Role of FGFs in skeletal muscle and limb development

Fibroblast growth factors (FGFs) are a family of nine proteins that bind to three distinct types of cell surface molecules: (i) FGF receptor tyrosine kinases (FGFR-1 through FGFR-4); (ii) a cysteine-rich FGF receptor (CFR); and (iii) heparan sulfate proteoglycans (HSPGs). Signaling by FGFs requires participation of at least two of these receptors: the FGFRs and HSPGs form a signaling complex. The length and sulfation pattern of the heparan sulfate chain determines both the activity of the signaling complex and, in part, the ligand specificity for FGFR-1. Thus, the heparan sulfate proteoglycans are likely to play an essential role in signaling. We have recently identified a role for FGF in limb bud development in vivo. In the chick limb bud, ectopic expression of the 18 kDa form of FGF-2 or FGF-2 fused to an artificial signal peptide at its amino terminus causes skeletal duplications. These data, and the observations that FGF-2 is localized to the subjacent mesoderm and the apical ectodermal ridge in the early developing limb, suggest that FGF-2 plays an important role in limb outgrowth. We propose that FGF-2 is an apical ectodermal ridgederived factor that participates in limb outgrowth and patterning. © 1994 Wiley-Liss, Inc.     

Phagocytosis of Intravenously Administered Particles by Leukocytes Adhered to the Aortic Endothelium of the Rat

Phagocytosis has been used to characterize on a functional basis leukocytes adhered to the aortic endothelium of the rat. After intravenous administration of particles, phagocytosis was observed microscopically in esterase-positive leukocytes adhered to the endothelium in whole mounts of aorta. Polybead^R blue and red, 0.5 and 1 μm particle size, were inadequate because they were insufficiently colored to be identified individually at 400. Fluoresbrite^tm YG 0.25 and 0.50 μm at doses of 0.2 and 2 ± 0.3 m1/100 g, respectively, produced endothelial lesions. The same occurred with Monastral blue B^R (MbB) at 0.3 ml/100 g, red iron at 2 ± 16 mg/100 g and India ink at different concentrations depending on the supplier. At lower particle doses, lesions were not found. Deferoxamine mesylate 1.5 mg/100 g intravenous and allopurinol 5 mg/100 g intraperitoneal administered before the particles diminished the number and intensity of lesions. In none of the cases studied was the percentage of phagocytic cells greater than 50%. Clearance curves of MbB and Fluoresbrite^tm indicated rapid disappearance of particles from the blood. Results indicate that administration of particulate suspensions is not a good method for characterizing the phagocytic leukocytes adhering to the aortic endothelium because low doses produce rapid clearance of particles, thus impeding sufficient leukocyte loading, and higher doses produce endothelial lesions that often impair reliable counting of the adhering leukocytes.     

Clonal growth in woody plants: A review

Bulkiness, longevity and solidity of the body in woody plants enable the successive development of accessory shoots and adventitious roots in (1) both proximal and distal positions on organs, (2) both the above-ground and below-ground space, (3) both the aerial and soil environments. In monocotyledons, woody rhizomes play an essential role in the basic growth habit and architectural models. In dicotyledonous and a few gymnospermous trees, attached and successively disconnected ramets play a multilateral role in the pertinent life strategies. The majority of sprouts, coppice shoots and root suckers behave as opportunistic organs (a) serving as means of vegetative reproduction, (b) securing colonization of unoccupied ground, (c) increasing competitive power of the species within the community, (d) increasing survival rate of the stressed/disturbed genet in marginal habitats, (e) forming replacement for ageing or damaged organs, and (f) enabling reiteration of the genet's entire architectural model.     

Physico-chemical characteristics of a permanent Spanish hypersaline lake: La Salada de Chiprana (NE Spain)

La Salada de Chiprana Lake, located in the Ebro River basin, northeastern Spain, is the only permanent and deep water hypersaline ecosystem in all of western Europe. With a total surface of 31 ha and a maximum depth of 5.6 m, it has several basins bounded by elongated sandstone-bodies or ribbons which are paleochannels of Miocene age. Its salinity varied from 30 to 73 g 1^–1 during the 1989 hydrological cycle and the most abundant ions were magnesium and sulphate. Depth-time distributions of major physico-chemical variables demonstrated that the lake was stratified in two distinctive layers during most of the year. The chemocline disappeared only in October, with the complete overturn of the water column. In the deep water, three conditions occurred which allowed development of green sulphur bacteria populations: (1) oxygen depletion, (2) presence of hydrogen sulphide and (3) presence of light. Benthic microbial mats covered the sediments of shallow shores of moderate slope.     

