Some New Phenomena in Macronuclear Development of Euplotes patella Exconjugants

Two new phenomena were observed during macronuclear development in E. patella. During the formation of giant chromosomes, the number of chromosomes decreased while individual chromosomes gradually became longer and thicker. Immediately before macronuclear elongation, ring-like anlagen appeared, which did not contain chromatin at their centers. The course of macronuclear development in Euplotes is reconsidered in light of these findings.     

Nuclear Division in the Ameboflagellate Adelphamoeba galeacystis

Nuclear division in synchronized cultures of the ameboflagellate Adelphamoeba galeacystis has been described. Division in this organism is typically promitotic. It occurs within an intact nuclear membrane and is characterized by the persistence of the nucleolus and its transformation into 2 polar masses. The nucleolus is stained with pyronin-Y by the methyl green pyronin-Y technic, and with Heidenhain's hematoxylin, but is unstained by the Feulgen reaction. The reaction with these stains is removed after digestion of the nucleolus by ribonuclease. During mitosis the nucleolus undergoes an orderly series of vacuolizations before forming the polar masses. The chromatin is Feulgen positive, stains with methyl green by the methyl green pyronin-Y technic and undergoes a series of characteristic changes during the division process. Synchronization of amebae grown on coverglasses was accomplished by transfer of cells from 30 to 38.5 C for a period of 100 min. A temporal sequence of nucleolar and chromatin participation in the nuclear division of this organism is suggested.     

Study of global motions in proteins by weighted masses molecular dynamics: Adenylate kinase as a test case

The weighted masses molecular dynamics (WMMD) technique is applied to the protein adenylate kinase. A novel set of restraints has been developed to allow the use of this technique with proteins. The WMMD simulation is successful in predicting the flexibility of the two mobile domains of the protein. The end product of the simulation is similar to the known open and AMP bound forms of the enzyme. The biological relevance of the restraints used and potential methods of improving the technique are discussed. © 1996 Wiley-Liss, Inc.     

Evolution of flatworm central nervous systems: Insights from polyclads

The nervous systems of flatworms have diversified extensively as a consequence of the broad range of adaptations in the group. Here we examined the central nervous system (CNS) of 12 species of polyclad flatworms belonging to 11 different families by morphological and histological studies. These comparisons revealed that the overall organization and architecture of polyclad central nervous systems can be classified into three categories (I, II, and III) based on the presence of globuli cell masses -ganglion cells of granular appearance-, the cross-sectional shape of the main nerve cords, and the tissue type surrounding the nerve cords. In addition, four different cell types were identified in polyclad brains based on location and size. We also characterize the serotonergic and FMRFamidergic nervous systems in the cotylean Boninia divae by immunocytochemistry. Although both neurotransmitters were broadly expressed, expression of serotonin was particularly strong in the sucker, whereas FMRFamide was particularly strong in the pharynx. Finally, we test some of the major hypothesized trends during the evolution of the CNS in the phylum by a character state reconstruction based on current understanding of the nervous system across different species of Platyhelminthes and on up-to-date molecular phylogenies.     

Water mass-specificity of bacterial communities in the North Atlantic revealed by massively parallel sequencing

Bacterial assemblages from subsurface (100 m depth), meso- (200-1000 m depth) and bathy-pelagic (below 1000 m depth) zones at 10 stations along a North Atlantic Ocean transect from 60°N to 5°S were characterized using massively parallel pyrotag sequencing of the V6 region of the 16S rRNA gene (V6 pyrotags). In a dataset of more than 830,000 pyrotags, we identified 10,780 OTUs of which 52% were singletons. The singletons accounted for less than 2% of the OTU abundance, whereas the 100 and 1000 most abundant OTUs represented 80% and 96% respectively of all recovered OTUs. Non-metric Multi-Dimensional Scaling and Canonical Correspondence Analysis of all the OTUs excluding the singletons revealed a clear clustering of the bacterial communities according to the water masses. More than 80% of the 1000 most abundant OTUs corresponded to Proteobacteria of which 55% were Alphaproteobacteria, mostly composed of the SAR11 cluster. Gammaproteobacteria increased with depth and included a relatively large number of OTUs belonging to Alteromonadales and Oceanospirillales. The bathypelagic zone showed higher taxonomic evenness than the overlying waters, albeit bacterial diversity was remarkably variable. Both abundant and low-abundance OTUs were responsible for the distinct bacterial communities characterizing the major deep-water masses. Taken together, our results reveal that deep-water masses act as bio-oceanographic islands for bacterioplankton leading to water mass-specific bacterial communities in the deep waters of the Atlantic.     

