Showing papers by "National Autonomous University of Mexico published in 1995"

Mandibular elongation and remodeling by distraction: a farewell to major osteotomies.

Abstract: A modified technique for mandibular distraction is reported: an oblique corticotomy is made in the external cortex of the mandible at the level of the gonial angle. Two intraosseous stainless steel pins are inserted and are joined by a softer distraction screw. We make two corticotomies, one horizontal and one vertical, and insert three pins to achieve bidirectional distraction when the mandibular body and the ascending ramus are hypoplasic. This procedure has been used in 87 patients with unilateral hemifacial microsomia and 19 patients with bilateral mandibular hypoplasia. A mean elongation of 19 mm was obtained in the unilateral group. In the bilateral cases a mean vertical elongation of 7.5 mm and a mean horizontal elongation of 14 mm were obtained. A great improvement of the facial asymmetry was achieved in all the patients. The follow-up in this series varies from 3 months to 3 1/2 years (mean, 19 months in unilateral cases and 12 months in bilateral cases). No relapses have been observed.

Patterns and regulation of mycorrhizal plant and fungal diversity

Abstract: The diversity of mycorrhizal fungi does not follow patterns of plant diversity, and the type of mycorrhiza may regulate plant species diversity. For instance, coniferous forests of northern latitudes may have more than 1000 species of ectomycorrhizal (EM) fungi where only a few ectomycorrhizal plant species dominate, but there are fewer than 25 species of arbuscular mycorrhizal (AM) fungi in tropical deciduous forest in Mexico with 1000 plant species. AM and EM fungi are distributed according to biome, with AM fungi predominant in arid and semiarid biomes, and EM fungi predominant in mesic biomes. In addition, AM fungi tend to be more abundant in soils of low organic matter, perhaps explaining their predominance in moist tropical forest, and EM fungi generally occur in soils with higher surface organic matter.

Cyclophosphamide: Review of its mutagenicity for an assessment of potential germ cell risks

Abstract: Cyclophosphamide (CP) is used to treat a wide range of neoplastic diseases as well as some non-malignant ones such as rheumatoid arthritis It is also used as an immunosuppressive agent prior to organ transplantation CP is, however, a known carcinogen in humans and produces secondary tumors There is little absorption either orally or intravenously and 10% of the drug is excreted unchanged CP is activated by hepatic mixed function oxidases and metabolites are delivered to neoplastic cells via the bloodstream Phosphoramide mustard is thought to be the major anti-neoplastic metabolite of CP while acrolein, which is highly toxic and is produced in equimolar amounts, is thought to be responsible for most of the toxic side effects DNA adducts have been formed after CP treatment in a variety of in vitro systems as well as in rats and mice using 3H-labeled CP 32P-postlabeling techniques have also been used in mice However, monitoring of adducts in humans has not yet been carried out CP has also been shown to induce unscheduled DNA synthesis in a human cell line CP has produced mutations in base-pair substituting strains of Salmonella tryphimurium in the presence of metabolic activation, but it has been shown to be negative in the E coli chromotest It has also been shown to be positive in Saccharomyces cerevisiae in D7 strain for many endpoints but negative in D62M for aneuploidy/malsegregation It has produced positive responses in Drosophila melanogaster for various endpoints and in Anopheles stephensi In somatic cells, CP has been shown to produce gene mutations, chromosome aberrations, micronuclei and sister chromatid exchanges in a variety of cultured cells in the presence of metabolic activation as well as sister chromatid exchanges without metabolic activation It has also produced chromosome damage and micronuclei in rats, mice and Chinese hamsters, and gene mutations in the mouse spot test and in the transgenic lacZ construct of Muta Mouse Increases in chromosome damage and gene mutations have been found in the peripheral blood lymphocytes of nurses, pharmacists and female workers occupationally exposured to CP during its production or distribution Chromosome aberrations, sister chromatid exchanges and gene mutations have been observed in somatic cells of patients treated therapeutically with CP In general, there is a maximum dose and an optimum time for the detection of genetic effects because the toxicity associated with high doses of CP will affect cell division In germ cells, CP has been shown to induce genetic damage in mice, rats and hamsters although the vast majority of such studies have used male mice(ABSTRACT TRUNCATED AT 400 WORDS)

