Trichobezoar.

Teaching point: A trichobezoar is a relatively rare entity that presents on imaging as a heterogeneous and multilayered mass molded by the stomach lumen.

JAK2 V617F constitutive activation requires JH2 residue F595: a pseudokinase domain target for specific inhibitors.

The JAK2 V617F mutation present in over 95% of Polycythemia Vera patients and in 50% of Essential Thrombocythemia and Primary Myelofibrosis patients renders the kinase constitutively active. In the absence of a three-dimensional structure for the full-length protein, the mechanism of activation of JAK2 V617F has remained elusive. In this study, we used functional mutagenesis to investigate the involvement of the JH2 alphaC helix in the constitutive activation of JAK2 V617F. We show that residue F595, located in the middle of the alphaC helix of JH2, is indispensable for the constitutive activity of JAK2 V617F. Mutation of F595 to Ala, Lys, Val or Ile significantly decreases the constitutive activity of JAK2 V617F, but F595W and F595Y are able to restore it, implying an aromaticity requirement at position 595. Substitution of F595 to Ala was also able to decrease the constitutive activity of two other JAK2 mutants, T875N and R683G, as well as JAK2 K539L, albeit to a lower extent. In contrast, the F595 mutants are activated by erythropoietin-bound EpoR. We also explored the relationship between the dimeric conformation of EpoR and several JAK2 mutants. Since residue F595 is crucial to the constitutive activation of JAK2 V617F but not to initiation of JAK2 activation by cytokines, we suggest that small molecules that target the region around this residue might specifically block oncogenic JAK2 and spare JAK2 wild-type.

Turnover of glycosomes during life-cycle differentiation of Trypanosoma brucei.

Protozoan Kinetoplastida, a group that comprises the pathogenic Trypanosoma brucei, compartmentalize several metabolic systems such as the major part of the glycolytic pathway, in multiple peroxisome-like organelles, designated glycosomes. Trypanosomes have a complicated life cycle, involving two major, distinct stages living in the mammalian bloodstream and several stages inhabiting different body parts of the tsetse fly. Previous studies on non-differentiating trypanosomes have shown that the metabolism and enzymatic contents of glycosomes in bloodstream-form and cultured procyclic cells, representative of the stage living in the insect's midgut, differ considerably. In this study, the morphology of glycosomes and their position relative to the lysosome were followed, as were the levels of some glycosomal enzymes and markers for other subcellular compartments, during the differentiation from bloodstream-form to procyclic trypanosomes. Our studies revealed a small tendency of glycosomes to associate with the lysosome when a population of long-slender bloodstream forms differentiated into short-stumpy forms which are pre-adapted to live in the fly. The same phenomenon was observed during the short-stumpy to procyclic transformation, but then the process was fast and many more glycosomes were associated with the dramatically enlarged degradation organelle. The observations suggested an efficient glycosome turnover involving autophagy. Changes observed in the levels of marker enzymes are consistent with the notion that, during differentiation, glycosomes with enzymatic contents specific for the old life-cycle stage are degraded and new glycosomes with different contents are synthesized, causing that the metabolic repertoire of trypanosomes is, at each stage, optimally adapted to the environmental conditions encountered.

Metabolic functions of glycosomes in trypanosomatids.

Protozoan Kinetoplastida, including the pathogenic trypanosomatids of the genera Trypanosoma and Leishmania, compartmentalize several important metabolic systems in their peroxisomes which are designated glycosomes. The enzymatic content of these organelles may vary considerably during the life-cycle of most trypanosomatid parasites which often are transmitted between their mammalian hosts by insects. The glycosomes of the Trypanosoma brucei form living in the mammalian bloodstream display the highest level of specialization; 90% of their protein content is made up of glycolytic enzymes. The compartmentation of glycolysis in these organelles appears essential for the regulation of this process and enables the cells to overcome short periods of anaerobiosis. Glycosomes of all other trypanosomatid forms studied contain an extended glycolytic pathway catalyzing the aerobic fermentation of glucose to succinate. In addition, these organelles contain enzymes for several other processes such as the pentose-phosphate pathway, beta-oxidation of fatty acids, purine salvage, and biosynthetic pathways for pyrimidines, ether-lipids and squalenes. The enzymatic content of glycosomes is rapidly changed during differentiation of mammalian bloodstream-form trypanosomes to the forms living in the insect midgut. Autophagy appears to play an important role in trypanosomatid differentiation, and several lines of evidence indicate that it is then also involved in the degradation of old glycosomes, while a population of new organelles containing different enzymes is synthesized. The compartmentation of environment-sensitive parts of the metabolic network within glycosomes would, through this way of organelle renewal, enable the parasites to adapt rapidly and efficiently to the new conditions.

High-resolution sonography of a scrotal abscess in a 2-week-old infant.

