Search

Skeletal scintigraphy is most performed in pediatric patients using the radiopharmaceutical 99mTc labelled methylene diphosphonate (99mTc-MDP). Reference biokinetic models for 99mTc-MDP indicate 50% of the administered activity is uniformly localized to the interior bone surfaces (trabecular and cortical regions), yet imaging data clearly show some preferential uptake to the epiphyseal growth plates of the long bones. To explore the dosimetric consequences of these regional activity concentrations, we have modified mesh-type computational phantoms of the International Commission on Radiological Protection (ICRP) reference pediatric series to explicitly include geometric models of the epiphyseal growth plates (2 mm in thickness) within the left/right, distal/proximal ends of the humeri, radii, ulnae, femora, tibia, and fibulae. Bone mineral activity from the ICRP Publication 128 biokinetic model for 99mTc-MDP (ICRP 2015) was then partitioned to the growth plates at values of 0.5%, 4.4%, 8.3%, 12.2%, 16.1%, and 20%. Radiation transport simulations were performed to compute 99mTc S-values and organ dose coefficients to the soft tissues and to bone site-specific regions of spongiosa. As the percentage of bone activity assigned to the growth plates was increased (from 0.5% to 20%), absorbed doses to the soft tissue organs, active bone marrow, bone endosteum (BE), as well as the detriment-weighted dose, were shown to decrease from their nominal values (no substantial growth plate activity), while epiphyseal plate self-doses increased. In the 15 year old male phantom, moving from 0.5% to 20% relative bone activity within the epiphyseal plates resulted in a 15% reduction in active marrow (AM) and BE dose, a 10% reduction in mean soft tissue and detriment-weighted dose, and a 6.3-fold increase in epiphyseal plate self-dose. In the newborn female phantom, we observed a 18% decrease in AM and BE dose, a 10% decrease in mean soft tissue dose, a 15% decrease in detriment-weighted dose, and 12.8-fold increase in epiphyseal plate self-dose. Increases (to 3 mm) and decreases (to 1 mm) in the assumed growth plate thickness of our models were shown to impact only the growth plate self-dose. Future work in differential quantification of 99mTc-MDP activity—growth plates versus other bone surfaces—is required to provide clinically realistic data on activity partitioning as a function of patient age, and perhaps skeletal site. The phantom series presented here may be used to develop more optimized age-related guidance on 99mTc-MDP administered activities to children. [ABSTRACT FROM AUTHOR]

MOD5 encodes a tRNA modification activity located in three subcellular compartments. Alternative translation initiation generates Mod5p-I, located in the mitochondria and the cytosol, and Mod5p-II, located in the cytosol and nucleus. Here we study the nucleus/cytosol distribution of overexpressed Mod5p-II. Nuclear Mod5p-II appears concentrated in the nucleolus, perhaps indicating that the nuclear pool may have a different biological role than the cytoplasmic and mitochondrial pools. Mod5p contains three motifs resembling bipartite-like nuclear localization sequences (NLSs), but only one is sufficient to locate a passenger protein to the nucleus. Mutations of basic residues of this motif cumulatively contribute to a cytosolic location for the fusion proteins. These alterations also cause decreased nuclear pools of endogenous Mod5p-II. Depletion of nuclear Mod5p-II does not affect tRN[A.sup.Tyr] function. Despite the NLS, most Mod5p is cytosolic. We assessed whether Mod5p sequences cause a karyophilic reporter to be located in the cytosol. By this assay, Mod5p may contain more than one region that functions as cytoplasmic retention and/or nuclear export sequences. Thus, distribution of ModSp results from the presence/absence of mitochondrial targeting information and sequences antagonistic for nuclear and cytosolic locations. Mod5p is highly conserved; sequences responsible for subcellular distribution appear to reside in 'accessory' motifs missing from prokaryotic counterparts.

Background: The receptor for advanced glycation end products (RAGE) is a multiligand receptor expressed in a number of cell types, including gingival epithelia. RAGE mediates inflammation and induces cellular oxidative stress. Upregulation of RAGE is associated with various diseases, such as periodontal and cardiovascular diseases. This study examines the hypothesis that the gingiva of rats fed a calorie-restriction (CR) diet expresses lower levels of RAGE than the gingiva of rats fed an ad libitum (AL) diet. Methods: Male F344BN rats (n = 16) from the National Institute on Aging (NIA) were fed a CR (n = 8) or AL (n = 8) diet according to NIA recommendations. Rats were sacrificed by guillotine at 8 (n = 5), 18 (n = 3), 29 (n = 4), and 38 (n = 4) months of age. The gingiva from around the molars was dissected and submitted for histologic and molecular analyses. Results: Immunohistochemistry revealed that RAGE was expressed in the plasma membrane and cytoplasm of gingival epithelial cells and endothelial cells from both groups. RAGE mRNA levels were quantified relative to levels of GAPDH mRNA by real-time reverse-transcriptase polymerase chain reaction. The mean relative RAGE mRNA level in the CR group (7.26 ± 0.54) was lower than in the AL group (10 ± 1.4) (P <0.05). There were no detectable differences in RAGE expression according to animal age. Conclusion: Gingival RAGE expression in rats is reduced by calorie restriction. [ABSTRACT FROM AUTHOR]

