Biomedical subjects

Anthony Hall

Publications and source records attributed to Anthony Hall.

13 recordsLinked to original sources

PubMed2006

Circadian control of isoprene emissions from oil palm (Elaeis guineensis).

The emission of isoprene from the biosphere to the atmosphere has a profound effect on the Earth's atmospheric system. Until now, it has been assumed that the primary short-term controls on isoprene emission are photosynthetically active radiation and temperature. Here we show that isoprene emissions from a tropical tree (oil palm, Elaeis guineensis) are under strong circadian control, and that the circadian clock is potentially able to gate light-induced isoprene emissions. These rhythms are robustly temperature compensated with isoprene emissions still under circadian control at 38 degrees C. This is well beyond the acknowledged temperature range of all previously described circadian phenomena in plants. Furthermore, rhythmic expression of LHY/CCA1, a genetic component of the central clock in Arabidopsis thaliana, is still maintained at these elevated temperatures in oil palm. Maintenance of the CCA1/LHY-TOC1 molecular oscillator at these temperatures in oil palm allows for the possibility that this system is involved in the control of isoprene emission rhythms. This study contradicts the accepted theory that isoprene emissions are primarily light-induced.

Base Sequence↗

PubMed2006

The molecular basis of temperature compensation in the Arabidopsis circadian clock.

Circadian clocks maintain robust and accurate timing over a broad range of physiological temperatures, a characteristic termed temperature compensation. In Arabidopsis thaliana, ambient temperature affects the rhythmic accumulation of transcripts encoding the clock components TIMING OF CAB EXPRESSION1 (TOC1), GIGANTEA (GI), and the partially redundant genes CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY). The amplitude and peak levels increase for TOC1 and GI RNA rhythms as the temperature increases (from 17 to 27 degrees C), whereas they decrease for LHY. However, as temperatures decrease (from 17 to 12 degrees C), CCA1 and LHY RNA rhythms increase in amplitude and peak expression level. At 27 degrees C, a dynamic balance between GI and LHY allows temperature compensation in wild-type plants, but circadian function is impaired in lhy and gi mutant plants. However, at 12 degrees C, CCA1 has more effect on the buffering mechanism than LHY, as the cca1 and gi mutations impair circadian rhythms more than lhy at the lower temperature. At 17 degrees C, GI is apparently dispensable for free-running circadian rhythms, although partial GI function can affect circadian period. Numerical simulations using the interlocking-loop model show that balancing LHY/CCA1 function against GI and other evening-expressed genes can largely account for temperature compensation in wild-type plants and the temperature-specific phenotypes of gi mutants.

Acclimatization↗

PubMed2006

FLOWERING LOCUS C mediates natural variation in the high-temperature response of the Arabidopsis circadian clock.

Temperature compensation contributes to the accuracy of biological timing by preventing circadian rhythms from running more quickly at high than at low temperatures. We previously identified quantitative trait loci (QTL) with temperature-specific effects on the circadian rhythm of leaf movement, including a QTL linked to the transcription factor FLOWERING LOCUS C (FLC). We have now analyzed FLC alleles in near-isogenic lines and induced mutants to eliminate other candidate genes. We showed that FLC lengthened the circadian period specifically at 27 degrees C, contributing to temperature compensation of the circadian clock. Known upstream regulators of FLC expression in flowering time pathways similarly controlled its circadian effect. We sought to identify downstream targets of FLC regulation in the molecular mechanism of the circadian clock using genome-wide analysis to identify FLC-responsive genes and 3503 transcripts controlled by the circadian clock. A Bayesian clustering method based on Fourier coefficients allowed us to discriminate putative regulatory genes. Among rhythmic FLC-responsive genes, transcripts of the transcription factor LUX ARRHYTHMO (LUX) correlated in peak abundance with the circadian period in flc mutants. Mathematical modeling indicated that the modest change in peak LUX RNA abundance was sufficient to cause the period change due to FLC, providing a molecular target for the crosstalk between flowering time pathways and circadian regulation.

Arabidopsis↗

PubMed2006

Analysis of phase of LUCIFERASE expression reveals novel circadian quantitative trait loci in Arabidopsis.

In response to exogenous rhythms of light and temperature, most organisms exhibit endogenous circadian rhythms (i.e. cycles of behavior and gene expression with a periodicity of approximately 24 h). One of the defining characteristics of the circadian clock is its ability to synchronize (entrain) to an environmental rhythm. Entrainment is arguably the most salient feature of the clock in evolutionary terms. Previous quantitative trait studies of circadian characteristics in Arabidopsis (Arabidopsis thaliana) considered leaf movement under constant (free-running) conditions. This study, however, addressed the important circadian parameter of phase, which reflects the entrained relationship between the clock and the external cycle. Here it is shown that, when exposed to the same photoperiod, Arabidopsis accessions differ dramatically in phase. Variation in the timing of circadian LUCIFERASE expression was used to map loci affecting the entrained phase of the clock in a recombinant population derived from two geographically distant accessions, Landsberg erecta and Cape Verde Islands. Four quantitative trait loci (QTL) were found with major effects on circadian phase. A QTL on chromosome 5 contained SIGNALING IN RED LIGHT REDUCED 1 and PSEUDORESPONSE REGULATOR 3, both genes known to affect the circadian clock. Previously unknown polymorphisms were found in both genes, making them candidates for the effect on phase. Fine mapping of two other QTL highlighted genomic regions not previously identified in any circadian screens, indicating their effects are likely due to genes not hitherto considered part of the circadian system.