Oaxaquia, a Proterozoic microcontinent accreted to North America during the late Paleozoic

Abstract: Grenville-age granulite facies rocks in southern, central, and northeastern Mexico have distinctive geologic features that suggest a common tectonic evolution. The similarities include northwest-trending structural grain from Oaxaca to Tamaulipas, massif-type anorthosite-charnockite complexes, protoliths rich in sedimentary rocks of shallow-marine platform or continental rift-related facies devoid of calc-alkaline volcanic rocks, common metamorphism under granulite facies conditions, U-Pb zircon ages of about 1.0 Ga., and an apparently common history of uplift and cooling. Altogether, this evidence strongly suggests a coherent geologic history for this block. Paleontologic data from the overlying sedimentary sequences indicate that Oaxaquia was not part of Laurentia during most of the Paleozoic. This precludes emplacement of Oaxaquia in its present position by simple lateral displacement from the southern United States as well as a Taconic time of emplacement. Oaxaquia was probably emplaced to its present position during late Paleozoic time. The concept of a Mesoproterozoic “Oaxaquia” microcontinent extending for about 1000 km in Mexico needs to be considered in the reconstruction of the Grenville orogen as a whole and for the Paleozoic tectonic interactions between eastern Laurentia and western Gondwana.

Sexual selection by cryptic female choice on male seminal products - a new bridge between sexual selection and reproductive physiology

Abstract: Selection clearly focuses on differences in reproduction, but studies of reproductive physiology generally have been carried out in a near vacuum of modern evolutionary theory. This lack of contact between the two fields may be about to change. New ideas indicate that sexual selection by cryptic female choice has affected the evolution of products in male semen that influence female reproductive behavior and physiology.

Global Patterns of Mammalian Diversity, Endemism, and Endangerment

Abstract: To assess the conservation status of the world’s land mammals, we compiled data on the number of total species, endemic species, recently extinct species, and currently endangered species for 155 countries. Total species richness was significantly correlated with territorial land area, whereas number of endemic species was only weakly correlated with both area and total number of species. The large amount of variation left unexplained by species-area regressions reflects the influence of other factors, such as latitude, topographic and habitat heterogeneity, and historical biogeography, on species richness and especially on patterns of endemism. Countries of particular conservation concern, because they have rich mammalian faunas containing many endemic species, are the large islands of Australia, Madagascar, Indonesia, and the Philippines, as well as continental Mexico. Patterns of recent extinctions and the current endangered status of species were difficult to interpret, largely because of inadequate and inconsistent data. The majority of officially listed endangered species are large, well known, and popular mammals, such as primates, ungulates, and carnivores, whereas the majority of species known to have gone recently extinct and likely to be currently threatened are small and inconspicuous, such as rodents and bats. Our work not only illustrates the role of ecological, evolutionary, and biogeographic processes in the origin and maintenance of land mammal diversity, it also presents the information at the level of biogeographic regions and political units where management and policy must be applied in order to slow the loss of this diversity. Para determinar el estado de conservacion de los mamiferos del mundo, compilamos una base de datos para 155 paises que incluyo al numero total de especies, al de las endemicas y al de las en peligro de extincion o extintas recientemente. El numero total de especies estuvo significativamente correlacionado con el area territorial; sin embargo, el numero de especies endemicas mostro una debil correlacion tanto con el area territorial como con el numero total de especies. La considerable proporcion de la variacion que no fue explicada por las regresiones entre al area y el numero de especies refleja la influencia de otros factores tales como la latitud, la heterogeneidad del habitat y topografia, y la biogeografia historica, en los patrones de diversidad y endemicidad Paises de especial interes para la conservacion debido a su diversa fauna de mamiferos, que incluye a muchas especies endemicas, son las islas de gran extension como Australia, Madagascar, Indonesia y Filipinas, y tambien Mexico. Los patrones de extinciones recientes y de especies en peligro de extincion fueron dificiles de interpretar, principalmente por la calidad e inconsistencia de la informacion disponible. La mayoria de los mamiferos en peligro de extincion son de gran tamano y esteticamente atractivos, tales como primates, ungulados y carnivoros. Sin embargo, la mayoria de las especies que se han extinguido son pequenas, tales como murcielagos y roedores. El presente estudio ademas de ilustrar el papel de procesos ecologicos, evolutivos y biogeograficos en el origen y mantenimiento de la diversidad de mamiferos terrestres, presenta informacion a niveles de regiones biogeograficas y unidades politicas en donde se deben aplicar las politicas de conservacion y manejo para reducir la perdida de esta diversidad.

