Search PubMed⌕ Search

Biomedical subjects

Michael C Miller

Publications and source records attributed to Michael C Miller.

10 recordsLinked to original sources
PubMed2007

A G protein/cAMP signal cascade is required for axonal convergence into olfactory glomeruli.

The mammalian odorant receptors (ORs) comprise a large family of G protein-coupled receptors that are critical determinants of both the odorant response profile and the axonal identity of the olfactory sensory neurons in which they are expressed. Although the pathway by which ORs activate odor transduction is well established, the mechanism by which they direct axons into proper glomerular relationships remains unknown. We have developed a gain-of-function approach by using injection of retroviral vectors into the embryonic olfactory epithelium to study the ORs' contribution to axon guidance. By ectopically expressing ORs, we demonstrate that functional OR proteins induce axonal coalescence. Furthermore, ectopic expression of Galpha mutants reveals that activation of the signal transduction cascade is sufficient to cause axonal convergence into glomeruli. Analysis of Galpha subunit expression indicates that development and odorant transduction use separate transduction pathways. Last, we establish that the generation of cAMP through adenylyl cyclase 3 is necessary to establish proper axonal identity. Our data point to a model in which axonal sorting is accomplished by OR stimulation of cAMP production by coupling to Galphas.

Animals↗
PubMed2006

RpoS controls the Vibrio cholerae mucosal escape response.

Vibrio cholerae causes a severe diarrhoeal disease by secreting a toxin during colonization of the epithelium in the small intestine. Whereas the initial steps of the infectious process have been intensively studied, the last phases have received little attention. Confocal microscopy of V. cholerae O1-infected rabbit ileal loops captured a distinctive stage in the infectious process: 12 h post-inoculation, bacteria detach from the epithelial surface and move into the fluid-filled lumen. Designated the "mucosal escape response," this phenomenon requires RpoS, the stationary phase alternative sigma factor. Quantitative in vivo localization assays corroborated the rpoS phenotype and showed that it also requires HapR. Expression profiling of bacteria isolated from ileal loop fluid and mucus demonstrated a significant RpoS-dependent upregulation of many chemotaxis and motility genes coincident with the emigration of bacteria from the epithelial surface. In stationary phase cultures, RpoS was also required for upregulation of chemotaxis and motility genes, for production of flagella, and for movement of bacteria across low nutrient swarm plates. The hapR mutant produced near-normal numbers of flagellated cells, but was significantly less motile than the wild-type parent. During in vitro growth under virulence-inducing conditions, the rpoS mutant produced 10- to 100-fold more cholera toxin than the wild-type parent. Although the rpoS mutant caused only a small over-expression of the genes encoding cholera toxin in the ileal loop, it resulted in a 30% increase in fluid accumulation compared to the wild-type. Together, these results show that the mucosal escape response is orchestrated by an RpoS-dependent genetic program that activates chemotaxis and motility functions. This may furthermore coincide with reduced virulence gene expression, thus preparing the organism for the next stage in its life cycle.

Animals↗
PubMed2003

Going beyond Prozac.

Explore the source record for details and available documents.

Antidepressive Agents, Second-Generation↗
PubMed2003

Roles for RNA in telomerase nucleotide and repeat addition processivity.

Telomerase is a ribonucleoprotein reverse transcriptase with two subunits critical for catalytic activity, the protein telomerase reverse transcriptase (TERT) and telomerase RNA. In this study, we establish additional roles of the telomerase RNA subunit by demonstrating that RNA motifs stimulate the processivity of nucleotide and repeat addition. These functions are both functionally and physically separable from the roles of other RNA motifs in establishing a properly defined template. Binding of Tetrahymena telomerase RNA stem IV to TERT enhances nucleotide addition processivity, while a cooperation of the RNA pseudoknot and stem IV promotes repeat addition processivity. The low processivity of DNA synthesis by telomerase ribonucleoproteins lacking the pseudoknot and/or stem IV can be rescued by addition of the deleted region in trans. These findings demonstrate RNA elements with roles in telomerase elongation processivity that are distinct from RNA elements that specify the internal template.