Amino Acid Sequence↗

PubMed2006

Forward genetic analysis of the circadian clock separates the multiple functions of ZEITLUPE.

The circadian system of Arabidopsis (Arabidopsis thaliana) includes feedback loops of gene regulation that generate 24-h oscillations. Components of these loops remain to be identified; none of the known components is completely understood, including ZEITLUPE (ZTL), a gene implicated in regulated protein degradation. ztl mutations affect both circadian and developmental responses to red light, possibly through ZTL interaction with PHYTOCHROME B (PHYB). We conducted a large-scale genetic screen that identified additional clock-affecting loci. Other mutants recovered include 11 new ztl alleles encompassing mutations in each of the ZTL protein domains. Each mutation lengthened the circadian period, even in dark-grown seedlings entrained to temperature cycles. A mutation of the LIGHT, OXYGEN, VOLTAGE (LOV)/Period-ARNT-Sim (PAS) domain was unique in retaining wild-type responses to red light both for the circadian period and for control of hypocotyl elongation. This uncoupling of ztl phenotypes indicates that interactions of ZTL protein with multiple factors must be disrupted to generate the full ztl mutant phenotype. Protein interaction assays showed that the ztl mutant phenotypes were not fully explained by impaired interactions with previously described partner proteins Arabidopsis S-phase kinase-related protein 1, TIMING OF CAB EXPRESSION 1, and PHYB. Interaction with PHYB was unaffected by mutation of any ZTL domain. Mutation of the kelch repeat domain affected protein binding at both the LOV/PAS and the F-box domains, indicating that interaction among ZTL domains leads to the strong phenotypes of kelch mutations. Forward genetics continues to provide insight regarding both known and newly discovered components of the circadian system, although current approaches have saturated mutations at some loci.

Alleles↗

PubMed2006

Predictors of poor follow-up in children that had cataract surgery.

BACKGROUND: Centers for high quality cataract surgery for children have been developed in a number of sub-Saharan African countries. Surgery, however, is only the first stage of a long, often complex, rehabilitation program. There are indications that follow-up in these settings is poor. In a setting with a high quality surgical service an active program to identify and manage children with cataract and a newly developed low vision program, we sought to measure routine follow-up and to determine the factors associated with good or poor follow-up. METHODS: This prospective study included all children (under the age of 16 years) having surgery for congenital, developmental, or traumatic cataract at KCMC Hospital between March 2003 and October 2004. Standardized data was collected pre-, intra-, and postoperation. Follow-up was assessed at two weeks and ten weeks. RESULTS: Among the 154 children included 35.1% had congenital cataract, 32.5% had developmental cataract, and 31.8% had traumatic cataract. Overall, 66.9% attended two-week follow-up and 42.9% attended ten-week follow-up. Multivariate analysis revealed that sex (being a boy), close proximity to a hospital, and minimal delay in presentation for surgery all independently predicted good follow-up at two weeks. Only distance from a hospital and preoperative vision (not blind in operative eye) predicted good ten-week follow up. DISCUSSION: Current follow-up practices are inadequate. Significant investment in surgical interventions may not lead to improved visual rehabilitation or quality of life, if investments in follow-up are not increased. Linking individual children, their families, and the hospital needs to be approached systematically, if follow-up is to be improved. Improved hospital-based counseling should focus on families who bring their child late for surgery and with girls.

Cataract↗

PubMed2006

Developing guidelines for syringe driver management.

The aim of this project was to develop clinical practice guidelines for the use and administration of pharmacological agents for symptom control via syringe drivers within Australia. By developing evidence-based clinical practice guidelines for the use of this common device, this project aimed to improve patient outcomes, reduce practice variation, minimize errors and encourage more efficient use of resources. A literature review identified current literature regarding syringe driver management and an expert panel was assembled to assist in the development of the guidelines. The development of these practice guidelines provides an example of how palliative care practitioners can use a framework of contemporary evidence to enhance clinical practice.

Clinical Nursing Research↗

PubMed2006

Luciferases as reporter genes.

