United we sense, divided we fail: context-driven perception of ambiguous visual stimuli

Ambiguous visual stimuli provide the brain with sensory information that contains conflicting evidence for multiple mutually exclusive interpretations. Two distinct aspects of the phenomenological experience associated with viewing ambiguous visual stimuli are the apparent stability of perception whenever one perceptual interpretation is dominant, and the instability of perception that causes perceptual dominance to alternate between perceptual interpretations upon extended viewing. This review summarizes several ways in which contextual information can help the brain resolve visual ambiguities and construct temporarily stable perceptual experiences. Temporal context through prior stimulation or internal brain states brought about by feedback from higher cortical processing levels may alter the response characteristics of specific neurons involved in rivalry resolution. Furthermore, spatial or crossmodal context may strengthen the neuronal representation of one of the possible perceptual interpretations and consequently bias the rivalry process towards it. We suggest that contextual influences on perceptual choices with ambiguous visual stimuli can be highly informative about the neuronal mechanisms of context-driven inference in the general processes of perceptual decision-making.     

Repair of UV-induced pyrimidine dimers in the individual genes Gart, Notch and white from Drosophila melanogaster cell lines.

The excision repair of UV-induced pyrimidine dimers was investigated in three genes: Gart, Notch and white in a permanent Drosophila cell line Kc, derived from wild type Drosophila melanogaster embryonic cells. In this cell line Gart and Notch are actively transcribed, whereas white is not expressed. In all three genes UV-induced pyrimidine dimers were removed with the same rate and to the same extent: 60% removal within 16 hours, up to 80-100% in 24 hours after irradiation with 10 or 15 J/m2 UV. These kinetics are similar to the time course of dimer removal measured in the genome overall. No difference in repair of the inactive white locus compared to the active Gart and Notch genes was found. Similar results were obtained using a different wild type cell line, SL2, although repair appeared to be somewhat slower in this cell line. The results are discussed with respect to the data found for gene specific repair in other eukaryotic systems.     

The role of the ACTH receptor in adrenal tumors: identification of a novel microsatellite marker.

In vitro, the growth inhibiting effect of ACTH on adrenocortical cells is well documented, even though there are reports of opposite effects under defined cell culture conditions. In vivo, activation of the ACTH receptor (ACTHR) has a trophic effect on the adrenal cortex, while the effects on proliferation are still under discussion, especially since other POMC derived peptides have been characterized. However, ACTH is thought to act as a differentiation factor with inhibiting effects on tumor growth. In undifferentiated adrenocortical carcinomas, ACTHR expression is frequently lost, which is associated with extensive tumor growth. We describe a new microsatellite marker within the intron of the ACTHR gene termed ACTHRint1. In a series of 114 patients with various adrenal and non-adrenal tumors, the rate of heterozygosity was 100 %. Only one out of 57 patients with adrenocortical adenoma showed LOH at the ACTHR locus, whereas 4 of 10 carcinomas had loss of one allele. Patients suffering from tumors with LOH showed a more aggressive disease course and had earlier recurrences with poor prognosis. These data confirm earlier findings that adrenocortical carcinomas frequently show loss of ACTHR expression, which is associated with a more aggressive tumor growth. However, whether the ACTHR is directly involved in tumor growth or acts a marker of differentiation that is lost in more advanced tumor stages is still not clear.     

New insight into the dynamic properties and the active site architecture of H-Ras p21 revealed by X-ray crystallography at very high resolution

Background  

In kinetic crystallography, the usually static method of X-ray diffraction is expanded to allow time-resolved analysis of conformational rearrangements in protein structures. To achieve this, reactions have to be triggered within the protein crystals of interest, and optical spectroscopy can be used to monitor the reaction state. For this approach, a modified form of H-Ras p21 was designed which allows reaction initiation and fluorescence readout of the initiated GTPase reaction within the crystalline state. Rearrangements within the crystallized protein due to the progressing reaction and associated heterogeneity in the protein conformations have to be considered in the subsequent refinement processes.     

A patient with an interstitial deletion in Xp22.3 locates the gene for X-linked recessive chondrodysplasia punctata to within a one megabase interval

A male patient carrying an interstitial deletion in Xp22.3 and affected by Kallmann syndrome, X-linked ichthyosis and mental retardation, but without chondrodysplasia punctata or short stature, was investigated with molecular probes from the distal Xp22.3 region. By means of a novel probe, M115, from the relevant region, the distal deletion breakpoint was shown to be between 3.18 and 3.57 Mb from Xptel. As the patient is not affected by X-linked recessive chondrodysplasia punctata, the gene for this disease can therefore be located to within an interval of less than one megabase proximal to the pseudoautosomal boundary. If the chondrodysplasia punctata gene is associated with a CpG island, this leaves only two islands at 2760 and 3180 kb from the Xp telomere as the most promising candidate sites for this gene.