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Biomedical subjects

R Larkin

Publications and source records attributed to R Larkin.

6 recordsLinked to original sources
PubMed2001

Arabidopsis genomes uncoupled 5 (GUN5) mutant reveals the involvement of Mg-chelatase H subunit in plastid-to-nucleus signal transduction.

A plastid-derived signal plays an important role in the coordinated expression of both nuclear- and chloroplast-localized genes that encode photosynthesis-related proteins. Arabidopsis GUN (genomes uncoupled) loci have been identified as components of plastid-to-nucleus signal transduction. Unlike wild-type plants, gun mutants have nuclear Lhcb1 expression in the absence of chloroplast development. We observed a synergistic phenotype in some gun double-mutant combinations, suggesting there are at least two independent pathways in plastid-to-nucleus signal transduction. There is a reduction of chlorophyll accumulation in gun4 and gun5 mutant plants, and a gun4gun5 double mutant shows an albino phenotype. We cloned the GUN5 gene, which encodes the ChlH subunit of Mg-chelatase. We also show that gun2 and gun3 are alleles of the known photomorphogenic mutants, hy1 and hy2, which are required for phytochromobilin synthesis from heme. These findings suggest that certain perturbations of the tetrapyrrole biosynthetic pathway generate a signal from chloroplasts that causes transcriptional repression of nuclear genes encoding plastid-localized proteins. The comparison of mutant phenotypes of gun5 and another Mg-chelatase subunit (ChlI) mutant suggests a specific function for ChlH protein in the plastid-signaling pathway.

Amino Acid Sequence↗
PubMed2001

Human natural killer cells mediate killing of intracellular Mycobacterium tuberculosis H37Rv via granule-independent mechanisms.

Despite the continued importance of tuberculosis as a world-wide threat to public health, little is known about the mechanisms used by human lymphocytes to contain and kill the intracellular pathogen Mycobacterium tuberculosis. We previously described an in vitro model of infection of human monocytes (MN) with virulent M. tuberculosis strain H37Rv in which the ability of peripheral blood lymphocytes to limit intracellular growth of the organism could be measured. In the current study, we determined that lymphocyte-mediated killing of intracellular M. tuberculosis occurs within the first 24 h of coculture with infected MN. Natural killer (NK) cells isolated from both purified protein derivative (PPD)-positive and PPD-negative subjects were capable of mediating this early killing of intracellular H37Rv. NK cell-mediated killing of intracellular M. tuberculosis was not associated with the production of gamma interferon. Transferred supernatants of cocultured NK cells and M. tuberculosis-infected MN could not mediate the killing of intracellular M. tuberculosis, and Transwell studies indicated that direct cell-to-cell contact was required for NK cells to mediate the killing of the organism. Killing was not dependent upon exocytosis of NK cell cytotoxic granules. NK cells induced apoptosis of mycobacterium-infected MN, but neither killing of intracellular M. tuberculosis by NK cells nor NK cell-induced apoptosis of infected MN was inhibited by blocking the interaction of FasL and Fas. Thus, human NK cells may mediate killing of intracellular M. tuberculosis via alternative apoptotic pathways.

Adult↗
PubMed1994

Use of 3D reconstruction to correct for patient motion in SPECT.

Patient motion occurring during data acquisition in single photon emission computed tomography (SPET) can cause serious reconstruction artefacts. We have developed a new approach to correct for head motion in brain SPECT. Prior to motion, projections are assigned to conventional projections. When head motion occurs, it is measured by a motion monitoring system, and subsequent projection data are mapped to 'virtual' projections. The appropriate position of each virtual projection is determined by applying the converse of the patient's accumulated motion to the actual camera projection. Conventional and virtual projections, taken together, form a consistent set that can be reconstructed using a three-dimensional (3D) algorithm. The technique has been tested on a range of simulated rotational movements, both within and out of the transaxial plane. For all simulated movements, the motion corrected images exhibited better agreement with a motion free reconstruction than did the uncorrected images. This technique may help to overcome one of the major remaining limitations on image quality and quantitative accuracy in SPECT.

Algorithms↗
PubMed1983

A simple estimated fetal weight equation based on real-time ultrasound measurements of fetuses less than thirty-four weeks' gestation.

Based on ultrasonographic mensuration, a number of equations have previously been devised for the purpose of estimating fetal weights. The objective of this study was to develop a mathematical equation that is simple, accurate, and easy to use when applied to preterm or low-birth weight fetuses (less than 2,500 gm). Real-time ultrasound measurements of fetal biparietal diameters (BPDs) and abdominal circumferences (ACs) were obtained in 62 pregnant women within one week of premature delivery. Mean gestational age and mean birth weight +/- SD for this study group of neonates were 28.5 +/- 3.5 weeks and 1,135 +/- 343 gm, respectively. With the aid of computer analysis, a simple regression equation was derived: EFW = (BPD x AC x 9.337) - 229. When predicted estimated fetal weight (EFW) was compared with actual birth weight (ABW), multiple regression analysis demonstrated a correlation coefficient (R) of 0.957. Preliminary results on 19 patients of a prospective study showed an absolute mean difference between the computed EFWs and the ABWs to be within 7.0% of ABW (70 gm/kg of ABW). The standard deviation of the difference was 9.3% of ABW (93 gm/kg of ABW). Based on these data, this simple equation appears to be clinically reliable and easy to use when estimating weights of preterm or low-birth weight fetuses of less than 2,500 gm.

Birth Weight↗