Analysis of cellular components in immunocompetent organs treated with ionizing radiations]

The nucleic acid and protein content has been evaluated in lymphoid cells from the thymus and the Bursa of Fabricius of chicks exposed to different doses of radiation. A different response to radiation damage of the two cell populations is suggested by these analysis when compared with ultrastructural data.     

Hinf I restriction endonuclease digestion on human fixed metaphase chromosomes

The authors report on the activity of Hinf I restriction endonuclease on human fixed metaphase chromosomes. Experiments performed by digesting chromosomes just after harvesting or after ageing in methanol-acetic acid displayed a different pattern of digestion on metaphases, since only aged preparations showed gaps on heterochromatic regions of chromosomes 1, 9 and 16 and C-like bands on other chromosomes. In this view, the authors suggest that structural modifications of the DNA, induced by acid fixation, can influence Hinf I activity on fixed metaphase chromosomes.     

Variants of Myxococcus virescens Exhibiting Dispersed Growth. Growth and Production of Extracellular Enzymes and Slime

The growth of two strains of Myxococcus virescens exhibiting dispersed growth was followed in casamino acids (N III-C) media and casitone media. The changes in optical density, pH, pigmentation as well as the secretion of bacteriolytic and proteolytic enzymes, DNA and polysaccharides during growth were recorded. In both media the bacteria grew exponentially with a generation time of 4 (casitone) and 20 hours (N III-C) respectively. The maximal cell mass was about 4 times higher in casitone than in casamino acids media. The amounts of bacteriolytic enzymes produced by the two strains in N III-C medium were different but in casitone medium they were about equal and considerably higher. The maximal values of proteolytic enzymes were about the same in both media and always occurred later than the bacteriolytic maxima. Both activity peaks appeared before the phase of decline. The polysaccharide production reached a maximum during the stationary growth phase in both media. A higher value was reached during growth in casitone medium than in N III-C medium. During the phase of decline a second increase of polysaccharide in the medium appeared. No DNA could be detected in the cell-free solutions until the beginning of the phase of decline.     

The development of normal and ectopic sensilla in the wings of hairy and Hairy wing mutants of Drosophila.

We have utilized enhancer trap markers to follow the development of ectopic sensillar precursors in the wings of Drosophila induced by the mutations hairy and Hairy wing. Normal sensilla are still present in these mutations, and can be distinguished from ectopic sensilla based upon both the position and the timing of their development. This correlates well with the development of ectopic achaete expression in these mutations: such staining is detected only after the appearance of normal staining. Thus, neither mutation appears to alter the specification of proneural clusters in the wing, as identified with anti-achaete, or the specification of sensillar precursors within these clusters. Rather, both act to induce the formation of a temporally and spatially distinct phase of sensillar development.     

The polarity of axon growth in the wings of Drosophila melanogaster

We have analyzed the growth of axons in the wings of the mutants Hairy wing and hairy of Drosophila melanogaster. These mutants produce many supernumerary bristle organs and sensilla campaniformia, whose axons grow between the two wing epithelia and can be visualized in both pupal and adult stages. The sensory axons of wild-type animals follow two paths in the wing, within longitudinal veins L1 and L3, and always grow with a distal to proximal polarity. In the mutants, all axons following these two paths likewise grow with correct polarity. Axons elsewhere in the wing, however, are found to grow in many different directions, including from proximal to distal and hence directly away from the central nervous system. A variety of patterns of axon growth and fasciculation are seen in different individuals. Only if the supernumerary axons encounter the two normal paths do they reliably grow toward the base of the wing. We conclude that these two paths provide polarity information for axon growth, information which is either not used or not available elsewhere in the wing in spite of the obvious morphological polarization of every epithelial cell. The time course of neural differentiation suggests that the normal sensory cells of mutant wings, which grow axons relatively early, may be the source of polarity information for the later-differentiating supernumerary cells.