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.     

Acetaldehyde binding increases the catabolism of rat serum low-density lipoproteins

Acetaldehyde was found to form adducts with rat serum lipoproteins. The binding of [14C]acetaldehyde to lipoproteins was studied at low concentrations which are known to exist during ethanol oxidation. The amount of lipoprotein adducts was a linear function of acetaldehyde concentration up to 250 microM. Incubation of rat plasma low-density lipoproteins (LDL) with 200 microM acetaldehyde increased the disappearance rate of the 3H-label from the cholesterol ester moiety of LDL injected into normal rats. The data show that even low concentrations of acetaldehyde are capable of affecting LDL metabolism. These findings may provide an explanation for the low concentrations of serum LDL in alcoholics.     

International Commission for Protection against Environmental Mutagens and Carcinogens. ICPEMC Working Paper No. 15/2. Metabolism and metabolic effects of ethanol, including interaction with drugs, carcinogens and nutrition

Different pathways of alcohol metabolism, the alcohol dehydrogenase pathway, the microsomal ethanol-oxidizing system and the catalase pathway are discussed. Alcohol consumption leads to accelerated ethanol metabolism by different mechanisms including an increased microsomal function. Microsomal induction leads to interactions of ethanol with drugs, hepatotoxic agents, steroids, vitamins and to an increased activation of mutagens/carcinogens. A number of ethanol-related complications may be explained by the production of its first metabolite, acetaldehyde, such as alterations of mitochondria, increased lipid peroxidation and microtubular alterations with its adverse effects on various cellular activities, including disturbances of cell division. Nutritional factors in alcoholics such as malnutrition are discussed especially with respect to its possible relation to cancer.     

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.     

Electropore diameters, lifetimes, numbers, and locations in individual erythrocyte ghosts

Low light level video microscopy was used to study the diameter, lifetime, number, and location characteristics of electric field-induced pores (electropores) in erythrocyte ghosts. The diameter of electropores was probed by following the efflux of soluble fluorescent-tagged molecules out of the resealed ghost cytoplasmic compartments. After reaching a peak radius of at least 8.4 nm the electropores resealed within 200 ms to a radius of about 0.5 nm and stayed at that radius thereafter. Video sequences clearly show that pores are induced preferentially in the cathodal hemisphere. Pores induced in the hemisphere facing the positive electrode were either never greater than 0.5 nm in radius, much smaller in number if they were greater than 0.5 nm in radius, or shorter lived. Calculations indicated that an upper limit of 700 electropores were induced per membrane.     

The effect of chronic alcohol feeding on lipid peroxidation in microsomes: lack of relationship to hydroxyl radical generation

Chronic alcohol feeding causes microsomal induction including increased generation of hydroxyl radicals. Ethanol induced liver injury may be mediated by lipid peroxidation for which hydroxyl radicals have been proposed as major mediators. Ethanol promotes lipid peroxidation when given acutely but also may serve as a hydroxyl radical scavenger. Therefore, we studied the acute and chronic effects of alcohol on microsomal lipid peroxidation and hydroxyl radical generation. Chronic alcohol feeding in rats increased microsomal generation of hydroxyl radicals but lipid peroxidation of endogenous lipid was inversely related to hydroxyl radical generation. Ethanol (50mM) had a slight inhibitory effect on hydroxyl radical production in peroxidizing microsomes, no effect on endogenous lipid peroxidation and enhanced the lysis of RBCs added as targets of peroxidation. Enhanced microsomal generation of hydroxyl radicals following chronic alcohol feeding is not an important mediator of lipid peroxidation.     

Time Course of Steroid Biosynthesis and Metabolism in Haplopappus heterophyllus

A single dose of mevalonic acid-2-¹⁴C was administered simultaneously to 6 Haplopappus heterophyllus plants. They were harvested at intervals ranging from 3 days to 6 months. Four groups of biosynthetically related sterols were found to be radioactive in each plant, and the changes in radioactivity with time were studied. The most striking finding was a radioactive phenolic material present only in the 6-month plant, which had flowered.     

Recombinant adenoviruses with large deletions generated by Cre-mediated excision exhibit different biological properties compared with first-generation vectors in vitro and in vivo.

In vivo gene transfer of recombinant E1-deficient adenoviruses results in early and late viral gene expression that elicits a host immune response, limiting the duration of transgene expression and the use of adenoviruses for gene therapy. The prokaryotic Cre-lox P recombination system was adapted to generate recombinant adenoviruses with extended deletions in the viral genome (referred to here as deleted viruses) in order to minimize expression of immunogenic and/or cytotoxic viral proteins. As an example, an adenovirus with a 25-kb deletion that lacked E1, E2, E3, and late gene expression with viral titers similar to those achieved with first-generation vectors and less than 0.5% contamination with E1-deficient virus was produced. Gene transfer was similar in HeLa cells, mouse hepatoma cells, and primary mouse hepatocytes in vitro and in vivo as determined by measuring reporter gene expression and DNA transfer. However, transgene expression and deleted viral DNA concentrations were not stable and declined to undetectable levels much more rapidly than those found for first-generation vectors. Intravenous administration of deleted vectors in mice resulted in no hepatocellular injury relative to that seen with first-generation vectors. The mechanism for stability of first-generation adenovirus vectors (E1a deleted) appeared to be linked in part to their ability to replicate in transduced cells in vivo and in vitro. Furthermore, the deleted vectors were stabilized in the presence of undeleted first-generation adenovirus vectors. These results have important consequences for the development of these and other nonintegrating vectors for gene therapy.     

The characterization of a mammalian DNA structure-specific endonuclease.

The repair of some types of DNA double-strand breaks is thought to proceed through DNA flap structure intermediates. A DNA flap is a bifurcated structure composed of double-stranded DNA and a displaced single-strand. To identify DNA flap cleaving activities in mammalian nuclear extracts, we created an assay utilizing a synthetic DNA flap substrate. This assay has allowed the first purification of a mammalian DNA structure-specific nuclease. The enzyme described here, flap endonuclease-1 (FEN-1), cleaves DNA flap strands that terminate with a 5' single-stranded end. As expected for an enzyme which functions in double-strand break repair flap resolution, FEN-1 cleavage is flap strand-specific and independent of flap strand length. Furthermore, efficient flap cleavage requires the presence of the entire flap structure. Substrates missing one strand are not cleaved by FEN-1. Other branch structures, including Holliday junctions, are also not cleaved by FEN-1. In addition to endonuclease activity, FEN-1 has a 5'-3' exonuclease activity which is specific for double-stranded DNA. The endo- and exonuclease activities of FEN-1 are discussed in the context of DNA replication, recombination and repair.