A subcortical, pigment-containing structure in Xenopus eggs with contractile properties

An accumulation of insoluble, finely granular material has been observed under the pigmented surface of Xenopus eggs by a specialized "dry fracture" technique and scanning electron microscopy. Cortical granules and pigment granules can be recognized with the techniques and can be seen to be embedded in the material. Thin sections show that the region also contains mitochondria and membranous vesicles or reticula. Yolk platelets are largely excluded from the heaviest accumulations of the material. The substance is most dense just under the cortex and grades off gradually into the more diffuse, yolk-containing network of the endoplasm. The accumulation of material is much thicker in the animal hemisphere of the egg than in the vegetal hemisphere, and the pigment embedded in it defines the pigmented area of the animal hemisphere. In the pigmented area the material excludes yolk for a thickness of 3-7+ microns from the surface. In the vegetal hemisphere there is no such accumulation and yolk platelets can be found almost touching the plasmalemma. Cortical contractions have been experimentally induced in eggs. Their relative strength correlates with the relative thickness of the finely granular, subcortical material. During contraction the material accumulates to much greater thicknesses, excluding yolk from thicknesses of 15-30+ microns from the surface. The contracting entity is, or is in, the finely granular material. Injection of cytochalasins into the eggs inhibits cleavage furrow operation but does not inhibit the induced cortical contractions. The thus do not seem to be dependent on actin microfilamentogenesis as is the operation of the contractile ring of the cleavage furrow. The differential sensitivity to cytochalasins of the contractile ring and the system responding in the induced cortical contractions, suggests a two-component system for cortical contractions in the egg. A model is presented which accommodates the available data.     

Antimicrobial activity of synthetic bactenecin

Bactenecin is an antimicrobial peptide isolated from bovine neutrophils. Bactenecin was synthesized by solid-phase peptide synthesis and renatured to a fully disulfide bonded form. The peptide inhibits the growth of Escherichia coli and Staphylococcus aureus at the same concentration reported for the peptide purified from bovine neutrophils. Bactenecin inhibits the growth of other medically important bacteria and yeast, and it kills the fungus Trichophyton rubrum. Acetylation and amidation of the amino- and carboxy-termini of bactenecin do not change its potency, while replacement of its two cysteine residues with serine decreases the potency.     

Are dicentric anaphase bridges formed by somatic recombination in X chromosome inversion heterozygotes of Drosophila melanogaster?

Summary Mitotic recombination has been induced with X-rays in Drosophila melanogaster larvae and assayed later as twin mosaic spots on the adult tergites. With the use of the In(1)sc ^4L sc ^8R chromosome which lacks the nucleolar organizer and is marked with yellow (y) indirect evidence was obtained that mitotic recombination between ring and rod chromosomes results, in a majority of cases, in XO spots, bearing the rod-X only. This was concluded from the relative scarcity and small sizes of y NO^- spots (uncovering the sc ⁴ sc ⁸ chromosome), compared to control sisters bearing an extra Y chromosome with its NO locus. Thus, dicentric chromatid bridges formed by mitotic recombination between the ring and rod chromosomes are probably eliminated at the next division.In In(1)sc ⁴ sc ⁸/f^36a (rod/rod) females, no effect of the Y chromosome on the frequency and sizes of cross-over spots was observed. Either any dicentric chromatid bridges formed by recombination between inverted rod chromosomes fragment at division, with a centromeric piece going to each pole, or such bridges are not usually formed by recombination. The latter case would indicate that somatic pairing of homologues is not accurate in X chromosome inversion heterozygotes and consequently, that recombination yields aneuploid cells.Additional studies are cited which indicate that X chromosome heterozygotes for entire arm inversions may not pair in the typical loop at the time of mitotic recombination.Supported in part by U.S.P.H.S. Grant GM 17096 to J.R.M., and the Kredit zur Förderung des akademischen Nachwuchses an der Universität Zürich to R.N.     

Landscape dynamics in Farmland

Farm landscapes are a product and a part of human culture. They also are functioning ecological systems. Landscape ecologists are interested in synthesizing a holistic view of this common environment. In this review the dynamic nature of the farm landscape is introduced through examples of small mammal populations, distribution and abundance of birds, ecological effects of matter moving to and from organisms and the forces of human intellectual activities such as politics and economics. This wide range of topics over which landscape ecology attempts its synthesis produces some conceptual and technical problems which are characteristic of this new field. Prominent among them are questions of heterogeneity and scale in both space and time.     