Scrotal abscess in infancy is rare and, in an otherwise healthy infant, an unexpected pathology. We present a 2-week-old boy with a unilateral scrotal swelling, imaged by high-resolution sonography. Sonography with colour Doppler demonstrated an encapsulated heterogeneous mass in the left scrotum with surrounding hyperaemia and a hypervascular spermatic cord. The testis was not demonstrable with full certainty and surgical exploration was undertaken. A scrotal abscess, indistinguishable from the testis and epididymis, had to be resected and on histology was found to have originated from the tunica vaginalis. Urogenital investigations did not reveal any associated abnormality and the final diagnosis was idiopathic scrotal abscess. High-resolution sonographic features with colour Doppler of a scrotal swelling can suggest an abscess and help determine appropriate therapy.

Autophagy and related processes in trypanosomatids: insights from genomic and bioinformatic analyses.

The targeting in eukaryotic cells of cellular components to the lysosome or vacuole for degradation is called autophagy. Not only cytoplasmic macromolecules and bulk cytoplasm are subject to this process; entire organelles such as peroxisomes can be degraded. Autophagy of peroxisomes is called pexophagy. Unpublished evidence suggests that the analogous processing of glycosomes in the protozoan kinetoplastids occurs. Taking advantage of the (near-) complete status of three trypanosomatid genomes, a census of components of autophagy and related processes has been undertaken in these organisms. Simple database searches were supplemented by more advanced analyses where necessary. At most, only half of the components characterized in yeasts are present in trypanosomatids suggesting an unexpectedly streamlined version of autophagy occurs in these organisms. The cytoplasm-to-vacuole targeting (Cvt) system for delivery of proteins to the vacuole seems entirely absent in trypanosomatids. The accuracy of the census is supported by the coordinated absence of functionally linked components such as the conjugation system involving ATG12, ATG5, ATG10 and ATG16 that acts at the step of vesicle expansion and completion. Overall, the results are consistent with a scenario of taxon-specific addition of components to a minimal core, a hypothesis that should be readily testable by further genomic surveys allied to laboratory experiments. A bioinformatics analysis of the trypanosomatidal proteins was carried out, highlighting the paucity of information available regarding their structures and enabling prioritization of targets for future structural biology work.

Peroxisomes, glyoxysomes and glycosomes (review).

Peroxisomes, glyoxysomes and glycosomes are related organelles found in different organisms. The morphology and enzymic content of the different members of this organelle family differ considerably, and may also be highly dependent on the cell's environmental conditions or life cycle. However, all peroxisome-like organelles have in common a number of characteristic enzymes or enzyme systems, notably enzymes dealing with reactive oxygen species. All organelles of the family follow essentially the same route of biogenesis, but with species-specific differences. Sets of proteins called peroxins are involved in different aspects of the formation and proliferation of peroxisomes such as import of proteins in the organellar matrix, insertion of proteins in the membrane, etc. In different eukaryotic lineages these functions are carried out by often--but not always--homologous yet poorly conserved peroxins. The process of biogenesis and the nature of the proteins involved suggest that all members of the peroxisome family evolved from a single organelle in an ancestral eukaryotic cell. This original peroxisome was possibly derived from a cellular membrane system such as the endoplasmic reticulum. Most of the organism-specific functions of the extant organelles have been acquired later in evolution.

Supine/left decubitus scanning: a valuable alternative to supine/prone scanning in CT colonography.

The purpose was to evaluate supine/left decubitus as an alternative to supine/prone scanning in computed tomographic colonography (CT colonography). Fifty patients were randomised to supine/prone, another 50 to supine/left decubitus scanning. Patients were scanned using a single-slice CT scanner. The colon was divided into eight segments. Comparisons of distension, breathing artefacts, residus and polyp detection were made between the two groups as well as between the different positions. Adequate distension was found in approximately 85, 97 and 95% of segments in the supine, prone and left decubitus positions, respectively. Combined scanning increased the percentage of adequate distension to 98.5% for prone-supine and 97.7% for left decubitus-supine scanning ( P<0.0005 compared to supine, P=0.001 compared to left decubitus and P=0.046 compared to prone scanning). Absence of residual material was found in approximately 62.7, 69.7 and 64% of segments in the supine, prone and left decubitus positions, respectively. Combined scanning increased this percentage to approximately 99% for both groups. No significant differences towards distension or residual material were found between combined supine-prone or supine-left decubitus scanning. In the supine-prone group, combined scanning additionally revealed four lesions and improved conspicuity in two cases of stalked polyps. In the supine-left decubitus group, combined scanning additionally revealed two lesions and improved conspicuity in one stalked polyp. There were significantly fewer breathing artefacts with left decubitus scanning than prone scanning ( P=0.005). A strong positive correlation was found between breathing artefacts and the age of patients in both patient groups. Colonic distension and preparation is improved by using supine and prone or supine and left decubitus scanning in combination, with a subsequent improved polyp detection. There were no significant differences between the two scanning protocols. Prone scanning, however, is hampered by breathing artefacts, especially in the elderly. Therefore, supine-left decubitus scanning is considered a valuable alternative to supine-prone scanning for the elderly.