Scielo RSS <![CDATA[Biological Research]]> vol. 32 num. 4 lang. en <![CDATA[SciELO Logo]]> <![CDATA[LA INVENCION DE LA CELULA]]> <![CDATA[Dysmyelination, demyelination and reactive astrogliosis in the optic nerve of the <I>taiep</I> rat]]> Taiep is an autosomal recessive mutant rat that shows a highly hypomyelinated central nervous system (CNS). Oligodendrocytes accumulate microtubules (MTs) in association with endoplasmic reticulum (ER) membranes forming MT-ER complexes. The microtubular defect in oligodendrocytes, the abnormal formation of CNS myelin and the astrocytic reaction were characterized by immunocytochemical and ultrastructural methods during the first year of life. Optic nerves of both control and taiep rats were processed by the immunoperoxidase method using antibodies against tubulin, myelin basic protein (MBP) and glial fibrillary acidic protein (GFAP). Taiep oligodendrocytes are strongly immunoreactive against tubulin, indicative of a significant accumulation of microtubules. Early differentiated oligodendrocytes observed with electron microscopy show that MT-ER complexes are mainly present in the cell body. This defect increases during the first year of life; oligodendrocytes show large MT-ER complexes projected within oligodendrocyte processes. Using anti-MBP, there was a progressive reduction of immunolabeling in the myelin sheaths as taiep rats grew older. Ultrastructural analysis revealed severely dysmyelinated axons with a frequently collapsed periaxonal collar. However, through age the myelin sheath became gradually infiltrated by MTs, suggesting their contribution to premature loss of myelin in the taiep rat. Axons of one-year-old taiep rats were severely demyelinated. Modifications in astrocytes revealed by the GFAP antibody showed a strong hypertrophy with increased immunostaining in their processes. As demyelination of axons progressed, taiep rats developed a strong astrogliosis. The present findings suggest that in taiep rats the early abnormal myelination of axons affects the adequate maintenance of myelin, leading to a progressive loss of myelin components and severe astrogliosis, features that should be considered in the pathogenesis of dysmyelinating diseases <![CDATA[Structural biology of chemokine receptors]]> Chemokine receptors are G protein-coupled receptors that mediate migration and activation of leukocytes as an important part of a protective immune response to injury and infection. In addition, chemokine receptors are used by HIV-1 to infect CD4 positive cells. The structural bases of chemokine receptor recognition and signal transduction are currently being investigated. High-resolution X-ray diffraction and NMR spectroscopy of chemokines indicate that all these peptides exhibit a common folding pattern, in spite of its low degree of primary-sequence homology. Chemokines' functional motifs have been identified by mutagenesis studies, and a possible mechanism for receptor recognition and activation is proposed, but high-resolution structure data of chemokine receptors is not yet available. Studies with receptor chimeras have identified the putative extracellular domains as the major selectivity determinants. Single-amino acid substitutions in the extracellular domains produce profound changes in receptor specificity, suggesting that motifs in these domains operate as a restrictive barrier to a common activation motif. Similarly HIV-1 usage of chemokine receptors involves interaction of one or more extracellular domains of the receptor with conserved and variable domains on the viral envelope protein gp 120, indicating a highly complex interaction. Elucidating the structural requirements for receptor interaction with chemokines and with HIV-1 will provide important insights into understanding the mechanisms of chemokine recognition and receptor activation. In addition, this information can greatly facilitate the design of effective inmunomodulatory and anti-HIV-1 therapeutic agents <![CDATA[<I>Trans</I> fatty acid isomers in human health and in the food industry]]> Trans fatty acids are unsaturated fatty acids with at least one double bond in the trans configuration. These fatty acids occur naturally in dairy and other natural fats and in some plants. However, industrial hydrogenation of vegetable or marine oils is largely the main source of trans fatty acids in our diet. The metabolic effect of trans isomers are today a matter of controversy generating diverse extreme positions in light of biochemical, nutritional, and epidemiological studies. Trans fatty acids also have been implicated in the etiology of various metabolic and functional disorders, but the main concern about its health effects arose because the structural similarity of these isomers to saturated fatty acids, the lack of specific metabolic functions, and its competition with essential fatty acids. The ingestion of trans fatty acids increases low density