Induction of cellular senescence in immortalized cells by human chromosome 1

The control of cellular senescence by specific human chromosomes was examined in interspecies cell hybrids between diploid human fibroblasts and an immortal, Syrian hamster cell line. Most such hybrids exhibited a limited life span comparable to that of the human fibroblasts, indicating that cellular senescence is dominant in these hybrids. Karyotypic analyses of the hybrid clones that did not senesce revealed that all these clones had lost both copies of human chromosome 1, whereas all other human chromosomes were observed in at least some of the immortal hybrids. The application of selective pressure for retention of human chromosome 1 to the cell hybrids resulted in an increased percentage of hybrids that senesced. Further, the introduction of a single copy of human chromosome 1 to the hamster cells by microcell fusion caused typical signs of cellular senescence. Transfer of chromosome 11 had no effect on the growth of the cells. These findings indicate that human chromosome 1 may participate in the control of cellular senescence and further support a genetic basis for cellular senescence.     

Atomic and molecular manipulation with the scanning tunneling microscope

The prospect of manipulating matter on the atomic scale has fascinated scientists for decades. This fascination may be motivated by scientific and technological opportunities, or from a curiosity about the consequences of being able to place atoms in a particular location. Advances in scanning tunneling microscopy have made this prospect a reality; single atoms can be placed at selected positions and structures can be built to a particular design atom-by-atom. Atoms and molecules may be manipulated in a variety of ways by using the interactions present in the tunnel junction of a scanning tunneling microscope. Some of these recent developments and some of the possible uses of atomic and molecular manipulation as a tool for science are discussed.     

Tumor formation dependent on proteoglycan biosynthesis

The role proteoglycans play in tumor formation was examined by measuring the tumorigenicity of proteoglycan-deficient Chinese hamster ovary cell mutants in nude mice. When 10(7) cells were injected subcutaneously, mutants with less than about 15% of the wild-type level of proteoglycan synthesis did not produce tumors. Mutants defective in the synthesis of heparan sulfate proteoglycans also did not form tumors, whereas mutants with altered chondroitin sulfate proteoglycans were tumorigenic. Tumors arose from mixtures of wild-type and nontumorigenic mutant cells and contained both cell types, suggesting that wild-type cell proteoglycans enabled mutant cells to survive. The failure of heparan sulfate-deficient mutants to form tumors depended on the ability of the host to mount a B cell-mediated immune reaction.     

The crystal structure of a T cell receptor in complex with peptide and MHC class II

The crystal structure of a complex involving the D10 T cell receptor (TCR), 16-residue foreign peptide antigen, and the I-Ak self major histocompatibility complex (MHC) class II molecule is reported at 3.2 angstrom resolution. The D10 TCR is oriented in an orthogonal mode relative to its peptide-MHC (pMHC) ligand, necessitated by the amino-terminal extension of peptide residues projecting from the MHC class II antigen-binding groove as part of a mini beta sheet. Consequently, the disposition of D10 complementarity-determining region loops is altered relative to that of most pMHCI-specific TCRs; the latter TCRs assume a diagonal orientation, although with substantial variability. Peptide recognition, which involves P-1 to P8 residues, is dominated by the Valpha domain, which also binds to the class II MHC beta1 helix. That docking is limited to one segment of MHC-bound peptide offers an explanation for epitope recognition and altered peptide ligand effects, suggests a structural basis for alloreactivity, and illustrates how bacterial superantigens can span the TCR-pMHCII surface.     

Dissemination of precision farming in Germany: acceptance, adoption, obstacles, knowledge transfer and training activities

The adoption of precision farming (PF) was studied on the basis of personal interviews conducted at several agricultural exhibitions in Germany. Between 6.65% and 11% of the interviewed farmers used PF. The majority used data collection techniques such as GPS-based area measurement and soil sampling rather than variable rate application techniques such as site-specific sowing and fertilising. Roughly half the farmers interviewed knew about PF. About 7–10% of them intended to start using PF in the future. The results indicated that a large number of farmers did not even know what PF meant. In order to get more insight into this situation, several interviews were conducted with farmers already using PF techniques. A further study in 2005 of PF education in Germany indicated that, especially at vocational and technical schools, the subject was only covered to a small extent although the aim was to give a better coverage in future. At higher education levels, such as at universities and technical colleges, the teaching of PF was clearly better established. In order to promote awareness of PF among farmers, information and teaching materials adapted to the relevant educational levels were developed and tried out at training events. The main topics addressed were parallel tracking systems, site-specific nitrogen fertilising, yield mapping in grain production and the use of PDAs in crop farming. Finally, preliminary survey results are presented showing how knowledge about PF can best lead to its adoption and transfer into daily practice.     

Radar images of Mars

Full disk images of Mars have been obtained with the use of the Very Large Array (VLA) to map the radar reflected flux density. The transmitter system was the 70-m antenna of the Deep Space Network at Goldstone, California. The surface of Mars was illuminated with continuous wave radiation at a wavelength of 3,5 cm. The reflected energy was mapped in individual 12-minute snapshots with the VLA in its largest configuration; fringe spacings as small as 67 km were obtained. The images reveal near-surface features including a region in the Tharsis volcano area, over 2000 km in east-west extent, that displayed no echo to the very low level of the radar system noise. The feature, called Stealth, is interpreted as a deposit of dust or ash with a density less than about 0.5 gram per cubic centimeter and free of rocks larger than 1 cm across. The deposit must be several meters thick and may be much deeper. The strongest reflecting geological feature was the south polar ice cap, which was reduced in size to the residual south polar ice cap at the season of observation. The cap image is interpreted as arising from nearly pure CO(2) or H(2)O ice with a small amount of martian dust (less than 2 percent by volume) and a depth greater than 2 to 5 m. Only one anomalous reflecting feature was identified outside of the Tharsis region, although the Elysium region was poorly sampled in this experiment and the north pole was not visible from Earth.