Histories and Stories from Chiapas: Border Identities in Southern Mexico.

Histories and Stories from Chiapas: Border Identities in Southern Mexico. R. Aída Hernández Castillo. Texas: University of Texas Press, 2001. 317 pp.     

Protein Phosphorylation and Calcium Uptake into Rat Forebrain Synaptosomes: Modulation by the σ Ligand, 1,3-Ditolylguanidine

Abstract: The σ ligand 1,3-di- O -tolylguanidine (DTG) increased basal dynamin and decreased depolarization-stimulated phosphorylation of the synaptosomal protein synapsin Ib without having direct effects on protein kinases or protein phosphatases. DTG dose-dependently decreased the basal cytosolic free Ca²⁺ concentration ([Ca²⁺]_i) and blocked the depolarization-dependent increases in [Ca²⁺]_i. These effects were inhibited by the σ antagonists rimcazole and BMY14802. The nitric oxide donors sodium nitroprusside (SNP) and 8-( p -chlorophenylthio)guanosine-3',5'-cyclic monophosphorothioate decreased basal [Ca²⁺]_i and the KCl-evoked rise in [Ca²⁺]_i to an extent similar to DTG. SNP, but not DTG, produced a rise in cyclic GMP levels, suggesting that the effect of DTG on [Ca²⁺]_i was not mediated via downstream regulation of cyclic GMP levels. DTG increased ⁴⁵Ca²⁺ uptake and efflux under basal conditions and inhibited the ⁴⁵Ca²⁺ uptake induced by depolarization with KCl. The KCl-evoked rise in [Ca²⁺]_i was inhibited by ω-conotoxin (ω-CgTx)-GVIA and -MVIIC but not nifedipine and ω-agatoxin-IVA. The effect of DTG on decreasing the KCl-evoked rise in [Ca²⁺]_i was additive with ω-CgTx-MVIIC but not with ω-CgTx-GVIA. These data suggest that DTG was producing some of its effects on synapsin I and dynamin phosphorylation and intrasynaptosomal Ca²⁺ levels via inhibition of N-type Ca²⁺ channels.     

Nicotine Enhances the Cyclic AMP-Dependent Protein Kinase-Mediated Phosphorylation of α4 Subunits of Neuronal Nicotinic Receptors

Abstract: Studies determined whether α4β2 or α3β2 neuronal nicotinic receptors expressed in Xenopus oocytes are substrates for cyclic AMP-dependent protein kinase (PKA) and whether nicotine affects receptor phosphorylation. The cRNAs for the subunits were coinjected into oocytes, and cells were incubated for 24 h in the absence or presence of nicotine (50 n M for α4β2 and 500 n M for α3β2 receptors). Nicotine did not interfere with the isolation of the receptors. When receptors isolated from oocytes expressing α4β2 receptors were incubated with [γ-³²P]ATP and the catalytic subunit of PKA, separated by electrophoresis, and visualized by autoradiography, a labeled phosphoprotein with the predicted molecular size of the α4 subunit was present. Phosphorylation of α4 subunits of α4β2 receptors increased within the first 5 min of incubation with nicotine and persisted for 24 h. In contrast, receptors isolated from oocytes expressing α3β2 receptors did not exhibit a labeled phosphoprotein corresponding to the size of the α3 subunit. Results suggest that the PKA-mediated phosphorylation of α4 and not α3 subunits may explain the differential inactivation by nicotine of these receptors subtypes expressed in oocytes.     

Adventitious regeneration of Juglans nigra L. (eastern black walnut)

Somatic embryos and adventitious shoots were initiated from immature cotyledons 10–14 weeks after anthesis. Maximum embryogenesis occurred 12 weeks after anthesis and maximum shoot organogenesis occurred 14 weeks after anthesis. The best treatment for induction of somatic embryos and adventitious shoots from immature cotyledon explants was on agar-solidified WPM supplemented with 0.1 M 2,4-D and 5.0 M TDZ and incubated in light for the first four weeks. Rooting of adventitious shoots was best if they were quickdipped in 2.5 mM IBA and 1.25 mM NAA in 1% dimethyl formamide and 3.9% ethanol (120 Wood's Rooting Compound: water, by volume). Plantlets from rooted adventitious shoots were acclimatized to the greenhouse.Abbreviations BA Benzyladenine - 2,4-D 2,4-dichlorophenoxyacetic acid - DKW Driver and Kuniyuki (1984) walnut medium - IBA indolebutyric acid - LP Long and Preece medium described herein - NAA naphthaleneacetic acid - PPF photosynthetic photon flux - TDZ thidiazuron - WPM Woody Plant Medium of Lloyd and McCown (1980)     

Isolation of a cDNA encoding a growth-arrest associated gene and characterization of its regulation