Accelerated heavy particles and the lens. VI. RBE studies at low doses

We report on the prevalence, hazard, and relative biological effectiveness (RBE) for various stages of lens opacification in rats induced by very low doses of fast argon ions of LET 88 keV/microns, compared to those for X rays. Doses of argon ions from 0.01 to 0.25 Gy were used and RBEs of these ions relative to X rays estimated using a nonparametric technique. At the end of the follow-up period, which encompasses a significant fraction of the animals' lifetime, 90% confidence intervals for the RBE of the argon ions relative to X rays were 4-8 at 0.25 Gy, 10-40 at 0.05 Gy, and 50-100 at 0.01 Gy. Our results are consistent with the point-estimate neutron RBEs in Japanese A-bomb survivors, though broad confidence bounds are present in the Japanese results. If a reasonable extrapolation to higher doses is used, our results are also consistent with data reported earlier at higher doses for argon-ion cataractogenesis in rats, mice, and rabbits. We conclude from these results that at very low doses the RBE for cataractogenesis from HZE particles in space is considerably more than 20, and use of a quality factor of at least 50 would be prudent.     

In vitro activity of 11 antibiotics against 74 anaerobes isolated from pediatric intra-abdominal infections

The in vitro activity of 11 antimicrobials was tested against 74 recent anaerobic isolates obtained from pretreatment cultures in pediatric patients with complicated intra-abdominal infections using the CLSI M11-A-6 agar dilution method. Carbapenems, beta-lactamase inhibitor combinations and metronidazole retained good activity, while all Bacteroides fragilis group species produced beta-lactamase and were penicillin resistant and 43% were either intermediately susceptible or resistant to clindamycin. Cefoxitin had moderate activity against B. fragilis but poor activity against Bacteroides thetaiotaomicron and other B. fragilis group isolates.     

Litterfall in two Canadian deciduous woods: quality, quantity and timing

Litterfall in two deciduous woods in Ontario, Canada, was caught in bag traps and by new screen traps for two years. The beech-maple wood produced 818 g m⁻² (8.2 t ha⁻¹) and the poplar wood produced only 450 g m⁻² (4.5 t ha⁻¹). Of these totals, canopy leaves alone made up 386 g m⁻² for the beech-maple wood and 270 g m⁻² for the poplar wood leaving 47% and 34%, espectively, for other litter components. Data are presented for seven types of litter in addition to canopy leaves.
Redistribution of litter on the ground causes spatial heterogeneity of substrate and of habitats for decomposers and hence of decomposition.
Temporal distributions of various types of litterfall differ between the two woods in relation to their vegetation structure. The diversity of litter types combines with extensive temporal distribution of litterfall in the beech-maple woodland to give that wood the potential for nearly continuous decomposition activity. In contrast, the poplar woodland has low diversity of litter and short duration of litterfall.     

Deficiency Analysis of the Tip of Chromosome 3R in DROSOPHILA MELANOGASTER

Region 98EF-100F in chromosome 3 is interesting for genetic analysis because it contains a number of genes of developmental importance. Although there are no preexisting simple deficiency stocks, this region is amenable to genetic manipulation using other types of rearrangements. In the present investigation we obtained deficiencies by combining the terminal deficiencies formed by segregation of Y;3 translocations with a series of duplications of the tip of 3R, both from Y;3 translocations with different breakpoints and from 3;1 duplications in which the 3R tip is carried as a second arm on the X chromosome. Analysis of such synthetic deficiencies reveals five haplo-abnormal loci in the 98A-100F interval. These include a haplolethal site, a newly described Minute and three previously reported Minute mutations. The newly discovered Minute has been designated M(3)99D and is localized cytologically to bands 99D1-9. The three previously reported Minute loci in the region have been localized more precisely: M(3)1 to bands 99B5-9, M(3)f to bands 99E4-F1 and M(3)g to region 100C-F. In addition, we have been able to obtain synthetic deficiencies uncovering all of the intervals from 99B5 to 100B. These deficiencies will be useful for future genetic and molecular analyses of the genes that map within the right tip of chromosome 3.