Presence of a unique glycoconjugate on the surface of rat primordial germ cells during migration

This investigation was undertaken to examine the chemical nature of components on the surface of primordial germ cells (PGCs) possibly related to their directed migration during development. To this end, lectins conjugated to horseradish peroxidase were used as specific histochemical probes to characterize the structure of PGC cell surface glycoconjugates and changes in their composition during and after their migration in the rat embryo. A lectin specific for terminal N-acetylgalactosamine (GalNAc) from Dolichos biflorus intensely stained the cell surface and a perinuclear region assumed to be Golgi zone of PGCs only during their migration. With one exception, no other site in the embryo stained with this lectin as migration proceeded. These observations suggest that the GalNAc-containing glycoconjugates on the surface of PGCs may be of functional importance in regulating the guidance and locomotion of these cells during the course of their extensive migration.     

MORPHOLOGICAL EVOLUTION OF THE DROSOPHILA VIRILIS SPECIES GROUP AS ASSESSED BY RATE TESTS FOR NATURAL SELECTION ON QUANTITATIVE CHARACTERS

Two rate tests for assessing natural selection on quantitative traits are discussed for their usefulness in macroevolutionary and adaptational studies. The underlying assumptions and parameter estimation for the constant-heritability (CH) and mutation-drift-equilibrium (MDE) models, which are the bases for these tests, are discussed. The purpose of these rate tests is to determine whether morphological change has occurred either too fast to be explained by neutral drift, which suggests directional selection, or too slow, which suggests stabilizing selection. Previous formulations of these rate tests have ignored the phylogenetic component. Several models of evolution are considered to help account for phylogeny in the context of rate tests. The MDE rate test for stabilizing selection was performed on nine morphological characters among several species of the Drosophila virilis species group. These tests can be interpreted to suggest that stabilizing selection has probably been a major factor in producing the observed similarity among the Drosophila species examined.     

Harnessing DNA for nanothermometry

Temperature measurement at the nanoscale has brought insight to a wide array of research interests in modern chemistry, physics, and biology. These measurements have been enabled by the advent of nanothermometers, which relay nanoscale temperature information through the analysis of their intrinsic photophysical behavior. In the past decade, several nanothermometers have been developed including dyes, nanodiamonds, fluorescent proteins, nucleotides, and nanoparticles. However, temperature measurement using intact DNA has not yet been achieved. Here, we present a method to study the temperature sensitivity of the DNA molecule within a physiologic temperature range when complexed with fluorescent dye. We theoretically and experimentally report the temperature sensitivity of the DNA-Hoechst 33342 complex in different sizes of double-stranded oligonucleotides and plasmids, showing its potential use as a nanothermometer. These findings allow for extending the thermal study of DNA to several research fields including DNA nanotechnology, optical tweezers, and DNA nanoparticles.     

Light microscopic histochemical detection of terminal galactose and N-acetylgalactosamine residues in rodent complex carbohydrates using a galactose oxidase--Schiff sequence and peanut lectin--horseradish peroxidase conjugate

A technique was investigated for the direct visualization on paraffin sections of galactose and N-acetylgalactosamine residues terminating saccharide chains in complex carbohydrates. Sections were incubated with the enzyme galactose oxidase (GO), which oxidizes the C-6 hydroxyl of galactose or N-acetylgalactosamine (GalNAc) residues, and the resulting aldehyde was visualized by its reaction with Schiff's reagent. Submaxillary and sublingual glands, pancreas, stomach, duodenum, and ileum from mice and rats were stained with the GO-Schiff sequence and results were compared with staining by a peanut lectin-horseradish peroxidase (PL-HRP) conjugate that binds selectively to terminal galactose and preferentially to the terminal dimer beta-D-Gal-(1 leads to 3)-D-GalNAc. Three classes of reactive sites were revealed: 1) those reactive with both GO-Schiff and PL-HRP, 2) those stained with the GO-Schiff sequence but unreactive with PL-HRP, and 3) those GO-Schiff unreactive but PL-HRP positive. Based on the carbohydrate binding specificity of GO and PL, it is suggested that tissue complex carbohydrates in group one contain terminal beta-galactose residues with unmodified hydroxyls at C-2, C-4, and C-6, whereas those in group two contain terminal GalNAc residues. The structure of oligosaccharides in group 3 sites remains enigmatic.     

Amphipod gigantism dictated by oxygen availability?

A recent study of gigantism in amphipods proposes a novel mechanism which could be used to explain Bergmann's rule, namely differences in environmental O₂ concentration. Consideration of the respiratory biology of this group indicates significant flaws in this proposal. Nonetheless, it is not unreasonable to predict a relationship between ectotherm body size and O₂ partial pressure ( p O₂) in some systems, where the partial pressure gradient is steep, either in time (comparison of Carboniferous and Permian atmospheres) or space (animals inhabiting oceanic O₂ minimum layers, and, particularly in freshwaters, living at high altitude). Animal gigantism can be correlated with periods of very high environmental p O₂ over geological time. Unfortunately, data for present day spatial patterns are scant.