MORPHOLOGICAL EVOLUTION IN MUROID RODENTS I. CONSERVATIVE PATTERNS OF CRANIOMETRIC COVARIANCE AND THEIR ONTOGENETIC BASIS IN THE NEOTROPICAL GENUS ZYGODONTOMYS

Analyses of craniodental measurement data from 15 wild-collected population samples of the Neotropical muroid rodent genus Zygodontomys reveal consistent patterns of relative variability and correlation that suggest a common latent structure. Eigenanalysis of each sample covariance matrix of logarithms yields a first principal component that accounts for a large fraction of the total variance. Variances of subsequent sample principal components are much smaller, and the results of bootstrap resampling together with asymptotic statistics suggest that characteristic roots of the covariance matrix after the first are seldom distinct. The coefficients of normalized first principal components are strikingly similar from sample to sample: inner products of these vectors reveal an average between-sample correlation of 0.989, and the mean angle of divergence is only about eight degrees. Since first principal component coefficients identify the same contrasts among variables as comparisons of relative variability and correlation, we conclude that a single factor accounts for most of the common latent determination of these sample dispersions. Analyses of variance based on toothwear (a coarse index of age) and sex in the wild-collected samples, and on known age and sex in a captive-bred population, reveal that specimen scores on sample first principal components are age- and sex-dependent; residual sample dispersion, however, is essentially unaffected by age, sex, or age × sex interaction. The sample first principal component therefore reflects the covariance among measured dimensions induced by general growth, and its coefficients are interpretable as exponents of postnatal growth allometry. Path-analytic models that incorporate prior knowledge of the equivalent allometric effects of general growth within these samples can be used to decompose the between-sample variance by factors corresponding to other ontogenetic mechanisms of form change. The genetic or environmental determinants of differences in sample mean phenotypes induced by such mechanisms, however, can be demonstrated only by experiment.     

The nitrogen cycle in a ‘Terra Firme’ rainforest on oxisol in the Amazon territory of Venezuela

Standing stocks and fluxes of nitrogen, including nitrogen fixation and denitrification, were measured in a tropical rainforest on Oxisol in the Amazon Territory of Venezuela. The standing stock of nitrogen was comparable to that of temperate forests, but was higher than that in an adjacent forest on Spodosol. Fluxes were higher than in forests in the temperate zone, but lower than in another tropical forest on more fertile soil. Even though nitrogen was abundant, this does not mean that nitrogen could not be limiting to agriculture if the forest is cleared and the land cultivated. The nitrogen fixing and nitrogen conserving mechanisms are dependent upon the structure of the undisturbed forest, and destruction of the forest would eventually decrease the input of nitrogen to the soil.     

Localization of essential rhombomeres for respiratory rhythm generation in bullfrog tadpoles using a binary search algorithm: Rhombomere 7 is essential for the gill rhythm and suppresses lung bursts before metamorphosis

Frog metamorphosis includes transition from water breathing to air breathing but the extent to which such a momentous change in behavior requires fundamental changes in the organization of the brainstem respiratory circuit is unknown. Here, we combine a vertically mounted isolated brainstem preparation, “the Sheep Dip,” with a search algorithm used in computer science, to identify essential rhombomeres for generation of ventilatory motor bursts in metamorphosing bullfrog tadpoles. Our data suggest that rhombomere 7, which in mammals hosts the PreBötC (PreBötzinger Complex; the likely inspiratory oscillator), is essential for gill and buccal bursts. Whereas rhombomere 5, in close proximity to a brainstem region associated with the mammalian expiratory oscillator, is essential for lung bursts at both stages. Therefore, we conclude there is no rhombomeric translocation of respiratory oscillators in bullfrogs as previously suggested. In premetamorphic tadpoles, functional ablation of rhombomere 7 caused ectopic expression of precocious lung bursts, suggesting the gill oscillator suppresses an otherwise functional lung oscillator in early development. © 2013 Wiley Periodicals, Inc. Develop Neurobiol 73: 888–898, 2013     