Amino Acid Motifs↗
PubMed2003

Can prostate specific antigen derivatives and pathological parameters predict significant change in expectant management criteria for prostate cancer?

PURPOSE: A prior report established that pretreatment criteria based on clinical and biopsy pathology parameters can predict men who harbor small volume prostate cancer who might be followed expectantly. However, some of these men will exhibit disease progression with time and will need definitive therapy. To detect those in whom disease may progress, repeat prostate biopsies are performed at yearly intervals. Therefore, we determined whether biomarkers could be used to determine those in whom disease is likely to progress and thus those who require definitive therapy. MATERIALS AND METHODS: Initial and repeat biopsy information along with transrectal ultrasound measurements of gland volume, total prostate specific antigen (PSA), %free PSA (%fPSA) and total PSA velocity were evaluated in 78 men, 45 from the prior study, in whom disease was being managed expectantly. Univariate and multivariate logistic regression analyses determined variables that predicted a favorable tumor burden based on biopsy pathology status at each subsequent repeat biopsy. A Cox proportional hazards model was produced using 67 of 78 evaluable cases having adequate temporal data to predict hazard ratios for conversion from favorable to unfavorable tumor burden status. RESULTS: At time zero for 78 patients %fPSA, total PSA, and gland volume univariately and multivariately differentiated unfavorable and favorable tumor burden groups (p <0.05). The receiver operator characteristic area under the curve (ROC-AUC) was 83%. At the first followup biopsy 17 of 67 (25.4%) men converted to unfavorable tumor burden status. The %fPSA, PSA velocity and gland volume univariately distinguished these 2 groups (p <0.05) with 82% ROC-AUC. At second repeat biopsy 6 of 36 (16.7%) men converted to unfavorable tumor burden status and the ROC-AUC was 76%. Of the 14 men who had a third repeat biopsy all demonstrated favorable tumor burden status. A Cox proportional hazards model stratified the 67 of 78 men into high (48) and low risk (19) groups based on %fPSA at a 20% cutoff (p <0.01). Classification and regression tree analysis using logistic regression multivariately selected variables predicted favorable tumor burden status with an accuracy that ranged from 75% to 84% during our study. CONCLUSIONS: PSA velocity, %fPSA and gland volume information improves the prediction of men undergoing expectant management who are more likely to have small volume disease based on a 12-core biopsy interpretation within the time of our observations. %fPSA proved to be a valuable marker to stratify the 2 risk groups. Therefore, based on these factors it may be possible to consider deferment of repeat prostate biopsy until adverse results are detected. This rational approach to the management of prostate cancer in older men with small volume cancer seems to be a reasonable strategy.

Aged↗
PubMed2002

Telomerase recognizes its template by using an adjacent RNA motif.

Telomerase adds telomeric repeats to chromosome 3' ends, forestalling the cellular senescence, apoptosis, and genomic instability that result from telomere loss caused by incomplete DNA replication. The telomerase ribonucleoprotein is dedicated to synthesis of tandem, simple-sequence repeats by virtue of its specialization for copying only a specific template region within the integral RNA. Here, using circularly permuted variants of Tetrahymena thermophila telomerase RNA, we identify the features that allow recognition of the template region within the RNA. We engineered a template-less telomerase ribonucleoprotein that can position and reverse transcribe an exchangeable RNA oligonucleotide template accurately. Only a short "template-recognition" element sequence tag is required to direct efficient use of adjacent 5' residues as a template for telomeric repeat synthesis. Our findings reveal molecular requirements for template selection by telomerase and physically resolve templating from other RNA functions in catalysis.

Animals↗
PubMed2002

Template boundary definition in Tetrahymena telomerase.

Telomerase elongates chromosome ends by addition of telomeric DNA repeats. The telomerase ribonucleoprotein can copy only a short template sequence within the telomerase RNA subunit. Here, we identify a region of telomerase RNA that is necessary for both correct 5' template boundary definition and high affinity telomerase reverse transcriptase (TERT) interaction. We also demonstrate that TERT mutants in the RNA binding domain compromise both 5' boundary definition and RNA binding. Our results indicate that sequence-specific interaction of a telomerase RNA element with the TERT RNA binding domain, not the active site motifs, defines the template boundary.

Animals↗