Ultrastructure and cytochemistry study of the yolk syncytial layer in the alevin of trout (Salmo fario trutta L.) after hatching

After hatching, the yolk syncytial layer of Salmo fario trutta may be subdivided into two zones, namely, the vitellolysis zone (containing numerous yolk platelets), and the cytoplasmic zone (where yolk platelets are rare). In the vitellolysis zone, two stages in the utilization of the yolk are observed: 1) The first stage, comprises the formation of yolk platelets from coalescent yolk by spherical cutting out and basal scission. This process seems to be achieved by the invagination of fibrillar elements into the coalescent yolk to form individual yolk platelets surrounded by a limiting membrane. 2) The second stage essentially consists of the extrusion or budding of yolk matter from a yolk platelet. Again, where the yolk matter leaves a platelet, fibrillar elements are evident and show an alkaline phosphatase activity. The platelets of the vitellolysis zone have a homogeneous content and variable diameter; they never acquire a heterogeneous and polymorphic aspect which could be interpreted as an intermediate stage in their degradation.     

Microtubules viewed as molecular ant colonies

Populations of ants and other social insects self-organize and develop 'emergent' properties through stigmergy in which individual ants communicate with one another via chemical trails of pheromones that attract or repulse other ants. In this way, sophisticated properties and functions develop. Under appropriate conditions, in vitro microtubule preparations, initially comprised of only tubulin and GTP, behave in a similar manner. They self-organize and develop other higher-level emergent phenomena by a process where individual microtubules are coupled together by the chemical trails they produce by their own reactive growing and shrinking. This behaviour is described and compared with the behaviour of ant colonies. Viewing microtubules as populations of molecular ants may provide new insights as to how the cytoskeleton may spontaneously develop high-level functions. It is plausible that such processes occur during the early stages of embryogenesis and in cells.     

Migration load in males and females

Many theories have been proposed for interpreting the relative sexual mortalities in natural populations, but the effects of maladaptive genes from migrants on sexual mortality have not been examined. In this study, I systematically explore the properties of migration load in dioecious plants where gender dimorphism is determined by sex chromosomes (the XX-XY or similar system). Two stages of gene flow (pollen and seed) and two stages of selection (gametophyte and sporophyte) are jointly examined in the one- and two-locus cases. The general results show that several factors, including the maladaptive allele frequencies in migrants, migration rate, selection, and linkage disequilibria, can individually or jointly alter the relative sexual mortalities at either the gametophyte or the sporophyte stage, or both. When there are the same values between sexes in the parameters relevant to the migrant gene frequencies and two-stage selection coefficients under the additive viability model (without Y-chromosome and linkage disequilibrium effects), the average mortality is higher in ovules than in pollen since the males do not inherit the maladaptive genes from migrating pollen. The average mortality per individual in the homogametic sex is almost twice as large as that in heterogametic sex at the sporophyte stage. Under the additive viability model, the relative sexual mortalities at the gametophyte stage are negatively related to the relative sexual mortalities at the sporophyte stage.     

Distinct spatio-temporal expression of ABCA and ABCG transporters in the developing and adult mouse brain

Using in situ hybridization for the mouse brain, we analyzed developmental changes in gene expression for the ATP-binding cassette (ABC) transporter subfamilies ABCA1-4 and 7, and ABCG1, 2, 4, 5 and 8. In the embryonic brains, ABCA1 and A7 were highly expressed in the ventricular (or germinal) zone, whereas ABCA2, A3 and G4 were enriched in the mantle (or differentiating) zone. At the postnatal stages, ABCA1 was detected in both the gray and white matter and in the choroid plexus. On the other hand, ABCA2, A3 and A7 were distributed in the gray matter. In addition, marked up-regulation of ABCA2 occurred in the white matter at 14 days-of-age when various myelin protein genes are known to be up-regulated. In marked contrast, ABCA4 was selective to the choroid plexus throughout development. ABCG1 was expressed in both the gray and white matters, whereas ABCG4 was confined to the gray matter. ABCG2 was diffusely and weakly detected throughout the brain at all stages examined. Immunohistochemistry of ABCG2 showed its preferential expression on the luminal membrane of brain capillaries. Expression signals for ABCG5 and G8 were barely detected at any stages. The distinct spatio-temporal expressions of individual ABCA and G transporters may reflect their distinct cellular expressions in the developing and adult brains, presumably, to regulate and maintain lipid homeostasis in the brain.     

