mathematical model. Since cellular networks are inherently noisy, we generalize the traditional bifurcation diagram of deterministic systems theory to stochastic dynamical systems. We demonstrate how statistical methods for density estimation, in particular, mixture density and conditional mixture density estimators, can be employed to establish empirical bifurcation diagrams describing the bistable genetic switch network controlling galactose utilization in yeast Saccharomyces cerevisiae. These approaches allow us to make novel qualitative and quantitative observations about the switching behavior of the galactose network, and provide a framework that might be useful to extract information needed for the development of quantitative network models.     

Parasites Affect Food Web Structure Primarily through Increased Diversity and Complexity

Comparative research on food web structure has revealed generalities in trophic organization, produced simple models, and allowed assessment of robustness to species loss. These studies have mostly focused on free-living species. Recent research has suggested that inclusion of parasites alters structure. We assess whether such changes in network structure result from unique roles and traits of parasites or from changes to diversity and complexity. We analyzed seven highly resolved food webs that include metazoan parasite data. Our analyses show that adding parasites usually increases link density and connectance (simple measures of complexity), particularly when including concomitant links (links from predators to parasites of their prey). However, we clarify prior claims that parasites “dominate” food web links. Although parasites can be involved in a majority of links, in most cases classic predation links outnumber classic parasitism links. Regarding network structure, observed changes in degree distributions, 14 commonly studied metrics, and link probabilities are consistent with scale-dependent changes in structure associated with changes in diversity and complexity. Parasite and free-living species thus have similar effects on these aspects of structure. However, two changes point to unique roles of parasites. First, adding parasites and concomitant links strongly alters the frequency of most motifs of interactions among three taxa, reflecting parasites'' roles as resources for predators of their hosts, driven by trophic intimacy with their hosts. Second, compared to free-living consumers, many parasites'' feeding niches appear broader and less contiguous, which may reflect complex life cycles and small body sizes. This study provides new insights about generic versus unique impacts of parasites on food web structure, extends the generality of food web theory, gives a more rigorous framework for assessing the impact of any species on trophic organization, identifies limitations of current food web models, and provides direction for future structural and dynamical models.     

四棱豆不同生育期叶片中过氧化物酶活力测定

比较了四棱豆不同生育期叶片中过氧化物酶活性,结果表明：该酶活力和比活力在不同生育期存在着明显差异,蛋白质含量变化不大。在成熟期,随着植株节位升高,酶活力及比活力均呈下降趋势,蛋白质含量则呈上升趋势。