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Biomedical subjects

C H Johnson

Publications and source records attributed to C H Johnson.

At least 19 recordsLinked to original sources
PubMed2003

Chlorine inactivation of spores of Encephalitozoon spp.

This report is an extension of a preliminary investigation on the use of chlorine to inactivate spores of Encephalitozoon intestinalis and to investigate the effect of chlorine on two other species, E cuniculi and E. hellem, associated with human infection. The 50% tissue culture infective doses of these three species were also determined. On the basis of the results obtained, it appears that chlorination of water is an effective means of controlling spores of these organisms in the aquatic environment.

Animals↗
PubMed2001

Circadian programming in cyanobacteria.

Prokaryotic cyanobacteria express robust circadian (daily) rhythms under the control of a timing mechanism that is independent of the cell division cycle. This biological clock orchestrates global regulation of gene expression. Competition experiments demonstrate that fitness is enhanced when the circadian period is consonant with the period of the environmental cycle. Mutational analyses have identified three clock genes in the organism, one of which is related to DNA recombinases and helicases. We propose a new model for the core 'clockwork' that implicates rhythmic changes in the status of the chromosome that underly the rhythms of gene expression.

Biological Clocks↗
PubMed2001

Genomic perspective on the photobiology of Halobacterium species NRC-1, a phototrophic, phototactic, and UV-tolerant haloarchaeon.

Halobacterium species display a variety of responses to light, including phototrophic growth, phototactic behavior, and photoprotective mechanisms. The complete genome sequence of Halobacterium species NRC-1 (Proc Natl Acad Sci USA 97: 12176-12181, 2000), coupled with the availability of a battery of methods for its analysis makes this an ideal model system for studying photobiology among the archaea. Here, we review: (1) the structure of the 2.57 Mbp Halobacterium NRC-1 genome, including a large chromosome, two minichromosomes, and 91 transposable IS elements; (2) the purple membrane regulon, which programs the accumulation of large quantities of the light-driven proton pump, bacteriorhodopsin, and allows for a period of phototrophic growth; (3) components of the sophisticated pathways for color-sensitive phototaxis; (4) the gas vesicle gene cluster, which codes for cell buoyancy organelles; (5) pathways for the production of carotenoid pigments and retinal, (6) processes for the repair of DNA damage; and (7) putative homologs of circadian rhythm regulators. We conclude with a discussion of the power of systems biology for comprehensive understanding of Halobacterium NRC-1 photobiology.

Journal Article↗
PubMed2001

Reconstruction after extirpation of the auricle.

The purpose of this study is to introduce the procedure and results of a combined free flap reconstruction with an external ear prosthesis after tumor extirpation from the lateral side of the head. Over the last 3 years, four patients have undergone total auricle extirpation for varying tumor processes. Each was reconstructed with a radial forearm flap, preserving the external auditory meatus. After primary healing and adjuvant therapy, a prosthetic pinna was applied. Combined use of microsurgical techniques with a prosthetic ear has produced an aesthetically superior result for large soft-tissue defects of the side of the head. This combined technique is able to provide the best aspects of both microsurgical and prosthetic reconstructions for a superior result for the patient.

Adult↗
PubMed2001

The fate of free flaps used to reconstruct defects in recurrent head and neck cancers.

The purpose of this study was to assess free-flap viability in patients treated for recurrent head and neck cancers. A 10-year retrospective review identified 121 patients who had had prior head and neck cancers extirpated for cure, who subsequently presented with documented recurrent cancers that were removed, and who then underwent reconstruction with free flaps. The charts of these patients were reviewed for patient demographics, tumor types, location, flaps used for reconstruction, size of area requiring reconstruction, length of operation, previous radiation, and all postoperative morbidity and mortality. The time to recurrence ranged from 21/2 months to 21 years. The majority of tumors treated were squamous cell carcinomas (n = 82). Most of them were located intraorally (n = 75). Radiation therapy had been delivered to 88 patients before their free-flap reconstructions. In this series, 31 percent of all patients required additional surgery for complications, 14 percent of free flaps were lost, and 4 percent of patients died within 30 days of their operation. The significant findings were that a flap that was >4 cm in diameter was related to flap loss (p = 0.03 by the chi2 method) and that flap loss was related to operative times greater than 11 hours (p = 0.03 by the chi2 method). It was concluded that recurrent head and neck cancers with large postextirpation defects that required prolonged operative times yielded a significantly high tendency toward flap failure.

Adult↗
PubMed2001

The calcium rhythms of different cell types oscillate with different circadian phases.