Differential adhesive properties of sequestered asexual and sexual stages of Plasmodium falciparum on human endothelial cells are tissue independent

The protozoan parasite Plasmodium falciparum, responsible for the most severe form of malaria, is able to sequester from peripheral circulation during infection. The asexual stage parasites sequester by binding to endothelial cell receptors in the microvasculature of various organs. P. falciparum gametocytes, the developmental stages responsible for parasite transmission from humans to Anopheles mosquitoes, also spend the almost ten days necessary for their maturation sequestered away from the peripheral circulation before they are released in blood mainstream. In contrast to those of asexual parasites, the mechanisms and cellular interactions responsible for immature gametocyte sequestration are largely unexplored, and controversial evidence has been produced so far on this matter. Here we present a systematic comparison of cell binding properties of asexual stages and immature and mature gametocytes from the reference P. falciparum clone 3D7 and from a patient parasite isolate on a panel of human endothelial cells from different tissues. This analysis includes assays on human bone marrow derived endothelial cell lines (HBMEC), as this tissue has been proposed as a major site of gametocyte maturation. Our results clearly demonstrate that cell adhesion of asexual stage parasites is consistently more efficient than that, virtually undetectable of immature gametocytes, irrespectively of the endothelial cell lines used and of parasite genotypes. Importantly, immature gametocytes of both lines tested here do not show a higher binding efficiency compared to asexual stages on bone marrow derived endothelial cells, unlike previously reported in the only study on this issue. This indicates that gametocyte-host interactions in this tissue are unlikely to be mediated by the same adhesion processes to specific endothelial receptors as seen with asexual forms.     

Adaptive explanations for sensitive windows in development

Development in many organisms appears to show evidence of sensitive windows—periods or stages in ontogeny in which individual experience has a particularly strong influence on the phenotype (compared to other periods or stages). Despite great interest in sensitive windows from both fundamental and applied perspectives, the functional (adaptive) reasons why they have evolved are unclear. Here we outline a conceptual framework for understanding when natural selection should favour changes in plasticity across development. Our approach builds on previous theory on the evolution of phenotypic plasticity, which relates individual and population differences in plasticity to two factors: the degree of uncertainty about the environmental conditions and the extent to which experiences during development (‘cues’) provide information about those conditions. We argue that systematic variation in these two factors often occurs within the lifetime of a single individual, which will select for developmental changes in plasticity. Of central importance is how informational properties of the environment interact with the life history of the organism. Phenotypes may be more or less sensitive to environmental cues at different points in development because of systematic changes in (i) the frequency of cues, (ii) the informativeness of cues, (iii) the fitness benefits of information and/or (iv) the constraints on plasticity. In relatively stable environments, a sensible null expectation is that plasticity will gradually decline with age as the developing individual gathers information. We review recent models on the evolution of developmental changes in plasticity and explain how they fit into our conceptual framework. Our aim is to encourage an adaptive perspective on sensitive windows in development.     

Hydrogen peroxide levels in mouse oocytes and early cleavage stage embryos developed in vitro or in vivo

We describe a fluorimetric method for measuring the level of H2O2 in individual mouse oocytes and early embryos. Levels of H2O2 are low but detectable in unfertilized oocytes recovered freshly from the female reproductive tract. The levels in early cleaving embryos (1-cell to 8-cell stages) immediately after recovery from the female tract seem to be slightly higher the later the stage examined. However, when embryos are cultured in vitro from the 1-cell or early 2-cell stage, H2O2 levels rise when the embryos reach the mid-2-cell stage and remain elevated until they enter the early 4-cell stage. No equivalent elevation of H2O2 is seen during the transition from 1-cell to 2-cell or from 4-cell to 8-cell stages. Embryos that are able to develop successfully in vitro, as well as those that show a developmental block at the 2-cell stage on culture in vitro, both show this rise in H2O2 levels after in vitro culture. The relationship between the rise in H2O2 and the '2-cell block' to development is discussed.     

Transport of Materials from the Cotyledons during Germination of Seeds of the Garden Pea (Pisum sativum L.)

