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.     

Identification of respiratory vagal feedback in awake normal subjects using pseudorandom unloading.

Evidence of the Hering-Breuer reflex has been found in humans during anesthesia and sleep but not during wakefulness. Cortical influences, present during wakefulness, may mask the effects of this reflex in awake humans. We hypothesized that, if lung volume were increased in awake subjects unaware of the stimulus, vagal feedback would modulate breathing on a breath-to-breath basis. To test this hypothesis, we employed proportional assist ventilation in a pseudorandom sequence to unload the respiratory system above and below the perceptual threshold in 17 normal subjects. Tidal volume, integrated respiratory muscle pressure per breath, and inspiratory time were recorded. Both sub- and suprathreshold stimulation evoked a significant increase in tidal volume and inspiratory flow rate, but a significant decrease in inspiratory time was present only during the application of a subthreshold stimulus. We conclude that vagal feedback modulates respiratory timing on a breath-by-breath basis in awake humans, as long as there is no awareness of the stimulus.     

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.     

Metabolism of 6-nitrochrysene by intestinal microflora.

Since bacterial nitroreduction may play a critical role in the activation of nitropolycyclic aromatic hydrocarbons, we have used batch and semicontinuous culture systems to determine the ability of intestinal microflora to metabolize the carcinogen 6-nitrochrysene (6-NC). 6-NC was metabolized by the intestinal microflora present in the semicontinuous culture system to 6-aminochrysene (6-AC), N-formyl-6-aminochrysene (6-FAC), and 6-nitrosochrysene (6-NOC). These metabolites were isolated and identified by high-performance liquid chromatography, mass spectrometry, and UV-visible spectrophotometry and compared with authentic compounds. Almost all of the 6-NC was metabolized after 10 days. Nitroreduction of 6-NC to 6-AC was rapid; the 6-AC concentration reached a maximum at 48 h. The ratio of the formation of 6-AC to 6-FAC to 6-NOC at 48 h was 93.4:6.3:0.3. Interestingly, compared with results in the semicontinuous culture system, the only metabolite detected in the batch studies was 6-AC. The rate of nitroreduction differed among human, rat, and mouse intestinal microflora, with human intestinal microflora metabolizing 6-NC to the greatest extent. Since 6-AC has been shown to be carcinogenic in mice and since nitroso derivatives of other nitropolycyclic aromatic hydrocarbons are biologically active, our results suggest that the intestinal microflora has the enzymatic capacity to generate genotoxic compounds and may play an important role in the carcinogenicity of 6-NC.     

Plasmid profile analysis of a salmonellosis outbreak and identification of a restriction and modification system.

After an outbreak of salmonellosis in humans caused by Salmonella typhimurium bacteriophage type 135, 62 isolates from human, animal, and water sources were retained for further analysis. Most of the isolates (92%) could be placed in one of five plasmid pattern groups, with a majority containing a common 60-kilobase plasmid and a smaller 3.8-kilobase-pair plasmid. This small plasmid, pIMVS1, was labeled with [32P]phosphate and used as a probe in subsequent colony and Southern hybridization studies. We concluded that pIMVS1 from isolates obtained from humans was genetically different from plasmids of a similar size found in isolates from chickens. Studies to characterize pIMVS1 were undertaken to determine if it codes for known virulence factors. It did not appear to be associated with the formation of attachment pili or major outer membrane proteins. By using transposon mutagenesis techniques, Tn3(Apr) was inserted into pIMVS1, and the existence of a restriction and modification system was deduced.     

Serological properties and processing in Escherichia coli K12 of OmpV fusion proteins of Vibrio cholerae

Summary Fusion proteins comprising the amino-terminal 99 amino acids of the bacteriophage MS2 replicase and various portions of OmpV a major outer membrane protein of Vibrio cholerae were expressed in Escherichia coli K12. These fusions were expressed under the control of the P_L promoter of bacteriophage , and expression was controlled using a cI_ts repressor. Fusions occurring within the secretory signal sequence of OmpV gave rise to the production of mature OmpV. The efficiency, however, decreased with progressive deletion of the signal sequence within the fusions. The reactivity of various OmpV fusions with antisera raised against purified OmpV and whole bacteria demonstrated the existence of two antigenic domains: one present in the denatured form and another in the membrane-associated form of OmpV. These domains correspond to markedly hydrophilic regions of the protein as would be predicted for surface-exposed epitopes.     

