Yeast lipin 1 orthologue pah1p regulates vacuole homeostasis and membrane fusion.

Vacuole homotypic fusion requires a group of regulatory lipids that includes diacylglycerol, a fusogenic lipid that is produced through multiple metabolic pathways including the dephosphorylation of phosphatidic acid (PA). Here we examined the relationship between membrane fusion and PA phosphatase activity. Pah1p is the single yeast homologue of the Lipin family of PA phosphatases. Deletion of PAH1 was sufficient to cause marked vacuole fragmentation and abolish vacuole fusion. The function of Pah1p solely depended on its phosphatase activity as complementation studies showed that wild type Pah1p restored fusion, whereas the phosphatase dead mutant Pah1p(D398E) had no effect. We discovered that the lack of PA phosphatase activity blocked fusion by inhibiting the binding of SNAREs to Sec18p, an N-ethylmaleimide-sensitive factor homologue responsible for priming inactive cis-SNARE complexes. In addition, pah1Δ vacuoles were devoid of the late endosome/vacuolar Rab Ypt7p, the phosphatidylinositol 3-kinase Vps34p, and Vps39p, a subunit of the HOPS (homotypic fusion and vacuole protein sorting) tethering complex, all of which are required for vacuole fusion. The lack of Vps34p resulted in the absence of phosphatidylinositol 3-phosphate, a lipid required for SNARE activity and vacuole fusion. These findings demonstrate that Pah1p and PA phosphatase activity are critical for vacuole homeostasis and fusion.

Gastrointestinal complications of Russell-Silver syndrome: a pilot study.

Russell-Silver syndrome (RSS) is a genetic syndrome with clinical manifestations of intrauterine and postnatal growth retardation, normal head circumference, body asymmetry, and distinctive facial appearance. We followed an infant diagnosed with RSS who had occurrence of multiple gastrointestinal complications. Although there are a number of published reports describing gastrointestinal problems associated with RSS, specific gastrointestinal diseases have not been recognized as major features. We hypothesize that gastrointestinal complications may be more frequent in RSS cases than previously reported. To address our hypothesis, we developed a pilot study of RSS cases to identify and characterize associated gastrointestinal complications. Surveys were distributed by MAGIC, a support group for individuals with RSS. Surveys included information on the objective and subjective characteristics used to diagnose RSS, as well as descriptions of gastrointestinal problems. Completed surveys were returned on 135 individuals. We used strict diagnostic guidelines to determine affected status of children reported in our survey. Of the 135 surveys completed, 65 were determined to have clear-cut RSS. The diagnoses were made without knowledge of the gastrointestinal symptoms of any of the subjects. Of the 65 subjects with "clear cut" RSS, 50 (77%) had gastrointestinal symptoms. Major specific symptoms included gastroesophageal reflux disease (34%), esophagitis (25%), food aversion (32%), and failure to thrive (63%). A common theme in gastrointestinal complications of RSS is significant gastroesophageal reflux that includes esophagitis and food aversion. Results of this survey suggest that there is an association of gastrointestinal complications with RSS that should be addressed in diagnosis as well as management protocols for children with this condition.

A facile approach to architecturally defined nanoparticles via intramolecular chain collapse.

A novel approach is presented for the controlled intramolecular collapse of linear polymer chains to give well-defined single-molecule nanoparticles whose structure is directly related to the original linear polymer. By employing a combination of living free radical polymerization and benzocyclobutene (BCB) chemistry, nanoparticles can be routinely prepared in multigram quantities with the size being accurately controlled by either the initial degree of polymerization of the linear chain or the level of incorporation of the BCB coupling groups. The latter also allows the cross-link density of the final nanoparticles to be manipulated. In analogy with dendritic macromolecules, a significant reduction of up to 75% in the hydrodynamic volume is observed on going from the starting random coil linear chains to the corresponding nanoparticles. The facile nature of the living free radical process also permits wide variation in monomer selection and functional group incorporation and allows novel macromolecular architectures to be prepared. Furthermore, the use of block copolymers functionalized with benzocyclobutene groups in only one of the blocks gives, after intramolecular collapse, a hybrid architecture in which a single linear polymer chain is attached to the globular nanoparticle.