The 'high dose-refuge' (HDR) strategy is commonly recommended and currently used for delaying or preventing pest adaptation to transgenic plants producing Bacillus thuringiensis (Bt) toxins. The efficiency of this strategy depends, among other factors, on the initial frequency of Bt resistance alleles and on the fitness costs associated with these alleles. Two years ago, an allele conferring resistance to Bt poplar was detected in a French population of the poplar pest Chrysomela tremulae F. Although this pest had never been subjected to Bt selection pressure due to human activities, the frequency of this allele was estimated at 0.0037, with a 95% credible (CI) interval of 0.00045-0.0080. We investigated the frequency of this allele in a second sample of C. tremulae collected more than 500 km from the site of the initial population. The estimated frequency in this sample was 0.0113 (95% CI 0.0031-0.0247), reinforcing the conclusion that resistance to Bt plants may be present at detectable frequencies in pest populations before selection resulting from pest management by humans. The frequency of the Bt resistance allele over the two samples was 0.0049 (95% CI 0.0020-0.0091). We also followed five laboratory lines in which the frequency of this allele was initially fixed at 0.500. After five generations maintained on non-Bt poplar leaves, the frequency of this allele decreased in all lines, whereas allelic frequencies at a neutral locus were unaffected. Thus, the Bt resistance allele detected in French populations of C. tremulae is probably associated with a fitness cost.
We describe an 18-year-old with moderate hereditary spherocytosis. The condition was associated with a 35% decrease in band 3. The underlying mutation was Arg to stop at codon 150 (CGA-->TGA) and was designated R150X, which defined allele Lyon of the EPB3 gene. The inheritance pattern was dominant. However, the mother, who also carried the allele Lyon, had a milder clinical presentation and only a 16% decrease of band 3. We suggested that the father had transmitted a modifying mutation that remained silent in the heterozygous state. Nucleotide sequencing after single strand conformation polymorphism analysis of the band 3 cDNA and promoter region revealed a G-->A substitution at position 89 from the cap site in the 5′-untranslated region, designated 89G-->A, which defined allele Genas. A ribonuclease protection assay showed that (1) the allele Genas (father) resulted in a 33% decrease in the amount of band 3 mRNA, (2) the reduction caused by the allele Lyon (mother) was 42%, and (3) the compound heterozygous state for both alleles (proband) resulted in a 58% decrease. These results suggest that some mildly deleterious alleles of the EPB3 gene are compensated for by the normal allele in the heterozygous state. They are shown through the aggravation of the clinical picture, based on more obvious molecular alterations when they occur in trans to an allele causing a manifest reduction of band 3 membrane protein concentration.
We present two distinct truncated variants of ankyrin associated with mild to moderate hereditary spherocytosis. Ankyrin Saint-Etienne 1 was manifested by an additional band located between bands 2.1 and 2.2. It was associated with a nonsense mutation in exon 39: TGG→TGA; W1721X. Ankyrin Saint-Etienne 2 appeared as two faint bands underlining bands 2.1 and 2.2. It was associated with a nonsense mutation in exon 41: CGA→TGA; R1833X. Overall ankyrin was diminished in splenectomized patients. Messenger RNAs Saint-Etienne 1 and 2 amounted to 20 and 37% of the total ankyrin mRNA, respectively. Ankyrin molecules truncated in their C-terminal region retain some ability to bind to the membrane whereas the bulk of nonsense mutations, located in more upstream regions, result in the mere disappearance of one haploid set of ankyrin. In the present cases, it was not possible to apportion the roles of ankyrin reduction and truncation in the pathogenesis of hereditary spherocytosis. Am.
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