Cathepsin S dominates autoantigen processing in human thymic dendritic cells

The interaction of developing thymocytes with peptide-MHC complexes on thymic antigen presenting cells (APC) is crucial for T cell development, both for positive selection of "useful" thymocytes as well as negative selection of autoreactive thymocytes to prevent autoimmunity. The peptides presented on MHC II molecules are generated by lysosomal proteases such as the cathepsins. At the same time, lysosomal proteases will also destroy other potential T cell epitopes from self-antigens. This will lead to a lack of presentation on negatively selecting thymic antigen presenting cells and consequently, escape of autoreactive T cells recognizing these epitopes. In order to understand the processes that govern generation or destruction of self-epitopes in thymic APC, we studied the antigen processing machinery and epitope processing in the human thymus. We find that each type of thymic APC expresses a different signature of lysosomal proteases, providing indirect evidence that positive and negative selection of CD4(+) T cells might occur on different sets of peptides, in analogy to what has been proposed for CD8(+) T cells. We also find that myeloid dendritic cells (DC) are more efficient in processing autoantigen than plasmacytoid DC. In addition, we observed that cathepsin S plays a central role in processing of the autoantigens myelin basic protein and proinsulin in thymic dendritic cells. Cathepsin S destroyed a number of known T cell epitopes, which would be expected to result in lack of presentation and consequently, escape of autoreactive T cells. Cathepsin S therefore appears to be an important factor that influences selection of autoreactive T cells.

The bona fide mouse U7 snRNA gene maps to a different chromosome than two U7 pseudogenes.

The U7 snRNA, together with both common and unique snRNP proteins, forms the U7 snRNP particle. This particle is a major component of the 3' processing machinery that converts histone pre-mRNA into mature mRNA in the eukaryotic nucleus. The genes for many snRNAs are present in multiple copies and often have many pseudogenes. Southern blot experiments using U7 oligonucleotide and gene probes have identified only one strongly hybridizing band and three weakly hybridizing bands in mouse genomic DNA. Previously, two laboratories isolated genomic clones encoding one functional U7 gene and three presumed pseudogenes. Since all the genes were isolated on separate, nonoverlapping genomic fragments, the four genes are not tightly clustered in the mouse genome. In this study, we use fluorescence in situ hybridization to determine the chromosomal locations of these clones and their possible linkage to histone loci. Two of the pseudogenes map to mouse Chromosome 1, but are many megabases apart, whereas the active U7 gene maps to Chromosome 6. Possible mechanisms for this localization pattern are discussed.

Nectar distribution and its relation to food quality in honeybee (Apis mellifera) colonies

In honeybees (Apis niellifera), the process of nectar collection is considered a straightforward example of task partitioning with two subtasks or two intersecting cycles of activity: (1) foraging and (2) storing of nectar, linked via its transfer between foragers and food processors. Many observations suggest, however, that nectar colleclion and processing in honeybees is a complex process, involving workers of other sub-castes and depending on variables such as resource profitability or the amount of stored honey. It has been observed that food processor bees often distribute food to other hive bees after receiving it from incoming foragers, instead of storing it immediately in honey cells. While there is little information about the sub-caste affiliation and the behaviour of these second-order receivers, this stage may be important for the rapid distribution of nutrients and related information. To investigate the identity of these second-order receivers, we quantified behaviours following nectar transfer and compared these behaviours with the behaviour of average worker hive-bees. Furthermore, we tested whether food quality (sugar concentration) affects the behaviour of the second-order receivers. Of all identified second-order receivers, 59.3% performed nurse duties, 18.5% performed food-processor duties and 22.2% performed forager duties. After food intake, these bees were more active, had more trophallaxes (especially offering contacts) compared to average workers and they were found mainly in the brood area, independent of food quality. Our results show that the liquid food can be distributed rapidly among many bees of the three main worker sub-castes, without being stored in honey cells first. Furthermore, the results suggest that the rapid distribution of food partly depends on the high activity of second-order receivers.

Food Volume Computation for Self Dietary Assessment Applications

There is great demand for easily-accessible, user-friendly dietary self-management applications. Yet accurate, fully-automatic estimation of nutritional intake using computer vision methods remains an open research problem. One key element of this problem is the volume estimation, which can be computed from 3D models obtained using multi-view geometry. The paper presents a computational system for volume estimation based on the processing of two meal images. A 3D model of the served meal is reconstructed using the acquired images and the volume is computed from the shape. The algorithm was tested on food models (dummy foods) with known volume and on real served food. Volume accuracy was in the order of 90 %, while the total execution time was below 15 seconds per image pair. The proposed system combines simple and computational affordable methods for 3D reconstruction, remained stable throughout the experiments, operates in near real time, and places minimum constraints on users.

CstF64: cell cycle regulation and functional role in 3' end processing of replication-dependent histone mRNAs.

The 3' end processing of animal replication-dependent histone mRNAs is activated during G1/S-phase transition. The processing site is recognized by stem-loop binding protein and the U7 snRNP, but cleavage additionally requires a heat-labile factor (HLF), composed of cleavage/polyadenylation specificity factor, symplekin, and cleavage stimulation factor 64 (CstF64). Although HLF has been shown to be cell cycle regulated, the mechanism of this regulation is unknown. Here we show that levels of CstF64 increase toward the S phase and its depletion affects histone RNA processing, S-phase progression, and cell proliferation. Moreover, analyses of the interactions between CstF64, symplekin, and the U7 snRNP-associated proteins FLASH and Lsm11 indicate that CstF64 is important for recruiting HLF to histone precursor mRNA (pre-mRNA)-resident proteins. Thus, CstF64 is central to the function of HLF and appears to be at least partly responsible for its cell cycle regulation. Additionally, we show that misprocessed histone transcripts generated upon CstF64 depletion mainly accumulate in the nucleus, where they are targets of the exosome machinery, while a small cytoplasmic fraction is partly associated with polysomes.