Self-assembling phospholipid filaments

Aqueous dispersions of double-chain phospholipids spontaneously assemble into closed bilayers called vesicles (or liposomes). Although the vesicles are in general topologically spherical, cylindrical and helical liposomes have sometimes been observed. We present here video-enhanced microscopic studies of a diacetylenic phospholipid dispersed in ethanol/water, which reveal the existence of unusual bilayer morphologies. On cooling the dispersion from the isotropic phase, we have observed the formation of long (of the order of hundreds of micrometres), thin (0.2-2 microns) filaments, which fluctuate strongly. When the temperature is decreased further, the filaments rapidly retract into a mass of lipid. At constant temperature, on the other hand, the filaments transform into torus or ring-like vesicles. Such non-spherical structures have been predicted theoretically but not previously observed experimentally.     

Normal osteoclast number and function in rat pups lacking parathyroid hormone

Summary In parathyroidectomized suckling rats, bone modeling and the number and activity of cells in the osteoclast population are normal. These findings are at variance with observations in older animals and suggest that factors other than parathyroid hormone influence osteoclast formation and function in the neonate.This work was supported by grants HD-07419 and DE-04629 from the NIH. We thank Darrell Iler for his excellent technical assistance.     

High tyrosine kinase activity in normal nonproliferating cells

Protein phosphorylation at serine and threonine residues has been implicated in the regulation of many cellular processes. More recently, tyrosine residue phosphorylation has been shown to be associated with stimulation of cell proliferation, including viral transformation and stimulation by epidermal growth factors (EGF), platelet-derived growth factor (PDGF) and other compounds related to cellular growth such as insulin and dimethyl sulphoxide. To compare protein kinases and phosphoproteins of normal and leukaemic human haematopoietic cells in vivo and in vitro, we first have investigated the percentages of phosphoserine, phosphothreonine and phosphotyrosine obtained after hydrolysis of proteins from different blood cell fractions phosphorylated in vitro. We report here that phosphotyrosine formed less than 1% of the soluble fractions from polymorphonuclear cells, mononuclear cells (80% circulating lymphocytes, 20% monocytes), blood platelets and red blood cells (not shown). Surprisingly, high percentages of phosphorylated tyrosine were found only in the particulate fractions from non-proliferating anuclear cells, platelets and red blood cells.     

A new member of the IL-1 receptor family highly expressed in hippocampus and involved in X-linked mental retardation.

We demonstrate here the importance of interleukin signalling pathways in cognitive function and the normal physiology of the CNS. Thorough investigation of an MRX critical region in Xp22.1-21.3 enabled us to identify a new gene expressed in brain that is responsible for a non-specific form of X-linked mental retardation. This gene encodes a 696 amino acid protein that has homology to IL-1 receptor accessory proteins. Non-overlapping deletions and a nonsense mutation in this gene were identified in patients with cognitive impairment only. Its high level of expression in post-natal brain structures involved in the hippocampal memory system suggests a specialized role for this new gene in the physiological processes underlying memory and learning abilities.     

Structure of the insulin receptor substrate IRS-1 defines a unique signal transduction protein.

Since the discovery of insulin nearly 70 years ago, there has been no problem more fundamental to diabetes research than understanding how insulin works at the cellular level. Insulin binds to the alpha subunit of the insulin receptor which activates the tyrosine kinase in the beta subunit, but the molecular events linking the receptor kinase to insulin-sensitive enzymes and transport processes are unknown. Our discovery that insulin stimulates tyrosine phosphorylation of a protein of relative molecular mass between 165,000 and 185,000, collectively called pp185, showed that the insulin receptor kinase has specific cellular substrates. The pp185 is a minor cytoplasmic phosphoprotein found in most cells and tissues; its phosphorylation is decreased in cells expressing mutant receptors defective in signalling. We have now cloned IRS-1, which encodes a component of the pp185 band. IRS-1 contains over ten potential tyrosine phosphorylation sites, six of which are in Tyr-Met-X-Met motifs. During insulin stimulation, the IRS-1 protein undergoes tyrosine phosphorylation and binds phosphatidylinositol 3-kinase, suggesting that IRS-1 acts as a multisite 'docking' protein to bind signal-transducing molecules containing Src-homology 2 and Src-homology-3 domains. Thus IRS-1 may link the insulin receptor kinase and enzymes regulating cellular growth and metabolism.     

Mechanisms linking obesity to insulin resistance and type 2 diabetes

Obesity is associated with an increased risk of developing insulin resistance and type 2 diabetes. In obese individuals, adipose tissue releases increased amounts of non-esterified fatty acids, glycerol, hormones, pro-inflammatory cytokines and other factors that are involved in the development of insulin resistance. When insulin resistance is accompanied by dysfunction of pancreatic islet beta-cells - the cells that release insulin - failure to control blood glucose levels results. Abnormalities in beta-cell function are therefore critical in defining the risk and development of type 2 diabetes. This knowledge is fostering exploration of the molecular and genetic basis of the disease and new approaches to its treatment and prevention.     

The role of insulin and IGF-1 signaling in longevity

There are many theories of aging and parameters that influence lifespan, including genetic instability, telomerase activity and oxidative stress. The role of caloric restriction, metabolism and insulin and insulin-like growth factor-1 signaling in the process of aging is especially well conserved throughout evolution. These latter factors interact with each other, the former factors and histone deacetylases of the SIR family in a complex interaction to influence lifespan.Received 8 July 2004; received after revision 25 August 2004; accepted 17 September 2004