Hierarchies of DNA repair in mammalian cells: biological consequences

Mammalian cells exposed to genotoxic agents exhibit heterogeneous levels of repair of certain types of DNA damage in various genomic regions. For UV-induced cyclobutane pyrimidine dimers we propose that at least three levels of repair exist: (1) slow repair of inactive (X-chromosomal) genes, (2) fast repair of active housekeeping genes, and (3) accelerated repair of the transcribed strand of active genes. These hierarchies of repair may be related to chromosomal banding patterns as obtained by Giemsa staining. The possible consequences of defective DNA repair in one or more of these levels may be manifested in different clinical features associated with UV-sensitive human syndromes. Moreover, molecular analysis of hprt mutations reveals that mutations are primarily generated by DNA damage in the poorly repaired non-transcribed strand of the gene.     

Photoresponses of transgenic tobacco plants expressing an oat phytochrome gene

The physiological responses of transgenic tobacco (Nicotiana tabacum L.) plants that express high levels of an introduced oat (Avena sativa L.) phytochrome (phyA) gene to various light treatments are compared with those of wild-type (WT) plants. Seeds, etiolated seedlings, and light-grown plants from a homozygous transgenic tobacco line (9A4) constructed by Keller et al. (EMBO J, 8, 1005–1012, 1989) were treated with red (R), far-red (FR), or white light (WL) with or without supplemental FR light, revealing major perturbations of the normal photobiological responses. White light stimulated germination of both WT and transgenic seed, but addition of FR to the WL treatment suppressed germination. In the WT, all fluence rates tested inhibited germination, but in the transgenics, reduction effluence rate partially relieved germination from the FR-mediated inhibition. It is suggested that the higher absolute levels of the FR-absorbing form of phytochrome (Pfr) in the irradiated transgenics, compared to the WT, may be responsible for the reduced FR-mediated inhibition of germination in the former. Hypocotyl extension of dark-grown seedlings of both WT and transgenic lines was inhibited by continuous R or FR irradiation, typical of the high-irradiance response (HIR). After 2 d of de-etiolation in WL, the WT seedlings had lost the FR-mediated inhibition of hypocotyl extension, whereas it was retained in the transgenics. The FR-mediated inhibition of hypocotyl extension in the transgenic seedlings after de-etiolation may reflect the persistence of an, FR-HIR response mediated by the overexpressed oat PhyA phytochrome. Light-grown WT seedlings exhibited typical shade-avoidance responses when treated with WL supplemented with high levels of FR radiation. Internode and petiole extension rates were markedly increased, and the chlorophyll ab ratio decreased, in the low-R: FR treatment. The transgenics, however, showed no increases in extension growth under low-R: FR treatments, and at low fluence rates both internode and petiole extension rates were significantly decreased by low R FR. Interpretation of these data is difficult. The depression of the chlorophyll ab ratio by low R FR was identical in WT and transgenic plants, indicating that not all shade-avoidance responses of light-grown plants were disrupted by the over-expression of the introduced oat phyA gene. The results are discussed in relation to the proposal that different members of the phytochrome family may have different physiological roles.Abbreviations FR far-red light - PAR photosynthetically active radiation - Pr, Pfr red- and FR-absorbing forms of phytochrome - Ptot total phytochrome - PhyA (PhyA) gene (encoded protein) for phytochrome - R red light - WL white light - WT wild type This work was supported by an Agricultural and Food Research Council research grant to H.S. and A.C.M.; the production of the transgenic seed was funded by the U.S. Department of Energy (DE-F602-88ER13968) to R.D.V., and by E.I. du Pont de Nemours; Dr. G.C. Whitelam is thanked for the provision of monoclonal antibodies for the immunoblot analyses.     

Home range size and activity of the wood lemming, Myopus schisticolor

We present the results from a radiotelemetric study on space use and activity in a natural population of the wood lemming Myopus schisticolor. Male home ranges were larger than females, and the ratio female home range to male home range was smaller than expected compared to other small rodents. Males moved distances 4-12 times longer than females. We argue that this difference in mobility gives a higher probability of capturing males than females in snap trap studies. If there is a sex biased trappability, this might explain the increasing female biased sex ratio during the snow free season (1:1 in spring, 3:1 [female:male| in autumn), as a higher mortality of males during the reproductive season.     

Plant cmolecular biology manual

Book Review

Plant cmolecular biology manualS.B. Galvin, R.A. Schilperoort and D.P.S. Verma (Eds.), Dordrecht, The Netherlands: Kluwer Academic Publishers, 1989. £52.00. ISBN 0-7923-0236-2     

Cell sorting within the prestalk zone of Dictyostelium discoideum

Abstract. The prestalk zone of slugs of Dictyostelium discoideum has been shown to contain three subregions in which the extracellular matrix genes ecmA and ecmB are differentially expressed; it is generally thought that these regions are defined by extracellular signals. Using β-galactosidase as a cell marker, we have shown that cells can sort specifically to all three regions. Cells from the posterior-prestalk zone ("prestalk 0 zone") which are injected into the slug tip move within 60 min back to their position of origin. When cells from the anterior prestalk zone (presumably containing a mixture of ecmA and ecmB expressers) are transplanted to the posterior prestalk zone, they move to the tip ("prestalk A zone") within 1 h and about 30 min subsequently are often found in a cone-shaped region within the tip ("prestalk B zone"). Cells transplanted to their own positions do not move significantly within this period. Since the sub-regions of the prestalk zone can be defined by sorting, it is possible that they are normally formed in this way rather than by position-dependent signals. Cells transplanted without a change in anterior-posterior position and cells which have sorted back to their positions of origin eventually spread out throughout the prestalk zone. This suggests that sorting preferences of cells are respecified. When posterior prestalk cells are transplanted to the prespore zone, respecification of sorting preference is suspended until the cells return to the prestalk zone and anterior-prestalk cells acquire posterior-prestalk sorting preferences.     

