Studies on the Formation and State of Determination of the Trunk Organizer in the Newt, Cynops Pyrrhogaster III. Tangential Induction in the Dorsal Marginal Zone

Analysis of the course of differentiation of combinants between the presumptive prechordal plate (PcP) and presumptive ectoderm (PE) by time-lapse filming showed that the PcP of early gastrulae has the capacity to induce mesoderm (notochord, muscle cells and migrating cells) in the PE. The mesoderm-inducing capacity of the PcP decreases sharply during gastrulation. Following invagination in the mid-gastrula, the PcP completely loses its mesoderm-inducing capacity. This change also occurred when the PcP of the earliest gastrula was aged in vitro for 18 hr. This shows that the mesoderm-inducing capacity of the PcP decreases autonomously with aging.
PE transplanted into the presumptive trunk organizer region of the dorsal marginal zone of the earlist gastrula, became mesodermized within 12 hr. It is clear that this mesodermization of the transplanted PE is due to "tangential induction" from the PcP. The stepwise formation of the trunk organizer in Cynops pyrrhogaster is discussed in consideration of these results.     

Compaction and particle segregation in myelin membrane arrays

Compacted membrane arrays are formed in the nerve myelin sheath by lowering the water activity (through evaporation or immersion in hypertonic solutions of nonelectrolytes or monovalent salts) or by binding specific cations (Ca(++), La(+++), and tetracaine at concentrations above 5-10 mM). X-ray diffraction observations on intact, hydrated nerves treated to induce compaction provide a control to assess the significance of structural changes seen by freeze-fracture electron microscopy. Compaction inevitably leads to lateral segregation of particles away from the closely packed membrane arrays into contiguous normal, or slightly expanded, period arrays. In the particle-enriched layers, the E fracture face is more particle-dense than the P face, whereas no particles are found on either face in the compacted layers. Morphologically, compaction induced by the all-or-nothing, relatively irreversible action of specific cations cannot be distinguished from compaction to the same extent induced by the graded, reversible effects of nonelectrolytes. Compaction by sodium chloride resembles that by specific- cation binding in that the repeat period is independent of reagent concentration; but, like dehydration by nonelectrolytes, the extent of compaction is reversibly related to reagent concentration. Sodium chloride-compacted myelin can be distinguished morphologically by a lack of the elongated border particles at the boundary between smooth and particle-enriched membrane observed for other compacting treatments. Fracture faces in compacted arrays are not always smooth, but the unusual appearances can be duplicated in purified myelin lipid multilayers subjected to similar treatments, which indicates that the particle-free membrane fracture faces are uninterrupted lipid hydrocarbon layers. Correlation of x-ray diffraction and electron microscopy observations provides a direct basis for identifying the intramembrane particles with transmembrane protein. The transmembrane protein appears to play a significant role in maintaining the normal membrane separation; swelling of the particle-enriched arrays in myelin compacted by tetracaine at low ionic strength provides information about the charge distribution on the transmembrane protein. Swelling of the compacted arrays following irreversible particle segregation shows that the interaction properties of the particle-free membranes are similar to those of pure lipid multilayers. Compaction and the consequent particle segregation in lyelin results from conditions stabilizing close apposition of the lipid bilayers. Particle segregation in areas of close contact between other cell membranes may also be driven by interbilayer attractive forces.     

Polyphosphate granules are an artefact of specimen preparation in the ectomycorrhizal fungusPisolithus tinctorius