The evolution of C/O in dwarf galaxies from Hubble Space Telescope FOS observations

Abstract: We present UV observations of seven H II regions in low-luminosity dwarf irregular galaxies and the Magellanic Clouds obtained with the Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST) in order to measure the C/O abundance ratio in the interstellar medium (ISM) of those galaxies. We measure both O III 1666 A and C III 1909 A in our spectra, enabling us to determine C(+2)/O(+2) with relatively small uncertainties. The results from our HST observations show a continuous increase in C/O with increasing O/H, consistent with a power law having an index of 0.43 +/- 0.09 over the range -4.7 to -3.6 in log (O/H). One possible interpretation of this trend is that the most metal-poor galaxies are the youngest and dominated by the products of early enrichment by massive stars, while more metal-rich galaxies show increasing, delayed contributions of carbon from intermediate-mass stars. Our results also suggest that it may not be appropiate to combine abundances in irregular galaxies with those in spiral galaxies to study the evolution of chemical abundances. Our measured C/O ratios in the most metal-poor galaxies are consistent with predictions of nucleosynthesis from massive stars for Weaver & Woosley's best estimate for the 12C(alpha, gamma) 16O nuclear reaction rate, assuming negligible contanmination from carbon produced in intermediate-mass stars in these galaxies. We detect a weak N III 1750 A multiplet in SMC N88A and obtain interesting upper limits for two other objects. Our 2 sigma uppr limits on the 1750 A feature indicate that the N(+2)/O(+2) ratios in these objects are not significantly larger than the N(+)/O(+) ratios measured from optical spectra. This behavior is consistent with predictions of photionization models, although better detections of N III are needed to confirm the results.

Effect of hydrolysis catalyst on the Ti deficiency and crystallite size of sol-gel-TiO2 crystalline phases

Abstract: We prepared sol-gel titania by using different hydrolysis catalysts, and characterized it by x-ray powder diffraction. The structure of the crystalline phases—brookite, anatase, and rutile—in the samples annealed between 70 and 900 °C was refined by using the Rietveld technique. From the refinement we obtained the structure parameters, the concentration of each phase, and their average crystallite size. These quantities and their evolution with temperature depended on the hydrolysis catalyst. Anatase and rutile were deficient in Ti, suggesting that their crystalline structure contained hydrogen atoms, forming OH− ions inside. In anatase this deficiency depended on its crystallite size, but it was constant in rutile. When anatase was annealed, it dehydroxylized, producing either crystallitc growing up or its conversion into rutile. From the analysis we also found the conditions for obtaining single-phase samples that could be used as precursors for making up titania single-phase thin films.