Transgenic tobacco (Nicotiana plumbaginifolia) seedlings containing the Ca(2+)-sensitive luminescent protein aequorin have been shown to exhibit circadian variations in cytosolic calcium. Concomitant measurements of cytosolic and nuclear calcium show that circadian variations in the cytoplasm are not expressed in the nucleus. To investigate whether all cells of transgenic seedlings contribute equally to circadian variations in cytosolic calcium, different promoters eliciting different expression patterns have been placed upstream of aequorin and used for transformation. The circadian peak occurred at different times in the three transgenic lines constructed. Luminescence imaging of these transgenic lines indicated that aequorin was differentially accumulated among the main tissues and cells of the seedlings and overcoat technology with applied epidermal strips indicated that the surface cell layers contribute the vast majority of luminescent light. We conclude that the Ca(2+) rhythmicities of cells and tissues oscillate with distinct differences in phase, that this might represent different underlying cellular control mechanisms and that these observations have significant implications for our understanding and study of Ca(2+) mediated signal transduction in plant cells.

Aequorin↗
PubMed2001

A clock- and light-regulated gene that links the circadian oscillator to LHCB gene expression.

We have identified and characterized a novel tobacco gene, called ZGT (from the Chinese phrase zhong guang tiaokong, or clock and light controlled), that is regulated by the circadian clock and light. ZGT transcripts have alternate forms that are differentially expressed in different tissues. ZGT is expressed rhythmically in light/dark cycles and in constant light. Constitutive expression of ZGT sustains the expression of the clock-controlled LHCB1*1 gene in constant darkness, when it would normally dampen, but does not affect LHCB1*1 expression in constant light. ZGT expression is induced rapidly by light, and overexpression of ZGT increases the sensitivity of the circadian oscillator to brief light pulses. The ZGT promoter includes a G-box motif that is found in many light-regulated promoters in plants and is the same as the E box described for rhythmically regulated promoters of animal circadian clock genes. The ZGT promoter also includes "evening element" motifs that are correlated with circadian control of plant genes. We postulate that light- and clock-regulated expression of ZGT acts as a coupling agent between the central circadian oscillator and rhythmic LHCB1*1 expression and that it may function as a component in plant phototransduction pathways.

Alternative Splicing↗
PubMed2001

Independence of circadian timing from cell division in cyanobacteria.

In the cyanobacterium Synechococcus elongatus, cell division is regulated by a circadian clock. Deletion of the circadian clock gene, kaiC, abolishes rhythms of gene expression and cell division timing. Overexpression of the ftsZ gene halted cell division but not growth, causing cells to grow as filaments without dividing. The nondividing filamentous cells still exhibited robust circadian rhythms of gene expression. This result indicates that the circadian timing system is independent of rhythmic cell division and, together with other results, suggests that the cyanobacterial circadian system is stable and well sustained under a wide range of intracellular conditions.

Bacterial Proteins↗
PubMed2001

Endogenous timekeepers in photosynthetic organisms.

Circadian and photoperiodic timing mechanisms were first described in photosynthetic organisms. These organisms depend upon sunlight for their energy, so adaptation to daily and seasonal fluctuations in light must have generated a strong selective pressure. Studies of the endogenous timekeepers of photosynthetic organisms provide evidence for both a fitness advantage and for selective pressures involved in early evolution of circadian clocks. Photoperiodic timing mechanisms in plants appear to use their circadian timers as the ruler by which the day/night length is measured. As in animals, the overall clock system in plants appears to be complex; the system includes multiple oscillators, several input pathways, and a myriad of outputs. Genes have now been isolated from plants that are likely to encode components of the central clockwork or at least that act very close to the central mechanism. Genetic and biochemical analyses of the central clockwork of a photosynthetic organism are most highly advanced in cyanobacteria, where a cluster of clock genes and interacting factors have been characterized.

Arabidopsis↗
PubMed2000

Circadian clock-protein expression in cyanobacteria: rhythms and phase setting.

The cyanobacterial gene cluster kaiABC encodes three essential circadian clock proteins: KaiA, KaiB and KaiC. The KaiB and KaiC protein levels are robustly rhythmical, whereas the KaiA protein abundance undergoes little if any circadian oscillation in constant light. The level of the KaiC protein is crucial for correct functioning of the clock because induction of the protein at phases when the protein level is normally low elicits phase resetting. Titration of the effects of the inducer upon phase resetting versus KaiC level shows a direct correlation between induction of the KaiC protein within the physiological range and significant phase shifting. The protein synthesis inhibitor chloramphenicol prevents the induction of KaiC and blocks phase shifting. When the metabolism is repressed by either translational inhibition or constant darkness, the rhythm of KaiC abundance persists; therefore, clock protein expression has a preferred status under a variety of conditions. These data indicate that rhythmic expression of KaiC appears to be a crucial component of clock precession in cyanobacteria.

