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.     

Exopolysaccharide-producing strains of thermophilic lactic acid bacteria cluster into groups according to their EPS structure

AIMS: To compare galactose-negative strains of Streptococcus thermophilus and Lactobacillus delbrueckii subspecies bulgaricus isolated from fermented milk products and known to produce exopolysaccharides (EPSs). METHODS AND RESULTS: The structures of the EPSs were determined using nuclear magnetic resonance (NMR) and their genetic relationships determined using restriction endonuclease analysis (REA) and random amplification of polymorphic DNA (RAPD). Similar groupings were apparent by REA and RAPD, and each group produced an EPS with a particular subunit structure. CONCLUSION: Although none of the strains assimilated galactose, all inserted a high proportion of galactose into their EPS when grown in skimmed milk, and fell into three distinct groups. Significance and Impact of the Study: This information should help in an understanding of genetic exchanges in lactic acid bacteria.     

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 family of serine protease genes expressed in adult buffalo fly (Haematobia irritans exigua)

Gene fragments encoding serine proteases expressed in adult buffalo fly (Haematobia irritans exigua) were amplified from cDNA using generic oligonucleotide PCR primers, based on conserved residues surrounding the active-site His and Ser amino acids found in all serine proteases. The PCR product consisted of a broad band extending from about 450 by to 520 bp, which suggested that the PCR product actually consisted of numerous DNA fragments of slightly variable sizes. Seventeen independent clones of these fragments, each with an insert of approximately 480 bp, were digested with HaeIII. Comparison of restriction fragment patterns indicated that 13 of these clones harboured different PCR products. This was confirmed by DNA sequence analysis of 9 clones. Each of the sequenced clones contained an open reading frame which included structurally conserved regions characteristic of the serine protease superfamily. This study reveals the expression of a large and highly variable repertoire of serine proteases in adult buffalo fly. Importantly, these data also demonstrate the utility of such an approach in obtaining DNA probes for use in further investigations of gene family organization and expression, as well as providing recombinant antigens in the form of fusion proteins which may be used as candidates for vaccine production.     

Subgroups of Tcr α chains and correlation with T-cell function

T-cell receptor (Tcr) chains are classified into four subgroups (I, II, III, and miscellaneous) based on the amino acid residues at positions 61 and 62. Subgroup I has Gly Phe at these positions, subgroup II has Arg Phe, subgroup III has Arg Leu, and subgroup miscellaneous has several other combinations. Variability plots for subgroups I, II, and III sequences show higher values around positions 93–103, 105, 108, 111, 113, and 115, suggesting that these positions may interact with the processed antigen molecules. Smaller peaks are present at various other regions which may bind the major histocompatibility complex class I or II molecules. The patterns of variability within one subgroup are similar for all species, for human alone, and for mouse alone. These subgroup patterns appear much less complicated than patterns for sequences in all subgroups taken together, implying that subgroups may be related to Tcr functions. Among 83 mouse chains, 15 are from cytotoxic cells and 40 from helper cells. Of the 15 from cytotoxic cells, 11, 2, 0, and 2 are in subgroups I, II, III, and miscellaneous; and of the 40 from helper cells, 9, 16, 12, ans 3 are in subgroups I, II, III, and miscellaneous, respectively. Thus, a correlation between sequence and function of Tcr chains seems possible. Address correspondence and offprint requests to: M. Schiffer.     

A mutant β-D-glucoside transport system of Escherichia coli resistant to catabolite inhibition

A mutant strain of Escherichia coli in which β-glucoside transport is resistant to catabolite inhibition by methyl α-glucoside was characterized. The mutation was probably within the gene, bglC, coding for the β-glucoside enzyme II. The mutant organism is shown to transport the β-glucoside substrate, salicin, in preference to methyl α-glucoside or fructose. Salicin also caused inducer exclusion of lactose in the mutant strain.