Gene conversions and unequal crossovers between CYP21 (steroid 21-hydroxylase gene) and CYP21P involve different mechanisms

Abstract: Most cases of congenital adrenal hyperplasia, the inherited inability to synthesize cortisol, are caused by mutations in the steroid 21-hydroxylase gene (CYP21). Steroid 21-hydroxylase deficiency is unusual among genetic diseases in that approximately 95% of the mutant alleles have apparently been generated by recombination between a normally active gene (CYP21) and a linked pseudogene (CYP21P). Approximately 20% of mutant alleles carry DNA deletions of 30 kb that have presumably been generated by unequal meiotic crossing-over, whereas 75% carry one or more mutations in CYP21 that are normally found in the CYP21P pseudogene. These latter mutations are termed "gene conversions," although the mechanism by which they are generated is not well understood. To assess the frequency at which these different recombination events occur, we have used PCR to detect de novo deletions and gene conversions in matched sperm and peripheral blood leukocyte DNA samples from normal individuals. Deletions with breakpoints in a 100-bp region in intron 2 and exon 3 were detected in sperm DNA samples with frequencies of approximately 1 in 10(5)-10(6) genomes but were never detected in the matching leukocyte DNA. Gene conversions in the same region occur in approximately 1 in 10(3)-10(5) genomes in both sperm and leukocyte DNA. These data suggest that whereas deletions occur exclusively in meiosis, gene conversions occur during both meiosis and mitosis, or perhaps only during mitosis. Thus, gene conversions must occur by a mechanism distinct from unequal crossing-over.

The origin of life--did it occur at high temperatures?

Abstract: A high-temperature origin of life has been proposed, largely for the reason that the hyperthermophiles are claimed to be the last common ancestor of modern organisms. Even if they are the oldest extant organisms, which is in dispute, their existence can say nothing about the temperatures of the origin of life, the RNA world, and organisms preceding the hyperthermophiles. There is no geological evidence for the physical setting of the origin of life because there are no unmetamorphosed rocks from that period. Prebiotic chemistry points to a low-temperature origin because most biochemicals decompose rather rapidly at temperatures of 100°C (e.g., half-lives are 73 min for ribose, 21 days for cytosine, and 204 days for adenine). Hyperthermophiles may appear at the base of some phylogenetic trees because they outcompeted the mesophiles when they adapted to lower temperatures, possibly due to enhanced production of heat-shock proteins.

Cloning of the two pyruvate kinase isoenzyme structural genes from Escherichia coli: the relative roles of these enzymes in pyruvate biosynthesis.

Abstract: We report the cloning of the pykA and pykF genes from Escherichia coli, which code for the two pyruvate kinase isoenzymes (ATP:pyruvate 2-O-phosphotransferases; EC 2.7.1.40) in this microorganism. These genes were insertionally inactivated with antibiotic resistance markers and utilized to interrupt one or both pyk genes in the E. coli chromosome. With these constructions, we were able to study the role of these isoenzymes in pyruvate biosynthesis.

Effect of total sleep deprivation on reaction time and waking EEG activity in man

Abstract: Nine paid volunteers were sleep deprived over a period of 40 hours. Every 2 hours during total sleep deprivation (TSD) and after recovery sleep, oral temperature (OT), reaction time (RT) in a vigilance task and electroencephalogram (EEG) with eyes open and closed (C3, C4, T3 and T4) were recorded. Ten artifact-free samples from each condition were Fourier transformed. Absolute power was calculated for six bands. Analyses of variance with deprivation and time of day as factors showed the following significant results : 1) TSD induced an increase in RT, of theta power in all derivations, of beta power in both centrals and a decrease of alpha power with eyes closed ; OT was not affected. 2) All bands showed a peak of power at 1800 hours, 2 hours in advance of the OT acrophase at 2000 hours. All variables recovered baseline values after 1 night of sleep. Significant linear correlations of hours of wakefulness with EEG and RT, and of EEG power with OT and RT, were observed. The present findings show a linear increase in EEG power and RT with TSD, and a diurnal oscillation of EEG power, which is independent of TSD.

