Drosophila studies support a role for a presynaptic synaptotagmin mutation in a human congenital myasthenic syndrome.

During chemical transmission, the function of synaptic proteins must be coordinated to efficiently release neurotransmitter. Synaptotagmin 2, the Ca2+ sensor for fast, synchronized neurotransmitter release at the human neuromuscular junction, has recently been implicated in a dominantly inherited congenital myasthenic syndrome associated with a non-progressive motor neuropathy. In one family, a proline residue within the C2B Ca2+-binding pocket of synaptotagmin is replaced by a leucine. The functional significance of this residue has not been investigated previously. Here we show that in silico modeling predicts disruption of the C2B Ca2+-binding pocket, and we examine the in vivo effects of the homologous mutation in Drosophila. When expressed in the absence of native synaptotagmin, this mutation is lethal, demonstrating for the first time that this residue plays a critical role in synaptotagmin function. To achieve expression similar to human patients, the mutation is expressed in flies carrying one copy of the wild type synaptotagmin gene. We now show that Drosophila carrying this mutation developed neurological and behavioral manifestations similar to those of human patients and provide insight into the mechanisms underlying these deficits. Our Drosophila studies support a role for this synaptotagmin point mutation in disease etiology.

Novel porcine model for calcium oxalate stone formation.

BACKGROUND: Mechanisms for calcium-based stone formation are not clearly delineated. Porcine are the most anatomically and physiologically congruent mammal to humans. Our objectives were to develop a cost-effective and easily reproducible porcine model for the study of calcium-based nephrolithiasis. METHODS: Crossbred male pigs (n = 16) were assigned randomly to one of the following treatments: (1) control; (2) ethylene glycol (EG) + vitamin D (VD); (3) EG + ammonium chloride (AC); (4) EG + gentamicin (G); (5) EG + Lasix; (6) EG + VD + AC; (7) EG + VD + G. Treatments were administered for 28 days; blood and urine were collected on day 0, 14, and 28. At the endpoint of the study, renal tissue was collected for gross and microscopic analysis of crystal stone formation and inflammation. RESULTS: Stone-forming parameters were observed in serum and urine. For control versus all other treatments, by day 28, serum BUN and creatinine were less (P < 0.01), urinary creatinine, citrate and pH were greater (P < 0.01), and urinary oxalate was less (P < 0.01). Histopathological analysis of H&E staining and stone analysis revealed formation of calcium oxalate stones and crystal formation within the renal cortex and medulla for all animals except control. Nephrotoxicity was observed in one animal from treatment EG + G. CONCLUSIONS: The treatments explored in this experiment provided novel examples of cost-effective porcine models for the study of nephrolithiasis. EG + VD had the strongest indicators of nephrolithiasis without nephrotoxicity.

Albumin Inhibits Pseudomonas aeruginosa Quorum Sensing and Alters Polymicrobial Interactions.

Polymicrobial interactions are complex and can influence the course of an infection, as is the case when two or more species exhibit a synergism that produces a disease state not seen with any of the individual species alone. Cell-to-cell signaling is key to many of these interactions, but little is understood about how the host environment influences polymicrobial interactions or signaling between bacteria. Chronic wounds are typically polymicrobial, with Staphylococcus aureus and Pseudomonas aeruginosa being the two most commonly isolated species. While P. aeruginosa readily kills S. aureusin vitro, the two species can coexist for long periods together in chronic wound infections. In this study, we investigated the ability of components of the wound environment to modulate interactions between P. aeruginosa and S. aureus We demonstrate that P. aeruginosa quorum sensing is inhibited by physiological levels of serum albumin, which appears to bind and sequester some homoserine lactone quorum signals, resulting in the inability of P. aeruginosa to produce virulence factors that kill S. aureus These data could provide important clues regarding the virulence of P. aeruginosa in albumin-depleted versus albumin-rich infection sites and an understanding of the nature of friendly versus antagonistic interactions between P. aeruginosa and S. aureus.