Horizontal cells invest retinal capillaries in the tree shrew Tupaia belangeri

Fibroblast growth factor (FGF) receptors constitute a family of four membrane-spanning tyrosine kinases (FGFR1-4) which serve as high-affinity receptors for 17 growth factors (FGF1-17). To study functions of FGF/ FGFR signals in development, mice that carry mutations in each receptor have been created by gene targeting. Analysis of these mutant mice revealed essential functions of FGF receptors in multiple biological processes, including mesoderm induction and patterning, cell growth and migration, organ formation and bone growth. In this review we discuss recent work with FGF receptors to illustrate mechanisms, through which the FGF/FGFR signals specify vertebrate limb initiation, outgrowth and patterning.     

The Occurrence of 4-Amino-4-Deoxy-Arabinose in LPS of Supersusceptible Strain Pseudomonas aeruginosa Z61: Noncorrelation with Polymyxin Resistance

Lipopolysaccharides (LPS) extracted from the supersusceptible strain Pseudomonas aeruginosa Z61 were compared with LPS from other strains with varying antimicrobial susceptibilities. The presence of 4-amino-4-deoxy-arabinose (4-AraN) in P. aeruginosa Z61 LPS was confirmed by gas-liquid chromatography/mass spectrometry (GLC-MS) and quantitated by high-performance liquid chromatography (HPLC). Z61 LPS (compared with wild-type strain PAO1) has reduced amounts of rhamnose and higher concentrations of hydroxy fatty acids, 4-AraN, and phosphates. ³¹P Nuclear magnetic resonance revealed that Z61 LPS phosphates are configured in monophosphates, phosphodiesters, pyrophosphomonoesters, and glycosidic pyrophosphodiester groups. The presence of 4-AraN in P. aeruginosa LPS did not correlate with antimicrobial resistance. Received: 31 August 1998 / Accepted: 5 November 1998     

Barotolerance is inducible by preincubation under hydrostatic pressure, cold-, osmotic- and acid-stress conditions in Lactobacillus sanfranciscensis DSM 20451T

AIMS: This study addresses the inducibility of barotolerance by preincubation of Lactobacillus sanfranciscensis DSM 20451T under various sublethal stress conditions. METHODS AND RESULTS: Stress conditions which reduce the growth rate of L. sanfranciscensis DSM 20451T to 10% of its maximum were determined. These conditions were met at 43, 12.5 degrees C, a pH value of 3.7, 1.9% NaCl, or 80 MPa respectively. In contrast to heat preincubation, other prestresses, including salt, cold and pressure led to an increase of barotolerance by hydrostatic pressure of 300 MPa for 30 min. Stationary-phase cells also showed an increased barotolerance. Sublethal pressure leads to enhanced heat tolerance. CONCLUSIONS: Stress response to salt, low temperature and acidic pH as well as starvation overlap with that one to high pressure by inducing barotolerance. SIGNIFICANCE AND IMPACT OF THE STUDY: Inactivation of bacteria by high pressure treatment is influenced by their history which modulates barotolerance. Mechanisms of barotolerance appear different from heat shock defence.     

Site-specific regulation of the GEF Cdc24p by the scaffold protein Far1p during yeast mating

Receptor-mediated cell polarization via heterotrimeric G-proteins induces cytoskeletal rearrangements in a variety of organisms. In yeast, Far1p is required for orienting cell growth towards the mating partner by linking activated Gbetagamma to the guanine-nucleotide exchange factor (GEF) Cdc24p, which activates the Rho-type GTPase Cdc42p. Here we investigated the role of Far1p in the regulation of Cdc24p in vivo. Using time-lapse microscopy of mating cells and artificial membrane targeting of Far1p, we show that Far1p is necessary and sufficient to recruit Cdc24p to the plasma membrane. Wild-type Far1p contains a PH-like domain, which is required for its membrane localization in vivo. Interestingly, expression of membrane-targeted Far1p causes toxicity, most likely by activating Cdc42p uniformly at the cell cortex. The ability of full-length Far1p to function as an activator of Cdc24p in vivo requires its interaction with Cdc24p and Gbetagamma. Our results imply that Gbetagamma not only targets Far1p to the correct site but may also trigger a conformational change in Far1p that is required for its ability to activate Cdc24p in vivo.     

