Study of genetic variability of human papillomavirus and determination of molecular targets for detection and typing
Diagnosis, cervical cancer, PCR, genotyping, molecular evolution
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Human papillomavirus (HPV) is a small circular double-stranded DNA virus, characterized as one of the most common sexually transmitted agents in the world, whose accurate detection and genotyping is only possible through molecular biology techniques. Different biological properties have been reported among the more than 170 types already characterized, so that a particular group of HPVs is strongly related to persistent infections, intraepithelial lesions of different degrees and progression to cancers such as cervical, anal, vulvar, vaginal, oropharyngeal and penis. In the present work, analyzes of genetic variability and molecular evolution were performed in the genomes of the main clinically important HPVs. Phylogenetic reconstructions and analyzes of genetic signature profiles in the genomes of each genotype suggested the presence of subgroups of HPVs defined by differences in the E1, E6, L1 and L2 gene sequences. Evolution tests at DNA level have shown a stronger acting of natural selection at specific codons, more often in the E1, E2, L1 and L2 genes. From the data obtained in the analyzes of variability, a new set of primers was designed for the detection and genotyping of HPVs of clinical importance by polymerase chain reaction (PCR) technique. E1 gene was chosen as the molecular target due to the presence of a conserved region of variable size among genotypes. The proposed system had its efficiency evaluated in vitro and was compared to the most used PCR protocol for HPV detection in clinical samples. Using the seminested nucleic acid amplification, the proposed system was able to detect some of the major oncogenic HPVs with good sensitivity and showed a better specificity than the generic primers GP5+/6+, even applying a considerably higher annealing temperature. The analysis of the size of the amplified fragments using agarose gel electrophoresis may favor the identification of the HPV type present in the samples, allowing the discrimination between those more prevalent in the population and the reduction of the time and cost necessary for the identification of the agent. Optionally, the separation of products into high resolution matrices and direct sequencing can be used for typing, enabling the identification of a wide variety of HPV genotypes described.