Characterization of bacterial diversity in pulque, a traditional Mexican alcoholic fermented beverage, as determined by 16S rDNA analysis

The bacterial diversity in pulque, a traditional Mexican alcoholic fermented beverage, was studied in 16S rDNA clone libraries from three pulque samples. Sequenced clones identified as Lactobacillus acidophilus, Lactobacillus strain ASF360, L. kefir, L. acetotolerans, L. hilgardii, L. plantarum, Leuconostoc pseudomesenteroides, Microbacterium arborescens, Flavobacterium johnsoniae, Acetobacter pomorium, Gluconobacter oxydans, and Hafnia alvei, were detected for the first time in pulque. Identity of 16S rDNA sequenced clones showed that bacterial diversity present among pulque samples is dominated by Lactobacillus species (80.97%). Seventy-eight clones exhibited less than 95% of relatedness to NCBI database sequences, which may indicate the presence of new species in pulque samples.     

Metabolism of 20-hydroxyeicosatetraenoic acid by cyclooxygenase. Formation and identification of novel endothelium-dependent vasoconstrictor metabolites

We recently demonstrated that 20-hydroxyeicosatetraenoic acid (20-HETE) constricts rat aortic rings. The contractile response was partially dependent on the presence of endothelium and was abolished by pretreatment of the rings with either indomethacin or the endoperoxide/thromboxane receptor antagonist, SQ29548. Addition of GSH or SnCl2 to the organ bath diminished the contractile response of 20-HETE, whereas preincubation of the rings with a thromboxane synthase inhibitor did not affect the 20-HETE induced contractions. Short time incubation (2 min) of 20-HETE with ram seminal vesicle microsomes in the presence of p-hydroxymercurybenzoate yielded metabolites which migrated similarly on thin layer chromatography to the known arachidonate endoperoxides prostaglandin (PG) G2 and PGH2 and possess vasoconstrictory properties. The vasoconstriction was dose-dependent with a half-life of approximately 6.3 +/- 0.6 min. Addition of SQ29548 to the aortic ring bath 1 min after metabolite elicited vasoconstriction produced immediate relaxation. Furthermore, pretreatment of the rings with SQ29548 totally abolished the contraction. SnCl2 reduction of the metabolites produced in incubation of rat seminal vesicles with 20-HETE and p-hydroxymercurybenzoate resulted in a single radioactive peak which was further identified by gas chromatography/mass spectrometry as 20-hydroxy-PGF2 alpha. The inhibitory effect of SQ29548, the appearance of labile metabolites with a half-life of approximately 6 min and the production of 20-hydroxy-PGF2 alpha by SnCl2 reduction clearly indicate that the vasoconstrictor metabolites of 20-HETE are the labile endoperoxides of 20-HETE, 20-hydroxy-PGG2, and 20-hydroxy-PGH2.     

Synthesis and cardiovascular activity of metoprolol analogues

The synthesis of four novel analogues of metoprolol, a well-known beta1-blocker used to reduce arterial blood pressure, is described. The preparation of (2S,2'S)-7, (2R,2'S)-7, (2R,2'R)-8, and (2S,2'R)-8 was based on the reaction of racemic 2-[4-(2'-methoxyethyl)-phenoxymethyl]-oxirane (4) with (R)- or (S)-2-amino-1-butanol. Salient characteristics of analogues 7 and 8 relative to metoprolol are the incorporation of an additional stereogenic center, as well as a methyl group and a hydroxyl function on the nitrogen-containing chain. These novel derivatives present significant hypotensive and bradycardiac activity, although no blocking action toward beta1 and beta2 adrenergic receptor.     