After the first week of germination the relationship betweenthe amounts of total dry matter, nitrogen, phosphorus, sulphur,and potassium transferred to the axis from the cotyledons inthe intact plant remained approximately constant irrespectiveof the conditions of growth. It is proposed that the ratio inwhich the individual elements are transported is determinedby the proportions in which they are released by the storagecells. Deviation from this ratio during the first week of germination,and over a longer period in deshooted plants is attributed tocompetition for the available nutrients between actively metabolizingcells in the cotyledons and axis. It is demonstrated by steam-girdling that movement of materialsfrom the cotyledons into the shoot probably occurs via the phloem.Calcium is mobile in the phloem during the early stages of germination,possibly because the amount of free calcium in the cotyledonsis high.     

Orderly and nonstochastic acquisition of CD94/NKG2 receptors by developing NK cells derived from embryonic stem cells in vitro

In mice there are two families of MHC class I-specific receptors, namely the Ly49 and CD94/NKG2 receptors. The latter receptors recognize the nonclassical MHC class I Qa-1(b) and are thought to be responsible for the recognition of missing-self and the maintenance of self-tolerance of fetal and neonatal NK cells that do not express Ly49. Currently, how NK cells acquire individual CD94/NKG2 receptors during their development is not known. In this study, we have established a multistep culture method to induce differentiation of embryonic stem (ES) cells into the NK cell lineage and examined the acquisition of CD94/NKG2 by NK cells as they differentiate from ES cells in vitro. ES-derived NK (ES-NK) cells express NK cell-associated proteins and they kill certain tumor cell lines as well as MHC class I-deficient lymphoblasts. They express CD94/NKG2 heterodimers, but not Ly49 molecules, and their cytotoxicity is inhibited by Qa-1(b) on target cells. Using RT-PCR analysis, we also report that the acquisition of these individual receptor gene expressions during different stages of differentiation from ES cells to NK cells follows a predetermined order, with their order of acquisition being first CD94; subsequently NKG2D, NKG2A, and NKG2E; and finally, NKG2C. Single-cell RT-PCR showed coexpression of CD94 and NKG2 genes in most ES-NK cells, and flow cytometric analysis also detected CD94/NKG2 on most ES-NK cells, suggesting that the acquisition of these receptors by ES-NK cells in vitro is nonstochastic, orderly, and cumulative.     

Regional,directional, and age-dependent properties of the brain undergoing large deformation

The large strain mechanical properties of adult porcine gray and white matter brain tissues were measured in shear and confirmed in compression. Consistent with local neuroarchitecture, gray matter showed the least amount of anisotropy, and corpus callosum exhibited the greatest degree of anisotropy. Mean regional properties were significantly distinct, demonstrating that brain tissue is inhomogeneous. Fresh adult human brain tissue properties were slightly stiffer than adult porcine properties but considerably less stiff than the human autopsy data in the literature. Mixed porcine gray/white matter samples were obtained from animals at "infant" and "toddler" stages of neurological development, and shear properties compared to those in the adult. Only the infant properties were significantly different (stiffer) from the adult.     

南京栖霞山铅锌银多金属矿床成矿流体中的分子化石

热液型金属矿床生物成矿作用研究的关键在于检测成矿流体中的有机质,尤其是其中的分子化石。以南京栖霞山多金属矿床为例,重点研究了成矿流体遗留下来的最直接的样品－有机包裹体中的分子化石。     

Living organisms and the quantum-mechanical wave properties of matter

Heat capacity data for the solid chemical elements and for 10 amino acids from proteins, and Kopp's Law heat capacity values for the chemical elements, show that proteins have extremely low heat capacities compared to other substances. The type of quantum-mechanical interaction that is highly predominant in low-heat-capacity substances reveals the quantum wave properties of matter. Therefore, the quantum-mechanical wave properties of matter are highly predominant in proteins. Some speculations about the meaning of this result are examined and assessed.     

Development of neurons in the abdominal ganglion of Aplysia californica. I. Axosomatic synaptic contacts.