Macromolecular properties of cepacian in water and in dimethylsulfoxide

Cepacian is the exopolysaccharide produced by the majority of the so far investigated clinical strains of the Burkholderia cepacia complex. This is a group of nine closely related bacterial species that might cause serious lung infections in cystic fibrosis patients, in some cases leading to death. In this paper the aggregation ability and the conformational properties of cepacian chain were investigated to understand its role in biofilm formation. Viscosity and atomic force microscopy studies in water and in mixed (dimethylsulfoxide/water) solvent indicated the formation of double stranded molecular structures in aqueous solutions. Inter-residue short distances along cepacian chain were investigated by NOE NMR, which showed that two side chains of cepacian were not conformationally free due to strong interactions with the polymer backbone. These interactions were attributed to hydrogen bonding and contributed to structure rigidity.     

Prehistoric mongoloid dispersals. Edited by Takeru Akazawa and Emöke J. E. Szathmáry. New York: Oxford University Press. 1996. 387 pp. ISBN 0-19-852318-1 $150.00 (cloth)

Studies of the dynamics of locomotor performances depend on knowledge of the distribution of body mass within and between limb segments. However, these data are difficult to derive. Segment mass properties have generally been estimated by modelling limbs as truncated cones, but this approach fails to take into account that some segments are of elliptical, not circular, cross section; and further, the profiles of real segments are generally curved. Thus, they are more appropriately modelled as solids of revolution, described by the rotation in space of convex or concave curves, and the possibility of an elliptical cross section needs to be taken into account. In this project we have set out to develop a general geometric model which can take these factors into account, and permit segment inertial properties to be derived from cadavers by segmentation, and from living individuals using linear external measurements. We present a model which may be described by up to four parameters, depending o the profile and serial cross section (circular or ellipsoidal) of the individual segments. The parameters are obtained from cadavers using a simplified complex-pendulum technique, and from intact specimens by calculation from measurements of segment diameters and lengths. From the parameters, the center of mass, moments of inertia, and radii of gyration may be derived, using simultaneous equations. Inertial properties of the body segments of four Pan troglodytes and a single Pongo were determined, and contrasted to comparable findings for humans. Using our approach, the mass distribution characteristics of any individual or species may be represented by a rigid-link segment model or “android.” If this is made to move according to motion functions derived from a real performance of the individual represented, we show that recordings of resulting ground reaction forces may be quite closely simulated by predictive dynamic modelling. © 1996 Wiley-Liss, Inc.     

超声弹性成像技术在乳腺肿块诊断中的研究进展及应用

超声弹性成像技术(UE)是一种新的超声成像技术,能够根据组织硬度进行成像,估计出组织内部的弹性信息,从而反映它的结构特点,该技术较传统触诊检查更加客观,在乳腺肿块的鉴别诊断中有较高的价值,其临床应用广泛并且得到了快速的发展。现就国内外文献对UE技术的原理、图像分析方法、技术研究进展及其在乳腺肿块鉴别诊断中的应用进行综述。     

EVOLUTION OF BASAL METABOLIC RATE AND ORGAN MASSES IN LABORATORY MICE

Animal species of similar body mass vary widely in basal metabolic rate (BMR). A central problem of evolutionary physiology concerns the anatomical/physiological origin and functional significance of that variation. It has been hypothesized that such interspecific differences in wild animals evolved adaptively from differences in relative sizes of metabolically active organs. In order to minimize confounding phenotypic effects and maximize relevant genetic variation, we tested for intraspecific correlations between body-mass-corrected BMR and masses of four organs (heart, kidney, liver, and small intestine) among six inbred strains of mice. We found significant differences between strains in BMR and in masses of all four organs. Strains with exceptionally high (or low) BMR tended to have disproportionately large (or small) organs. The mass of each organ was correlated with the masses of each of the other three organs. Variation in organ masses accounted for 52% of the observed variation in BMR, of which 42% represented between-strain variation, and 10% represented within-strain variation. This conclusion is supported by published measurements of metabolic rates of tissue slices from the four organs. The correlation between BMR and intestine or heart mass arose exclusively from differences between strains, while the correlation between BMR and liver or kidney mass also appeared in comparing individual mice within the same strain. Thus, even though the masses of the four examined organs account for no more than 17% of total body mass, their high metabolic activities or correlated factors account for much of the variation in BMR among mice. We suggest that large masses of metabolically active organs are subject to natural selection through evolutionary trade-offs. On the one hand, they make possible high-energy budgets (advantageous under some conditions), but on the other hand they are energetically expensive to maintain.