RESUMO
Background: A reliable method to detect gene polymorphisms must be established to eliminate genotyping errors due to false PCR amplification. In the previous study, we have developed AS-PCR (Allele Specific-Polymerase Chain Reaction) to detect HER2 Ile655Val gene polymorphism with good specificity and sensitivity, yet it produces some errors. This study is aimed to eliminate the source of genotyping errors mainly by betaine treatment and PCR program modification. Methods: Genotyping errors produced by AS-PCR was qualitatively and quantitatively evaluated using two genomic DNA that each contained AA genotype and GG genotype of HER2 Gene. Betaine treatment or PCR program modification was tested to eliminate the occurrence of genotyping errors during AS-PCR amplification. Results: The types of genotyping errors exhibited by HER2 Ile655Val AS-PCR are diverse, ranging from LDO (Locus Drop Out), preferential amplification to ADO (Allele Drop Out). The rate of genotyping errors was from 10% to 50% depending on the amount and ratio of DNA template and the annealing temperature of PCR. In the mixed DNA template model, the betaine treatment has shown to reduce ADO only in preferentially amplified GG genotype amplicon. Alternatively, reducing the template of the heterozygous DNA by half ( -0.5 ng of DNA template) for such case has effectively recovered the AS-PCR from ADO. Furthermore, increasing the denaturation temperature to 96 °C with an annealing time of 40 s at the first 10 cycles of AS-PCR has succeeded in eliminating severe preferential amplification of AA genotype amplicon by preventing the DNA template with GG genotype from forming into a G-quadruplex structure. The guideline offered in this study has been successfully applied for clinical samples of breast cancer that show preferential amplification. Conclusion: Betaine and the modifying AS-PCR program can reduce significantly genotyping errors making AS-PCR for HER2 Ile655Val detection more reliable to be used as a molecular tool for genotyping purpose (AU)
Assuntos
Feminino , Adulto , Polimorfismo Genético , Códon , Reação em Cadeia da Polimerase , Genes erbB-2 , Alelos , Fator de Crescimento Epidérmico , Técnicas de GenotipagemRESUMO
Tamandua tetradactyla (Pilosa), the lesser anteater, is a medium-size mammal from South America. Its wide distribution through different landscapes, solitary and nocturnal habits, and the difficulty to capture and contain specimens limit the amount of individuals and populations sampled during fieldworks. These features along with the lack of specific molecular markers for the lesser anteater might be the causes for paucity in population genetic studies for the species. Historical samples from museum specimens, such as skins, and non-invasive samples, such as plucked hair, can be supplementary sources of DNA samples. However, the DNA quantity and quality of these samples may be limiting factors in molecular studies. In this study, we describe nine microsatellite loci for T. tetradactyla and test the amplification success, data reliability and estimate errors on both historical and non-invasive sample sets. We tested nine polymorphic microsatellites and applied the quality index approach to evaluate the relative performance in genotype analysis of 138 historical samples (study skin) and 19 non-invasive samples (plucked hair). The observed results show a much superior DNA quality of non-invasive over historical samples and support the quality index analysis as a practical tool to exclude samples with doubtful performance in genetic studies. We also found a relationship between the age of non-invasive samples and DNA quality, but lack of evidence of this pattern for historical samples.