Optimizing purebred selection for crossbred performance using QTL with different degrees of dominance

A method was developed to optimize simultaneous selection for a quantitative trait with a known QTL within a male and a female line to maximize crossbred performance from a two-way cross. Strategies to maximize cumulative discounted response in crossbred performance over ten generations were derived by optimizing weights in an index of a QTL and phenotype. Strategies were compared to selection on purebred phenotype. Extra responses were limited for QTL with additive and partial dominance effects, but substantial for QTL with over-dominance, for which optimal QTL selection resulted in differential selection in male and female lines to increase the frequency of heterozygotes and polygenic responses. For over-dominant QTL, maximization of crossbred performance one generation at a time resulted in similar responses as optimization across all generations and simultaneous optimal selection in a male and female line resulted in greater response than optimal selection within a single line without crossbreeding. Results show that strategic use of information on over-dominant QTL can enhance crossbred performance without crossbred testing.     

A new promotor of nerve growth: naftidrofuryl

20 day-old rat thoracic dorsal root ganglia were grown for 48 hrs. in Iscove's medium supplemented with 8% fetal calf serum and 600 mg/100 ml glucose. Naftidrofuryl was added at 10(-6), 10(-7), 10(-8) and 10(-9) M concentrations to the culture medium. The 10(-7) and 10(-8) M concentrations induced a statistically significant increase of the number (30 to 40%; p = .0054 and .0016, respectively) and length (20 to 30%; p = .0012 and .001, respectively) of neurites of the outgrowth measured after Bodian's protargol impregnation. The width of the cell spread in the outgrowth was also enlarged at the 10(-7) and 10(-8) M concentrations (18 to 26%; p = .0012; p less than .0001, respectively).     

Effect of postnatal development on calcium currents and slow charge movement in mammalian skeletal muscle

Single- (whole-cell patch) and two-electrode voltage-clamp techniques were used to measure transient (Ifast) and sustained (Islow) calcium currents, linear capacitance, and slow, voltage-dependent charge movements in freshly dissociated fibers of the flexor digitorum brevis (FDB) muscle of rats of various postnatal ages. Peak Ifast was largest in FDB fibers of neonatal (1-5 d) rats, having a magnitude in 10 mM external Ca of 1.4 +/- 0.9 pA/pF (mean +/- SD; current normalized by linear fiber capacitance). Peak Ifast was smaller in FDB fibers of older animals, and by approximately 3 wk postnatal, it was so small as to be unmeasurable. By contrast, the magnitudes of Islow and charge movement increased substantially during postnatal development. Peak Islow was 3.6 +/- 2.5 pA/pF in FDB fibers of 1-5-d rats and increased to 16.4 +/- 6.5 pA/pF in 45-50-d-old rats; for these same two age groups, Qmax, the total mobile charge measurable as charge movement, was 6.0 +/- 1.7 and 23.8 +/- 4.0 nC/microF, respectively. As both Islow and charge movement are thought to arise in the transverse-tubular system, linear capacitance normalized by the area of fiber surface was determined as an indirect measure of the membrane area of the t-system relative to that of the fiber surface. This parameter increased from 1.5 +/- 0.2 microF/cm2 in 2-d fibers to 2.9 +/- 0.4 microF/cm2 in 44-d fibers. The increases in peak Islow, Qmax, and normalized linear capacitance all had similar time courses. Although the function of Islow is unknown, the substantial postnatal increase in its magnitude suggests that it plays an important role in the physiology of skeletal muscle.     

A nuclear gene encoding the beta subunit of the mitochondrial ATP synthase in Nicotiana plumbaginifolia.

The beta subunit of the mitochondrial ATP synthase in Nicotiana plumbaginifolia is encoded by two nuclear genes, atp2-1 and atp2-2, which are both expressed. The complete nucleotide sequence of atp2-1 has been determined. It contains eight introns ranging from 88 to 1453 bp. The last intron contains a putative insertion element (Inp), of 812 bp bordered by 35-bp inverted repeats which share an 11-bp homology with Agrobacterium tumefaciens T-DNA borders. Sequences homologous to Inp are present in multiple copies in the N. plumbaginifolia and the N. tabacum genome but not in more distant species. The atp2-1 encoded polypeptide is highly homologous to beta subunits from other ATP synthases but it contains an extension at the N terminus which is probably involved in mitochondrial targeting. A sequence homology between exon 4 of atp2-1 and exon 1 of the human ras genes suggests a common ancestral origin for these exons.     