Abstract: Extrachromosomal rDNA circles (ERCs) and recombinant origin-containing plasmids (ARS-plasmids) are thought to reduce replicative life span in the budding yeast Saccharomyces cerevisiae due to their accumulation in yeast cells by an asymmetric inheritance process known as mother cell bias. Most commonly used laboratory yeast strains contain the naturally occurring, high copy number 2-micron circle plasmid. 2-micron plasmids are known to exhibit stable mitotic inheritance, unlike ARS-plasmids and ERCs, but the fidelity of inheritance during replicative aging and cell senescence has not been studied. This raises the question: do 2-micron circles reduce replicative life span? To address this question we have used a convenient method to cure laboratory yeast strains of the 2-micron plasmid. We find no difference in the replicative life spans of otherwise isogenic cir+ and cir0 strains, with and without the 2-micron plasmid. Consistent with this, we find that 2-micron circles do not accumulate in old yeast cells. These findings indicate that naturally occurring levels of 2-micron plasmids do not adversely affect life span, and that accumulation due to asymmetric inheritance is required for reduction of replicative life span by DNA episomes. [Copyright &y& Elsevier]

Modern yeast living in fleshy fruits rapidly convert sugars into bulk ethanol through pyruvate. Pyruvate loses carbon dioxide to produce acetaldehyde, which is reduced by alcohol dehydrogenase 1 (Adh1) to ethanol, which accumulates. Yeast later consumes the accumulated ethanol, exploiting Adh2, an Adh1 homolog differing by 24 (of 348) amino acids. As many microorganisms cannot grow in ethanol, accumulated ethanol may help yeast defend resources in the fruit. We report here the resurrection of the last common ancestor of Adh1 and Adh2, called AdhA. The kinetic behavior of AdhA suggests that the ancestor was optimized to make (not consume) ethanol. This is consistent with the hypothesis that before the Adh1-Adh2 duplication, yeast did not accumulate ethanol for later consumption but rather used AdhA to recycle NADH generated in the glycolytic pathway. Silent nucleotide dating suggests that the Adh1-Adh2 duplication occurred near the time of duplication of several other proteins involved in the accumulation of ethanol, possibly in the Cretaceous age when fleshy fruits arose. These results help to connect the chemical behavior of these enzymes through systems analysis to a time of global ecosystem change, a small but useful step towards a planetary systems biology. [ABSTRACT FROM AUTHOR]

Aging in the yeast Saccharomyces cerevisiae is under the control of multiple pathways. The production and accumulation of extrachromosomal rDNA circles (ERCs) is one pathway that has been proposed to bring about aging in yeast. To test this proposal, we have developed a plasmid-based model system to study the role of DNA episomes in reduction of yeast life span. Recombinant plasmids containing different replication origins, cisacting partitioning elements, and selectable marker genes were constructed and analyzed for their effects on yeast replicative life span. Plasmids containing the ARS1 replication origin reduce life span to the greatest extent of the plasmids analyzed. This reduction in life span is partially suppressed by a CEN4 centromeric element on ARS1 plasmids. Plasmids containing a replication origin from the endogenous yeast 2 µ circle also reduce life span, but to a lesser extent than ARS1 plasraids. Consistent with this, ARS1 and 2 μ origin plasmids accumulate in ∼7-generation-old cells, but ARS1/CEN4 plasmids do not. Importantly, ARS1 plasmids accumulate to higher levels in old cells than 2 μ origin plasmids, suggesting a correlation between plasmid accumulation and life span reduction. Reduction in life span is neither an indirect effect of increased ERC levels nor the result of stochastic cessation of growth. The presence of a fully functional 9.1-kb rDNA repeat on plasmids is not required for, and does not augment, reduction in life span. These findings support the view that accumulation of DNA episomes, including episomes such as ERCs, cause cell senescence in yeast. [ABSTRACT FROM AUTHOR]

The 35S rRNA genes at the RDN1 locus in Saccharomyces cerevisiae can be transcribed by RNA polymerase (Pol) II in addition to Pol I, but Pol II transcription is usually silenced. The deletion of RRN9 encoding an essential subunit of the Pol I transcription factor, upstream activation factor, is known to abolish Pol I transcription and derepress Pol II transcription of rRNA genes, giving rise to polymerase switched (PSW) variants. We found that deletion of histone deacetylase gene RPD3 inhibits the appearance of PSW variants in rrn9 deletion mutants. This inhibition can be explained by the observed specific inhibition of Pol II transcription of rRNA genes by the rpd3 Δ mutation. We propose that Rpd3 plays a role in the maintenance of an rRNA gene chromatin structure(s) that allows Pol II transcription of rRNA genes, which may explain the apparently paradoxical previous observation that rpd3 mutations increase, rather than decrease, silencing of reporter Pol II genes inserted in rRNA genes. We have additionally demonstrated that Rpd3 is not required for inhibition of Pol I transcription by rapamycin, supporting the model that Tor-dependent repression of the active form of rRNA genes during entry into stationary phase is Rpd3 independent. [ABSTRACT FROM AUTHOR]