Bacterial Proteins↗
PubMed2000

Circadian control of cell division in unicellular organisms.

Cell division cycles and circadian rhythms are major periodic phenomena in organisms. Circadian oscillators control biochemical, physiological, and behavioral events in a wide range of living systems including almost all eukaryotes that have been tested and some prokaryotes-in particular, the cyanobacteria. Gating of cell division is one of the key processes that has been reported to be regulated by circadian clocks in many organisms. We survey studies of the circadian control of cell division in eukaryotic microorganisms and introduce recent progress on understanding the interaction between circadian rhythms and cell division cycles in cyanobacteria.

Animals↗
PubMed2000

Opportunities for intervention: discussing physical abuse during prenatal care visits.

BACKGROUND: The American Academy of Pediatrics and the American College of Obstetricians and Gynecologists recommend that screening for physical abuse during prenatal care visits becomes routine. Although prenatal care visits offer a unique intervention opportunity, screening is not yet standard practice. DATA AND METHODS: We used data from the 1996 and 1997 Pregnancy Risk Assessment Monitoring System (PRAMS) to assess the prevalence of and the factors associated with health care providers' discussion of physical abuse with pregnant women in 14 states. PRAMS is a state-specific, population-based surveillance system that collects information from women on maternal behaviors before and during pregnancy, and at 2 to 6 months postpartum. RESULTS: Between 22% and 39% of the women surveyed reported that health care providers talked with them about physical abuse during prenatal care visits. Health care providers were more likely to discuss physical abuse with women who were black, Hispanic, young (aged <20 and 20 to 29), had a high school education or less, or paid for prenatal care with Medicaid. CONCLUSIONS: Our results indicate that most pregnant women do not report that their prenatal care providers discussed physical abuse with them. Logistic regression analyses identified consistent associations across the 14 states between discussion of abuse and demographic and pregnancy-related factors. A better understanding of the factors associated with whether a health care provider discusses physical abuse with a pregnant woman could increase intervention opportunities.

Adult↗
PubMed2000

Pregnancy intendedness and physical abuse around the time of pregnancy: findings from the pregnancy risk assessment monitoring system, 1996-1997. PRAMS Working Group. Pregnancy Risk Assessment Monitoring System.

OBJECTIVE: This study examines whether unintended pregnancy is associated with physical abuse of women occurring around the time of pregnancy, independent of other factors. METHODS: In 1996-1997, state-specific population-based data were obtained from the Pregnancy Risk Assessment Monitoring System (PRAMS) from 39,348 women in 14 states who had delivered a live-born infant within the previous 2-6 months. The study questionnaire asked about maternal behaviors and characteristics around the time of pregnancy. RESULTS: Women who had mistimed or unwanted pregnancies reported significantly higher levels of abuse at any time during the 12 months before conception or during pregnancy (12.6% and 15.3%, respectively) compared with those with intended pregnancies (5.3%). Higher rates of abuse were reported by women who were younger, Black, unmarried, less educated, on Medicaid, living in crowded conditions, entering prenatal care late, or smoking during the third trimester. Overall, women with unintended pregnancies had 2.5 times the risk of experiencing physical abuse compared with those whose pregnancies were intended. This association was modified by maternal characteristics, the association was strongest among women who were older, more educated, White, married, not on Medicaid, not living in crowded conditions, receiving first trimester prenatal care, or nonsmoking during the third trimester. CONCLUSIONS: Women with unintended pregnancies are at increased risk of physical abuse around the time of pregnancy compared with women whose pregnancies are intended. Prenatal care can provide an important point of contact where women can be screened for violence and referred to services that can assist them.

Adult↗
PubMed2000

Use of microvascular free-tissue transfer following ablative surgery of the skull base.

The purpose of this study was to validate the use of free flaps in reconstruction of skullbase defects after extensive resection of advanced tumors, and to justify microvascular reconstruction to improve the quality of life and survival in this population. The treatment outcome after ablative resection of skullbase tumors with free flap reconstruction over a 7-year period (1988 to 1995) was studied. Complete removal of the tumor was originally attempted in all patients. All cases had immediate reconstruction. Criteria for reconstruction with free flaps were based on extensive defects in which local flaps were insufficient. Twenty patients were identified male:female, 11:9). The most common tumor was sarcoma, followed by squamous-cell carcinoma. Coverage of the dura was required in 12 patients. Muscles used were the rectus abdominis and latissimus dorsi. Complications included flap necrosis (n = 2) and ventral hernia (n = 2). Control of pain was achieved in 66 percent of cases. Patients with regional metastasis died within 2 years, and those with distant metastasis died within 18 months. Patients with primary tumors had an increased survival rate. The authors confirm the technical feasibility and success of free flaps to reconstruct extensive defects in the skull base. In patients with potentially complete resection of primary/recurrent lesions, overall survival justifies the procedure. Patients with regional/distant metastasis warrant an individualized approach.

