Deletion of N-terminal rapsyn domains disrupts clustering and has dominant negative effects on clustering of full-length rapsyn

The peripheral muscle membrane protein rapsyn is essential for the formation and maintenance of high density acetylcholine receptor aggregates at the neuromuscular synapse. Rapsyn is concentrated at synaptic sites and is colocalized with acetylcholine receptors from the earliest stages of synaptogenesis. Previous studies have shown that recombinant rapsyn expressed in heterologous cells forms clusters, and acetylcholine receptors coexpressed with rapsyn are colocalized with rapsyn clusters. However, the molecular interactions involved in clustering of rapsyn are not well defined. To analyze the process of cluster formation by rapsyn we examined the formation of rapsyn clusters and complexes using mutant constructs specifically deleted for individual domains of rapsyn in the presence and absence of tagged, full-length rapsyn. Specific deletions of the tetratricopeptide repeat (TPR) domains 1 and 3 of rapsyn abrogated not only clustering of mutant rapsyns, but also, in a dominant negative fashion, the clustering of tagged, full-length rapsyn. We also analyzed rapsyn protein complexes isolated from cells transfected with tagged and untagged rapsyn. Our results show that both tagged and untagged rapsyn are present in immunoprecipitates of rapsyn from cotransfected cells, demonstrating that rapsyn molecules interact directly or indirectly to form oligomers. Mutants that were dominant negatives were also present in complexes containing tagged, full-length rapsyn. Together these results indicate that rapsyn forms clusters at the synapse by oligomerization, and suggest models for the mechanistic bases of this oligomerization via interactions mediated by TPRs 1 and 3.     

Heterogeneity in synaptic transmission along a Drosophila larval motor axon

At the Drosophila melanogaster larval neuromuscular junction (NMJ), a motor neuron releases glutamate from 30-100 boutons onto the muscle it innervates. How transmission strength is distributed among the boutons of the NMJ is unknown. To address this, we created synapcam, a version of the Ca2+ reporter Cameleon. Synapcam localizes to the postsynaptic terminal and selectively reports Ca2+ influx through glutamate receptors (GluRs) with single-impulse and single-bouton resolution. GluR-based Ca2+ signals were uniform within a given connection (that is, a given bouton/postsynaptic terminal pair) but differed considerably among connections of an NMJ. A steep gradient of transmission strength was observed along axonal branches, from weak proximal connections to strong distal ones. Presynaptic imaging showed a matching axonal gradient, with higher Ca2+ influx and exocytosis at distal boutons. The results suggest that transmission strength is mainly determined presynaptically at the level of individual boutons, possibly by one or more factors existing in a gradient.     

Determination of gallium concentration in "blood-free" tissues using a radiolabeled blood marker

Radioiodinated serum albumin has been used as a blood marker to define and quantitate physiological volumes for 12 organs and tissue types. The concentration of gallium-67 in "blood-free" tissues of rats was also determined at various times after intravenous administration. Tissues were divided into two kinetically distinguishable types based on reported nonuniform distribution of the blood marker and the gallium distribution observed in the present study. Gallium distribution into the liver and spleen was observed to be slow, with a discernable accumulation phase followed by monoexponential elimination. In contrast, gallium accumulation into the stomach, small and large intestines, heart, lung, skin/adipose tissue, and muscle was rapid and elimination was monophasic.     

APOE ε4 and late-life cognition: mediation by structural brain imaging markers

European Journal of Epidemiology - The apolipoprotein E allele 4 (APOE-ε4) is established as a major genetic risk factor for cognitive decline and late-onset Alzheimer’s disease....     

An empirical comparison of rural and urban safety-net hospitals

This study compares the characteristics of rural hospitals with urban safety-net hospitals and with "other urban hospitals" (non-teaching, non-safety-net urban hospitals that provide mainstream care in the United States). The objective is to examine if there are similarities between rural and urban safety-net hospitals, both of which serve underserved populations. The authors also wish to study if there are areas in which rural and urban safety-net hospitals are closer together compared to "other" urban hospitals. Based on the results, some potential areas of cooperation between rural and urban safety-net hospitals are discussed.     

RRM1 and PTEN as prognostic parameters for overall and disease-free survival in patients with non-small-cell lung cancer.

PURPOSE: RRM1 has important functions in the determination of the malignant phenotype. It controls cell proliferation through deoxynucleotide production and metastatic propensity through PTEN induction. It is located in a region of loss of heterozygosity in non-small-cell lung cancer (NSCLC), which is a predictor of poor survival. We hypothesized that RRM1 expression would be a significant predictor of outcome in NSCLC. PATIENTS AND METHODS: A retrospective data set of 49 patients and a prospective data set of 77 patients with resectable NSCLC were studied. RNA was extracted from tumor and normal lung tissue, and expression of the genes RRM1, PTEN, and RRM2 was determined by real-time quantitative polymerase chain reaction. RESULTS: RRM1 expression was significantly correlated with PTEN and RRM2 expression in tumor tissue. RRM1 and PTEN expression in tumor tissue was highly predictive of overall (P =.011 and.018, respectively) and disease-free survival (P =.002 and.026, respectively). Patients with high levels of expression lived longer and had disease recurrence later than patients with low levels of RRM1 and PTEN. In a multivariate analysis, high RRM1 expression was predictive of long survival independent of tumor stage, performance status, and weight loss. CONCLUSION: RRM1 is a biologically and clinically important determinant of malignant behavior in NSCLC. Knowing the level of expression of this gene adds significant information to management decisions independent of the currently used outcome predictors of tumor stage, performance status, and weight loss. Future clinical trials should stratify patients based on expression of this gene to avoid unwanted biases.     

Antenatal corticosteroid therapy and risk of osteoporosis

Objective To assess the risk of maternal osteoporosis associated with antenatal corticosterioid administration for neonatal respiratory distress syndrome prophylaxis.
Design Prospective longitudinal study.
Setting Maternity unit of Chelsea and Westminster Hospital, London.
Population Fourteen pregnant women who received dexamethasone therapy for fetal lung maturation in anticipation of delivery before 34 completed weeks of gestation.
Methods Blood samples were collected before dexamethasone administration, 24 hours and 48 hours after the course of dexamethasone, and within 24 hours of delivery. Serum levels of carboxy terminal pro-peptide of type I pro-collagen (PICP) were measured to monitor the rate of bone formation, and serum levels of cross-linked carboxy terminal telopeptide (ICTP) were measured as a marker of bone resorption.
Main outcome measures Changes in the markers of bone turnover following dexamethasone administration.
Results Serum PICP levels dropped 24 hours after dexamethasone therapy (   P = 0.001  ), but partially recovered by 48 hours (   P = 0.014  ) to reach higher than pre-therapy levels at delivery (   P = 0.044  ). Although there were no corresponding changes in the serum levels of ICTP after 24 and 48 hours of therapy, levels increased from pretherapy to delivery (   P = 0.006  ).
Conclusion Antenatal corticosteroid therapy leads to a transient suppression of, followed by an increase in, bone formation without any significant alteration in the pattern of bone resorption expected during pregnancy.