New World Podostemaceae: Ecological and evolutionary enigmas

Abstract: The largely tropical Podostemaceae occur in a unique habitat for angiosperms: attached to rocks in river rapids and waterfalls. Little taxonomic work has been published on New World Podostemaceae since Van Royen's monograph in the early 1950s. A paucity of complete herbarium material severely limits taxonomic study and precludes addressing a range of enigmatic ecological and evolutionary issues that relate to the family. The size, high level of endemism, and life history of the family are discussed. The distributions of two species in Mexico are used to illustrate the need for concerted collecting efforts. Recommendations for collection strategies are made that reflect the unusual habitat and life history of these plants.

Starvation stress modulates the expression of the Aspergillus nidulans brlA regulatory gene.

Abstract: SUMMARY: Expression of the Aspergillus nidulans brlA gene plays a fundamental role in the switch from vegetative growth to asexual reproduction. Using a media-shifting protocol to induce submerged sporulation and brlA-lacZ as an expression marker, it was shown that carbon and nitrogen starvation stress induced brlA transcription to different degrees. Glucose starvation induced brlA rapidly to high levels and resulted in spore formation on reduced conidiophores, whereas nitrogen starvation induced brlA gradually to lower levels and sporulation occurred to a lesser extent but from more complex conidiophores. β-Galactosidase activity paralleled brlAα and brlAβ mRNA. No clear qualitative differences between the two brlA transcripts were found in these starvation conditions, suggesting that the different patterns of sporulation could be explained by quantitative expression differences. Since brlA mRNA did not accumulate in the presence of a high glucose concentration, we investigated the role of other carbon sources on brlA expression. Non-repressing carbon sources such as glycerol, acetate and arabinose were as effective as glucose in preventing brlA mRNA accumulation, suggesting that the glucose effects on brlA expression could be explained as a response to nutrient starvation, rather than by carbon catabolite repression. Despite similar low levels of brlA transcripts being detected during growth in glucose or non-repressing carbon sources, conidiophores were formed only in medium containing glycerol, acetate or arabinose. When mycelia were not shifted to starvation conditions, sporulation was not observed in standard minimal medium even after glucose was exhausted, unless the medium was buffered. This and other results suggest that strong deviation from external neutral pH partially prevented full induction and/or function of brlA.

Comparing plant life histories using elasticity analysis: the importance of life span and the number of life-cycle stages.

Abstract: Recent studies have used transition matrix elasticity analysis to investigate the relative role of survival (L), growth (G) and fecundity (F) in determining the estimated rate of population increase for perennial plants. The relative importance of these three variables has then been used as a framework for comparing patterns of plant life history in a triangular parameter space. Here we analyse the ways in which the number of life-cycle stages chosen to describe a species (transition matrix dimensionality) might influence the interpretation of such comparisons. Because transition matrix elements describing survival ("stasis") and growth are not independent, the number of stages used to describe a species influences their relative contribution to the population growth rate. Reduction in the number of stages increases the apparent importance of stasis relative to growth, since each becomes broader and fewer individuals make the transition to the next stage per unit time period. Analysis of a test matrix for a hypothetical tree species divided into 4-32 life-cycle stages confirms this. If the number of stages were defined in relation to species longevity so that mean residence time in each stage were approximately constant, then the elasticity of G would reflect the importance of relative growth rate to λ. An alternative, and simpler, approach to ensure comparability of results between species may be to use the same number of stages regardless of species longevity. Published studies for both herbaceous and woody species have tended to use relatively few stages to describe life cycles (herbs: n=45, [Formula: see text]; woody plants: n=21, [Formula: see text]) and so approximate this approach. By using the same number of stages regardless of longevities, the position of species along the G-L side of the triangular parameter space largely reflects differences in longevity. The extent of variation in elasticity for L, G and F within and between species may also be related to factors such as successional status and habitat. For example, the shade-tolerant woody species, Araucaria cunninghamii, shows greater importance for stasis (L), while the gap-phase congener species, Araucaria hunsteinii, shows higher values for G (although values are likely to vary with the stage of stand development).