Distribution patterns of Dikarya in arid and semiarid soils of Baja California,Mexico

Approximately four-fifths of the land area of Baja California (BC) in Mexico are occupied by arid and semiarid soils, the mycobiota of which is virtually uncharacterized. In the first culture-independent study of the mycobiota of BC, we collected soil from five different locations in the region and constructed a Dikarya-specific gene library for the ITS region of nuclear ribosomal DNA. Clones were analyzed by RFLP, were sequenced for phylogenetic analyses, and diversity and similarity indices were calculated. The ascomycete Penicillium dipodomyicola was the most frequent fungus found in soil at the most arid location studied, and the basidiomycete Coprinellus radians was the most frequent at the location receiving the highest rainfall. Other frequent members of the soil mycobiota were identified as Alternaria spp., Ceratobasidium sp., Coniozyma leucospermi, Nematoctonus robustus, Penicillium griseofulvum, Tulostoma kotlabae and uncultured members of the Dikarya. Several sequences were identified as those of uncultured fungi, one of which was previously reported from other hot deserts. Arid soils and the transitional zones between arid and semiarid soils had the most similar fungal diversity, with the former soils having a community from which basidiomycetes were absent, and the soil receiving the highest precipitation having a community dominated by basidiomycetes.     

Muscle Tissue Damage Induced by the Venom of Bothrops asper: Identification of Early and Late Pathological Events through Proteomic Analysis

The time-course of the pathological effects induced by the venom of the snake Bothrops asper in muscle tissue was investigated by a combination of histology, proteomic analysis of exudates collected in the vicinity of damaged muscle, and immunodetection of extracellular matrix proteins in exudates. Proteomic assay of exudates has become an excellent new methodological tool to detect key biomarkers of tissue alterations for a more integrative perspective of snake venom-induced pathology. The time-course analysis of the intracellular proteins showed an early presence of cytosolic and mitochondrial proteins in exudates, while cytoskeletal proteins increased later on. This underscores the rapid cytotoxic effect of venom, especially in muscle fibers, due to the action of myotoxic phospholipases A₂, followed by the action of proteinases in the cytoskeleton of damaged muscle fibers. Similarly, the early presence of basement membrane (BM) and other extracellular matrix (ECM) proteins in exudates reflects the rapid microvascular damage and hemorrhage induced by snake venom metalloproteinases. The presence of fragments of type IV collagen and perlecan one hour after envenoming suggests that hydrolysis of these mechanically/structurally-relevant BM components plays a key role in the genesis of hemorrhage. On the other hand, the increment of some ECM proteins in the exudate at later time intervals is likely a consequence of the action of endogenous matrix metalloproteinases (MMPs) or of de novo synthesis of ECM proteins during tissue remodeling as part of the inflammatory reaction. Our results offer relevant insights for a more integrative and systematic understanding of the time-course dynamics of muscle tissue damage induced by B. asper venom and possibly other viperid venoms.     

Role of SP65 in assembly of the Dictyostelium discoideum spore coat

Like the cyst walls of other protists, the spore coat of Dictyostelium discoideum is formed de novo to protect the enclosed dormant cell from stress. Spore coat assembly is initiated by exocytosis of protein and polysaccharide precursors at the cell surface, followed by the infusion of nascent cellulose fibrils, resulting in an asymmetrical trilaminar sandwich with cellulose filling the middle layer. A molecular complex consisting of cellulose and two proteins, SP85 and SP65, is associated with the inner and middle layers and is required for proper organization of distinct proteins in the outer layer. Here we show that, unlike SP85 and other protein precursors, which are stored in prespore vesicles, SP65 is, like cellulose, synthesized just in time. By tagging the SP65 locus with green fluorescent protein, we find that SP65 is delivered to the cell surface via largely distinct vesicles, suggesting that separate delivery of components of the cellulose-SP85-SP65 complex regulates its formation at the cell surface. In support of previous in vivo studies, recombinant SP65 and SP85 are shown to interact directly. In addition, truncation of SP65 causes a defect of the outer layer permeability barrier as seen previously for SP85 mutants. These observations suggest that assembly of the cellulose-SP85-SP65 triad at the cell surface is biosynthetically regulated both temporally and spatially and that the complex contributes an essential function to outer layer architecture and function.