Disruption of the mouse mTOR gene leads to early postimplantation lethality and prohibits embryonic stem cell development

The mammalian target of rapamycin (mTOR) is a key component of a signaling pathway which integrates inputs from nutrients and growth factors to regulate cell growth. Recent studies demonstrated that mice harboring an ethylnitrosourea-induced mutation in the gene encoding mTOR die at embryonic day 12.5 (E12.5). However, others have shown that the treatment of E4.5 blastocysts with rapamycin blocks trophoblast outgrowth, suggesting that the absence of mTOR should lead to embryonic lethality at an earlier stage. To resolve this discrepancy, we set out to disrupt the mTOR gene and analyze the outcome in both heterozygous and homozygous settings. Heterozygous mTOR (mTOR(+/-)) mice do not display any overt phenotype, although mouse embryonic fibroblasts derived from these mice show a 50% reduction in mTOR protein levels and phosphorylation of S6 kinase 1 T389, a site whose phosphorylation is directly mediated by mTOR. However, S6 phosphorylation, raptor levels, cell size, and cell cycle transit times are not diminished in these cells. In contrast to the situation in mTOR(+/-) mice, embryonic development of homozygous mTOR(-/-) mice appears to be arrested at E5.5; such embryos are severely runted and display an aberrant developmental phenotype. The ability of these embryos to implant corresponds to a limited level of trophoblast outgrowth in vitro, reflecting a maternal mRNA contribution, which has been shown to persist during preimplantation development. Moreover, mTOR(-/-) embryos display a lesion in inner cell mass proliferation, consistent with the inability to establish embryonic stem cells from mTOR(-/-) embryos.     

Rap2B-dependent stimulation of phospholipase C-epsilon by epidermal growth factor receptor mediated by c-Src phosphorylation of RasGRP3

Receptor tyrosine kinase regulation of phospholipase C-epsilon (PLC-epsilon), which is under the control of Ras-like and Rho GTPases, was studied with HEK-293 cells endogenously expressing PLC-coupled epidermal growth factor (EGF) receptors. PLC and Ca(2+) signaling by the EGF receptor, which activated both PLC-gamma1 and PLC-epsilon, was specifically suppressed by inactivation of Ras-related GTPases with clostridial toxins and expression of dominant-negative Rap2B. EGF induced rapid and sustained GTP loading of Rap2B, binding of Rap2B to PLC-epsilon, and Rap2B-dependent translocation of PLC-epsilon to the plasma membrane. GTP loading of Rap2B by EGF was inhibited by chelation of intracellular Ca(2+) and expression of lipase-inactive PLC-gamma1 but not of PLC-epsilon. Expression of RasGRP3, a Ca(2+)/diacylglycerol-regulated guanine nucleotide exchange factor for Ras-like GTPases, but not expression of various other exchange factors enhanced GTP loading of Rap2B and PLC/Ca(2+) signaling by the EGF receptor. EGF induced tyrosine phosphorylation of RasGRP3, but not RasGRP1, apparently caused by c-Src; inhibition of c-Src interfered with EGF-induced Rap2B activation and PLC stimulation. Collectively, these data suggest that the EGF receptor triggers activation of Rap2B via PLC-gamma1 activation and tyrosine phosphorylation of RasGRP3 by c-Src, finally resulting in stimulation of PLC-epsilon.     

Fine mapping of the Schnyder’s crystalline corneal dystrophy locus

Schnyders crystalline corneal dystrophy (SCCD) is a rare autosomal dominant eye disease with a spectrum of clinical manifestations that may include bilateral corneal clouding, arcus lipoides, and anterior corneal crystalline cholesterol deposition. We have previously performed a genome-wide linkage analysis on two large Swede-Finn families and mapped the SCCD locus to a 16-cM interval between markers D1S2633 and D1S228 on chromosome 1p36. We have collected 11 additional families from Finland, Germany, Turkey, and USA to narrow the critical region for SCCD. Here, we have used haplotype analysis with densely spaced microsatellite markers in a total of 13 families to refine the candidate interval. A common disease haplotype was observed among the four Swede-Finn families indicating the presence of a founder effect. Recombination results from all 13 families refined the SCCD locus to 2.32 Mbp between markers D1S1160 and D1S1635. Within this interval, identity-by-state was present in all 13 families for two markers D1S244 and D1S3153, further refining the candidate region to 1.58 Mbp.