We are interested in understanding the molecular events associated with the growth-arrest of vascular SMCs. We constructed a subtracted cDNA library enriched in nucleotide sequences associated with quiescent SMCs. This library was screened with similarly subtracted ³²P-labeled cDNAs to identify growth-arrest associated cDNA clones. Characterization of 19 of these cDNA clones revealed that 9 hybridized to mRNAs that exhibited a 2–3 fold increase in growth-arrested SMCs. In addition, two other cDNAs hybridized to a 5 Kb mRNA that was elevated approximately 10-fold in high density growth-arrested SMCs. Genomic Southern blot hybridization and DNA sequencing analysis indicated that these cDNAs encoded the same gene (LG7) and that this gene may be a member of a multigene family or that it may contain a sequence shared by other unrelated genes. Augmented expression of LG7 was associated with both high cell density and serum deprivation induced growth-arrest. LG7 mRNA expression was down-regulated when SMCs were incubated with FBS or with reagents that arrest cells in early S-phase. Additional analysis with cell cycle specific inhibitors indicated that LG7 mRNA levels were also low when cells were blocked at the G₂ phase of the cell cycle but blockage at mitosis resulted in an elevated level of LG7 mRNA. We further demonstrated that the expression of LG7 was dependent on the presence of a relatively labile protein since protein synthesis inhibitors specifically blocked the expression of this mRNA but not the mRNA expression of α₁(III) collagen or ferritin H-chain. Finally, we demonstrated that Bt₂cAMP was able to induce mRNA expression of LG7 within 2 h, suggesting that this gene may be directly regulated via the cyclic-AMP-dependent protein kinase pathway.     

Reflective organelles in the anterior pigment epithelium of the iris of the European starling Sturnus vulgaris

The ultrastructure and chemical composition of reflective organelles in the anterior pigment epithelium of the iris of the European starling Sturnus vulgaris were examined. The reflective organelles produced a diffuse white reflectance at the iris mid-section which was visible only when the stroma was removed. The pigment granules were clear, angular, and birefringent under the light microscope. In electron micrographs the granules were irregular in shape and density, sometimes crystalline in appearance, but more often they were lost during sectioning or staining. Guanine was abundant in the modified pigment epithelium of the starling, but not in the pigment epithelia of other birds that lacked birefringent granules. Pteridines, such as xanthopterin and leucopterin, were present in small amounts. Pteridines were also present in the iris stroma which had no reflective organelles. The reflective organelles in the starling pigment epithelium resemble both the reflecting platelets of lower vertebrate chromatophores and the reflective granules in the tapeta of various vertebrates. Possible derivation of the organelles from these sources is discussed.     

β-glucuronidase as a marker for clonal analysis of tomato lateral roots

In higher plants, the root-shoot axis established during embryogenesis is extended and modified by the development of primary and lateral apical meristems. While the structure of several shoot apical meristems has been deduced by combining histological studies with clonal analysis, the application of this approach to root apical meristems has been limited by a lack of visible genetic markers. We have tested the feasibility of using a synthetic gene consisting of the maize transposable elementActivator (Ac) inserted between a 35S CaMV promoter and the coding region of a -glucuronidase (GUS) reporter gene as a means of marking cell lineages in roots. The GUS gene was activated in individual cells byAc excision, and the resulting sectors of GUS-expressing cells were detected with the histochemical stain X-Gluc. Sectors in lateral roots originated from bothAc excision in meristematic cells and from parent root sectors that bisect the founder cell population for the lateral root initial. Analysis of root tip sectors confirmed that the root cap, and root proper have separate initials. Large sectors in the body of the lateral root encompassed both cortex and vascular tissues. The number of primary initial cells predicted from the size and arrangement of the sectors observed ranged from two to four and appeared to vary between roots. We conclude that transposon-based clonal analysis using GUS expression as a genetic marker is an effective approach for deducing the functional organization of root apical meristems.     

Characterization of freeze-thaw induced ultrastructural damage to endothelial cells in vitro

Summary The pathophysiology of endothelial cells is important to a variety of vascular conditions including coagulation and hemostasis resulting from clinical frostbite. Use of an in vitro model system demonstrated that when bovine endothelial cells were frozen at 1°C or 20°C/min and thawed immediately (20°C/min), a variety of ultrastructural alterations occurred. Membraneous structures were most extensively damaged, with mitochondria the most sensitive organelle. Low amplitude mitochondrial swelling, first evident at 0°C, progressed to high amplitude swelling by −10°C (frozen). In addition, the rough endoplasmic reticulum was dilated and formed large vesicles with a homogeneous matrix. Nuclear changes first occurred at −15°C. These included separation and distortion of the nuclear membrane, changes in chromatin distribution, and disruption of the nucleolus. Scanning electron microscopy revealed perforated plasma membranes in some cells at −10°C (frozen) and in most cells by −20°C. Cultures frozen at 20°C/min revealed mostly the same ultrastructural damage noted at 1°C/min except a higher percentage of cells exhibited alterations. Data from the recovery index and lactic dehydrogenase (LDH) release correlated well with observed ultrastructural changes. Early swelling of mitochondria and dilation of rough endoplasmic reticulum was not lethal in the absence of freezing. Increased swelling in cytoplasmic organelles coupled with nuclear alterations at −15°C resulted in a decreased survival rate and release of significant quantities of LDH by −20°C. No unique morphological changes were temperature specific, but the total number of cells that displayed alterations increased as temperature decreased. The views, opinions or findings, or both, contained in this report are those of the authros and should not be construed as indicative of an official Department of the Army position, policy, or decision unless so designated by other official documentation.