Evidence for related virulence sequences in plasmids of Salmonella dublin and Salmonella typhimurium

Transposon-insertion mutants were prepared from virulent field isolates of Salmonella dublin and Salmonella typhimurium. Detailed restriction-enzyme mapping of the single sites of TnA insertion in two mutants (M51 and M173) of S. dublin that showed diminished virulence in a mouse assay indicated that these sites were about 5 kbp apart on the approximately 70 kbp plasmid harboured by the isolate. A Tn10-insertion mutant (M242) of S. typhimurium that showed diminished virulence was also identified. A single copy of Tn10 was inserted into the approximately 90 kbp plasmid harboured by this isolate. Hybridization studies indicated that homology existed between the region encompassing the sites of TnA insertion in M51 and M173 and that encompassing the site of Tn10 insertion in M242. Restriction mapping indicated that the two regions were very similar and could even be identical and, if so, the Tn10 insertion in M242 could be mapped to a point 1.5 kbp from the TnA insertion in M51 and 6.5 kbp from that in M173. It appeared that the maximal extent of the putative similarity/identity was between 13 and 23 kbp. It is proposed that this stretch of high homology could represent a virulence sequence that has been conserved during the evolutionary divergence of the two Salmonella serotypes.     

The development and ultrastructure of the testa and tracheid bar inErythrina lysistemon Hutch. (Leguminosae: Papilionoideae)

Summary The development of the testa was studied inErythrina lysistemon using both light and electron microscopy. Cells of the outer epidermis of the outer integument divide anticlinally and undergo radial elongation to form a palisade layer. The outer tangential walls are thickened at an early stage, and deposition of fluted thickenings on the radial walls occurs at maturity. Palisade cells in the hilar region differentiate from sub-funicular tissue, and at maturity the outer ends of the cells undergo extensive deposition of secondary walls and associated lignification. The light line occurs at the junction between the outer, thickened portions of the cells and the inner, less thickened portions. An electron-translucent (suberised) cap develops in the outer tangential walls of the palisade cells at a late stage. Microtubules and dictyosomes are closely associated with the developing thickenings in palisade and tracheid bar, and the microtubules run parallel to the wall microfibrils. Differentiation of the tracheid bar coincides with final secondary wall deposition and lignification in the hilar palisade. The cells of the tracheid bar are dead at maturity, but are surrounded by sheaths of elongate parenchyma.     

The trajectory of a stiff rod in a curved potential energy trough

The equilibrium trajectory of the axis of a rod subject to an externally imposed curved potential energy trough tends to conform to the shape of the curved trough, but also tends to be straight because of elastic resistance to bending. The actual path of the axis is a balance between the two extremes. We consider a potential energy trough centered along a circular arc of radiusR. For a rod of small length compared toR, we show that the axis at equilibrium forms an arc of a circle of radius greater thanR. The value of the radius of the axial path depends on the relative values of the Hooke’s Law bending constant for the rod and the depth and width of the trough. Motivation for the calculation is provided by nucleosomal DNA, which conforms to the surface of a roughtly cylindrical histone core at physiological ionic strength, but is observed to unwind into a partially extended conformation at very low ionic strength. We suggest that the rigidity to bending of short DNA segments becomes sufficiently great at low ionic strength to overcome attractive interactions with the histone surface. Alternately, of course, if during the cell cycle mutually attractive forces between DNA and histone core are weakened at constant ionic strength, the same type of unfolding would be expected to occur as the strength of the DNA-histone contacts drops below the level required to overcome elastic resistance to bending of the DNA rod.