lipoprotein (LDL) to a degree similar to that of saturated fats, but it also reduces high density lipoproteins (HDL), therefore trans isomers are considered more atherogenic than saturated fatty acids. Trans isomers increase lipoprotein(a), a non-dietary-related risk of atherogenesis, to levels higher than the corresponding chain-length saturated fatty acid. There is little evidence that trans fatty acids are related to cancer risk at any of the major cancer sites. Considerable improvement has been obtained with respect to the metabolic effect of trans fatty acids due the development of analytical procedures to evaluate the different isomers in both biological and food samples. The oleochemical food industries have developed several strategies to reduce the trans content of hydrogenated oils, and now margarine and other hydrogenated-derived products containing low trans or virtually zero trans are available and can be obtained in the retail market. The present review provides an outline of the present status of trans fatty acids including origin, analytical procedures, estimated ingestion, metabolic effects, efforts to reduce trans isomers in our diet, and considerations for future prospects on trans isomers <![CDATA[Statistical studies on anatomical modifications in the radicle and hypocotyl of cotton induced by NaCl]]> Salinity affects extensive arid and semiarid areas all over the world, producing diminished yields of many crops. Even though there is a variety of research and reviews related to physiological and anatomical modifications produced in salinity-tolerant species, today there are different points of view in relation to this topic, and especially due to technical limitations, there are few articles in which anatomical modifications have been quantified. The aim of this research is to quantitatively and statistically evaluate the modifications that are produced in radicles and hypocotyles of cotton seedlings growing in NaCl concentrations that affect the early ontogenetic stages of this crop. Germination of two varieties of cotton at increasing concentrations (0 to 450 meq/l) of NaCl was studied as well as the growth of seedlings after their germination in water. Anatomical modifications induced in radicles and hypocotyles were analyzed quantitatively with an image analyzer. There were no differences among varieties. While the percentage of germination decreased at the 252 meq/l NaCl level, the velocity of the process and seedling growth was inhibited at lower concentrations. With increased salinity, the cortex and pith of radicle increased in width, while the xylem decreased. In the hypocotyl, the width of cortex increased, as did the number and diameter of gossypol glands. This change deserves further studies in relation to the participation of these glands in the capacity of the seedlings to tolerate salinity <![CDATA[G<SUB>2</SUB> repair and chromosomal damage in lymphocytes from workers occupationally exposed to low-level ionizing radiation]]> The effect of the G2 repair of chromosomal damage in lymphocytes from workers exposed to low levels of X- or g-rays was evaluated. Samples of peripheral blood were collected from 15 radiation workers, 20 subjects working in radiodiagnostics, and 30 healthy control donors. Chromosomal aberrations (CA) were evaluated by scoring the presence of chromatid and isochromatid breaks, dicentric and ring chromosomes in lymphocytes with/without 5mM caffeine plus 3mM-aminobenzamide (3-AB) treatment during G2. Our results showed that the mean value of basal aberrations in lymphocytes from exposed workers was higher than in control cells (p&lt; 0.001). The chromosomal damage in G2, detected with caffeine plus 3-AB treatment was higher than the basal damage (untreated conditions), both in control and exposed populations (p&lt; 0.05). In the exposed workers group, the mean value of chromosomal abnormalities in G2 was higher than in the control (p&lt; 0.0001). No correlation was found between the frequency of chromosome type of aberrations (basal or in G2), and the absorbed dose. Nevertheless, significant correlation coefficients (p&lt; 0.05) between absorbed dose and basal aberrations yield (r = 0.430) or in G2 (r = 0.448) were detected when chromatid breaks were included in the total aberrations yield. Under this latter condition no significant effect of age, years of employment or smoking habit on the chromosomal aberrations yield was detected. However, analysis of the relationship between basal aberrations yield and the efficiency of G2 repair mechanisms, defined as the percentage of chromosomal lesions repaired in G2, showed a significant correlation coefficient (r = -0.802; p&lt; 0.001). These results suggest that in addition to the absorbed dose, the individual G2 repair efficiency may be another important factor affecting the chromosomal aberrations yield detected in workers exposed to low-level ionizing radiation