Accuracy and direction of error in the sexing of the skeleton: implications for paleodemography

Determinations of sex by subjective assessment of the skulls from a skeletal series of known sex were compared to fully independent assessments based on pelves of the same specimens. Within-sex correlations of cranial and pelvic morphologies measured on an android-gynecoid scale were smaller than expected. Subjective assessment by means of the skull compared favorably to that of the linear discriminant functions of Giles and Elliot; however, the direction of error was similar for both procedures. Of course, estimations based on the pelves were generally superior to both in terms of frequency and overall bias of error. The bias of sex estimation for paleodemographic purposes is contingent upon completeness of skeletal remains.     

Cholesterol-free phospholipid domains may be the membrane feature selected by N epsilon-dansyl-L-lysine and merocyanine 540

We have used N epsilon-dansyl-L-lysine as a fluorescent membrane probe, to study cells taken from tissues concerned with immune function. There is a striking similarity between the staining selectivity of this compound and that reported by others for merocyanine 540. Both compounds stain leukemic, human, peripheral leukocytes, an erythroleukemia line, and some mouse bone marrow cells, suggesting common selectivity for a membrane feature of hemopoietic cells. Both compounds fail to stain red blood cells, normal human leukocytes, mouse spleen and thymus cells. We have recently reported that dansyl-lysine apparently selects for cholesterol-free phospholipid domains in liposomes and now report similar selectivity for merocyanine 540 staining of liposomes.     

Dansyl lysine: a structure-selective fluorescent membrane stain?

Dansyl lysine (DL) is a fluorescent compound that has significantly higher solubility in synthetic phosphatidylcholine (PC) membranes with a low cholesterol content than it does in water or in membranes having a high cholesterol content. Its fluorescence intensity is enhanced at least 50-fold when dissolved in PC membranes. Therefore, membranes with mole fractions of cholesterol (Xch) less than or equal to 0.5-0.3 are stained by aqueous solutions of DL: those with a higher cholesterol content, 0.3-0.4 less than or equal to Xch less than or equal to 0.5, are not. It is proposed that DL selects for a structural feature of membranes: cholesterol-free domains. The phenomenon has provided evidence for long-lived compositional heterogeneity in large multilamellar PC-cholesterol liposomes having Xch less than or equal to 0.2. This is not consistent with a model in which the homogeneous state is thermodynamically favored and both intermembrane transfer and transmembrane transfer (flip-flop) of cholesterol are fast. These studies are of potential importance for understanding cell membrane structure, in particular lipid-phase equilibria and the maintenance of compositional heterogeneity between the different membranes of cells.     

Effect of neurotensin on pancreatic function in man

The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs.     

Membrane structure and the tenuously maintained resistance to staining with N epsilon-dansyl-L-lysine shown by many cells

The ability to resist staining by N epsilon-dansyl-L-lysine is tenuously maintained in the majority of live nucleated cells taken from tissues concerned with immune function. Resistance is lost under a variety of nonphysiological conditions known to, or likely to, cause protein denaturation or aggregation. In contrast to that of dansyl-gamma-aminobutyrate, the fluorescence intensity of N epsilon-dansyl-L-lysine is only weakly enhanced by native proteins. This is further reduced on denaturation or aggregation of the proteins. It is unlikely, therefore, that cellular uptake of, and staining by, N epsilon-dansyl-L-lysine is a direct consequence of membrane protein denaturation/aggregation but may result from a decrease in protein-phospholipid interactions leading to formation of phospholipid domains. Previous work has indicated that such features are stained by N epsilon-dansyl-L-lysine (Humphries, G.M.K., Lovejoy, J.P., 1983, Biophys. J. 42:307-310; Humphries, G.M.K., Lovejoy, J.R., 1983, Biochem. Biophys. Res. Commun. 111:768-774). Although it appears likely that passage through a dansyl-lysine-staining state is a common, if not universal, prelude to cell death (as monitored by uptake of trypan blue), not all cells that lose resistance to dansyl-lysine staining are moribund. Resistance to staining is also lost by macrophages on binding to solid substrates and multivalent ligands. The possible physiological significance of this is discussed.     

Small Thaw Ponds: An Unaccounted Source of Methane in the Canadian High Arctic

Thawing permafrost in the Canadian Arctic tundra leads to peat erosion and slumping in narrow and shallow runnel ponds that surround more commonly studied polygonal ponds. Here we compared the methane production between runnel and polygonal ponds using stable isotope ratios, ¹⁴C signatures, and investigated potential methanogenic communities through high-throughput sequencing archaeal 16S rRNA genes. We found that runnel ponds had significantly higher methane and carbon dioxide emissions, produced from a slightly larger fraction of old carbon, compared to polygonal ponds. The methane stable isotopic signature indicated production through acetoclastic methanogenesis, but gene signatures from acetoclastic and hydrogenotrophic methanogenic Archaea were detected in both polygonal and runnel ponds. We conclude that runnel ponds represent a source of methane from potentially older C, and that they contain methanogenic communities able to use diverse sources of carbon, increasing the risk of augmented methane release under a warmer climate.