The effects of ageing and chronic dietary restriction on in vivo hepatic protein synthesis in the rat

Hepatic growth and protein synthesis in vivo was studied with age in ad libitum-fed and dietary restricted rats in which the mean and maximum lifespan was significantly extended. Livers from underfed rats showed significantly lower DNA, RNA and protein contents, and total protein synthesis. The fractional rate of synthesis although initially depressed by restricted feeding, showed no consistent trend with age when compared with control values. The lower fractional rate of synthesis observed in livers from dietary restricted rats at 7 weeks of age is attributable to a significant decrease in ribosomal capacity, with no effect on ribosomal activity being evident. Liver tissue from rats fed ad libitum demonstrated a progressive loss of translational efficiency with age which was delayed by chronic dietary restriction.     

Two-dimensional time-resolved X-ray diffraction studies of live isometrically contracting frog sartorius muscle

Summary Results were obtained from contracting frog muscles by collecting high quality time-resolved, two-dimensional, X-ray diffraction patterns at the British Synchrotron Radiation Source (SERC, Daresbury, Laboratory). The structural transitions associated with isometric tension generation were recorded under conditions in which the three-dimensional order characteristic of the rest state is either present or absent. In both cases, new layer lines appear during tension generation, subsequent to changes from activation events in the filaments. Compared with the decorated actin layer lines of the rigor state, the spacings of the new layer lines are similar whereas their intensities differ substantially. We conclude that in contracting muscle an actomyosin complex is formed whose structure is not like that in rigor, although it is possible that the interacting sites are the same. Transition from rest to plateau of tension is accompanied by approximately 1.6% increase in the axial spacing of the myosin layer lines. This is explained as arising from the axial disposition of the interacting myosin heads in the actomyosin complex. Model calculations are presented which support this view. We argue that in a situation where an actomyosin complex is formed during contraction, one cannot describe the diffraction features as being either thick or thin filament based. Accordingly, the layer lines seen during tension generation are referred to as actomyosin layer lines. It is shown that these layer lines can be indexed as submultiples of a minimum axial repeat of approximately 218.7 nm. After lattice disorder effects are taken into account, the intensity increases on the 15th and 21st AM layer lines at spacings of approximately 14.58 and 10.4 nm respectively, show the same time course as tension rise. However, the time course of the intensity increase of the other actomyosin layer lines and of the spacing change (which is the same for both phenomena) shows a substantial lead over tension rise. These findings suggest that the actomyosin complex formed prior to tension rise is a non-tension-generating state and that this is followed by a transition of the complex to a tension-generating state. The intensity increase in the 15th actomyosin layer line, which parallels tension rise, can be accounted for assuming that in the tension-generating state the attached heads adopt (axially) a more perpendicular orientation with respect to the muscle axis than is seen at rest or in the non-tension-generating state. This suggests the existence of at least two structurally distinct interacting myosin head conformations. The results of comparing the meridional intensities between the myosin layer lines at rest and the actomyosin layer lines at the plateau of tension (measured to a resolution of approximately 2.6 nm) are interpreted to indicate that the majority of the myosin heads in the actomyosin complex do not perform random axial rotations with a mean value greater than approximately 3.0 nm. From this we conclude that the extent of axial order in the interacting heads must be at least as high as is that of resting heads.     

Composite activities on B cells of products released by T cells activated by concanavalin A.

Supernatants from murine spleen cells cultured for 48 h in the presence of 1.0 μg of concanavalin A (Con A) induced polyclonal antibody synthesis in cultures of spleen cells from both normal and athymic mice in the absence of exogeneous antigen. Moreover, the Con A-induced supernatant rescued B cells which had been rendered unresponsive by a tolerogen [haptenated poly(D Glu,D Lys)]. The capacity of the supernatant to induce cell proliferation was studied under both high and low-density culture conditions. In contrast to antibody secretion, proliferation was only detectable in low-density cultures. The Con A-induced supernatant also contained suppressive components, since the primary anti-sheep red blood cell (SRBC) response was markedly suppressed when the antigen added to cultures consisted of SRBC which had previously been used for absorbing the supernatants. Absorbed supernatants displayed enhanced helper activity indicating that only the suppressor component was removable by antigen. The suppressive component was eluted from erythrocytes with ammonium thiocyanate and was itself strongly suppressive when added to cultures with fresh erythrocytes. Furthermore, the suppressive component proved to be highly antigen-specific, as the SRBC-absorbed factor did not affect the response to horse RBC. The results indicate that supernatants from Con A-activated spleen cells contain both helper and suppressor factors, the latter having easily demonstrable antigen specificity. They further suggest that a nonantigen-derived signal is sufficient to trigger both proliferation and antibody synthesis by B cells.     

Dynamic imaging of the lungs using x-ray phase contrast

High quality real-time imaging of lungs in vivo presents considerable challenges. We demonstrate here that phase contrast x-ray imaging is capable of dynamically imaging the lungs. It retains many of the advantages of simple x-ray imaging, whilst also being able to map weakly absorbing soft tissues based on refractive index differences. Preliminary results reported herein show that this novel imaging technique can identify and locate airway liquid and allows lung aeration in newborn rabbit pups to be dynamically visualized.     

NKG2D blockade prevents autoimmune diabetes in NOD mice

NKG2D is an activating receptor on CD8(+) T cells and NK cells that has been implicated in immunity against tumors and microbial pathogens. Here we show that RAE-1 is present in prediabetic pancreas islets of NOD mice and that autoreactive CD8(+) T cells infiltrating the pancreas express NKG2D. Treatment with a nondepleting anti-NKG2D monoclonal antibody (mAb) during the prediabetic stage completely prevented disease by impairing the expansion and function of autoreactive CD8(+) T cells. These findings demonstrate that NKG2D is essential for disease progression and suggest a new therapeutic target for autoimmune type I diabetes.     

Cell-free fetal DNA and intact fetal cells in maternal blood circulation: implications for first and second trimester non-invasive prenatal diagnosis

Both intact fetal cells as well as cell-free fetal DNA are present in the maternal circulation and can be recovered for non-invasive prenatal genetic diagnosis. Although methods for enrichment and isolation of rare intact fetal cells have been challenging, diagnosis of fetal chromosomal aneuploidy including trisomy 21 in first- and second-trimester pregnancies has been achieved with a 50-75% detection rate. Similarly, cell-free fetal DNA can be reliably recovered from maternal plasma and assessed by quantitative PCR to detect fetal trisomy 21 and paternally derived single gene mutations. Real-time PCR assays are robust in detecting low-level fetal DNA concentrations, with sensitivity of approximately 95-100% and specificity near 100%. Comparing intact fetal cell versus cell-free fetal DNA methods for non-invasive prenatal screening for fetal chromosomal aneuploidy reveals that the latter is at least four times more sensitive. These preliminary results do not support a relationship between frequency of intact fetal cells and concentration of cell-free fetal DNA. The above results imply that the concentration of fetal DNA in maternal plasma may not be dependent on circulating intact fetal cells but rather be a product of growth and cellular turnover during embryonic or fetal development.