Identification of the zebrafish homologues of IMPG2, a retinal proteoglycan

Photoreceptor outer segments are surrounded by a carbohydrate-rich matrix, the interphotoreceptor matrix, necessary for physiological retinal function. Few roles for molecules characterizing the interphotoreceptor matrix have been clearly defined. Recent studies have found the presence of nonsense mutations in the interphotoreceptor matrix proteoglycan 2 (IMPG2) gene in patients affected by retinal dystrophies. IMPG2 encodes for a proteoglycan synthesized by photoreceptors and secreted in the interphotoreceptor matrix. Little is known about the structure and function of this protein, we thus decided to characterize zebrafish impg2. In zebrafish there are two Impg2 proteins, Impg2a and Impg2b. We generated a phylogenetic tree based on IMPG2 protein sequence similarity among vertebrates, showing a significant similarity between humans and teleosts. The human and zebrafish proteins share conserved domains, as also shown by homology models. Expression analyses of impg2a and impg2b show a continued expression in the photoreceptor layer starting from developmental stages and continuing through adulthood. Between 1 and 6 months post-fertilization, there is a significant shift of Impg2 expression toward the outer segment region, suggesting an increase in secretion. This raises intriguing hypotheses about its possible role(s) during retinal maturation, laying the groundwork for the generation of most needed models for the study of IMPG2-related inherited retinal dystrophies.

All-atom calculation of protein free-energy profiles

The Bias Functional (BF) approach is a variational method which enables one to efficiently generate ensembles of reactive trajectories for complex biomolecular transitions, using ordinary computer clusters. For example, this scheme was applied to simulate in atomistic detail the folding of proteins consisting of several hundreds of amino acids and with experimental folding time of several minutes. A drawback of the BF approach is that it produces trajectories which do not satisfy microscopic reversibility. Consequently, this method cannot be used to directly compute equilibrium observables, such as free energy landscapes or equilibrium constants. In this work, we develop a statistical analysis which permits us to compute the potential of mean-force (PMF) along an arbitrary collective coordinate, by exploiting the information contained in the reactive trajectories calculated with the BF approach. We assess the accuracy and computational efficiency of this scheme by comparing its results with the PMF obtained for a small protein by means of plain molecular dynamics.

Quantum Phase Transitions with Parity-Symmetry Breaking and Hysteresis

Symmetry-breaking quantum phase transitions play a key role in several condensed matter, cosmology and nuclear physics theoretical models1-3. Its observation in real systems is often hampered by finite temperatures and limited control of the system parameters. In this work we report for the first time the experimental observation of the full quantum phase diagram across a transition where the spatial parity symmetry is broken. Our system is made of an ultra-cold gas with tunable attractive interactions trapped in a spatially symmetric double-well potential. At a critical value of the interaction strength, we observe a continuous quantum phase transition where the gas spontaneously localizes in one well or the other, thus breaking the underlying symmetry of the system. Furthermore, we show the robustness of the asymmetric state against controlled energy mismatch between the two wells. This is the result of hysteresis associated with an additional discontinuous quantum phase transition that we fully characterize. Our results pave the way to the study of quantum critical phenomena at finite temperature4, the investigation of macroscopic quantum tunneling of the order parameter in the hysteretic regime and the production of strongly quantum entangled states at critical points5.

Clinical validity of the elbow flexion test for the diagnosis of ulnar nerve compression at the cubital tunnel

We evaluated the elbow flexion test in 216 elbows without compression of the ulnar nerve at the cubital tunnel and without other neuropathies. We used Rayan's four positions as our test. The percentage of positive tests was only 3.6% at one minute, whereas evaluating the responses at three minutes we saw positive results in 16.2%. Therefore we find that if the test is performed for one minute it may be useful to help in diagnosing ulnar nerve compression at the cubital tunnel.

Trapeziometacarpal joint arthrodesis for osteoarthritis. Results of power staple fixation

Fifty-two cases of trapeziometacarpal joint osteoarthritis were treated with arthrodesis using small staple fixation. Eighty-five per cent of the patients were free of pain, with normal thumb. Opposition to the fourth finger tip was always possible and opposition to the little finger tip was observed in 94% of cases. Four patients (7.6%) developed a non-union but only two complained of pain. Arthrodesis with power staple fixation minimizes bone resection and postoperative immobilization (mean 28 days) because of the good stability following this procedure.

Nodular fasciitis of the hallux: difficulties in diagnosis

Nodular fasciitis or proliferative fasciitis is currently classified as a tumor-like hyperplastic lesion of soft tissues. Histological characteristics of this lesion have often caused diagnostic problems since it can be mistaken for a malignant mesenchymal neoplasm. To highlight this we report a case of nodular fasciitis that was difficult to diagnose because of its atypical radiographic and clinical features.

Osteoid osteoma of the carpus. Case reports and a review of the literature

Osteoid osteoma mainly affects long bones, and is rarely observed at the hand. The authors report three cases of osteoid osteoma in the carpus (one case in the scaphoid, one in the triquetral, one in the capitate), treated by removal of the entire nidus. No bone grafting or intercarpal arthrodesis was necessary. There were no recurrences.