Multiwavelength Energy Distributions and Bolometric Luminosities of the 12--Micron Galaxy Sample

Abstract: Aperture photometry from our own observations and the literature is presented for the 12\um\ Galaxies in the near infrared J, H and K bands and, in some cases, in the L band. These data are corrected to ``total'' near--infrared magnitudes, (with a typical uncertainty of 0.3 magnitudes) for a direct comparison with our IRAS fluxes which apply to the entire galaxy. The corrected data are used to derive integrated total NIR and FIR luminosities. We then combine these with blue photometry and an estimate of the flux contribution from cold dust at wavelengths longward of 100\um\ to derive the first {\it bolometric\/} luminosities for a large sample of galaxies. We use multiwavelength correlations to identify several combinations of infrared colors which discriminate between Seyfert~1 and~2 galaxies, LINERs, and ultraluminous starbursts. We find that bolometric luminosity is more closely proportional to 12-micron luminosity than to 60-micron, 25-micron or optical luminosity.

Geometry of deformations of relativistic membranes.

Abstract: A kinematical description of infinitesimal deformations of the world sheet spanned in spacetime by a relativistic membrane is presented. This provides a framework for obtaining both the classical equations of motion and the equations describing infinitesimal deformations about solutions of these equations when the action describing the dynamics of this membrane is constructed using any local geometrical world sheet scalars. As examples, we consider a Nambu membrane, and an action quadratic in the extrinsic curvature of the world sheet.

Exact solvability of the calogero and sutherland models

Abstract: Translationally invariant symmetric polynomials as coordinates for N-body problems with identical particles are proposed. It is shown that in those coordinates the Calogero and Sutherland N-body Hamiltonians, after appropriate gauge transformations, can be presented as a quadratic polynomial in the generators of the algebra slN in finitedimensional degenerate representation. The exact solvability of these models follows from the existence of the infinite flag of such representation spaces, preserved by the above Hamiltonians. A connection with Jack polynomials is discussed.

The early clinical recognition of juvenile‐onset ankylosing spondylitis and its differentiation from juvenile rheumatoid arthritis

Abstract: Objective. To determine which early clinical data differentiate juvenile-onset ankylosing spondylitis (AS) from juvenile rheumatoid arthritis (JRA). Methods. Medical records of 35 patients with juvenile-onset AS and 75 with JRA (excluding type II pauciarticular JRA), all of whom had disease onset at age ≤16 years, disease duration of ≤2½ years at the initial visit to the rheumatology clinic, and followup of ≥ 10 years, were analyzed retrospectively with regard to features of disease found 6 months, 12 months, and 10 years after onset. Results. At 6 months, various features appeared more frequently in the juvenile-onset AS group than in the JRA group, i.e., pauciarthritis (54.3% versus 30.7%; P = 0.03, odds ratio [OR] = 2.7), enthesopathy (82.9% versus 0%; P < 0.0001, OR = 321.4), tarsal disease (71.4% versus 1.3%; P < 0.0001, OR = 185.0), and lumbar/sacroiliac symptoms (11.4% versus 0%; P = 0.02, OR = 11.9). At 12 months, the features found more frequently among juvenile-onset AS patients than JRA patients were enthesopathy (88.6% versus 4.0%; P < 0.0001, OR = 186.0), tarsal disease (85.7% versus 10.7%; P < 0.0001, OR = 50.3), and knee disease (100.0% versus 82.7%; P = 0.04, OR = 8.0). Involvement of the upper extremities (especially the hands) was found in significantly fewer juvenile-onset AS patients compared with the JRA group. Definite involvement of the spine and sacroiliitis in juvenile-onset AS occurred after a mean ± SD of 7.3 ± 2.0 years. Conclusion. Regardless of axial disease, enthes opathy and tarsal disease in children who have arthritis of the lower, but not of the upper extremities differentiate juvenile-onset AS from JRA within 1 year of symptoms. The discriminative value of these parameters approaches that of axial disease (the gold standard) throughout the followup period.