Polysialic acid (PSA) is a dynamically regulated product of post-translational modification of the neural cell adhesion molecule, NCAM. Presence of the large anionic carbohydrate modulates NCAM binding properties and, by increasing the intercellular space, influences interactions between other cell surface molecules. PSA expression underlies cell type- and developmental-specific alterations and correlates with stages of cellular motility. In the adult, PSA becomes restricted to regions of permanent neural plasticity and regenerating neural and muscle tissues. Recent data implicate its important function in spatial learning and memory, and in tumour biology. Here we describe the molecular characterization of polysialyltransferase-1, the key enzyme of eukaryotic PSA synthesis. In reconstitution experiments, the newly cloned enzyme induces PSA synthesis in all NCAM-expressing cell lines. Our data therefore represent convincing evidence that the polycondensation of alpha-2,8-linked sialic acids in mammals is the result of a single enzymatic activity and provide a new basis for studying the functional role of PSA in neuro- and tumour biology.

To cite this article: Kurniawan NA, Grimbergen J, Koopman J, Koenderink GH. Factor XIII stiffens fibrin clots by causing fiber compaction. 2014; 12: 1687-96. Summary. Background: Factor XIII-induced cross-linking has long been associated with the ability of fibrin blood clots to resist mechanical deformation, but how FXIII can directly modulate clot stiffness is unknown. Objectives and Methods: We hypothesized that FXIII affects the selfassembly of fibrin fibers by altering the lateral association between protofibrils. To test this hypothesis, we studied the cross-linking kinetics and the structural evolution of the fibers and clots during the formation of plasmaderived and recombinant fibrins by using light scattering, and the response of the clots to mechanical stresses by using rheology. Results: We show that the lateral aggregation of fibrin protofibrils initially results in the formation of floppy fibril bundles, which then compact to form tight and more rigid fibers. The first stage is reflected in a fast (10 min) increase in clot stiffness, whereas the compaction phase is characterized by a slow (hours) development of clot stiffness. Inhibition of FXIII completely abrogates the slow compaction. FXIII strongly increases the linear elastic modulus of the clots, but does not affect the nonlinear response at large deformations. Conclusions: We propose a multiscale structural model whereby FXIIImediated cross-linking tightens the coupling between the protofibrils within a fibrin fiber, thus making the fiber stiffer and less porous. At small strains, fiber stiffening enhances clot stiffness, because the clot response is governed by the entropic elasticity of the fibers, but once the clot is sufficiently stressed, the modulus is independent of protofibril coupling, because clot stiffness is governed by individual protofibril stretching. J Thromb Haemost

The molecular defect in the abnormal fibrinogen Dusart (Paris V) that is associated with thrombophilia was determined by sequence analysis of genomic DNA that had been amplified using the polymerase chain reaction. The propositus was heterozygous for a single base change (C -> T) in the Aa-chain gene, resulting in the amino acid substitution Aa 554 Arg Cys. Restriction analysis of the amplified DNA derived from the family members showed that his father and his two sons were also heterozygous. Electron microscopic studies on fibrin formed from purified fibrinogen Dusart demonstrated fibers that were much thinner than in normal fibrin. In contrast to the previously observed defective binding of plasminogen, the binding of thrombospondin to immobilized fibrinogen Dusart was similar to that of normal fibrinogen. Immunoblot analysis of plasma fibrinogen demonstrated that a substantial part of the fibrinogen Dusart molecules were disulfide-linked to albumin. The plasma of the affected family members also contained fibrinogen-albumin complexes. Furthermore, small amounts of high molecular weight complexes containing fibrinogen were detected in all the heterozygous individuals. These data indicate that the molecular abnormality in fibrinogen Dusart (Aa 554 Arg -n Cys) results in defective lateral association of the fibrin fibers and disulfide-linked complex formation with albumin, and is associated with a family history of recurrent thrombosis in the affected individuals. (J. Clin. Invest. 1993.

Purpose: The aim of this study was to find the ergonomically optimal operating surface height for laparoscopic surgery in order to reduce discomfort in the upper extremities of the operators and the assistants. The operating surface height was defined as the level of the abdominal wall of a patient with pneumoperitoneum.Materials and Methods: Two pelvi-trainer tests were performed. One test was performed on six different operating surface heights. The (extreme) joint excursions of the shoulder, elbow, and wrist were measured by a video analysis method. Another test was performed by holding a laparoscope for 15 minutes while an electromyelograph of the biceps brachii was made. The results of both tests were evaluated subjectively by a questionnaire.Results: The ergonomically optimal operating surface height lies between a factor 0.7 and 0.8 of the elbow height of the operator/assistant. At this height, the joint excursions stay in the neutral zone for more than 90% of the total manipulation time, and the activity of the biceps brachii when holding the laparoscope stays within 15% of the maximum muscle activity.Conclusions: The operating surface height influences the (extreme) upper joint excursions of the surgeon. The ergonomically optimal operating surface height reduces the discomfort in the shoulders, back, and wrists of the surgeon during laparoscopic surgery. This optimal table height range for laparoscopic surgery is lower than those currently available.