A new method of in situ hybridization

A new method for gene mapping at the chromosome level using in situ hybridization and scanning electron microscopy is described and has been applied to mapping the rRNA genes of Drosophila melanogaster. Biotin is covalently attached to Drosophila rRNA via a cytochrome c bridge at a ratio of one cytochrome-biotin per 130 nucleotides by a chemical procedure. Polymethacrylate spheres with a diameter of ca. 60 nm are prepared by emulsion polymerization and are covalently attached to the protein avidin at a ratio of 5–20 avidins per sphere. The biotin-labeled rRNA is hybridized to denatured DNA in a chromosome squash. Upon incubation with a sphere solution, some of the biotin sites become labeled with spheres because of the strong non-covalent interaction between biotin and avidin. The chromosome squash is examined in the scanning electron microscope (SEM). Polymer spheres, which are visible in the SEM, are observed to label the nucleolus, where the rRNA genes are located.Contribution number 5121 from the Department of Chemistry.     

Studies on the mechanism of action of calciferol VII. Localization of 1,25-dihydroxy-vitamin D3 in chick parathyroid glands.

When 1,25(OH)₂-vitamin D₃ was administered to vitamin D-deficient chicks, within two hours the parathyroid glands were observed to accumulate this steroid to a concentration four times that present in the blood and equivalent to levels observed in the target intestine. Similarly, when 25-(OH)-vitamin D₃ was administered, the parathyroid glands had 2.4 times the concentration of the metabolite, 1,25-(OH)₂-vitamin D₃ as that seen in the blood and 60% of that found in the intestine. These results are consistent with the concept that the hormonally active form of vitamin D, 1,25-(OH)₂-vitamin D₃, may interact with the parathyroid glands to effect changes in parathyroid hormone secretion.     

Productivity and organic consumption in Cassiopea and Condylactus

Oxygen production and consumption was determined for Cassiopea and Condylactus containing symbiotic algae (zooxanthellae). 88 % of both animals produce more organic material than they consumed during a 12-h light period.It is suggested that zooxanthellae contribute a significant nutritional supplementation and a greater ecological efficiency to the host animals.     

Carbon dioxide output and mating in adult cabbage looper moths exposed to discrete light régimes

Carbon dioxide discharge and the number of spermatophores transferred were recorded from populations of adult cabbage loopers, Trichoplusia ni, maintained under various wavelengths and intensities of light. Nocturnal CO₂ output was enhanced by retaining 1 per cent of the diurnal intensity of near-u.v. and blue lights during the scotophase. However, addition of < 10 per cent of the diurnal intensities of u.v., blue, and white lights suppressed CO₂ production. Exposure to gold light resulted in the lowest 24 hr CO₂ accumulations, and red was intermediate. Similarly, maximum levels of mating occurred when cabbage loopers were exposed to nocturnal intensities of 1 per cent of the diurnal u.v., blue, or white lights, even though higher intensities were inhibitory. Considering all nocturnal intensities ranging from 0 to 100 per cent of diurnal levels, u.v. and red yielded the highest mating frequencies, blue and gold were intermediate, and white was lowest. Thus, relatively unique action spectra resulted from each régime.     

Chlamydomonas raudensis (UWO 241), Chlorophyceae,exhibits the capacity for rapid D1 repair in response to chronic photoinhibition at low temperature1

Maximum photosynthetic capacity indicates that the Antarctic psychrophile Chlamydomonas raudensis H. Ettl UWO 241 is photosynthetically adapted to low temperature. Despite this finding, C. raudensis UWO 241 exhibited greater sensitivity to low‐temperature photoinhibition of PSII than the mesophile Chlamydomonas reinhardtii P. A. Dang. However, in contrast with results for C. reinhardtii, the quantum requirement to induce 50% photoinhibition of PSII in C. raudensis UWO 241 (50 μmol photons) was comparable at either 8°C or 29°C. To our knowledge, this is the first report of a photoautotroph whose susceptibility to photoinhibition is temperature independent. In contrast, the capacity of the psychrophile to recover from photoinhibition of PSII was sensitive to temperature and inhibited at 29°C. The maximum rate of recovery from photoinhibition of the psychrophile at 8°C was comparable to the maximum rate of recovery of the mesophile at 29°C. We provide evidence that photoinhibition in C. raudensis UWO 241 is chronic rather than dynamic. The photoinhibition‐induced decrease in the D1 content in C. raudensis recovered within 30 min at 8°C. Both the recovery of the D1 content as well as the initial fast phase of the recovery of F_v/F_m at 8°C were inhibited by lincomycin, a chloroplast protein synthesis inhibitor. We conclude that the susceptibility of C. raudensis UWO 241 to low‐temperature photoinhibition reflects its adaptation to low growth irradiance, whereas the unusually rapid rate of recovery at low temperature exhibited by this psychrophile is due to a novel D1 repair cycle that is adapted to and is maximally operative at low temperature.     

Controlling tick-borne diseases through domestic animal management: a theoretical approach

Vector-borne diseases are of global importance to human and animal health. Empirical trials of effective methods to control vectors and their pathogens can be difficult for practical, financial and ethical reasons. Here, therefore, we use a mathematical model to predict the effectiveness of a vector-borne disease control method. As a case study, we use the tick-louping ill virus system, where sheep are treated with acaricide in an attempt to control ticks and disease in red grouse , an economically important game bird. We ran the model under different scenarios of sheep flock sizes, alternative host (deer) densities, acaricide efficacies and tick burdens. The model predicted that, with very low deer densities, using sheep as tick mops can reduce the tick population and virus prevalence. However, treatment is ineffective above a certain threshold deer density, dependent on the comparative tick burden on sheep and deer. The model also predicted that high efficacy levels of acaricide must be maintained for effective tick control. This study suggests that benignly managing one host species to protect another host species from a vector and pathogen can be effective under certain conditions. It also highlights the importance of understanding the ecological complexity of a system, in order to target control methods only under certain circumstances for maximum effectiveness.