Expression of N-linked sialyl Le(x) determinants and O-glycans in the carbohydrate moiety of human amniotic fluid transferrin during pregnancy

Transferrin, a glycoprotein involved in iron transport in body fluids, was isolated from amniotic fluid of a hydramniospatient by sequential anion-exchange chromatography and gel filtration. The N-glycans of human amniotic fluid transferrin (hAFT) were enzymatically liberated by PNGase-F digestion, isolated by gel filtration and fractionated by (high-pH) anion-exchange chromatography. After alkaline borohydride treatment of native hAFT, the released O-glycans were isolated by gel filtration and fractionated by anion-exchange chroma-tography. Structure elucidation of 14 N- and 2 O-glycans was performed by 500 or 600 MHz1H-NMR spectroscopy. Besides conventional N-glycans established earlier for human serum transferrin (hST), new (alpha1-3)-fucosylated N- glycans were found, representing sialyl Le(x) elements. Furthermore, as compared to hST, a higher degree of (alpha1-6)-fucosylation and an increase in branching from di- to triantennary compounds has been detected. The presence of O-glycans is demonstrated for the first time in transferrin.      

Terminal phase of cytokinesis in D-98S cells

The events leading to the completion of cytokinesis after the formation of the midbody and intercellular bridge in D-98S cells were studied with light and electron microscopy. Pairs of daughter cells corresponding to different stages of cytokineses, as determined previously form time lapse films, were selected from embedded monolayers for serial sectioning. Separation of daughter cells is preceded by the reduction in diameter of the intercellular bridge from 1-1.5 μm to approx. 0.2 μm. Two processes contribute to this reduction: (a) The intercellular bridge becomes gradually thinner after telophase; a progressive breakdown of midbody structures accompanies this change; and (b) the more significant contribution to reduction in bridge diameter occurs through the localized constriction of a segment of the intercellular bridge.. The microtubules within the constricted portion of the bridge are forced closer together, and some microtubules disappear as this narrowing progresses. The plasma membrane over the narrowed segments is thrown into a series of wavelike ripples. Separation of daughter cells is achieved through movements of the cells which stretch and break the diameter-reduced bridge. The midbody is discarded after separation and begins to deteriorate. Occasional pairs of daughter cells were found in which incomplete karyokineses resulted in their nuclei being connected by a strand of nuclear material traversing the bridge and midbody. Such cells do not complete cytokinesis but merge together several hours after telophase. This merging of daughter cells coincides with the nearly complete breakdown of the midbody.     

Vegetal cover estimated by digital photographs related to biomass in a grassland site in northern Mexico

A regression model was used to determine the relationship between aerial herbaceous biomass and vegetation coverage estimated by digital images. Four samplings (n=36 each date) of vegetation cover and herbaceous biomass were performed during the growing season in 2011 in a grassland dominated by Bouteloua gracilis in La Cieneguilla, Municipality of Villa Hidalgo, Durango. Average production of dry biomass was 37.36 ± 9.66 g/m², and mean vegetation cover 30.02%. Dry biomass data were tested for normality using the test of Kolmogorov Smirnov, finding a lack of fit. The data were subjected to a logarithmic transformation and the model Ln(y) = 1.637926 + 0.08501X - 0.000586X² with an adjusted R² = 0.89 was found. In order to validate this model, another five samplings were carried out in 2013 at the same site during summer and autumn, using the same sampling size for each date as in 2011. Data collected in 2013 were analyzed with the model Ln (y) = β₀ + β₁X + β₂X². A comparison of regression coefficients was carried out between the 2011 and 2013 models with t (180+144-9-11-2=302, p<0.05) = 1.967. The results indicated that it is possible to use the 2011 regression model to estimate herbaceous aerial biomass from vegetation cover measurements with aerial photographs in La Cieneguilla site during summer and fall.     

Sexual selection,germline mutation rate and sperm competition

Background  

An important component of sexual selection arises because females obtain viability benefits for their offspring from their mate choice. Females choosing extra-pair fertilization generally favor males with exaggerated secondary sexual characters, and extra-pair paternity increases the variance in male reproductive success. Furthermore, females are assumed to benefit from 'good genes' from extra-pair sires. How additive genetic variance in such viability genes is maintained despite strong directional selection remains an evolutionary enigma. We propose that sexual selection is associated with elevated mutation rates, changing the balance between mutation and selection, thereby increasing variance in fitness and hence the benefits to be obtained from good genes sexual selection. Two hypotheses may account for such elevated mutation: (1) Increased sperm production associated with sperm competition may increase mutation rate. (2) Mutator alleles increase mutation rates that are revealed by the expression of condition-dependent secondary sexual characters used by choosy females during their mate choice. M Petrie has independently developed the idea that mutator alleles may account for the maintenance of genetic variation in viability despite strong directional selection.     

微藻光合作用制氢——能源危机的最终出路?

微藻光合作用制氢是解决能源短缺问题的有效途径.本文介绍了微藻光合作用制氢的机理,包括蓝藻固氮酶和可逆氢酶产氢以及绿藻可逆氢酶产氢的机理.在分析光合制氢限制因素的基础上,指出筛选和构建高效放氢藻株是制氢的有效途径.然后介绍了“直接生物光解”、固氮酶放氢和“间接生物光解”等制氢方式.利用绿藻“间接生物光解”水制氢是一种最有发展潜力的制氢方式.本文最后展望了微藻光合制氢的前景.     

Genome-wide analysis of the diatom cell cycle unveils a novel type of cyclins involved in environmental signaling

Background

Despite the enormous importance of diatoms in aquatic ecosystems and their broad industrial potential, little is known about their life cycle control. Diatoms typically inhabit rapidly changing and unstable environments, suggesting that cell cycle regulation in diatoms must have evolved to adequately integrate various environmental signals. The recent genome sequencing of Thalassiosira pseudonana and Phaeodactylum tricornutum allows us to explore the molecular conservation of cell cycle regulation in diatoms.

Results

By profile-based annotation of cell cycle genes, counterparts of conserved as well as new regulators were identified in T. pseudonana and P. tricornutum. In particular, the cyclin gene family was found to be expanded extensively compared to that of other eukaryotes and a novel type of cyclins was discovered, the diatom-specific cyclins. We established a synchronization method for P. tricornutum that enabled assignment of the different annotated genes to specific cell cycle phase transitions. The diatom-specific cyclins are predominantly expressed at the G1-to-S transition and some respond to phosphate availability, hinting at a role in connecting cell division to environmental stimuli.

Conclusion

The discovery of highly conserved and new cell cycle regulators suggests the evolution of unique control mechanisms for diatom cell division, probably contributing to their ability to adapt and survive under highly fluctuating environmental conditions.