Genetic analysis of autosomal and X-linked markers across a mouse hybrid zone

In this paper, we present results of the first comprehensive study of the introgression of both autosomal and sex-chromosome markers across the central European portion of the hybrid zone between two house mouse subspecies, Mus musculus musculus and M. m. domesticus. More than 1800 individuals sampled from 105 sites were analyzed with a set of allozyme loci (hopefully representing neutral or nearly neutral markers) and X-linked loci (which are assumed to be under selection). The zone center is best modeled as a single straight line independent of fine-scale local geographic or climatic conditions, being maintained by a balance between dispersal and selection against hybrids. The width (w) of the multilocus autosomal cline was estimated as 9.6 km whereas the estimate for the compound X-chromosome cline was about 4.6 km only. As the former estimate is comparable to that of the Danish portion of the zone (assumed to be much younger than the central European one), zone width does not appear to be related to its age. The strength (B) of the central barrier was estimated as about 20 km; with dispersal (sigma) of about 1 km/gen(1/2), this means effective selection (s*) is approximately 0.06-0.09 for autosomal loci and about 0.25 for X-linked loci. The number of loci under selection was estimated as N= 56-99 for autosomes and about 380 for X-linked loci. Finally, we highlight some potential pitfalls in hybrid zone analyses and in comparisons of different transects. We suggest that conclusions about parts of the mouse genome involved in reproductive isolation and speciation should be drawn with caution and that analytical approaches always providing some estimates should not be used without due care regarding the support or confidence of such estimates, especially if conclusions are based on the difference between these estimates. Finally, we recommend that analysis in two-dimensional space, dense sampling, and rigorous treatment of data, including inspection of likelihood profiles, are essential for hybrid zone studies.     

Engineering the acceptor substrate specificity in the xyloglucan endotransglycosylase TmXET6.3 from nasturtium seeds (Tropaeolum majus L.)

Plant Molecular Biology - The knowledge of substrate specificity of XET enzymes is important for the general understanding of metabolic pathways to challenge the established notion that these...     

Metallohelix vectors for efficient gene delivery via cationic DNA nanoparticles

The design of efficient and safe gene delivery vehicles remains a major challenge for the application of gene therapy. Of the many reported gene delivery systems, metal complexes with high affinity for nucleic acids are emerging as an attractive option. We have discovered that certain metallohelices—optically pure, self-assembling triple-stranded arrays of fully encapsulated Fe—act as nonviral DNA delivery vectors capable of mediating efficient gene transfection. They induce formation of globular DNA particles which protect the DNA from degradation by various restriction endonucleases, are of suitable size and electrostatic potential for efficient membrane transport and are successfully processed by cells. The activity is highly structure-dependent—compact and shorter metallohelix enantiomers are far less efficient than less compact and longer enantiomers.     

Metabolism of l-threonine and fatty acids and tylosin biosynthesis in Streptomyces fradiae

Abstract In Streptomyces fradiae l -threonine is catabolized by threonine dehydratase or threonine aldolase to 2-ketobutyrate or acetaldehyde and glycine, respectively. Threonine dehydratase synthesis is repressed and its activity is inhibited by NH₄⁺ ions. Threonine aldolase is not repressed by NH₄⁺ ions and its activity is slightly stimulated by these ions. The addition of threonine to the medium increased pronouncedly the fraction of non-branched fatty acids with an even carbon number under conditions when threonine dehydratase was repressed and inhibited. The results indicate that threonine serves as a source of propionyl-CoA and 2-methylbutyryl-CoA and also of acetyl-CoA required for tylosin and fatty acid biosynthesis.     

Maturation of rat brain is accompanied by differential expression of the long and short splice variants of G(s)alpha protein: identification of cytosolic forms of G(s)alpha

Distribution of the alpha subunit of the stimulatory G protein (G(s)alpha) was analyzed in membrane and cytosolic (supernatant 200 000 g) fractions from rat cortex, thalamus and hippocampus during the course of post-natal development. In parallel, changes in beta-adrenoceptor density and adenylyl cyclase activity were determined. Long (G(s)alphaL) and short (G(s)alphaS) variants of G(s)alpha were assessed by immunoblotting using specific polyclonal antisera reacting with both G(s)alpha isoforms. Post-natal development was associated with an increase in the total amount of brain G(s)alpha. G(s)alphaL was the dominant isoform of G(s)alpha in the membrane fractions of all studied brain regions and its amount increased markedly between post-natal day (PD) 1 and 90. The level of membrane-bound G(s)alphaS also elevated during post-natal development, but more pronounced changes were found in cytosolic G(s)alphaS. Although only a small amount of G(s)alphaS (much smaller than G(s)alphaL) was detected among soluble proteins shortly after birth, G(s)alphaS prevailed over G(s)alphaL at PD90. The G(s)alphaL/G(s)alphaS ratio decreased, respectively, from 3.2 to 1.2 and from 5.0 to 1.5 in the membrane fractions of cortex and hippocampus, but remained almost constant in thalamus between PD1 and 90. More dramatic changes were found in the cytosolic fractions of all studied brain regions: the G(s)alphaL/G(s)alphaS ratio decreased sharply in cortex (from 14.1 to 0.9), hippocampus (from 3.7 to 0.8), and also in thalamus (from 9.5 to 0.5). These results demonstrate that the membrane-cytosol balance of G(s)alpha proteins alters dramatically during the course of brain development. Both G(s)alphaL and G(s)alphaS were expressed in a region- and age-specific manner, which suggests different roles in the maturation of the brain tissue. A cyc(-) reconstitutive assay of cytosolic G(s)alpha indicated that only approximately 20% of this protein was functional, compared with membrane-bound G(s)alpha, and its ability to reconstitute adenylyl cyclase activity increased during the course of maturation. The number of beta-adrenoceptors increased sharply during early post-natal development but only slightly in adulthood, and both GTP- and isoproterenol-stimulated adenylate cyclase activity reached peak values around PD12.     

Manipulation of division symmetry and developmental fate in cultures of potato microspores

The effect of media composition on microspore culture was investigated in one tetraploid and two diploid potatoes. The viability of microspores isolated from 4.5 to 5 mm buds was in the range of 33 to 52%. In media for anther culture, microspores showed no further development and lost viability within 2 days. In M1 medium containing mineral components, sucrose, uridine, cytidine, myo-inositol, glutamine and lactalbumin hydrolysate, 18 to 37% of microspores underwent mitosis within 14 days. Up to 95% of the divisions were symmetric and produced equal nuclei. Some symmetrically divided microspores eventually produced structures with 3 to 10 nuclei. The proportion of the total microspore population producing multinuclear structures reached 9% in diploid clones responsive to anther culture and 1 to 2% in recalcitrant cv. Borka. Symmetric mitoses in M1 medium were induced in the presence of glutamine and lactalbumin hydrolysate. Nucleosides and myo-inositol had no effect on microspore division. In the absence of all organic components except sucrose, most mitoses were asymmetric, formation of multinuclear structures was reduced and most pollen accumulated starch indicative of gametophytic fate. In complete M1 medium, starch accumulation was suppressed. Suppression also occurred in asymmetrically divided microspores, indicating a direct inhibition of pollen development independent of the mode of microspore division. This inhibitory effect of M1 medium might present a stress which triggers the induction of symmetric microspore division and subsequent formation of multinuclear structures. This revised version was published online in June 2006 with corrections to the Cover Date.