Complementation of a Schizosaccharomyces pombe mutant lacking the beta subunit of the mitochondrial ATPase by the ATP2 gene of Saccharomyces cerevisiae

A chimeric plasmid carrying the structural gene (ATP2) for the mitochondrial ATPase beta subunit of Saccharomyces cerevisiae has been used to complement a mutant of Schizosaccharomyces pombe lacking the beta subunit (Boutry, M., and Goffeau, A. (1982) Eur. J. Biochem. 125, 471-477). Transformation with ATP2 restored the growth rate of S. pombe mutant on glycerol as well as the mitochondrial ATPase and 32Pi-ATP exchange activities to approximately 20% of the parental strain. Mitochondria prepared from the transformant contained a normal amount of a hybrid F1-ATPase consisting of the S. cerevisiae beta subunit assembled with the remaining subunits of the S. pombe ATPase complex. The presence of the S. cerevisiae beta subunit in the S. pombe ATPase complex conferred a sensitivity to the energy transfer inhibitors citreoviridin and oligomycin which was like that of the intact S. cerevisiae enzyme. The S. cerevisiae beta subunit assembled into the hybrid ATPase complex was the same size as the mature subunit in S. cerevisiae. These data indicate that the mechanism of mitochondrial import and the assembly of the cytoplasmically synthesized subunits is similar or identical in these evolutionary divergent yeasts. In addition, this study provides a new approach for the construction of hybrid mitochondrial ATPase complexes which can be used to examine the function of selected subunits in energy transduction.     

Mitochondrial DNA polymorphism and phylogenetic relationships inHevea brasiliensis

Using fourteen random mitochondrial DNA probes, we have examined restriction fragment length polymorphism (RFLP) in wild and cultivatedHevea brasiliensis. A total of 395 accessions, including 345 from various prospectings collected in Brazil, Colombia and Peru and 50 cultivated clones, were analyzed. Two other species (H. benthamiana andH. pauciflora) were also included in the study for comparison. The high level of mitochondrial polymorphism allowed us to divide all the accessions analyzed into 212 distinct genotypes. The genetic variability of cultivated clones was limited to four genotypes forming two clusters. In contrast, considerable genetic variation was found in the wild collections. In almost all cases, accessions displaying the same RFLP profile were restricted to the same geographical area (same or neighbor administrative districts). In addition, accessions whose genetic closeness was predicted by RFLP profiles were also clustered according to geographical origin. In a few cases, however, similar RFLP profiles were found for accessions originating from geographically distant districts. This discrepancy can be explained either by seed dispersion (by river) or possibly by similar genetic events occurring independently in different geographical locations. Chloroplast DNA RFLP was also analyzed in 217 accessions, representative of 126 distinct mitochondrial genotypes. Very few differences were found, indicating that the chloroplast genome is more highly conserved than the mitochondrial genome.     

Purification and preliminary characterization of mitochondrial complex I (NADH: ubiquinone reductase) from broad bean (Vicia faba L.).

NADH:ubiquinone reductase (EC 1.6.19.3), or complex I, was isolated from broad bean (Vicia faba L.) mitochondria. Osmotic shock and sequential treatment with 0.2% (v/v) Triton X-100 and 0.5% (w/v) [3-cholamidopropyl)dimethylammonio]-1-propanesulfate (CHAPS) removed all other NADH dehydrogenase activities. Complex I was solubilized in the presence of 4% Triton X-100 and then purified by sucrose-gradient centrifugation in the presence of the same detergent. The second purification step was hydroxylapatite chromatography. Substitution of CHAPS for Triton X-100 helped remove contaminants such as ATPase. The high molecular mass complex is composed of at least 26 subunits with molecular masses ranging from 6000 to 75,000 kD. The purified complex I reduced ferricyanide and ubiquinone analogs but not cytochrome c. NADPH could not substitute for NADH as an electron donor. The KM for NADH was 20 microM at the optimum pH of 8.0. The NH2-terminal sequence of several subunits was determined, revealing the ambiguous nature of the 42-kD subunit.