The development of mariculture techniques for the raising of Aplysia californica in the laboratory from fertilized egg to reproductively mature adult permits the study of the developmental program whereby individual identified neurons in the abdominal ganglion acquire their specific adult properties. In this paper, we describe one of the early steps of this developmental program: the outgrowth of axonal processes by neurons of the abdominal ganglion. Axonal outgrowth is correlated with and may be triggered by the transient appearance of morphologically identifiable axosomatic contacts between the as yet undifferentiated cell body of specific neurons and an axon terminal from an incoming nerve fiber from the pleuroabdominal connective. The evidence that transient axosomatic contacts may signal neuronal differentiation is the following: (1) Axosomatic contacts have not been observed in the abdominal ganglion of adult animals, whereas they are commonly observed during the early stages of development. (2) Cells that receive axosomatic contacts are undifferentiated morphologically and do not as yet have axons. By contrast, cells with axons do not have soma contacts. (3) Individual cells that can be identified from animal to animal in the same and succeeding developmental stages receive axosomatic contacts on similar topographic postions of the cell body at one point in development. Axon outgrowth then occurs at the site of contact. Later in development, with further axon extension, these cells no longer have synaptic contacts on the cell body or axon.     

The Pattern of Distribution of Phosphorus and Dry Matter with Time in Spring Wheat

The pattern of distribution of dry matter and phosphorus wasfollowed in individual plants harvested from a field crop ofspring wheat throughout its development. There was a continueduptake of phosphorus with time and almost half of the totalphosphorus was accumulated in the post-anthesis period of growth.The various component parts of the main shoot were followedin detail and both individual leaves and the stem showed substantialnet losses of phosphorus with time well before they reachedtheir dry weight maxima. The ear was the major sink for phosphorusand it was estimated that approximately one third of its phosphoruscontent was supplied by retranslocation. The main shoot stemand leaves also showed a significant decline in d. wt duringthe final stages of grain development. Half-ear removal at anthesisincreased both grain set and the growth of the grain of theupper florets of the remaining spikelets. Defoliation had littleeffect on grain yield but resulted in a reduction in the phosphoruscontent of the grain. Triticum aestivum L, spring wheat, phosphorus distribution, dry matter distribution     

Origins of the parasitic habit in the Nematoda

Circumstances that probably attended and influenced the adoption and development of the parasitic habit amongst the Nematoda are examined. Features that allowed early terrestrial nematodes to exploit discontinuous habitats such as decomposing organic matter, are considered to have been advantageous to microbivorous Secernentea that became parasites of animals and plants. This development followed the appearance of a land flora and that the Amphibia were the first vertebrate hosts of nematodes. Life cycles involving intermediate hosts were essential in drier environments and in aquatic ones where intermediate hosts preserve the infective stages; keeps them “in circulation”, and makes them attractive to predators. It is concluded that the parasitic habit was adopted repeatedly in both Secernentea and Adenophorea, though the latter did not diversify as much. Convergence is a common feature of nematode evolution, and the typical life history pattern of 5 stadia separated by 4 moults is often greatly modified by suppression, extension and diversification of stages and their roles. There is a need to examine the nematodes, especially of invertebrates in the remaining rain forests of Gondwanaland before they disappear.     

土壤有机质概念和分组技术研究进展

土壤有机质一直是土壤学研究领域的重点,在过去的50年里,对土壤质量可持续性观念的增强和寻找快速判断人为因素对土壤质量影响方向指标的强烈愿望导致了土壤有机质的研究重点发生了急剧变化：对农业措施反映慢的土壤腐殖质类物质的研究正在退出土壤有机质研究领域,而侧重点逐渐转向了土壤中未受微生物作用或正在受微生物降解的有机残体;也出现了新的土壤有机质研究概念和对应测试手段：土壤有机质的比重分组、与有机质结合的土壤颗粒大小分组、土壤团聚体中的POM和iPOM以及土壤水溶性有机质和微生物体C等概念和测试手段被相继提了出来,土壤有机质的研究重点正在从土壤微生物的作用产物(腐殖质)向土壤微生物作用前的、具有部分生物活性的有机质(轻组有机质、砂粒组和粗粉砂粒组中的有机质、POM和iPOM)和完全具有生物活性的有机质(微生物体C和水溶性有机质)转移,这一过程与土壤有机质概念的拓展密不可分。     

