Nuclear coupling and polarization in molecular transport junctions: beyond tunneling to function

Much current experimental research on transport in molecular junctions focuses on finite voltages, where substantial polarization-induced nonlinearities may result in technologically relevant device-type responses. Because molecules have strong polarization responses to changing charge state or external field, molecules isolated between electrodes can show strongly nonlinear current-voltage responses. For small applied voltages (up to approximately 0.3 volt), weak interaction between transporting electrons and molecular vibrations provides the basis for inelastic electron tunneling spectroscopy. At higher voltages and for certain time scale regimes, strong coupling effects occur, including Coulomb blockade, negative differential resistance, dynamical switching and switching noise, current hysteresis, heating, and chemical reactions. We discuss a general picture for such phenomena that arise from charging, strong correlation, and polarization (electronic and vibrational) effects in the molecule and at the interface.     

Electron transport in molecular wire junctions

Molecular conductance junctions are structures in which single molecules or small groups of molecules conduct electrical current between two electrodes. In such junctions, the connection between the molecule and the electrodes greatly affects the current-voltage characteristics. Despite several experimental and theoretical advances, including the understanding of simple systems, there is still limited correspondence between experimental and theoretical studies of these systems.     

The yin and yang of corpus luteum-derived endothelial cells: balancing life and death

A dense network of capillaries irrigates the corpus luteum (CL) allowing an intricate cross talk between luteal steroiodgenic and endothelial cell (EC) types. Indeed, luteal endothelial cells (LEC) play pivotal roles throughout the entire CL life-span. Microvascular endothelial cells are locally specialized to accommodate the needs of individual tissues, therefore unraveling the characteristics of LEC is imperative in CL physiology. Numerous studies demonstrated that endothelium-derived endothelin-1 (ET-1) is upregulated by the luteolytic hormone-prostaglandin F2alpha (PGF2alpha) and functions as an important element of the luteolytic cascade. To have a better insight on its synthesis and action, members of ET system (ET-1, ET converting enzyme -ECE-1 and ET(A) and ET(B) receptors) were quantified in LEC. The characteristic phenotype of these cells, identified by high ET-1 receptor expression (both ET(A), ET(B)) and low ET-1 and ECE-1 levels, was gradually lost during culture suggesting that luteal microenvironment sustains the selective phenotype of its resident endothelial cells. Proper vascularization and endothelial cell activity per se are essential for normal CL function. Therefore, factors affecting vascular growth are expected to play major role in the regulation of luteal function. Concomitantly with the angiogenic process, luteal PGF2alpha and its receptors (PGFR) are induced and maintained during most of the CL life-span, suggesting a possible role of PGF2alpha in LEC proliferation and function. Dispersed LEC expressed PGFR and incubation with the prostaglandin stimulated mitogen-activated protein kinase (MAPK) signaling cascade. PGF2alpha activated p42/44 MAPK phosphorylation also in long-term cultured LEC. In this cell type, PGF2alpha increased cell number, 3H-Thymidine incorporation and cell survival. Additionally, PGF2alpha rapidly and transiently stimulated the expression of immediate-early response genes, i.e. c-fos and c-jun mRNA, further suggesting a mitogenic effect for this prostaglandin in LEC. These data imply that PGF2alpha may assume different and perhaps opposing roles depending on luteal microenvironment.     

Microcephalin, a gene regulating brain size, continues to evolve adaptively in humans

The gene Microcephalin (MCPH1) regulates brain size and has evolved under strong positive selection in the human evolutionary lineage. We show that one genetic variant of Microcephalin in modern humans, which arose approximately 37,000 years ago, increased in frequency too rapidly to be compatible with neutral drift. This indicates that it has spread under strong positive selection, although the exact nature of the selection is unknown. The finding that an important brain gene has continued to evolve adaptively in anatomically modern humans suggests the ongoing evolutionary plasticity of the human brain. It also makes Microcephalin an attractive candidate locus for studying the genetics of human variation in brain-related phenotypes.     