Luciferase is the ideal reporter gene to provide temporal and spatial information on promoter activity in Arabidopsis and other eukaryotes; the noninvasive detection of luminescence and short half-life of luciferase activity allow repeated measurements of individual seedlings over several days to assay dynamic changes in gene expression. Transgenic or transiently transformed plants with a luciferase gene under the control of a promoter of interest are required. Detection of the low level of luminescence produced by the luciferase gene in Arabidopsis requires the use of low light detecting charge-coupled device (CCD) cameras or scintillation counters. This chapter contains protocols on assaying and imaging luciferase in vivo and the automation for high-resolution timecourses.

Arabidopsis↗

PubMed2005

Plant circadian clocks increase photosynthesis, growth, survival, and competitive advantage.

Circadian clocks are believed to confer an advantage to plants, but the nature of that advantage has been unknown. We show that a substantial photosynthetic advantage is conferred by correct matching of the circadian clock period with that of the external light-dark cycle. In wild type and in long- and short-circadian period mutants of Arabidopsis thaliana, plants with a clock period matched to the environment contain more chlorophyll, fix more carbon, grow faster, and survive better than plants with circadian periods differing from their environment. This explains why plants gain advantage from circadian control.

Arabidopsis↗

PubMed2004

Changing trends in sympathetic ophthalmia.

Sympathetic ophthalmia is a rare and potentially visually devastating bilateral panuveitis, typically following non-surgical penetrating injury to one eye. Three patients are presented where sympathetic ophthalmia developed after repeated vitreoretinal surgery. Prompt and effective management with systemic immunosuppressive agents permitted control of their disease and retention of good visual acuity in their remaining eye. Vitreoretinal surgery is an important risk factor in sympathetic ophthalmia. Informed consent for vitreoretinal surgery (especially in the re-operation setting) should now include the risk of sympathetic ophthalmia (approximately 1 in 800). Diverse clinical presentations are possible in sympathetic ophthalmia and any bilateral uveitis following vitreoretinal surgery should alert the surgeon to the possibility of sympathetic ophthalmia. Modern immunosuppressive therapy with systemic steroids and steroid-sparing agents such as cyclosporin A and azathioprine have improved the prognosis. This is particularly so in cases where early diagnosis is made and prompt and suitable immunotherapy is commenced.

Aged↗

PubMed2003

The TIME FOR COFFEE gene maintains the amplitude and timing of Arabidopsis circadian clocks.

Plants synchronize developmental and metabolic processes with the earth's 24-h rotation through the integration of circadian rhythms and responses to light. We characterize the time for coffee (tic) mutant that disrupts circadian gating, photoperiodism, and multiple circadian rhythms, with differential effects among rhythms. TIC is distinct in physiological functions and genetic map position from other rhythm mutants and their homologous loci. Detailed rhythm analysis shows that the chlorophyll a/b-binding protein gene expression rhythm requires TIC function in the mid to late subjective night, when human activity may require coffee, in contrast to the function of EARLY-FLOWERING3 (ELF3) in the late day to early night. tic mutants misexpress genes that are thought to be critical for circadian timing, consistent with our functional analysis. Thus, we identify TIC as a regulator of the clock gene circuit. In contrast to tic and elf3 single mutants, tic elf3 double mutants are completely arrhythmic. Even the robust circadian clock of plants cannot function with defects at two different phases.

Arabidopsis↗

PubMed2003

Response regulator homologues have complementary, light-dependent functions in the Arabidopsis circadian clock.

TIMING OF CAB EXPRESSION 1 ( TOC1) functions with CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1) in a transcriptional feedback loop that is important for the circadian clock in Arabidopsis thaliana (L.) Heynh. TOC1 and its four paralogues, the Arabidopsis PSEUDO-RESPONSE REGULATOR (PRR) genes, are expressed in an intriguing daily sequence. This was proposed to form a second feedback loop, similar to the interlocking clock gene circuits in other taxa. We show that prr9 and prr5 null mutants have reciprocal period defects for multiple circadian rhythms, consistent with subtly altered expression patterns of CCA1 and TOC1. The period defects are conditional on light quality and combine additively in double-mutant plants. Thus PRR9 and PRR5 modulate light input to the circadian clock but are neither uniquely required for rhythm generation nor form a linear series of mutual PRR gene regulation.

Arabidopsis↗

PubMed2002

Distinct regulation of CAB and PHYB gene expression by similar circadian clocks.

Phytochrome B (phyB) is a major phytochrome active in light-grown plants. The circadian clock controls the expression of the PHYB gene. We have used the luciferase reporter gene (LUC) to monitor the rhythmic expression of PHYB in photoreceptor and clock-associated mutant backgrounds. Surprisingly, we found that PHYB and CAB expression have different free-running periods, indicating that separate circadian clocks control these genes. The effects of mutations show that the clocks share common components. This suggests that they are copies of the same clock mechanism in different locations, most likely in different cell layers. Furthermore, we show that phyB is required for a negative feedback loop that strongly antagonises the expression of PHYB. Compared to a system with only one clock, this regulatory complexity might allow the phase of peak expression for one clock-controlled gene to alter, relative to other genes or to changing environmental conditions.

Arabidopsis↗