Brain morphological signatures for chronic pain

Chronic pain can be understood not only as an altered functional state, but also as a consequence of neuronal plasticity. Here we use in vivo structural MRI to compare global, local, and architectural changes in gray matter properties in patients suffering from chronic back pain (CBP), complex regional pain syndrome (CRPS) and knee osteoarthritis (OA), relative to healthy controls. We find that different chronic pain types exhibit unique anatomical 'brain signatures'. Only the CBP group showed altered whole-brain gray matter volume, while regional gray matter density was distinct for each group. Voxel-wise comparison of gray matter density showed that the impact on the extent of chronicity of pain was localized to a common set of regions across all conditions. When gray matter density was examined for large regions approximating Brodmann areas, it exhibited unique large-scale distributed networks for each group. We derived a barcode, summarized by a single index of within-subject co-variation of gray matter density, which enabled classification of individual brains to their conditions with high accuracy. This index also enabled calculating time constants and asymptotic amplitudes for an exponential increase in brain re-organization with pain chronicity, and showed that brain reorganization with pain chronicity was 6 times slower and twice as large in CBP in comparison to CRPS. The results show an exuberance of brain anatomical reorganization peculiar to each condition and as such reflecting the unique maladaptive physiology of different types of chronic pain.     

Electron microscopy studies of ciliated cells in the larval epidermis of Rana t. temporaria (L.) (Amphibia, Anura)

Examination of the epidermis of Rana temporaria in various stages of development revealed the presence of densely ciliated cells from the late neurula until shortly before metamorphosis. Unlike the other epidermal cells, these ciliated cells do not divide; once formed, they are constant in number until they disappear. In shape, size, and structure, however, they vary depending on stage of development and on their position in the body. In older larval stages and young tadpoles they are fully differentiated and strongly basophilic. Their function is to improve the hydrodynamic properties of the larval body, and hence ultimately to optimize the energy balance during locomotion.     

Action potentials dependent on monovalent cations in developing mouse embryos

Action potentials were examined using intracellular recording techniques to study the ionic mechanisms of excitability in oocytes and embryos of the mouse from the 1-cell through to the 16-cell stages of development. At all stages examined, action potentials dependent on monovalent cations (Na+ or Li+) were observed under Ca2+-free conditions, and the maximum rate of rise (MRR) of the Na action potential was larger than that of the Li action potential at a given concentration of monovalent cations. Both the Na and Li action potentials were insensitive to tetrodotoxin, and they were blocked by inorganic (Co2+, Cd2+, Mn2+, La3+) and organic (diltiazem) Ca antagonists. These properties were exactly the same as those of the Ca channels present in the membranes of the mouse embryos. In addition, competition was observed between permeant monovalent and divalent cations: the overshoot and MRR of the Na or Li action potentials were reduced in the presence of Ca2+. These results suggest that Na+ or Li+ go through the Ca channels when the external Ca2+ concentration was very low, and that the Ca channels are more permeable to Na+ than to Li+. Separate Na channels could not be detected or induced at any stages of development.     

Four-cell stage mouse blastomeres have different developmental properties

Blastomeres of the early mouse embryo are thought to be equivalent in their developmental properties at least until the eight-cell stage. However, the experiments that have led to this conclusion could not have taken into account either the spatial origin of individual blastomeres or the spatial allocation and fate of their progeny. We have therefore readdressed this issue having defined cell lineages in mouse embryos undergoing different patterns of cleavage in their second division cycle. This has enabled us to identify a major group of embryos in which we can predict not only the spatial origin of each given four-cell blastomeres, but also which region of the blastocyst is most likely to be occupied by its progeny. We show that a pattern of second cleavage divisions in which a meridional division is followed by one that is equatorial or oblique allows us to identify blastomeres that differ in their fate and in their developmental properties both from each other and from their cousins. We find that one of these four-cell stage blastomeres that inherits some vegetal membrane marked in the previous cleavage cycle tends to contribute to mural trophectoderm. The progeny of its sister tend to donate cells to part of the ICM lining the blastocyst cavity and its associated trophectoderm. Chimaeras made entirely of these equatorially or obliquely derived blastomeres show developmental abnormalities in both late preimplantation and early postimplantation development. By contrast, chimaeras made from four-cell stage blastomeres from early meridional divisions develop normally. The developmental defects of chimaeras made from the most vegetal blastomeres that result from later second cleavages are the most severe and following transplantation into foster mothers they fail to develop to term. However, when such individual four-cell blastomeres are surrounded by blastomeres from random positions, they are able to contribute to all embryonic lineages. In conclusion, this study shows that while all four-cell blastomeres can have full developmental potential, they differ in their individual developmental properties according to their origin in the embryo from as early as the four-cell stage.