Normal development of the skeleton in chick limb buds devoid of dorsal ectoderm

It has been suggested that the ectoderm on the dorsal and ventral faces of the limb bud plays a part in controlling the pattern of cartilage differentiation. To test this, the dorsal wing bud ectoderm in the chick embryo was destroyed by irradiation with ultraviolet light at stage 17-19, at the very beginning of limb bud development, but the apical ectodermal ridge was spared. The irradiated ectoderm disappeared within 24 hr (by stage 23-24) and did not regenerate thereafter; thus the dorsal surface of the limb bud was kept denuded throughout most of the period of skeletal pattern formation. By 6 or 7 days after the irradiation (stage 35), when the rudiments of all the adult skeletal elements are normally present in recognizable form, the irradiated wings could be placed into two categories, those that were approximately normal in shape and those that had curled dorsally. All of these limbs were reduced in size, to varying degrees, when compared to their controls and lacked dorsal soft tissues. The limbs that were normal in shape, however, even though sometimes denuded over practically the whole extent of their dorsal surface, almost always had a complete and normally proportioned cartilage pattern, suggesting that ectoderm (other than the apical ectodermal ridge) does not exert any direct control over the development of the limb cartilage pattern. However, many of those limbs that had curled as a result of the irradiation did have major pattern deformities, suggesting that the topology of cartilage differentiation does depend on the shape of the limb bud.     

Secondary succession impairment in restored mangroves

In this work it was hypothesized that secondary succession on sites that have been managed by single planting of mangrove species is compromised by residual stressors, which could reduce the ecosystem??s structural development and lower its functions. Forest structure and environmental characteristics of three planted mangrove stands are compared with reference sites. Structural attributes showed significant differences in the comparison of planted and reference stands. Avicennia schaueriana was the dominant species within both natural regeneration and old-growth stands in terms of basal area (99.2 and 99.4?%, 69.6 and 84.5?%, and 59.0 and 87.1?% for Itacorubi, Saco Grande, and Ratones, respectively). Restoration stands were dominated by Laguncularia racemosa (80.6 and 94.2?% for Saco Grande and Ratones, respectively), except at one site (Itacorubi), where A. schaueriana prevailed (99.7?%). Even though restoration and regeneration stands at Itacorubi showed similar species composition and dominance, cohort sorting revealed an inferior regeneration potential in the restoration stand. Multiple correlation analysis indicated that variables related to elevation disruptions (p _w ?=?0.521) were the environmental drivers responsible for the differences observed in forest structure. At restoration sites an impaired pattern of secondary succession was observed, indicating that single species plantings may be ineffective if characteristics of the site, as well as of the area surrounding it, are not considered. The inadequate management of restoration sites can therefore have implications for both immediate and long-term large-scale ecosystem services.     

The new higher level classification of eukaryotes with emphasis on the taxonomy of protists

This revision of the classification of unicellular eukaryotes updates that of Levine et al. (1980) for the protozoa and expands it to include other protists. Whereas the previous revision was primarily to incorporate the results of ultrastructural studies, this revision incorporates results from both ultrastructural research since 1980 and molecular phylogenetic studies. We propose a scheme that is based on nameless ranked systematics. The vocabulary of the taxonomy is updated, particularly to clarify the naming of groups that have been repositioned. We recognize six clusters of eukaryotes that may represent the basic groupings similar to traditional "kingdoms." The multicellular lineages emerged from within monophyletic protist lineages: animals and fungi from Opisthokonta, plants from Archaeplastida, and brown algae from Stramenopiles.     