Carcinoma, Squamous Cell↗
PubMed2000

Free fibula donor-site morbidity: the Mayo experience with 100 consecutive harvests.

A retrospective analysis of 100 consecutive patients undergoing free fibula harvest at the Mayo Clinic is presented. Every patient was analyzed by reviewing postoperative physical examination data. All patients were evaluated and followed in the early postoperative course by the physical medicine and rehabilitation services. Patients were followed from 3 to 60 months, with an average follow up of 17.42 months. In the patient group, 72 flaps were osseous and 28 osteocutaneous. Thirty-six complications at the donor site were observed in 30 patients. An additional 19 patients required prolonged pharmacologic pain control beyond the first 6 postoperative weeks, with no donor-site complications clinically detectable. Hammertoe was observed in six patients and wound dehiscence in seven patients. Tendon exposure was observed in five patients; partial split-thickness skin graft loss was observed in eight. Numbness of the foot was reported in 10 patients. Fifteen patient had limited maximum ambulatory distance to less than 1000 m. An additional six patients reported difficulty walking stairs. Attention to details and meticulous wound care are required to further reduce wound-healing complications. Immediate postoperative involvement of the physical medicine and rehabilitation services was beneficial in early patient mobilization and achievement of preoperative ambulation levels. After a short rehabilitation period, the majority of patients were able to engage in all daily activities.

Adult↗
PubMed2000

A spore counting method and cell culture model for chlorine disinfection studies of Encephalitozoon syn. Septata intestinalis.

The microsporidia have recently been recognized as a group of pathogens that have potential for waterborne transmission; however, little is known about the effects of routine disinfection on microsporidian spore viability. In this study, in vitro growth of Encephalitozoon syn. Septata intestinalis, a microsporidium found in the human gut, was used as a model to assess the effect of chlorine on the infectivity and viability of microsporidian spores. Spore inoculum concentrations were determined by using spectrophotometric measurements (percent transmittance at 625 nm) and by traditional hemacytometer counting. To determine quantitative dose-response data for spore infectivity, we optimized a rabbit kidney cell culture system in 24-well plates, which facilitated calculation of a 50% tissue culture infective dose (TCID(50)) and a minimal infective dose (MID) for E. intestinalis. The TCID(50) is a quantitative measure of infectivity and growth and is the number of organisms that must be present to infect 50% of the cell culture wells tested. The MID is as a measure of a system's permissiveness to infection and a measure of spore infectivity. A standardized MID and a standardized TCID(50) have not been reported previously for any microsporidian species. Both types of doses are reported in this paper, and the values were used to evaluate the effects of chlorine disinfection on the in vitro growth of microsporidia. Spores were treated with chlorine at concentrations of 0, 1, 2, 5, and 10 mg/liter. The exposure times ranged from 0 to 80 min at 25 degrees C and pH 7. MID data for E. intestinalis were compared before and after chlorine disinfection. A 3-log reduction (99.9% inhibition) in the E. intestinalis MID was observed at a chlorine concentration of 2 mg/liter after a minimum exposure time of 16 min. The log(10) reduction results based on percent transmittance-derived spore counts were equivalent to the results based on hemacytometer-derived spore counts. Our data suggest that chlorine treatment may be an effective water treatment for E. intestinalis and that spectrophotometric methods may be substituted for labor-intensive hemacytometer methods when spores are counted in laboratory-based chlorine disinfection studies.

Animals↗
PubMed2000

Daily and circadian variation in survival from ultraviolet radiation in Chlamydomonas reinhardtii.

The survival of organisms depends on their ability to adapt to their environment, one important aspect of which is the daily cycle of day and night. During the day, organisms use a variety of strategies to protect themselves from deleterious ultraviolet (UV) wavelengths of sunlight. Among those strategies could be timing of UV-sensitive cellular processes to occur at night to avoid UV-induced damage. We tested whether the unicellular alga Chlamydomonas reinhardtii uses this strategy by measuring the survival of cells following exposure to UV radiation at different phases of the day. Chlamydomonas cells displayed a rhythm of survival from UV radiation where the most sensitive phases occurred during the end of the day and at the beginning of the night. This phase of sensitivity corresponds to the time of nuclear division. The rhythm continues in constant light indicating control by a circadian clock. The results presented here suggest a hypothesis of how circadian clocks may have evolved; a temporal program whereby light-sensitive processes are timed to avoid sunlight-induced damage would be advantageous and therefore selected.

Animals↗