AII amacrine neurons of the rat retina show diurnal and circadian rhythms of parvalbumin immunoreactivity

We investigated parvalbumin immunoreactivity (PA-IR) in the retinas of rats maintained on a 12:12 h light:dark cycle, or after being placed in constant darkness for 24–72 h. Retinas were harvested at zeitgeber and circadian times 02:00, 06:00, 10:00, 14:00, 18:00 and 22:00 h. PA-IR was found primarily in retinal amacrine cells of the AII subtype. In a light/dark cycle, PA-IR showed a clear rhythm, with a low near zeitgeber time (ZT) 10:00 h and a peak near ZT 18:00 h. The ratio of immunofluorescence intensities at these timepoints was >15-fold. When animals were kept in complete darkness for 1–3 days, the rhythm of PA-IR was still preserved, but was progressively reduced in amplitude. The rhythm of PA-IR inferred from immunohistochemical data was confirmed by Western blots. We conclude that PA-IR in the rat retina shows an underlying circadian rhythm that is enhanced by cyclic light. The regulation may involve translocation of the protein between cell compartments and/or new protein synthesis.This study was supported by an OTKA grant (T 34160), NIH grants NS 37919 (R.S.) and ET 03570, NSF grant IBN-96418886 (R.S.), and grants from the Helen Hoffritz Charitable Trust and Research to Prevent Blindness, Inc. R.G. was also in receipt of a János Bolyai fellowship     

PRMT3 is a ribosomal protein methyltransferase that affects the cellular levels of ribosomal subunits

The mammalian protein arginine methyltransferase 3 (PRMT3) catalyzes the formation of asymmetric (type I) dimethylarginine in vitro. As yet, natural substrates and cellular pathways modulated by PRMT3 remain unknown. Here, we have identified an ortholog of PRMT3 in fission yeast. Tandem affinity purification of fission yeast PRMT3 coupled with mass spectrometric protein identification revealed that PRMT3 associates with components of the translational machinery. We identified the 40S ribosomal protein S2 as the first physiological substrate of PRMT3. In addition, a fraction of yeast and human PRMT3 cosedimented with free 40S ribosomal subunits, as determined by sucrose gradient velocity centrifugation. The activity of PRMT3 is not essential since prmt3-disrupted cells are viable. Interestingly, cells lacking PRMT3 showed an accumulation of free 60S ribosomal subunits resulting in an imbalance in the 40S:60S free subunits ratio; yet pre-rRNA processing appeared to occur normally. Our results identify PRMT3 as the first type I ribosomal protein arginine methyltransferase and suggest that it regulates ribosome biosynthesis at a stage beyond pre-rRNA processing.     

Synthesis and GABA receptor potency of 3-thiomethyl-4-(hetero)aryl-5-amino-1-phenylpyrazoles

A convenient synthetic route to novel 4-arylpyrazoles is described. The potential for insecticidal activity through GABA channel blockage by this series of compounds, as well as their selectivity for insect versus mammalian receptors, are explored through in vitro and in vivo assays.     

Mechanobiology of cartilage: how do internal and external stresses affect mechanochemical transduction and elastic energy storage?

 Articular cartilage is a multilayered structure that lines the surfaces of all articulating joints. It contains cells, collagen fibrils, and proteoglycans with compositions that vary from the surface layer to the layer in contact with bone. It is composed of several zones that vary in structure, composition, and mechanical properties. In this paper we analyze the structure of the extracellular matrix found in articular cartilage in an effort to relate it to the ability of cartilage to store, transmit, and dissipate mechanical energy during locomotion. Energy storage and dissipation is related to possible mechanisms of mechanochemical transduction and to changes in cartilage structure and function that occur in osteoarthritis. In addition, we analyze how passive and active internal stresses affect mechanochemical transduction in cartilage, and how this may affect cartilage behavior in health and disease. Received: 8 February 2002 / Accepted: 9 July 2002     

Gates and oscillators: a network model of the brain clock

The suprachiasmatic nuclei (SCN) control circadian oscillations of physiology and behavior. Measurements of electrical activity and of gene expression indicate that these heterogeneous structures are composed of both rhythmic and nonrhythmic cells. A fundamental question with regard to the organization of the circadian system is how the SCN achieve a coherent output while their constituent independent cellular oscillators express a wide range of periods. Previously, the consensus output of individual oscillators had been attributed to coupling among cells. The authors propose a model that incorporates nonrhythmic "gate" cells and rhythmic oscillator cells with a wide range of periods, that neither requires nor excludes a role for interoscillator coupling. The gate provides daily input to oscillator cells and is in turn regulated (directly or indirectly) by the oscillator cells. In the authors' model, individual oscillators with initial random phases are able to self-assemble so as to maintain cohesive rhythmic output. In this view, SCN circuits are important for self-sustained oscillation, and their network properties distinguish these nuclei from other tissues that rhythmically express clock genes. The model explains how individual SCN cells oscillate independently and yet work together to produce a coherent rhythm.     

Lethal injection,autonomy and the proper ends of medicine

Gerald Dworkin has argued that it is inconsistent with the proper ends of medicine for a physician to participate in an execution by lethal injection. He does this by proposing a principle by which we are to judge whether an action is consistent with the proper ends of medicine. I argue: (a) that this principle, if valid, does not show that it is inconsistent with the proper ends of medicine for a physician to participate in an execution by lethal injection; and (b) that this principle is not valid, and this is because it mistakenly views the promotion of patient autonomy as one of the proper ends of medicine. Rather, I propose, we should view respect for a patient's autonomy as a constraint on the pursuit of the proper ends of medicine, rather than as one of the proper ends itself. With this revised understanding of the proper ends of medicine, we can conclude that it is inconsistent with the proper ends of medicine for a physician to participate in an execution by lethal injection.     

The structure and oligomerization of the yeast arginine methyltransferase, Hmt1

Protein methylation at arginines is ubiquitous in eukaryotes and affects signal transduction, gene expression and protein sorting. Hmt1/Rmt1, the major arginine methyltransferase in yeast, catalyzes methylation of arginine residues in several mRNA-binding proteins and facilitates their export from the nucleus. We now report the crystal structure of Hmt1 at 2.9 A resolution. Hmt1 forms a hexamer with approximate 32 symmetry. The surface of the oligomer is dominated by large acidic cavities at the dimer interfaces. Mutation of dimer contact sites eliminates activity of Hmt1 both in vivo and in vitro. Mutating residues in the acidic cavity significantly reduces binding and methylation of the substrate Npl3.