Seismic signal transmission between burrows of the Cape mole-rat,Georychus capensis

Summary Both seismic and auditory signals were tested for their propagation characteristics in a field study of the Cape mole-rat (Georychus capensis), a subterranean rodent in the family Bathyergidae. This solitary animal is entirely fossorial and apparently communicates with its conspecifics by alternately drumming its hind legs on the burrow floor. Signal production in this species is sexually dimorphic, and mate attraction is likely mediated primarily by seismic signalling between individuals in neighboring burrows. Measurements within, and at various distances away from, natural burrows suggest that seismic signals propagate at least an order of magnitude better than auditory signals. Moreover, using a mechanical thumper which could be triggered from a tape recording of the mole-rat's seismic signals, we established that the vertically-polarized surface wave (Rayleigh wave) propagates with less attenuation than either of the two horizontally-polarized waves. Thus, we tentatively hypothesize that Rayleigh waves subserve intraspecific communication in this species.Abbreviations PPM pulses per min - SB simulated burrow - SD standard deviation - SPL sound pressure level     

Babesia major: protection of intact calves against homologous challenge by the injection of irradiated piroplasms.

Blood from a splenectomized calf infected with Babesia major was divided into 20 ml aliquots which were γ-irradiated at doses of 0, 23.3, 27.3, 31.4, 35.4 and 39.5 krad and then inoculated into groups of three intact calves. Animals receiving non-irradiated blood had typical mild B. major reactions, but those receiving blood irradiated at 23.3, 27.3 and 31.4 krad and 2 of 3 receiving blood irradiated at 35.4 krad had minimal reactions. The remaining 4 animals had no detectable parasitaemic reactions. When the calves were challenged with a similar number (6.0 × 10⁹) of homologous parasites, they were all immune with the exception of the 4 animals which had not reacted initially. The immune status of individual cattle was reflected accurately in the results of the micro-ELISA test, which detected a significant rise in serum antibody titre of the 4 susceptible animals 7 days after challenge.     

THE THEORY OF DIFFUSION IN CELL MODELS

The differential equations which describe the simultaneous diffusion of water and a salt in a cell model have been formulated and solved. The equations have been derived from the general laws which describe diffusion processes, thereby furnishing a physical interpretation for the constants which enter into the theory. The theoretical time curves for the two diffusing substances are in good agreement with the experimentally determined curves and accurately reproduce all of the essential characteristics of the experiment.     

Gene doctoring: a method for recombineering in laboratory and pathogenic Escherichia coli strains

Background  

Homologous recombination mediated by the λ-Red genes is a common method for making chromosomal modifications in Escherichia coli. Several protocols have been developed that differ in the mechanisms by which DNA, carrying regions homologous to the chromosome, are delivered into the cell. A common technique is to electroporate linear DNA fragments into cells. Alternatively, DNA fragments are generated in vivo by digestion of a donor plasmid with a nuclease that does not cleave the host genome. In both cases the λ-Red gene products recombine homologous regions carried on the linear DNA fragments with the chromosome. We have successfully used both techniques to generate chromosomal mutations in E. coli K-12 strains. However, we have had limited success with these λ-Red based recombination techniques in pathogenic E. coli strains, which has led us to develop an enhanced protocol for recombineering in such strains.     

Active versus passive anti-cytokine antibody therapy against cytokine-associated chronic diseases

Current therapeutic vaccine trials in major chronic diseases including AIDS, cancer, allergy and autoimmunity, target antigenic pathogens but not the pathogenic stromal cytokines which can be major sources of histopathologic processes. Considering that the limited efficacy of these vaccines has been ascribed to local pathogen-induced cytokine dysfunction, we propose to antagonize pathogenic cytokine(s) by high affinity neutralizing auto-Abs triggered by specific anti-cytokine vaccines. As anticipated by theoretical considerations, animal experiments and initial clinical trials showed that anti-cytokine immunization was safe, well tolerated and triggered transient high titers Abs neutralizing pathogenic cytokines but, in contrast to conventional vaccines, no relevant cellular response was observed. Advantages of active versus passive anti-cytokine Ab therapy, particularly for long-term treatments, as those required in AIDS, cancer, allergy and autoimmunity include greater ease of maintaining high Ab titers, lack of anti-antibody responses and low cost.