Summary Polyphosphate granules are precipitated in the vacuoles of the ectomycorrhizal fungusPisolithus tinctorius (Pers.) Coker & Couch by various treatments, including conventional specimen preparation. Granules are not produced by glutaraldehyde fixation but appear at early stages of ethanol dehydration and are visible with Nomarski DIC microscopy. They show -metachromasy with toluidine blue O at low pH, are extracted by cold trichloroacetic acid and contain phosphorus and calcium as demonstrated by X-ray microanalysis. The granules are surrounded by electron-lucent areas that do not contain these elements at detectable levels. In contrast, vacuoles of freeze-substituted hyphae contain evenly dispersed flocculent material. Phosphorus and potassium are distributed more or less uniformly throughout, but calcium is not detected. This indicates that polyphosphate is present in the vacuole of living hyphae in soluble form and is precipitated to form granules by various treatments. It is thought that granules form when membranes, including the tonoplast, become leaky and there is an influx of precipitating ions such as calcium.Abbreviations DIC differential interference contrast - GMA glycol methacrylate - MMN modified Melin Norkrans - NMR nuclear magnetic resonance - P_i inorganic phosphate - STEM scanning transmission electron microscope     

Application of parsimony analysis of endemicity in Amazonian biogeography: an example with primates

The distributions of 51 non-human primate species are used for Parsimony Analysis of Endemicity (PAE) to determine the relationships among 14 interfluvial regions in the Amazon basin, South America. Two most parsimonious cladograms were found. The strict consensus tree of these cladograms suggests an early separation between Lower Amazonia (eastern) and Upper Amazonia (western). The major clusters of interfluvial regions identified in the PAE cladogram are congruent with the areas of endemism delimited for birds. When interfluvial regions are converted into avian areas of endemism, the PAE cladogram is congruent with one of the two general areas cladograms suggested for Amazonia based on phylogenies of several clades of forest birds. Our analysis suggests that PAE can be used as a tool to objectively identify areas of endemism at an intra-continental scale as well as to make historical inferences. However, the value of a PAE cladogram in this latter application should be always evaluated by congruence with area cladograms built upon cladistic biogeography procedures.     

Polymorphism and Ultrastructure of a Colpodean Ciliate of the Genus Platyophryides Foissner, 1987

ABSTRACT. A ciliate isolated from a pond in Brazil, transformed to a giant form when its food was shifted from a bacterial prey to a ciliate prey. This polymorphism is immediately reversible when the prey ciliates, either Tetrahymena or Colpidium , disappear from the culture medium. By its life cycle, morphology, and ultrastructure, this ciliate belongs to the Class Colpodea. it could belong to the genus Platyophryides Foissner, 1987, except that its micronucleus is not enveloped by the macronuclear membrane. The systematic position of the genus Platyophryides , the validity of the three species in this genus, and the characteristics of the Cyrtolophosidida are discussed.     

On the origin and colonization of house mice in the Madeira Islands

The skulls and skins of adult house mice from the Madeira Islands have been studied and compared with those from the Salvage Islands and with material from the neighbouring Portuguese mainland man-associated and wild forms, respectively Mus musclus domesticus Rutty, 1772 and M. sprelus Lataste, 1883. Differences between island and mainland populations were found in some of the analysed features. Insular skins of mice were found to be smaller than those of specimens from the mainland. However, in Madeiran and Salvage mice the toothrows were much more developed than in the mainland house mice. It is considered that the causes of these differences lie in the different characteristics of the habitats, mainly food availability, and also in the isolation of populations. Mus musculus domesticus appears to be the only form of the house mouse to have so far successfully colonized the Madeiras.     

A Comparison of the Use of In Vitro-Transcribed and Native rRNA for the Quantification of Microorganisms in the Environment

Abstract Nearly full-length, small subunit (SSU) rRNA was transcribed in vitro from clones of SSU rDNA genes. Comparing the use of in vitro-transcribed and native rRNA indicated that, when in vitro-transcribed rRNA was used as a standard for quantitative hybridizations with oligonucleotide probes, the population was consistently underestimated. The population abundance was expressed as a percentage of specific target SSU rRNA (determined with a specific oligonucleotide probe), relative to the total SSU rRNA (measured with a universal probe). Differences in hybridization signals could be related to specific probe target locations and rRNA denaturation conditions, suggesting that higher order structure is important in quantitative membrane hybridizations. Therefore, in vitro-transcribed rRNA cannot always be used for the absolute quantification of microbial populations, but can be employed as a standard to quantify shifts in population abundance over time, and to compare community structure in various environments.