Induction of the murine “W phenotype” in long-term cultures of human cord blood cells by c-kit antisense oligomers

The murine white (W) spotting locus is the site of the c-kit gene and encodes a tyrosine kinase receptor while the complementary Steel (Sl) iocus encodes its ligand. Mutations at either locus have profound effects on hematopoiesis, particularly erythroid and mast cell proliferation. We added c-kit antisense oligonucleotides to long-term suspension cultures of enriched human umbilical cord progenitor cells. This resulted in the suppression of c-kit gene expression and the preferential suppression of the generation of erythroid burst-forming cells (BFU-E) which extended over the life of the culture (3 weeks). The results provide an in vitro model of the “W phenotype” in human hematopoiesis and confirm the importance of c-kit gene function in early erythropoiesis. Because the generation of BFU-E was suppressed even after c-kit gene expression had recovered, this gene product may be critical to the erythroid commitment process. © 1993 Wiley-Liss, Inc.     

Ammonium Injection Induces an N-Methyl-d-Aspartate Receptor-Mediated Proteolysis of the Microtubule-Associated Protein MAP-2

Abstract: We have shown previously that chronic hyperammonemia increases, in brain, the polymerization of microtubules that is regulated mainly by the level and state of phosphorylation of microtubule-associated protein 2 (MAP-2). Activation of the N -methyl- d -aspartate (NMDA) receptor dephosphorylates MAP-2. Because we have found that acute ammonia toxicity is mediated by the NMDA receptor, we have tested the effect of high ammonia levels on MAP-2 in brain. Microtubules isolated from rats injected intraperitoneally with 6 mmol/kg ammonium acetate showed a marked decrease of MAP-2. Also, the amount of MAP-2 in brain homogenates, determined by immunoblotting. was markedly reduced, presumably by proteolysis. The content of MAP-2 was decreased by ∼75% 1-2 h after ammonium injection and returned to normal values after 4 h. Proteolysis of MAP-2 was prevented completely by injection of 2 mg/kg MK-801, a specific antagonist of the NMDA receptor, suggesting that proteolysis is mediated by activation of this receptor. l -Carnitine, which protects rats against ammonia toxicity, also prevented MAP-2 degradation. Because activation of the NMDA receptor increases [Ca²⁺]_i, we determined whether rat brain contains a Ca²⁺-dependent protease that selectively degrades MAP-2. We show that there is a cytosolic Ca²⁺-dependent protease that degrades MAP-2, but no other brain proteins. The protease has been identified tentatively as calpain I, for it is inhibited by a specific inhibitor of this protease. Our results suggest that ammonium injection activates the NMDA receptor, leading to an increase in [Ca²⁺]_i, which activates calpain I. This, in turn, selectively degrades MAP-2. Possible implications in chronic hyperammonemic states and in the mechanism of ammonia toxicity are discussed.     

Striatal L-DOPA Decarboxylase Activity in Parkinson's Disease In Vivo: Implications for the Regulation of Dopamine Synthesis

Abstract: L-DOPA is a large neutral amino acid subject to transport out of, as well as into, brain tissue. Competition between dopamine synthesis and L-DOPA egress from striatum must favor L-DOPA egress if decarboxylation declines relatively more than transport in Parkinson's disease. To test this hypothesis, we injected patients with Parkinson's disease with a radidabeled analogue of L-DOPA and recorded regional brain radioactivity as a function of time by means of positron emission tomography. We simultaneously estimated the activity of the decarboxylating enzyme and the amino acid transport. In the striatum of patients, we found the L-DOPA decarboxylase activity to be reduced in the head of the caudate nucleus and the putamen. However, the rate of egress of the DOPA analogue was unaffected by the disease and thus inhibited dopamine synthesis more than predicted in the absence of L-DOPA egress.     

Reduction in Glial Fibrillary Acidic Protein mRNA Abundance Induced by (—)-Deprenyl and Other Monoamine Oxidase B Inhibitors in C6 Glioma Cells

Abstract: Gliosis is commonly observed in the CNS following tissue damage, and it also occurs in aging and in many neurodegen-erative diseases. Glial fibrillary acidic protein (GFAP) accumulation is a prominent feature of astrocytic gliosis. An inhibition or delay in GFAP synthesis could mitigate scar formation and thus reduce the formation of a physical barrier. The consequence of this would be to allow neurons and oligodendrocytes to reestablish a functional environment. (—)-Deprenyl, a specific monoamine oxidase (MAO) B inhibitor, has been used as an effective antipar-kinsonian drug, and it has been reported to possess neuroprotective and neurorescue properties. Using northern and slot blots to detect GFAP mRNA in C6 glioma cells, we have demonstrated that (—)-deprenyl decreases the abundance of GFAP mRNA in a time- and dose-dependent manner. The effect seems to be specific to MA0 B inhibitors because (+)-deprenyl and clorgyline exhibit no effect. This study indicates therefore that (-)-deprenyl may be useful for regulating astrogliosis following CNS injury as well as in some neurodegenerative diseases.