Activities of amylase, trypsin and lipase in the pancreas and small intestine of the laying hen during egg formation

1. During a cycle of 14 h artificial light and 10 h darkness, dry matter and enzyme concentrations were measured in the pancreas and gut of egg-forming hens. 2. Dry or fresh pancreas weight did not show significant variation but pancreatic enzyme activities increased gradually from 2 to 22 h after oviposition. 3. Total wet and dry matter contents of the small intestine gradually increased from 2 to 18 h after oviposition and then decreased significantly. Intestinal tryptic activity followed the same pattern whereas intestinal amylase gradually decreased from 2 h after oviposition; intestinal lipase activity tended to decrease during the light period (2 to 10 h after oviposition) and to increase during the dark period (14 to 22 h after oviposition). 4. By contrast, patterns of enzyme activity in the pancreas were similar. It is proposed that modification of the chyme and transit rates during the day may affect pancreatic enzyme fate and distribution in the small intestine. 5. In non-egg-forming birds intestinal contents and enzyme activities were less than in egg-forming birds. The reverse was observed in the case of the pancreas where contents and enzyme activities were increased. A relationship with food intake pattern is discussed.     

What makes us human: revisiting an age-old question in the genomic era

In 1970, Karl Pribram took on the immense challenge of asking the question, what makes us human? Nearly four decades later, the most significant finding has been the undeniable realization of how incredibly subtle and fine-scaled the unique biological features of our species must be. The recent explosion in the availability of large-scale sequence data, however, and the consequent emergence of comparative genomics, are rapidly transforming the study of human evolution. The field of comparative genomics is allowing us to reach unparalleled resolution, reframing our questions in reference to DNA sequence – the very unit that evolution operates on. But like any reductionist approach, it comes at a price. Comparative genomics may provide the necessary resolution for identifying rare DNA sequence differences in a vast sea of conservation, but ultimately we will have to face the challenge of figuring out how DNA sequence divergence translates into phenotypic divergence. Our goal here is to provide a brief outline of the major findings made in the study of human brain evolution since the Pribram lecture, focusing specifically on the field of comparative genomics. We then discuss the broader implications of these findings and the future challenges that are in store.     

Colonization of rotation crops and weeds by the potato black dot pathogenColletotrichum coccodes

The rotation crops wheat, barley, oat, maize, soybean, rye, yellow mustard, alfalfa, and spring canola and weeds eastern black nightshade, velvetleaf, timothy grass, orchard grass, and Giant foxtail common to potato-growing areas in North America were used to study the host range ofColletotrichum coccodes, the causal agent of potato black dot. The fungus was isolated from nine of 14 rotation crops and weeds that were inoculated: yellow mustard, soybean, spring canola, alfalfa, oat, eastern black nightshade, velvetleaf, giant foxtail, and timothy grass. In all, colonization was highest in black nightshades (87%) and velvetleaf (80%). Among the rotation crops, colonization was highest on yellow mustard (59%) followed by spring canola (33%) and soybean (30%).Colletotrichum coccodes was not isolated from wheat, barley, rye, maize, or orchard grass. The results indicated that crops used for rotation with potato should be selected carefully to prevent the increase ofC. coccodes inoculum in the soil and that weeds may help maintain viable inoculum ofC. coccodes in the absence of potato. Based on these results we recommend that wheat, barley, maize, or rye be used in rotation with potato in areas whereC. coccodes is present in high levels in the soil.     

Effect of temperature and pH onin vitro growth rate and sclerotial density ofColletotrichum coccodes isolates from different VCGs

The radial growth rate and sclerotial density ofColletotrichum coccodes isolates representing four major vegetative compatibility groups (VCGs) were determined at three temperatures (21,25, and 30 C) and three pH levels (pH 5, 6, and 7). This is the first report indicating thatC. coccodes isolates characterized to the same VCG share common physiological traits. The optimal temperature for growth of isolates from all four VCGs was 25 C, except for VCG1 isolates, for which growth at 21 and 25 C was equivalent. The growth rate of all isolates, of all VCG groups was decreased at 30 C, whereas sclerotia development was enhanced. The optimal pH level for growth of all isolates was pH 6 and pH 7. Interactions between VCGs and temperature or pH were observed in relation to radial growth rate and sclerotia density. At 25 C, isolates from VCG1 and 2 demonstrated the most rapid growth rate. At 21 and 30 C, VCG1 isolates demonstrated the fastest growth compared with all other VCGs. In response to pH, VCG1 and 2 demonstrated the fastest growth rates at all pH levels. VCG3 and 4 demonstrated the highest sclerotial density at 25 C and at pH 6; and VCG2 and 4 demonstrated the highest sclerotial density at 30 C.