George Nounesis

Bio: George Nounesis is an academic researcher from University of Minnesota. The author has contributed to research in topics: Liquid crystal & Phase transition. The author has an hindex of 29, co-authored 110 publications receiving 2238 citations. Previous affiliations of George Nounesis include Massachusetts Institute of Technology.

Nanoparticle-induced widening of the temperature range of liquid-crystalline blue phases

Abstract: Liquid-crystalline blue phases exhibit exceptional properties for applications in the display and sensor industry. However, in single component systems, they are stable only for very narrow temperature range between the isotropic and the chiral nematic phase, a feature that severely hinders their applicability. Systematic high-resolution calorimetric studies reveal that blue phase III is effectively stabilized in a wide temperature range by mixing surface-functionalized nanoparticles with chiral liquid crystals. This effect is present for two liquid crystals, yielding a robust method to stabilize blue phases, especially blue phase III. Theoretical arguments show that the aggregation of nanoparticles at disclination lines is responsible for the observed effects.

PLCζ causes Ca2+ oscillations in mouse eggs by targeting intracellular and not plasma membrane PI(4,5)P2

Abstract: Sperm-specific phospholipase C ζ (PLCζ) activates embryo development by triggering intracellular Ca2+ oscillations in mammalian eggs indistinguishable from those at fertilization. Somatic PLC isozymes generate inositol 1,4,5-trisphophate–mediated Ca2+ release by hydrolyzing phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) in the plasma membrane. Here we examine the subcellular source of PI(4,5)P2 targeted by sperm PLCζ in mouse eggs. By monitoring egg plasma membrane PI(4,5)P2 with a green fluorescent protein–tagged PH domain, we show that PLCζ effects minimal loss of PI(4,5)P2 from the oolemma in contrast to control PLCδ1, despite the much higher potency of PLCζ in eliciting Ca2+ oscillations. Specific depletion of this PI(4,5)P2 pool by plasma membrane targeting of an inositol polyphosphate-5-phosphatase (Inp54p) blocked PLCδ1-mediated Ca2+ oscillations but not those stimulated by PLCζ or sperm. Immunolocalization of PI(4,5)P2, PLCζ, and catalytically inactive PLCζ (ciPLCζ) revealed their colocalization to distinct vesicular structures inside the egg cortex. These vesicles displayed decreased PI(4,5)P2 after PLCζ injection. Targeted depletion of vesicular PI(4,5)P2 by expression of ciPLCζ-fused Inp54p inhibited the Ca2+ oscillations triggered by PLCζ or sperm but failed to affect those mediated by PLCδ1. In contrast to somatic PLCs, our data indicate that sperm PLCζ induces Ca2+ mobilization by hydrolyzing internal PI(4,5)P2 stores, suggesting that the mechanism of mammalian fertilization comprises a novel phosphoinositide signaling pathway.

Theoretical and experimental study of the nanoparticle-driven blue phase stabilisation

Abstract: We have studied theoretically and experimentally the effects of various types of nanoparticles (NPs) on the temperature stability range $ \Delta$ T BP of liquid-crystalline (LC) blue phases. Using a mesoscopic Landau-de Gennes type approach we obtain that the defect core replacement (DCR) mechanism yields in the diluted regime $ \Delta$ T BP(x) $ \propto$ 1/(1 - xb) , where x stands for the concentration of NPs and b is a constant. Our calculations suggest that the DCR mechanism is efficient if a local NP environment resembles the core structure of disclinations, which represent the characteristic property of BP structures. These predictions are in line with high-resolution ac calorimetry and optical polarising microscopy experiments using the CE8 LC and CdSe or aerosil NPs. In mixtures with CdSe NPs of 3.5nm diameter and hydrophobic coating the BPIII stability range has been extended up to 20K. On the contrary, the effect of aerosil silica nanoparticles of 7.0nm diameter and hydrophilic coating is very weak.

Phosphoinositides: Tiny Lipids With Giant Impact on Cell Regulation

Abstract: Phosphoinositides (PIs) make up only a small fraction of cellular phospholipids, yet they control almost all aspects of a cell's life and death. These lipids gained tremendous research interest as plasma membrane signaling molecules when discovered in the 1970s and 1980s. Research in the last 15 years has added a wide range of biological processes regulated by PIs, turning these lipids into one of the most universal signaling entities in eukaryotic cells. PIs control organelle biology by regulating vesicular trafficking, but they also modulate lipid distribution and metabolism via their close relationship with lipid transfer proteins. PIs regulate ion channels, pumps, and transporters and control both endocytic and exocytic processes. The nuclear phosphoinositides have grown from being an epiphenomenon to a research area of its own. As expected from such pleiotropic regulators, derangements of phosphoinositide metabolism are responsible for a number of human diseases ranging from rare genetic disorders to the most common ones such as cancer, obesity, and diabetes. Moreover, it is increasingly evident that a number of infectious agents hijack the PI regulatory systems of host cells for their intracellular movements, replication, and assembly. As a result, PI converting enzymes began to be noticed by pharmaceutical companies as potential therapeutic targets. This review is an attempt to give an overview of this enormous research field focusing on major developments in diverse areas of basic science linked to cellular physiology and disease.