Context-dependent changes in the perception of odor quality

Ambiguous odor compounds, partly citrus-like and partly woodyin odor character, were seen to change in odor quality whenevaluated in the same session as more prototypical odors. Whentested with characteristically citrus odors, the ambiguous compoundsseemed more woody, and when tested with characteristically woodyodors, the ambiguous odorants were higher in citrus character,an example of perceptual contrast. Response frequency biaseswere ruled out as an explanation for this shift by an experimentin which responses other than citrus and woody ratings wereasked of the subjects during the contextual exposure. Simplesensory adaptation was found to be a potential contributor tothe effect, and a sufficient condition to produce similar shiftsin odor quality. However, adaptation was not a necessary conditionto produce the effect. This was seen in reversed pair experimentsin which the contextual odors were presented after the ambiguousstimuli. The contextual shift was robust—it was obtainedwith different ambiguous odors, contextual (conditioning) odors,numbers of contextual odors, orders of presentation of contextualodors relative to ambiguous odors, scale types, and rating tasksduring the presentation of contextual odors.     

Long-term effects of biofeedback-induced facial relaxation on measures of asthma severity in children

We studied the effects of electromyographic biofeedback on measures of asthma severity in children. Fifteen children received biofeedback training to reduce facial tension, and 14 children, who served as controls, received biofeedback training to maintain facial tension at a stable level. Assignment to experimental condition was random. As a result of training, electromyographic levels decreased in children trained in facial relaxation and remained fairly constant in children trained in facial tension stability. Biofeedback training was augmented for children in both groups by having them practice their facial exercises at home. Each child's condition was followed for a five-month period subsequent to biofeedback training. Throughout the experiment, the following measures of asthma severity were monitored: lung function, self-rated asthma severity, medication usage, and frequency of asthma attacks. In addition, standardized measures of attitudes toward asthma, self-concept, and chronic anxiety were recorded at regular intervals. As compared to the facial stability subjects, the facial relaxation subjects exhibited higher pulmonary scores, more positive attitudes toward asthma, and lower chronic anxiety during the followup period. Subjects in the two groups, however, did not differ on self-rated asthma severity, medication usage, frequency of asthma attacks, or self-concept. Based on the improvements we observed in pulmonary, attitude, and anxiety measures, we concluded that biofeedback training for facial relaxation contributes to the self-control of asthma and would be a valuable addition to asthma self-management programs.This research was supported by NIH grant No. HL27402. We are grateful to Anita D. Baker, Lisa Barclay, Deborah L. Harm, and Douglas J. Miller for serving as experimenters and to Constance K. Cottrell and Cindy Stout for compiling summaries of the data.     

Low Prevalence of Hepatitis B Infections Among Residents of an Institution for the Mentally Retarded in New Mexico

Residential institutions for the mentally retarded are considered high-risk settings for hepatitis B (HB) infection. Accordingly, HB vaccine is recommended for susceptible clients and selected staff of such facilities. However, a serologic screening program among 364 residents of Los Lunas Hospital and Training School (LLHTS) in New Mexico found only 11 residents to be anti-HBc positive (3%) and only one of these residents was also HBsAg-positive (0.3%). The unexpectedly low prevalence of HB infections at LLHTS probably reflects infrequent HB introductions into the institution. Using these serologic data, a vaccination program was instituted to prevent HB infection among LLHTS residents, thereby eliminating the need for mass screening and HB vaccination of LLHTS employees. Serologic screening among residents of other smaller institutions for the mentally retarded is recommended before design of HB prevention programs for clients and staff.     

Thermal denaturation of mononucleosomes in the presence of spermine,spermidine, N1-acetylspermidine,N8-acetylspermidine or putrescine: implications for chromosome structure

Putrescine (a diamine) raises the thermal denaturation temperature of mononucleosomes but produces only minor changes in the overall shape of the thermal denaturation curve. This is similar to the effect of sodium ions and is consistent with nonspecific binding to the DNA of the nucleosome. At very low levels of spermidine or spermine the same simple rise in thermal denaturation temperature is seen but at higher levels (above 1 M for total spermidine concentration) the thermal denaturation curve becomes substantially sharper and the premelt region of the curve diminishes in area. The acetylspermidines display intermediate effects. The change in shape of the thermal denaturation curve was resolved into components (R1 and R2) due to mononucleosomes in their original conformation plus a component (T) induced by the presence of spermidine or spermine. The proportion of component T was substantially reduced with acetylspermidine, compared to equivalent concentrations of spermidine. Hence, we suggest that spermidine acetylationin vivo has the potential to partially destabilise the nucleosome structure, possibly in coordination with histone acetylation.     

Factors affecting adventitious bud induction in Pinus elliottii (Engelm.) embryos cultured in vitro

Embryos of slash pine (Pinus elliottii Engelm.) were induced to form adventitious buds when placed in culture on nutrient media supplemented with cytokinin. Buds were induced on media containing Risser & White major salts. The high content in nitrogen of Murashige & Skoog formulation seems to be deleterious for this in vitro system, since morphogenic responses were only promoted when nitrogen concentration was drastically reduced in the macronutrient formulation. Factors such as concentration of cytokinin (6-benzyladenine) and time and method of exposure (liquid or solid induction medium) strongly influenced bud formation and development. The greatest number of buds and shoots were obtained from 22.0 M cytokinin, but these shoots showed less and slower development than those induced with low dosages of cytokinin. The presence of naphthaleneacetic acid in combination with cytokinin in the induction medium decreased the frequency of bud formation.Abbreviations (BA) 6-benzyladenine - (NAA) 1-naphthaleneacetic acid